Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Statistical Measurement [Domain] Statistical Measurement [Domain] Cumulative revenue during performance period, percentage Share-Based Compensation Arrangement By Share-Based Payment Award, Performance Metric Percentage Weight, Cumulative Revenue Share-Based Compensation Arrangement By Share-Based Payment Award, Performance Metric Percentage Weight, Cumulative Revenue Restricted cash Restricted cash Restricted Cash, Current Award Timing Predetermined Award Timing Predetermined [Flag] Related Party Transaction [Axis] Related Party Transaction [Axis] Warranty balance, beginning Warranty balance, ending Standard and Extended Product Warranty Accrual Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Entity File Number Entity File Number Additional Paid-In Capital Additional Paid-in Capital [Member] Factoring discount Transfer Of Financial Assets Accounted for As Sales, Discount Transfer Of Financial Assets Accounted for As Sales, Discount Convertible Senior Notes, Net Debt, Policy [Policy Text Block] Tabular List, Table Tabular List [Table Text Block] Leases [Abstract] Liquidity ratio Debt Instrument, Covenant, Liquidity Ratio Debt Instrument, Covenant, Liquidity Ratio Class B units issued (in shares) Business Combination, Consideration Transferred, Equity Interest, Share Issued, Number of Shares Recent Accounting Standards Adopted and Recent Accounting Standards Not Yet Adopted New Accounting Pronouncements, Policy [Policy Text Block] Schedule of Related Party Transactions Schedule of Related Party Transactions [Table Text Block] Accounts payable Increase (Decrease) in Accounts Payable Unbilled receivables Contract with Customer, Asset, after Allowance for Credit Loss, Current Interest expense (income), net Interest Income (Expense), Nonoperating Class A common stock withheld related to settlement of employee taxes for stock-based compensation awards Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] 2027 Other Commitment, to be Paid, Year Two Basic (in usd per share) Net income (loss) attributable to Fluence Energy, Inc., $ per share - basic (in usd per share) Earnings Per Share, Basic Adjustment to Compensation: Adjustment to Compensation [Axis] Related-Party Transactions Related Party Transactions Disclosure [Text Block] Convertible Senior Notes 2030 Convertible Senior Notes, 2030 [Member] Convertible Senior Notes, 2030 Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Cost Inventory, Gross Other Other Assets, Miscellaneous, Current Class A common stock reserved (in shares) Common Stock, Capital Shares Reserved for Future Issuance Revenue from Contracts with Customers Revenue from Contract with Customer [Text Block] Purchasing receivables outstanding amount Continuing Involvement with Derecognized Transferred Financial Assets, Amount Outstanding Schedule of Stock by Class [Table] Stock, Class of Stock [Table] Unbilled receivables Unbilled Receivables, Current Total other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Advances to suppliers Increase (Decrease) to Advances on Inventory Purchases Increase (Decrease) to Advances to Inventory Purchases Inventory Disclosure [Abstract] Debt instrument, threshold percentage of stock price trigger Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger London Interbank Offered Rate (LIBOR) Or Euro Interbank Offered Rate (EURIBOR) London Interbank Offered Rate (LIBOR) Or Euro Interbank Offered Rate (EURIBOR) [Member] London Interbank Offered Rate (LIBOR) Or Euro Interbank Offered Rate (EURIBOR) Amount of remaining performance obligations Revenue, Remaining Performance Obligation, Amount Adjustment to Compensation, Amount Adjustment to Compensation Amount Affiliated Entity Affiliated Entity [Member] Total revenue percentage Concentration Risk, Percentage Unamortized Debt Issuance Costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Percentage of remaining performance obligations Revenue, Remaining Performance Obligation, Percentage Consolidation Consolidation, Policy [Policy Text Block] Stock-based compensation Share-Based Payment Arrangement, Noncash Expense Outstanding pre-IPO options issued pursuant to the 2020 Unit Option Plan Share-Based Payment Arrangement, Option [Member] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Category of Item Purchased [Axis] Category of Item Purchased [Axis] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Total stockholders’ equity attributable to Fluence Energy, Inc. Equity, Attributable to Parent Insider Trading Policies and Procedures [Line Items] Stock-based compensation Share-Based Payment Arrangement, Expense Accruals and Provisions Long-Term Contracts or Programs Disclosure [Text Block] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Surety bonds Surety Bond [Member] Goodwill and Intangible Assets Disclosure [Abstract] Current assets: Assets, Current [Abstract] Total liabilities and stockholders’ equity Liabilities and Equity Other current liabilities Increase (Decrease) in Other Current Liabilities Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Liabilities and Stockholders’ Equity Liabilities and Equity [Abstract] Cover [Abstract] Second Offering Secondary Offering [Member] Secondary Offering Debt instrument, threshold consecutive trading days Debt Instrument, Convertible, Threshold Consecutive Trading Days Maximum Maximum [Member] General and administrative General and Administrative Expense [Member] Useful life Finite-Lived Intangible Asset, Useful Life 2028 Purchase Obligation, to be Paid, Year Three Net income (loss) attributable to non-controlling interest Net Income (Loss) Attributable to Noncontrolling Interest Net Finite-Lived Intangible Assets, Net Concentration Risk Type [Domain] Concentration Risk Type [Domain] Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Debt Instrument [Line Items] Debt Instrument [Line Items] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Treasury Stock Treasury Stock, Common [Member] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Foreign Currency Fair Value Hedge Derivative [Line Items] Foreign Currency Fair Value Hedge Derivative [Line Items] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Rounds of grants Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Rounds Of Grants Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Rounds Of Grants Lease liabilities: Liabilities [Abstract] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Income (loss) before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Entity Shell Company Entity Shell Company Other non-current liabilities Other Liabilities, Noncurrent Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Proceeds from issuance of debt Proceeds from Issuance of Debt Impairment of goodwill Goodwill, Impairment Loss Statement of Stockholders' Equity [Abstract] Remaining lease term Lessee, Operating Lease, Remaining Lease Term AES and Affiliates AES And Affiliates [Member] AES And Affiliates Statement of Cash Flows [Abstract] Current portion of borrowings against note receivable - pledged as collateral Long-Term Debt, Current Maturities Company Selected Measure Amount Company Selected Measure Amount Comprehensive income (loss) attributable to non-controlling interest Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Line of Credit Facility [Table] Line of Credit Facility [Table] Other non-current liabilities Increase (Decrease) in Other Noncurrent Liabilities Total comprehensive income (loss) attributable to Fluence Energy, Inc. Comprehensive Income (Loss), Net of Tax, Attributable to Parent Schedule of Other Current Assets Schedule of Other Current Assets [Table Text Block] Debt Conversion, Name [Domain] Debt Conversion, Name [Domain] Name Measure Name Letter of Credit Letter of Credit [Member] Schedule of Ownership Interests Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table Text Block] Schedule of Stock Based Compensation Expense Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Operating leases, Other current liabilities Operating Lease, Liability, Current Class of Stock [Line Items] Class of Stock [Line Items] Deferred income tax liability Deferred Income Tax Liabilities, Net Capitalized internal-use software Software and Software Development Costs [Member] Document Fiscal Period Focus Document Fiscal Period Focus New SCF Facility New SCF Facility [Member] New SCF Facility Award Timing Method Award Timing Method [Text Block] Litigation Case [Domain] Litigation Case [Domain] Award Type [Axis] Award Type [Axis] Long term debt Net Carrying Amount Long-Term Debt Legal Entity [Axis] Legal Entity [Axis] Purchases of Capped Calls related to 2023 Convertible Senior Notes Premium paid Adjustments To Additional Paid In Capital, Option Indexed To Issuer's Equity Adjustments To Additional Paid In Capital, Option Indexed To Issuer's Equity Total assets Assets Investing activities Cash Provided by (Used in) Investing Activity, Continuing Operation [Abstract] Trading Symbol Trading Symbol Contract With Customer, Liability [Roll Forward] Contract With Customer, Liability [Roll Forward] Contract With Customer, Liability Warranties issued and assumed in period Standard and Extended Product Warranty Accrual, Increase for Warranties Issued Cash, Cash Equivalents, and Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Two Customers Two Customers [Member] Two Customers Geographical [Domain] Geographical [Domain] Stock-based compensation (in shares) Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Entity Address, City or Town Entity Address, City or Town Short-term Debt, Type [Domain] Short-Term Debt, Type [Domain] Summary of Significant Accounting Policies and Estimates Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Purchases of Capped Calls related to 2030 Convertible Senior Notes Payments Of Capped Calls Related To Convertible Notes Payments Of Capped Calls Related To Convertible Notes Inventory capacity guarantee Inventory, Capacity Guarantee [Member] Inventory, Capacity Guarantee Intangible Assets, Net Intangible Assets Disclosure [Text Block] Effect of exchange rate changes on cash and cash equivalents Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Concentration Risk Type [Axis] Concentration Risk Type [Axis] Inventory, Net Inventory Disclosure [Text Block] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Income Statement Location [Domain] Statement of Income Location, Balance [Domain] Outstanding restricted stock units (“RSUs”) Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Emerging Growth Company Entity Emerging Growth Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Shares outstanding, options (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number Selling Stockholders Selling Stockholders [Member] Selling Stockholders Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Debt issuance costs, net Debt Issuance Costs, Net 2028 Other Commitment, to be Paid, Year Three Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Related Party Related Party [Member] Debt Conversion Description [Axis] Debt Conversion Description [Axis] Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Plan Name [Axis] Plan Name [Axis] Document Information [Table] Document Information [Table] PEO PEO [Member] 2025 Other Commitment, to be Paid, Remainder of Fiscal Year Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Changes in operating assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Proceeds from exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Schedule of Warranty Liabilities Schedule of Product Warranty Liability [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Accumulated Deficit Retained Earnings [Member] Term deposits Term Deposit [Member] Term Deposit Effective percentage Debt Instrument, Interest Rate, Effective Percentage Schedule of Accruals and Provisions Schedule of Accrued Liabilities [Table Text Block] Current portion of notes receivable - pledged as collateral Accounts Receivable from Securitization Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Letters of credit under 2024 Revolver Letters of Credit Under Revolver [Member] Letters of Credit Under Revolver Share-based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] Cash, cash equivalents, and restricted cash as of the beginning of the period Cash, cash equivalents, and restricted cash as of the end of the period Total cash, cash equivalents and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Income Statement [Abstract] Income tax expense Income Tax Expense (Benefit) 2029 and thereafter Other Commitment, To Be Paid, Year Four And After Other Commitment, To Be Paid, Year Four And After Interest rate Debt Instrument, Basis Spread on Variable Rate Sale of Stock [Domain] Sale of Stock [Domain] Taxes payable Taxes Payable, Current Other Current Liabilities Derivative Liability, Noncurrent Document Information [Line Items] Document Information [Line Items] Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Number of parties involved Supply Chain Financing, Number Of Parties Supply Chain Financing, Number Of Parties Product and Service [Domain] Product and Service [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Customer Concentration Risk Customer Concentration Risk [Member] Schedule of Contractual Obligations Schedule of Contractual Obligations [Table Text Block] Schedule of Contractual Obligations (Loss) gain on cash flow hedges, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Long-Term Purchase Commitment [Table] Long-Term Purchase Commitment [Table] Coupon interest Interest Expense, Debt, Excluding Amortization Prime Rate Prime Rate [Member] Net income (loss) Net income (loss) Net loss Net loss Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Notional Value Derivative, Notional Amount Business Combination, Consideration Transferred, Equity Interest, Type [Axis] Business Combination, Consideration Transferred, Equity Interest, Type [Axis] Loss per Share [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Other current assets Increase (Decrease) in Other Current Assets Investment owned, balance, percentage Investment Owned, Balance, Percentage Investment Owned, Balance, Percentage Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Proceeds from exercise of stock options Proceeds from Stock Options Exercised City Area Code City Area Code Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Accruals and provisions Accruals and provisions Accrued Liabilities, Current Shares outstanding (in shares) Outstanding, beginning balance (in shares) Outstanding, ending balance (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Number Commitments and Contingencies Disclosure [Abstract] Warranty balance, net of recoverable warranty costs from suppliers, at end of period Standard And Extended Product Warranty Accrual, Net Of Supplier Recoveries Standard And Extended Product Warranty Accrual, Net Of Supplier Recoveries Schedule of Change in Contract Liability Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Foreign currency forward contracts Foreign Currency Forward Contract [Member] Foreign Currency Forward Contract General and administrative General and administrative expenses General and Administrative Expense Convertible senior notes, net Convertible Notes Payable, Noncurrent Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net cash (used in) provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Hosting Arrangements Development Cost And Hosting Arrangements [Member] Development Cost And Hosting Arrangements Related Party Transactions [Abstract] Preferred stock, par value (in usd per share) Preferred Stock, Par or Stated Value Per Share Subsequent Event Subsequent Event [Member] Cost of goods and services Cost of Sales [Member] Interest expense (income), net Interest Income (Expense), Operating Goodwill Goodwill, Beginning of the period Goodwill, End of the period Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Debt Conversion Terms Three Debt Conversion Terms Three [Member] Debt Conversion Terms Three Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Weighted average number of Class A common shares outstanding: Weighted Average Number of Shares Outstanding, Basic [Abstract] Equity Components [Axis] Equity Components [Axis] Convertible Debt Convertible Debt [Member] Organization and Operations Nature of Operations [Text Block] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] 2026 Other Commitment, to be Paid, Year One Revenue from energy storage products and solutions Product [Member] Number of reportable segments Number of Reportable Segments Sale of Receivable under Master Receivables Purchase Agreement Transfers and Servicing of Financial Assets [Text Block] Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward] Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward] Revenue from digital applications and solutions Digital Applications And Solutions [Member] Digital Applications And Solutions Supplemental Cash Flows Information Supplemental Cash Flow Information [Abstract] Capitalized software costs Capitalized Computer Software, Additions Other Performance Measure, Amount Other Performance Measure, Amount Foreign currency forward contracts, net of tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax Inventory [Line Items] Inventory [Line Items] Schedule of Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Entity Address, State or Province Entity Address, State or Province Principal payments on finance leases Finance Lease, Principal Payments Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Security, Excluded EPS Calculation [Table] Supplier Finance Program [Line Items] Supplier Finance Program [Line Items] Fair Value Measurements Fair Value Measurement, Policy [Policy Text Block] Related Party [Domain] Related and Nonrelated Parties [Domain] Total current liabilities Liabilities, Current Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] Inventory [Axis] Inventory [Axis] Derivative Instrument [Axis] Derivative Instrument [Axis] Long-term Purchase Commitment, Category of Item Purchased [Domain] Long-Term Purchase Commitment, Category of Item Purchased [Domain] Individual: Individual [Axis] Vesting [Axis] Vesting [Axis] Total restricted cash Restricted Cash Other current assets Total Other Assets, Current Research and development Research and Development Expense [Member] Entity [Domain] Entity [Domain] Net cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Expected time period of satisfaction (in years) Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] 2026 Purchase Obligation, to be Paid, Year One Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Principles of Accounting Basis of Accounting, Policy [Policy Text Block] Operating lease, Other non-current assets Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Non-Controlling Interest Ownership (AES) Subsidiary, Ownership Percentage, Noncontrolling Owner Effective tax rate Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Capital expenditures on software Payments for Software Operating activities Cash Provided by (Used in) Operating Activity, Continuing Operation [Abstract] Plan Name [Domain] Plan Name [Domain] Debt Conversion Terms One Debt Conversion Terms One [Member] Debt Conversion Terms One Proceeds from exercise of stock options (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period Stockholders’ Equity: Equity [Abstract] Revenue and Cost Recognition Revenue from Contract with Customer [Policy Text Block] Estimated litigation liability Estimated Litigation Liability Purchase obligation Purchase Obligation Schedule of Long-Term Purchase Commitment Long-Term Purchase Commitment [Table Text Block] 2029 and thereafter Purchase Obligation, To Be Paid, Year Four And After Purchase Obligation, To Be Paid, Year Four And After Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Other Commitments [Line Items] Other Commitments [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Ownership [Domain] Ownership [Domain] Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] Amortization expense Amortization of Intangible Assets Leases Lessee, Leases [Policy Text Block] External-Use Software Development Cost External-Use Software Development Cost [Member] External-Use Software Development Cost Deferred income tax asset Deferred Income Tax Assets, Net Depreciation and amortization Depreciation, Depletion and Amortization Guarantees and commitments Guarantees and Commitments [Member] Guarantees and Commitments Other non-current assets Other Assets, Noncurrent Debt instrument, convertible, conversion ratio Debt Instrument, Convertible, Conversion Ratio Customer [Domain] Customer [Domain] Entity Central Index Key Entity Central Index Key PEO Name PEO Name Debt instrument, conversion price (in usd per share) Debt Instrument, Convertible, Conversion Price Aggregate net proceeds from stock offering Sale of Stock, Consideration Received on Transaction Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year Prior Year End Fair Value of Equity Awards Granted in Any Prior Year that Fail to Meet Applicable Vesting Conditions During Covered Year [Member] 2027 Purchase Obligation, to be Paid, Year Two Receivables from related parties Increase (Decrease) in Due from Related Parties, Current Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Revolving Credit Facility Revolving Credit Facility [Member] Arrangement Duration Trading Arrangement Duration Invoices issued during the period Supplier Finance Program, Obligation, Addition 6 month anniversary of IPO Share-Based Payment Arrangement, Tranche One [Member] Change in estimate of transaction price Contract with Customer, Liability, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price Deferred revenue Contract with Customer, Liability, Current Debt Conversion Terms Two Debt Conversion Terms Two [Member] Debt Conversion Terms Two Net proceeds sale of receivable Transfer of Financial Assets Accounted for as Sales, Cash Proceeds Received for Assets Derecognized, Amount Current portion of warranty accrual Product Warranty Accrual, Current Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Class of Stock [Domain] Class of Stock [Domain] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Deferred revenue Share-Based Payment Arrangement, Nonvested Award, Excluding Option, Cost Not yet Recognized, Amount Inventory, Current [Table] Inventory, Current [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Stock-Based Compensation Share-Based Payment Arrangement [Text Block] Liquidated Damages Liquidated Damages [Member] Liquidated Damages Right-of-use assets: Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Nonrelated Party Nonrelated Party [Member] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Schedule of Supplier Finance Program Supplier Finance Program [Table Text Block] Vesting [Domain] Vesting [Domain] Other Commitments [Axis] Other Commitments [Axis] Debt Instrument [Axis] Debt Instrument [Axis] Credit Facility [Domain] Credit Facility [Domain] Cost Finite-Lived Intangible Assets, Gross Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Award vesting percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Research and development Research and development expenses Research and Development Expense Factoring income Gain (Loss) on Securitization of Financial Assets Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Stated percentage Debt Instrument, Interest Rate, Stated Percentage Operating lease, Other non-current liabilities Operating Lease, Liability, Noncurrent Class A common stock withheld related to settlement of employee taxes for stock-based compensation awards (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Effect of AES Grid Stability redemption of Class B-1 common stock for Class A common stock (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Redemption Redemption [Member] Redemption Award settlement period Share-Based Compensation Arrangement By Share-Based Payment Award, Award Settlement Period After Vesting Share-Based Compensation Arrangement by Share-Based Payment Award, Award Settlement Period After Vesting Ownership [Axis] Ownership [Axis] Derivatives and Hedging Derivative Instruments and Hedging Activities Disclosure [Text Block] Americas (North, Central, and South America) Americas [Member] Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name The Revolver The Revolver [Member] The Revolver Other non-current assets Increase (Decrease) in Other Noncurrent Assets Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Capitalized software amortization expense Capitalized Computer Software, Amortization Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period Schedule of Cash Flow Hedging Instruments Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Strike price (in usd per unit) Option Indexed to Issuer's Equity, Strike Price Forfeited (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Forfeited in Period Unrecognized stock compensation expense Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Related Party Transaction [Line Items] Related Party Transaction [Line Items] Document Quarterly Report Document Quarterly Report Long-term debt, fair value Long-Term Debt, Fair Value Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Number of operating segments Number of Operating Segments Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Schedule of Net Carrying Value and Fair Value of the Convertible Senior Notes Schedule of Debt [Table Text Block] Related Party [Axis] Related and Nonrelated Parties [Axis] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Revenue from services Service [Member] Schedule of Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Restatement Determination Date: Restatement Determination Date [Axis] Supplier Finance Program [Table] Supplier Finance Program [Table] Non-PEO NEO Non-PEO NEO [Member] Letters of credit outstanding, amount Letters of Credit Outstanding, Amount Spare parts Shipping Containers And Spare Parts [Member] Shipping Containers And Spare Parts Purchase Commitment Purchase Obligation, Fiscal Year Maturity [Abstract] Number of categories Number of Categories Number of Categories Number of Agreements Number of Contractual Obligation Agreements Number of Contractual Obligation Agreements Interest expense Total Interest Expense, Debt Amount reclassified from accumulated other comprehensive income (loss) into earnings Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Sale of Stock [Axis] Sale of Stock [Axis] Name Trading Arrangement, Individual Name Award Type [Domain] Award Type [Domain] Goodwill Goodwill Disclosure [Text Block] Non-Controlling interests Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Cap price (in usd per unit) Derivative, Cap Price Compensation Amount Outstanding Recovery Compensation Amount Principal amount Debt Instrument, Face Amount 2025 Purchase Obligation, to be Paid, Remainder of Fiscal Year Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement of Comprehensive Income [Abstract] 2021 Plan 2021 Plan [Member] 2021 Plan Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Revenue recognized related to amounts that were included in beginning balance of deferred revenue Contract with Customer, Liability, Revenue Recognized Limited warranty, period Limited Warranty, Period Limited Warranty, Period MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name Restricted cash included in “Other non-current assets” Restricted Cash, Noncurrent Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Liquidated damages Other Commitment Effect of AES Grid Stability redemption of Class B-1 common stock for Class A common stock Stock Issued During Period, Value, Conversion of Convertible Securities Inventory [Domain] Inventory [Domain] Stock-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Treasury stock, at cost Treasury Stock, Value Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Sales and marketing Selling and Marketing Expense Long-Term Purchase Commitment [Line Items] Long-Term Purchase Commitment [Line Items] Financial Instruments [Domain] Financial Instruments [Domain] Litigation Case [Axis] Litigation Case [Axis] Total lease liabilities Lease, Liability Lease, Liability Income Statement Location [Axis] Statement of Income Location, Balance [Axis] Damages sought, value Loss Contingency, Damages Sought, Value EMEA (Europe, Middle-East, and Africa) EMEA [Member] Total non-current assets Assets, Noncurrent Outstanding performance share units (“PSUs”) Performance Shares [Member] Schedule of Cash and Cash Equivalents [Table] Cash and Cash Equivalent [Table] Number of shares covered by capped calls (in shares) Option Indexed to Issuer's Equity, Indexed Shares Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Inventory Increase (Decrease) in Inventories Schedule of Accounting Standards Update and Change in Accounting Principle Accounting Standards Update and Change in Accounting Principle [Table Text Block] Inventory, net Net Inventory, Net Developed technology Developed Technology Rights [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Minimum Minimum [Member] Non-current assets: Assets, Noncurrent [Abstract] Loss per Share Earnings Per Share, Policy [Policy Text Block] Non-Controlling Interest Consolidation, Subsidiaries or Other Investments, Consolidated Entities, Policy [Policy Text Block] Company Selected Measure Name Company Selected Measure Name Debt Convertible Senior Notes, Net Debt Disclosure [Text Block] Preferred stock, $0.00001 per share, 10,000,000 shares authorized; no shares issued and outstanding as of June 30, 2025 and September 30, 2024 Preferred Stock, Value, Issued Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Financing receivable, amount transferred Financing Receivable, after Allowance for Credit Loss, Transferred Financing Receivable, after Allowance for Credit Loss, Transferred Net income (loss) attributable to Fluence Energy, Inc. - diluted Net Income (Loss) Available to Common Stockholders, Diluted All Executive Categories All Executive Categories [Member] The Option Plan The Option Plan [Member] The Option Plan Common stock Common Stock, Value, Issued Finance lease, Property and equipment, net Finance Lease, Right-of-Use Asset, after Accumulated Amortization Goodwill [Roll Forward] Goodwill [Roll Forward] Current portion of recoverable warranty costs from suppliers Standard and Extended Product Warranty Accrual, Current Supplier Recoveries Standard and Extended Product Warranty Accrual, Current Supplier Recoveries Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] 18 month anniversary of IPO Share-Based Payment Arrangement, Tranche Two [Member] Diluted (in shares) Net income (loss) attributable to Fluence Energy, Inc., shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Global minimum tax threshold percentage Global Minimum Tax Threshold Percentage Global Minimum Tax Threshold Percentage Business Combination [Axis] Business Combination [Axis] Total comprehensive income (loss) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Entity Small Business Entity Small Business Sales and marketing Selling and Marketing Expense [Member] Schedule of Revenue by Geographical Regions Revenue from External Customers by Geographic Areas [Table Text Block] Income Tax Disclosure [Abstract] Less: Recoverable warranty costs from suppliers Standard And Extended Product Warranty Accrual, Supplier Recoveries Standard And Extended Product Warranty Accrual, Supplier Recoveries Non-Controlling interest Noncontrolling Interest [Member] Supply Chain Financing Supplier Finance Program [Text Block] Preferred stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Document Transition Report Document Transition Report Supplier Finance Program, Obligation [Roll Forward] Supplier Finance Program, Obligation [Roll Forward] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Underlying Securities Award Underlying Securities Amount Daily Simple RFR Daily Simple RFR [Member] Daily Simple RFR Accruals for software development costs Accrued Software Development Costs, Current Accrued Software Development Costs, Current Equity Component [Domain] Equity Component [Domain] Nispera Nispera [Member] Nispera Document Period End Date Document Period End Date PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Extended payment terms period Supply Chain Financing, Extended Payment Terms Period Supply Chain Financing, Extended Payment Terms Period Fluence v.s. Diablo Energy Storage Fluence v.s. Diablo Energy Storage [Member] Fluence v.s. Diablo Energy Storage Cash and Cash Equivalents [Domain] Cash and Cash Equivalents [Domain] Income Taxes Income Tax Disclosure [Text Block] Class A common stock Class A Common Class A [Member] Amount Contractual Obligation Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Payment for debt issuance costs Payments Of Debt Issuance Costs, Revolving Facilities Payments Of Debt Issuance Costs, Revolving Facilities Financial performance metric Share-Based Compensation Arrangement By Share-Based Payment Award, Financial Performance Metric Share-Based Compensation Arrangement By Share-Based Payment Award, Financial Performance Metric Total stockholders’ equity Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest Document Type Document Type Income (loss) per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Loss Contingencies [Table] Loss Contingencies [Table] Additional paid-in capital Additional Paid in Capital Product and Service [Axis] Product and Service [Axis] Foreign currency forward contracts Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax Derivative Contract [Domain] Derivative Contract [Domain] Advances to suppliers Advance payment Advances on Inventory Purchases Revenue from Contract with Customer Benchmark Revenue from Contract with Customer Benchmark [Member] Total revenue Revenue Revenue from Contract with Customer, Excluding Assessed Tax Change in estimates Standard Product Warranty Accrual, Change In Estimates Standard Product Warranty Accrual, Change In Estimates All Individuals All Individuals [Member] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name Options expiration period (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Commitment fee Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Receivables from related parties Accounts receivable Other Receivables, Net, Current Liquidated Damages Liquidated Damages [Abstract] Liquidated Damages Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Foreign currency adjustment Goodwill, Foreign Currency Translation, Gain (Loss) Class A common stock withheld related to settlement of employee taxes for stock-based compensation awards Payment, Tax Withholding, Share-Based Payment Arrangement Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Net income (loss) attributable to Fluence Energy, Inc.- basic Net Income (Loss) Available to Common Stockholders, Basic Written notice period Continuing Involvement With Derecognized Transferred Financial Assets, Termination Notice Period Continuing Involvement With Derecognized Transferred Financial Assets, Termination Notice Period Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Schedule of Finite-Lived Intangible Assets [Table] Intangible Asset, Finite-Lived [Table] Current liabilities: Liabilities, Current [Abstract] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Leverage ratio Debt Instrument, Covenant, Net Leverage Ratio, Maximum Threshold Debt Instrument, Covenant, Net Leverage Ratio, Maximum Threshold Geographical [Axis] Geographical [Axis] Qualitative and Quantitative Information, Transferor's Continuing Involvement [Line Items] Qualitative and Quantitative Information, Transferor's Continuing Involvement [Line Items] Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Derivatives and Hedging Derivatives, Methods of Accounting, Hedging Derivatives [Policy Text Block] Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Letter of Credit Issued Letter of Credit Issued [Member] Letter of Credit Issued Outstanding borrowings Long-Term Line of Credit Letters of credit under bilateral credit facilities Letters of Credit Under the Bilateral Credit Facility [Member] Letters of Credit Under the Bilateral Credit Facility Accruals and provisions Increase (Decrease) in Accrued Liabilities Schedule of Related Party Transactions, by Related Party [Table] Related Party Transaction [Table] APAC (Asia Pacific) Asia Pacific [Member] Diluted (in usd per share) Net income (loss) attributable to Fluence Energy, Inc., $ per share - diluted (in usd per share) Earnings Per Share, Diluted AES Grid Stability AES Grid Stability, LLC [Member] AES Grid Stability, LLC Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Trade receivables, net Accounts Receivable, after Allowance for Credit Loss, Current Interest income, operating Interest Income, Operating Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Title of 12(b) Security Title of 12(b) Security Lessee, Lease, Description [Table] Lessee, Lease, Description [Table] Proceeds from borrowings against note receivable Proceeds From Borrowings Against Note Receivable Proceeds From Borrowings Against Note Receivable Guarantees issued Supply Chain Financing Guarantee By Related Party Supply Chain Financing Guarantee By Related Party Prepaid insurance Prepaid Insurance Shares sold in offering (in shares) Sale of Stock, Number of Shares Issued in Transaction Beginning balance (in shares) Ending balance (in shares) Treasury Stock, Common, Shares Income (loss) per share of Class A common stock: Earnings Per Share [Abstract] Other (income) expense, net Nonoperating Income (Expense) Controlling Interest Ownership Subsidiary, Ownership Percentage, Parent Collateral for surety program Surety Program Collateral [Member] Surety Program Collateral Payments for acquisitions Payments of Merger Related Costs, Financing Activities Siemens Industry Siemens Industry, Inc. [Member] Siemens Industry, Inc. Asset-Backed Securities, Securitized Loans and Receivables Asset-Backed Securities, Securitized Loans and Receivables [Member] Gross profit Gross Profit Schedule of Dilutive Securities Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Net changes in liability for warranty expirations, costs incurred, and foreign exchange impact Standard and Extended Product Warranty Accrual, Increase (Decrease) for Preexisting Warranties Schedule of Interest Expense Interest Income and Interest Expense Disclosure [Table Text Block] Performance period Share-Based Compensation Arrangement By Share-Based Payment Award, Cumulative Adjusted EBITDA During Performance Period Share-Based Compensation Arrangement By Share-Based Payment Award, Cumulative Adjusted EBITDA During Performance Period Deferred revenue Increase (Decrease) in Contract with Customer, Liability Short-term Debt, Type [Axis] Short-Term Debt, Type [Axis] 2024 Revolver 2024 Revolver [Member] 2024 Revolver Foreign currency forward contracts Revenue From Contract With Customer, Excluding Assessed Tax [Member] Revenue From Contract With Customer, Excluding Assessed Tax Provisions for expected project losses Provision for Loss on Contracts Commitment fee threshold percent Debt Instrument, Commitment Fee Per Annum Threshold Percentage Debt Instrument, Commitment Fee Per Annum Threshold Percentage Cash and Cash Equivalents [Line Items] Cash and Cash Equivalents [Line Items] Cash (refund) paid on income taxes Income Taxes Paid, Net Cubes, batteries, and other equipment Cubes, Batteries, And Other Equipment [Member] Cubes, Batteries, And Other Equipment Restricted Cash and Cash Equivalents [Axis] Restricted Cash and Cash Equivalents [Axis] Award Timing Disclosures [Line Items] Adjust Term SOFR Rate, Adjusted EURIBOR Rate, Or Adjusted Term CORRA Rate Adjust Term SOFR Rate, Adjusted EURIBOR Rate, Or Adjusted Term CORRA Rate [Member] Adjust Term SOFR Rate, Adjusted EURIBOR Rate, Or Adjusted Term CORRA Rate Total Accrued Liabilities Schedule of Inventory, Current Schedule of Inventory, Current [Table Text Block] Options granted, weighted average exercise price per share (in usd per share) Share-Based Compensation Arrangements by Share-Based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Personnel related liabilities Employee-related Liabilities, Current Amount recognized in accumulated other comprehensive income (loss) Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Foreign Currency Fair Value Hedge Derivative [Table] Foreign Currency Fair Value Hedge Derivative [Table] Contractual period Revenue From Contract With Customer, Contractual Period Revenue From Contract With Customer, Contractual Period Fluence Energy, Inc Fluence Energy, INC [Member] Fluence Energy, INC Maximum exposure range for each agreement Contractual Obligation, Exposure Per Agreement Contractual Obligation, Exposure Per Agreement Distribution to AES Grid Stability Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Investment owned (in shares) Investment Owned, Balance, Shares Net income (loss) attributable to Fluence Energy, Inc. Net Income (Loss) Attributable to Parent Subsequent Event [Table] Subsequent Event [Table] Expiration Date Trading Arrangement Expiration Date Non-current liabilities: Liabilities, Noncurrent [Abstract] Other Commitments [Domain] Other Commitments [Domain] Accruals Other Accrued Liabilities, Current Effect of remeasurement of non-controlling interest due to other share transactions Noncontrolling Interest, Decrease from Remeasurement Noncontrolling Interest, Decrease from Remeasurement Service requirement (in years) Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period Other Current Assets Other Current Assets [Text Block] Property and equipment, net Property, Plant and Equipment, Net Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Adoption Date Trading Arrangement Adoption Date Base Rate Base Rate [Member] Outstanding non-qualified stock options (“NQSOs”) Non-Qualified Stock Options [Member] Non-Qualified Stock Options Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Trade receivables, net Increase (Decrease) in Accounts Receivable Inventory, Net Inventory, Policy [Policy Text Block] Shares underlying the conversion option in the 2030 Convertible Senior Notes Shares Underlying The Conversion Option In The 2030 Convertible Senior Notes [Member] Shares Underlying The Conversion Option In The 2030 Convertible Senior Notes Entity Current Reporting Status Entity Current Reporting Status Useful life (in years) Lessee, Operating Lease, Term of Contract Customer [Axis] Customer [Axis] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Financing activities Cash Provided by (Used in) Financing Activity, Continuing Operation [Abstract] Customer relationship Customer Relationships [Member] Proceeds from issuance of 2030 Convertible Senior Notes Proceeds from Convertible Debt Non Qualified Stock Option Non Qualified Stock Option [Member] Non Qualified Stock Option Line of Credit Line of Credit [Member] Accumulated deficit Retained Earnings (Accumulated Deficit) Financial Instrument [Axis] Financial Instrument [Axis] Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Number of suppliers Number of Suppliers Participating in Program Number of Suppliers Participating in Program Finance Lease, Other current liabilities Finance Lease, Liability, Current Collateral for credit card program Credit Card Program Collateral [Member] Credit Card Program Collateral Provision Inventory Valuation Reserves Current Fiscal Year End Date Current Fiscal Year End Date Class of Stock [Axis] Class of Stock [Axis] Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Cumulative adjusted EBITDA during performance period, percentage Share-Based Compensation Arrangement By Share-Based Payment Award, Performance Metric Weight Percentage, Adjusted EBITDA Share-Based Compensation Arrangement By Share-Based Payment Award, Performance Metric Weight Percentage, Adjusted EBITDA Payables and Accruals [Abstract] Other (income) expense, net Other Nonoperating Income (Expense) Statement [Table] Statement [Table] Deferred income taxes Deferred Income Tax Expense (Benefit) Adjustments to reconcile net loss to net cash (used in) provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Fluence Energy, LLC Fluence Energy, LLC [Member] Fluence Energy, LLC Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Total receivables from related parties Receivables, Net, Current Variable Rate [Domain] Variable Rate [Domain] Deferred revenue, beginning of period Deferred revenue end of period Contract with Customer, Liability Finance lease, Other non-current liabilities Finance Lease, Liability, Noncurrent Threshold performance, percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Below-Threshold Performance, Percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Below-Threshold Performance, Percentage Unrecognized tax benefits Unrecognized Tax Benefits Antidilutive securities (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount All Adjustments to Compensation All Adjustments to Compensation [Member] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table] Amendment Flag Amendment Flag Sale of stock, price per share (usd in per share) Sale of Stock, Price Per Share Transfers and Servicing [Abstract] Other Commitments [Table] Other Commitments [Table] Leases Lessee, Operating Leases [Text Block] Termination Date Trading Arrangement Termination Date Net cash provided by (used in) financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Unbilled receivables Increase (Decrease) in Contract with Customer, Asset Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Line cap additional threshold amount Debt Instrument, Covenant, Line Cap Additional Threshold Amount, Total Liquidity Debt Instrument, Covenant, Line Cap Additional Threshold Amount, Total Liquidity Patents and licenses Patents And Licensing Agreements [Member] Patents And Licensing Agreements 30 month anniversary of IPO Share-Based Payment Arrangement, Tranche Three [Member] Total right-of-use assets Lease, Right-of-Use Asset Lease, Right-of-Use Asset Schedule of Outstanding Options Granted Share-Based Payment Arrangement, Option, Activity [Table Text Block] Basic (in shares) Net income (loss) attributable to Fluence Energy, Inc., shares - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Inventory provision Inventory Write-down Cost of goods and services Cost of goods and services Cost of Product and Service Sold Schedule of Earnings Per Share, Basic and Diluted Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Related Party Transaction [Domain] Related Party Transaction [Domain] Subsequent Events [Abstract] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Obligations outstanding at the beginning of the period Obligations outstanding at the end of the period Supplier Finance Program, Obligation Debt Disclosure [Abstract] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Amortization of debt issuance costs Amortization of Debt Issuance Costs Entity Tax Identification Number Entity Tax Identification Number Schedule of Assets and Liabilities, Operating Lease Assets and Liabilities, Lessee [Table Text Block] Assets and Liabilities, Lessee Capitalized software to be sold Capitalized Software To Be Sold [Member] Capitalized Software To Be Sold Options outstanding, weighted average exercise price per share (usd per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Weighted Average Exercise Price Asset-Based Lending Facility Asset-Based Lending Facility [Member] Asset-Based Lending Facility Class B-2 common stock Common Class B-2 [Member] Common Class B-2 Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Consulting Services Revenue Consulting Services Revenue [Member] Consulting Services Revenue Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items] Common stock, par value (in usd per share) Common Stock, Par or Stated Value Per Share Number of classes of common stock Number Of Classes Of Common Stock Number Of Classes Of Common Stock Common stock, shares issued (in shares) Common Stock, Shares, Issued Taxes recoverable Income Taxes Receivable, Current Qualitative and Quantitative Information, Transferor's Continuing Involvement [Table] Qualitative and Quantitative Information, Transferor's Continuing Involvement [Table] Granted (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross Class B-1 common stock Class B-1 common stock Common Class B-1 [Member] Common Class B-1 Use of Estimates Use of Estimates, Policy [Policy Text Block] Invoices paid during the period Supplier Finance Program, Obligation, Settlement Schedule of Goodwill Schedule of Goodwill [Table Text Block] Trading Arrangement: Trading Arrangement [Axis] Other Current Assets Derivative Asset, Current Additions Contract with Customer, Liability, Additions Contract with Customer, Liability, Additions Taxes payable Increase (Decrease) in Income Taxes Payable Total Shareholder Return Amount Total Shareholder Return Amount Loss Contingencies [Line Items] Loss Contingencies [Line Items] Subsequent Events Subsequent Events [Text Block] Gain (loss) on foreign currency translation, net of tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Insider Trading Arrangements [Line Items] Security Exchange Name Security Exchange Name Total non-current liabilities Liabilities, Noncurrent Total liabilities Liabilities Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Distribution to AES Grid Stability Payments of Ordinary Dividends, Noncontrolling Interest Provision for receivables from related parties Receivables, Related Parties, Allowance For Credit Loss Receivables, Related Parties, Allowance For Credit Loss Letter of credit participation fee Line of Credit Facility, Commitment Fee Percentage Maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Business Combination, Consideration Transferred, Equity Interest, Type [Domain] Business Combination, Consideration Transferred, Equity Interest, Type [Domain] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Prepaid expenses Prepaid Expense, Current Operating expenses: Operating Expenses [Abstract] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Other current liabilities Other Liabilities, Current Trade names/Trademarks Trademarks and Trade Names [Member] Outstanding phantom units Phantom Share Units (PSUs) [Member] Collateral for outstanding bank guarantees Outstanding Bank Guarantee Collateral [Member] Outstanding Bank Guarantee Collateral Statement [Line Items] Statement [Line Items] Variable Rate [Axis] Variable Rate [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] AOCI Attributable To Parent Before Reclassification And Tax [Roll Forward] AOCI Attributable To Parent Before Reclassification And Tax [Roll Forward] AOCI Attributable To Parent Before Reclassification And Tax Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Cash and cash equivalents Cash and Cash Equivalent Counterparty Name [Axis] Counterparty Name [Axis] Effect of remeasurement of non-controlling interest due to other share transactions (in shares) Noncontrolling Interest, Decrease from Remeasurement, Shares Noncontrolling Interest, Decrease from Remeasurement, Shares Subsequent Event [Line Items] Subsequent Event [Line Items] Debt instrument, threshold trading days Debt Instrument, Convertible, Threshold Trading Days Common Stock Common Stock [Member] Vested (in shares) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period Software Development Costs Goodwill and Intangible Assets, Intangible Assets, Policy [Policy Text Block] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Non-NEOs Non-NEOs [Member] Net (decrease) increase in cash, cash equivalents, and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation