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Siemens Industry Siemens Industry, Inc. [Member] Siemens Industry, Inc. 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Arrangement Terminated [Flag] Cost Finite-Lived Intangible Assets, Gross Income tax expense (benefit) Income Tax Expense (Benefit) Rebecca Boll Plan, Class A Common Stock [Member] Rebecca Boll Plan, Class A Common Stock Personnel related liabilities Employee-related Liabilities, Current Vesting [Axis] Vesting [Axis] Number of operating segments Number of Operating Segments Total Revenues Revenue Benchmark [Member] Name Trading Arrangement, Individual Name Credit Card Program Collateral Credit Card Program Collateral [Member] Credit Card Program Collateral Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Issuance of class A common stock in IPO, net of issuance costs Stock Issued During Period, Value, New Issues Stockholders’ Equity: Equity [Abstract] Inventory, Net Inventory Disclosure [Text Block] Total revenue Revenue from Contract with Customer, Excluding Assessed Tax Receivables from related parties Accounts receivable Other Receivables, Net, Current Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Cash and Cash Equivalents [Line Items] Cash and Cash Equivalents [Line Items] Amendment Flag Amendment Flag Intangible Assets, Net Intangible Assets Disclosure [Text Block] Fluence Energy, LLC Fluence Energy, LLC [Member] Fluence Energy, LLC Increase in borrowing capacity Line of Credit Facility, Increase in Borrowing Capacity Line of Credit Facility, Increase in Borrowing Capacity Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Payments for acquisition of businesses, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activities Total comprehensive loss Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Credit Facility [Domain] Credit Facility [Domain] Interest rate Debt Instrument, Basis Spread on Variable Rate Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Goodwill Goodwill Disclosure [Text Block] Borrowings against note receivable - pledged as collateral Long-Term Debt, Excluding Current Maturities Sales and marketing (a) Selling and Marketing Expense [Member] Weighted average number of Class A common shares outstanding, diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Total Accrued Liabilities Patents and licenses Patents And Licensing Agreements [Member] Patents And Licensing Agreements Other Commitment, Total Other Commitment Change in Contract Liability Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Operating expenses: Operating Expenses [Abstract] Revenue from Contracts with Customers Revenue from Contract with Customer [Text Block] Purchase of property and equipment Payments to Acquire Property, Plant, and Equipment Company Selected Measure Amount Company Selected Measure Amount Additional Paid-In Capital Additional Paid-in Capital [Member] Total assets Assets Name Awards Close in Time to MNPI Disclosures, Individual Name Loss Contingencies [Line Items] Loss Contingencies [Line Items] Cover [Abstract] Category of Item Purchased [Axis] Category of Item Purchased [Axis] Subsequent Events Subsequent Events [Text Block] Stock-based compensation expense and related vesting APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Amortization of debt issuance costs Amortization of Debt Issuance Costs Capitalized software to be sold Capitalized Software To Be Sold [Member] Capitalized Software To Be Sold Restructuring and Related Activities [Abstract] Other non-current liabilities Other Liabilities, Noncurrent Class B-2 common stock Common Class B-2 [Member] Common Class B-2 Vested, weighted average grant date fair value (USD per share) Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Consulting Services Revenue Consulting Services Revenue [Member] Consulting Services Revenue Non-NEOs Non-NEOs [Member] Amount of remaining performance obligations Revenue, Remaining Performance Obligation, Amount Short-term investments Beginning balance Ending balance Short-Term Investments Provisions for expected project losses Provision for Loss on Contracts Net (decrease) increase in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Effect of Siemens Industry redemption of class B-1 common stock for class A common stock (in shares) Stock Redeemed or Called During Period, Shares Class B-1 common stock Class B-1 common stock Common Class B-1 [Member] Common Class B-1 Warranties issued and assumed in period - recurring product warranty Standard and Extended Product Warranty Accrual, Increase for Warranties Issued, Recurring Product Warranty Standard and Extended Product Warranty Accrual, Increase for Warranties Issued, Recurring Product Warranty Non-PEO NEO Non-PEO NEO [Member] Equity Component [Domain] Equity Component [Domain] Rebecca Boll Plan, Vested Stock Options, Class A Common Stock [Member] Rebecca Boll Plan, Vested Stock Options, Class A Common Stock Adjustment to Compensation: Adjustment to Compensation [Axis] Additions Contract with Customer, Liability, Additions Contract with Customer, Liability, Additions Amount (in $ millions) Contractual Obligation Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Scenario [Axis] Scenario [Axis] Weighted average number of Class A common shares outstanding, basic (in shares) Weighted Average Number of Shares Outstanding, Basic Entity Current Reporting Status Entity Current Reporting Status Concentration Risk Type [Domain] Concentration Risk Type [Domain] Provision for receivables from related parties Receivables, Related Parties, Allowance For Credit Loss Receivables, Related Parties, Allowance For Credit Loss Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Proceeds from issuance of Class A common stock sold in an IPO, net of underwriting discounts and commissions Proceeds from Issuance Initial Public Offering Warranty issued and assumed in period - specific campaigns Standard and Extended Product Warranty Accrual, Increase for Warranties Issued, Specific Campaigns Standard and Extended Product Warranty Accrual, Increase for Warranties Issued, Specific Campaigns Related Party Transaction [Axis] Related Party Transaction [Axis] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Commitment fee Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Operating activities Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract] Statement [Line Items] Statement [Line Items] Outstanding Bank Guarantee Collateral Outstanding Bank Guarantee Collateral [Member] Outstanding Bank Guarantee Collateral Effect of the transactions related to the IPO Stock Issued During Period, Value, Conversion of Convertible Securities Scenario [Domain] Scenario [Domain] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Outstanding borrowings Long-Term Line of Credit Customer relationship Customer Relationships [Member] Financial Instruments Owned and Pledged as Collateral [Line Items] Financial Instruments Owned and Pledged as Collateral [Line Items] Less: non-current portion Accrued Liabilities, Noncurrent Accrued Liabilities, Noncurrent 6 month anniversary of IPO Share-Based Payment Arrangement, Tranche One [Member] Non-Controlling interest Noncontrolling Interest [Member]