Trading Arrangements, by Individual Trading Arrangements, by Individual [Table] Trading Arrangement: Trading Arrangement [Axis] Maximum Maximum [Member] Statistical Measurement [Domain] Statistical Measurement [Domain] Title of 12(b) Security Title of 12(b) Security Document Fiscal Year Focus Document Fiscal Year Focus Revenue, remaining performance obligation, expected timing of satisfaction, period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Adjustment to Compensation, Amount Adjustment to Compensation Amount Required to make quarterly principal payments as a percentage of original principal amount Debt Instrument, Periodic Payment, Percent Of Original Principal Debt Instrument, Periodic Payment, Percent Of Original Principal Customer [Axis] Customer [Axis] Segment Reporting [Abstract] Common stock, $0.01 par value, 1,000,000,000 shares authorized; 244,319,846 shares issued and outstanding at July 3, 2026 and 243,464,776 shares issued and outstanding at October 3, 2025. Common Stock, Value, Issued Accrued compensation and benefits Employee-related Liabilities, Current Schedule of Debt Schedule of Long-Term Debt Instruments [Table Text Block] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Line of Credit Line of Credit [Member] Restatement Determination Date Restatement Determination Date Increase in the valuation allowance against deferred tax assets Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Derivative Instrument [Axis] Derivative Instrument [Axis] Other comprehensive income (loss) before reclassification, tax Other Comprehensive Income (Loss) before Reclassifications, Tax Contract with Customer, Basis of Pricing [Domain] Contract with Customer, Basis of Pricing [Domain] Amendment Flag Amendment Flag Consolidated Entities [Axis] Consolidated Entities [Axis] Goodwill [Line Items] Goodwill [Line Items] Current liabilities: Liabilities, Current [Abstract] Measurement period adjustments Adjustment To Additional Paid In Capital, Acquisitions, Measurement Period Adjustments Adjustment To Additional Paid In Capital, Acquisitions, Measurement Period Adjustments Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Other Other Debt [Member] Other Debt Other comprehensive income: Other Comprehensive Income (Loss), Net of Tax [Abstract] Non-current liabilities Liabilities, Noncurrent Consolidated Entities [Domain] Consolidated Entities [Domain] Equity Method Investee Equity Method Investee [Member] Distributions to non-controlling interests Payments to Noncontrolling Interests Pension adjustments Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Entity Address, State or Province Entity Address, State or Province PEO Total Compensation Amount PEO Total Compensation Amount Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Weighted-average number of basic shares outstanding during the period (in shares) Weighted Average Number of Shares Outstanding, Basic Derivative, notional amount Derivative, Notional Amount Contract assets Contract with Customer, Asset, after Allowance for Credit Loss, Current Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Senior Secured Term Loan A Facility September 2026 Through June 2028 Senior Secured Term Loan A Facility September 2026 Through June 2028 [Member] Senior Secured Term Loan A Facility September 2026 Through June 2028 Number of reportable segments Number of Reportable Segments Total current liabilities Current liabilities Liabilities, Current Alternative Base Rate or Canadian Prime Rate Alternative Base Rate Or Canadian Prime Rate [Member] Alternative Base Rate Or Canadian Prime Rate Customer relationship intangible assets Customer Relationships [Member] Term Loan B Senior Secured Term Loan B Facility Term Loan B Due September 2031 [Member] Senior Secured Term Loan B Facility Term Loan B Due September 2031 Entity Address, City or Town Entity Address, City or Town Number of active joint ventures Number Of Equity Method Investments Number Of Equity Method Investments Statement of Financial Position [Abstract] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Intangible assets, net Total intangible assets, net Intangible Asset, Finite-Lived, after Accumulated Amortization Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Returns of capital from equity method investments Proceeds from Equity Method Investment, Distribution, Return of Capital Accumulated Amortization Intangible Asset, Finite-Lived, Accumulated Amortization Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Other comprehensive income, net of tax Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Current portion of long-term debt Less current portion of long-term debt Long-Term Debt, Current Maturities United States UNITED STATES Schedule of Long-Term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Line of credit facility, increase (decrease) in maximum borrowing capacity Line Of Credit Facility, Maximum Borrowing Capacity, Increase (Decrease) Line Of Credit Facility, Maximum Borrowing Capacity, Increase (Decrease) Revenue, Remaining Performance Obligation, Period [Domain] Revenue, Remaining Performance Obligation, Period [Domain] Revenue, Remaining Performance Obligation, Period [Domain] Accounting Standards Updates Issued but Not Yet Adopted New Accounting Pronouncements, Policy [Policy Text Block] Schedule of Segment Reporting Information Segment Reporting [Table Text Block] Non-controlling Interests Noncontrolling Interest [Member] Related and Nonrelated Parties [Axis] Related and Nonrelated Parties [Axis] Payments on revolving credit facilities Payments on revolving credit facilities Repayments of Lines of Credit Other comprehensive income Other Comprehensive Income (Loss), before Tax Total debt, net of original issue discount and deferred financing costs Long-Term Debt Document Period End Date Document Period End Date Changes in assets and liabilities, net of effects of business acquisition: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Net cash (used in) provided by investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Debt instrument, face amount Debt Instrument, Face Amount Security Exchange Name Security Exchange Name Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Segments Segment Reporting, Policy [Policy Text Block] Statement of Comprehensive Income [Abstract] Earnings Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Earnings per share: Earnings Per Share [Abstract] Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] Document Fiscal Period Focus Document Fiscal Period Focus Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Reamining Performance Obligation Period 1 Remaining Performance Obligation Period 1 [Member] Remaining Performance Obligation Period 1 Total liabilities Liabilities Trading Symbol Trading Symbol Joint Ventures Consolidation, Variable Interest Entity, Policy [Policy Text Block] Geographical [Domain] Geographical [Domain] Payments for property and equipment Payments to Acquire Property, Plant, and Equipment 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] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Company Selected Measure Name Company Selected Measure Name Income Tax Disclosure [Abstract] Divestitures, net of cash conveyed Proceeds from Divestiture of Businesses, Net of Cash Divested Pension Related Adjustments Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Total debt Long-Term Debt, Gross Credit Facility [Domain] Credit Facility [Domain] Cash flows from operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Compensation Amount Outstanding Recovery Compensation Amount Individual: Individual [Axis] Weighted-average number of diluted shares outstanding during the period (in shares) Weighted Average Number of Shares Outstanding, Diluted Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Prime contractor Sales Channel, Directly to Consumer [Member] Backlog Order or Production Backlog [Member] Entity Emerging Growth Company Entity Emerging Growth Company Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Underlying Security Market Price Change Underlying Security Market Price Change, Percent Borrowings on revolving credit facilities Proceeds from Lines of Credit Deferred income taxes Deferred Income Taxes and Tax Credits Property and equipment, net Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Maximum exposure to losses Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Revenue from Contract with Customer [Abstract] Unfavorable earnings at completion adjustments Contract With Customer Asset, Cumulative Catch Up Adjustment To Revenue, Unfavorable Adjustment Contract With Customer Asset, Cumulative Catch Up Adjustment To Revenue, Unfavorable Adjustment Award Timing Predetermined Award Timing Predetermined [Flag] Intangible Asset, Goodwill and Other [Abstract] Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Stock-based compensation and other APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Impact on diluted earnings per share attributable to common shareholders (in dollars per share) Contract With Customer, Asset, Effect On Diluted Earnings (Loss) Per Share Contract With Customer, Asset, Effect On Diluted Earnings (Loss) Per Share Effective tax rate Effective Income Tax Rate Reconciliation, Percent Organization, Consolidation and Presentation of Financial Statements [Abstract] Dilutive effect of equity awards (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements All Executive Categories All Executive Categories [Member] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Net cash inflow from sold receivables Payments For (Proceeds From) Transfer Of Financial Assets Accounted For As Sales Payments For (Proceeds From) Transfer Of Financial Assets Accounted For As Sales Depreciation Depreciation Depreciation AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Schedule of Earnings Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Debt Disclosure [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Segment Information Segment Reporting [Text Block] Minimum Minimum [Member] Expiration Date Trading Arrangement Expiration Date Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] Joint Ventures Variable Interest Entity Disclosure [Text Block] Effect of exchange rate changes on cash Effect of Exchange Rate on Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Total shareholders' equity Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest 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] Nonrelated Party Nonrelated Party [Member] Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Common stock, shares authorized (in shares) Common Stock, Shares Authorized Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Exercise Price Award Exercise Price Cash flows from investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Segment Reporting [Line Items] Segment Reporting [Line Items] Document Quarterly Report Document Quarterly Report 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] Segments [Domain] Segments [Domain] Interest Rate Swap Interest Rate Swap [Member] Senior Secured Term Loan A Facility September 2026 Senior Secured Term Loan B Facility September 2026 [Member] Senior Secured Term Loan A Facility September 2026 Debt Debt Disclosure [Text Block] Long-term contract assets Contract with Customer, Asset, after Allowance for Credit Loss, Noncurrent Unamortized original issue discount and unamortized deferred financing costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Equity method investments Equity Method Investments Equity Component [Domain] Equity Component [Domain] Commercial and International Commercial And International [Member] Commercial And International PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Term Loan Secured Debt [Member] Adoption Date Trading Arrangement Adoption Date Contributions to equity method investments Payments to Acquire Equity Method Investments Debt instrument, interest rate, stated percentage Debt Instrument, Interest Rate, Stated Percentage Total Amentum shareholders' equity Total Amentum equity Equity, Attributable to Parent ASSETS Assets [Abstract] Title Trading Arrangement, Individual Title Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Accounting Policies [Abstract] Restatement does not require Recovery Restatement Does Not Require Recovery [Text Block] Maximum amount of receivables sold (up to) Transfers Of Financial Assets Accounted For As Sales, Maximum Amount Of Receivables Sold Transfers Of Financial Assets Accounted For As Sales, Maximum Amount Of Receivables Sold Insider Trading Policies and Procedures [Line Items] Other Proceeds from (Payment for) Other Financing Activity Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Selling, general, and administrative expenses Selling, General and Administrative Expense Department of War and U.S. Intelligence Community Department Of Defense And U.S. Intelligence Community [Member] Department Of Defense And U.S. Intelligence Community Interest expense and other, net Interest expense and other, net Interest Income (Expense), Nonoperating Letter of Credit Letter of Credit [Member] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Number of operating segments Number of Operating Segments Beginning balance, tax Ending balance, tax AOCI Including Portion Attributable to Noncontrolling Interest, Tax Entity Central Index Key Entity Central Index Key Revenue, Remaining Performance Obligation, Period [Axis] Revenue, Remaining Performance Obligation, Period [Axis] Revenue, Remaining Performance Obligation, Period All Adjustments to Compensation All Adjustments to Compensation [Member] Equity [Abstract] 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] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Legal Proceedings and Commitments and Contingencies Legal Matters and Contingencies [Text Block] Revenue, remaining performance obligation, percentage Revenue, Remaining Performance Obligation, Percentage Other comprehensive income before reclassification Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Income Statement [Abstract] SHAREHOLDERS' EQUITY Equity, Attributable to Parent [Abstract] Document Transition Report Document Transition Report Investment, Name [Axis] Investment, Name [Axis] Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Schedule of Intangible Assets, Net Intangible Asset, Finite-Lived [Table Text Block] Debt instrument, basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate City Area Code City Area Code Variable Rate [Domain] Variable Rate [Domain] Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income AOCI Attributable to Parent [Member] All Individuals All Individuals [Member] Name Forgone Recovery, Individual Name Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Non-current assets Assets, Noncurrent Statement [Line Items] Statement [Line Items] Total assets Assets Joint Ventures Investment Joint Ventures, Investment [Member] Joint Ventures, Investment Other comprehensive income (loss) before reclassification and taxes Other Comprehensive Income (Loss), before Reclassifications, before Tax Issuances of common stock (in shares) Stock Issued During Period, Shares, New Issues PEO PEO [Member] Senior Secured Term Loan Facility Due September 2031 Senior Secured Term Loan Facility Due September 2031 [Member] Senior Secured Term Loan Facility Due September 2031 Stock-based compensation Share-Based Payment Arrangement, Expense Other long-term liabilities Other Liabilities, Noncurrent Goodwill Goodwill Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Revenue recognized Contract with Customer, Liability, Revenue Recognized Retained Deficit Retained Earnings [Member] Revolving Credit Facility Revolving Credit Facility [Member] Distributions to non-controlling interests Noncontrolling Interest, Adjustment To Distributions to Noncontrolling Interest Holders Noncontrolling Interest, Adjustment To Distributions to Noncontrolling Interest Holders Erroneously Awarded Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common stock, outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Award Timing Disclosures [Line Items] Foreign Currency Translation Adjustments Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Diluted (in dollars per share) Diluted earnings per share (in dollars per share) Earnings Per Share, Diluted Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Entity Current Reporting Status Entity Current Reporting Status GES GES Global Engineering Solutions Segment [Member] Global Engineering Solutions Segment Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Total Shareholder Return Amount Total Shareholder Return Amount Prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Accrued compensation and benefits Increase (Decrease) in Employee Related Liabilities Amortization of intangibles Amortization of intangibles Amortization expense Amortization of intangibles Intangible Asset, Finite-Lived, Amortization Expense Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Intangible Asset, Finite-Lived [Line Items] Intangible Asset, Finite-Lived [Line Items] Remaining sold receivables Transfer Of Financial Assets Accounted For As Sales, Receivables Sold, Outstanding, Net Of Cash Collected, And Not Remitted Transfer Of Financial Assets Accounted For As Sales, Receivables Sold, Outstanding, Net Of Cash Collected, And Not Remitted Senior Secured Term Loan A Facility September 2028 Through June 2030 Senior Secured Term Loan A Facility September 2028 Through June 2030 [Member] Senior Secured Term Loan A Facility September 2028 Through June 2030 Amounts reclassified from accumulated other comprehensive income (loss) income, tax Reclassification from AOCI, Current Period, Tax Cash flows from financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Revenues Total revenues Revenue from Contract with Customer, Excluding Assessed Tax Line of credit facility, remaining borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity New Credit Facility New Credit Facility [Member] New Credit Facility Intangible Asset, Finite-Lived, Class [Axis] Intangible Asset, Finite-Lived, Class [Axis] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Goodwill and Intangible Assets Intangible Asset and Goodwill [Text Block] Underlying Securities Award Underlying Securities Amount Net income attributable to non-controlling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Revenues Contract Balances Revenue from Contract with Customer [Text Block] Utilization of fair market value adjustments Utilization Of Fair Market Value Adjustments Utilization Of Fair Market Value Adjustments Other Payment for (Proceeds from) Other Investing Activity Beginning balance, before tax Ending balance before tax AOCI Including Portion Attributable to Noncontrolling Interest, before Tax Capitalized Contract Cost [Table] Capitalized Contract Cost [Table] Segment Reporting [Table] Segment Reporting [Table] Common stock issued for the Transaction Stock Issued Contract with Customer, Sales Channel [Axis] Contract with Customer, Sales Channel [Axis] Current assets Other Assets, Current Commitments and Contingencies Disclosure [Abstract] All Trading Arrangements All Trading Arrangements [Member] Other Performance Measure, Amount Other Performance Measure, Amount Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Operating income Operating Income (Loss) Revenue, remaining performance obligation, amount Revenue, Remaining Performance Obligation, Amount Current Fiscal Year End Date Current Fiscal Year End Date Sales of receivables Transfer Of Financial Assets Accounted For As Sales, Receivables Sold During Period Transfer Of Financial Assets Accounted For As Sales, Receivables Sold During Period Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Secured Overnight Financing Rate (SOFR), EURIBOR, or Term Canadian Overnight Report Rate Average (CORRA) Secured Overnight Financing Rate (SOFR), EURIBOR, Or Term Canadian Overnight Report Rate Average (CORRA) [Member] Secured Overnight Financing Rate (SOFR), EURIBOR, Or Term Canadian Overnight Report Rate Average (CORRA) Transfer Of Financial Assets Accounted For As Sales [Roll Forward] Transfer Of Financial Assets Accounted For As Sales [Roll Forward] Transfer Of Financial Assets Accounted For As Sales 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] Entity File Number Entity File Number Rule 10b5-1 Arrangement Adopted Rule 10b5-1 Arrangement Adopted [Flag] Beginning balance: Outstanding balance sold to Purchaser Transfer Of Financial Assets Accounted For As Sales, Receivables Sold, Outstanding Transfer Of Financial Assets Accounted For As Sales, Receivables Sold, Outstanding Distributions to non-controlling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Common stock, issued (in shares) Common Stock, Shares, Issued Measure: Measure [Axis] Schedule of Selected Financial Information for our Consolidated Joint Ventures VIEs Schedule of Variable Interest Entities [Table Text Block] Contract with Customer, Basis of Pricing [Axis] Contract with Customer, Basis of Pricing [Axis] Accumulated Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Equity Components [Axis] Equity Components [Axis] Related Party Related Party [Member] Income taxes paid, net of receipts Income Tax Paid, after Refund Received Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Entity Interactive Data Current Entity Interactive Data Current Variable Rate [Axis] Variable Rate [Axis] Less: net income (loss) attributable to non-controlling interests Non-controlling interests Net income (loss) attributable to non-controlling interests Net Income (Loss) Attributable to Noncontrolling Interest Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Deferred tax liabilities Deferred Income Tax Liabilities, Net Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Entity Small Business Entity Small Business Comprehensive income attributable to common shareholders Comprehensive Income (Loss), Net of Tax, Attributable to Parent Termination Date Trading Arrangement Termination Date Compensation Actually Paid vs. Total Shareholder Return Compensation Actually Paid vs. Total Shareholder Return [Text Block] MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Other current liabilities Other Liabilities, Current Other long-term assets Other Assets, Noncurrent Document Type Document Type Acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Loss on extinguishment of debt Loss on extinguishment of debt Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Fixed-price Fixed-Price Contract [Member] Fair Value as of Grant Date Award Grant Date Fair Value Goodwill [Table] Goodwill [Table] Transfers and Servicing of Financial Assets [Abstract] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Arrangement Duration Trading Arrangement Duration Statement of Stockholders' Equity [Abstract] Cost-plus-fee Cost Plus Fee Contract [Member] Cost Plus Fee Contract Local Phone Number Local Phone Number Entity Address, Postal Zip Code Entity Address, Postal Zip Code Registrant Name Entity Registrant Name Income before income taxes Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Commitments and contingencies (Note 13) Commitments and Contingencies Gross Carrying Value Intangible Asset, Finite-Lived, before Accumulated Amortization Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Equity earnings of non-consolidated subsidiaries Equity earnings of non-consolidated subsidiaries Income (Loss) from Equity Method Investments Forgone Recovery due to Expense of Enforcement, Amount Forgone Recovery due to Expense of Enforcement, Amount Executive Category: Executive Category [Axis] Income tax provision related to items of other comprehensive income Other Comprehensive Income (Loss), Tax Capitalized Contract Cost [Line Items] Capitalized Contract Cost [Line Items] LIABILITIES Liabilities and Equity [Abstract] Intangible Asset, Finite-Lived, Class [Domain] Intangible Asset, Finite-Lived, Class [Domain] All Award Types Award Type [Domain] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount Variable Interest Entity [Table] Variable Interest Entity [Table] Supplemental disclosure of cash flow information Supplemental Cash Flow Information [Abstract] PEO Name PEO Name Geographical [Axis] Geographical [Axis] Gain (Loss) on Derivative Instruments Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] DS DS Digital Solutions Segment [Member] Digital Solutions Segment Other segment expenses Segment Reporting, Other Segment Item, Amount Repayments of borrowings under the credit agreement Repayments of Secured Debt Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Entity Tax Identification Number Entity Tax Identification Number Reamining Performance Obligation Period 2 Remaining Performance Obligation Period 2 [Member] Remaining Performance Obligation Period 2 Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Goodwill [Table] Intangible Asset, Finite-Lived [Table] Net favorable adjustments Contract with Customer, Asset, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Material Terms of Trading Arrangement Material Terms of Trading Arrangement [Text Block] Non-NEOs Non-NEOs [Member] 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] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Debt Instrument [Axis] Debt Instrument [Axis] Cash collected, not remitted to Purchaser Transfers Of Financial Assets Accounted For As Sales, Cash Collected Not Remitted To Purchaser Transfers Of Financial Assets Accounted For As Sales, Cash Collected Not Remitted To Purchaser Ownership percentage Equity Method Investment, Ownership Percentage Stock-based compensation Share-Based Payment Arrangement, Noncash Expense Accounts payable, contract liabilities, and other current liabilities Increase (Decrease) In Accounts Payable, Contract Liabilities, Other Current Liabilities Increase (Decrease) In Accounts Payable, Contract Liabilities, Other Current Liabilities Investment, Name [Domain] Investment, Name [Domain] Customer [Domain] Customer [Domain] Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Basic (in dollars per share) Basic earnings per share (in dollars per share) Earnings Per Share, Basic Contract liabilities Contract liabilities - deferred revenues and other contract liabilities Contract with Customer, Liability, Current Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Insider Trading Arrangements [Line Items] Long-term debt, net of current portion Total long-term debt, net of current portion Long-Term Debt, Excluding Current Maturities Cost of revenues Cost of Revenue Award Type Award Type [Axis] Named Executive Officers, Footnote Named Executive Officers, Footnote [Text Block] Accounts receivable, net Related party receivables due from our equity method investments Accounts Receivable, after Allowance for Credit Loss, Current Retained deficit Retained Earnings (Accumulated Deficit) Revolver Revolver [Member] Revolver 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] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Proceeds from borrowing under the term loans Proceeds from Issuance of Secured Debt Common Stock Common Stock [Member] Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Cover [Abstract] International Non-US [Member] Derivative Contract [Domain] Derivative Contract [Domain] Equity Awards Adjustments Equity Awards Adjustments [Member] Total liabilities and shareholders' equity Liabilities and Equity Employee Stock Option Share-Based Payment Arrangement, Option [Member] Amounts reclassified from accumulated other comprehensive income (loss), before tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Non-controlling interests Non-controlling interests Equity, Attributable to Noncontrolling Interest Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Favorable earnings at completion adjustments Contract With Customer Asset, Cumulative Catch Up Adjustment To Revenue, Favorable Adjustment Contract With Customer Asset, Cumulative Catch Up Adjustment To Revenue, Favorable Adjustment Related and Nonrelated Parties [Domain] Related and Nonrelated Parties [Domain] Tabular List, Table Tabular List [Table Text Block] Additional paid-in capital Additional Paid in Capital Schedule of MARPA Activity Transfer of Financial Assets Accounted for as Sales [Table Text Block] Other long-term liabilities Increase (Decrease) in Other Noncurrent Liabilities Total Shareholders' Equity Attributable to Amentum Holdings, Inc. Parent [Member] Name Awards Close in Time to MNPI Disclosures, Individual Name 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] Accounts receivable, net Receivables, Net, Current Adjustment to Compensation: Adjustment to Compensation [Axis] Amounts reclassified from accumulated other comprehensive income Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Rule 10b5-1 Arrangement Terminated Rule 10b5-1 Arrangement Terminated [Flag] Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Interest paid Interest Paid, Excluding Capitalized Interest, Operating Activity Statement of Cash Flows [Abstract] Term Loan A Senior Secured Term Loan A Facility Term Loan A Due April 2031 [Member] Senior Secured Term Loan A Facility Term Loan A Due April 2031 Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Other U.S. Government Agencies Other U.S. Government Agencies [Member] Other U.S. Government Agencies Name Measure Name Income Taxes Income Tax Disclosure [Text Block] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax Accounts payable Accounts Payable, Current Pay vs Performance Disclosure [Line Items] Other Other Noncash Income (Expense) Debt Instrument [Line Items] Debt Instrument [Line Items] Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Net unrealized gain on interest rate swaps Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification, before Tax Additional Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Subcontractor Sales Channel, Through Intermediary [Member] Cash collections Transfers Of Financial Assets Accounted For As Sales, Cash Collected Transfers Of Financial Assets Accounted For As Sales, Cash Collected Name Trading Arrangement, Individual Name Cash and cash equivalents Cash and cash equivalents Cash and Cash Equivalent Company Selected Measure Amount Company Selected Measure Amount Distributions from equity method investments Proceeds from Equity Method Investment, Distribution Secured Overnight Financing Rate (SOFR) Secured Overnight Financing Rate (SOFR) [Member] Net income (loss) including non-controlling interests Net income (loss) including non-controlling interests Net income including non-controlling interests Net income including non-controlling interests Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Acquisition, transaction and integration costs Acquisition, Transaction And Integration Costs Acquisition, Transaction And Integration Costs Credit Agreement Credit Agreement [Member] Credit Agreement Contract with Customer, Sales Channel [Domain] Contract with Customer, Sales Channel [Domain] Current assets: Assets, Current [Abstract] Non-PEO NEO Non-PEO NEO [Member] Senior notes Senior Notes [Member] Entity Address, Address Line One Entity Address, Address Line One Provision for income taxes Income Tax Expense (Benefit) Adjustments to reconcile net income including non-controlling interests to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Noncash Item [Abstract] Cost of revenues Cost of revenues Cost of Product and Service Sold Capitalized software Technology-Based Intangible Assets [Member] Award Timing Method Award Timing Method [Text Block] Adjusted EBITDA attributable to Amentum Holdings, Inc. Adjusted Earnings Before Interest, Tax, Depreciation And Amortization Adjusted Earnings Before Interest, Tax, Depreciation And Amortization Net change in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Sales of Receivables Transfers and Servicing of Financial Assets [Text Block] Time-and-materials Time-and-Materials Contract [Member] Recent Accounting Pronouncements Accounting Standards Update and Change in Accounting Principle [Text Block] Net income attributable to common shareholders Net income attributable to common shareholders Net Income (Loss) Attributable to Parent Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Bridge Loan Bridge Loan [Member] Statement [Table] Statement [Table] Restatement Determination Date: Restatement Determination Date [Axis] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Schedule of Changes in Estimated Contract Earnings Schedule of Contract Balances Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Accounts receivable, net Increase (Decrease) in Receivables Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block]