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Cover [Abstract] International Non-US [Member] Foreign currency translation adjustments Goodwill, Foreign Currency Translation, Gain (Loss) Equity Awards Adjustments Equity Awards Adjustments [Member] Revenue, Initial Application Period Cumulative Effect Transition [Line Items] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items] $1,000 million notes, due February 2031 Notes Which Mature On February Two Thousand Thirty One [Member] Notes Which Mature On February Two Thousand Thirty One Homeland Homeland Segment [Member] Homeland Segment Total liabilities and stockholders' equity Liabilities and Equity Employee Stock Option Share-Based Payment Arrangement, Option [Member] Current portion of long-term debt Debt, Current Non-controlling interest Equity, Attributable to Noncontrolling Interest Segments [Axis] Segments [Axis] Segments [Axis] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Accounts payable and accrued liabilities and 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Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Impact on diluted EPS attributable to Leidos common stockholders (in dollars per share) Increase (Decrease) In Income From Change In Contract Estimates Per Diluted Share Increase (Decrease) In Income From Change In Contract Estimates Per Diluted Share Receivables, net Receivables, Net, Current Adjustment to Compensation: Adjustment to Compensation [Axis] Reclassification from AOCI 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 Cash paid for interest Interest Paid, Excluding Capitalized Interest, Operating Activity Payments for property, equipment and software Payments to Acquire Productive Assets Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Total Other Commitment Time-and-materials and fixed-price-level-of-effort Time-And-Materials And Fixed-Price-Level-Of-Effort [Member] Time-and-materials and Fixed-price-level-of-effort [Member] Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Long-term debt, net of current portion Total long-term debt, net of current portion Long-Term Debt and Lease Obligation Direct labor Cost, Direct Labor $750 million notes, due March 2033 Notes Which Mature On March Two Thousand Thirty Three [Member] Notes Which Mature On March Two Thousand Thirty Three Name Measure Name Property, plant and equipment additions Property, Plant and Additions, Non-cash Investing Activity Property, Plant and Additions, Non-cash Investing Activity Income Taxes Income Tax Disclosure [Text Block] 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] Purchase consideration Business Combination, Consideration Transferred Additional paid-in capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Kudu Dynamics Kudu Dynamics [Member] Kudu Dynamics Cost-reimbursement and fixed-price-incentive-fee Cost-Reimbursement And Fixed-Price-Incentive-Fee [Member] Cost-reimbursement and Fixed-price-incentive-fee [Member] Revenue recognized Revenue Not from Contract with Customer Name Trading Arrangement, Individual Name Cash and cash equivalents Cash and cash equivalents at end of period Cash and Cash Equivalent 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, Continuing Operation Company Selected Measure Amount Company Selected Measure Amount Depreciation and amortization 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Consolidated Total Debt To Consolidated EBITDA Ratio Debt Instrument, Covenant, Adjusted Consolidated Total Debt To Consolidated EBITDA Ratio Income tax expense Income Tax Expense (Benefit) Legal Proceedings [Line Items] Legal Proceedings [Line Items] Legal Proceedings [Line Items] Award Timing Method Award Timing Method [Text Block] Consolidation Consolidation, Policy [Policy Text Block] Net (decrease) increase in cash, cash equivalents and restricted cash, including cash classified in current assets held for sale 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] Deferred tax liabilities Business Combination, Recognized Liability Assumed, Deferred Tax Liability Net income attributable to Leidos common stockholders 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] Goodwill Disposal Group, Including Discontinued Operation, Goodwill Statement [Table] Statement [Table] Restatement Determination Date: Restatement Determination Date [Axis] Schedule of Changes in the Components of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Transfers to assets held for sale Goodwill, Transfers Schedule of Components of Contract Assets and Contract Liabilities Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Receivables Increase (Decrease) in Receivables Accrued payroll and employee benefits Business Combination, Recognized Liability Assumed, Accrued Payroll And Employee Benefits Business Combination, Recognized Liability Assumed, Accrued Payroll And Employee Benefits Schedule of Preliminary Fair Value of Intangible Assets Acquire Weighted Average Amortization Business Combination, Intangible Asset, Acquired, Indefinite-Lived [Table Text Block] Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Significant Accounting Policies [Text Block] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block]