Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Changes in Goodwill by Segment Schedule of Goodwill [Table Text Block] Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Receivables, net Receivables, Net, Current Inventory, prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Total current assets Assets, Current Property, plant and equipment, net Property, Plant and Equipment, Net Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Goodwill Goodwill Deferred tax assets Deferred Tax Assets, Net of Valuation Allowance, Noncurrent Other assets Other Assets, Noncurrent Total assets Assets LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued liabilities Accrued Liabilities, Current Accrued payroll and employee benefits Employee-related Liabilities, Current Dividends payable Dividends Payable, Current Income taxes payable Taxes Payable, Current Notes payable and long-term debt, current portion Debt, Current Total current liabilities Liabilities, Current Notes payable and long-term debt, net of current portion Long-term Debt and Capital Lease Obligations Deferred tax liabilities Deferred Tax Liabilities, Net, Noncurrent Other long-term liabilities Other Liabilities, Noncurrent Stockholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock, $.0001 par value, 500 million shares authorized, 151 million and 150 million shares issued and outstanding at March 31, 2017 and December 30, 2016, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated deficit Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Total Leidos stockholders’ equity Stockholders' Equity Attributable to Parent Non-controlling interest Stockholders' Equity Attributable to Noncontrolling Interest Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Total liabilities and stockholders' equity Liabilities and Equity Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Fair Value Hedging Fair Value Hedging [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Asset Derivatives Interest Rate Swap [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) London Interbank Offered Rate (LIBOR) [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Secured Debt Secured Debt [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Term Loan A Term Loan A [Member] Term Loan A [Member] Notes Which Mature In December 2020 Notes Which Mature On December Two Thousand Twenty [Member] Notes Which Mature on December Two Thousand Twenty [Member] Term Loan B Term Loan B Due August Twenty Twenty Three [Member] Term Loan B Dollar One Thousand and One Hundred and Thirty One Million Due August Twenty Twenty Three [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Long-term debt Long-term Debt, Gross Unamortized discount Debt Instrument, Unamortized Discount Debt issuance costs Debt Issuance Costs, Net Derivative asset Derivative Asset Variable rate (in percentage) Debt Instrument, Basis Spread on Variable Rate Note payable, face amount Debt Instrument, Face Amount Debt instrument, decrease in basis points Debt Instrument, Decrease in Basis Points Debt Instrument, Decrease in Basis Points Stated interest rate (in percentage) Debt Instrument, Interest Rate, Stated Percentage Goodwill Goodwill and Intangible Assets Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments Commitments Disclosure [Text Block] Discontinued Operations and Disposal Groups [Abstract] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Other Operating Income (Expense) Other Operating Income (Expense) [Member] Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Civil Civil Segment [Member] Civil Segment [Member] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Disposal Group, Disposed of by Sale, Not Discontinued Operations Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Plainfield Plainfield Renewal Energy Holdings LLC [Member] Plainfield Renewal Energy Holdings LLC [Member] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Groups, Including Discontinued Operations, Name [Domain] Disposal Group Name [Domain] One Business One Business [Member] One Business [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Proceeds from divestitures of the business Proceeds from Divestiture of Businesses, Net of Cash Divested Gain on sale of business Gain (Loss) on Disposition of Business Receivable, net Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net Other assets Disposal Group, Including Discontinued Operation, Other Assets Accounts payable and accrued liabilities Disposal Group, Including Discontinued Operation, Accounts Payable and Accrued Liabilities, Current Liability in connection with issuance of a performance guarantee on a contract sold Accounts Payable and Accrued Liabilities, Current Selling expense Selling Expense Disposal, consideration Disposal Group, Including Discontinued Operation, Consideration Proceeds from divestiture of interest Proceeds from Divestiture of Interest in Consolidated Subsidiaries Amount of consideration received Noncash or Part Noncash Divestiture, Amount of Consideration Received Proceeds from collections on promissory note Proceeds from Collection of Notes Receivable, Including Interest Proceeds from Collection of Notes Receivable, Including Interest Intangible Assets Intangible Assets Disclosure [Text Block] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Indefinite-lived Intangible Assets by Major Class [Axis] Indefinite-lived Intangible Assets [Axis] Indefinite-lived Intangible Assets, Major Class Name [Domain] Indefinite-lived Intangible Assets, Major Class Name [Domain] Trade names Trade Names [Member] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Programs and contract intangibles Contract-Based Intangible Assets [Member] Backlog Order or Production Backlog [Member] Customer relationships Customer Relationships [Member] Software and technology Computer Software, Intangible Asset [Member] Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Gross carrying value Finite-Lived Intangible Assets, Gross Accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Net carrying value Finite-Lived Intangible Assets, Net Indefinite-lived intangible assets Indefinite-Lived Intangible Assets (Excluding Goodwill) Total intangible assets, Gross carrying value Intangible Assets, Gross (Excluding Goodwill) Total intangible assets, Net carrying value Statement of Cash Flows [Abstract] Cash flows from operations: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income to net cash used in operations: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Stock-based compensation Share-based Compensation Other Other Noncash Income (Expense) Change in assets and liabilities, net of effects of acquisitions and dispositions: Increase (Decrease) in Operating Capital [Abstract] Receivables Increase (Decrease) in Receivables Inventory, prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Accounts payable and accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Accrued payroll and employee benefits Increase (Decrease) in Employee Related Liabilities Deferred income taxes and income taxes receivable/payable Increase (Decrease) in Income Taxes Other long-term assets/liabilities Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net Total cash flows used in operating activities of continuing operations Net Cash Provided by (Used in) Operating Activities, Continuing Operations Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Payments for property, plant and equipment Payments to Acquire Property, Plant, and Equipment Proceeds from collections on promissory note Proceeds from Collection of Notes Receivable Net proceeds from sale of assets Proceeds from Sale of Property, Plant, and Equipment Total cash flows used in investing activities of continuing operations Net Cash Provided by (Used in) Investing Activities, Continuing Operations Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Payments of long-term debt Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities Proceeds from issuances of stock Proceeds from Issuance or Sale of Equity Repurchases of stock and other Payments for Repurchase of Equity Dividend payments Payments of Ordinary Dividends Total cash flows used in financing activities of continuing operations Net Cash Provided by (Used in) Financing Activities, Continuing Operations Decrease in cash and cash equivalents from continuing operations Net Cash Provided by (Used in) Continuing Operations Cash flows from discontinued operations: Net Cash Provided by (Used in) Discontinued Operations [Abstract] Cash used in investing activities of discontinued operations Cash Provided by (Used in) Investing Activities, Discontinued Operations Decrease in cash and cash equivalents from discontinued operations Net Cash Provided by (Used in) Discontinued Operations Total decrease in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and Cash Equivalents, at Carrying Value, Including Discontinued Operations Cash and cash equivalents at end of period Accounting Policies [Abstract] Nature of Operations and Basis of Presentation Business Description and Accounting Policies [Text Block] Changes in Estimates on Contracts Changes In Estimates On Contracts [Policy Text Block] Changes In Estimates On Contracts [Policy Text Block] Accounting Standards Updates Adopted New Accounting Pronouncements, Policy [Policy Text Block] Accounting Standards Updates Issued But Not Yet Adopted Description Of New Accounting Pronouncements Not Yet Adopted Policy [Policy Text Block] Description of New Accounting Pronouncements Not yet Adopted Derivative Instruments and Hedging Activities Disclosure [Abstract] Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location Schedule of Cash Flow Hedging Instruments, Statements of Financial Performance and Financial Position, Location [Table Text Block] Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location [Table Text Block] Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location [Table Text Block] Restructuring and Related Activities [Abstract] Schedule of Restructuring and Related Costs [Table] Schedule of Restructuring and Related Costs [Table] Restructuring Plan [Axis] Restructuring Plan [Axis] Restructuring Plan [Domain] Restructuring Plan [Domain] Restructuring Due To IS&GS Acquisition IS&GS Acquisition [Member] Restructuring Due To IS&GS Acquisition [Member] Restructuring Type [Axis] Restructuring Type [Axis] Type of Restructuring [Domain] Type of Restructuring [Domain] Severance costs Employee Severance [Member] Lease termination expenses Contract Termination [Member] Restructuring Cost and Reserve [Line Items] Restructuring Cost and Reserve [Line Items] Restructuring Reserve [Roll Forward] Restructuring Reserve [Roll Forward] Restructuring reserve, opening balance Restructuring Reserve Restructuring expenses Restructuring Charges Cash payments Payments for Restructuring Restructuring reserve, closing balance Period to settle restructuring liability, minimum (in years) Restructuring Liability, Period to Settle Restructuring Liability, Period to Settle Senior Notes Senior Notes [Member] Unsecured Debt Unsecured Debt [Member] Notes Which Mature In December 2040 Notes Which Mature On December Two Thousand Forty [Member] Notes Which Mature On December Two Thousand Forty [Member] Term Loan A $400 million due August 2019 Term Loan A Due August Twenty Nineteen [Member] Term Loan A Due August Twenty Nineteen [Member] Term Loan A $690 million due August 2021 Term Loan A Dollar Six Hundred and Ninety Million Due August Twenty Twenty One [Member] Term Loan A Dollar Six Hundred and Ninety Million Due August Twenty Twenty One [Member] Term Loan A $310 million due August 2021 Term Loan A Dollar Three Hundred and Ten Million Due August Twenty Twenty One [Member] Term Loan A Dollar Three Hundred and Ten Million Due August Twenty Twenty One [Member] Term Loan B $1,131 million due August 2023 Notes Which Mature In July 2032 Notes Which Mature On July Two Thousand Thirty Two [Member] Notes Which Mature On July Two Thousand Thirty Two [Member] Notes Which Mature In July 2033 Notes Which Mature On July Two Thousand Thirty Three [Member] Notes Which Mature On July Two Thousand Thirty Three [Member] Capital leases and other notes payable due on various dates through fiscal 2020 Capital Leases And Other Notes Payable Due On Various Dates Through Fiscal Two Thousand Twenty [Member] Capital Leases And Other Notes Payable Due On Various Dates Through Fiscal Two Thousand Twenty One [Member] Senior secured notes: Senior Notes Senior secured term loans: Secured Debt Senior unsecured notes: Unsecured Debt Capital leases due on various dates through fiscal 2020 Capital Lease Obligations Total notes payable and long-term debt Long-term Debt and Capital Lease Obligations, Including Current Maturities Less: current portion Long-term Debt and Capital Lease Obligations, Current Total notes payable and long-term debt, net of current portion Effective interest rate Debt Instrument, Interest Rate, Effective Percentage Senior unsecured notes, face amount 2017 (remainder of year) Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year 2018 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Five 2022 and thereafter Finite-Lived Intangible Assets, Amortization Expense, after Year Five Supplemental Cash Flow Information [Abstract] Supplementary Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block] Schedule of Intangible Assets Including Estimates of Assets Acquired Schedule of Intangible Assets and Goodwill [Table Text Block] Schedule of Amortization Expense for Finite-Lived Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Divestitures Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Legal Proceedings [Table] Legal Proceedings [Table] Legal Proceedings [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Member] Subsequent Event [Member] Information Systems & Global Solutions Business of Lockheed Martin Information Systems & Global Solutions Business of Lockheed Martin [Member] Information Systems & Global Solutions Business of Lockheed Martin [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Lockheed Martin Lockheed Martin [Member] Lockheed Martin [Member] Virnet X Inc Virnet X Inc [Member] Virnet X Inc [Member] Leidos Leidos [Member] Leidos [Member] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] MSA Venture MSA Venture [Member] MSA Venture [Member] Data Privacy Litigation Data Privacy Litigation [Member] Data Privacy Litigation [Member] Contracts by Third Party [Axis] Contracts By Third Party [Axis] Contracts by Third Party [Axis] Contracts by Third Party [Domain] Contracts By Third Party [Domain] Contracts by Third Party [Domain] Greek Government Contract Greek Government Contract [Member] Greek Government Contract [Member] Legal Proceedings And Related Matters [Axis] Legal Proceedings And Related Matters [Axis] Legal Proceedings And Related Matters [Axis] Legal Proceedings And Related Matters [Domain] Legal Proceedings And Related Matters [Domain] Legal Proceedings And Related Matters [Domain] Securities Class Actions Securities Class Actions [Member] Securities Class Actions [Member] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Letters Of Credit Related System Support And Maintenance Letters Of Credit Related System Support And Maintenance [Member] Letters of Credit Related System Support and Maintenance [Member] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Invoice for Undisputed Portion of Contract Invoice For Undisputed Portion Of Contract [Member] Invoice for Undisputed Portion of Contract [Member] Value Added Taxes Value Added Taxes [Member] Value Added Taxes [Member] Letters of Credit Relating to Delivery Letters Of Credit Relating To Delivery [Member] Letters of Credit Relating to Delivery [Member] Standby Letters of Credit Standby Letters of Credit [Member] Legal Proceedings [Line Items] Legal Proceedings [Line Items] Legal Proceedings [Line Items] Estimate of possible loss Loss Contingency, Estimate of Possible Loss Percentage of damages covered, between $38 million and $64 million (percentage) Loss Contingency, Percentage of Damages Covered, Between Thirty Eight Million and Sixty Four Million Settlement Amount Loss Contingency, Percentage of Damages Covered, Between Thirty Eight Million and Sixty Four Million Settlement Amount Percentage of damages covered, excess of $64 million settlement amount (percentage) Loss Contingency, Percentage of Damages Covered, Excess of Sixty Four Million Settlement Amount Loss Contingency, Percentage of Damages Covered, Excess of Sixty Four Million Settlement Amount Contingency accrual Loss Contingency Accrual Indemnification asset Business Combination, Indemnification Assets, Amount as of Acquisition Date Number of plaintiffs Loss Contingency, Number of Plaintiffs Number of lawsuits Number Of Lawsuits Number Of Lawsuits Number of lawsuits, withdrawn Loss Contingency Claims Resolved Loss Contingency Claims Resolved Number of lawsuits, consolidated Consolidated Cases Number Of Lawsuits Consolidated Cases Number Of Lawsuits Number of former Chief Executive Officers Number of Former Chief Executive Officers Number of Former Chief Executive Officers Contracts receivable Contract Receivable Arbitral award Gain Contingency, Unrecorded Amount Recorded losses Cumulative Contract Losses Cumulative losses on a customer contract. Amount outstanding Long-term Line of Credit Letter of credit available to the company Third Party Credit Enhancement Amount Third Party Credit Enhancement, Amount Gain contingency, patents found infringed upon, number Gain Contingency, Patents Found Infringed upon, Number Litigation settlement Litigation Settlement, Amount Litigation Settlement, percentage of total (percentage) Litigation Settlement, Amount, Percentage of Total Litigation Settlement, Amount, Percentage of Total Restructuring Expenses Restructuring and Related Activities Disclosure [Text Block] Schedule of Supplementary Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Line Items] Business Acquisition [Line Items] Acquisition costs Strategic Acquisition and Integration Costs Strategic Acquisition and Integration Costs Integration costs Other Integration Costs Other Integration Costs Total acquisition and integration costs Acquisition and Integration Costs Acquisition and Integration Costs Cash paid for interest Interest Paid Cash paid for income taxes, net of refunds Income Taxes Paid, Net Non-cash financing activity: Noncash Investing and Financing Items [Abstract] Capital lease obligation Capital Lease Obligations Incurred Equity [Abstract] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Total accumulated other comprehensive income (loss) AOCI Attributable to Parent [Member] Foreign currency translation adjustments Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Unrecognized (loss) gain on derivative instruments Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Pension liability adjustments Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Balance, value Other comprehensive income Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent Taxes Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent Balance, value Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying value Reported Value Measurement [Member] Estimate of Fair Value Measurement [Member] Estimate of Fair Value Measurement [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Derivative Asset Stated interest rate (in percentage) Derivative, Fixed Interest Rate Derivative Liability, Notional Amount Derivative Liability, Notional Amount Notes Receivable, Fair Value Disclosure Notes Receivable, Fair Value Disclosure Debt Instrument, Fair Value Disclosure Debt Instrument, Fair Value Disclosure Long-term Debt and Capital Lease Obligations, Including Current Maturities Acquisitions Business Combination Disclosure [Text Block] Business Combination, Consideration Transferred [Abstract] Business Combination, Consideration Transferred [Abstract] Value of common stock issued to Lockheed Martin stockholders(1) Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Equity consideration for replacement awards Business Combination, Consideration Transferred, Equity Interests Issued and Issuable, Equity -based Awards Business Combination, Consideration Transferred, Equity Interests Issued and Issuable, Equity -based Awards Preliminary working capital adjustments Consideration Transfered, Working Capital Adjustment Consideration Transfered, Working Capital Adjustment Preliminary purchase price Business Combination, Consideration Transferred Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract] Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract] Cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Receivables Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables Inventory, prepaid expenses and other current assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets Property, plant and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Deferred tax assets Business Combination Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Other assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Assets Accounts payable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable Accrued liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accrued Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accrued Liabilities Accrued payroll and employee benefits Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Long-term debt, current portion Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt Deferred tax liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Long-term debt, net of current portion Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities Other long-term liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Total identifiable net liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Non-controlling interest Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value Goodwill Preliminary purchase price Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest Earnings Per Share [Abstract] Earnings Per Share (EPS) Earnings Per Share [Text Block] Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Defense Solutions Defense Solution Segment [Member] Defense Solution Segment [Member] Civil Health Health Segment [Member] Health Segment [Member] Corporate Corporate Segment [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Revenues Revenues Operating income (loss) Operating Income (Loss) Schedule of Notes Payable and Long-Term Debt Schedule of Long-term Debt Instruments [Table Text Block] Business Segments Segment Reporting Disclosure [Text Block] Restructuring and Related Costs Restructuring and Related Costs [Table Text Block] Schedule of Restructuring Reserve by Type of Cost Schedule of Restructuring Reserve by Type of Cost [Table Text Block] Schedule of Integration Costs Schedule of Business Acquisitions, by Acquisition [Table Text Block] Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Business Acquisition, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Debt Long-term Debt [Text Block] Document Documentand Entity Information [Abstract] Document Documentand Entity Information [Abstract] Document Type Document Type Amendment Flag Amendment Flag Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Trading Symbol Trading Symbol Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Common stock, par value per share (dollar per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized Common Stock, Shares Authorized Common stock, shares issued Common Stock, Shares, Issued Common stock, shares outstanding Common Stock, Shares, Outstanding Basic weighted average number of shares outstanding (shares) Weighted Average Number of Shares Outstanding, Basic Dilutive common share equivalents-stock options and other stock awards (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Diluted weighted average number of shares outstanding (shares) Weighted Average Number of Shares Outstanding, Diluted Line of Credit Line of Credit [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Unsecured borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Statement of Comprehensive Income [Abstract] Net income Other comprehensive income, net of taxes: Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent [Abstract] Foreign currency translation adjustments Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax Unrecognized gain on derivative instruments Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Total other comprehensive income, net of taxes Other Comprehensive Income (Loss), Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less: comprehensive income attributable to non-controlling interest, net of taxes Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Comprehensive income attributable to Leidos common stockholders Comprehensive Income (Loss), Net of Tax, Attributable to Parent Income Statement [Abstract] Cost of revenues Cost of Revenue Selling, general and administrative expenses Selling, General and Administrative Expense Acquisition and integration costs Equity earnings of non-consolidated subsidiaries Income (Loss) from Equity Method Investments Operating income Interest income Interest Income, Other Interest expense Interest Expense Other income, net Other Nonoperating Income (Expense) Income from continuing operations before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Less: net income attributable to non-controlling interest, net of taxes Net Income (Loss) Attributable to Noncontrolling Interest Net income attributable to Leidos common stockholders Net Income (Loss) Attributable to Parent Earnings per share: Basic (dollar per share) Earnings Per Share, Basic Diluted (dollar per share) Earnings Per Share, Diluted Cash dividends declared per share (dollars per share) Common Stock, Dividends, Per Share, Declared Fair Value Measurements Fair Value Disclosures [Text Block] Property, Plant and Equipment [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Computers and other equipment Computer and Other Equipment [Member] Computer and Other Equipment [Member] Leasehold improvements Leasehold Improvements [Member] Buildings and improvements Building and Building Improvements [Member] Office furniture and fixtures Furniture and Fixtures [Member] Land Land [Member] Construction in progress Construction in Progress [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Property, plant and equipment, gross Property, Plant and Equipment, Gross Less: accumulated depreciation and amortization Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Property, plant and equipment, net Depreciation Depreciation Schedule of Changes In Estimates On Contracts Schedule of Change in Accounting Estimate [Table Text Block] Derivative Instruments Derivative Instruments and Hedging Activities Disclosure [Text Block] Derivative [Table] Derivative [Table] Cash Flow Hedging Cash Flow Hedging [Member] Asset Derivatives Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other long-term liabilities Long-term Debt [Member] Other assets Other Assets [Member] Derivative [Line Items] Derivative [Line Items] Hedged instrument, face amount Derivative asset Derivative Asset, Fair Value, Gross Asset Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Effective portion reclassified from accumulated other comprehensive income (loss) to earnings Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion Gains expected to be reclassified in the next 12 months Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Programs and contract intangibles Number of shares Lockheed Martin shareholders will receive from Leidos (in shares) Business Combination, Merger Agreement, Equity Interest Issued or Issuable , Number of Shares Business Combination, Merger Agreement, Equity Interest Issued or Issuable , Number of Shares Share price (in usd per share) Share Price Special dividend declared (usd per share) Special Dividend Paid, Per Share Special Dividend Paid, Per Share Decrease in PPE Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment Increase in other assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Assets Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Other Assets Increase in accounts payable Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Payable Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accounts Payable Increase in accrued liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accrued Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Accrued Liabilities Increase in deferred tax liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Deferred Tax Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Deferred Tax Liabilities Fair value of non controlling interest Goodwill acquired, expected tax deductible amount Business Acquisition, Goodwill, Expected Tax Deductible Amount Acquisition related costs Business Combination, Acquisition Related Costs Acquired intangible assets, weighted average useful life (in years) Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Intangible acquired, fair value Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles Contingencies Contingencies Disclosure [Text Block] Schedule of Goodwill [Table] Schedule of Goodwill [Table] Business Segments [Axis] Goodwill [Line Items] Goodwill [Line Items] Goodwill [Roll Forward] Goodwill [Roll Forward] Beginning balance, Goodwill Acquisition of the IS&GS Business Goodwill, Acquired During Period Adjustment to original purchase price allocation Goodwill, Translation and Purchase Accounting Adjustments Ending balance, Goodwill Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock Options Employee Stock options and Vesting Stock Awards [Member] Employee Stock options and Vesting Stock Awards [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive stock based awards Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Reconciliation of Weighted Average Number of Shares Outstanding Schedule of Weighted Average Number of Shares [Table Text Block] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Property, Plant and Equipment Property, Plant and Equipment [Table Text Block] Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Amortization of intangible assets Amortization of Intangible Assets Basis of Presentation and Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Net favorable impact to income from continuing operations before taxes Increase (Decrease) In Income From Change In Contract Estimates Increase (Decrease) In Income From Change In Contract Estimates Increase in income from continuing operations per diluted share (usd 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 Accumulated Other Comprehensive Income (Loss) Stockholders' Equity Note Disclosure [Text Block] Schedule of Segment Reporting Information by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Significant Accounting Policies [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-09, Excess Tax Benefit Component Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member] Accounting Standards Update 2016-09, Excess Tax Benefit Component [Member] New Accounting Pronouncement, Early Adoption [Axis] New Accounting Pronouncement, Early Adoption [Axis] New Accounting Principles, Early Adoption [Domain] New Accounting Principles, Early Adoption [Domain] New Accounting Pronouncement, Early Adoption, Effect New Accounting Pronouncement, Early Adoption, Effect [Member] Leidos, Inc. Subsidiaries [Member] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Significant Accounting Policies [Line Items] Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount Ownership interest (in percentage) Equity Method Investment, Ownership Percentage Cash flows provided by operating activities of continuing operations Cash flows used in financing activities of continuing operations Other Commitments And Contingencies [Table] Other Commitments And Contingencies [Table] Other Commitments And Contingencies [Table] Performance Guarantee Performance Guarantee [Member] Other Commitments And Contingencies [Line Items] Other Commitments And Contingencies [Line Items] Other Commitments And Contingencies [Line Items] Amount outstanding Letters of Credit Outstanding, Amount Surety bonds Surety Bonds Amount Outstanding Surety Bonds, Amount Outstanding Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Leidos Holdings, Inc. Leidos Holdings, Inc [Member] Leidos Holdings, Inc [Member] Revenues Business Acquisition, Pro Forma Revenue Income from continuing operations Business Acquisition, Pro Forma Income (Loss) from Continuing Operations, Net of Tax Earnings per share: Business Acquisition, Pro Forma Earning Per Share [Abstract] Business Acquisition, Pro Forma Earning Per Share [Abstract] Basic (usd per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Diluted (usd per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Property, Plant and Equipment Property, Plant and Equipment Disclosure [Text Block]