Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Oct. 31, 2014
Accounting Policies [Abstract]
Nature of Operations and Basis of Presentation	Nature of Operations and Basis of Presentation Leidos Holdings, Inc. ("Leidos") is a holding company whose direct 100%-owned subsidiary is Leidos, Inc., a company focused on delivering science and technology solutions and services primarily in the areas of national security, health and engineering to agencies of the U.S. Department of Defense ("DoD"), the intelligence community, the U.S. Department of Homeland Security and other U.S. Government civil agencies, state and local government agencies, foreign governments, and customers across a variety of commercial markets. Unless indicated otherwise, references to the "Company," "we," "us," and "our" refer collectively to Leidos, Leidos, Inc., and its consolidated subsidiaries. On September 27, 2013 (the "Distribution Date"), Leidos completed the spin-off of its technical services and enterprise information technology services business into an independent, publicly traded company named Science Applications International Corporation (“New SAIC”). The separation was effected through a tax-free distribution to Leidos' stockholders of 100% of the shares of New SAIC's common stock. On the Distribution Date, New SAIC's common stock was distributed, on a pro rata basis, to Leidos' stockholders of record as of the close of business on September 19, 2013, the record date. Each holder of Leidos common stock received one share of New SAIC common stock for every seven shares of Leidos common stock held on the record date. Prior to the Distribution Date, Leidos Holdings, Inc. was named SAIC, Inc. and Leidos, Inc. was named Science Applications International Corporation. As a result of the spin-off, the assets, liabilities, results of operations, and cash flows of New SAIC have been classified as discontinued operations for all periods presented. References to financial data are to the Company’s continuing operations, unless otherwise noted. See Note 2–Dispositions for further information. Immediately following the spin-off, Leidos effectuated a one-for-four reverse stock split of its shares of common stock, so that every four shares of Leidos common stock issued and outstanding were combined and converted into one share of Leidos common stock. Each reference to the number of shares outstanding or per share amounts has been adjusted to reflect the reverse stock split for all periods presented. The condensed consolidated financial statements of Leidos include the accounts of its majority-owned and 100%-owned subsidiaries, including Leidos, Inc. The condensed consolidated financial statements of Leidos, Inc. include the accounts of its majority-owned and 100%-owned subsidiaries. Leidos does not have separate operations, assets or liabilities independent of Leidos, Inc., except for a note with Leidos, Inc. (the “related party note”), on which interest is recognized. From time to time, Leidos issues stock to employees of Leidos, Inc. and its subsidiaries, which is reflected in Leidos’ Condensed Consolidated Statement of Stockholders’ Equity and results in an increase to the related party note. All intercompany transactions and accounts have been eliminated in consolidation. The accompanying financial information has been prepared by the Company pursuant to the rules and regulations of the U.S. Securities and Exchange Commission ("SEC") and accounting principles generally accepted in the United States of America ("GAAP"). Certain disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and combined notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended January 31, 2014. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingencies at the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting periods. Estimates have been prepared by management on the basis of the most current and best available information at the time of estimation and actual results could differ from those estimates. In the opinion of management, the financial information as of October 31, 2014 and for the three and nine months ended October 31, 2014 and November 1, 2013 reflects all adjustments, which consist of normal recurring adjustments, necessary for a fair presentation thereof. Operating results for the three and nine months ended October 31, 2014 are not necessarily indicative of the results that may be expected for the fiscal year ending January 30, 2015, or any future period.
Reporting Periods	Unless otherwise noted, references to fiscal years are to fiscal years ended the Friday closest to January 31. Fiscal 2015 began on February 1, 2014 and ends on January 30, 2015. The third quarter of fiscal 2015 ended on October 31, 2014.
Receivables	Receivables The Company’s accounts receivable include both amounts billed and currently due from customers, and unbilled receivables consisting of costs and fees billable upon contract completion or the occurrence of a specified event, substantially all of which are expected to be billed and collected within one year. Unbilled receivables are stated at estimated realizable value. Since the Company’s receivables are primarily with the U.S. Government, the Company does not have a material credit risk exposure. Contract retentions are billed when the Company has negotiated final indirect rates with the U.S. Government and, once billed, are subject to audit and approval by government representatives. Consequently, the timing of collection of retention balances is outside the Company’s control. Based on the Company’s historical experience, the majority of retention balances are expected to be collected beyond one year and write-offs of retention balances have not been significant. The Company has extended deferred payment terms with contractual maturities that may exceed one year to commercial customers related to certain construction projects. As of October 31, 2014, the Company had outstanding receivables of $28 million, net of allowance of $7 million, related to one construction project with deferred payment terms, which have not been paid in accordance with the initial payment terms established with the customer. The Company has filed a legal claim to enforce the payment terms as established in the contract. Based on these events, the Company has determined that the receivables are not expected to be collected within the next 12 months. Accordingly, the receivables are classified as non-current in “Other Assets” on the condensed consolidated balance sheet as of October 31, 2014. When events or conditions indicate that amounts outstanding from customers may become uncollectible, an allowance is estimated and recorded.
Fair Value Measurement	Fair Value Measurements The accounting standard for fair value measurements establishes a three-tier value hierarchy, which prioritizes the inputs used in measuring fair value as follows: observable inputs such as quoted prices in active markets (Level 1); inputs other than the quoted prices in active markets that are observable either directly or indirectly (Level 2); and unobservable inputs in which there is little or no market data, which requires the Company to develop its own assumptions (Level 3). The fair value of financial instruments is determined based on quoted market prices, if available, or management’s best estimate. It is management’s belief that the carrying amounts of the Company’s financial instruments other than derivatives (see below), which include cash equivalents and long-term investments in private equity securities are reasonable estimates of their related fair values. Cash equivalents are recorded at historical cost which equals fair value based on quoted market prices (Level 1 input). The Company’s cash equivalents were primarily comprised of investments in several large institutional money market funds and bank deposits. There are no restrictions on the withdrawal of the Company’s cash and cash equivalents. Management evaluates its investments for other-than-temporary impairment at each balance sheet date. When testing long-term investments for recovery of carrying value, the fair value of long-term investments in private equity securities is determined using various valuation techniques and factors, such as market prices of comparable companies (Level 2 input), discounted cash flow models (Level 3 input) and recent capital transactions of the portfolio companies being valued (Level 3 input). If management determines that an other-than-temporary decline in the fair value of an investment has occurred, an impairment loss is recognized to reduce the investment to its estimated fair value (Level 2 input). The fair value of long-term debt is determined based on current interest rates available for debt with terms and maturities similar to the Company’s existing debt arrangements (Level 2). The carrying value of accounts receivable, accounts payable, and accrued expenses approximate their fair value.
Financial Instruments	Financial Instruments The Company is exposed to certain market risks which are inherent in certain transactions entered into during the normal course of business. These transactions include sales or purchase contracts denominated in foreign currencies, investments in equity securities and exposure to changing interest rates. The Company uses a risk management policy to assess and manage cash flow and fair value exposure. The policy permits the use of derivative instruments with certain restrictions. The Company uses interest rate swaps to hedge its fixed rate debt against changes in fair value due to variability in interest rates. The Company is party to interest rate swap agreements that have been designated as fair value hedges and are recorded at fair value on the condensed consolidated balance sheet. The fair value of the interest rate swaps are determined based on observed values for underlying interest rates on the LIBOR yield curve (Level 2). The Company does not hold derivative instruments for trading or speculative purposes.
Changes in Estimates on Contracts	Changes in Estimates on Contracts Changes in estimates related to certain types of contracts accounted for using the percentage of completion method of accounting are recognized in the period in which such changes are made for the inception-to-date effect of the changes. Changes in these estimates can routinely occur over the contract performance period for a variety of reasons, including changes in contract scope, changes in contract cost estimates due to unanticipated cost growth or retirements of risk for amounts different than estimated and changes in estimated incentive or award fees. Aggregate changes in contract estimates resulted in an increase to operating income of $6 million and an increase of $0.05 per diluted share for the three months ended October 31, 2014, and an increase to operating income of $24 million and an increase of $0.20 per diluted share for the nine months ended October 31, 2014. Aggregate changes in contract estimates resulted in a decrease to operating income of $1 million and a decrease of $0.02 per diluted share for the three months ended November 1, 2013, and a decrease to operating income of $29 million and a decrease of $0.22 per diluted share for the nine months ended November 1, 2013.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill Goodwill represents purchase consideration paid in a business combination that exceeds the values assigned to the net assets of acquired businesses. Goodwill is not amortized, but instead is tested for impairment at the reporting unit level annually, at the beginning of the fourth quarter and during interim periods whenever events or circumstances indicate that the carrying value may not be recoverable. Goodwill is evaluated for impairment either under a qualitative assessment option or a two-step quantitative approach depending on facts and circumstances of a reporting unit, including the excess of fair value over carrying amount in previous assessments and changes in business environment. When performing a qualitative assessment, the Company considers factors including, but not limited to, current macroeconomic conditions, industry and market conditions, cost factors, financial performance and other events relevant to the entity or reporting unit under evaluation to determine whether it is more likely or not that the fair value of a reporting unit is less than its carrying amount. If the Company determines that it is more likely than not that a reporting unit’s fair value is less than its carrying amount, a quantitative two-step goodwill impairment test is performed. In evaluating the first step of the two-step quantitative goodwill impairment test, the estimated fair value of each reporting unit is compared to its carrying value, which includes the allocated goodwill. If the estimated fair value of a reporting unit is more than its carrying value, including allocated goodwill, no further analysis is required. If the estimated fair value of a reporting unit is less than its carrying value, including allocated goodwill, a second step is performed to compute the amount of the impairment by determining an implied fair value of goodwill. The implied fair value of goodwill is the residual fair value derived by deducting the fair value of a reporting unit’s identifiable assets and liabilities from its estimated fair value calculated in the first step. If the carrying value of a reporting unit’s goodwill exceeds its implied fair value, then the Company records an impairment charge equal to the difference. The Company estimates the fair value of each reporting unit using both market and income approaches (Level 3) when a quantitative analysis is required. The market approach consists of the guideline public company method which is a valuation technique where the fair value is calculated based on market prices obtained from a detailed market analysis of publicly traded companies that provide a reasonable basis of comparison for each reporting unit. Valuation ratios are selected that relate market prices to selected financial metrics from comparable companies. These ratios are applied after consideration of adjustments and weightings related to financial position, growth, volatility, working capital movement, and other factors. Due to the fact that stock prices of comparable companies represent minority interests the Company also considers an acquisition control premium to reflect the impact of additional value associated with a controlling interest. The income approach is a valuation technique where the fair value is calculated based on forecasted future cash flows within the projection period discounted back to the present value with appropriate risk adjusted discount rates, which represent the weighted-average cost of capital ("WACC") for each reporting unit. This includes assessing the cost of equity and debt capital as of the valuation date. In addition, a terminal value is developed for forecasted future cash flows beyond the projection period discounted back to the present value. The forecasts used in the Company’s estimation of fair value are developed by management based on known business and market considerations. The goodwill impairment test process and valuation model is based upon certain key assumptions that require the exercise of significant judgment including judgments for the use of appropriate financial projections, economic expectations, discount rates and WACC as well as using available market data. An interim goodwill impairment evaluation was performed during the second quarter of fiscal 2015 and resulted in goodwill impairment charges of $486 million for the three months ended August 1, 2014. See Note 4–Goodwill and Intangible Assets for further information. Intangible assets Intangible assets with finite lives are amortized using the method that best reflects how their economic benefits are utilized or, if a pattern of economic benefits cannot be reliably determined, on a straight-line basis over their estimated useful lives. Intangible assets with finite lives are assessed for impairment whenever events or changes in circumstances indicate that the carrying value may not be recoverable. See Note 4–Goodwill and Intangible Assets for impairment charges taken during the period. Intangible assets with indefinite lives are not amortized but are assessed for impairment at the beginning of the fourth quarter and whenever events or changes in circumstances indicate that the carrying value may not be recoverable.
Accounting Standards Updates Adopted	Accounting Standards Updates Adopted In February 2013, the Financial Accounting Standards Board ("FASB") issued ASU 2013-04: Liabilities (Topic 405): Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation Is Fixed at the Reporting Date. This standard requires an entity to measure obligations resulting from joint and several liability arrangements for which the total amount of the obligation within the scope of this guidance is fixed at the reporting date, as the sum of the amount the reporting entity agreed to pay on the basis of its arrangement among its co-obligors and any additional amount the reporting entity expects to pay on behalf of its co-obligors. The guidance also requires an entity to disclose the nature and amount of the obligation as well as other information about those obligations. The amendments in this update are effective for fiscal years, and interim periods within those years, beginning after December 15, 2013. The adoption of the provisions of ASU 2013-04 did not have a material effect on the Company's consolidated financial position, results of operations, or cash flows. In March 2013, the FASB issued ASU No. 2013-05, Foreign Currency Matters (Topic 830): Parent’s Accounting for the Cumulative Translation Adjustment upon Derecognition of Certain Subsidiaries or Groups of Assets within a Foreign Entity or of an Investment in a Foreign Entity. This standard applies to the release of the cumulative translation adjustment into net income when a parent either sells a part of or all of its investment in a foreign entity or no longer holds a controlling financial interest in a subsidiary or group of assets that is a nonprofit activity or a business within a foreign entity. In addition, the amendments resolve the diversity in practice for the treatment of business combinations achieved in stages (i.e., step acquisitions) involving a foreign entity. The amendments in this ASU are effective for fiscal years, and interim periods within those years, beginning after December 15, 2013. The adoption of the provisions of ASU 2013-05 did not have a material effect on the Company's consolidated financial position, results of operations, or cash flows. In June 2014, the FASB issued ASU No. 2014-12, Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period. This standard was issued to provide guidance on share based payment awards in which a performance target may be achieved after an employee completes the requisite service period to achieve the award. In some instances, this has led to a performance award being granted subsequent to the employee no longer rendering services to the issuing company. Previously, no guidance had been included in the codification on how to account for these transactions. The amendments require that a performance target that affects vesting and that could be achieved after the requisite service period be treated as a performance condition. The amendments in this ASU are effective for all entities for annual periods and interim periods within those annual periods beginning after December 15, 2015. Early adoption is permitted. The amendments may be adopted prospectively or retrospectively. The Company elected to early adopt the provisions of ASU No. 2014-12 and the standard did not have a material effect on the Company's financial position, results of operations, or cash flows. During the quarter presented, the Company adopted various other accounting standards issued by the FASB, none of which had a material effect on the Company's consolidated financial position, results of operations, or cash flows.
Accounting Standards Updates Issued But Not Yet Adopted	Accounting Standards Updates Issued But Not Yet Adopted In April 2014, the FASB issued ASU No. 2014-08, Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity. The amendments in the ASU change the criteria for reporting discontinued operations while enhancing disclosures in this area. Under the new guidance, only disposals representing a strategic shift in operations should be presented as discontinued operations. Those strategic shifts should have a major effect on the organization’s operations and financial results. Examples include a disposal of a major geographic location, a major line of business or a major equity method investment. In addition, the new guidance requires expanded disclosures about discontinued operations that will provide financial statement users with more information about the assets, liabilities, income and expenses of discontinued operations. The new guidance also requires disclosure of the pre-tax income attributable to a disposal of a significant part of an organization that does not qualify for discontinued operations reporting. This disclosure will provide users with information about the ongoing trends in a reporting organization’s results from continuing operations. The amendments in the ASU are effective in the first quarter of 2015 for public organizations with calendar year ends. Early adoption is permitted.