Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
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 subsidiaries and principal operating companies are Leidos, Inc. and Leidos Innovations Corporation ("Leidos Innovations"). Leidos is a global science and technology company that provides technology and engineering services and solutions in the defense, intelligence, civil and health markets. Leidos' domestic customers include the U.S. Department of Defense ("DoD"), the U.S. Intelligence Community, the U.S. Department of Homeland Security ("DHS"), the Federal Aviation Administration ("FAA"), the Department of Health and Human Services ("HHS"), U.S. Government civil agencies and state and local government agencies. Leidos' international customers include foreign governments and their agencies, primarily located in the United Kingdom, the Middle East and Australia. Unless indicated otherwise, references to the "Company," "we," "us" and "our" refer collectively to Leidos Holdings, Inc. and its consolidated subsidiaries. The unaudited condensed consolidated financial statements of Leidos include the balances of its majority-owned and 100%-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. The accompanying unaudited condensed financial information has been prepared in accordance with the rules 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. 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. Management evaluates these estimates and assumptions on an ongoing basis, including those relating to indirect billing rates, allowances for doubtful accounts, inventories, fair value and impairment of intangible assets and goodwill, income taxes, estimated profitability of long-term contracts, pension benefits, stock-based compensation expense and contingencies. Estimates have been prepared by management on the basis of the most current and best available information; however, actual results could differ materially from those estimates. In the opinion of management, the accompanying unaudited condensed consolidated financial statements reflect all adjustments, which consist of normal recurring adjustments, necessary for a fair presentation thereof. The results reported in these unaudited condensed consolidated financial statements are not necessarily indicative of the results that may be expected for the entire year. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K filed on February 24, 2017. During the quarter ended March 31, 2017, the Company completed its business reorganization, which resulted in identification of new reportable segments. The Company commenced operating and reporting under the new organizational structure effective the beginning of fiscal 2017. As a result of this change, prior year segment results and disclosures have been recast to reflect the new reportable segments. The Company now operates in the following segments: Defense Solutions, Civil, Health and Corporate (see "Note 14–Business Segments"). Certain amounts in the prior year financial statements have been reclassified to conform to the current year presentation. The Company separately disclosed "Accounts payable" and "Accrued liabilities," which were previously aggregated within "Accounts payable and accrued liabilities" on the condensed consolidated balance sheets. Additionally, the Company disaggregated "Interest expense, net" into "Interest income" and "Interest expense" on the condensed consolidated statements of income.
Changes in Estimates on Contracts	Changes in Estimates on Contracts Changes in estimates related to long-term 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, with the exception of contracts acquired through the acquisition of the IS&GS Business (see "Note 2–Acquisitions"), where the adjustment is made for the period commencing from the date of acquisition. Changes in these estimates can occur over the contract performance period for a variety of reasons, including changes in contract scope, contract cost estimates and estimated incentive or award fees.
Accounting Standards Updates Adopted	Accounting Standards Updates Adopted In March 2016, the FASB issued ASU 2016-09 Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The ASU requires that an entity, (i) recognize excess tax benefits and deficiencies related to employee share-based payment transactions as an income tax expense or benefit in the income statement rather than in equity; (ii) present the excess tax benefits as an operating activity on the statement of cash flows versus current guidance to present them as financing activities; and, (iii) elect to either recognize stock forfeitures as they occur or estimate them. During the quarter ended July 1, 2016, the Company elected to early adopt the provisions of the ASU prospectively from January 2, 2016, including continuation of estimating forfeitures instead of recording them as they occur. Consequently, the Company recognized a $3 million and $7 million discrete tax benefit for the quarter and six months ended July 1, 2016, respectively, and operating cash flows for the six months ended July 1, 2016, increased $7 million with a corresponding decrease to financing cash flows. In January 2017, the FASB issued ASU 2017-04, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. This ASU eliminates Step 2 of the goodwill impairment test and simplifies how the amount of an impairment loss is determined. The update is effective for public companies in the beginning of fiscal year 2020 and shall be applied on a prospective basis. Early adoption is permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company adopted the provisions of ASU 2017-04 prospectively in the first quarter of fiscal 2017.
Accounting Standards Updates Issued But Not Yet Adopted	Accounting Standards Updates Issued But Not Yet Adopted In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). This ASU affects any entity that either enters into contracts with customers to transfer goods or services or enters into contracts for the transfer of non-financial assets unless those contracts are within the scope of other standards (for example, insurance contracts or lease contracts). This ASU will supersede all revenue recognition requirements in Topic 605, Revenue Recognition, and industry-specific guidance throughout the Industry Topics of the codification. The guidance's core principle is that an entity should recognize revenue to depict the transfer of control for promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In applying the revenue principles, an entity will identify the contract(s) with a customer, identify the performance obligations, determine the transaction price, allocate the transaction price to the performance obligations and recognize revenue when the performance obligation is satisfied (i.e., either over time or point in time). The ASU further states that an entity should disclose sufficient information to enable users of financial statements to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. The original effective date for public companies was the beginning of fiscal 2017. Subsequently, in August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which approved a one-year deferral of the effective date of the ASU to the beginning of fiscal 2018, with an option for early adoption of the standard on the original effective date. The Company will adopt the new revenue standard in the beginning of fiscal 2018, under the modified retrospective method, where the cumulative effect is recognized at the date of initial application. An initial assessment of the new standard has been completed and the Company believes the majority of its long-term contracts will continue to recognize revenue over time as the work progresses because of the continuous transfer of control to the customer, generally using an input measure (e.g., cost incurred) to reflect progress. The Company is in the process of quantifying the financial statement impact, revising current accounting policies and determining the appropriate changes to business processes and controls.