Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 28, 2024
Accounting Policies [Abstract]
Consolidation	We have a controlling interest in Mission Support Alliance, LLC ("MSA"), a joint venture with Centerra Group, LLC. We also have a controlling interest in Hanford Mission Integration Solutions, LLC ("HMIS"), the legal entity for the follow-on contract to MSA's contract and a joint venture with Centerra Group, LLC and Parsons Government Services, Inc. The financial results for MSA and HMIS are consolidated into our unaudited condensed consolidated financial statements. The unaudited condensed consolidated financial statements also include the balances of all voting interest entities in which Leidos has a controlling voting interest ("subsidiaries") and a variable interest entity ("VIE") in which Leidos is the primary beneficiary. The consolidated balances of the VIE are not material to the unaudited condensed consolidated financial statements for the periods presented. Intercompany accounts and transactions between consolidated companies have been eliminated in consolidation.
Basis of Accounting	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the rules of the U.S. Securities and Exchange Commission 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.
Estimates	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 estimated profitability of long-term contracts, indirect billing rates, allowances for doubtful accounts, inventories, right-of-use assets and lease liabilities, fair value and impairment of intangible assets and goodwill, income taxes, stock-based compensation expense and contingencies. These 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. Certain amounts in the prior year financial statements have been reclassified to conform to the current year presentation. We combined "Deferred tax liabilities" into "Other long-term liabilities" on the condensed consolidated balance sheets.
Accounting Standards Updates Issued But Not Yet Adopted	Accounting Standards Updates Issued But Not Yet Adopted ASU 2023-07 Segment Reporting In November 2023, the FASB issued ASU 2023-07, to improve reportable segment disclosure requirements. This update requires companies to disclose significant segment expense categories that are regularly provided to the chief operating decision maker ("CODM") on an interim and annual basis and expands disclosure requirements for interim reporting. Companies must also disclose how segment measures of profit or loss are used by the CODM. The amendments in this update are effective for public entities for annual periods beginning after December 15, 2023, and interim periods beginning after December 15, 2024. The amendments should be adopted on a retrospective basis and early adoption is permitted. We are evaluating the impact of the update and will adopt the amendments for annual disclosures in fiscal 2024. ASU 2023-09 Income Taxes In December 2023, the FASB issued ASU 2023-09, to enhance the transparency and usefulness of income tax disclosures. The update requires enhancements to the annual rate reconciliation, including disclosure of specific categories and additional information for reconciling items meeting a quantitative threshold. The update also requires disclosure of income taxes paid disaggregated by federal, state and foreign taxes, and individual jurisdictions meeting a quantitative threshold. The amendments in this update are effective for public business entities for annual periods beginning after December 15, 2024, and may be adopted on a prospective or retrospective basis. Early adoption is permitted. We are currently evaluating the impacts of this update and plan to adopt these amendments using the prospective approach for annual disclosures in fiscal 2025.
Changes in Estimates on Contracts	Changes in Estimates on Contracts Changes in estimates related to contracts accounted for using the cost-to-cost 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 a business combination, where the adjustment is made for the period commencing from the date of acquisition. The impact on diluted earnings per share ("EPS") attributable to Leidos common stockholders is calculated using the statutory tax rate. The changes are primarily related to revisions of variable consideration including award and incentive fees, and revisions to estimates at completion resulting from changes in contract scope, mitigation of contract risks or true-ups of contract estimates at the end of contract performance.
Cash and Cash Equivalents	Cash and Cash Equivalents Our cash equivalents are primarily comprised of investments in several large institutional money market accounts, with original maturity of three months or less.
Restricted Cash	Restricted Cash We have restricted cash balances, primarily representing advances from customers that are restricted for use on certain expenditures related to that customer's contract. Restricted cash balances are included as "Other current assets" in the condensed consolidated balance sheets.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 28, 2024

We have a controlling interest in Mission Support Alliance, LLC ("MSA"), a joint venture with Centerra Group, LLC. We also have a controlling interest in Hanford Mission Integration Solutions, LLC ("HMIS"), the legal entity for the follow-on contract to MSA's contract and a joint venture with Centerra Group, LLC and Parsons Government Services, Inc. The financial results for MSA and HMIS are consolidated into our unaudited condensed consolidated financial statements. The unaudited condensed consolidated financial statements also include the balances of all voting interest entities in which Leidos has a controlling voting interest ("subsidiaries") and a variable interest entity ("VIE") in which Leidos is the primary beneficiary. The consolidated balances of the VIE are not material to the unaudited condensed consolidated financial statements for the periods presented. Intercompany accounts and transactions between consolidated companies have been eliminated in consolidation.

Basis of Accounting

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with the rules of the U.S. Securities and Exchange Commission 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.

Estimates

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 estimated profitability of long-term contracts, indirect billing rates, allowances for doubtful accounts, inventories, right-of-use assets and lease liabilities, fair value and impairment of intangible assets and goodwill, income taxes, stock-based compensation expense and contingencies. These 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.

Certain amounts in the prior year financial statements have been reclassified to conform to the current year presentation. We combined "Deferred tax liabilities" into "Other long-term liabilities" on the condensed consolidated balance sheets.

Accounting Standards Updates Issued But Not Yet Adopted

ASU 2023-07 Segment Reporting

In November 2023, the FASB issued ASU 2023-07, to improve reportable segment disclosure requirements. This update requires companies to disclose significant segment expense categories that are regularly provided to the chief operating decision maker ("CODM") on an interim and annual basis and expands disclosure requirements for interim reporting. Companies must also disclose how segment measures of profit or loss are used by the CODM.

The amendments in this update are effective for public entities for annual periods beginning after December 15, 2023, and interim periods beginning after December 15, 2024. The amendments should be adopted on a retrospective basis and early adoption is permitted. We are evaluating the impact of the update and will adopt the amendments for annual disclosures in fiscal 2024.

ASU 2023-09 Income Taxes

In December 2023, the FASB issued ASU 2023-09, to enhance the transparency and usefulness of income tax disclosures. The update requires enhancements to the annual rate reconciliation, including disclosure of specific categories and additional information for reconciling items meeting a quantitative threshold. The update also requires disclosure of income taxes paid disaggregated by federal, state and foreign taxes, and individual jurisdictions meeting a quantitative threshold.

The amendments in this update are effective for public business entities for annual periods beginning after December 15, 2024, and may be adopted on a prospective or retrospective basis. Early adoption is permitted. We are currently evaluating the impacts of this update and plan to adopt these amendments using the prospective approach for annual disclosures in fiscal 2025.

Changes in Estimates on Contracts

Changes in estimates related to contracts accounted for using the cost-to-cost 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 a business combination, where the adjustment is made for the period commencing from the date of acquisition.

The impact on diluted earnings per share ("EPS") attributable to Leidos common stockholders is calculated using the statutory tax rate.

The changes are primarily related to revisions of variable consideration including award and incentive fees, and revisions to estimates at completion resulting from changes in contract scope, mitigation of contract risks or true-ups of contract estimates at the end of contract performance.

Cash and Cash Equivalents

Our cash equivalents are primarily comprised of investments in several large institutional money market accounts, with original maturity of three months or less.

Restricted Cash

We have restricted cash balances, primarily representing advances from customers that are restricted for use on certain expenditures related to that customer's contract. Restricted cash balances are included as "Other current assets" in the condensed consolidated balance sheets.