Background and Basis of Presentation (Policies)	9 Months Ended
Background and Basis of Presentation (Policies)	Sep. 26, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The unaudited condensed consolidated financial statements have been prepared in U.S. dollars and in accordance with generally accepted accounting principles in the United States (“GAAP”).
Basis of Presentation	The preparation of the unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amount of assets and liabilities, disclosure of contingent assets and liabilities and the reported amounts of revenues and expenses. Actual results may differ from those estimates.
Basis of Presentation	The unaudited condensed consolidated financial statements include the accounts of the Company, its wholly owned subsidiaries and entities in which they own or control more than 50.0% of the voting shares. In the opinion of management, all adjustments necessary for a fair statement of results of operations, cash flows and financial position have been made. All intercompany balances and transactions have been eliminated in consolidation and all normal recurring adjustments necessary for a fair statement have been included in the results reported.
Basis of Presentation	The results of entities disposed of are included in the unaudited condensed consolidated financial statements up to the date of disposal, and where appropriate, these operations have been reported in discontinued operations. Divestitures of product lines and businesses not meeting the criteria for discontinued operations have been reflected in continuing operations.
Fiscal Year	Fiscal Year The Company has reported its results based on a “52-53 week” year ending on the last Friday of December. Unless otherwise indicated, the three and nine months ended September 26, 2025 and September 27, 2024 refer to the thirteen and thirty-nine week periods ended September 26, 2025 and September 27, 2024, respectively. In the fourth quarter of fiscal year 2025, the Company determined to change its fiscal year end from a 52-53-week year, ending on the last Friday of December, to a calendar year, ending on December 31, 2025. The Company will make the fiscal year change on a prospective basis for fiscal year 2025 and will not adjust operating results for prior periods. Effective for fiscal year 2026, the Company’s fiscal year will begin on January 1 and end on December 31 of each year. The number of operating days in the quarterly periods in fiscal year 2026 under a calendar year end will change as compared to the 52-53 weeks periods in fiscal year 2025 and prior periods, which will have an impact on the Company’s quarterly financial results as well as the comparative presentation of period over period information. The change in the Company’s fiscal year end to a calendar year end results in five additional operating days in fiscal year 2025, because fiscal year 2025 began on December 28, 2024, and will end on December 31, 2025, instead of December 26, 2025, and two additional operating days in the fiscal year 2026.
Acquisitions	The Company accounts for business combinations under the acquisition method of accounting. Assets acquired and liabilities assumed are generally recognized at their estimated fair values at the date of acquisition. The determination of the estimated fair value of assets acquired and liabilities assumed requires significant estimates and assumptions. Any excess of the purchase price over the estimated fair value of the identifiable net assets acquired is recorded as goodwill. Based on the assessment of additional information during the measurement period, which may be up to one year from the acquisition date, the Company may record adjustments to the estimated fair value of assets acquired and liabilities assumed.
Government Assistance Transactions	In connection with the Business Combination, the Company acquired the U.S. Government Cooperative Agreement (as defined below). Under the terms of the U.S. Government Cooperative Agreement, the Rochester, Michigan manufacturing facility will establish new sterile fill-finish manufacturing assets capable of processing liquid or lyophilized products requiring Biosafety Level (“BSL”) 2 containment in order to establish and sustain BSL 2 sterile fill-finish production capacity to create and maintain industrial base capabilities for the national defense. In connection with the Separation, the U.S. Government Cooperative Agreement was transitioned to Par Health, Inc. (“Par Health”) and/or certain of its subsidiaries. Refer to Note 13 for further information on the U.S. Government Cooperative Agreement. The Company concluded that reimbursements it receives pursuant to the U.S. Government Cooperative Agreement are not within the scope of Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“ASC 606”) because the U.S. government does not meet the definition of a “customer” as defined by ASC 606. The Company accounts for the U.S. Government Cooperative Agreement under other guidance, including elements of the contract for which there is no authoritative guidance under GAAP by applying certain accounting principles in International Accounting Standards (“IAS”) 20, Accounting for Government Grants and Disclosure of Government Assistance (“IAS 20”) by analogy. Under this model, reimbursements the Company receives from the U.S. government for qualifying capital expenditures meet the definition of grants related to assets as the primary purpose for the reimbursements is to fund the purchase and construction of capital assets to increase production capacity. Under IAS 20, government grants related to assets are presented in the Condensed Consolidated Balance Sheets either by presenting the grant as deferred income or by deducting the grant in arriving at the carrying amount of the asset. Either of these two methods of presentation of grants related to assets in the Condensed Consolidated Balance Sheets are regarded as acceptable alternatives under IAS 20. Reimbursements received prior to the asset being placed into service are recognized as deferred income in the Condensed Consolidated Balance Sheets as either Accrued and other current liabilities (for any current portion) or Other liabilities (for any noncurrent portion) when there is reasonable assurance the conditions of the grant will be met and the grant will be received. When the constructed capital assets are placed into service, the Company deducts the grant reimbursement from property, plant and equipment and the grant income is recognized over the useful life of the asset as a reduction to depreciation expense.
Recently Issued Accounting Standards Not Yet Adopted	Recently Issued Accounting Standards Not Yet Adopted The Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures in December 2023. This ASU requires public business entities to disclose additional information in specified categories with respect to the reconciliation of the effective tax rate to the statutory rate (“rate reconciliation”) for federal, state, and foreign income taxes. It also requires greater detail about individual reconciling items in the rate reconciliation to the extent the impact of those items exceeds a specified threshold. ASU 2023-09 is effective for the Company for the fiscal year ending December 31, 2025. The adoption of ASU 2023-09 will expand our income tax disclosures, but will have no impact on reported income tax expense or related tax assets or liabilities. The Company will adopt this standard prospectively beginning with the fiscal year ended December 31, 2025. In November 2024, the FASB issued ASU 2024-03, Income Statement - Reporting Comprehensive Income - Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. This ASU requires new financial statement disclosures about the nature, amount, and timing of relevant expense categories underlying income statement expense, including purchases of inventory, employee compensation, depreciation, and amortization in commonly presented expense captions such as cost of revenue and selling, general and administrative (“SG&A”) expenses. ASU 2024-03 is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027, with early adoption permitted. The disclosure updates are required to be applied prospectively with the option for retrospective application. The Company is currently evaluating the disclosure requirements of this standard. No other new accounting pronouncement issued has had, or is expected to have, a material impact on the Company’s unaudited condensed consolidated financial statements.

Mallinckrodt plc 10-Q