Liabilities Subject to Compromise (Details) - USD ($) $ in Millions			12 Months Ended
		Sep. 02, 2021	Dec. 31, 2021	Dec. 25, 2020
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)			$ 6,397.7	$ 4,192.6
Secured Debt			3,485.1	3,622.6
Opioid Claimant Trust [Member]
Liabilities Subject to Compromise [Line Items]
Restructuring Support Agreement Proposed Settlement, Year Eight		$ 125.0
Lease rejection
Liabilities Subject to Compromise [Line Items]
Increase (Decrease) Other current and non-current liabilities			34.8
Contingent Consideration
Liabilities Subject to Compromise [Line Items]
Increase (Decrease) Other current and non-current liabilities			15.6
Royalty Accruals
Liabilities Subject to Compromise [Line Items]
Increase (Decrease) Other current and non-current liabilities			17.3
Ten Point Zero Percent Second Lien Notes [Member]
Liabilities Subject to Compromise [Line Items]
Secured Debt			322.9	322.9
Interest Payable, Current
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)			35.2	35.2
Accounts Payable
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[1]		42.9	61.9
Long-term Debt [Member]
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[2],[3]		3,750.8	1,660.7
Long-term Debt [Member] | Term Loans due Sept 2024 and Feb 2025 [Member]
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)			1,767.2
Medicaid Lawsuit [Member]
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)			634.7	638.9
Opioid-related litigation settlement liability
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[4]		1,725.0	1,600.0
Other Liabilities
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[5]		125.1	163.5
Liability, Defined Benefit Plan, Noncurrent
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)			32.0	32.4
Accrued Environmental Loss Contingencies
Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[6]		$ 52.0	$ 0.0

[1] Pre-petition accounts payable balances have been repaid under effectuated trade agreements pursuant to the critical vendor motion approved by the Bankruptcy Court.

[2] In connection with the Company's Chapter 11 Cases, $3,750.8 million and $1,660.7 million of outstanding debt instruments have been classified as LSTC in the Company's consolidated balance sheets as of December 31, 2021 and December 25, 2020, respectively. Up to the Petition Date, the Company continued to accrue interest expense in relation to the unsecured debt instruments classified as LSTC. The Company continues to accrue and pay interest on the outstanding secured debt instruments classified as LSTC in conjunction with the cash collateral order. Refer to Note 2 for further information.

[3] Subsequent to December 25, 2020, in accordance with the agreement in principle reached with the Settling Second Lien Noteholders on September 2, 2021 and Joinder and Amendment to the RSA entered into in March 2021, $322.9 million of Second Lien Notes and $1,767.2 million of outstanding senior secured term loans, respectively, were classified as LSTC in the Company's consolidated balance sheet as of December 31, 2021.

[4] In accordance with the agreement in principle reached with the Opioid Claimants on September 2, 2021, and subsequently memorialized in the Amended Plan on September 29, 2021, the Company recorded an accrual of $125.0 million related to the additional payment expected to be made on the eighth anniversary of the effective date of emergence, which has been classified as LSTC in the Company's consolidated balance sheet as of December 31, 2021.

[5] The decrease in other current and non-current liabilities was attributable to (1) the Bankruptcy Court's approval of the Company's rejection of its Bedminster facility lease, which resulted in a $34.8 million adjustment to the carrying value of the respective lease liability in LSTC to reflect the estimated allowed claim amount and (2) a decrease of $15.6 million in the fair value of contingent consideration related to MNK-6105 and MNK-6106 . These decreases were partially offset by an increase of $17.3 million related to Acthar Gel royalty accruals as a result of the December 2021 Bankruptcy Court ruling, which found that the Acthar Insurance Claimants' (as defined in Note 19) administrative claims were without merit. The remaining change in other current and non-current liabilities was attributable to various increases and decreases as a result of adjustments in the ordinary course of business.

[6] Represents certain environmental liabilities intended to be discharged upon effectiveness of the plan of reorganization.