Liabilities Subject to Compromise (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 24, 2021	Sep. 24, 2021	Sep. 25, 2020	Dec. 25, 2020
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)		$ 6,335.5	$ 6,335.5		$ 4,192.6
Opioid-related litigation settlement liability		125.0	125.0	$ 0.0
Lease rejection
Schedule of Liabilities Subject to Compromise [Line Items]
Increase (Decrease) Other current and non-current liabilities			34.8
Contingent Consideration
Schedule of Liabilities Subject to Compromise [Line Items]
Increase (Decrease) Other current and non-current liabilities			15.6
Accounts Payable
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[1]	43.5	43.5		61.9
Interest Payable, Current
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)		35.2	35.2		35.2
Long-term Debt
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[2],[3]	3,760.1	3,760.1		1,660.7
Long-term Debt | Term Loans due Sept 2024 and Feb 2025
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)		1,776.5	1,776.5
Medicaid Lawsuit [Member]
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)		634.1	634.1		638.9
Opioid-related litigation settlement liability
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[4]	1,725.0	1,725.0		1,600.0
Other current and non-current liabilities
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)	[5]	107.3	107.3		163.5
Liability, Defined Benefit Plan, Noncurrent
Schedule of Liabilities Subject to Compromise [Line Items]
Liabilities subject to compromise (Note 2)		$ 30.3	$ 30.3		$ 32.4

[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, $3,760.1 million and $1,660.7 million outstanding secured and unsecured debt instruments have been reclassified to LSTC in the Company's unaudited condensed consolidated balance sheets as of September 24, 2021 and December 25, 2020, respectively. Up to the date of reclassification to LSTC, the Company continued to accrue interest expense in relation to the unsecured debt instruments reclassified to 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 $1,776.5 million of outstanding senior secured term loans, respectively, were classified as LSTC in the Company's unaudited condensed consolidated balance sheet as of September 24, 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 unaudited condensed consolidated balance sheet as of September 24, 2021.

[5] The decrease in other current and non-current liabilities was primarily attributable to 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. The remaining decrease was primarily attributable to a decrease of $15.6 million in the fair value of contingent consideration related to an asset for which the Company is no longer pursuing further development. Refer to Note 12 for further information on the valuation of contingent consideration.