Fresh-Start Accounting - Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Millions			6 Months Ended	11 Months Ended
	Nov. 14, 2023	Jun. 16, 2022	Jun. 16, 2022	Nov. 14, 2023	Dec. 29, 2023	Jun. 16, 2023	Dec. 30, 2022	Dec. 31, 2021	Dec. 25, 2020
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents	$ 186.7	$ 297.9	$ 297.9	$ 186.7	$ 262.7		$ 409.5	$ 1,345.0
Accounts receivable, less allowance for doubtful accounts of $6.5 and $4.4					377.5		405.3
Inventory, Net					982.7		947.6
Total current assets					1,761.8		2,035.8
Property, plant and equipment, net					321.7		457.6
Intangible Assets, Net (Excluding Goodwill)					608.4		2,843.8
Other assets					240.7		201.1
Assets					3,733.6		6,013.8
Current maturities of long-term debt					6.5		44.1
Accounts Payable, Current					100.4		114.0
Accrued payroll and payroll-related costs					82.8		49.5
Accrued interest					20.1		29.0
Opioid-Related Litigation Settlement liability					0.0		200.0
Accrued and other current liabilities					269.9		290.7
Total current liabilities					501.2		743.8
Long-term debt					1,755.9		3,027.7
Opioid-Related Litigation Settlement liability					0.0		379.9
Pension and postretirement benefits					40.6		41.0
Environmental liabilities					35.1		35.8
Deferred income taxes					97.3		224.4
Other income tax liabilities					19.6		18.2
Other Liabilities, Noncurrent					92.5		78.7
Acthar Gel-Related Settlement liability					128.5		75.0
Liabilities					2,573.4		4,400.1
Additional paid-in capital					1,194.6		2,191.0
Accumulated Other Comprehensive Income (Loss), Net of Tax					3.6		10.8
Retained deficit					(38.2)		(588.2)
Shareholders' equity	1,194.8	2,203.6	2,203.6	1,194.8	1,160.2		1,613.7	$ 313.4	$ 1,019.2
Total Liabilities and Shareholders' Equity					3,733.6		6,013.8
Cancellation of Predecessor equity			(0.5)	9.2
Opioid Claimant Trust [Member]
Reorganization, Chapter 11 [Line Items]
Opioid-Related Settlement, Payment Year One and Two		200.0	200.0
Reorganization, Chapter 11, Predecessor, before Adjustment
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents	314.1	1,392.6	1,392.6	314.1
Accounts receivable, less allowance for doubtful accounts of $6.5 and $4.4	467.7	387.4	387.4	467.7
Inventory, Net	778.7	375.2	375.2	778.7
Prepaid Expense and Other Assets, Current	149.3	322.6	322.6	149.3
Assets Held-for-sale, Not Part of Disposal Group, Current		0.0	0.0
Total current assets	1,709.8	2,477.8	2,477.8	1,709.8
Property, plant and equipment, net	468.6	748.6	748.6	468.6
Intangible Assets, Net (Excluding Goodwill)	2,258.3	5,166.6	5,166.6	2,258.3
Deferred Tax Assets, Net	0.0	0.0	0.0	0.0
Other assets	222.9	222.8	222.8	222.9
Assets	4,659.6	8,615.8	8,615.8	4,659.6
Current maturities of long-term debt	378.7	1,389.9	1,389.9	378.7
Accounts Payable, Current	93.2	156.4	156.4	93.2
Accrued payroll and payroll-related costs	81.6	71.4	71.4	81.6
Accrued interest	32.2	20.8	20.8	32.2
Taxes Payable	2.7			2.7
Acthar Gel-Related Settlement, Current	0.0	0.0	0.0	0.0
Opioid-Related Litigation Settlement liability		0.0	0.0
Accrued and other current liabilities	222.1	296.1	296.1	222.1
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		0.0	0.0
Total current liabilities	810.5	1,934.6	1,934.6	810.5
Long-term debt	0.0	0.0	0.0	0.0
Opioid-Related Litigation Settlement liability		0.0	0.0
Pension and postretirement benefits	39.4	27.6	27.6	39.4
Environmental liabilities	34.6	37.1	37.1	34.6
Deferred income taxes	1.3	20.4	20.4	1.3
Other income tax liabilities	19.6	75.9	75.9	19.6
Other Liabilities, Noncurrent	65.9	68.6	68.6	65.9
Acthar Gel-Related Settlement liability	0.0	0.0	0.0	0.0
Liabilities subject to compromise	4,932.1	6,402.7	6,402.7	4,932.1
Liabilities	5,903.4	8,566.9	8,566.9	5,903.4
Preferred Stock, Value, Outstanding		0.0	0.0
Common Stock, Other Value, Outstanding		0.0	0.0
Successor ordinary shares held in treasury at cost, none and none	(0.1)	(1,616.1)	(1,616.1)	(0.1)
Accumulated Other Comprehensive Income (Loss), Net of Tax	10.4	(9.9)	(9.9)	10.4
Retained deficit	(3,454.1)	(3,943.5)	(3,943.5)	(3,454.1)
Shareholders' equity	(1,243.8)	48.9	48.9	(1,243.8)
Total Liabilities and Shareholders' Equity	4,659.6	8,615.8	8,615.8	4,659.6
Reorganization, Chapter 11, Plan Effect Adjustment
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents	(127.3)	(1,094.7)	(1,094.7)	(127.3)		$ (1,094.7)
Accounts receivable, less allowance for doubtful accounts of $6.5 and $4.4	0.0	0.0	0.0	0.0
Inventory, Net	0.0	0.0	0.0	0.0
Prepaid Expense and Other Assets, Current	6.4	75.3	75.3	6.4
Assets Held-for-sale, Not Part of Disposal Group, Current		0.0	0.0
Total current assets	(120.9)	(1,019.4)	(1,019.4)	(120.9)
Property, plant and equipment, net	0.0	0.0	0.0	0.0
Intangible Assets, Net (Excluding Goodwill)	0.0	0.0	0.0	0.0
Deferred Tax Assets, Net	586.6	0.0	0.0	586.6
Other assets	(2.4)	(3.9)	(3.9)	(2.4)
Assets	463.3	(1,023.3)	(1,023.3)	463.3
Current maturities of long-term debt	(370.0)	(1,355.2)	(1,355.2)	(370.0)
Accounts Payable, Current	(19.4)	(53.8)	(53.8)	(19.4)
Accrued payroll and payroll-related costs	0.0	0.0	0.0	0.0
Accrued interest	(31.5)	(13.0)	(13.0)	(31.5)
Taxes Payable	0.0			0.0
Acthar Gel-Related Settlement, Current	21.4	16.5	16.5	21.4
Opioid-Related Litigation Settlement liability		200.0	200.0
Accrued and other current liabilities	31.6	50.8	50.8	31.6
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		35.0	35.0
Total current liabilities	(367.9)	(1,119.7)	(1,119.7)	(367.9)
Long-term debt	1,858.9	3,050.9	3,050.9	1,858.9
Opioid-Related Litigation Settlement liability		304.3	304.3
Pension and postretirement benefits	0.0	27.2	27.2	0.0
Environmental liabilities	0.0	0.0	0.0	0.0
Deferred income taxes	0.0	102.7	102.7	0.0
Other income tax liabilities	0.0	0.0	0.0	0.0
Other Liabilities, Noncurrent	7.5	23.6	23.6	7.5
Acthar Gel-Related Settlement liability	214.7	63.2	63.2	214.7
Liabilities subject to compromise	(4,932.1)	(6,402.7)	(6,402.7)	(4,932.1)
Liabilities	(3,218.9)	(3,950.5)	(3,950.5)	(3,218.9)
Successor ordinary shares held in treasury at cost, none and none	0.1	1,616.1	1,616.1	0.1
Additional paid-in capital	1,194.6			1,194.6
Accumulated Other Comprehensive Income (Loss), Net of Tax	0.7	0.0	0.0	0.7
Retained deficit	4,686.6	4,725.9	4,725.9	4,686.6
Shareholders' equity	3,682.2	2,927.2	2,927.2	3,682.2
Total Liabilities and Shareholders' Equity	463.3	(1,023.3)	(1,023.3)	463.3
Cancellation of Predecessor equity	2,199.9	4,002.3
Derivative Liability, Current	7.6			7.6
Reorganization, Chapter 11, Fresh-Start Adjustment
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents	0.0	0.0	0.0	0.0
Accounts receivable, less allowance for doubtful accounts of $6.5 and $4.4	0.0	0.0	0.0	0.0
Inventory, Net	257.6	851.8	851.8	257.6
Prepaid Expense and Other Assets, Current	(0.7)	(58.3)	(58.3)	(0.7)
Assets Held-for-sale, Not Part of Disposal Group, Current		100.0	100.0
Total current assets	256.9	893.5	893.5	256.9
Property, plant and equipment, net	(150.2)	(299.2)	(299.2)	(150.2)
Intangible Assets, Net (Excluding Goodwill)	(1,633.7)	(2,014.4)	(2,014.4)	(1,633.7)
Deferred Tax Assets, Net	208.5	453.4	453.4	208.5
Other assets	12.5	(23.5)	(23.5)	12.5
Assets	(1,306.0)	(990.2)	(990.2)	(1,306.0)
Current maturities of long-term debt	0.0	0.0	0.0	0.0
Accounts Payable, Current	0.0	0.0	0.0	0.0
Accrued payroll and payroll-related costs	0.0	0.0	0.0	0.0
Accrued interest	0.0	0.0	0.0	0.0
Taxes Payable	0.0			0.0
Acthar Gel-Related Settlement, Current	0.0	0.0	0.0	0.0
Opioid-Related Litigation Settlement liability		0.0	0.0
Accrued and other current liabilities	(0.1)	(6.1)	(6.1)	(0.1)
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		0.0	0.0
Total current liabilities	(0.1)	(6.1)	(6.1)	(0.1)
Long-term debt	0.0	(18.4)	(18.4)	0.0
Opioid-Related Litigation Settlement liability		0.0	0.0
Pension and postretirement benefits	0.0	0.0	0.0	0.0
Environmental liabilities	0.0	0.0	0.0	0.0
Deferred income taxes	(1.3)	(121.7)	(121.7)	(1.3)
Other income tax liabilities	0.0	(61.9)	(61.9)	0.0
Other Liabilities, Noncurrent	27.6	(9.6)	(9.6)	27.6
Acthar Gel-Related Settlement liability	(88.6)	0.0	0.0	(88.6)
Liabilities subject to compromise	0.0	0.0	0.0	0.0
Liabilities	(62.4)	(217.7)	(217.7)	(62.4)
Preferred Stock, Value, Outstanding		0.0	0.0
Common Stock, Other Value, Outstanding		0.0	0.0
Successor ordinary shares held in treasury at cost, none and none	0.0	0.0	0.0	0.0
Additional paid-in capital	0.0			0.0
Accumulated Other Comprehensive Income (Loss), Net of Tax	(11.1)	9.9	9.9	(11.1)
Retained deficit	(1,232.5)	(782.4)	(782.4)	(1,232.5)
Shareholders' equity	(1,243.6)	(772.5)	(772.5)	(1,243.6)
Total Liabilities and Shareholders' Equity	(1,306.0)	(990.2)	(990.2)	(1,306.0)
Reorganization, Chapter11, Post Adjustment, Successor
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents	186.8	297.9	297.9	186.8
Accounts receivable, less allowance for doubtful accounts of $6.5 and $4.4	467.7	387.4	387.4	467.7
Inventory, Net	1,036.3	1,227.0	1,227.0	1,036.3
Prepaid Expense and Other Assets, Current	155.0	339.6	339.6	155.0
Assets Held-for-sale, Not Part of Disposal Group, Current		100.0	100.0
Total current assets	1,845.8	2,351.9	2,351.9	1,845.8
Property, plant and equipment, net	318.4	449.4	449.4	318.4
Intangible Assets, Net (Excluding Goodwill)	624.6	3,152.2	3,152.2	624.6
Deferred Tax Assets, Net	795.1	453.4	453.4	795.1
Other assets	233.0	195.4	195.4	233.0
Assets	3,816.9	6,602.3	6,602.3	3,816.9
Current maturities of long-term debt	8.7	34.7	34.7	8.7
Accounts Payable, Current	73.8	102.6	102.6	73.8
Accrued payroll and payroll-related costs	81.6	71.4	71.4	81.6
Accrued interest	0.7	7.8	7.8	0.7
Taxes Payable	2.7			2.7
Acthar Gel-Related Settlement, Current	21.4	16.5	16.5	21.4
Opioid-Related Litigation Settlement liability		200.0	200.0
Accrued and other current liabilities	253.6	340.8	340.8	253.6
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		35.0	35.0
Total current liabilities	442.5	808.8	808.8	442.5
Long-term debt	1,858.9	3,032.5	3,032.5	1,858.9
Opioid-Related Litigation Settlement liability		304.3	304.3
Pension and postretirement benefits	39.4	54.8	54.8	39.4
Environmental liabilities	34.6	37.1	37.1	34.6
Deferred income taxes	0.0	1.4	1.4	0.0
Other income tax liabilities	19.6	14.0	14.0	19.6
Other Liabilities, Noncurrent	101.0	82.6	82.6	101.0
Acthar Gel-Related Settlement liability	126.1	63.2	63.2	126.1
Liabilities subject to compromise	0.0	0.0	0.0	0.0
Liabilities	2,622.1	4,398.7	4,398.7	2,622.1
Preferred Stock, Value, Outstanding		0.0	0.0
Common Stock, Other Value, Outstanding		0.0	0.0
Successor ordinary shares held in treasury at cost, none and none	0.0	0.0	0.0	0.0
Additional paid-in capital	1,194.6			1,194.6
Accumulated Other Comprehensive Income (Loss), Net of Tax	0.0	0.0	0.0	0.0
Retained deficit	0.0	0.0	0.0	0.0
Shareholders' equity	1,194.8	2,203.6	2,203.6	1,194.8
Total Liabilities and Shareholders' Equity	3,816.9	6,602.3	6,602.3	3,816.9
Predecessor Reorganization
Reorganization, Chapter 11 [Line Items]
Preferred Stock, Value, Outstanding					0.0		0.0
Common Stock, Other Value, Outstanding					0.0		0.0
Common Stock, Value, Outstanding					$ 0.0		$ 0.1
Predecessor Reorganization | Reorganization, Chapter 11, Predecessor, before Adjustment
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.1	18.9	18.9	0.1
Additional paid-in capital	2,199.9	5,599.5	5,599.5	2,199.9
Predecessor Reorganization | Reorganization, Chapter 11, Plan Effect Adjustment
Reorganization, Chapter 11 [Line Items]
Preferred Stock, Value, Outstanding		0.0	0.0
Common Stock, Other Value, Outstanding		0.0	0.0
Common Stock, Value, Outstanding	(0.1)	(18.9)	(18.9)	(0.1)
Additional paid-in capital		(5,599.5)	(5,599.5)
Predecessor Reorganization | Reorganization, Chapter 11, Fresh-Start Adjustment
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.0	0.0	0.0	0.0
Additional paid-in capital		0.0	0.0
Predecessor Reorganization | Reorganization, Chapter11, Post Adjustment, Successor
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.0	0.0	0.0	0.0
Additional paid-in capital		0.0	0.0
Successor, Fresh-Start Adjustments | Reorganization, Chapter 11, Predecessor, before Adjustment
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.0	0.0	0.0	0.0
Additional paid-in capital	0.0	0.0	0.0	0.0
Successor, Fresh-Start Adjustments | Reorganization, Chapter 11, Plan Effect Adjustment
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.2	0.1	0.1	0.2
Additional paid-in capital	(2,199.9)	2,203.5	2,203.5	(2,199.9)
Successor, Fresh-Start Adjustments | Reorganization, Chapter 11, Fresh-Start Adjustment
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.0	0.0	0.0	0.0
Additional paid-in capital	0.0	0.0	0.0	0.0
Successor, Fresh-Start Adjustments | Reorganization, Chapter11, Post Adjustment, Successor
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding	0.2	0.1	0.1	0.2
Additional paid-in capital	$ 0.0	$ 2,203.5	$ 2,203.5	$ 0.0