Fresh-Start Accounting - Condensed Consolidated Balance Sheet (Details) - USD ($) $ in Millions	Dec. 30, 2022	Jun. 16, 2022	Dec. 31, 2021	Dec. 25, 2020	Dec. 27, 2019
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents	$ 409.5	$ 297.9	$ 1,345.0	$ 1,070.6
Accounts receivable, less allowance for doubtful accounts of $4.4 and $4.7	405.3		439.1
Inventory, Net	947.6		347.2
Total current assets	2,035.8		2,309.6
Property, plant and equipment, net	457.6		776.0
Intangible Assets, Net (Excluding Goodwill)	2,843.8		5,448.4
Other assets	201.1		382.3
Assets	6,013.8		8,916.3
Current maturities of long-term debt	44.1		1,388.9
Accounts Payable, Current	114.0		123.0
Accrued payroll and payroll-related costs	49.5		84.6
Accrued interest	29.0		17.0
Acthar Gel-Related Settlement, Current		260.0
Opioid-Related Litigation Settlement liability, Current	200.0		0.0
Accrued and other current liabilities	290.7		328.7
Total current liabilities	743.8		1,942.2
Long-term debt	3,027.7		0.0
Opioid-Related Litigation Settlement liability, Non-current	379.9		0.0
Pension and postretirement benefits	41.0		30.1
Environmental liabilities	35.8		43.0
Deferred income taxes	224.4		175.6
Other income tax liabilities	18.2		83.2
Other Liabilities, Noncurrent	78.4		85.8
Liabilities subject to compromise	0.0		6,397.7
Liabilities	4,400.1		8,602.9
Ordinary shares held in treasury at cost, none and 9,569,645	0.0		(1,616.1)
Additional paid-in capital	2,191.0		5,597.8
Accumulated Other Comprehensive Income (Loss), Net of Tax	10.8		(8.3)
Retained deficit	(588.2)		(3,678.9)
Shareholders' equity	1,613.7	2,203.6	313.4	$ 1,019.2	$ 1,940.7
Total Liabilities and Shareholders' Equity	6,013.8		8,916.3
Opioid Claimant Trust [Member]
Reorganization, Chapter 11 [Line Items]
Opioid-Related Settlement, Payment Year One and Two		200.0
Predecessor Reorganization
Reorganization, Chapter 11 [Line Items]
Predecessor preferred shares, $0.20 par value, 500,000,000 authorized; none issued or outstanding	0.0		0.0
Predecessor ordinary shares, $0.20 par value, 500,000,000 authorized; 94,296,235 issued; 84,726,590 outstanding	0.0		0.0
Common Stock, Value, Outstanding	$ 0.0		$ 18.9
Reorganization, Chapter 11, Predecessor, before Adjustment
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents		1,392.6
Accounts receivable, less allowance for doubtful accounts of $4.4 and $4.7		387.4
Inventory, Net		375.2
Prepaid Expense and Other Assets, Current		322.6
Assets Held-for-sale, Not Part of Disposal Group, Current		0.0
Total current assets		2,477.8
Property, plant and equipment, net		748.6
Intangible Assets, Net (Excluding Goodwill)		5,166.6
Deferred Tax Assets, Net		0.0
Other assets		222.8
Assets		8,615.8
Current maturities of long-term debt		1,389.9
Accounts Payable, Current		156.4
Accrued payroll and payroll-related costs		71.4
Accrued interest		20.8
Acthar Gel-Related Settlement, Current		0.0
Opioid-Related Litigation Settlement liability, Current		0.0
Accrued and other current liabilities		296.1
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		0.0
Total current liabilities		1,934.6
Long-term debt		0.0
Acthar Gel-Related Settlement, Non-current		0.0
Opioid-Related Litigation Settlement liability, Non-current		0.0
Pension and postretirement benefits		27.6
Environmental liabilities		37.1
Deferred income taxes		20.4
Other income tax liabilities		75.9
Other Liabilities, Noncurrent		68.6
Liabilities subject to compromise		6,402.7
Liabilities		8,566.9
Predecessor preferred shares, $0.20 par value, 500,000,000 authorized; none issued or outstanding		0.0
Predecessor ordinary shares, $0.20 par value, 500,000,000 authorized; 94,296,235 issued; 84,726,590 outstanding		0.0
Ordinary shares held in treasury at cost, none and 9,569,645		(1,616.1)
Accumulated Other Comprehensive Income (Loss), Net of Tax		(9.9)
Retained deficit		(3,943.5)
Shareholders' equity		48.9
Total Liabilities and Shareholders' Equity		8,615.8
Reorganization, Chapter 11, Predecessor, before Adjustment | Predecessor Reorganization
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		18.9
Additional paid-in capital		5,599.5
Reorganization, Chapter 11, Predecessor, before Adjustment | Successor, Fresh-Start Adjustments
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		0.0
Additional paid-in capital		0.0
Reorganization, Chapter 11, Plan Effect Adjustment
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents		(1,094.7)
Accounts receivable, less allowance for doubtful accounts of $4.4 and $4.7		0.0
Inventory, Net		0.0
Prepaid Expense and Other Assets, Current		75.3
Assets Held-for-sale, Not Part of Disposal Group, Current		0.0
Total current assets		(1,019.4)
Property, plant and equipment, net		0.0
Intangible Assets, Net (Excluding Goodwill)		0.0
Deferred Tax Assets, Net		0.0
Other assets		(3.9)
Assets		(1,023.3)
Current maturities of long-term debt		(1,355.2)
Accounts Payable, Current		(53.8)
Accrued payroll and payroll-related costs		0.0
Accrued interest		(13.0)
Acthar Gel-Related Settlement, Current		16.5
Opioid-Related Litigation Settlement liability, Current		200.0
Accrued and other current liabilities		50.8
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		35.0
Total current liabilities		(1,119.7)
Long-term debt		3,050.9
Acthar Gel-Related Settlement, Non-current		63.2
Opioid-Related Litigation Settlement liability, Non-current		304.3
Pension and postretirement benefits		27.2
Environmental liabilities		0.0
Deferred income taxes		102.7
Other income tax liabilities		0.0
Other Liabilities, Noncurrent		23.6
Liabilities subject to compromise		(6,402.7)
Liabilities		(3,950.5)
Predecessor preferred shares, $0.20 par value, 500,000,000 authorized; none issued or outstanding		0.0
Predecessor ordinary shares, $0.20 par value, 500,000,000 authorized; 94,296,235 issued; 84,726,590 outstanding		0.0
Ordinary shares held in treasury at cost, none and 9,569,645		1,616.1
Accumulated Other Comprehensive Income (Loss), Net of Tax		0.0
Retained deficit		4,725.9
Shareholders' equity		2,927.2
Total Liabilities and Shareholders' Equity		(1,023.3)
Reorganization, Chapter 11, Plan Effect Adjustment | Predecessor Reorganization
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		(18.9)
Additional paid-in capital		(5,599.5)
Reorganization, Chapter 11, Plan Effect Adjustment | Successor, Fresh-Start Adjustments
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		0.1
Additional paid-in capital		2,203.5
Reorganization, Chapter 11, Fresh-Start Adjustment
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents		0.0
Accounts receivable, less allowance for doubtful accounts of $4.4 and $4.7		0.0
Inventory, Net		851.8
Prepaid Expense and Other Assets, Current		(58.3)
Assets Held-for-sale, Not Part of Disposal Group, Current		100.0
Total current assets		893.5
Property, plant and equipment, net		(299.2)
Intangible Assets, Net (Excluding Goodwill)		(2,014.4)
Deferred Tax Assets, Net		453.4
Other assets		(23.5)
Assets		(990.2)
Current maturities of long-term debt		0.0
Accounts Payable, Current		0.0
Accrued payroll and payroll-related costs		0.0
Accrued interest		0.0
Acthar Gel-Related Settlement, Current		0.0
Opioid-Related Litigation Settlement liability, Current		0.0
Accrued and other current liabilities		(6.1)
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		0.0
Total current liabilities		(6.1)
Long-term debt		(18.4)
Acthar Gel-Related Settlement, Non-current		0.0
Opioid-Related Litigation Settlement liability, Non-current		0.0
Pension and postretirement benefits		0.0
Environmental liabilities		0.0
Deferred income taxes		(121.7)
Other income tax liabilities		(61.9)
Other Liabilities, Noncurrent		(9.6)
Liabilities subject to compromise		0.0
Liabilities		(217.7)
Predecessor preferred shares, $0.20 par value, 500,000,000 authorized; none issued or outstanding		0.0
Predecessor ordinary shares, $0.20 par value, 500,000,000 authorized; 94,296,235 issued; 84,726,590 outstanding		0.0
Ordinary shares held in treasury at cost, none and 9,569,645		0.0
Accumulated Other Comprehensive Income (Loss), Net of Tax		9.9
Retained deficit		(782.4)
Shareholders' equity		(772.5)
Total Liabilities and Shareholders' Equity		(990.2)
Reorganization, Chapter 11, Fresh-Start Adjustment | Predecessor Reorganization
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		0.0
Additional paid-in capital		0.0
Reorganization, Chapter 11, Fresh-Start Adjustment | Successor, Fresh-Start Adjustments
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		0.0
Additional paid-in capital		0.0
Reorganization, Chapter11, Post Adjustment, Successor
Reorganization, Chapter 11 [Line Items]
Cash and cash equivalents		297.9
Accounts receivable, less allowance for doubtful accounts of $4.4 and $4.7		387.4
Inventory, Net		1,227.0
Prepaid Expense and Other Assets, Current		339.6
Assets Held-for-sale, Not Part of Disposal Group, Current		100.0
Total current assets		2,351.9
Property, plant and equipment, net		449.4
Intangible Assets, Net (Excluding Goodwill)		3,152.2
Deferred Tax Assets, Net		453.4
Other assets		195.4
Assets		6,602.3
Current maturities of long-term debt		34.7
Accounts Payable, Current		102.6
Accrued payroll and payroll-related costs		71.4
Accrued interest		7.8
Acthar Gel-Related Settlement, Current		16.5
Opioid-Related Litigation Settlement liability, Current		200.0
Accrued and other current liabilities		340.8
Liabilities Held-for-Sales, Not Part of Disposal Group, Current		35.0
Total current liabilities		808.8
Long-term debt		3,032.5
Acthar Gel-Related Settlement, Non-current		63.2
Opioid-Related Litigation Settlement liability, Non-current		304.3
Pension and postretirement benefits		54.8
Environmental liabilities		37.1
Deferred income taxes		1.4
Other income tax liabilities		14.0
Other Liabilities, Noncurrent		82.6
Liabilities subject to compromise		0.0
Liabilities		4,398.7
Predecessor preferred shares, $0.20 par value, 500,000,000 authorized; none issued or outstanding		0.0
Predecessor ordinary shares, $0.20 par value, 500,000,000 authorized; 94,296,235 issued; 84,726,590 outstanding		0.0
Ordinary shares held in treasury at cost, none and 9,569,645		0.0
Accumulated Other Comprehensive Income (Loss), Net of Tax		0.0
Retained deficit		0.0
Shareholders' equity		2,203.6
Total Liabilities and Shareholders' Equity		6,602.3
Reorganization, Chapter11, Post Adjustment, Successor | Predecessor Reorganization
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		0.0
Additional paid-in capital		0.0
Reorganization, Chapter11, Post Adjustment, Successor | Successor, Fresh-Start Adjustments
Reorganization, Chapter 11 [Line Items]
Common Stock, Value, Outstanding		0.1
Additional paid-in capital		$ 2,203.5