Revenue from Contracts with Customers (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 25, 2020		Sep. 27, 2019	Sep. 25, 2020		Sep. 27, 2019	Dec. 27, 2019	Dec. 28, 2018
Disaggregation of Revenue [Line Items]
Revenue Reserves		$ 861.4		$ 339.3	$ 861.4		$ 339.3	$ 337.4	$ 405.4
Revenue Reserve Provision					1,520.3		1,842.4
Revenue Reserve Payments or Credits					(1,531.4)		(1,908.5)
Deferred Revenue, Revenue Recognized					4.7		10.3
Contract with Customer, Liability		3.4			3.4			6.2
Contract with Customer, Liability, Current		3.0			3.0			5.6
Capitalized Contract Cost, Gross		26.8			26.8			26.5
Capitalized Contract Cost, Amortization					4.0		5.1
Contract with Customer, Liability, Noncurrent		0.4			0.4			0.6
Net sales (includes refined estimate of the retrospective one-time charge of $0.7 and $535.1 related to the Medicaid lawsuit for the three and nine months ended September 25, 2020, respectively)		698.3		743.7	1,530.6		2,357.6
Medicaid lawsuit (Note 11)					640.2
Medicaid Lawsuit [Member]
Disaggregation of Revenue [Line Items]
Decrease in revenue		22.2			30.8
Operating Expense [Member]
Disaggregation of Revenue [Line Items]
Medicaid lawsuit (Note 11)		(0.2)		0.0	105.1		0.0
Sales [Member]
Disaggregation of Revenue [Line Items]
Medicaid lawsuit (Note 11)		$ 0.7		$ 0.0	$ 535.1		$ 0.0
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue		79.50%		81.40%	78.50%		81.70%
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue		20.50%		18.60%	21.50%		18.30%
Royalty [Member]
Disaggregation of Revenue [Line Items]
Net sales (includes refined estimate of the retrospective one-time charge of $0.7 and $535.1 related to the Medicaid lawsuit for the three and nine months ended September 25, 2020, respectively)		$ 20.4		$ 19.5	$ 52.3		$ 56.3
Rebates and Chargebacks [Member]
Disaggregation of Revenue [Line Items]
Revenue Reserves		823.3	[1]	282.8	823.3	[1]	282.8	295.8	354.3
Revenue Reserve Provision					1,453.7		1,772.9
Revenue Reserve Payments or Credits					(1,461.3)		(1,844.4)
Rebates and Chargebacks [Member] | Sales [Member]
Disaggregation of Revenue [Line Items]
Medicaid lawsuit (Note 11)	[1]				535.1
Allowance for Sales Returns [Member]
Disaggregation of Revenue [Line Items]
Revenue Reserves		26.4		29.9	26.4		29.9	28.4	34.0
Revenue Reserve Provision					22.3		18.8
Revenue Reserve Payments or Credits					(24.3)		(22.9)
Medicaid lawsuit (Note 11)					0.0
Other Sales Deductions [Member]
Disaggregation of Revenue [Line Items]
Revenue Reserves		$ 11.7		$ 26.6	11.7		26.6	$ 13.2	$ 17.1
Revenue Reserve Provision					44.3		50.7
Revenue Reserve Payments or Credits					(45.8)		$ (41.2)
Medicaid lawsuit (Note 11)					$ 0.0
Minimum
Disaggregation of Revenue [Line Items]
Royalty Rate Percentage					18.00%
Maximum
Disaggregation of Revenue [Line Items]
Royalty Rate Percentage					26.00%

[1] Excludes the $105.1 million that is reflected as a component of operating expenses as it represents a pre-acquisition contingency related to the portion of the liability that arose from sales of Acthar Gel prior to the Company’s acquisition of Questcor Pharmaceuticals Inc. ("Questcor") in August 2014. See Note 11 for further detail on the status of the Medicaid lawsuit.