- Additional Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		21 Months Ended
	Mar. 30, 2015	Oct. 01, 2016	Sep. 26, 2015	Oct. 01, 2016	Sep. 26, 2015	Oct. 01, 2016	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Non-current deferred income taxes		$ 798.0		$ 798.0		$ 798.0		$ 1,372.7
Net income (loss)		(1,590.2)	$ 260.9	(2,653.7)	$ 216.4
Foreign currency translation adjustments		27.5	(39.9)	71.5	50.9
Adjustments | Tax Basis Intangible Assets Misstatements
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Non-current deferred income taxes							$ (236.3)
Adjustments | Tysabri Royalty Stream Fair Value Option Adjustments and Other Misstatements
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)		(335.0)	148.3	1,300.0	$ (142.2)
Foreign currency translation adjustments		$ (0.5)	$ (0.1)	$ (0.3)
Cumulative effect on retained earnings						$ 0.0
Omega
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Acquisition date	Mar. 30, 2015