Fair Value Measurements - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017	Apr. 01, 2017
Liabilities:
Definite-lived intangible assets		$ 4,732.4	$ 4,661.7
Measured at fair value on a recurring basis: | Level 1
Assets:
Investment securities		13.8	17.0
Measured at fair value on a recurring basis: | Level 2
Assets:
Foreign currency forward contracts		5.0	6.3
Funds associated with Israeli severance liability		15.0	16.3
Total level 2 assets		20.0	22.6
Liabilities:
Foreign currency forward contracts		3.8	3.8
Measured at fair value on a recurring basis: | Level 3
Liabilities:
Contingent consideration		18.1	22.0
Measured at fair value on a non-recurring basis:
Liabilities:
Definite-lived intangible assets			31.2
Measured at fair value on a non-recurring basis: | Level 3
Assets:
Definite-lived intangible assets	[1]	0.0	11.5
Royalty Pharma Contingent Milestone Payments | Measured at fair value on a recurring basis: | Level 3
Assets:
Royalty Pharma contingent milestone payments		$ 124.9	$ 134.5	$ 184.5

[1] (1) As of December 31, 2017, definite-lived intangible assets with a carrying amount of $31.2 million were written down to a fair value of $11.5 million.