Fair Value Measurements - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016		Oct. 02, 2016	Sep. 30, 2016	Apr. 03, 2016	Mar. 01, 2016	Dec. 31, 2015
Assets:
Royalty Pharma contingent milestone payments									$ 30.0
Financial assets		$ 0.0		$ 2,350.0						$ 5,310.0
Indefinite-lived intangible assets							$ 674.4
Liabilities:
Indefinite-lived intangible assets, gross		90.3		114.5						1,916.3
Definite lived assets, gross		4,661.7		4,417.2						3,705.3
Recurring | Level 1
Assets:
Investment securities		17.0		38.2						14.9
Recurring | Level 2
Assets:
Foreign currency forward contracts		6.3		3.8						4.8
Funds associated with Israeli severance liability		16.3		15.9						17.2
Total assets		22.6		19.7						22.0
Liabilities:
Interest rate swap agreements		0.0		0.0						0.3
Foreign currency forward contracts		3.8		5.0						3.9
Total liabilities		3.8		5.0						4.2
Recurring | Level 3
Assets:
Royalty Pharma contingent milestone payments		134.5		0.0						0.0
Financial assets		0.0		2,350.0						5,310.0
Total assets		134.5		2,350.0						5,310.0
Liabilities:
Contingent consideration		22.0		69.9						17.9
Nonrecurring
Assets:
Indefinite-lived intangible assets								$ 364.5
Liabilities:
Intangible assets, gross										1,200.0
Definite lived assets, gross		31.2		2,300.0
Nonrecurring | Level 3
Assets:
Goodwill	[1]	0.0		1,148.4						0.0
Indefinite-lived intangible assets		0.0	[2]	0.3	[2]	$ 674.2				1,031.8	[2]
Definite-lived intangible assets	[3]	11.5		758.0						0.0
Assets held for sale, net		0.0		18.2						37.5
Total assets		$ 11.5		1,924.9						$ 1,069.3
Liabilities:
Goodwill, gross				2,200.0
Indefinite-lived intangible assets, gross				$ 0.7

[1] As of December 31, 2016, goodwill with a carrying amount of $2.2 billion was written down to its implied fair value of $1.1 billion.

[2] As of December 31, 2016, indefinite-lived intangible assets with a carrying amount of $0.7 million were written down to a fair value of $0.3 million. As of December 31, 2015, indefinite-lived intangible assets with a carrying amount of $1.2 billion were written down to a fair value of $1.0 billion.

[3] 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. As of December 31, 2016, definite-lived intangible assets with a carrying amount of $2.3 billion were written down to a fair value of $758.0 million. Included in this balance are indefinite-lived intangible assets with a fair value of $364.5 million and $674.2 million that were reclassified to definite-lived assets at April 3, 2016 and October 2, 2016, respectively.