Fair Value Measurements - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions		Dec. 31, 2020		Sep. 26, 2020	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Assets:
Goodwill		$ 3,768.8			$ 4,116.7		$ 3,979.8
Definite-lived intangible assets, net		2,974.3			2,921.2
Recurring | Level 1
Assets:
Investment securities		2.5			6.6
Foreign currency forward contracts		0.0			0.0
Cross-currency swap		0.0			0.0
Funds associated with Israeli severance liability		0.0			0.0
Royalty Pharma contingent milestone payments		0.0			0.0
Total assets		2.5			6.6
Liabilities:
Foreign currency forward contracts		0.0			0.0
Contingent consideration		0.0			0.0
Total liabilities		0.0			0.0
Recurring | Level 2
Assets:
Investment securities		0.0			0.0
Foreign currency forward contracts		21.5			4.3
Cross-currency swap		6.3			26.3
Funds associated with Israeli severance liability		15.7			14.6
Royalty Pharma contingent milestone payments		0.0			0.0
Total assets		43.5			45.2
Liabilities:
Foreign currency forward contracts		8.2			8.4
Contingent consideration		0.0			0.0
Total liabilities		8.2			8.4
Recurring | Level 3
Assets:
Investment securities		0.0			0.0
Foreign currency forward contracts		0.0			0.0
Cross-currency swap		0.0			0.0
Funds associated with Israeli severance liability		0.0			0.0
Royalty Pharma contingent milestone payments		0.0			95.3
Total assets		0.0			95.3
Liabilities:
Foreign currency forward contracts		0.0			0.0
Contingent consideration		13.2			11.9		15.3		$ 22.0
Total liabilities		13.2			11.9
Nonrecurring
Assets:
Definite-lived intangible assets, net					55.3
Nonrecurring | Level 1
Assets:
Goodwill	[1]	0.0			0.0
Definite-lived intangible assets	[2]	0.0			0.0
Total assets		0.0			0.0
Nonrecurring | Level 2
Assets:
Goodwill	[1]	0.0			0.0
Definite-lived intangible assets	[2]	0.0			0.0
Total assets		0.0			0.0
Nonrecurring | Level 3
Assets:
Goodwill	[1]	673.1			1,013.1
Definite-lived intangible assets	[2]	0.0			23.3
Total assets		673.1			1,036.4
CSCA
Assets:
Goodwill		1,905.0			1,899.1		1,713.7
CSCA | Nonrecurring
Assets:
Goodwill		1,019.9
RX
Assets:
Goodwill		$ 673.1	[3]	$ 811.1	1,013.9	[3]	$ 1,114.8	[3]
RX | Nonrecurring
Assets:
Goodwill					$ 1,122.3

[1] During the year ended December 31, 2020, goodwill with a carrying amount of $1,019.9 million was written down to a fair value of $673.1 million. During the year ended December 31, 2019, goodwill with a carrying amount of $1,122.3 million was written down to a fair value of $1,013.1 million.

[2] During the year ended December 31, 2019, definite-lived intangible assets with a carrying amount of $55.3 million were written down to a fair value of $23.3 million.

[3] We had accumulated goodwill impairments of $109.2 million and $456.0 million as of December 31, 2019 and December 31, 2020, respectivel