Fair Value Measurements - Additional Information (Details) $ in Millions		3 Months Ended			12 Months Ended
	Mar. 27, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Apr. 01, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Nov. 21, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net proceeds from sale of business and other assets					$ 5.2	$ 154.6	$ 69.1
Gain (loss) on disposition of business				$ (21.8)
Payment of guaranty liability					3.3
Gain (loss) on settlement of contingent consideration						17.4
Provision for new credit guarantees						$ 12.5
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guarantee on certain obligations		$ 10.5			$ 10.5			$ 13.8
Specialty Sciences
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on disposition of business			$ 17.1
Royalty Pharma
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Sale price of divestiture - cash plus non-cash	$ 2,850.0
Net proceeds from sale of business and other assets	2,200.0
Contingent proceeds from divestiture of business, milestone one, maximum	250.0
Contingent proceeds from divestiture of business, milestone two, maximum	$ 400.0
Rate of return (percent)					8.05%	8.07%
Royalty Pharma Contingent Milestone Payments | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value					$ (188.7)	$ 42.0
Royalty Pharma 2018 Contingent Milestone Payments | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value					(170.1)
Royalty Pharma 2020 Contingent Milestone Payments | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value					(18.6)
Tysabri Royalty Stream | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value						0.0	2,608.2
Contingent consideration | Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Provision for new credit guarantees					$ 0.0	$ 12.5	$ 0.0
Price volatility | Royalty Pharma
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Volatility (percent)		0.300	0.300		0.300	0.300
Long-term growth rate | CHCA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discounted cash flow (percent)		0.025
Indefinite-lived intangible assets, measurement input (percent)		(0.003)
Discount rate | CHCA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discounted cash flow (percent)		0.098
Indefinite-lived intangible assets, measurement input (percent)		0.098
Tax rate | CHCA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discounted cash flow (percent)		0.228
Indefinite-lived intangible assets, measurement input (percent)		0.228