Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2018	May 25, 2018
Quarterly Financial Information [Line Items]
Total revenues	$ 1,384.3	$ 1,263.1	$ 1,203.3	$ 1,140.4	$ 1,128.8	$ 1,026.5	$ 1,045.0	$ 930.9	$ 4,991.1	$ 4,131.2	$ 3,551.1
Cost of sales	114.3	95.2	99.2	85.8	96.8	90.6	95.3	91.6	394.5	374.3	454.2
Gross Profit	1,270.0	1,167.9	1,104.1	1,054.6	1,032.0	935.9	949.7	839.3
Total operating expenses	729.0	637.9	571.5	537.8	988.3	577.3	1,349.8	571.9	2,476.2	3,487.3	2,469.5
Operating income	541.0	530.0	532.6	516.8	43.7	358.6	(400.1)	267.4	2,120.4	269.6	627.4
Net income (loss)	$ 889.0	$ 467.6	$ 459.8	$ 587.9	$ (45.0)	$ 330.9	$ (457.4)	$ 249.1	$ 2,404.3	$ 77.6	$ 443.3
Earnings per common share
Basic (in dollars per share)	$ 4.02	$ 2.09	$ 2.05	$ 2.63	$ (0.20)	$ 1.48	$ (2.05)	$ 1.12	$ 10.77	$ 0.35	$ 1.98
Diluted (in dollars per share)	$ 4.00	$ 2.08	$ 2.04	$ 2.61	$ (0.20)	$ 1.47	$ (2.05)	$ 1.11	$ 10.70	$ 0.35	$ 1.97
Deferred tax benefit									$ 455.5	$ (32.9)	$ 45.9
Effective income tax rate reconciliation, Tax Cuts and Jobs Act of 2017, amount										(56.5)	$ 45.8
In Process Research and Development [Member]
Earnings per common share
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, Finite-Lived Intangibles													$ 803.7
Syntimmune, Inc [Member]
Earnings per common share
Asset Acquisition, Recognized Identifiable Assets Acquired And Liabilities Assumed, In-Process Research And Development					$ 379.3					$ 379.3		$ 375.2
Syntimmune, Inc [Member] | In Process Research and Development [Member]
Earnings per common share
Asset Acquisition, Recognized Benefit From Previously Acquired Research And Development			$ 4.1
Intellectual Property Election [Member]
Earnings per common share
Deferred tax benefit, asset transfer	$ 382.2
Intellectual Property Election [Member] | Wilson Therapeutics [Member]
Earnings per common share
Deferred tax benefit				$ 95.7					95.7
Valuation Allowance Release [Member]
Earnings per common share
Deferred tax benefit				$ 30.3					$ 30.3