Acquisitions (Narrative) (Details)	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2021 USD ($) right $ / shares	Feb. 29, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Business Acquisition [Line Items]
Acquired IPR&D Expense			$ 174,000,000	$ 0	$ 498,300,000	$ 294,100,000
Cash paid, net of cash acquired					747,400,000	849,300,000
Goodwill			$ 3,884,100,000		3,884,100,000		$ 3,766,500,000
Repayments of long-term debt					$ 1,905,300,000	$ 276,300,000
Prevail Therapeutics Inc.
Business Acquisition [Line Items]
Business acquisition, share price (in dollars per share) | $ / shares	$ 22.50
Cash paid, net of cash acquired	$ 747,400,000
Consideration transferred, number of contingent value rights | right	1
Contingent value right, additional price per share (up to) (in dollars per share) | $ / shares	$ 4.00
Contingent value right, additional price per share, aggregate amount	$ 160,000,000
Contingent value right, monthly reduction (in cents per share) | $ / shares	$ 0.083
Goodwill	$ 118,800,000
Acquired IPR&D	824,000,000.0
Deferred income taxes assumed	$ 98,000,000.0
Dermira
Business Acquisition [Line Items]
Purchase price		$ 849,300,000
Goodwill		86,800,000
Acquired IPR&D		1,200,000,000
Deferred income taxes assumed		49,500,000
Long-term debt assumed		$ 375,500,000
Repayments of long-term debt							$ 276,200,000