Acquisitions (Narrative) (Details) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Jan. 31, 2021 USD ($) right $ / shares	Dec. 31, 2022 USD ($) right $ / shares	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Business Acquisition [Line Items]
Acquired in-process research and development and development milestones			$ 62.4	$ 177.6	$ 668.4	$ 532.4
Cash paid, net of cash acquired					0.0	$ 747.4
Acquired IPR&D Expense					$ 333.8
Prevail Therapeutics Inc.
Business Acquisition [Line Items]
Business acquisition, share price (in dollars per share) | $ / shares	$ 22.50
Cash paid, net of cash acquired	$ 747.4
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	$ 160.0
Contingent value right, monthly reduction (in cents per share) | $ / shares	$ 0.083
Akouos Acquisition | Forecast
Business Acquisition [Line Items]
Business acquisition, share price (in dollars per share) | $ / shares		$ 12.50
Consideration transferred, number of contingent value rights | right		1
Contingent value right, additional price per share (up to) (in dollars per share) | $ / shares		$ 3.00
Contingent value right, additional price per share, aggregate amount		$ 123.0
Payments to acquire businesses		$ 487.0