Acquisitions (Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Millions				1 Months Ended
	Dec. 27, 2023	Dec. 01, 2022	Jan. 22, 2021	Dec. 31, 2022	Jan. 31, 2021	Dec. 31, 2023
Business Acquisition [Line Items]
Goodwill				$ 4,073.0		$ 4,939.7
Biopharma Global Inc
Business Acquisition [Line Items]
Cash	$ 302.7
Acquired IPR&D	196.0
Goodwill	859.1
Other assets and liabilities, net	(19.3)
Acquisition date fair value of consideration transferred	1,338.5
Cash acquired	(302.7)
Cash paid, net of cash acquired	$ 1,035.8
Akouos Acquisition
Business Acquisition [Line Items]
Cash		$ 153.2
Acquired IPR&D		184.0
Goodwill		185.6
Other assets and liabilities, net		24.5
Acquisition date fair value of consideration transferred		547.3
Cash acquired		(153.2)
Fair value of CVR liability		$ (66.9)
Cash paid, net of cash acquired				$ 327.2
Prevail Therapeutics Inc.
Business Acquisition [Line Items]
Cash			$ 90.5
Acquired IPR&D			824.0
Goodwill			126.8
Deferred tax liabilities			(106.0)
Other assets and liabilities, net			(31.5)
Acquisition date fair value of consideration transferred			903.8
Cash acquired			(90.5)
Fair value of CVR liability			(65.9)
Cash paid, net of cash acquired			$ 747.4		$ 747.4