Marketable Securities - Schedule of Fair Value and Unrealized Losses of Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value
Less than 12 Months	$ 11,826.9	$ 12,179.8
12 Months or Greater	665.8	1,219.5
Total	12,492.7	13,399.3
Unrealized Losses
Less than 12 Months	(6.3)	(21.0)
12 Months or Greater	(11.4)	(18.0)
Total	(17.7)	(39.0)
Corporate bonds
Fair Value
Less than 12 Months	7,982.1	7,175.8
12 Months or Greater	593.5	1,044.8
Total	8,575.6	8,220.6
Unrealized Losses
Less than 12 Months	(4.1)	(14.2)
12 Months or Greater	(11.0)	(17.2)
Total	(15.1)	(31.4)
U.S. government and government agency obligations
Fair Value
Less than 12 Months	3,473.9	4,675.3
12 Months or Greater	61.3	141.7
Total	3,535.2	4,817.0
Unrealized Losses
Less than 12 Months	(1.9)	(6.2)
12 Months or Greater	(0.4)	(0.7)
Total	(2.3)	(6.9)
Sovereign bonds
Fair Value
Less than 12 Months	60.2	63.3
12 Months or Greater	0.0	19.1
Total	60.2	82.4
Unrealized Losses
Less than 12 Months	(0.1)	(0.3)
12 Months or Greater	0.0	(0.1)
Total	(0.1)	(0.4)
Asset-backed securities
Fair Value
Less than 12 Months	310.7	265.4
12 Months or Greater	11.0	13.9
Total	321.7	279.3
Unrealized Losses
Less than 12 Months	(0.2)	(0.3)
12 Months or Greater	0.0	0.0
Total	$ (0.2)	$ (0.3)

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