Marketable Securities - Schedule of Fair Value and Unrealized Losses of Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Fair Value
Less than 12 Months	$ 13,898.1	$ 12,179.8
12 Months or Greater	573.1	1,219.5
Total	14,471.2	13,399.3
Unrealized Losses
Less than 12 Months	(2.0)	(21.0)
12 Months or Greater	(4.0)	(18.0)
Total	(6.0)	(39.0)
Corporate bonds
Fair Value
Less than 12 Months	9,300.3	7,175.8
12 Months or Greater	397.4	1,044.8
Total	9,697.7	8,220.6
Unrealized Losses
Less than 12 Months	(1.5)	(14.2)
12 Months or Greater	(3.9)	(17.2)
Total	(5.4)	(31.4)
U.S. government and government agency obligations
Fair Value
Less than 12 Months	4,541.8	4,675.3
12 Months or Greater	161.5	141.7
Total	4,703.3	4,817.0
Unrealized Losses
Less than 12 Months	(0.4)	(6.2)
12 Months or Greater	(0.1)	(0.7)
Total	(0.5)	(6.9)
Sovereign bonds
Fair Value
Less than 12 Months	56.0	63.3
12 Months or Greater	14.2	19.1
Total	70.2	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		265.4
12 Months or Greater		13.9
Total		279.3
Unrealized Losses
Less than 12 Months		(0.3)
12 Months or Greater		0.0
Total		$ (0.3)