Fair Value Measurements - Unrealized Loss Position (Details) $ in Millions	Mar. 31, 2026 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	$ 5,560.3
Unrealized Losses within 12 months, Unrealized Losses	(19.5)
Unrealized Losses 12 months or greater, Fair Value	16.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	5,576.3
Total, Unrealized Losses	(19.5)
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	10.0
Unrealized Losses within 12 months, Unrealized Losses	0.0
Unrealized Losses 12 months or greater, Fair Value	0.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	10.0
Total, Unrealized Losses	0.0
U.S. government notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	1,560.6
Unrealized Losses within 12 months, Unrealized Losses	(3.8)
Unrealized Losses 12 months or greater, Fair Value	10.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	1,570.6
Total, Unrealized Losses	(3.8)
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	2,925.3
Unrealized Losses within 12 months, Unrealized Losses	(11.3)
Unrealized Losses 12 months or greater, Fair Value	6.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	2,931.3
Total, Unrealized Losses	(11.3)
Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	11.4
Unrealized Losses within 12 months, Unrealized Losses	0.0
Unrealized Losses 12 months or greater, Fair Value	0.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	11.4
Total, Unrealized Losses	0.0
Agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	1,053.0
Unrealized Losses within 12 months, Unrealized Losses	(4.4)
Unrealized Losses 12 months or greater, Fair Value	0.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	1,053.0
Total, Unrealized Losses	$ (4.4)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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