Fair Value Measurements - Unrealized Loss Position (Details) $ in Millions	Dec. 31, 2025 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	$ 1,606.2
Unrealized Losses within 12 months, Unrealized Losses	(1.5)
Unrealized Losses 12 months or greater, Fair Value	44.9
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	1,651.1
Total, Unrealized Losses	(1.5)
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	9.9
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	9.9
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	260.8
Unrealized Losses within 12 months, Unrealized Losses	0.0
Unrealized Losses 12 months or greater, Fair Value	15.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	275.8
Total, Unrealized Losses	0.0
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	857.7
Unrealized Losses within 12 months, Unrealized Losses	(0.9)
Unrealized Losses 12 months or greater, Fair Value	29.9
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	887.6
Total, Unrealized Losses	(0.9)
Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Losses within 12 months, Fair Value	4.7
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	4.7
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	473.1
Unrealized Losses within 12 months, Unrealized Losses	(0.6)
Unrealized Losses 12 months or greater, Fair Value	0.0
Unrealized Losses 12 months or greater, Unrealized Losses	0.0
Total, Fair Value	473.1
Total, Unrealized Losses	$ (0.6)