Investments - Amortized Cost and Fair Values (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 706.0	$ 607.1
Gross unrealized gains	2.8	1.6
Gross unrealized losses	0.0	(1.3)
Fair Value	708.8	607.4
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	499.2	470.6
Gross unrealized gains	2.0	1.3
Gross unrealized losses	0.0	(1.1)
Fair Value	501.2	470.8
U.S. Government obligations
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	139.5	107.6
Gross unrealized gains	0.6	0.3
Gross unrealized losses	0.0	(0.2)
Fair Value	140.1	107.7
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	45.3	22.9
Gross unrealized gains	0.2	0.0
Gross unrealized losses	0.0	0.0
Fair Value	45.5	22.9
Non-U.S. government obligations
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	22.0	6.0
Gross unrealized gains	0.0	0.0
Gross unrealized losses	0.0	0.0
Fair Value	22.0	6.0
Fixed Income Securities
Debt Securities, Available-for-sale [Line Items]
Gross unrealized losses	$ (0.1)	$ (1.3)