Investments - Continuous Loss Position (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Less than 12 months
Fair Value	$ 362.5	$ 52.7
Gross Unrealized Losses	(12.9)	0.0
12 months or more
Fair Value	18.9	26.1
Gross Unrealized Losses	(1.6)	(1.5)
Total
Fair Value	381.4	78.8
Gross Unrealized Losses	(14.5)	(1.5)
U.S. government and agencies
Less than 12 months
Fair Value	90.9	17.1
Gross Unrealized Losses	(2.4)	0.0
12 months or more
Fair Value	1.8	3.2
Gross Unrealized Losses	(0.1)	(0.1)
Total
Fair Value	92.7	20.3
Gross Unrealized Losses	(2.5)	(0.1)
States and other territories
Less than 12 months
Fair Value	5.2	0.9
Gross Unrealized Losses	(0.2)	0.0
12 months or more
Fair Value	1.6	2.6
Gross Unrealized Losses	(0.1)	(0.1)
Total
Fair Value	6.8	3.5
Gross Unrealized Losses	(0.3)	(0.1)
Corporate securities
Less than 12 months
Fair Value	216.5	7.5
Gross Unrealized Losses	(7.8)	0.0
12 months or more
Fair Value	6.7	8.6
Gross Unrealized Losses	(0.1)	(0.2)
Total
Fair Value	223.2	16.1
Gross Unrealized Losses	(7.9)	(0.2)
Residential mortgage-backed securities
Less than 12 months
Fair Value	49.5	7.2
Gross Unrealized Losses	(2.5)	0.0
12 months or more
Fair Value	7.2	8.6
Gross Unrealized Losses	(1.1)	(0.9)
Total
Fair Value	56.7	15.8
Gross Unrealized Losses	(3.6)	(0.9)
Commercial mortgage-backed securities
Less than 12 months
Fair Value	0.4	0.8
Gross Unrealized Losses	0.0	0.0
12 months or more
Fair Value	1.6	2.9
Gross Unrealized Losses	(0.2)	(0.2)
Total
Fair Value	2.0	3.7
Gross Unrealized Losses	$ (0.2)	(0.2)
Asset backed securities
Less than 12 months
Fair Value		13.0
Gross Unrealized Losses		0.0
12 months or more
Fair Value		0.2
Gross Unrealized Losses		0.0
Total
Fair Value		13.2
Gross Unrealized Losses		0.0
Corporate securities
Less than 12 months
Fair Value		6.2
Gross Unrealized Losses		0.0
12 months or more
Fair Value		0.0
Gross Unrealized Losses		0.0
Total
Fair Value		6.2
Gross Unrealized Losses		$ 0.0

Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer

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