Investments - Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Net Investment Income [Line Items]
Net investment income	$ 10.3	$ 9.7	$ 29.8	$ 28.6
Total	10.4	9.8	30.1	28.9
Investment expense	0.1	0.1	0.3	0.3
Interest on cash and cash equivalents
Net Investment Income [Line Items]
Net investment income	1.9	2.1	5.9	6.3
Fixed maturities
Net Investment Income [Line Items]
Net investment income	7.9	7.5	23.4	21.9
Short-term investments
Net Investment Income [Line Items]
Net investment income	$ 0.6	$ 0.2	$ 0.8	$ 0.7

Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.