Income from Investments - Net Realized Gains on Sales of Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Equity Securities:
Realized Investment Gains	$ 28.6	$ 6.7	$ 41.3
Realized Investment Losses	(7.5)	(13.4)	(38.7)
Net Realized Investment Gains (Losses)	13.2	(18.6)	4.3
Fixed Maturities:
Fixed Maturities:
Gains on Sales	20.2	5.9	31.6
Losses on Sales	(3.2)	(10.9)	(31.9)
Equity Securities
Equity Securities:
Gains on Sales	4.2	0.6	9.7
Losses on Sales	(0.1)	(2.5)	(6.8)
Derivative
Equity Securities:
(Losses) Gains on Hedging Activity	(7.9)	(11.9)	1.7
Other Long-Term Investments
Equity Securities:
Realized Investment Gains	4.2	0.2	0.0
Realized Investment Losses	$ (4.2)	$ 0.0	$ 0.0