Investments - Net Investment Gains (Losses) By Transaction Type (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ 0.3	$ (0.4)	$ (3.1)
Intent-to-sell impairments	(0.2)	(6.7)	(7.6)
Total impairments	0.1	(7.1)	(10.7)
Sales and other, net	(24.3)	(25.0)	(17.8)
Change in fair value - equity securities	7.4	7.9	(33.2)
Change in fair value and losses realized on settlements - derivatives	(0.5)	0.2	5.2
Net investment losses	$ (17.3)	$ (24.0)	$ (56.5)	[1]

[1] Recast for the adoption of ASU 2018-12.