Investments - Net Investment Gains (Losses) By Transaction Type (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ (3.1)	$ (8.1)	$ 0.0
Intent-to-sell impairments	(7.6)	(2.3)	(5.3)
Total impairments	(10.7)	(10.4)	(5.3)
Sales and other, net	(17.8)	4.3	15.0
Change in fair value - equity securities	(33.2)	(2.3)	(0.2)
Change in fair value and losses realized on settlements - derivatives	5.2	(2.6)	(11.8)
Net investment losses	$ (56.5)	$ (11.0)	$ (2.3)