Investments - Net Investment Gains (Losses) by Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ (0.5)	$ (1.3)	$ (0.5)	$ (2.2)
Intent-to-sell impairments	(6.1)	(0.5)	(6.1)	(1.4)
Total impairments	(6.6)	(1.8)	(6.6)	(3.6)
Sales and other, net	(19.3)	(1.1)	(21.7)	0.0
Change in fair value - equity securities	7.7	(12.6)	6.7	(29.7)
Change in fair value and gains (losses) realized on settlements - derivatives	0.8	0.0	0.3	2.3
Net investment losses	$ (17.4)	$ (15.5)	$ (21.3)	$ (31.0)