Investments - Net Investment Gains (Losses) by Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ 0.0	$ (0.9)
Intent-to-sell impairments	0.0	(0.9)
Total impairments	0.0	(1.8)
Sales and other, net	(2.4)	1.1
Change in fair value - equity securities	(1.0)	(17.1)
Change in fair value and gains (losses) realized on settlements - derivatives	(0.5)	2.3
Net investment losses	$ (3.9)	$ (15.5)