Investments - Net Investment Gains (Losses) By Transaction Type (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ (8.1)	$ 0.0	$ (1.1)
Intent-to-sell impairments	(2.3)	(5.3)	(0.3)
Total impairments on investments recognized in net income	(10.4)	(5.3)	(1.4)
Sales and other, net	4.3	15.0	151.5
Change in fair value - equity securities	(2.3)	(0.2)	7.3
Change in fair value and losses realized on settlements - derivatives	(2.6)	(11.8)	(4.1)
Net investment (losses) gains	$ (11.0)	$ (2.3)	$ 153.3