Investments - Net Investment (Losses) Gains By Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Credit loss impairments	$ (1.3)	$ 0.0	$ (2.2)	$ (1.1)
Intent-to-sell impairments	(0.5)	0.0	(1.4)	(2.1)
Total impairments on investments recognized in net income	(1.8)	0.0	(3.6)	(3.2)
Sales and other, net	(1.1)	1.6	0.0	(0.5)
Change in fair value - equity securities	(12.6)	4.3	(29.7)	1.5
Change in fair value and gains (losses) realized on settlements - derivatives	0.0	(1.0)	2.3	(1.9)
Net investment gains (losses)	$ (15.5)	$ 4.9	$ (31.0)	$ (4.1)