Investments - Net Investment Losses by Transaction Type (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Write-offs	$ (0.6)	$ (6.6)	$ (2.8)	$ (7.7)
Intent-to-sell impairments	(6.2)	0.0	(7.6)	(2.1)
Total impairments	(6.8)	(6.6)	(10.4)	(9.8)
Sales and other, net	(3.9)	2.7	(3.9)	2.2
Change in fair value - equity securities	(4.4)	(1.1)	(34.1)	0.4
Change in fair value and gains (losses) realized on settlements - derivatives	2.3	(1.5)	4.6	(3.4)
Net investment losses	$ (12.8)	$ (6.5)	$ (43.8)	$ (10.6)