Income from Investments - Net Impairment Losses Recognized in Earnings (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Investment Income [Line Items]
Impairment Losses	$ 0.5	$ (1.0)	$ (7.0)	$ (12.0)	$ (1.7)	$ (1.8)	$ (6.7)	$ (3.6)	$ (19.5)	$ (13.8)	$ (4.5)
Fixed Maturities:
Net Investment Income [Line Items]
Impairment Losses									(16.7)	(13.3)	(2.0)
Equity Securities
Net Investment Income [Line Items]
Impairment Losses									$ (2.8)	$ (0.5)	$ (2.5)