Income from Investments - Net Impairment Losses Recognized in Earnings (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings	$ (1.7)	$ (1.8)	$ (6.7)	$ (3.6)	$ (2.2)	$ (1.8)	$ 0.0	$ (0.5)	$ (13.8)	$ (4.5)	$ (14.3)
Fixed Maturities:
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings									(13.3)	(2.0)	(12.1)
Equity Securities
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings									$ (0.5)	$ (2.5)	$ (2.2)