Investments - OTTI losses Recognized in Accumulated Other Comprehensive Income (Details) - Fixed Maturities: - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative Balance of Pre-tax Credit Losses Recognized in Retained Earnings at Beginning of Year	$ 1.1	$ 1.6	$ 1.4
Pre-tax Credit Losses on Fixed Maturities without Pre-tax Credit Losses Included in Cumulative Balance at Beginning of Year	0.2	0.0	1.2
Reductions for Change in Impairment Status:
From Status of Credit Loss to Status of Intent-to-sell or Required-to-sell	0.0	(0.5)	(0.7)
Reductions for Investments Sold During Year	(0.1)	0.0	(0.3)
Cumulative Balance of Pre-tax Credit Losses Recognized in Retained Earnings at End of Year	$ 1.2	$ 1.1	$ 1.6