Investments - OTTI losses Recognized in Accumulated Other Comprehensive Income (Details) - Fixed Maturities [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at Beginning of Year	$ 5.1	$ 5.3	$ 9.9
Additions for Previously Unrecognized OTTI Credit Losses	2.7	0.2	2.4
Increases to Previously Recognized OTTI Credit Losses	0.0	0.0	0.6
Reduction due to Intent to Sell Investments	(6.3)	(0.4)	(2.4)
Reductions for Investments Sold During Period	(0.1)	0.0	(5.2)
Balance at End of Year	$ 1.4	$ 5.1	$ 5.3