Investments - OTTI OCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 19.1	$ 21.8	$ 19.3	$ 22.4
Additional Credit Impairments [Abstract]
On securities previously impaired	0.2	0.0	0.5	0.8
Reductions [Abstract]
Increase in cash flows	0.0	0.0	0.1	0.1
Securities sold, matured, prepaid, or paid down	0.6	0.4	1.0	1.7
Balance, ending	$ 18.7	$ 21.4	$ 18.7	$ 21.4