Investments - OTTI OCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 21.8	$ 28.0	$ 22.4	$ 28.0
Additional Credit Impairments [Abstract]
On securities not previously impaired	0.0	0.0	0.0	0.7
On securities previously impaired	0.0	0.1	0.8	0.2
Reductions [Abstract]
Increase in cash flows	0.0	0.0	(0.1)	0.0
Securities sold, matured, prepaid, or paid down	(0.4)	(0.7)	(1.7)	(1.5)
Balance, ending	$ 21.4	$ 27.4	$ 21.4	$ 27.4