Investments - OTTI OCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 19.6	$ 19.8	$ 19.6	$ 20.0
Additional Credit Impairments [Abstract]
On securities not previously impaired	0	0.6	0.7	0.8
On securities previously impaired	0.1	0.6	0.2	1.0
Reductions [Abstract]
Securities sold, matured, prepaid, or paid down	0.7	0.8	1.5	1.6
Balance, ending	$ 19.0	$ 20.2	$ 19.0	$ 20.2