Investments - OTTI OCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 19.0	$ 20.2	$ 19.6	$ 20.0
Additional Credit Impairments [Abstract]
On securities not previously impaired	0	0.3	0.7	1.1
On securities previously impaired	0.3	0.4	0.5	1.4
Reductions [Abstract]
Securities sold, matured, prepaid, or paid down	1.1	1.1	2.6	2.7
Balance, ending	$ 18.2	$ 19.8	$ 18.2	$ 19.8