Investments - OTTI OCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 19.6	$ 20.0
Additional Credit Impairments [Abstract]
On securities not previously impaired	0.7	0.2
On securities previously impaired	0.1	0.4
Reductions [Abstract]
Securities sold, matured, prepaid, or paid down	0.8	0.8
Balance, ending	$ 19.6	$ 19.8