Investments - OTTI OCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other than Temporary Impairment, Recognized in Accumulated Other Comprehensive Income [Roll Forward]
Balance, beginning	$ 20.2	$ 20.0	$ 20.0	$ 19.5
Additional Credit Impairments [Abstract]
On securities not previously impaired	0.3	0	1.1	0.1
On securities previously impaired	0.4	3.1	1.4	4.8
Reductions [Abstract]
Securities intent impairments	0	0	0	0
Securities sold, matured, prepaid, or paid down	(1.1)	(2.5)	(2.7)	(3.8)
Balance, ending	$ 19.8	$ 20.6	$ 19.8	$ 20.6