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	$ 92.6	$ 109.9	$ 102.8	$ 114.7
Additional credit impairments:
On securities not previously impaired	0.3	0.2	1.4	2.4
On securities previously impaired	1.7	0.9	3.2	6.9
Reductions:
Securities sold, matured, prepaid, or paid down	3.6	6.4	16.4	19.4
Balance, ending	$ 91.0	$ 104.6	$ 91.0	$ 104.6