Investments - OTTI losses Recognized in Accumulated Other Comprehensive Income (Details) (Fixed Maturities [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fixed Maturities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at Beginning of Year	$ 3.9	$ 2.4	$ 3.7
Additions for Previously Unrecognized OTTI Credit Losses	1.1	2.2	5.3
Increases to Previously Recognized OTTI Credit Losses	0	0	0.4
Reductions to Previously Recognized OTTI Credit Losses	(0.1)	(0.7)	(1.7)
Reduction due to Intent to Sell Investments	0	0	(5.1)
Reductions for Investments Sold During Period	(0.3)	0	(0.2)
Balance at End of Year	$ 4.6	$ 3.9	$ 2.4