Investments - Schedule of Other Than Temporary Impairment (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Reductions due to Intent to Sell Investments	$ 0	$ (5.1)	$ 0	$ (2.6)
Fixed Maturities [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at Beginning of Period	2.1	5.4	2.4	3.7
Additions for Previously Unrecognized OTTI Credit Losses	0	0	0	3.1
Increases to Previously Recognized OTTI Credit Losses	0	0	0	2.6
Reductions to Previously Recognized OTTI Credit Losses	(0.2)	(0.1)	(0.5)	(1.6)
Balance at End of Period	$ 1.9	$ 2.7	$ 1.9	$ 2.7