(Cumulative Credit-Related Losses on Securities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative Credit-Related Losses on Securities Held - Beginning of Period	$ 5.2	$ 12.7	$ 5.2	$ 8.8
Plus: Losses on Newly Identified Impairments	0.0	0.0	0.0	1.8
Additional Losses on Previously Identified Impairments	0.0	0.0	0.0	2.1
Less: Current and Prior Period Losses on Securities Sold During the Period	0.0	(1.8)	0.0	(1.8)
Cumulative Credit-Related Losses on Securities Held - End of Period	$ 5.2	$ 10.9	$ 5.2	$ 10.9