Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Available for Sale - Cost
Due in One Year or Less	$ 8,454.1
Due After One Year Through Five Years	17,915.3
Due After Five Years Through Ten Years	3,677.6
Due After Ten Years	960.6
Total	31,007.6
Held to Maturity - Amortized Cost
Due in One Year or Less	2,499.8
Due After One Year Through Five Years	3,278.4
Due After Five Years Through Ten Years	15.5
Due After Ten Years	52.8
Total	5,846.5	$ 4,170.8
Available for Sale - Value
Due in One Year or Less	8,478.9
Due After One Year Through Five Years	17,971.4
Due After Five Years Through Ten Years	3,678.8
Due After Ten Years	962.6
Total	31,091.7
Held to Maturity - Fair Value
Due in One Year or Less	2,501.3
Due After One Year Through Five Years	3,292.3
Due After Five Years Through Ten Years	12.2
Due After Ten Years	26.8
Total	$ 5,832.6	$ 4,176.1