Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Available for Sale - Cost
Due in One Year or Less	$ 9,294.5
Due After One Year Through Five Years	20,249.7
Due After Five Years Through Ten Years	5,450.1
Due After Ten Years	877.5
Total	35,871.8
Held to Maturity - Amortized Cost
Due in One Year or Less	3,722.5
Due After One Year Through Five Years	4,863.2
Due After Five Years Through Ten Years	71.8
Due After Ten Years	58.5
Total	8,716.0	$ 5,248.3
Available for Sale - Value
Due in One Year or Less	9,313.6
Due After One Year Through Five Years	20,328.0
Due After Five Years Through Ten Years	5,456.2
Due After Ten Years	875.8
Total	35,973.6
Held to Maturity - Fair Value
Due in One Year or Less	3,727.8
Due After One Year Through Five Years	4,901.5
Due After Five Years Through Ten Years	69.7
Due After Ten Years	34.1
Total	$ 8,733.1	$ 5,227.5