Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Available for Sale - Cost
Due in One Year or Less	$ 6,665.1
Due After One Year Through Five Years	21,136.2
Due After Five Years Through Ten Years	6,015.5
Due After Ten Years	1,201.9
Total	35,018.7
Held to Maturity - Amortized Cost
Due in One Year or Less	2,914.6
Due After One Year Through Five Years	5,764.1
Due After Five Years Through Ten Years	201.2
Due After Ten Years	58.5
Total	8,938.4	$ 8,921.1
Available for Sale - Value
Due in One Year or Less	6,660.1
Due After One Year Through Five Years	21,124.3
Due After Five Years Through Ten Years	6,017.7
Due After Ten Years	1,195.5
Total	34,997.6
Held to Maturity - Fair Value
Due in One Year or Less	2,916.9
Due After One Year Through Five Years	5,783.4
Due After Five Years Through Ten Years	200.2
Due After Ten Years	32.9
Total	$ 8,933.4	$ 8,905.1