Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Available for Sale - Cost
Due in One Year or Less	$ 9,795.2
Due After One Year Through Five Years	17,443.3
Due After Five Years Through Ten Years	4,742.3
Due After Ten Years	1,279.1
Total	33,259.9
Held to Maturity - Amortized Cost
Due in One Year or Less	1,979.0
Due After One Year Through Five Years	3,823.7
Due After Five Years Through Ten Years	13.8
Due After Ten Years	53.1
Total	5,869.6	$ 5,248.3
Available for Sale - Value
Due in One Year or Less	9,807.1
Due After One Year Through Five Years	17,498.9
Due After Five Years Through Ten Years	4,745.1
Due After Ten Years	1,279.1
Total	33,330.2
Held to Maturity - Fair Value
Due in One Year or Less	1,982.8
Due After One Year Through Five Years	3,841.9
Due After Five Years Through Ten Years	11.1
Due After Ten Years	25.7
Total	$ 5,861.5	$ 5,227.5