Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Available for Sale - Cost
Due in One Year or Less	$ 9,817.1
Due After One Year Through Five Years	19,289.8
Due After Five Years Through Ten Years	4,406.7
Due After Ten Years	994.3
Total	34,507.9
Held to Maturity - Amortized Cost
Due in One Year or Less	2,476.2
Due After One Year Through Five Years	3,825.3
Due After Five Years Through Ten Years	13.8
Due After Ten Years	55.6
Total	6,370.9	$ 5,248.3
Available for Sale - Value
Due in One Year or Less	9,836.2
Due After One Year Through Five Years	19,386.0
Due After Five Years Through Ten Years	4,415.3
Due After Ten Years	994.6
Total	34,632.1
Held to Maturity - Fair Value
Due in One Year or Less	2,481.2
Due After One Year Through Five Years	3,851.0
Due After Five Years Through Ten Years	11.4
Due After Ten Years	32.6
Total	$ 6,376.2	$ 5,227.5