Securities - Remaining Maturity of Securities Available for Sale (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Available for Sale - Amortized Cost
Due in One Year or Less	$ 6,249.5	$ 7,880.8
Due After One Year Through Five Years	20,017.2	21,094.8
Due After Five Years Through Ten Years	6,545.3	5,759.1
Due After Ten Years	1,052.8	897.2
Total	33,864.8	35,631.9
Available for Sale - Fair Value
Due in One Year or Less	6,227.0	7,876.6
Due After One Year Through Five Years	19,937.8	21,058.7
Due After Five Years Through Ten Years	6,535.1	5,753.6
Due After Ten Years	1,042.2	890.9
Total	$ 33,742.1	$ 35,579.8