Remaining Maturity of Securities Held to Maturity (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Held to Maturity - Amortized Cost
Due in One Year or Less	$ 3,631.6	$ 1,908.8
Due After One Year Through Five Years	5,072.7	3,271.1
Due After Five Years Through Ten Years	158.7	14.9
Due After Ten Years	58.1	53.5
Amortized Cost	8,921.1	5,248.3
Held to Maturity - Fair Value
Due in One Year or Less	3,635.9	1,913.2
Due After One Year Through Five Years	5,081.6	3,278.3
Due After Five Years Through Ten Years	156.1	11.7
Due After Ten Years	31.5	24.3
Total	$ 8,905.1	$ 5,227.5