Remaining Maturity of Securities Available for Sale (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Available for Sale - Amortized Cost
Due in One Year or Less	$ 9,335.0	$ 7,467.4
Due After One Year Through Five Years	17,808.8	17,132.7
Due After Five Years Through Ten Years	4,036.5	3,394.2
Due After Ten Years	1,187.5	1,519.8
Available for Sale - Fair Value
Due in One Year or Less	9,332.6	7,487.9
Due After One Year Through Five Years	17,777.0	17,157.6
Due After Five Years Through Ten Years	4,023.1	3,418.0
Due After Ten Years	1,185.2	1,495.0
Available-for-sale Securities, Amortized Cost Basis	32,367.8	29,514.1
Total	$ 32,317.9	$ 29,558.5