Remaining Maturity of Securities Available for Sale and Held to Maturity (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Available for Sale - Cost
Due in One Year or Less	$ 7,702.6
Due After One Year Through Five Years	18,210.8
Due After Five Years Through Ten Years	3,650.7
Due After Ten Years	1,250.5
Total	30,814.6
Held to Maturity - Amortized Cost
Due in One Year or Less	3,219.3
Due After One Year Through Five Years	2,374.5
Due After Five Years Through Ten Years	21.4
Due After Ten Years	40.6
Amortized Cost	5,655.8	4,170.8
Available for Sale - Value
Due in One Year or Less	7,731.3
Due After One Year Through Five Years	18,295.1
Due After Five Years Through Ten Years	3,659.6
Due After Ten Years	1,259.7
Total	30,945.7
Held to Maturity - Fair Value
Due in One Year or Less	3,220.7
Due After One Year Through Five Years	2,397.5
Due After Five Years Through Ten Years	19.4
Due After Ten Years	27.4
Total	$ 5,665.0	$ 4,176.1