Remaining Maturity of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Available for Sale - Amortized Cost
Due in One Year or Less	$ 6,818.3
Due After One Year Through Five Years	17,678.8
Due After Five Years Through Ten Years	1,748.5
Due After Ten Years	713.4
Total	26,959.0
Held to Maturity - Amortized Cost
Due in One Year or Less	2,430.0
Due After One Year Through Five Years	429.3
Due After Five Years Through Ten Years	37.9
Due After Ten Years	34.5
Total	2,931.7	2,382.0
Available for Sale - Fair Value
Due in One Year or Less	6,839.7
Due After One Year Through Five Years	17,850.1
Due After Five Years Through Ten Years	1,762.7
Due After Ten Years	719.4
Total	27,171.9
Held to Maturity - Fair Value
Due in One Year or Less	2,431.9
Due After One Year Through Five Years	440.4
Due After Five Years Through Ten Years	41.9
Due After Ten Years	29.1
Fair Value	$ 2,943.3	$ 2,394.8