Remaining Maturity of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Available for Sale - Amortized Cost
Due in One Year or Less	$ 7,555.2
Due After One Year Through Five Years	17,189.8
Due After Five Years Through Ten Years	1,935.8
Due After Ten Years	756.8
Total	27,437.6
Held to Maturity - Amortized Cost
Due in One Year or Less	1,999.7
Due After One Year Through Five Years	691.5
Due After Five Years Through Ten Years	39.3
Due After Ten Years	35.6
Total	2,766.1	2,382.0
Available for Sale - Fair Value
Due in One Year or Less	7,565.7
Due After One Year Through Five Years	17,250.7
Due After Five Years Through Ten Years	1,908.2
Due After Ten Years	751.9
Total	27,476.5
Held to Maturity - Fair Value
Due in One Year or Less	2,001.5
Due After One Year Through Five Years	696.0
Due After Five Years Through Ten Years	42.0
Due After Ten Years	28.3
Fair Value	$ 2,767.8	$ 2,394.8