Remaining Maturity of Securities Available for Sale (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Available for Sale - Amortized Cost
Due in One Year or Less	$ 10,552.9
Due After One Year Through Five Years	18,176.5
Due After Five Years Through Ten Years	1,342.1
Due After Ten Years	704.3
Total	30,775.8
Held to Maturity - Amortized Cost
Due in One Year or Less	135.4
Due After One Year Through Five Years	252.6
Due After Five Years Through Ten Years	172.7
Due After Ten Years	149.0
Total	709.7	799.2
Available for Sale - Fair Value
Due in One Year or Less	10,554.8
Due After One Year Through Five Years	18,295.8
Due After Five Years Through Ten Years	1,343.6
Due After Ten Years	712.6
Total	30,906.8
Held to Maturity - Fair Value
Due in One Year or Less	136.1
Due After One Year Through Five Years	261.2
Due After Five Years Through Ten Years	180.8
Due After Ten Years	149.1
Fair Value	$ 727.2	$ 817.1