Risk Rating Under the Risk Rating System (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	$ 49,111	$ 47,719	$ 44,220
Pass
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	48,401	46,825	43,179
Risk Level Special Mention [Member]
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	326	480	453
Risk Level, Substandard
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	361	403	572
Risk Level, Doubtful
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	$ 23	$ 11	$ 16