Risk Rating Under the Risk Rating System (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	$ 53,832	$ 53,403
Pass
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	53,314	52,812
Risk Level, Special Mention
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	337	370
Risk Level, Substandard
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	178	221
Risk Level, Doubtful
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	$ 3