Risk Rating Under the Risk Rating System (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	$ 51,205	$ 47,719	$ 45,099
Pass
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	50,549	46,825	44,090
Risk Level Special Mention [Member]
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	354	480	520
Risk Level, Substandard
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	302	403	451
Risk Level, Doubtful
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit		$ 11	$ 38