Risk Rating Under the Risk Rating System (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	$ 53,403	$ 47,719
Pass
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	52,812	46,825
Risk Level Special Mention [Member]
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	370	480
Risk Level, Substandard
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit	221	403
Risk Level, Doubtful
Credit Risk Associated With Commitments To Extend Credit [Line Items]
Commitments To Extend Credit		$ 11