Risk Rating Under the Risk Rating System (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	$ 56,151	$ 53,403
Pass
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	55,539	52,812
Risk Level, Special Mention
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	311	370
Risk Level, Substandard
Credit Risk Associated With Commitments To Extend Credit
Commitments To Extend Credit	$ 301	$ 221