Risk Rating Under the Risk Rating System (Detail) (Commitments to Extend Credit, USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Commitments	$ 63,379	$ 62,050
Pass
Line of Credit Facility [Line Items]
Commitments	62,333	61,364
Risk Level, Special Mention
Line of Credit Facility [Line Items]
Commitments	603	369
Risk Level, Substandard
Line of Credit Facility [Line Items]
Commitments	441	316
Risk Level, Doubtful
Line of Credit Facility [Line Items]
Commitments	$ 2	$ 1