Risk Rating Under the Risk Rating System (Detail) (Commitments to Extend Credit, USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Commitments	$ 63,827	$ 62,050
Pass
Line of Credit Facility [Line Items]
Commitments	62,787	61,364
Special Mention
Line of Credit Facility [Line Items]
Commitments	660	369
Risk Level, Substandard
Line of Credit Facility [Line Items]
Commitments	380	316
Risk Level, Doubtful
Line of Credit Facility [Line Items]
Commitments		$ 1