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Fair Values of Assets and Liabilities - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Standby Letters of Credit and Unfunded Commitments [Member]
Dec. 31, 2013
Standby Letters of Credit and Unfunded Commitments [Member]
Jun. 30, 2014
Other Guarantees [Member]
Dec. 31, 2013
Other Guarantees [Member]
Jun. 30, 2014
Minimum [Member]
Jun. 30, 2014
Maximum [Member]
Jun. 30, 2014
Average [Member]
Fair Value Disclosures [Abstract]                      
Fair value measurement transfers from one level to another     $ 0 $ 0              
Mortgage loans held for sale measured at fair value gain (loss) 46 (146) 98 (321)              
Assumed credit valuation adjustment as percentage of underlying fair value of underlying derivative contracts                 0.00% 99.00% 7.00%
Carrying value of guarantee obligations         $ 405 $ 382 $ 262 $ 278