Fair Value Measurements - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (Nonrecurring [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	$ 22	$ 25	$ 81
Loans held for sale		9	15
Accrued income and other assets	16	22	42
Total assets at fair value	38	56	138
Level 1 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans
Loans held for sale
Accrued income and other assets
Total assets at fair value
Level 2 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans
Loans held for sale
Accrued income and other assets		2	17
Total assets at fair value		2	17
Level 3 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	22	25	81
Loans held for sale		9	15
Accrued income and other assets	16	20	25
Total assets at fair value	$ 38	$ 54	$ 121