Fair Value Measurements - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (Nonrecurring [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	$ 18	$ 25	$ 101
Loans held for sale	12	9	25
Accrued income and other assets	16	22	46
Total assets at fair value	46	56	172
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	2	30
Total assets at fair value	2	2	30
Level 3 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	18	25	101
Loans held for sale	12	9	25
Accrued income and other assets	14	20	16
Total assets at fair value	$ 44	$ 54	$ 142