Fair Value Measurements - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	$ 0	$ 0
Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	5	16
Loans held for sale	0	0
Accrued income and other assets	13	14
Total assets at fair value	18	30
Level 1 [Member] | Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	0	0
Level 2 [Member] | Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Loans held for sale	0	0
Level 3 [Member] | Nonrecurring [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans	5	16
Loans held for sale	0	0
Accrued income and other assets	13	14
Total assets at fair value	$ 18	$ 30