Fair Value Measurements - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (Nonrecurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	$ 25	$ 149
Loans held for sale	9	15
Accrued income and other assets	22	44
Total assets at fair value	56	208
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans
Loans held for sale
Accrued income and other assets
Total assets at fair value
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued income and other assets	2	19
Total assets at fair value	2	19
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	25	149
Loans held for sale	9	15
Accrued income and other assets	20	25
Total assets at fair value	$ 54	$ 189