Fair Value Measurement and Fair Value of Financial Instruments - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Loans:
Loans Held for Sale
Impaired loans	620		620		572
Impaired loans	(34)	(28)	(70)	(79)
Other assets:
OREO	(3)	(8)	(20)	(27)
Private equity investments			(2)
Total	(37)	(36)	(92)	(106)
Fair Value Measurements, Nonrecurring [Member]
Loans:
Loans Held for Sale		2		2
Impaired loans	111	199	111	199
Other assets:
OREO			47	123
Total			158	324
Fair Value Measurements, Nonrecurring [Member] | Level 3 [Member]
Loans:
Loans Held for Sale		2		2
Impaired loans	111	199	111	199
Other assets:
OREO			47	123
Total			$ 158	$ 324