Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012	Dec. 31, 2011
Servicing Asset at Fair Value, Amount	$ 1,025				$ 899
Amortization	(6)		(11)
Origination of Mortgage Servicing Rights (MSRs)	110		83
Due to changes in inputs or assumptions	90	[1]	124	[1]
Servicing Asset at Fair Value, Other Changes in Fair Value	(74)	[2]	(57)	[2]
Sale of MSRs			(1)
Ending Balance	1,076		1,155		956	1,017
Core Deposits [Member]
Amortization	(3)		(6)
Origination of Mortgage Servicing Rights (MSRs)	0		0
Due to changes in inputs or assumptions	0		0
Servicing Asset at Fair Value, Other Changes in Fair Value	0		0
Sale of MSRs			0
Ending Balance	14		32		17	38
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount	1,025		1,070		899	921
Amortization	0		0
Origination of Mortgage Servicing Rights (MSRs)	110		83
Due to changes in inputs or assumptions	90	[1]	124	[1]
Servicing Asset at Fair Value, Other Changes in Fair Value	(74)	[2]	(57)	[2]
Sale of MSRs			(1)
Other Intangible Assets [Member]
Amortization	(3)		(5)
Origination of Mortgage Servicing Rights (MSRs)	0		0
Due to changes in inputs or assumptions	0		0
Servicing Asset at Fair Value, Other Changes in Fair Value	0		0
Sale of MSRs			0
Ending Balance	$ 37		$ 53		$ 40	$ 58

[1] Primarily reflects changes in discount rates and prepayment speed assumptions, due to changes in interest rates.

[2] Represents changes due to the collection of expected cash flows, net of accretion, due to the passage of time.