Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012	Dec. 31, 2011
Servicing Asset at Fair Value, Amount	$ 1,199				$ 899
Amortization	(12)		(22)
Origination of Mortgage Servicing Rights (MSRs)	203		161
Due to changes in inputs or assumptions	250	[1]	(102)	[1]
Servicing Asset at Fair Value, Other Changes in Fair Value	(152)	[2]	(112)	[2]
Servicing Asset at Fair Value, Disposals	1		3
Ending Balance	1,244		939		956	1,017
Core Deposits [Member]
Amortization	(7)		(11)
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
Servicing Asset at Fair Value, Disposals	0		0
Ending Balance	10		27		17	38
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount	1,199		865		899	921
Amortization	0		0
Origination of Mortgage Servicing Rights (MSRs)	203		161
Due to changes in inputs or assumptions	250	[1]	(102)	[1]
Servicing Asset at Fair Value, Other Changes in Fair Value	(152)	[2]	(112)	[2]
Servicing Asset at Fair Value, Disposals	1		3
Other Intangible Assets [Member]
Amortization	(5)		(11)
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
Servicing Asset at Fair Value, Disposals	0		0
Ending Balance	$ 35		$ 47		$ 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.