Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Servicing Asset at Fair Value, Amount	$ 1,206		$ 1,300
Amortization	(12)		(23)
Origination of Mortgage Servicing Rights (MSRs)	178		352		336
Servicing Assets at Fair Value, Purchased	130
Due to changes in inputs or assumptions	(234)	[1]	302	[1]
Servicing Asset at Fair Value, Other Changes in Fair Value	(167)	[2]	(252)	[2]
Servicing Asset at Fair Value, Disposals	(1)		(1)
Intangible Assets, Written off Related to Sale of Business Unit	(9)
Ending Balance	1,219		1,334		956
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount	1,206		1,300		899
Amortization	0		0
Origination of Mortgage Servicing Rights (MSRs)	178		352
Servicing Assets at Fair Value, Purchased	130
Due to changes in inputs or assumptions	(234)	[1]	302	[1]
Servicing Asset at Fair Value, Other Changes in Fair Value	(167)	[2]	(252)	[2]
Servicing Asset at Fair Value, Disposals	(1)		(1)
Intangible Assets, Written off Related to Sale of Business Unit	0
Other Intangible Assets [Member]
Amortization	(8)		(10)
Origination of Mortgage Servicing Rights (MSRs)			0
Servicing Assets at Fair Value, Purchased	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
Intangible Assets, Written off Related to Sale of Business Unit	(9)
Ending Balance	13		30		40
Core Deposits [Member]
Amortization	(4)		(13)
Origination of Mortgage Servicing Rights (MSRs)			0
Servicing Assets at Fair Value, Purchased	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
Intangible Assets, Written off Related to Sale of Business Unit	0
Ending Balance	$ 0		$ 4		$ 17

[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.