Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Servicing Asset at Fair Value, Amount		$ 1,119
Intangible Assets, Net (Excluding Goodwill)		1,131	$ 1,282	$ 1,325	$ 1,219
Amortization	[1]	(6)	(6)
Origination of Mortgage Servicing Rights (MSRs)		198	198
Servicing Assets at Fair Value, Purchased		104	109
Due to changes in inputs or assumptions	[2]	(328)	(74)
Servicing Asset at Fair Value, Other Changes in Fair Value	[3]	(160)	(161)
Servicing Asset at Fair Value, Disposals		(2)	(3)
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount		1,119	1,262	1,307	1,206
Amortization	[1]	0	0
Origination of Mortgage Servicing Rights (MSRs)		198	185
Servicing Assets at Fair Value, Purchased		104	109
Due to changes in inputs or assumptions	[2]	(328)	(74)
Servicing Asset at Fair Value, Other Changes in Fair Value	[3]	(160)	(161)
Servicing Asset at Fair Value, Disposals		(2)	(3)
Other Intangible Assets [Member]
Intangible Assets, Net (Excluding Goodwill)		12	20	$ 18	$ 13
Amortization	[1]	(6)	(6)
Origination of Mortgage Servicing Rights (MSRs)		0	13
Servicing Assets at Fair Value, Purchased		0	0
Due to changes in inputs or assumptions	[2]	0	0
Servicing Asset at Fair Value, Other Changes in Fair Value	[3]	0	0
Servicing Asset at Fair Value, Disposals		$ 0	$ 0

[1] Does not include expense associated with non-qualified community development investments. See Note 8, "Certain Transfers of Financial Assets and Variable Interest Entities," for additional information.

[2] Primarily reflects changes in option adjusted spreads and prepayment speed assumptions, due to changes in interest rates.

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