Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement		$ 285,301		$ 278,197
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(42)		(22)
Finite-Lived Intangible Assets, Net	[2]	69
Intangible Assets, Net (Excluding Goodwill)		1,791	[1]	1,657	[1]	$ 1,325
Amortization	[3]	(20)		(9)
Origination of Mortgage Servicing Rights (MSRs)		411		312
Servicing Assets at Fair Value, Purchased				200
Due to changes in inputs or assumptions	[4]	(22)		(13)
Servicing Asset at Fair Value, Other Changes in Fair Value	[5]	(226)		(232)
Servicing Asset at Fair Value, Disposals		(8)		(2)
Finite-Lived Intangible Assets, Purchase Accounting Adjustments	[6]	(1)
Indefinite-Lived Intangible Assets (Excluding Goodwill)		12		10
Intangible Assets, Gross (Excluding Goodwill)	[1]	1,833		1,679
Mortgage Servicing Rights, Fair Value [Member]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement		165,500		160,200
Servicing Asset at Fair Value, Amount		1,710		1,572		1,307
Amortization	[3]	0		0
Origination of Mortgage Servicing Rights (MSRs)		394		312
Servicing Assets at Fair Value, Purchased				200
Due to changes in inputs or assumptions	[4]	(22)		(13)
Servicing Asset at Fair Value, Other Changes in Fair Value	[5]	(226)		(232)
Servicing Asset at Fair Value, Disposals		(8)		(2)
Servicing Asset at Fair Value, Other Changes that Affect Balance		0
Other Intangible Assets [Member]
Finite-Lived Intangible Assets, Gross	[1]	32		35
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(28)		(22)
Finite-Lived Intangible Assets, Net	[1]	4		13
Intangible Assets, Net (Excluding Goodwill)		81		85		$ 18
Amortization	[3]	(20)		(9)
Servicing Assets at Fair Value, Purchased				0
Finite-lived Intangible Assets Acquired	[7]			14
Due to changes in inputs or assumptions	[4]	0		0
Servicing Asset at Fair Value, Other Changes in Fair Value	[5]	0		0
Servicing Asset at Fair Value, Disposals		0		0
Finite-Lived Intangible Assets, Purchase Accounting Adjustments	[6]	(1)
Commercial Mortgage Servicing Rights [Member]
Principal Amount Outstanding on Loans Managed and Securitized or Asset-backed Financing Arrangement		5,800		4,800
Finite-Lived Intangible Assets, Gross	[1]	79		62
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(14)		0
Finite-Lived Intangible Assets, Net	[1]	65		62
Servicing Asset at Fair Value, Amount		75		62
Origination of Mortgage Servicing Rights (MSRs)		17		0
Servicing Asset at Amortized Cost, Additions				62
Fair Value, Measurements, Recurring [Member]
Servicing Asset at Fair Value, Amount		$ 1,710		$ 1,572

[1] Excludes fully amortized other intangible assets.

[2] Does not include indefinite-lived intangible assets of $12 million.

[3] Does not include expense associated with non-qualified community development investments. See Note 10, "Certain Transfers of Financial Assets and Variable Interest Entities," for additional information.

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

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

[6] Represents the first quarter of 2017 measurement period adjustment on other intangible assets acquired previously in the Pillar acquisition.

[7] The majority of other intangible assets acquired from Pillar relate to indefinite-lived agency licenses.