Goodwill and Other Intangible Assets - Changes in the Carrying Amounts of Other Intangible Assets (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017	Dec. 31, 2017		Dec. 31, 2016
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	$ (32)			$ (42)
Intangible Assets, Net (Excluding Goodwill)		1,996	[1]	$ 1,729	1,791	[1]	$ 1,657
Amortization	[2]	(5)		(5)
Origination of Mortgage Servicing Rights (MSRs)		80		101
Servicing Assets at Fair Value, Purchased		74
Due to changes in inputs or assumptions	[3]	111		27
Servicing Asset at Fair Value, Other Changes in Fair Value	[4]	(55)		(50)
Intangible Assets, Written off Related to Sale of Business Unit	[5]			(1)
Indefinite-Lived Intangible Assets (Excluding Goodwill)		12			12
Intangible Assets, Gross (Excluding Goodwill)	[1]	2,028			1,833
Mortgage Servicing Rights, Fair Value [Member]
Servicing Asset at Fair Value, Amount		1,916		1,645	1,710		1,572
Amortization	[2]	0		0
Origination of Mortgage Servicing Rights (MSRs)		76		96
Servicing Assets at Fair Value, Purchased		74
Due to changes in inputs or assumptions	[3]	111		27
Servicing Asset at Fair Value, Other Changes in Fair Value	[4]	(55)		(50)
Intangible Assets, Written off Related to Sale of Business Unit				0
Other Intangible Assets [Member]
Finite-Lived Intangible Assets, Gross	[1]	17			32
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(13)			(28)
Finite-Lived Intangible Assets, Net	[1]	4			4
Intangible Assets, Net (Excluding Goodwill)		80		84	81		$ 85
Amortization	[2]	(5)		(5)
Origination of Mortgage Servicing Rights (MSRs)		4		5
Servicing Assets at Fair Value, Purchased		0
Due to changes in inputs or assumptions	[3]	0		0
Servicing Asset at Fair Value, Other Changes in Fair Value	[4]	0		0
Intangible Assets, Written off Related to Sale of Business Unit	[5]			$ (1)
Commercial Mortgage Servicing Rights [Member]
Finite-Lived Intangible Assets, Gross	[1]	83			79
Finite-Lived Intangible Assets, Accumulated Amortization	[1]	(19)			(14)
Finite-Lived Intangible Assets, Net	[1]	64			65
Fair Value, Measurements, Recurring [Member]
Servicing Asset at Fair Value, Amount		$ 1,916			$ 1,710

[1] Excludes fully amortized other intangible assets.

[2] 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.

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

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

[5] Represents measurement period adjustment on other intangible assets acquired previously in the Pillar acquisition.