Fair Value Measurements - Assets and Liabilities Recorded as Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)		$ (13)	$ (367)	$ (1,030)	$ (372)
Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[1]	0	0	0	0
Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[2]	4	(2)	11	(6)
Commercial Loans Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[3]	(16)		(25)
Commercial Loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[4]	6	1	(164)	0
Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[5]	0	(1)	1	(1)
Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[6]	0	(365)	(784)	(365)
Leases [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[7]	(7)	0	(69)	0
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		736		736			$ 456
Fair Value, Nonrecurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		0		0			0
Fair Value, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		414		414			32
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		322		322			424
Fair Value, Nonrecurring [Member] | Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	4		4			12
Fair Value, Nonrecurring [Member] | Residential Mortgage [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	0		0			0
Fair Value, Nonrecurring [Member] | Residential Mortgage [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	4		4			12
Fair Value, Nonrecurring [Member] | Residential Mortgage [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	0		0			0
Fair Value, Nonrecurring [Member] | Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	318		318			14
Fair Value, Nonrecurring [Member] | Consumer loans [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	0		0			0
Fair Value, Nonrecurring [Member] | Consumer loans [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	318		318			14
Fair Value, Nonrecurring [Member] | Consumer loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	0		0			0
Fair Value, Nonrecurring [Member] | Commercial Loans Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	91		91
Fair Value, Nonrecurring [Member] | Commercial Loans Held for Sale [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	0		0
Fair Value, Nonrecurring [Member] | Commercial Loans Held for Sale [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	91		91
Fair Value, Nonrecurring [Member] | Commercial Loans Held for Sale [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	0		0
Fair Value, Nonrecurring [Member] | Commercial Loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[4]	298		298			50
Fair Value, Nonrecurring [Member] | Commercial Loans [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[4]	0		0			0
Fair Value, Nonrecurring [Member] | Commercial Loans [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[4]	0		0			0
Fair Value, Nonrecurring [Member] | Commercial Loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[4]	298		298			50
Fair Value, Nonrecurring [Member] | Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[5]	1		1			6
Fair Value, Nonrecurring [Member] | Real Estate Owned [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[5]	0		0			0
Fair Value, Nonrecurring [Member] | Real Estate Owned [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[5]	1		1			6
Fair Value, Nonrecurring [Member] | Real Estate Owned [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[5]	0		0			0
Fair Value, Nonrecurring [Member] | Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	0		0			372
Fair Value, Nonrecurring [Member] | Goodwill [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	0		0			0
Fair Value, Nonrecurring [Member] | Goodwill [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	0		0			0
Fair Value, Nonrecurring [Member] | Goodwill [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	0		0			372
Fair Value, Nonrecurring [Member] | Leases [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[7]	24		24			2
Fair Value, Nonrecurring [Member] | Leases [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[7]	0		0			0
Fair Value, Nonrecurring [Member] | Leases [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[7]	0		0			0
Fair Value, Nonrecurring [Member] | Leases [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[7]	$ 24		$ 24			$ 2
RBWM [Member] | Fair Value, Nonrecurring [Member] | Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]		$ 372		$ 372	$ 0

[1] At September 30, 2020 and December 31, 2019, the fair value of the loans held for sale was below cost.

[2] Represents residential mortgage loans held for investment whose carrying amount was adjusted during the period based on the fair value of the underlying collateral. The increase at September 30, 2020 reflects the impact of adopting new accounting guidance which requires expected recoveries related to subsequent increases in the fair value of collateral for collateral-dependent loans to be recognized in the allowance for credit losses beginning January 1, 2020. See Note 21, "New Accounting Pronouncements," for additional discussion.⁽³⁾At September 30, 2020, the fair value of the loans held for sale was below cost.

[3] At September 30, 2020, the fair value of the loans held for sale was below cost.

[4] Certain commercial loans are individually assessed for impairment. We measure the credit impairment of a collateral-dependent loan based on the fair value of the collateral asset. The collateral often involves real estate properties that are illiquid due to market conditions. As a result, these loans are classified as a Level 3 fair value measurement within the fair value hierarchy.

[5] Real estate owned is required to be reported on the balance sheet net of transactions costs. The real estate owned amounts in the table above reflect the fair value unadjusted for transaction costs.

[6] During the first quarter of 2020, the goodwill allocated to our previously separate RBWM and PB businesses were both written down to $0 million. During the third quarter of 2019, the goodwill allocated to our previously separate RBWM business was written down to $372 million. See Note 8, "Goodwill and Other Long-Lived Assets," in this Form 10-Q for further discussion of the results of our goodwill impairment testing, including the events and circumstances leading to the impairments.

[7] Beginning in the fourth quarter of 2019 and into the first quarter of 2020, we determined that we would exit certain branches and, as a result, the lease ROU assets and leasehold improvement assets associated with these branches were written down based on their estimated remaining useful lives. During the third quarter of 2020, we also wrote down the lease ROU assets associated with certain office space that we determined we would exit. See Note 2, "Strategic Initiatives," in this Form 10-Q and Note 10, "Leases" in our 2019 Form 10-K for further discussion.