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, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020		Dec. 31, 2020	Mar. 31, 2020
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)		$ (15)	$ (13)	$ (7)		$ (1,030)
Consumer loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[1]	(1)	0	(1)		0
Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[2]	2	4	8		11
Commercial loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[3]	0	(16)	(12)		(25)
Commercial Loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)		(12)	6	57	[4]	(164)	[4]
Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[5]		0			1
Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[6]		0			(784)
Leases [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[7]	(4)	$ (7)	(59)		$ (69)
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1,236		1,236				$ 658
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		207		207				385
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1,029		1,029				273
Fair Value, Nonrecurring [Member] | Consumer loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	804		804				4
Fair Value, Nonrecurring [Member] | Consumer loans held for sale [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] | Consumer loans held for sale [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	9		9				4
Fair Value, Nonrecurring [Member] | Consumer loans held for sale [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	795		795				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]	198		198				312
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]	198		198				312
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]	92		92				68
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				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]	0		0				68
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]	92		92				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]	142		142				270
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]	142		142				270
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
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
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
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
Fair Value, Nonrecurring [Member] | Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]							0
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
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
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
Fair Value, Nonrecurring [Member] | Leases [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[7]	0		0				3
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]	$ 0		$ 0				$ 3
Wealth and Personal Banking [Member] | Fair Value, Nonrecurring [Member] | Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]								$ 0

[1] At September 30, 2021 and December 31, 2020, the fair value of the loans held for sale was below cost. During the second quarter of 2021, certain consumer loans were transferred to held for sale for which significant inputs in estimating fair value were unobservable.

[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.

[3] At September 30, 2021 and December 31, 2020, the fair value of the loans held for sale was below cost. During the second quarter of 2021, certain commercial loans were transferred to held for sale for which significant inputs in estimating fair value were unobservable.

[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. See Note 9, "Goodwill," in this From 10-Q for further discussion of the results of our goodwill impairment testing, including the events and circumstances leading to the impairments.

[7] During the second quarter of 2021, we determined that we would exit certain branches and, as a result, the lease ROU assets, leasehold improvement assets and equipment assets associated with these branches were written off. During the three and nine months ended September 30, 2021, we also wrote down the lease ROU assets and leasehold improvement assets primarily associated with certain office space that we determined we would exit. During 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 for further discussion.