Fair Value Measurements - Assets and Liabilities Recorded as Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)		$ (1,048)	$ (411)
Residential Mortgage [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[1]	0	0
Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[2]	18	(7)
Commercial Loans Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[3]	(23)
Commercial Loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[4]	(169)	(25)
Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[5]	2	(1)
Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[6]	(784)	(365)
Leases [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[7]	(92)	(13)
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		658	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
Fair Value, Nonrecurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		385	32
Fair Value, Nonrecurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		273	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	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
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	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
Fair Value, Nonrecurring [Member] | Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	312	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
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]	312	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
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]	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
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]	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]	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]	270	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
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
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]	270	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	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
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	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
Fair Value, Nonrecurring [Member] | Goodwill [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[6]	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
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
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	372
Fair Value, Nonrecurring [Member] | Leases [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[7]	3	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
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
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]	$ 3	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	$ 0

[1] At December 31, 2020 and 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 December 31, 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 2, "Summary of Significant Accounting Policies and New Accounting Pronouncements," for additional discussion.(3)At December 31, 2020, the fair value of the loans held for sale was below cost.

[3] At December 31, 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 2019, the goodwill allocated to our previously separate RBWM business was written down to $372 million. See Note 10, "Goodwill and Other Long-Lived Assets," for further discussion of the results of our goodwill impairment testing, including the events and circumstances leading to the impairments.

[7] Beginning in 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 2020, we also wrote down the lease ROU assets associated with certain office space that we determined we would exit. See Note 3, "Strategic Initiatives," and Note 11, "Leases," for further discussion.