Fair Value Measurements - Quantitative Information about Nonrecurring Fair Value Measurement of Assets and Liabilities Classified as Level 3 (Detail) - Fair Value, Nonrecurring [Member] $ in Millions		Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		$ 1,236	$ 658
Consumer loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	804	4
Commercial loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	92	68
Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	142	270
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure		1,029	273
Level 3 [Member] | Consumer loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[1]	795	0
Level 3 [Member] | Commercial loans held for sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[2]	92	0
Level 3 [Member] | Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	[3]	$ 142	$ 270
Measurement Input, Adjusted Market Price [Member] | Level 3 [Member] | Consumer loans held for sale [Member] | Minimum [Member] | Market comparables and internal assumptions [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input		0.95
Measurement Input, Adjusted Market Price [Member] | Level 3 [Member] | Consumer loans held for sale [Member] | Maximum [Member] | Market comparables and internal assumptions [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input		1
Measurement Input, Adjusted Market Price [Member] | Level 3 [Member] | Consumer loans held for sale [Member] | Weighted Average [Member] | Market comparables and internal assumptions [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input		0.99
Measurement Input, Adjusted Market Price [Member] | Level 3 [Member] | Commercial loans held for sale [Member] | Market comparables and internal assumptions [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input		0.94
Measurement Input, Loss Severity Rates [Member] | Level 3 [Member] | Impaired commercial loans [Member] | Minimum [Member] | Valuation of third party appraisal on underlying collateral [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input		0.08	0
Measurement Input, Loss Severity Rates [Member] | Level 3 [Member] | Impaired commercial loans [Member] | Maximum [Member] | Valuation of third party appraisal on underlying collateral [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input		0.78	0.76
Measurement Input, Loss Severity Rates [Member] | Level 3 [Member] | Impaired commercial loans [Member] | Weighted Average [Member] | Valuation of third party appraisal on underlying collateral [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Loans, Measurement Input	[4]	0.30	0.35

[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] 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.

[3] 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.

[4] Weighted average is calculated based on the carrying value of the loans.N/A Not Applicable