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Fair Value Measurements - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Measurement Input [Extensible List] us-gaap:MeasurementInputComparabilityAdjustmentMember   us-gaap:MeasurementInputComparabilityAdjustmentMember    
Minimum [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Discount rates for fair value estimations     15.00%    
Maximum [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Discount rates for fair value estimations     90.00%    
Significant Unobservable Inputs (Level 3) [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves $ 46 $ 50 $ 104 $ 50  
Significant Unobservable Inputs (Level 3) [Member] | Residential Mortgage Loans [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Capitalized servicing rights 152   152   $ 159
Capitalized servicing rights, valuation allowance     29   $ 30
Changes in fair value recognized for impairment of capitalized servicing rights   10   20  
Valuation Charge Recognized 8   $ (1)    
Weighted-average prepayment speeds     15.61%   16.01%
Discounted rate represented weighted-average option-adjusted basis spread point percentage     900.00%   900.00%
Fair Value, Measurements, Nonrecurring [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Loans measured at fair value on nonrecurring basis 629 248 $ 629 248 $ 652
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis 10 31 10 31  
Fair Value, Measurements, Nonrecurring [Member] | Significant Observable Inputs (Level 2) [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Loans measured at fair value on nonrecurring basis 386 145 386 145 339
Fair Value, Measurements, Nonrecurring [Member] | Significant Unobservable Inputs (Level 3) [Member]          
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]          
Loans measured at fair value on nonrecurring basis $ 243 $ 103 $ 243 $ 103 $ 313