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Capitalized Servicing Assets - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Jan. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Residential Mortgage Loans [Member]            
Servicing Assets at Fair Value [Line Items]            
Mortgage loans serviced for others $ 26,300 $ 32,300   $ 26,300 $ 32,300 $ 22,200
Fair value of residential loan servicing assets $ 240 $ 297   $ 240 $ 297  
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets 9.40% 10.60%        
Residential Mortgage Loans [Member] | LIBOR [Member]            
Servicing Assets at Fair Value [Line Items]            
Discounted rate represented weighted-average option-adjusted basis spread point percentage       9.18% 9.28%  
Residential Mortgage Sub Servicing Loan [Member]            
Servicing Assets at Fair Value [Line Items]            
Mortgage loans serviced for others $ 68,100 $ 62,800   $ 68,100 $ 62,800 56,800
Residential Real Estate [Member]            
Servicing Assets at Fair Value [Line Items]            
Fair value of residential loan servicing assets     $ 13,300      
Purchase price of servicing rights     $ 144      
Commercial Mortgage Loans [Member]            
Servicing Assets at Fair Value [Line Items]            
Mortgage loans serviced for others 18,900 17,600   18,900 17,600 15,500
Fair value of residential loan servicing assets $ 160 $ 153   $ 160 153  
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets 18.00% 18.00%   18.00%    
Commercial Mortgage Sub Servicing Loan [Member]            
Servicing Assets at Fair Value [Line Items]            
Mortgage loans serviced for others $ 3,300 $ 3,400   $ 3,300 $ 3,400 $ 2,700