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Capitalized Servicing Assets - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Jan. 31, 2019
Dec. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Residential Mortgage Loans [Member]            
Servicing Assets at Fair Value [Line Items]            
Mortgage loans serviced for others $ 32,300   $ 22,200 $ 32,300 $ 22,200 $ 22,600
Fair value of residential loan servicing assets $ 297   $ 240 $ 297 $ 240  
Weighted average discount rates used to estimate fair value of capitalized mortgaged loan servicing assets 10.60%   11.40%      
Residential Mortgage Loans [Member] | LIBOR [Member]            
Servicing Assets at Fair Value [Line Items]            
Discounted rate represented weighted-average option-adjusted basis spread point percentage       9.28% 9.63%  
Residential Mortgage Sub Servicing Loan [Member]            
Servicing Assets at Fair Value [Line Items]            
Mortgage loans serviced for others $ 62,800   $ 56,800 $ 62,800 $ 56,800 56,600
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 17,600   15,500 17,600 15,500 13,600
Fair value of residential loan servicing assets $ 153   $ 135 $ 153 135  
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 $ 3,400   $ 2,700 $ 3,400 $ 2,700 $ 2,600