v3.20.4
Loans - Summary of Changes in Allowance for Credit Losses (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Allowance for loan losses    
Balance, beginning of period $ 1,441 $ 1,066
Impact of CECL adoption 727  
Beginning balance, adjusted 2,168  
Net charge-offs (907) (490)
Provision 2,853 990
Other (240) (125)
Balance, end of period $ 3,874 $ 1,441
Allowance ratio 3.70% 1.60%
Net charge-off ratio 0.90% 0.60%
Allowance for losses on lending commitments    
Balance, beginning of period $ 361 $ 286
Impact of CECL adoption (48)  
Beginning balance, adjusted 313  
Provision 244 75
Balance, end of period 557 361
Wholesale [Member]    
Allowance for loan losses    
Balance, beginning of period 879 658
Impact of CECL adoption 452  
Beginning balance, adjusted 1,331  
Net charge-offs (615) (121)
Provision 2,108 469
Other (240) (127)
Balance, end of period $ 2,584 $ 879
Allowance ratio 2.70% 1.10%
Net charge-off ratio 0.60% 0.20%
Allowance for losses on lending commitments    
Balance, beginning of period $ 361 $ 286
Impact of CECL adoption (48)  
Beginning balance, adjusted 313  
Provision 244 75
Balance, end of period 557 361
Consumer [Member]    
Allowance for loan losses    
Balance, beginning of period 393 292
Impact of CECL adoption 444  
Beginning balance, adjusted 837  
Net charge-offs (292) (317)
Provision 745 418
Balance, end of period $ 1,290 $ 393
Allowance ratio 15.90% 6.00%
Net charge-off ratio 4.20% 6.20%
PCI [Member]    
Allowance for loan losses    
Balance, beginning of period $ 169 $ 116
Impact of CECL adoption $ (169)  
Net charge-offs   (52)
Provision   103
Other   2
Balance, end of period   $ 169
Allowance ratio   10.40%
Net charge-off ratio   3.20%