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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Fair Value Disclosures [Abstract]      
Carrying value of unfunded commitments, deferred non-yield related loan fees and standby letters of credit $ 691   $ 774
Other guarantees carrying value 288   $ 362
Changes to fair value of these MLHFS $ (215) $ 93  
Minimum [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 0.00%    
Maximum [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 95.00%    
Weighted-average [Member]      
Fair Value Disclosures [Abstract]      
Assumed credit valuation adjustment as percentage of derivative contract fair value 1.00%