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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Dec. 31, 2019
Fair Value Disclosures [Abstract]          
Carrying value of unfunded commitments, deferred non-yield related loan fees and standby letters of credit $ 585   $ 585   $ 528
Other guarantees carrying value 333   333   $ 200
Changes to fair value of these MLHFS $ 81 $ 25 $ 174 $ 43  
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     90.00%    
Weighted Average [Member]          
Fair Value Disclosures [Abstract]          
Assumed credit valuation adjustment as percentage of derivative contract fair value     2.00%