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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Fair Value Disclosures [Abstract]          
Mortgage loans held for sale measured at fair value, net gain (loss) $ (18) $ 97 $ (135) $ 271  
Carrying value of unfunded commitments, deferred non-yield related loan fees and standby letters of credit 577   577   $ 774
Other guarantees carrying value $ 278   $ 278   $ 362
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     97.00%    
Weighted-average [Member]          
Fair Value Disclosures [Abstract]          
Assumed credit valuation adjustment as percentage of derivative contract fair value     2.00%