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Fair Values of Assets and Liabilities - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Fair Value Disclosures [Abstract]          
Mortgage loans held for sale measured at fair value, net gain (loss) $ 25 $ (6) $ 43 $ (57)  
Carrying value of unfunded commitments, deferred non-yield related loan fees and standby letters of credit 502   502   $ 532
Other guarantees carrying value $ 236   $ 236   $ 263
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     155.00%    
Weighted Average [Member]          
Fair Value Disclosures [Abstract]          
Assumed credit valuation adjustment as percentage of derivative contract fair value     1.00%