Loans Receivable - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans Receivable [Line Items]
Estimated fair Value of loans receivable	$ 86,410	$ 80,740
Carrying value of lending commitments liabilities	508	443
Lending commitments liabilities, allowance for losses	354	286	$ 274
Estimated fair value of lending commitments liabilities	3,170	3,780
PCI and consumer loans	7,470	7,580
Impaired loans receivable (excluding PCI loans) on non-accrual status	1,390	838
Corporate loans modified in a troubled debt restructuring	319	27
Lending commitments related to loans modified in a troubled debt restructuring	0	0
Amount of loans 30 days or more past due	225	208
Impaired loans and lending commitments	$ 705	$ 484
Gross loans receivable deemed impaired and subject to specific loan-level reserves	1.60%	1.00%
Allowance for loan losses as a percentage of total gross loans receivable	1.50%	1.30%
Annualized net charge-offs as a percentage of average total gross loans receivable	0.50%	0.50%
Amount Of Lending Commitments Held For Investment	$ 139,060	$ 120,997
Credit card [Member]
Loans Receivable [Line Items]
Amount Of Lending Commitments Held For Investment	9,596
Level 2 [Member]
Loans Receivable [Line Items]
Estimated fair Value of loans receivable	45,270	40,640
Estimated fair value of lending commitments liabilities	1,200	1,120
Level 3 [Member]
Loans Receivable [Line Items]
Estimated fair Value of loans receivable	41,140	40,100
Estimated fair value of lending commitments liabilities	$ 1,970	$ 2,660