Loans - Credit Card Portfolio, Loan Modifications (Details) - Credit card $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) loan_payment	Jun. 30, 2019 USD ($)
Financing Receivable, Impaired [Line Items]
Fixed payment plan period			60 months
New enrollments, percent of total retained credit card loans (less than)			1.00%
Balance of new TDRs	$ 151	$ 226	$ 428	$ 475
Weighted-average interest rate of loans – before TDR	17.93%	19.38%	18.50%	19.25%
Weighted-average interest rate of loans – after TDR	5.16%	4.71%	4.42%	4.88%
Balance of loans that redefaulted within one year of modification	$ 25	$ 32	$ 61	$ 66
Number of years before payment default under a modified loan			1 year
Modified loans, payment default, number of payments past due | loan_payment			2