Loans - Credit Card Portfolio, Loan Modifications (Details) - Credit card $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) loan_payment	Sep. 30, 2020 USD ($)
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	$ 82	$ 220	$ 315	$ 648
Weighted-average interest rate of loans – before TDR	17.75%	17.65%	17.79%	18.21%
Weighted-average interest rate of loans – after TDR	5.15%	4.80%	5.19%	4.55%
Balance of loans that redefaulted within one year of modification	$ 13	$ 22	$ 45	$ 83
Number of years before payment default under a modified loan			1 year
Modified loans, payment default, number of payments past due | loan_payment			2