Noninterest Income - Credit Card Fees (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Card interchange fees, net	$ 29	$ 18	$ 78	$ 55
Revenue from contracts with customers	315	247	948	757
Revenue not from contract with customer	357	300	1,229	461
Total credit card fees	34	23	93	72
Merchant service fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	4	12	14
Card service fees
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	$ 1	$ 1	$ 3	$ 3