Noninterest Income - Credit Card Fees (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Card interchange fees, net	$ 26	$ 15	$ 49	$ 37
Revenue from contracts with customers	306	285	633	506
Revenue not from contract with customer	455	84	872	164
Total credit card fees	31	21	59	50
Merchant service fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	5	8	10
Card service fees
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	$ 1	$ 1	$ 2	$ 3