Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 1,084,850	$ 1,089,598	$ 1,018,397
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 180,079	$ 185,175
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	85.30%	86.80%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	14.50%	13.00%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, No FICO available	0.20%	0.20%
Credit card | California
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 27,424	$ 28,154
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	18,924	19,171
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,657	15,046
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	12,778	12,905
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,781	10,089
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7,410	7,643
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,545	5,792
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,420	5,493
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,231	5,517
Credit card | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,392	4,487
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 68,517	$ 70,878