Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 1,018,397	$ 1,010,206	$ 948,642
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 152,283	$ 154,296
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	87.90%	88.50%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	11.90%	11.30%
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	$ 22,865	$ 23,030
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,808	15,879
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	12,539	12,652
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10,388	10,412
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,428	8,530
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	6,273	6,367
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,807	4,923
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,562	4,573
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,548	4,708
Credit card | Michigan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,682	3,773
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 58,383	$ 59,449