Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 1,265,941	$ 1,089,598	$ 1,068,073
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 196,935	$ 185,175
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	85.80%	86.80%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	14.00%	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	$ 30,227	$ 28,154
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	20,654	19,171
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,996	15,046
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,957	12,905
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10,721	10,089
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8,148	7,643
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,989	5,493
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,987	5,792
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,653	5,517
Credit card | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,828	4,487
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 74,775	$ 70,878