Loans - Credit Card Loan Portfolio, Other Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 1,285,370	$ 1,280,870	$ 1,265,941
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 219,542	$ 211,123
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Equal to or greater than 660	85.10%	85.80%
Percentage of portfolio based on carrying value with estimated refreshed FICO scores, Less than 660	14.70%	14.00%
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]
Total retained loans	$ 34,251	$ 32,652
Credit card | Texas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	23,119	22,086
Credit card | New York
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	17,751	16,915
Credit card | Florida
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	16,029	15,103
Credit card | Illinois
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	11,817	11,364
Credit card | New Jersey
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	9,152	8,688
Credit card | Colorado
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,673	6,307
Credit card | Ohio
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,533	6,424
Credit card | Pennsylvania
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	6,150	6,088
Credit card | Arizona
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	5,469	5,209
Credit card | All other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 82,598	$ 80,287