Loans and Card Member Receivables - Summary (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 134,548		$ 125,995
Less: Reserves for credit losses	5,588	$ 5,321	5,118	$ 4,721	$ 4,390	$ 3,747
Financing receivables, net	128,960		120,877
Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	102,236		98,111
Card Member Loans | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	32,275		27,833
Card Member Loans | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	37		51
Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Less: Reserves for credit losses	154		126
Financing receivables, net	8,306		6,960
Card Member Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	59,042		60,411
Less: Reserves for credit losses	156	$ 171	174	$ 174	$ 210	$ 229
Financing receivables, net	58,886		60,237
Card Member Receivables | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	23,426		25,578
Card Member Receivables | Small Business
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	18,925		19,286
Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	16,691		15,547
Variable Interest Entity, Primary Beneficiary | Card Member Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	26,935		28,590
Variable Interest Entity, Primary Beneficiary | Card Member Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	26,900		28,600
Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	4,530		4,587
Variable Interest Entity, Primary Beneficiary | Card Member Receivables | Corporate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivables, gross	$ 4,500		$ 4,600