Loans and Card Member Receivables (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Card Member Loans
Loans segment information
Financing receivables, gross	$ 70,100	$ 73,373
Less: Reserves for credit losses	4,467	5,344	$ 5,236	$ 4,027
Financing receivables, net	65,633	68,029
Other Loans
Loans segment information
Less: Reserves for credit losses	143	238
Financing receivables, net	2,133	2,614
Card Member Receivables
Loans segment information
Financing receivables, gross	42,002	43,701
Less: Reserves for credit losses	202	267	$ 459	$ 126
Financing receivables, net	41,800	43,434
PPP Loans | Other Loans
Loans segment information
Financing receivables, gross	500	600
Variable Interest Entity, Primary Beneficiary | Card Member Loans
Loans segment information
Financing receivables, gross	24,088	25,908
Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Loans segment information
Financing receivables, gross	4,221	4,296
GCSG | Card Member Loans
Loans segment information
Financing receivables, gross	56,265	60,084
GCSG | Card Member Receivables
Loans segment information
Financing receivables, gross	17,228	18,685
GCSG | Variable Interest Entity, Primary Beneficiary | Card Member Loans
Loans segment information
Financing receivables, gross	24,100	25,900
GCS | Card Member Loans
Loans segment information
Financing receivables, gross	13,835	13,289
GCS | Card Member Receivables
Loans segment information
Financing receivables, gross	24,774	25,016
GCS | Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Loans segment information
Financing receivables, gross	$ 4,200	$ 4,300