Loans and Card Member Receivables (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Card Member Loans
Loans segment information
Financing receivables, gross	$ 75,610		$ 73,373
Less: Reserves for credit losses	3,835	$ 4,467	5,344	$ 5,628	$ 5,236	$ 4,027
Financing receivables, net	71,775		68,029
Card Member Receivables
Loans segment information
Financing receivables, gross	47,585		43,701
Less: Reserves for credit losses	73	$ 202	267	$ 519	$ 459	$ 126
Financing receivables, net	47,512		43,434
Other Loans
Loans segment information
Less: Reserves for credit losses	72		238
Financing receivables, net	2,154		2,614
PPP Loans | Other Loans
Loans segment information
Financing receivables, gross	200		600
Variable Interest Entity, Primary Beneficiary | Card Member Loans
Loans segment information
Financing receivables, gross	25,149		25,908
Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Loans segment information
Financing receivables, gross	4,787		4,296
GCSG | Card Member Loans
Loans segment information
Financing receivables, gross	60,561		60,084
GCSG | Card Member Receivables
Loans segment information
Financing receivables, gross	19,932		18,685
GCSG | Variable Interest Entity, Primary Beneficiary | Card Member Loans
Loans segment information
Financing receivables, gross	25,100		25,900
GCS | Card Member Loans
Loans segment information
Financing receivables, gross	15,049		13,289
GCS | Card Member Receivables
Loans segment information
Financing receivables, gross	27,653		25,016
GCS | Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Loans segment information
Financing receivables, gross	$ 4,800		$ 4,300