Loans and Card Member Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Card Member Loans
Loans segment information
Financing receivables, gross	$ 77,026		$ 73,373
Less: Reserves for credit losses	3,489	$ 3,835	5,344	$ 5,688	$ 5,628	$ 4,027
Financing receivables, net	73,537		68,029
Other Loans
Loans segment information
Less: Reserves for credit losses	66		238
Financing receivables, net	2,349		2,614
Card Member Receivables
Loans segment information
Financing receivables, gross	48,758		43,701
Less: Reserves for credit losses	30	$ 73	267	$ 422	$ 519	$ 126
Financing receivables, net	48,728		43,434
PPP Loans | Other Loans
Loans segment information
Financing receivables, gross	100		600
Variable Interest Entity, Primary Beneficiary | Card Member Loans
Loans segment information
Financing receivables, gross	24,675		25,908
Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Loans segment information
Financing receivables, gross	5,101		4,296
GCSG | Card Member Loans
Loans segment information
Financing receivables, gross	61,625		60,084
GCSG | Card Member Receivables
Loans segment information
Financing receivables, gross	19,499		18,685
GCSG | Variable Interest Entity, Primary Beneficiary | Card Member Loans
Loans segment information
Financing receivables, gross	24,700		25,900
GCS | Card Member Loans
Loans segment information
Financing receivables, gross	15,401		13,289
GCS | Card Member Receivables
Loans segment information
Financing receivables, gross	29,259		25,016
GCS | Variable Interest Entity, Primary Beneficiary | Card Member Receivables
Loans segment information
Financing receivables, gross	$ 5,100		$ 4,300