Regulatory Matters and Capital Adequacy (Details) $ in Millions	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Regulatory Matters And Capital Adequacy
Common Equity Tier 1 required, Minimum capital ratio	0.045
Risk-based capital required, Minimum capital ratios	0.060
Minimum capital ratios	0.080
Leverage capital required, Minimum capital ratios	0.040
Parent Company [Member] | American Express Company [Member]
Regulatory capital ratios
CET1 capital	$ 18,693	$ 18,056
Tier 1 capital	20,277	19,628
Total capital	$ 22,385	$ 22,213
CET1 capital ratio	0.135	0.107
Tier 1 capital ratio	0.147	0.116
Total capital ratio	0.162	0.132
Tier 1 leverage ratio	0.110	0.102
Regulatory Matters And Capital Adequacy
Common Equity Tier 1 Required, Basel III Standards 2020	0.070
Risk-based capital required, Well-capitalized ratios	0.060
Tier 1 capital ratio, effective minimum	0.085
Well-capitalized ratios	0.100
Basel III Standards 2020	0.105
Leverage Capital Required, Basel III Standards 2020	0.040
Subsidiaries [Member] | American Express National Bank [Member]
Regulatory capital ratios
CET1 capital	$ 14,617	$ 13,600
Tier 1 capital	14,617	13,600
Total capital	$ 16,578	$ 15,688
CET1 capital ratio	0.162	0.134
Tier 1 capital ratio	0.162	0.134
Total capital ratio	0.183	0.154
Tier 1 leverage ratio	0.109	0.111
Regulatory Matters And Capital Adequacy
Common Equity Tier 1 required, Well-capitalized ratios	0.065
Common Equity Tier 1 Required, Basel III Standards 2020	0.070
Risk-based capital required, Well-capitalized ratios	0.080
Tier 1 capital ratio, effective minimum	0.085
Well-capitalized ratios	0.100
Basel III Standards 2020	0.105
Leverage capital required, Well-capitalized ratios	0.050
Leverage Capital Required, Basel III Standards 2020	0.040