Regulatory Matters and Capital Adequacy (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Regulatory Matters And Capital Adequacy [Abstract]
Well-capitalized ratios	10.00%
Minimum capital ratios	8.00%
Leverage capital required, Well-capitalized ratios	5.00%
Leverage capital required, Minimum capital ratios	4.00%
Risk-based capital required, Well-capitalized ratios	8.00%
Risk-based capital required, Minimum capital ratios	6.00%
Common Equity Tier 1 required, Minimum capital ratio	4.50%
Common Equity Tier 1 required, Well-capitalized ratio	6.50%
SLR, Minimum capital ratio	3.00%
SLR, Basel III Standards 2018	3.00%
Basel III Standards 2018	9.90%
Leverage capital required, Basel III Standards 2018	4.00%
Risk-based capital required, Basel III Standards 2018	7.90%
Common Equity Tier 1 required, Basel III Standards 2018	6.40%
Parent Company [Member]
Regulatory capital ratios
Tier 1 capital	$ 18,208	$ 14,721
Total capital	$ 20,737	$ 17,142
Tier 1 capital ratio	11.80%	10.10%
Total capital ratio	13.40%	11.80%
Tier 1 leverage ratio	10.10%	8.60%
CET1 capital	$ 16,636	$ 13,189
CET1 capital ratio	10.80%	9.00%
SLR ratio	8.60%
American Express National Bank [Member]
Regulatory capital ratios
Tier 1 capital	$ 11,504
Total capital	$ 13,465
Tier 1 capital ratio	12.50%
Total capital ratio	14.60%
Tier 1 leverage ratio	10.00%
CET1 capital	$ 11,504
CET1 capital ratio	12.50%
SLR ratio	8.30%
American Express Centurion Bank [Member]
Regulatory capital ratios
Tier 1 capital		$ 5,954
Total capital		$ 6,547
Tier 1 capital ratio		12.70%
Total capital ratio		14.00%
Tier 1 leverage ratio		10.20%
CET1 capital		$ 5,954
CET1 capital ratio		12.70%
American Express Bank, FSB [Member]
Regulatory capital ratios
Tier 1 capital		$ 6,065
Total capital		$ 6,653
Tier 1 capital ratio		12.90%
Total capital ratio		14.20%
Tier 1 leverage ratio		11.70%
CET1 capital		$ 6,065
CET1 capital ratio		12.90%