Fair Values (Details 2) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	$ 32,927	$ 25,208	$ 22,762	$ 22,288
Financial assets carried at other than fair value
Other loans, net	2,607	1,419
Financial liabilities carried at other than fair value
Certificates of deposit	16,994
Long-term debt	55,804	46,990
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	53,526	46,841
Card Member loans, net	71,693	64,042
Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	18,560	15,113
Carrying Value [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	33,000	25,000
Other financial assets	57,000	51,000
Financial assets carried at other than fair value
Other loans, net	74,000	65,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	76,000	67,000
Financial liabilities carried at other than fair value
Certificates of deposit	17,000	12,000
Long-term debt	56,000	47,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	33,000	25,000
Other financial assets	57,000	51,000
Financial assets carried at other than fair value
Other loans, net	75,000	66,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	76,000	67,000
Financial liabilities carried at other than fair value
Certificates of deposit	17,000	12,000
Long-term debt	57,000	48,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	18,600	15,200
Fair Values (Textuals) [Abstract]
Card Member loans, net	25,600	26,000
Level 1 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	32,000	22,000
Other financial assets	0	0
Financial assets carried at other than fair value
Other loans, net	0	0
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	0	0
Financial liabilities carried at other than fair value
Certificates of deposit	0	0
Long-term debt	0	0
Level 2 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	1,000	3,000
Other financial assets	57,000	51,000
Financial assets carried at other than fair value
Other loans, net	0	0
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	76,000	67,000
Financial liabilities carried at other than fair value
Certificates of deposit	17,000	12,000
Long-term debt	57,000	48,000
Level 3 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	0	0
Other financial assets	0	0
Financial assets carried at other than fair value
Other loans, net	75,000	66,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	0	0
Financial liabilities carried at other than fair value
Certificates of deposit	0	0
Long-term debt	$ 0	$ 0