Fair Values (Details 2) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	$ 26,168	$ 25,208	$ 26,520	$ 22,762
Financial liabilities carried at other than fair value
Certificates of deposit	17,538
Long-term debt	48,762	46,990
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	51,002	46,841
Card Member loans, net	66,376	64,042
Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	15,026	15,113
Carrying Value [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	26,000	25,000
Other financial assets	56,000	51,000
Financial assets carried at other than fair value
Loans, net	69,000	65,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	69,000	67,000
Financial liabilities carried at other than fair value
Certificates of deposit	18,000	12,000
Long-term debt	49,000	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	26,000	25,000
Other financial assets	56,000	51,000
Financial assets carried at other than fair value
Loans, net	69,000	66,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	69,000	67,000
Financial liabilities carried at other than fair value
Certificates of deposit	18,000	12,000
Long-term debt	50,000	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	15,100	15,200
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	7,800	8,800
Card Member loans, net	24,100	26,000
Level 1 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	24,000	22,000
Other financial assets	0	0
Financial assets carried at other than fair value
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	2,000	3,000
Other financial assets	56,000	51,000
Financial assets carried at other than fair value
Loans, net	0	0
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	69,000	67,000
Financial liabilities carried at other than fair value
Certificates of deposit	18,000	12,000
Long-term debt	50,000	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
Loans, net	69,000	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