Fair Values (Details 2) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheet	$ 31,092	$ 32,927	$ 29,366	$ 25,208
Financial liabilities carried at other than fair value
Certificates of deposit	16,805
Long-term debt	52,461	55,804
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	53,676	53,526
Card Member loans, net	71,034	71,693
Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	15,800	18,560
Carrying Value [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheet	31,000	33,000
Other financial assets	57,000	57,000
Financial assets carried at other than fair value
Loans, net	74,000	74,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	77,000	76,000
Financial liabilities carried at other than fair value
Certificates of deposit	17,000	17,000
Long-term debt	52,000	56,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheet	31,000	33,000
Other financial assets	57,000	57,000
Financial assets carried at other than fair value
Loans, net	75,000	75,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	77,000	76,000
Financial liabilities carried at other than fair value
Certificates of deposit	17,000	17,000
Long-term debt	53,000	57,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	15,700	18,600
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	7,800	8,900
Card Member loans, net	23,900	25,600
Level 1 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheet	30,000	32,000
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 per Consolidated Balance Sheet	1,000	1,000
Other financial assets	57,000	57,000
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	77,000	76,000
Financial liabilities carried at other than fair value
Certificates of deposit	17,000	17,000
Long-term debt	53,000	57,000
Level 3 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheet	0	0
Other financial assets	0	0
Financial assets carried at other than fair value
Loans, net	75,000	75,000
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