Fair Values (Details 2) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	$ 30,231	$ 32,927	$ 26,168	$ 25,208
Financial liabilities carried at other than fair value
Certificates of deposit	15,847
Long-term debt	55,300	55,804
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	54,972	53,526
Card Member loans, net	75,666	71,693
Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	18,637	18,560
Carrying Value [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	30,000	33,000
Other financial assets	59,000	57,000
Financial assets carried at other than fair value
Loans, Net	79,000	74,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	82,000	76,000
Financial liabilities carried at other than fair value
Certificates of deposit	16,000	17,000
Long-term debt	55,000	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 Sheets	30,000	33,000
Other financial assets	59,000	57,000
Financial assets carried at other than fair value
Loans, Net	80,000	75,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	82,000	76,000
Financial liabilities carried at other than fair value
Certificates of deposit	16,000	17,000
Long-term debt	56,000	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	18,500	18,600
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	7,700	8,900
Card Member loans, net	23,600	25,600
Level 1 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	29,000	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 Sheets	1,000	1,000
Other financial assets	59,000	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	82,000	76,000
Financial liabilities carried at other than fair value
Certificates of deposit	16,000	17,000
Long-term debt	56,000	57,000
Level 3 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	0	0
Other financial assets	0	0
Financial assets carried at other than fair value
Loans, Net	80,000	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