Fair Values (Details 2) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	$ 33,177	$ 27,445	$ 31,092	$ 32,927
Financial liabilities carried at other than fair value
Certificates of deposit	13,313
Long-term debt	58,418	58,423
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	56,227	55,320
Card Member loans, net	78,874	79,720
Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	19,538	19,509
Carrying Value [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	33,000	27,000
Other financial assets	60,000	58,000
Financial assets carried at other than fair value
Loans, Net	83,000	83,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	88,000	81,000
Financial liabilities carried at other than fair value
Certificates of deposit	13,000	13,000
Long-term debt	58,000	58,000
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	33,000	27,000
Other financial assets	60,000	58,000
Financial assets carried at other than fair value
Loans, Net	83,000	84,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	88,000	81,000
Financial liabilities carried at other than fair value
Certificates of deposit	13,000	13,000
Long-term debt	60,000	59,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Variable Interest Enterprise [Member]
Financial liabilities carried at other than fair value
Long-term debt	19,600	19,400
Fair Values (Textuals) [Abstract]
Accounts receivable, less reserves	7,700	8,500
Card Member loans, net	31,300	33,000
Level 1 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	32,000	26,000
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	60,000	58,000
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	88,000	81,000
Financial liabilities carried at other than fair value
Certificates of deposit	13,000	13,000
Long-term debt	60,000	59,000
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	83,000	84,000
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