Fair Value 1 (Details) - 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	$ 200	$ 196	$ 1,341	$ 1,211
Financial assets carried at other than fair value [Abstract]
Card Member loans, less reserves	585	556
Loans to affiliates and other	13,579	14,527
Financial liabilities carried at other than fair value [Abstract]
Total Long-term Debt	21,384	24,153
Long Term Debt with Affiliates	268	270
Carrying Value [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	200	200
Other financial assets	26,000	20,600
Financial assets carried at other than fair value [Abstract]
Card Member loans, less reserves	600	600
Loans to affiliates and other	13,600	14,500
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	15,700	8,600
Financial liabilities carried at other than fair value [Abstract]
Total Long-term Debt	21,400	24,200
Long Term Debt with Affiliates	300	300
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	200	200
Other financial assets	26,000	20,600
Financial assets carried at other than fair value [Abstract]
Card Member loans, less reserves	600	600
Loans to affiliates and other	13,500	14,400
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	15,700	8,600
Financial liabilities carried at other than fair value [Abstract]
Total Long-term Debt	21,500	24,500
Long Term Debt with Affiliates	300	300
Level 1 [Member]
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents per Consolidated Balance Sheets	200	200
Other financial assets	100	100
Financial assets carried at other than fair value [Abstract]
Card Member loans, less reserves	0	0
Loans to affiliates and other	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 [Abstract]
Total Long-term Debt	0	0
Long Term Debt with Affiliates	0	0
Level 2 [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	25,900	20,500
Financial assets carried at other than fair value [Abstract]
Card Member loans, less reserves	0	0
Loans to affiliates and other	8,400	10,000
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	15,700	8,600
Financial liabilities carried at other than fair value [Abstract]
Total Long-term Debt	21,500	24,500
Long Term Debt with Affiliates	300	300
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 [Abstract]
Card Member loans, less reserves	600	600
Loans to affiliates and other	5,100	4,400
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	0	0
Financial liabilities carried at other than fair value [Abstract]
Total Long-term Debt	0	0
Long Term Debt with Affiliates	$ 0	$ 0