Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Discount revenue	$ 19,186	$ 18,680	$ 19,297
Other	1,732	2,029	2,033
Expenses
Marketing and promotion	3,217	3,650	3,109
Card Member rewards	7,608	6,793	$ 6,996
Revenue Recognition Standard [Member]
Revenues
Discount revenue	3,707	3,699
Other	(278)	(253)
Expenses
Marketing and promotion	2,350	2,420
Card Member rewards	$ 1,079	$ 1,026