Reserves for Losses (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Receivable Reserve Roll Forward [line Items]
Balance, January 1	$ 467	$ 462	$ 465
Provision For Doubtful Accounts	795	696	737
Other	(5)	(17)	(27)
Balance, December 31	521	467	462
Principal Write-Offs [Member]
Accounts Receivable Reserve Roll Forward [line Items]
Card Member receivables net write-offs	$ (736)	$ (674)	$ (713)