Reserves for Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in the Card Member loans reserve for losses [Line Items]
Balance, January 1	$ 1,223	$ 1,028	$ 1,201
Card Member loans provisions	1,868	1,235	1,190
Reserves transferred to Held for Sale portfolio	0	0	(224)
Balance, December 31	1,706	1,223	1,028
Provisions for loans and lease losses deductions net write offs principal
Changes in the Card Member loans reserve for losses [Line Items]
Net Write-Offs Principal, Interest, Fees and Other	1,181	930	967
Provisions for loans and lease losses deductions net write offs interest and fees
Changes in the Card Member loans reserve for losses [Line Items]
Net Write-Offs Principal, Interest, Fees and Other	227	175	162
Provisions for loans and lease losses other
Changes in the Card Member loans reserve for losses [Line Items]
Net Write-Offs Principal, Interest, Fees and Other	$ 23	$ 65	$ (10)