Reserves for Losses (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Changes in the Card Member loans reserve for losses [Line Items]
Balance, January 1	$ 1,706	$ 1,223
Card Member loans provisions	1,027	741
Balance, June 30	1,840	1,320
Other	2	19
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 and Fees	(747)	(557)
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 and Fees	$ (148)	$ (106)