Reserves for Losses (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Changes in the Card Member loans reserve for losses [Line Items]
Balance, January 1	$ 1,706	$ 1,223
Card Member loans provisions	1,587	1,272
Balance, June 30	1,937	1,502
Other	9	26
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	(1,140)	(856)
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	$ (225)	$ (163)