Reserves for Losses (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Card Members Receivable Reserve [Roll Forward]
Balance, January 1	$ 167	$ 145
Provisions	160	186
Other credits	13	51
Net write-offs	(166)	(173)
Other debits	(6)	(26)
Balance, September 30	$ 168	$ 183