Loans and Accounts Receivable (Details 6) pure in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) M bp	Sep. 30, 2017 USD ($) M bp	Sep. 30, 2018 USD ($) M bp	Sep. 30, 2017 USD ($) M bp
Financing Receivable, Modifications [Line Items]
Number of Accounts (in thousands)	14	9	40	27
Aggregated Outstanding Balance	$ 122	$ 75	$ 345	$ 224
Card Member Loans [Member]
Financing Receivable, Modifications [Line Items]
Number of Accounts (in thousands)	13	8	36	23
Aggregated Outstanding Balance	$ 98	$ 57	$ 267	$ 160
Average Interest Rate Reduction By Class Of Financial Instrument | bp	12	9	12	10
Card Member Receivables [Member]
Financing Receivable, Modifications [Line Items]
Number of Accounts (in thousands)	1	1	4	4
Aggregated Outstanding Balance	$ 24	$ 18	$ 78	$ 64
Average payment term extension | M	27	31	28	27