Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Net revenues	$ 4,305	$ 3,857	$ 8,433	$ 7,542
Transaction revenues
Disaggregation of Revenue [Line Items]
Net revenues	3,878	3,318	7,609	6,515
Other value added services
Disaggregation of Revenue [Line Items]
Net revenues	427	539	824	1,027
Interest, fees and gains earned on loan and interest receivables, net and held for sale portfolio, hedging gains and interest earned on customer balances
Disaggregation of Revenue [Line Items]
Net revenues which do not represent revenues recognized in the scope of ASC Topic 606	276	441	533	800
United States (“U.S.”)
Disaggregation of Revenue [Line Items]
Net revenues	2,297	2,150	4,484	4,173
United Kingdom (“U.K.”)
Disaggregation of Revenue [Line Items]
Net revenues	454	402	887	794
Other Countries
Disaggregation of Revenue [Line Items]
Net revenues	$ 1,554	$ 1,305	$ 3,062	$ 2,575