Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 4,961	$ 4,378	$ 4,305	$ 4,128	$ 4,226	$ 3,683	$ 3,857	$ 3,685	$ 17,772	$ 15,451	$ 13,094
Transaction revenues
Disaggregation of Revenue [Line Items]
Total revenues									16,099	13,709	11,501
Other value added services
Disaggregation of Revenue [Line Items]
Total revenues									1,673	1,742	1,593
Interest, fees and gains earned on loan and interest receivables, net and held for sale portfolio, hedging gains or losses and interest earned on customer balances
Disaggregation of Revenue [Line Items]
Revenues which do not represent revenues recognized in the scope of ASC Topic 606									1,100	1,200	1,300
United States (“U.S.”)
Disaggregation of Revenue [Line Items]
Total revenues									9,417	8,324	7,084
United Kingdom (“U.K.”)
Disaggregation of Revenue [Line Items]
Total revenues									1,872	1,658	1,402
Other countries
Disaggregation of Revenue [Line Items]
Total revenues									$ 6,483	$ 5,469	$ 4,608