Financial Statement Schedule (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowances for Doubtful Accounts and Authorized Credits
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	$ 81	$ 84	$ 86
Charged/Credited to Net Income	91	68	66
Charged to Other Account	0	0	0
Charges Utilized/Write-offs	(70)	(71)	(68)
Balance at End of Period	102	81	84
Allowance for Transaction Losses
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	23	34	27
Charged/Credited to Net Income	181	162	205
Charged to Other Account	0	0	0
Charges Utilized/Write-offs	(179)	(173)	(198)
Balance at End of Period	25	23	34
Tax Valuation Allowance
Movement in Valuation Allowances and Reserves
Balance at Beginning of Period	37	41	25
Charged/Credited to Net Income	(20)	(6)	19
Charged to Other Account	2	2	(3)
Charges Utilized/Write-offs	0	0	0
Balance at End of Period	$ 19	$ 37	$ 41