Advances and Other Receivables, Net - Advances and Other Receivables Roll Forward (Details) - Reserves for Advances and Other Receivables - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance - beginning of period	$ 71	$ 277	$ 47	$ 284
Provision and other additions	37	38	67	60
Write-offs	(10)	(21)	(16)	(50)
Balance - end of period	$ 98	$ 294	$ 98	$ 294