Consolidated Variable Interest Entities - Schedule of Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Capital lease obligations		$ 191	$ 191
Cash and cash equivalents		570	1,062
Accounts receivable, net		998	755
Property and equipment, net		353	341
Deferred income tax assets		113	82
Other non-current assets		434	408
Accounts payable, accrued expenses and other		2,150	1,821
Long-term debt		6,556	6,583
Consolidated VIEs [Member]
Variable Interest Entity [Line Items]
Cash and cash equivalents		73	57
Accounts receivable, net		16	14
Property and equipment, net		57	52
Deferred income tax assets		56	58
Other non-current assets		57	53
Accounts payable, accrued expenses and other		43	33
Long-term debt	[1]	$ 212	$ 212

[1] Includes capital lease obligations of $191 million as of December 31, 2017 and 2016.