BUSINESS SEGMENTS - Segment Profits (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits	$ 422	$ 596	$ 818	$ 530	$ 424	$ 790	$ 744	$ 546	$ 2,366	$ 2,504	$ 1,424
Interest expense, net of interest income									(318)	(250)	(199)
Income taxes		(91)	(207)	(112)					(438)	(1,523)	(431)
Net income	$ 317	$ 503	$ 667	$ 420	$ 114	$ 485	$ 489	$ 371	1,907	1,459	808
Total segment | International Operations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									1,155	837	446
Total segment | Asia Pacific
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									456
Total segment | Europe
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									266
Total segment | Caribbean and Latin America
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									242
Total segment | Middle East And Africa
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									62
Total segment | Other Locations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									129
Total segment | North American Full-Service
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									1,153	1,238	801
Total segment | North American Limited-Service
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									786	827	702
Total segment | Asia Pacific
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									456	361	160
Total segment | Other International
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									570	420	222
Unallocated corporate
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									$ (302)	$ 386	$ (447)