BUSINESS SEGMENTS - Segment Profits (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
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits	$ 274	$ 607	$ 409	$ 510	$ 422	$ 596	$ 818	$ 530	$ 1,800	$ 2,366	$ 2,504
Interest expense, net of interest income									(368)	(318)	(250)
Income taxes									(326)	(438)	(1,523)
Net income	$ 279	$ 387	$ 232	$ 375	$ 317	$ 503	$ 667	$ 420	1,273	1,907	1,459
Total segment | International Operations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									982	1,155	837
Total segment | Asia Pacific
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									369
Total segment | Europe
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									272
Total segment | Caribbean and Latin America
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									118
Total segment | Middle East And Africa
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									45
Total segment | Other Locations
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									178
Total segment | North American Full-Service
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									1,148	1,153	1,238
Total segment | North American Limited-Service
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									852	786	827
Total segment | Asia Pacific
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									369	456	361
Total segment | Other International
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									435	570	420
Unallocated corporate
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segments profits									$ (837)	$ (302)	$ 386