BUSINESS SEGMENTS - Depreciation and Amortization (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Segment Reporting Information [Line Items]
Depreciation, amortization, and other	$ 52	$ 58	$ 54	$ 226	[1]	$ 229	[1]	$ 119	[1]
Total segment | North American Full-Service
Segment Reporting Information [Line Items]
Depreciation, amortization, and other				82		82		43
Total segment | North American Limited-Service
Segment Reporting Information [Line Items]
Depreciation, amortization, and other				15		14		13
Total segment | Asia Pacific
Segment Reporting Information [Line Items]
Depreciation, amortization, and other				26		32		8
Total segment | Other International
Segment Reporting Information [Line Items]
Depreciation, amortization, and other				70		71		34
Unallocated corporate
Segment Reporting Information [Line Items]
Depreciation, amortization, and other				$ 33		$ 30		$ 21

[1] See Footnote 18. Related Party Transactions for disclosure of related party amounts.