Basis of Presentation - Effect of Adoption of ASU 2014-09 on Statement of Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
REVENUES
Base management fees	$ 273	$ 264
Franchise fees	417	355
Incentive management fees	155	140
Gross fee revenues	845	759
Contract investment amortization	(18)	(11)
Net fee revenues	827	748
Owned, leased, and other revenue	406	428
Cost reimbursement revenue	3,773	3,736
Revenues	5,006	4,912
OPERATING COSTS AND EXPENSES
Owned, leased, and other-direct	336	356
Depreciation, amortization, and other	54	51
General, administrative, and other	247	212
Merger-related costs and charges	34	51
Reimbursed expenses	3,835	3,696
Costs and expenses	4,506	4,366
OPERATING INCOME	500	546
Gains and other income, net	59	0
Interest expense	(75)	(70)
Interest income	5	7
Equity in earnings	13	11
INCOME BEFORE INCOME TAXES	502	494
Income taxes	(104)	(123)
NET INCOME	$ 398	$ 371
EARNINGS PER SHARE
Earnings per share - basic (in USD per share)	$ 1.11	$ 0.96
Earnings per share - diluted (in USD per share)	$ 1.09	$ 0.95
As Previously Reported
REVENUES
Base management fees		$ 264
Franchise fees		365
Incentive management fees		153
Gross fee revenues		782
Contract investment amortization		0
Net fee revenues		782
Owned, leased, and other revenue		439
Cost reimbursement revenue		4,340
Revenues		5,561
OPERATING COSTS AND EXPENSES
Owned, leased, and other-direct		358
Depreciation, amortization, and other		65
General, administrative, and other		210
Merger-related costs and charges		51
Reimbursed expenses		4,340
Costs and expenses		5,024
OPERATING INCOME		537
Gains and other income, net		0
Interest expense		(70)
Interest income		7
Equity in earnings		11
INCOME BEFORE INCOME TAXES		485
Income taxes		(120)
NET INCOME		$ 365
EARNINGS PER SHARE
Earnings per share - basic (in USD per share)		$ 0.95
Earnings per share - diluted (in USD per share)		$ 0.94
Adoption of ASU 2014-09 | Adjustment
REVENUES
Base management fees		$ 0
Franchise fees		(10)
Incentive management fees		(13)
Gross fee revenues		(23)
Contract investment amortization		(11)
Net fee revenues		(34)
Owned, leased, and other revenue		(11)
Cost reimbursement revenue		(604)
Revenues		(649)
OPERATING COSTS AND EXPENSES
Owned, leased, and other-direct		(2)
Depreciation, amortization, and other		(14)
General, administrative, and other		2
Merger-related costs and charges		0
Reimbursed expenses		(644)
Costs and expenses		(658)
OPERATING INCOME		9
Gains and other income, net		0
Interest expense		0
Interest income		0
Equity in earnings		0
INCOME BEFORE INCOME TAXES		9
Income taxes		(3)
NET INCOME		$ 6
EARNINGS PER SHARE
Earnings per share - basic (in USD per share)		$ 0.01
Earnings per share - diluted (in USD per share)		$ 0.01