Revenues - Disaggregation of Revenue Stream (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 5,049	$ 5,078	$ 15,401	$ 15,201
Segments
Disaggregation of Revenue [Line Items]
Revenues	4,834	4,813	14,815	14,500
Segments | North American Full-Service
Disaggregation of Revenue [Line Items]
Revenues	3,123	3,096	9,778	9,613
Segments | North American Limited-Service
Disaggregation of Revenue [Line Items]
Revenues	875	863	2,524	2,440
Segments | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	275	263	818	756
Segments | Other International
Disaggregation of Revenue [Line Items]
Revenues	561	591	1,695	1,691
Unallocated corporate
Disaggregation of Revenue [Line Items]
Revenues	215	265	586	701
Fee revenues
Disaggregation of Revenue [Line Items]
Gross revenues	932	826	2,728	2,433
Contract investment amortization	(13)	(11)	(44)	(34)
Revenues	919	815	2,684	2,399
Fee revenues | Segments
Disaggregation of Revenue [Line Items]
Gross revenues	805	741	2,372	2,184
Contract investment amortization	(13)	(11)	(44)	(34)
Revenues	792	730	2,328	2,150
Fee revenues | Segments | North American Full-Service
Disaggregation of Revenue [Line Items]
Gross revenues	305	285	949	891
Contract investment amortization	(7)	(7)	(25)	(19)
Revenues	298	278	924	872
Fee revenues | Segments | North American Limited-Service
Disaggregation of Revenue [Line Items]
Gross revenues	246	232	692	643
Contract investment amortization	(3)	(2)	(9)	(8)
Revenues	243	230	683	635
Fee revenues | Segments | Asia Pacific
Disaggregation of Revenue [Line Items]
Gross revenues	119	106	346	301
Contract investment amortization	0	0	(1)	(1)
Revenues	119	106	345	300
Fee revenues | Segments | Other International
Disaggregation of Revenue [Line Items]
Gross revenues	135	118	385	349
Contract investment amortization	(3)	(2)	(9)	(6)
Revenues	132	116	376	343
Owned, leased, and other
Disaggregation of Revenue [Line Items]
Revenues	397	433	1,226	1,309
Owned, leased, and other | Segments
Disaggregation of Revenue [Line Items]
Revenues	382	421	1,178	1,276
Owned, leased, and other | Segments | North American Full-Service
Disaggregation of Revenue [Line Items]
Revenues	137	157	432	535
Owned, leased, and other | Segments | North American Limited-Service
Disaggregation of Revenue [Line Items]
Revenues	34	37	104	100
Owned, leased, and other | Segments | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	46	48	141	138
Owned, leased, and other | Segments | Other International
Disaggregation of Revenue [Line Items]
Revenues	165	179	501	503
Reimbursements
Disaggregation of Revenue [Line Items]
Revenues	3,733	3,830	11,491	11,493
Reimbursements | Segments
Disaggregation of Revenue [Line Items]
Revenues	3,660	3,662	11,309	11,074
Reimbursements | Segments | North American Full-Service
Disaggregation of Revenue [Line Items]
Revenues	2,688	2,661	8,422	8,206
Reimbursements | Segments | North American Limited-Service
Disaggregation of Revenue [Line Items]
Revenues	598	596	1,737	1,705
Reimbursements | Segments | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenues	110	109	332	318
Reimbursements | Segments | Other International
Disaggregation of Revenue [Line Items]
Revenues	$ 264	$ 296	$ 818	$ 845