Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation	$ 66		$ 72	$ 205	$ 213
Net capital lease assets included in property and equipment	1			1		$ 20
Accumulated depreciation of capital lease assets included in property and equipment	0			0		10
Hurricanes Irma and Maria [Member]
Property, Plant and Equipment [Line Items]
Expenses on property and equipment from hurricane damage				32		20
Loss on property and equipment from hurricane damage		$ 22				$ 54
Additional insurance receivable recognized for property and equipment damaged from hurricanes				54
Insurance proceeds received on hurricanes damage				108
Hurricanes Irma and Maria [Member] | Ancillary Hotel [Member]
Property, Plant and Equipment [Line Items]
Business interruption insurance recovery				15
Reimbursements expense				6
Hurricanes Irma and Maria [Member] | Other Assets [Member]
Property, Plant and Equipment [Line Items]
Insurance settlements receivable on hurricanes damage	$ 23			$ 23