Variable Interest Entities (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Schedule Of Transfer And Financial Assets [Line Items]
Restricted cash and cash equivalents	$ 80	$ 67
Property and equipment, net	1,112	1,081
Write-down of property and equipment to fair value		37
Purchased property and equipment	28		$ 28
VIO Saint Thomas [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule Of Transfer And Financial Assets [Line Items]
Property and equipment, net		64
Long-term debt		104
Clearwater FL Property [Member]
Schedule Of Transfer And Financial Assets [Line Items]
Noncash transaction for property and equipment and long-term debt	51
Long-term debt	83
Midtown 45, NYC Property [Member]
Schedule Of Transfer And Financial Assets [Line Items]
Long-term debt		131
Purchased property and equipment	8		22
Mortgage Note - SPE [Member] | Clearwater FL Property [Member]
Schedule Of Transfer And Financial Assets [Line Items]
Debt instrument, face amount	83		$ 51
Inventory Purchase, Period			2 years
Mortgage Note - SPE [Member] | Midtown 45, NYC Property [Member]
Schedule Of Transfer And Financial Assets [Line Items]
Debt instrument, face amount		131
Non Securitized Receivable [Member]
Schedule Of Transfer And Financial Assets [Line Items]
Non-securitized contract receivables	$ 1,048	$ 1,039