Revenues Deferred Revenue (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Deferred Revenue Rollforward [Line Items]
Document Period End Date	Jun. 30, 2018
Deferred Revenue	$ 303	$ 194
Deferred Revenue, Additions	999
Deferred Revenue, Revenue Recognized	890
Prepaid Rentals [Member]
Deferred Revenue Rollforward [Line Items]
Deferred Revenue	210	101
Deferred Revenue, Additions	891
Deferred Revenue, Revenue Recognized	782
Other Deferred Revenue [Member]
Deferred Revenue Rollforward [Line Items]
Deferred Revenue	93	$ 93
Deferred Revenue, Additions	108
Deferred Revenue, Revenue Recognized	108
Accounts Payable and Accrued Liabilities [Member] | Other Deferred Revenue [Member]
Deferred Revenue Rollforward [Line Items]
Deferred Revenue	37
Other Noncurrent Liabilities [Member] | Other Deferred Revenue [Member]
Deferred Revenue Rollforward [Line Items]
Deferred Revenue	$ 56