Other Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Additional Financial Information Disclosure [Abstract]
Impairment of asset	$ 1	$ 11	$ 0
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid expenses	42	48
Assets held for sale	0	8
Other	56	73
Total other current assets	98	129
Accounts Payable, Current [Abstract]
Accounts payable	317	398
Capital expenditures incurred but not yet paid	$ 86	$ 53