|12 Months Ended|
Dec. 31, 2017
|Accrued Liabilities, Current [Abstract]|
As of December 31, 2017 and 2016, accrued liabilities consisted of the following (in millions):
The entire disclosure for accounts payable and accrued liabilities at the end of the reporting period.
Reference 1: http://www.xbrl.org/2003/role/presentationRef