|6 Months Ended|
Jun. 30, 2018
|Accrued Liabilities, Current [Abstract]|
As of June 30, 2018 and December 31, 2017, 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