Supplemental Cash Flows Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Supplemental Cash Flow Information [Abstract]
(Increase) decrease in accrued capital expenditures	$ (13)	$ (4)
(Increase) decrease in asset retirement costs	$ (1)	$ (4)

The increase (decrease) during the reporting period in accrued costs that represent future cash outlays for restoration and reclamation of oil and gas producing properties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Name:	us-gaap_IncreaseDecreaseInAccruedCostOfOilAndGasReclamation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration