Litigation (Details) $ in Millions					1 Months Ended		12 Months Ended
	Mar. 27, 2017 defendant	Nov. 13, 2013 USD ($)	Aug. 03, 2012 USD ($)	Feb. 14, 2011 USD ($)	Sep. 30, 2010 USD ($)	Aug. 31, 2010	Dec. 31, 1991 USD ($)	Sep. 30, 2018 LegalMatter	Nov. 06, 2012	Jan. 03, 2012	Dec. 31, 2008 USD ($)
MTBE | Pending Litigation
Loss Contingencies [Line Items]
Pending lawsuits and claims (in number of claims) | LegalMatter								8
Ecuador | Pending Litigation
Loss Contingencies [Line Items]
Conducted remediation program							3 years
Remediation program							$ 40
Financial compensation for purported damages on mining engineer's report											$ 18,900
Assessment for purported unjust enrichment on mining engineer's report											$ 8,400
Court order requiring the parties to provide their positions on damages within (in days)						45 days
Amount assessed in damages		$ 9,500		$ 8,600
Amount assessed for plaintiffs representatives				900
Additional amount assessed in punitive damages				$ 8,600
Public apology date within judgment/clarification ruling (in days)				15 days
Proposed additional payment for plaintiff attorney fees as percentage of judgment										0.10%
Litigation settlement, amount awarded to			$ 19,100
Percentage of payments withheld by third parties due to freeze order									40.00%
Percentage of funds withheld by banks due to freeze order									40.00%
Ecuador | Pending Litigation | Minimum
Loss Contingencies [Line Items]
Approximate damages on plaintiffs' submission					$ 16,000
Approximate unjust enrichment on plaintiffs' submission					5,000
Ecuador | Pending Litigation | Maximum
Loss Contingencies [Line Items]
Approximate damages on plaintiffs' submission					76,000
Approximate unjust enrichment on plaintiffs' submission					$ 38,000
Ecuador | Declaratory Relief Claim
Loss Contingencies [Line Items]
Pending lawsuits and claims (in number of claims) | LegalMatter								1
Writ of Certiorari
Loss Contingencies [Line Items]
Number of defendants | defendant	2