Oil and Natural Gas Property Transactions - VPP Transactions Table (Details) MMBbls in Millions, $ in Millions, Bcfe in Billions, Bcf in Billions	12 Months Ended
Dec. 31, 2018 USD ($) Bcfe VPP MMBbls Bcf	Dec. 31, 2016 VPP
VPP Transactions [Line Items]
VPP \| VPP	9	4
VPP 9 Mid-Continent [Member]
VPP Transactions [Line Items]
Cash proceeds \| $	$ 853
Proved developed reserves (energy) \| Bcfe	177
VPP 9 Mid-Continent [Member] \| Oil [Member]
VPP Transactions [Line Items]
Proved developed reserves (volume)	1.7
VPP 9 Mid-Continent [Member] \| Natural gas [Member]
VPP Transactions [Line Items]
Proved developed reserves (volume) \| Bcf	138
VPP 9 Mid-Continent [Member] \| NGL [Member]
VPP Transactions [Line Items]
Proved developed reserves (volume)	4.8

Net quantities of an enterprise's interests in proved developed reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Form 20-F
-Section Item 18
-Subsection Instruction 2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61797-109447

Name:	srt_ProvedDevelopedReservesVolume
Namespace Prefix:	srt_
Data Type:	num:volumeItemType
Balance Type:	na
Period Type:	instant