Derivatives Derivatives - Schedule of mark-to-market impact and commodity derivative settlements (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Net loss on commodity derivatives	$ (72)	$ (14)	$ (36)
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net loss on commodity derivatives	(124)	267	(81)
Derivative Instrument Not Designated As Hedging Instruments, Gain (Loss) On Settlements, Net	$ 52	$ (281)	$ 45

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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Balance Type:	credit
Period Type:	duration