Commitments and Contingencies New Plant (Details)	3 Months Ended
Mar. 31, 2018
New Plants [Member]
Property, Plant and Equipment [Line Items]
Qualitative and Quantitative Information, Transferor's Continuing Involvement, Third Party Commitments	two
Natural Gas [Member]
Property, Plant and Equipment [Line Items]
Qualitative and Quantitative Information, Transferor's Continuing Involvement, Third Party Commitments	200

Information about any liquidity arrangements, guarantees and/or other commitments by third parties related to the transferred financial assets that may affect the fair value or risk of interest that continues to be held by the transferor.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(5)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

Name:	us-gaap_QualitativeAndQuantitativeInformationAssetsOrLiabilitiesForTransferorsContinuingInvolvementInSecuritizationOrAssetbackedFinancingArrangementThirdPartyCommitments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration