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 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



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ContextID="I2013Q2_nwe_SiteContingecyBySiteAxis_nwe_ColstripUnit4Member_us-gaap_JointlyOwnedUtilityPlantAxis_us-gaap_JointlyOwnedElectricityGenerationPlantMember_us-gaap_SiteContingencyByNatureAxis_nwe_CleanAirActRulesAndAssociatedEmissionControlEquipmentExpendituresMember" UnitID="ratio"><Id>8</Id><IsNumeric>true</IsNumeric><IsRatio>true</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0.30</NumericAmount><RoundedNumericAmount>0.30</RoundedNumericAmount><NonNumbericText /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>num:percentItemType</ElementDataType><SimpleDataType>pure</SimpleDataType><ElementDefenition>The proportionate share of interest (percent) in a jointly owned utility plant.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

 -Publisher FASB

 -Name Accounting Standards Codification

 -Topic 980

 -SubTopic 360

 -Section S99

 -Paragraph 1

 -Subparagraph (SAB TOPIC 10.C)

 -URI http://asc.fasb.org/extlink&amp;oid=6500719&amp;loc=d3e659983-123033



Reference 2: http://www.xbrl.org/2003/role/presentationRef

 -Publisher SEC

 -Name Staff Accounting Bulletin (SAB)

 -Number Topic 10

 -Section C



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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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