2.4.0.82101100 - Disclosure - Nature of Operations and Basis of Consolidationtruefalsefalse1false falsefalseD2013Q2YTDhttp://www.sec.gov/CIK0000073088duration2013-01-01T00:00:002013-06-30T00:00:001true 1us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstractus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Organization, Consolidation and Presentation of Financial Statements [Abstract]2false 2us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureAndSignificantAccountingPoliciesTextBlockus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00<div style="font-family:Times New Roman;font-size:10pt;"><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;font-weight:bold;">Nature of Operations and Basis of Consolidation</font></div><div style="line-height:120%;text-align:justify;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"> </font></div><div style="line-height:120%;text-align:left;text-indent:26px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">NorthWestern Corporation, doing business as NorthWestern Energy, provides electricity and natural gas to approximately </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">673,200</font><font style="font-family:inherit;font-size:10pt;"> customers in Montana, South Dakota and Nebraska. </font></div><div style="line-height:120%;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"><br clear="none"/></font></div><div style="line-height:120%;text-align:left;text-indent:26px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions that may affect the reported amounts of assets, liabilities, revenues and expenses during the reporting period. Actual results could differ from those estimates. The unaudited Condensed Consolidated Financial Statements (Financial Statements) reflect all adjustments (which unless otherwise noted are normal and recurring in nature) that are, in the opinion of management, necessary to fairly present our financial position, results of operations and cash flows. The actual results for the interim periods are not necessarily indicative of the operating results to be expected for a full year or for other interim periods. Events occurring subsequent to </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">June 30, 2013</font><font style="font-family:inherit;font-size:10pt;">, have been evaluated as to their potential impact to the Financial Statements through the date of issuance.</font></div><div style="line-height:120%;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"><br clear="none"/></font></div><div style="line-height:120%;text-align:left;text-indent:26px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">The Financial Statements included herein have been prepared by NorthWestern, without audit, pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations; however, management believes that the condensed disclosures provided are adequate to make the information presented not misleading. Management recommends that these unaudited Financial Statements be read in conjunction with the audited financial statements and related footnotes included in our Annual Report on Form 10-K for the year ended </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">December 31, 2012</font><font style="font-family:inherit;font-size:10pt;">.</font></div><div style="line-height:120%;text-align:left;text-indent:36px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"><br clear="none"/></font></div><div style="line-height:120%;text-align:left;text-indent:26px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;font-weight:bold;">Variable Interest Entities</font></div><div style="line-height:120%;text-align:left;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"><br clear="none"/></font></div><div style="line-height:120%;text-align:left;text-indent:26px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">A reporting company is required to consolidate a variable interest entity (VIE) as its primary beneficiary, which means it has a controlling financial interest, when it has both the power to direct the activities of the VIE that most significantly impact the VIE's economic performance, and the obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. An entity is considered to be a VIE when its total equity investment at risk is not sufficient to permit the entity to finance its activities without additional subordinated financial support, or its equity investors, as a group, lack the characteristics of having a controlling financial interest. The determination of whether a company is required to consolidate an entity is based on, among other things, an entity’s purpose and design and a company’s ability to direct the activities of the entity that most significantly impact the entity’s economic performance. </font></div><div style="line-height:120%;text-align:left;text-indent:36px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"><br clear="none"/></font></div><div style="line-height:120%;text-align:left;text-indent:26px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">Certain long-term purchase power and tolling contracts may be considered variable interests. We have various long-term purchase power contracts with other utilities and certain Qualifying Facility (QF) plants. We identified one QF contract that may constitute a VIE. We entered into a power purchase contract in </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">1984</font><font style="font-family:inherit;font-size:10pt;"> with this </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">35</font><font style="font-family:inherit;font-size:10pt;"> Megawatt (MW) coal-fired QF to purchase substantially all of the facility's capacity and electrical output over a substantial portion of its estimated useful life. We absorb a portion of the facility's variability through annual changes to the price we pay per Megawatt Hour (MWH) (energy payment). After making exhaustive efforts, we have been unable to obtain the information from the facility necessary to determine whether the facility is a VIE or whether we are the primary beneficiary of the facility. The contract with the facility contains no provision which legally obligates the facility to release this information. We have accounted for this QF contract as an executory contract. Based on the current contract terms with this QF, our estimated gross contractual payments aggregate approximately </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">$297.4 million</font><font style="font-family:inherit;font-size:10pt;"> through </font><font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;">2024</font><font style="font-family:inherit;font-size:10pt;">. </font></div><div style="line-height:120%;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;"><br clear="none"/></font></div></div>falsefalsefalsenonnum:textBlockItemTypenaThe entire disclosure for the organization, consolidation and basis of presentation of financial statements disclosure, and significant accounting policies of the reporting entity. May be provided in more than one note to the financial statements, as long as users are provided with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows. Describes procedure if disclosures are provided in more than one note to the financial statements.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 22 -Paragraph 8 -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. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 94-6 -Paragraph 10 -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. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 46R -Paragraph 4, 14, 15 -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. false0Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block]falseNature of Operations and Basis of ConsolidationUnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.northwesternenergy.com/role/NatureOfOperationsAndBasisOfConsolidation12