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Customer Sharing Percentage Of Amounts Exceeding Deadband

No definition available.

Name:	nwe_CustomerSharingPercentageOfAmountsExceedingDeadband
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Data Type:	num:percentItemType
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Deadband Around Base Electric Supply Costs

No definition available.

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An increase in recoverable costs due to a change in statute associated with electric supply costs.

No definition available.

Name:	nwe_IncreaseInRecoveryDuetoChangeinStatute
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Data Type:	xbrli:monetaryItemType
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Increase in revenues due to implementation of interim rates, subject to refund.

No definition available.

Name:	nwe_IncreasedRevenueDuetoChangeinRatesSubjecttoRefund
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Data Type:	xbrli:monetaryItemType
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Interim Change in Depreciation Resulting From Rate Review

No definition available.

Name:	nwe_InterimRecognizedChangeinDepreciationResultingFromRateReview
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Data Type:	xbrli:monetaryItemType
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Shareholder Sharing Percentage Of Amounts Exceeding Deadband

No definition available.

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Data Type:	num:percentItemType
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Amount of deferred revenue recognized for transactions arising during the current reporting period. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an Entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

No definition available.

Name:	us-gaap_DeferredRevenueAdditions
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Data Type:	xbrli:monetaryItemType
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
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Data Type:	xbrli:stringItemType
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Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesInterimRateIncreaseDecreaseAmount
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Data Type:	xbrli:monetaryItemType
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Amount of public utility's requested rate increase (decrease) with regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Percentage of public utility's requested return on equity.

No definition available.

Name:	us-gaap_PublicUtilitiesRequestedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382