Name:	npc_FairValueMeasurementsWithUnobservableInputsReconciliationRecurringBasisAssetsAndLiabilityNetSettlements
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of gain (loss) recognized in regulatory assets or liabilities, net, arising from assets, liabilities and financial instruments classified in shareholders' equity measured at fair value on a recurring basis using unobservable inputs (level 3).

No definition available.

Name:	npc_FairValueMeasurementsWithUnobservableInputsReconciliationRecurringBasisGainLossIncludedInRegulatoryAssetsAndLiabilitiesNet
Namespace Prefix:	npc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

This element represents assets and liabilities, net measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

No definition available.

Name:	npc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLiabilityNetValue
Namespace Prefix:	npc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The net amount of regulatory assets and liabilities as of the balance sheet date representing the net effective portion of unrealized losses and gains on derivatives not designated as hedging instruments and used for domestic regulated operations. Unrealized losses and gains on derivatives used for domestic regulated operations are generally recorded as regulatory assets or liabilities due to the realized losses and gains on such derivatives being included in regulated rates.

No definition available.

Name:	npc_NetRegulatoryAssetLiabilityUnrealizedLossGainOnDerivativeContracts
Namespace Prefix:	npc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258