COMMITMENTS AND CONTINGENCIES (Details) (USD $)	6 Months Ended
Jun. 30, 2011 MW Integer
Litigation Contingencies [Abstract]
Proceeds from Sale of hydro units	$ 8,000,000
ON Line TUA [Abstract]
Capacity Of Interconnection	500
Utilities' aggregate share transmission line project	25.00%
GBT-South's share in the ON Line project (in hundredths)	75.00%
Capitalized construction costs	51,500,000
NPC [Member]
Environmental [Abstract]
Reclamation estimate of coal washing and load-out facility site	5,000,000
Litigation Contingencies [Abstract]
Damages sought in DC Lawsuit	600,000,000
Minimum punitive damages sought in DC Lawsuit	1,000,000,000
Number of hydro generating units sold	4
Total capacity of hydro generating units sold (in MW)	10.3000
Capacity of the Farad Hydro generating unit (in MW)	2.8
Estimate to rebuild the diversion dam of the Farad Hydro generating unit	20,000,000
Amount entitled to recovered for costs incurred to date on Farad Dam	4,000,000
Duration period to rebuild the Farad dam from the date of the Court's decision	three years
Amount of actual cash value entitled to if Farad Dam is not rebuilt	1,300,000
ON Line TUA [Abstract]
Capacity Of Interconnection	500
Utilities' aggregate share transmission line project	25.00%
GBT-South's share in the ON Line project (in hundredths)	75.00%
Capitalized construction costs	50,100,000
NPC [Member] \| Navajo Generating Station [Member]
Investments in Generating Stations Involved in Litigation [Line Items]
Ownership interest in the generating stations (in hundredths)	11.00%
NPC [Member] \| Mohave Generating Station [Member]
Investments in Generating Stations Involved in Litigation [Line Items]
Ownership interest in the generating stations (in hundredths)	14.00%
SPPC [Member]
Environmental [Abstract]
Third party ownership percentage in Valmy Generating Station (in hundredths)	50.00%
ON Line TUA [Abstract]
Capacity Of Interconnection	500
Utilities' aggregate share transmission line project	25.00%
GBT-South's share in the ON Line project (in hundredths)	75.00%
Capitalized construction costs	$ 1,400,000

The U.S. District Court for the District of Nevada ruling on the amount to be recovered for costs incurred to date.

Name:	nve_AmountEntitledToRecoveredForCostsIncurredToDate
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of actual cash value that the U.S. District Court for the District of Nevada determined the Company was entitled to in the event the Farad Dam is not rebuilt.

+ Details

Name:	nve_AmountOfActualCashValueEntitledToIfDamIsNotRebuilt
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	nve_CapacityOfInterconnection
Namespace Prefix:	nve
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Capacity of the Farad Hydro generating unit, which has been out of service since the summer of 1996 due to a collapsed flume.

+ Details

Name:	nve_CapacityOfOutOfServiceGeneratingUnit
Namespace Prefix:	nve
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of construction costs capitalized in CWIP associated with GBT's interest in the ON Line project, with a corresponding credit to other deferred liabilities.

+ Details

Name:	nve_CapitalizedConstructionCostsAssociatedWithRemainingShareOfTransmissionLineProject
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of time from the date of the U.S. District Court for the District of Nevada's decision for the Farad dam to be rebuilt.

+ Details

Name:	nve_DurationPeriodToRebuildFaradDam
Namespace Prefix:	nve
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	nve_EnvironmentalAbstract
Namespace Prefix:	nve
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimate to rebuild the diversion dam of the Farad Hydro generating unit, which has been out of services since the summer of 1996 due to a collapsed flume.

+ Details

Name:	nve_EstimateToRebuildDiversionDam
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ Details

Name:	nve_InvestmentsInGeneratingStationsInvolvedInLitigationLineItems
Namespace Prefix:	nve
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	nve_LitigationContingenciesAbstract
Namespace Prefix:	nve
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Describes the amount of money award the plaintiff seeks in the legal matter.

+ Details

Name:	nve_LossContingencyAmountOfDamagesSought
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Describes the amount of money award the plaintiff seeks for punitive damages in the legal matter.

+ Details

Name:	nve_LossContingencyAmountOfMinimumPunitiveDamagesSought
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of hydro generating units, located in Nevada and California, sold to Truckee Meadows Water Authority.

+ Details

Name:	nve_NumberOfHydroGeneratingUnitsSold
Namespace Prefix:	nve
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage interest owned in the generating stations subject to litigation contingencies.

+ Details

Name:	nve_OwnershipInterestInGeneratingStations
Namespace Prefix:	nve
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Sale of hydro units.

+ Details

Name:	nve_ProceedsFromSaleOfHydroUnits
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Estimated amount, supported by a bond, of a reclamation liability that is associated with a coal washing and load-out facility site in Wellington, Utah.

+ Details

Name:	nve_ReclamationEstimateOfCoalWashingAndLoadOutFacilitySite
Namespace Prefix:	nve
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

GBT-South's share of the ON Line project, for which the Utilities have entered into a TUA with GBT-South in Phase I.

+ Details

Name:	nve_RemainingShareTransmissionLineProject
Namespace Prefix:	nve
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Ownership percentage in Valmy Generating Station, located in Valmy, Nevada, held by Idaho Power Company.

+ Details

Name:	nve_ThirdPartyOwnershipPercentageInGeneratingStation
Namespace Prefix:	nve
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total capacity, in MW, of hydro generating units, located in Nevada and California, sold to Truckee Meadows Water Authority.

+ Details

Name:	nve_TotalCapacityOfHydroGeneratingUnitsSold
Namespace Prefix:	nve
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	nve_TransmissionLineProjectAbstract
Namespace Prefix:	nve
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The Utilities' aggregate share in the On Line project. a 250 mile 500 kV transmission lie connecting the northern and southern service territories.

+ Details

Name:	nve_UtilitiesAggregateShareTransmissionLineProject
Namespace Prefix:	nve
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant