RETIREMENT PLAN AND POST-RETIREMENT BENEFITS, Components of Net Periodic Cost and Expected Benefit Payments (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)	33.80%	33.20%
DefinedBenefitPlanEffectOfPlanAmendmentOnAccumulatedBenefitObligation	$ 11,000,000
United States Pension Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	5,132,000	4,406,000
Interest cost	9,303,000	10,228,000
Expected return on plan assets	(12,708,000)	(12,447,000)
Amortization of:
Prior service (credit)/cost	(720,000)	(724,000)
Actuarial (gain)/loss	4,797,000	3,473,000
Total net benefit cost	5,804,000	4,936,000
Average percentage of net periodic costs capitalized [Abstract]
PensionAndOtherPostretirementBenefitContributions	0
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	660,000	595,000
Interest cost	1,677,000	1,905,000
Expected return on plan assets	(1,687,000)	(1,563,000)
Amortization of:
Prior service (credit)/cost	(952,000)	(987,000)
Actuarial (gain)/loss	890,000	731,000
Total net benefit cost	588,000	681,000
Average percentage of net periodic costs capitalized [Abstract]
PensionAndOtherPostretirementBenefitContributions	0
Nevada Power Company [Member]
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)	35.10%	35.60%
Nevada Power Company [Member] | United States Pension Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	2,761,000	2,358,000
Interest cost	4,453,000	4,881,000
Expected return on plan assets	(6,270,000)	(6,237,000)
Amortization of:
Prior service (credit)/cost	(453,000)	(456,000)
Actuarial (gain)/loss	2,117,000	1,363,000
Total net benefit cost	2,608,000	1,909,000
Nevada Power Company [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	389,000	350,000
Interest cost	556,000	602,000
Expected return on plan assets	(631,000)	(592,000)
Amortization of:
Prior service (credit)/cost	(23,000)	229,000
Actuarial (gain)/loss	289,000	221,000
Total net benefit cost	580,000	810,000
Sierra Pacific Power Company [Member]
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)	34.40%	33.00%
Sierra Pacific Power Company [Member] | United States Pension Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	1,926,000	1,695,000
Interest cost	4,558,000	5,043,000
Expected return on plan assets	(6,162,000)	(5,937,000)
Amortization of:
Prior service (credit)/cost	(277,000)	(277,000)
Actuarial (gain)/loss	2,501,000	2,026,000
Total net benefit cost	2,546,000	2,550,000
Sierra Pacific Power Company [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	251,000	227,000
Interest cost	1,104,000	1,283,000
Expected return on plan assets	(1,022,000)	(941,000)
Amortization of:
Prior service (credit)/cost	(933,000)	(1,220,000)
Actuarial (gain)/loss	592,000	504,000
Total net benefit cost	$ (8,000)	(147,000)