RETIREMENT PLAN AND POST-RETIREMENT BENEFITS, Components of Net Periodic Cost and Expected Benefit Payments (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)			34.50%	35.00%
DefinedBenefitPlanEffectOfPlanAmendmentOnAccumulatedBenefitObligation	$ 21,500,000		$ 21,500,000
United States Pension Plans of US Entity, Defined Benefit
Net periodic benefit cost [Abstract]
Service cost	5,132,000	4,406,000	15,396,000	13,220,000
Interest cost	9,303,000	10,228,000	27,911,000	30,684,000
Expected return on plan assets	(12,708,000)	(12,447,000)	(38,124,000)	(37,341,000)
Amortization of:
Prior service (credit)/cost	(720,000)	(724,000)	(2,162,000)	(2,173,000)
Actuarial (gain)/loss	4,797,000	3,473,000	14,391,000	10,418,000
Total net benefit cost	5,804,000	4,936,000	17,412,000	14,808,000
Average percentage of net periodic costs capitalized [Abstract]
PensionAndOtherPostretirementBenefitContributions			20,000,000	15,000,000
United States Postretirement Benefit Plans of US Entity, Defined Benefit
Net periodic benefit cost [Abstract]
Service cost	660,000	595,000	1,980,000	1,787,000
Interest cost	1,677,000	1,905,000	5,030,000	5,715,000
Expected return on plan assets	(1,687,000)	(1,563,000)	(5,060,000)	(4,690,000)
Amortization of:
Prior service (credit)/cost	(952,000)	(987,000)	(2,857,000)	(2,961,000)
Actuarial (gain)/loss	890,000	731,000	2,671,000	2,193,000
Total net benefit cost	588,000	681,000	1,764,000	2,044,000
Average percentage of net periodic costs capitalized [Abstract]
PensionAndOtherPostretirementBenefitContributions			5,000,000	7,100,000
Nevada Power Company
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)			35.90%	36.90%
Nevada Power Company | United States Pension Plans of US Entity, Defined Benefit
Net periodic benefit cost [Abstract]
Service cost	2,761,000	2,358,000	8,283,000	7,072,000
Interest cost	4,453,000	4,881,000	13,358,000	14,643,000
Expected return on plan assets	(6,270,000)	(6,237,000)	(18,810,000)	(18,711,000)
Amortization of:
Prior service (credit)/cost	(453,000)	(456,000)	(1,358,000)	(1,367,000)
Actuarial (gain)/loss	2,117,000	1,363,000	6,351,000	4,089,000
Total net benefit cost	2,608,000	1,909,000	7,824,000	5,726,000
Nevada Power Company | United States Postretirement Benefit Plans of US Entity, Defined Benefit
Net periodic benefit cost [Abstract]
Service cost	389,000	350,000	1,167,000	1,050,000
Interest cost	556,000	602,000	1,667,000	1,807,000
Expected return on plan assets	(631,000)	(592,000)	(1,892,000)	(1,775,000)
Amortization of:
Prior service (credit)/cost	(23,000)	229,000	(69,000)	687,000
Actuarial (gain)/loss	289,000	221,000	867,000	662,000
Total net benefit cost	580,000	810,000	1,740,000	2,431,000
Sierra Pacific Power Company
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)			35.60%	35.10%
Sierra Pacific Power Company | United States Pension Plans of US Entity, Defined Benefit
Net periodic benefit cost [Abstract]
Service cost	1,926,000	1,695,000	5,778,000	5,086,000
Interest cost	4,558,000	5,043,000	13,676,000	15,130,000
Expected return on plan assets	(6,162,000)	(5,937,000)	(18,486,000)	(17,813,000)
Amortization of:
Prior service (credit)/cost	(277,000)	(277,000)	(831,000)	(831,000)
Actuarial (gain)/loss	2,501,000	2,026,000	7,502,000	6,078,000
Total net benefit cost	2,546,000	2,550,000	7,639,000	7,650,000
Sierra Pacific Power Company | United States Postretirement Benefit Plans of US Entity, Defined Benefit
Net periodic benefit cost [Abstract]
Service cost	251,000	227,000	752,000	682,000
Interest cost	1,104,000	1,283,000	3,310,000	3,848,000
Expected return on plan assets	(1,022,000)	(941,000)	(3,065,000)	(2,823,000)
Amortization of:
Prior service (credit)/cost	(933,000)	(1,220,000)	(2,798,000)	(3,658,000)
Actuarial (gain)/loss	592,000	504,000	1,777,000	1,511,000
Total net benefit cost	$ (8,000)	$ (147,000)	$ (24,000)	$ (440,000)