RETIREMENT PLAN AND POST-RETIREMENT BENEFITS, Components of Net Periodic Cost and Expected Benefit Payments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)	34.60%	33.40%	34.00%
Expected federal subsidy [Abstract]
2013	$ 0
2014	0
2015	0
2016	0
2017	0
PrescriptionDrugSubsidyReceipts	0
United States Pension Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	17,627	18,427	18,910
Interest cost	40,912	40,676	42,872
Expected return on plan assets	(49,789)	(48,767)	(44,275)
Amortization of:
Prior service (credit)/cost	(2,897)	(2,952)	(1,794)
Actuarial (gain)/loss	13,891	16,620	15,106
Remeasurement adjustment	0	0	0
Total net benefit cost	19,744	24,004	30,819
Special termination benefits excluded from net periodic cost	0	286
Expected cash flows for the plans, including trust accounts [Abstract]
2013	57,488
2014	59,705
2015	58,211
2016	66,837
2017	56,057
2018-2022	311,999
United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	2,383	2,611	2,466
Interest cost	7,620	8,360	8,736
Expected return on plan assets	(6,253)	(6,386)	(6,223)
Amortization of:
Prior service (credit)/cost	(3,947)	(3,947)	(3,890)
Actuarial (gain)/loss	2,924	4,333	4,342
Remeasurement adjustment	0	0	0
Total net benefit cost	2,727	4,971	5,431
Special termination benefits excluded from net periodic cost	0	100
Expected cash flows for the plans, including trust accounts [Abstract]
2013	9,497
2014	9,891
2015	9,974
2016	10,108
2017	10,052
2018-2022	49,872
Nevada Power Company [Member]
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)	37.00%	36.90%	37.00%
Nevada Power Company [Member] | United States Pension Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	9,429	9,781	9,567
Interest cost	19,524	19,521	20,092
Expected return on plan assets	(24,948)	(24,677)	(21,447)
Amortization of:
Prior service (credit)/cost	(1,823)	(1,879)	(1,733)
Actuarial (gain)/loss	5,452	6,758	7,056
Remeasurement adjustment	0	0	0
Total net benefit cost	7,634	9,504	13,535
Nevada Power Company [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	1,400	1,454	1,413
Interest cost	2,409	2,459	2,474
Expected return on plan assets	(2,366)	(2,360)	(2,270)
Amortization of:
Prior service (credit)/cost	916	916	946
Actuarial (gain)/loss	883	1,208	1,199
Remeasurement adjustment	0	0	0
Total net benefit cost	3,242	3,677	3,762
Sierra Pacific Power Company [Member]
Average percentage of net periodic costs capitalized [Abstract]
Average percentage of net periodic costs capitalized (in hundredths)	35.30%	31.70%	34.20%
Sierra Pacific Power Company [Member] | United States Pension Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	6,781	7,361	8,016
Interest cost	20,173	20,050	21,557
Expected return on plan assets	(23,751)	(22,964)	(21,723)
Amortization of:
Prior service (credit)/cost	(1,108)	(1,108)	(104)
Actuarial (gain)/loss	8,105	9,647	7,876
Remeasurement adjustment	0	0	0
Total net benefit cost	10,200	12,986	15,622
Sierra Pacific Power Company [Member] | United States Postretirement Benefit Plans of US Entity, Defined Benefit [Member]
Net periodic benefit cost [Abstract]
Service cost	910	1,086	977
Interest cost	5,131	5,830	6,187
Expected return on plan assets	(3,763)	(3,905)	(3,844)
Amortization of:
Prior service (credit)/cost	(4,878)	(4,878)	(4,851)
Actuarial (gain)/loss	2,014	3,092	3,109
Remeasurement adjustment	0	0	0
Total net benefit cost	$ (586)	1,225	1,578