INCOME TAXES (BENEFITS) (Details2) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income tax reconciliation [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ (25,248,000)	$ 173,462,000	$ 12,888,000	$ 2,330,000	$ 14,213,000	$ 177,546,000	$ 36,946,000	$ (1,721,000)	$ 163,432,000	$ 226,984,000	$ 182,936,000
Income Tax Expense (Benefit)									86,915,000	113,764,000	75,451,000
Income Before Income Tax Expense									250,347,000	340,748,000	258,387,000
Statutory tax rate (in hundredths)									35.00%	35.00%	35.00%
Federal income tax expense									87,600,000	119,300,000	90,400,000
Depreciation									3,100,000	4,100,000	(2,100,000)
AFUDC - equity									3,800,000	9,800,000	8,500,000
Investment tax credit amortization									3,100,000	3,300,000	3,300,000
Regulatory asset for goodwill									2,700,000	2,700,000	2,700,000
Research and development credit									200,000	1,000,000	1,100,000
Income Tax Reconciliation, Other Reconciling Items									600,000	1,800,000	(2,500,000)
Effective tax rate (in hundredths)									34.70%	33.40%	29.20%
Nevada Power Company [Member]
Income tax reconciliation [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(29,065,000)	154,608,000	16,063,000	(9,020,000)	9,557,000	158,928,000	29,784,000	(12,326,000)	132,586,000	185,943,000	134,284,000
Income Tax Expense (Benefit)									70,737,000	91,757,000	61,652,000
Income Before Income Tax Expense									203,323,000	277,700,000	195,936,000
Statutory tax rate (in hundredths)									35.00%	35.00%	35.00%
Federal income tax expense									71,200,000	97,200,000	68,600,000
Depreciation									2,000,000	1,800,000	1,700,000
AFUDC - equity									2,900,000	8,800,000	7,400,000
Investment tax credit amortization									1,200,000	1,400,000	1,300,000
Regulatory asset for goodwill									1,700,000	1,700,000	1,700,000
Research and development credit									100,000	800,000	1,000,000
Income Tax Reconciliation, Other Reconciling Items									0	2,100,000	(600,000)
Effective tax rate (in hundredths)									34.80%	33.10%	31.50%
Sierra Pacific Power Company [Member]
Income tax reconciliation [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	14,462,000	25,336,000	3,512,000	16,576,000	19,478,000	24,462,000	11,315,000	17,120,000	59,886,000	72,375,000	73,085,000
Income Tax Expense (Benefit)									31,197,000	40,404,000	31,225,000
Income Before Income Tax Expense									91,083,000	112,779,000	104,310,000
Statutory tax rate (in hundredths)									35.00%	35.00%	35.00%
Federal income tax expense									31,900,000	39,500,000	36,500,000
Depreciation									1,100,000	2,300,000	(3,800,000)
AFUDC - equity									900,000	1,000,000	1,100,000
Investment tax credit amortization									1,900,000	1,900,000	2,100,000
Regulatory asset for goodwill									1,000,000	1,000,000	1,000,000
Research and development credit									100,000	200,000	200,000
Income Tax Reconciliation, Other Reconciling Items									$ 100,000	$ 700,000	$ 900,000
Effective tax rate (in hundredths)									34.20%	35.80%	29.90%