INCOME TAXES (BENEFITS) (Details2) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income tax reconciliation [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 17,164,000	$ 223,170,000	$ 69,439,000	$ 12,173,000	$ (25,248,000)	$ 173,462,000	$ 12,888,000	$ 2,330,000	$ 321,946,000	$ 163,432,000	$ 226,984,000
Income Tax Expense (Benefit)									166,592,000	86,915,000	113,764,000
Income Before Income Tax Expense									488,538,000	250,347,000	340,748,000
Statutory tax rate (in hundredths)									35.00%	35.00%	35.00%
Federal income tax expense									171,000,000	87,600,000	119,300,000
Depreciation									2,400,000	3,100,000	4,100,000
AFUDC - equity									(3,200,000)	(3,800,000)	(9,800,000)
Investment tax credit amortization									(2,600,000)	(3,100,000)	(3,300,000)
Regulatory asset for goodwill									2,700,000	2,700,000	2,700,000
Research and development credit									(4,200,000)	(200,000)	(1,000,000)
Income Tax Reconciliation, Other Reconciling Items									500,000	600,000	1,800,000
Total provision for income taxes									166,600,000	86,900,000	113,800,000
Effective tax rate (in hundredths)									34.10%	34.70%	33.40%
Nevada Power Company [Member]
Income tax reconciliation [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	1,587,000	195,170,000	62,297,000	(1,316,000)	(29,065,000)	154,608,000	16,063,000	(9,020,000)	257,738,000	132,586,000	185,943,000
Income Tax Expense (Benefit)									138,113,000	70,737,000	91,757,000
Income Before Income Tax Expense									395,851,000	203,323,000	277,700,000
Statutory tax rate (in hundredths)									35.00%	35.00%	35.00%
Federal income tax expense									138,500,000	71,200,000	97,200,000
Depreciation									3,500,000	2,000,000	1,800,000
AFUDC - equity									(2,300,000)	(2,900,000)	(8,800,000)
Investment tax credit amortization									(1,400,000)	(1,200,000)	(1,400,000)
Regulatory asset for goodwill									1,700,000	1,700,000	1,700,000
Research and development credit									(2,800,000)	(100,000)	(800,000)
Income Tax Reconciliation, Other Reconciling Items									900,000	0	2,100,000
Total provision for income taxes									138,100,000	70,700,000	91,800,000
Effective tax rate (in hundredths)									34.90%	34.80%	33.10%
Sierra Pacific Power Company [Member]
Income tax reconciliation [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	18,604,000	34,427,000	12,679,000	18,644,000	14,462,000	25,336,000	3,512,000	16,576,000	84,354,000	59,886,000	72,375,000
Income Tax Expense (Benefit)									40,221,000	31,197,000	40,404,000
Income Before Income Tax Expense									124,575,000	91,083,000	112,779,000
Statutory tax rate (in hundredths)									35.00%	35.00%	35.00%
Federal income tax expense									43,600,000	31,900,000	39,500,000
Depreciation									(1,100,000)	1,100,000	2,300,000
AFUDC - equity									(900,000)	(900,000)	(1,000,000)
Investment tax credit amortization									(1,200,000)	(1,900,000)	(1,900,000)
Regulatory asset for goodwill									1,000,000	1,000,000	1,000,000
Research and development credit									(1,400,000)	(100,000)	(200,000)
Income Tax Reconciliation, Other Reconciling Items									200,000	100,000	700,000
Total provision for income taxes									$ 40,200,000	$ 31,200,000	$ 40,400,000
Effective tax rate (in hundredths)									32.30%	34.20%	35.80%