SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 number	Dec. 31, 2011	Dec. 31, 2010
Basis of Presentation
Tax Adjustment to balance sheet		$ 32,000,000	$ 30,600,000
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
CWIP	708,109,000	487,427,000
Total Utility Property, Gross	12,739,162,000	12,411,144,000
Asset retirement obligation [Roll Forward]
ARO balance at January 1	70,984,000	55,204,000
Liabilities incurred in current period	0	3,282,000
Liabilities settled in current period	0	(6,996,000)
Accretion expense	4,064,000	3,866,000
Revision in estimated cash flows	145,000	16,391,000
Gain Loss On Settlement	0	(763,000)
ARO balance at December 31	75,193,000	70,984,000
Nevada Power Company [Member]
Basis of Presentation
Percentage of subsidiary assets to consolidated assets (in hundredths)	72.00%
Number of electricity customers	850,000
Equity Carrying Charges
Accumulated equity carrying charges	11,100,000	12,700,000
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
CWIP	567,941,000	352,541,000
Total Utility Property, Gross	8,931,507,000	8,698,312,000
Public Utilities, Allowance for Funds Used During Construction, Net Increase [Abstract]
Public Utilities, Allowance for Funds Used During Construction, Rate	8.09%	8.47%	8.32%
Depreciation
Composite depreciation rate for plants in service (in hundredths)	3.22%	3.04%	2.99%
Regulated and Unregulated Operating Revenue [Abstract]
Unbilled Receivables, Current	86,000,000	93,000,000
Asset retirement obligation [Roll Forward]
ARO balance at January 1	61,020,000	47,128,000
Liabilities incurred in current period	0	3,282,000
Liabilities settled in current period	0	(6,996,000)
Accretion expense	3,453,000	3,348,000
Revision in estimated cash flows	(4,002,000)	15,021,000
Gain Loss On Settlement	0	(763,000)
ARO balance at December 31	60,471,000	61,020,000	47,128,000
Cost of Removal
Regulatory liabilities - cost of removal	252,600,000	232,000,000
Sierra Pacific Power Company [Member]
Basis of Presentation
Percentage of subsidiary assets to consolidated assets (in hundredths)	28.00%
Number of electricity customers	324,000
Electricity service area (in square miles)	42,000
Number of natural gas customers	153,000
Natural gas service area (in square miles)	800
Tax Adjustment to balance sheet		32,000,000	30,600,000
Equity Carrying Charges
Accumulated equity carrying charges	600,000	900,000
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
CWIP	140,168,000	134,886,000
Total Utility Property, Gross	3,807,655,000	3,712,832,000
Depreciation
Composite depreciation rate for plants in service (in hundredths)	2.94%	2.89%	3.02%
Regulated and Unregulated Operating Revenue [Abstract]
Unbilled Receivables, Current	50,000,000	51,000,000
Asset retirement obligation [Roll Forward]
ARO balance at January 1	9,964,000	8,076,000
Liabilities incurred in current period	0	0
Liabilities settled in current period	0	0
Accretion expense	611,000	518,000
Revision in estimated cash flows	4,147,000	1,370,000
Gain Loss On Settlement	0	0
ARO balance at December 31	14,722,000	9,964,000	8,076,000
Cost of Removal
Regulatory liabilities - cost of removal	204,400,000	189,900,000
General Plant [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
General, Intangible plant	685,000,000	659,000,000
CWIP	683,000,000	443,000,000
General Plant [Member] | Nevada Power Company [Member]
Estimated useful lives by major class [Abtract]
General Plant assets (in years)	5 to 65 years
General Plant [Member] | Sierra Pacific Power Company [Member]
Public Utilities, Allowance for Funds Used During Construction, Net Increase [Abstract]
Public Utilities, Allowance for Funds Used During Construction, Rate	7.59%
Estimated useful lives by major class [Abtract]
General Plant assets (in years)	5 to 65 years
Electric General Plant [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation assets	4,766,000,000	4,791,000,000
Electric General Plant [Member] | Nevada Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation assets	3,706,000,000	3,724,000,000
General, Intangible plant	583,000,000	564,000,000
CWIP	568,000,000	353,000,000
Estimated useful lives by major class [Abtract]
Generation assets (in years)	25 to 125 years
Electric General Plant [Member] | Sierra Pacific Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Generation assets	1,060,000,000	1,067,000,000
General, Intangible plant	102,000,000	95,000,000
CWIP	115,000,000	90,000,000
Estimated useful lives by major class [Abtract]
Generation assets (in years)	25 to 125 years
Transmission assets (in years)	50 to 70 years
Natural Gas General Plant [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
General, Intangible plant	13,000,000	3,000,000
CWIP	6,000,000	14,000,000
Natural Gas General Plant [Member] | Sierra Pacific Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
General, Intangible plant	13,000,000	3,000,000
CWIP	6,000,000	14,000,000
Common [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
General, Intangible plant	218,000,000	197,000,000
CWIP	18,000,000	31,000,000
Common [Member] | Sierra Pacific Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
General, Intangible plant	218,000,000	197,000,000
CWIP	18,000,000	31,000,000
Electric Plant Transmission and Distribution [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Transmission assets	1,867,000,000	1,853,000,000
Distribution assets	4,142,000,000	4,108,000,000
Electric Plant Transmission and Distribution [Member] | Nevada Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Transmission assets	1,189,000,000	1,183,000,000
Distribution assets	2,886,000,000	2,874,000,000
Estimated useful lives by major class [Abtract]
Transmission assets (in years)	45 to 65 years
Distribution assets (in years)	20 to 65 years
Electric Plant Transmission and Distribution [Member] | Sierra Pacific Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Transmission assets	678,000,000	670,000,000
Distribution assets	1,256,000,000	1,234,000,000
Public Utilities, Allowance for Funds Used During Construction, Net Increase [Abstract]
Public Utilities, Allowance for Funds Used During Construction, Rate	7.86%	7.86%	7.85%
Estimated useful lives by major class [Abtract]
Distribution assets (in years)	30 to 65 years
Gas Distribution [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Distribution assets	341,000,000	312,000,000
Gas Distribution [Member] | Nevada Power Company [Member]
Estimated useful lives by major class [Abtract]
Distribution assets (in years)	N/A
Gas Distribution [Member] | Sierra Pacific Power Company [Member]
Public Utilities, Property, Plant and Equipment, Plant in Service [Abstract]
Distribution assets	$ 341,000,000	$ 312,000,000
Public Utilities, Allowance for Funds Used During Construction, Net Increase [Abstract]
Public Utilities, Allowance for Funds Used During Construction, Rate	5.15%	5.15%
Estimated useful lives by major class [Abtract]
Distribution assets (in years)	40 to 70 years