REGULATORY ACTIONS, Summary of Regulatory Actions (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Ely Energy Center [Abstract]
Spending amount approved by Public Utility Commission of Nevada on Ely Energy Center			$ 130.0
Amount spent on Ely Energy Center and recorded as other deferred asset			58.0
Energy Efficiency Program Rate [Abstract]
Frequency of rate filings for energy efficiency program costs (in years)	three years
Nevada Power Company [Member]
Ely Energy Center [Abstract]
Farming Asset Reclassification			23.1
EEC Development Costs			23.2
Energy Efficiency Implementation Rate [Abstract]
Approximate revenues filed for estimated reduced kWh sales from energy efficiency program			35.1
Increases to EEIR base rates authorized			14.5
Pre-tax adjustment to earnings for revenue previously recorded			4.5
Revenues recognized for EEIR			15.5
Energy Efficiency Program Rate [Abstract]
Approximate costs filed for implementing energy efficiency programs			71.0
Increases to Energy Efficiency Program base rates authorized			58.4
EEPR revenues recorded			37.3
Revenue Requirement Subject To Change:
Authorized Revenue Requirement	127.6		(60.6)
Present Revenue Requirement	126.6	[1]	18.0	[1]
$ Change in Revenue Requirement	1.0		(78.6)
Nevada Power Company [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2012	[2]	Oct. 2011
Authorized Revenue Requirement	11.5	[2]	(188.9)
Present Revenue Requirement	0	[1],[2]	(101.0)	[1]
$ Change in Revenue Requirement	11.5	[2]	(87.9)
DEAA Filings [Abstract]
Requested rate increase (decrease)					(9.2)
Requested rate increase (decrease) percentage (in hundredths)					(0.41%)
Deferred costs refund requested					102.0
Amount Of Over Collection Against Deferred Btgr Debit Balance					102.0
Deferred Base Tariff General Rate balance					95.8
Nevada Power Company [Member] | REPR [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2012	[3]	Oct. 2011
Authorized Revenue Requirement	37.4	[3]	8.6
Present Revenue Requirement	8.5	[1],[3]	29.8	[1]
$ Change in Revenue Requirement	28.9	[3]	(21.2)
Nevada Power Company [Member] | TRED [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2012	[3]	Oct. 2011
Authorized Revenue Requirement	15.3	[3]	18.1
Present Revenue Requirement	18.0	[1],[3]	16.3	[1]
$ Change in Revenue Requirement	(2.7)	[3]	1.8
Nevada Power Company [Member] | EEPR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013	[3]	Oct. 2011
Authorized Revenue Requirement	33.1	[3]	58.4
Present Revenue Requirement	57.3	[1],[3]	58.4	[1]
$ Change in Revenue Requirement	(24.2)	[3]	0
Nevada Power Company [Member] | EEPR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013	[3]	Oct. 2011
Authorized Revenue Requirement	8.9	[3]	21.3
Present Revenue Requirement	21.2	[1],[3]	0	[1]
$ Change in Revenue Requirement	(12.3)	[3]	21.3
Nevada Power Company [Member] | EEIR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013		Oct. 2011
Authorized Revenue Requirement	11.0		17.1
Present Revenue Requirement	16.8	[1]	14.5	[1]
$ Change in Revenue Requirement	(5.8)		2.6
Nevada Power Company [Member] | EEIR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013		Oct. 2011
Authorized Revenue Requirement	10.4	[2]	4.8	[4]
Present Revenue Requirement	4.8	[1]	0	[1]
$ Change in Revenue Requirement	5.6		4.8
Amount expected to be collected from customers			4.8
Nevada Power Company [Member] | GRC [Member]
GRC Filings [Abstract]
Requested Increase In General Rates			249.9
Requested return on equity (in hundredths)			11.25%
Requested rate of return (in hundredths)			8.64%
Recovery, excluding AFUDC, for the expansion at the Harry Allen Generating Station			635.9
Increase in General Rates			158.6
Percentage Overall Increase In General Rates			8.30%
Approved ROE			10.00%
Allowed ROR			8.09%
EEC Project Development Costs Recovery			23.2
Dsm Costs			17.7
Mohave Closure Costs			12.7
EWAM Postponement Amount			46.9
Net Rate Case Adjustments			15.9
Sierra Pacific Power Company [Member]
Ely Energy Center [Abstract]
Development And Farming Asset Reclassification			11.6
Energy Efficiency Implementation Rate [Abstract]
Approximate revenues filed for estimated reduced kWh sales from energy efficiency program			7.6
Increases to EEIR base rates authorized			2.6
Pre-tax adjustment to earnings for revenue previously recorded			4.1
Revenues recognized for EEIR			2.5
Energy Efficiency Program Rate [Abstract]
Approximate costs filed for implementing energy efficiency programs			12.1
Increases to Energy Efficiency Program base rates authorized			9.7
EEPR revenues recorded			6.2
Sierra Pacific Power Company [Member] | SPPC Gas [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Effective Date	October 1, 2012		October 1, 2011		October 1, 2010
$ Change in Revenue Requirement	0.2		(12.1)
DEAA Filings [Abstract]
Requested rate increase (decrease)					(8.3)
Requested rate increase (decrease) percentage (in hundredths)					(4.69%)
Deferred costs refund requested					17.0
Sierra Pacific Power Company [Member] | SPPC Gas [Member] | GRC [Member]
GRC Filings [Abstract]
Requested Increase In General Rates					4.3
Requested return on equity (in hundredths)					10.75%
Requested rate of return (in hundredths)					5.48%
Increase in General Rates					2.7
Percentage Overall Increase In General Rates					1.93%
Approved ROE					10.00%
Allowed ROR					5.15%
Revenue Requirement Subject To Change:
Effective Date					January 1, 2011
Sierra Pacific Power Company [Member] | SPPC Electric [Member]
Revenue Requirement Subject To Change:
Authorized Revenue Requirement	63.3		(50.9)
Present Revenue Requirement	65.8	[1]	(42.7)	[1]
$ Change in Revenue Requirement	(2.5)		(8.2)
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Effective Date			Oct. 2011		October 1, 2010
Authorized Revenue Requirement			(115.9)
Present Revenue Requirement			(99.5)	[1]
$ Change in Revenue Requirement			(16.4)
DEAA Filings [Abstract]
Requested rate increase (decrease)					(47.0)
Requested rate increase (decrease) percentage (in hundredths)					(6.31%)
Deferred costs refund requested					101.0
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | REPR [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2012	[3]	Oct. 2011
Authorized Revenue Requirement	43.3	[3]	38.0
Present Revenue Requirement	38.5	[1],[3]	36.6	[1]
$ Change in Revenue Requirement	4.8	[3]	1.4
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | TRED [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2012	[3]	Oct. 2011
Authorized Revenue Requirement	6.1	[3]	9.1
Present Revenue Requirement	9.2	[1],[3]	7.9	[1]
$ Change in Revenue Requirement	(3.1)	[3]	1.2
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | EEPR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013	[3]	Oct. 2011
Authorized Revenue Requirement	5.4	[3]	9.7
Present Revenue Requirement	9.8	[1],[3]	9.7	[1]
$ Change in Revenue Requirement	(4.4)	[3]	0
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | EEPR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013	[3]	Oct. 2011
Authorized Revenue Requirement	1.7	[3]	4.6
Present Revenue Requirement	4.7	[1],[3]	0	[1]
$ Change in Revenue Requirement	(3.0)	[3]	4.6
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | EEIR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013		Oct. 2011
Authorized Revenue Requirement	4.9		3.1
Present Revenue Requirement	3.1	[1]	2.6	[1]
$ Change in Revenue Requirement	1.8		0.5
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | EEIR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Jan. 2013		Oct. 2011
Authorized Revenue Requirement	1.9		0.5	[5]
Present Revenue Requirement	0.5	[1]	0	[1]
$ Change in Revenue Requirement	1.4		0.5
Amount expected to be collected from customers			0.5
Sierra Pacific Power Company [Member] | SPPC Electric [Member] | GRC [Member]
GRC Filings [Abstract]
Requested Increase In General Rates					29.3
Requested return on equity (in hundredths)					10.75%
Requested rate of return (in hundredths)					8.14%
Increase in General Rates					$ 13.1
Percentage Overall Increase In General Rates					1.90%
Approved ROE					10.10%
Allowed ROR					7.86%
Revenue Requirement Subject To Change:
Effective Date					January 1, 2011

[1] Represents present revenue requirement at the time of filing.

[2] This rate request represents revenues previously recorded as a result of NPC's 2008 GRC. As such, NPC will not record furtherrevenue related to this rate component, but will collect such amounts from its customers. Refer to Regulatory Actions, NPC 2012 DEAA, below for further discussion.

[3] Represents programs that require the Utilities to collect funds from customers for which the related costs are equal to therevenues collected. As a result, such programs have no effect on Operating or Net Income.

[4] In accordance with Alternative Revenue Accounting, NPC recognized approximately $4.8 million in revenues pertaining to 2010. Based on the order from the PUCN in May 2011, which clarified the calculation of EEIR revenues, NPC does not expect to recordfurther revenue from this rate request; however, NPC does expect to collect approximately $4.8 million from its customers.

[5] In accordance with Alternative Revenue Accounting, SPPC recognized approximately $0.5 million in revenues pertaining to 2010. Based on the order from the PUCN in May 2011, which clarified the calculation of EEIR revenues, SPPC does not expect to recordfurther revenue from this rate request; however, SPPC does expect to collect approximately $0.5 million from its customers.