REGULATORY ACTIONS (Details) (USD $)	9 Months Ended
	Sep. 30, 2011		Dec. 31, 2010
Nevada Deferred Energy
Cumulative Balance authorized in 2011 DEAA	$ (334,102,000)
2011 Amortization	166,081,000
2011 Deferred Energy Over Collections	(129,925,000)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(297,946,000)
Reinstatement of deferred energy (effective 6/07, 10 years)	120,678,000
Total Deferred Energy	(177,268,000)
Deferred Assets
Deferred energy	105,778,000		117,623,000
Current Liabilities
Deferred energy	(283,046,000)		(315,839,000)
Total Deferred Energy	(177,268,000)
Ely Energy Center [Abstract]
Spending amount approved by PUCN on EEC	130,000,000
Amount spent on EEC and recorded as other deferred asset	65,300,000
NPC Electric [Member]
Nevada Deferred Energy
Cumulative Balance authorized in 2011 DEAA	(189,032,000)	[2]
2011 Amortization	78,624,000
2011 Deferred Energy Over Collections	(78,647,000)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(189,055,000)
Reinstatement of deferred energy (effective 6/07, 10 years)	120,678,000
Total Deferred Energy	(68,377,000)
Current Liabilities
Total Deferred Energy	(68,377,000)
SPPC [Member] | SPPC Electric [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	(115,900,000)
Present Revenue Requirement	(99,500,000)
$ Change in Revenue Requirement	(16,400,000)
SPPC [Member] | SPPC Electric [Member] | REPR [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	38,000,000
Present Revenue Requirement	36,600,000
$ Change in Revenue Requirement	1,400,000
SPPC [Member] | SPPC Electric [Member] | TRED [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	9,100,000
Present Revenue Requirement	7,900,000
$ Change in Revenue Requirement	1,200,000
SPPC [Member] | SPPC Electric [Member] | EEPR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	9,700,000
Present Revenue Requirement	9,700,000
$ Change in Revenue Requirement	0
SPPC [Member] | SPPC Electric [Member] | EEPR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	4,600,000
Present Revenue Requirement	0
$ Change in Revenue Requirement	4,600,000
SPPC [Member] | SPPC Electric [Member] | EEIR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	3,100,000
Present Revenue Requirement	2,600,000
$ Change in Revenue Requirement	500,000
SPPC [Member] | SPPC Electric [Member] | EEIR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	500,000	[3]
Present Revenue Requirement	0
$ Change in Revenue Requirement	500,000
SPPC Electric [Member]
Nevada Deferred Energy
Cumulative Balance authorized in 2011 DEAA	(115,955,000)
2011 Amortization	75,464,000
2011 Deferred Energy Over Collections	(34,646,000)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(75,137,000)
Total Deferred Energy	(75,137,000)
Current Liabilities
Deferred energy	75,137,000
Total Deferred Energy	(75,137,000)
SPPC Electric [Member]
Revenue Requirement Subject To Change:
Authorized Revenue Requirement	(50,900,000)
Present Revenue Requirement	(42,700,000)
$ Change in Revenue Requirement	(8,200,000)
Amount of amortization recognized in revenues	500,000
Amount expected to be collected from customers	500,000
SPPC [Member] | SPPC Gas [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	(29,100,000)
Present Revenue Requirement	(16,700,000)
$ Change in Revenue Requirement	(12,400,000)
SPPC [Member] | SPPC Gas [Member] | STPR [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	300,000
Present Revenue Requirement	0
$ Change in Revenue Requirement	300,000
SPPC Gas [Member]
Nevada Deferred Energy
Cumulative Balance authorized in 2011 DEAA	(29,115,000)
2011 Amortization	11,993,000
2011 Deferred Energy Over Collections	(16,632,000)	[1]
Nevada Deferred Energy Balance at period end - Subtotal	(33,754,000)
Total Deferred Energy	(33,754,000)
Current Liabilities
Deferred energy	33,754,000
Total Deferred Energy	(33,754,000)
SPPC Gas [Member]
Revenue Requirement Subject To Change:
Authorized Revenue Requirement	(28,800,000)
Present Revenue Requirement	(16,700,000)
$ Change in Revenue Requirement	(12,100,000)
NPC [Member]
Deferred Assets
Deferred energy	105,778,000		117,623,000
Current Liabilities
Deferred energy	(174,155,000)		(171,349,000)
Energy Efficiency Implementation Rate [Abstract]
Approximate revenues filed for estimated reduced kWh sales from energy efficiency programs	35,100,000
Increases to EEIR base rates authorized	14,500,000
Pre-tax adjustment to earnings for revenue previously recorded	4,500,000
Revenues recognized of the authorized base amounts	10,400,000
Revenues recognized in accordance with FASC 980-605-25, Alternative Revenue Programs	7,400,000
Energy Efficiency Program Rate [Abstract]
Approximate costs filed for implementing energy efficiency programs	71,000,000
Increases to EEPR base rates authorized	58,400,000
EEPR revenues recorded	20,500,000
NPC 2011 GRC [Abstract]
Requested increase in general rates	249,900,000
Requested return on equity (in hundredths)	11.25%
Requested rate of return (in hundredths)	8.64%
Requested recovery, excluding AFUDC, for the expansion at the Harry Allen Generating Station	638,700,000
Requested authorization to defer collection	79,700,000
Remaining requested increase, approximately equal to revenue requirement decreases	170,200,000
Revenue Requirement Subject To Change:
Authorized Revenue Requirement	(60,600,000)
Present Revenue Requirement	18,000,000
$ Change in Revenue Requirement	(78,600,000)
Amount of amortization recognized in revenues	4,800,000
Amount expected to be collected from customers	4,800,000
NPC Harry Allen Regulatory Asset Filing [Abstract]
Planned expansion at generating station, capacity increase (in MW)	500
Expenses not to be recovered due to regulatory lag	40,000,000
NPC [Member] | DEAA [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	(188,900,000)
Present Revenue Requirement	(101,000,000)
$ Change in Revenue Requirement	(87,900,000)
NPC [Member] | REPR [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	8,600,000
Present Revenue Requirement	29,800,000
$ Change in Revenue Requirement	(21,200,000)
NPC [Member] | TRED [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	18,100,000
Present Revenue Requirement	16,300,000
$ Change in Revenue Requirement	1,800,000
NPC [Member] | EEPR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	58,400,000
Present Revenue Requirement	58,400,000
$ Change in Revenue Requirement	0
NPC [Member] | EEPR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	21,300,000
Present Revenue Requirement	0
$ Change in Revenue Requirement	21,300,000
NPC [Member] | EEIR Base [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	17,100,000
Present Revenue Requirement	14,500,000
$ Change in Revenue Requirement	2,600,000
NPC [Member] | EEIR Amortization [Member]
Revenue Requirement Subject To Change:
Effective Date	Oct. 2011
Authorized Revenue Requirement	4,800,000	[4]
Present Revenue Requirement	0
$ Change in Revenue Requirement	4,800,000
SPPC [Member]
Current Liabilities
Deferred energy	(108,891,000)		(144,490,000)
Energy Efficiency Implementation Rate [Abstract]
Approximate revenues filed for estimated reduced kWh sales from energy efficiency programs	7,600,000
Increases to EEIR base rates authorized	2,600,000
Pre-tax adjustment to earnings for revenue previously recorded	4,100,000
Revenues recognized of the authorized base amounts	4,100,000
Revenues recognized in accordance with FASC 980-605-25, Alternative Revenue Programs	1,000,000
Energy Efficiency Program Rate [Abstract]
Approximate costs filed for implementing energy efficiency programs	12,100,000
Increases to EEPR base rates authorized	9,700,000
EEPR revenues recorded	$ 2,600,000

[1] These deferred energy over collections will be filed in the March 2012 DEAA filings.

[2] Refer to NPC 2010 DEAA Settled Regulatory Actions in Note 3, Regulatory Actions, of the Notes to Financial Statements in the 2010 Form 10-K for separate discussion regarding rate offset of this balance.

[3] In accordance with Alternative Revenue Accounting, SPPC has 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 record further revenue from this rate request; however, SPPC does expect to collect approximately $0.5 million from their customers.

[4] In accordance with Alternative Revenue Accounting, NPC has 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 record further revenue from this rate request; however, NPC does expect to collect approximately $4.8 million from its customers.