DERIVATIVES AND HEDGING ACTIVITIES, Fair Value of Open Derivative Positions (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Derivative Contracts
Risk management assets - current	$ 0		$ 4,007,000
Risk management liabilities - current	3,678,000		33,229,000
Risk management liabilities - noncurrent	1,055,000		0
NPC [Member]
Derivative Contracts
Risk management assets - current	0		3,476,000
Risk management assets - noncurrent	0		0
Risk management liabilities - current	3,678,000		22,764,000
Risk management liabilities - noncurrent	0		0
SPPC [Member]
Derivative Contracts
Risk management assets - current	0		531,000
Risk management assets - noncurrent	0		0
Risk management liabilities - current	0		10,465,000
Risk management liabilities - noncurrent	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Contracts
Risk management assets - current	0		2,100,000
Risk management assets - noncurrent	0		0
Total risk management assets	0		2,100,000
Risk management liabilities - current	2,400,000		32,900,000
Risk management liabilities - noncurrent	1,100,000		0
Derivative Liabilities	3,500,000		32,900,000
Risk management regulatory assets/liabilities - net	(3,500,000)	[1]	(30,800,000)
Gains on risk management assets, deferred to risk management regulatory assets	27,300,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | NPC [Member]
Derivative Contracts
Risk management assets - current	0		2,100,000
Risk management assets - noncurrent	0		0
Total risk management assets	0		2,100,000
Risk management liabilities - current	2,400,000		22,400,000
Risk management liabilities - noncurrent	0		0
Derivative Liabilities	2,400,000		22,400,000
Risk management regulatory assets/liabilities - net	(2,400,000)	[1]	(20,300,000)
Gains on risk management assets, deferred to risk management regulatory assets	17,900,000
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | SPPC [Member]
Derivative Contracts
Risk management assets - current	0		0
Risk management assets - noncurrent	0		0
Total risk management assets	0		0
Risk management liabilities - current	0		10,500,000
Risk management liabilities - noncurrent	0		0
Derivative Liabilities	0		10,500,000
Risk management regulatory assets/liabilities - net	0	[1]	(10,500,000)
Gains on risk management assets, deferred to risk management regulatory assets	$ 10,500,000

[1] For the year ended December 31, 2011, NVE, NPC and SPPC would have recorded cumulative gains of $ 27.3 million, $ 17.9 million and $ 10.5 million, respectively. However, as permitted by the Regulated Operations Topic of the FASB Accounting Standards Codification, NVE and the Utilities deferred these gains, which are included in the risk management regulatory asset - net amounts above.