DERIVATIVES AND HEDGING ACTIVITIES (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011 MMBTU		Sep. 30, 2011 MMBTU		Dec. 31, 2010 MMBTU
Derivative [Line Items]
Fixed interest rate (in hundredths)	2.81%		2.81%
Commodity volume liabilities- current (MMBTU)	0.6	[1]	0.6	[1]	18.1	[1]
Option Premiums [Line Items]
Current Assets	$ 100,000		$ 100,000		$ 1,900,000
Current Liabilities	(300,000)		(300,000)		(400,000)
Non-current Liabilities	(200,000)		(200,000)		0
Derivative Contracts
Gains on risk management assets, deferred to risk management regulatory assets	3,500,000		29,300,000
NPC [Member]
Derivative [Line Items]
Number of instruments held	2		2
Underlying risk			interest rate
Aggregated notional amount	350,000,000		350,000,000
Amount of hedged item	350,000,000		350,000,000
Description of hedged item			$350 million 8.25% General and Refunding Mortgage Notes, Series A, due June 1, 2011.
Commodity volume liabilities- current (MMBTU)	0.5	[1]	0.5	[1]	12.9	[1]
Option Premiums [Line Items]
Current Assets	100,000		100,000		1,400,000
Current Liabilities	(300,000)		(300,000)		(400,000)
Non-current Liabilities	(200,000)		(200,000)		0
Derivative Contracts
Gains on risk management assets, deferred to risk management regulatory assets	2,900,000		19,100,000
NPC [Member] | Level 2 [Member]
Derivative Contracts
Risk management assets - current	0		0		2,100,000
Risk management liabilities - current	900,000		900,000		22,400,000
Risk management liabilities - non-current	300,000		300,000		0
Risk management regulatory assets/liabilities - net	(1,200,000)	[2]	(1,200,000)	[2]	(20,300,000)	[2]
SPPC [Member]
Derivative [Line Items]
Commodity volume liabilities- current (MMBTU)	0.1	[1]	0.1	[1]	5.2	[1]
Option Premiums [Line Items]
Current Assets	0		0		500,000
Current Liabilities	0		0		0
Non-current Liabilities	0		0		0
Derivative Contracts
Gains on risk management assets, deferred to risk management regulatory assets	600,000		10,200,000
SPPC [Member] | Level 2 [Member]
Derivative Contracts
Risk management assets - current	0		0		0
Risk management liabilities - current	300,000		300,000		10,500,000
Risk management liabilities - non-current	0		0		0
Risk management regulatory assets/liabilities - net	(300,000)	[2]	(300,000)	[2]	(10,500,000)	[2]
Recurring Fair Value Measures [Member] | Level 2 [Member]
Derivative Contracts
Risk management assets - current	0		0		2,100,000
Risk management liabilities - current	1,200,000		1,200,000		32,900,000
Risk management liabilities - non-current	300,000		300,000		0
Risk management regulatory assets/liabilities - net	$ (1,500,000)	[2]	$ (1,500,000)	[2]	$ (30,800,000)	[2]

[1] The change in commodity volumes at September 30, 2011, as compared to December 31, 2010, is primarily due to the suspension of the Utilities hedging program as of October 2009. As such, the Utilities exposure to mark-to-market hedging transactions has declined.

[2] When amount is negative it represents a risk management regulatory asset, when positive it represents a risk management regulatory liability. For the three months ended September 30, 2011, NVE, NPC and SPPC would have recorded cumulative gains of $3.5 million, $2.9 million and $0.6 million, respectively, and for the nine months ended September 30, 2011, NVE, NPC and SPPC would have recorded gains of $29.3 million, $19.1 million, and $10.2 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 liability - net amounts above.