SEGMENT INFORMATION (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Segment Reporting Information [Line Items]
OPERATING REVENUES	$ 1,017,796,000	[1]	$ 1,128,039,000	[2],[3]	$ 2,333,710,000	[1]	$ 2,625,211,000	[2],[3]
Energy Costs:
Fuel for power generation	216,779,000		247,233,000		519,920,000		650,514,000
Purchased power	223,348,000		249,854,000		518,672,000		522,538,000
Gas purchased for resale	10,137,000		10,823,000		87,753,000		101,536,000
Deferred Energy	(33,620,000)		34,055,000		(43,678,000)		106,554,000
Total energy costs	416,644,000		541,965,000		1,082,667,000		1,381,142,000
Gross Margin	601,152,000		586,074,000	[2],[3]	1,251,043,000		1,244,069,000	[2],[3]
Other operating expenses	127,645,000	[1]	112,741,000		331,166,000	[1]	320,755,000
Maintenance	11,369,000		31,126,000		73,317,000		85,715,000
Depreciation and amortization	93,737,000		83,423,000		266,445,000		249,067,000
Taxes other than income	15,205,000		15,420,000		46,134,000		47,532,000
OPERATING INCOME	353,196,000		343,364,000	[3]	533,981,000		541,000,000	[3]
NPC Electric [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	798,914,000	[1]	870,950,000	[2],[3]	1,662,880,000	[1]	1,836,144,000	[2],[3]
Energy Costs:
Fuel for power generation	162,976,000		181,100,000		378,790,000		469,282,000
Purchased power	181,733,000		216,309,000		399,707,000		412,276,000
Deferred Energy	(10,354,000)		22,296,000		(1,274,000)		81,719,000
Total energy costs	334,355,000		419,705,000		777,223,000		963,277,000
Gross Margin	464,559,000		451,245,000	[2],[3]	885,657,000		872,867,000	[2],[3]
Other operating expenses	88,455,000	[1]	73,762,000		215,491,000	[1]	203,773,000
Maintenance	3,460,000		23,707,000		45,122,000		58,945,000
Depreciation and amortization	67,212,000		56,575,000		186,798,000		169,330,000
Taxes other than income	9,105,000		9,038,000		28,209,000		28,857,000
OPERATING INCOME	296,327,000		288,163,000	[3]	410,037,000		411,962,000	[3]
SPPC Electric [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	202,263,000	[1]	237,798,000	[2]	545,462,000	[1]	649,337,000	[2]
Energy Costs:
Fuel for power generation	53,803,000		66,133,000		141,130,000		181,232,000
Purchased power	41,615,000		33,545,000		118,965,000		110,262,000
Deferred Energy	(22,095,000)		9,964,000		(45,924,000)		17,189,000
Total energy costs	73,323,000		109,642,000		214,171,000		308,683,000
Gross Margin	128,940,000		128,156,000	[2]	331,291,000		340,654,000	[2]
SPPC Gas [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	16,615,000		19,286,000		125,357,000		139,711,000
Energy Costs:
Gas purchased for resale	10,137,000		10,823,000		87,753,000		101,536,000
Deferred Energy	(1,171,000)		1,795,000		3,520,000		7,646,000
Total energy costs	8,966,000		12,618,000		91,273,000		109,182,000
Gross Margin	7,649,000		6,668,000		34,084,000		30,529,000
SPPC Total [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUES	218,878,000	[1]	257,084,000	[2]	670,819,000	[1]	789,048,000	[2]
Energy Costs:
Fuel for power generation	53,803,000		66,133,000		141,130,000		181,232,000
Purchased power	41,615,000		33,545,000		118,965,000		110,262,000
Gas purchased for resale	10,137,000		10,823,000		87,753,000		101,536,000
Deferred Energy	(23,266,000)		11,759,000		(42,404,000)		24,835,000
Total energy costs	82,289,000		122,260,000		305,444,000		417,865,000
Gross Margin	136,589,000		134,824,000	[2]	365,375,000		371,183,000	[2]
Other operating expenses	38,529,000	[1]	38,004,000		113,432,000	[1]	114,371,000
Maintenance	7,909,000		7,419,000		28,195,000		26,770,000
Depreciation and amortization	26,525,000		26,848,000		79,647,000		79,737,000
Taxes other than income	6,052,000		6,330,000		17,675,000		18,494,000
OPERATING INCOME	57,574,000		56,223,000		126,426,000		131,811,000
NVE Other
Segment Reporting Information [Line Items]
OPERATING REVENUES	4,000		5,000		11,000		19,000
Energy Costs:
Gross Margin	4,000		5,000		11,000		19,000
Other operating expenses	661,000		975,000		2,243,000		2,611,000
Taxes other than income	48,000		52,000		250,000		181,000
OPERATING INCOME	$ (705,000)		$ (1,022,000)		$ (2,482,000)		$ (2,773,000)

[1] Effective July 1, 2011, included in operating revenues were EEPR revenues, for which costs related to the program are included in other operating expense and therefore have no effect on operating income. See Note 3, Regulatory Actions.

[2] As reported in our 2010 Form 10-K, amounts for REPR are presented net. As such, revenues and gross margin for the three months ended September 30, 2010 were reduced by $3.5 million, $2.0 million and $1.5 million for NVE, NPC and SPPC, respectively, from that reported in the Forms 10-Q for the period ended September 30, 2010. Revenues and gross margin for the nine months ended September 30, 2010 were reduced by $8.7 million, $4.6 million and $4.1 million for NVE, NPC and SPPC, respectively, from that reported in the Forms 10-Q for the period ended September 30, 2010.

[3] During the third quarter 2010, NPC terminated a long-term service agreement from one of its generating stations. The estimated termination payment was not considered material to the third quarter but would have been material to the fourth quarter; therefore, as disclosed in our 2010 Form 10-K, third quarter 2010 was revised to reflect the estimated termination payment. As such, operating income for the three and nine months ended September 30, 2010 was reduced by $8.0 million, before tax, for NVE and NPC, from that reported in the Forms 10-Q for the quarterly period ended September 30, 2010. See Note 1, Summary of Significant Accounting Policies.