QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Data [Line Items]
Operating Revenues	$ 600,571		$ 1,026,488		$ 740,698		$ 611,420		$ 609,597	$ 1,017,796	$ 674,931	$ 640,983	$ 2,979,177	$ 2,943,307	$ 3,280,222
Operating Income	96,519		411,240		180,836		96,468		76,684	353,196	106,919	73,866	785,063	610,665	644,435
Net Income (Loss)	17,164		223,170		69,439		12,173		(25,248)	173,462	12,888	2,330	321,946	163,432	226,984
Earnings Per Share, Basic and Diluted [Abstract]
Net income per share - basic	$ 0.07	[1]	$ 0.95	[1]	$ 0.29	[1]	$ 0.05	[1]	$ (0.11)	$ 0.74	$ 0.05	$ 0.01	$ 1.37	$ 0.69	$ 0.97
Net income per share - diluted	$ 0.07		$ 0.94		$ 0.29		$ 0.05		$ (0.11)	$ 0.73	$ 0.05	$ 0.01	$ 1.35	$ 0.69	$ 0.96
Income Tax Expense (Benefit)													166,592	86,915	113,764
Nevada Power Company [Member]
Quarterly Financial Data [Line Items]
Operating Revenues	394,076		802,334		553,143		395,688		391,513	798,914	473,898	390,068	2,145,241	2,054,393	2,252,377
Operating Income	56,395		346,225		146,991		52,684		33,759	296,327	82,177	31,533	602,295	443,796	467,412
Net Income (Loss)	1,587		195,170		62,297		(1,316)		(29,065)	154,608	16,063	(9,020)	257,738	132,586	185,943
Earnings Per Share, Basic and Diluted [Abstract]
Income Tax Expense (Benefit)													138,113	70,737	91,757
Sierra Pacific Power Company [Member]
Quarterly Financial Data [Line Items]
Operating Revenues	206,491		224,150		187,551		215,728		218,080	218,878	201,030	250,911	833,920	888,899	1,027,822
Operating Income	42,854		65,664		34,953		44,679		45,007	57,574	25,703	43,149	188,150	171,433	180,995
Net Income (Loss)	18,604		34,427		12,679		18,644		14,462	25,336	3,512	16,576	84,354	59,886	72,375
Earnings Per Share, Basic and Diluted [Abstract]
Income Tax Expense (Benefit)													$ 40,221	$ 31,197	$ 40,404

[1] Total Net Income per Share per the Consolidated Statement of Comprehensive Income may differ slightly due to rounding.