REGULATORY ACTIONS, Regulatory Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	$ 562,133	[1]
Receiving Regulatory Recovery - Not Earning a Return	661,952
Pending Regulatory Review	189,878
Total regulatory assets	1,413,963		1,433,784
Regulatory liabilities
Receiving Regulatory Treatment - Earning a Return	506,673	[1]
Receiving Regulatory Treatment - Not Earning a Return	15,142
Pending Regulatory Treatment	28,872
Total regulatory liabilities	550,687		486,259
Cost of Removal [Member]
Regulatory liabilities
Remaining Amortization Period	Various
Receiving Regulatory Treatment - Earning a Return	457,074	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	457,074		422,033
Deferred Income Tax Charges [Member]
Regulatory liabilities
Remaining Amortization Period	Various
Receiving Regulatory Treatment - Earning a Return	0	[1]
Receiving Regulatory Treatment - Not Earning a Return	15,142
Pending Regulatory Treatment	0
Total regulatory liabilities	15,142		17,433
Gain on Property Sales [Member]
Regulatory liabilities
Remaining Amortization Period	2013
Receiving Regulatory Treatment - Earning a Return	2,222	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	27,300
Total regulatory liabilities	29,522		37,288
Renewable Energy Programs Regulatory Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	460	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	460		1,046
Other Regulatory Liabilities [Member]
Regulatory liabilities
Remaining Amortization Period	Various thru 2043
Receiving Regulatory Treatment - Earning a Return	5,400	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	1,572	[3]
Total regulatory liabilities	6,972		8,459
Energy Efficiency Program Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	34,727	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	34,727		0
Energy Efficiency Implementation Regulatory Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	6,790	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	6,790		0
Loss on Reacquired Debt [Member]
Regulatory assets
Remaining Amortization Period	Term of Related Debt
Receiving Regulatory Recovery - Earning a Return	66,911	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	66,911		72,408
Deferred Income Tax Charges Assets [Member]
Regulatory assets
Remaining Amortization Period	Various
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	269,693
Pending Regulatory Review	0
Total regulatory assets	269,693		283,315
Merger Costs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2046
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	257,185
Pending Regulatory Review	0
Total regulatory assets	257,185		268,668
Lenzie Generating Station [Member]
Regulatory assets
Remaining Amortization Period	2042
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	65,139
Pending Regulatory Review	0
Total regulatory assets	65,139		67,351
Mohave Generating Station and Deferred Costs [Member]
Regulatory assets
Remaining Amortization Period	2017
Receiving Regulatory Recovery - Earning a Return	6,931	[1]
Receiving Regulatory Recovery - Not Earning a Return	10,545
Pending Regulatory Review	4,230	[4]
Total regulatory assets	21,706		24,160
Pinon Pine [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2029
Receiving Regulatory Recovery - Earning a Return	25,805	[1]
Receiving Regulatory Recovery - Not Earning a Return	3,837
Pending Regulatory Review	0
Total regulatory assets	29,642		34,393
Asset Retirement Obligation Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	66,559	[4]
Total regulatory assets	66,559		67,891
Conservation Programs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2017
Receiving Regulatory Recovery - Earning a Return	110,246	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	12,310	[3]
Total regulatory assets	122,556		158,447
Ely Energy Center [Member]
Regulatory assets
Remaining Amortization Period	2017
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	19,503
Pending Regulatory Review	34,359	[4]
Total regulatory assets	53,862		57,966
Legacy Meters [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	64,112
Total regulatory assets	64,112		21,777
Renewable Energy Programs Regulatory Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	23,703	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	23,703		29,592
Peabody Coal Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	18,305
Pending Regulatory Review	0
Total regulatory assets	18,305		17,899
Deferred Rate Increase [Member]
Regulatory assets
Remaining Amortization Period	2013
Receiving Regulatory Recovery - Earning a Return	8,550	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	8,550		12,177
Other Costs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2031
Receiving Regulatory Recovery - Earning a Return	21,451	[1]
Receiving Regulatory Recovery - Not Earning a Return	17,745
Pending Regulatory Review	8,308	[3],[4]
Total regulatory assets	47,504		57,643
Regulatory Assets Subtotal - excluding pensions [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	280,938	[1]
Receiving Regulatory Recovery - Not Earning a Return	661,952
Pending Regulatory Review	189,878
Total regulatory assets	1,132,768		1,218,128
Pension Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	281,195	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	281,195		215,656
Energy Efficiency Program Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	4,744	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	4,744		30,379
Energy Efficiency Implementation Rate Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	12,597	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	12,597		14,062
Nevada Power Company [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	322,204	[1]
Receiving Regulatory Recovery - Not Earning a Return	458,855
Pending Regulatory Review	159,636
Total regulatory assets	940,695		961,517
Regulatory liabilities
Receiving Regulatory Treatment - Earning a Return	289,885	[1]
Receiving Regulatory Treatment - Not Earning a Return	4,707
Pending Regulatory Treatment	28,808
Total regulatory liabilities	323,400		274,951
Nevada Power Company [Member] | Cost of Removal [Member]
Regulatory liabilities
Remaining Amortization Period	Various
Receiving Regulatory Treatment - Earning a Return	252,648	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	252,648		232,093
Nevada Power Company [Member] | Deferred Income Tax Charges [Member]
Regulatory liabilities
Remaining Amortization Period	Various
Receiving Regulatory Treatment - Earning a Return	0	[1]
Receiving Regulatory Treatment - Not Earning a Return	4,707
Pending Regulatory Treatment	0
Total regulatory liabilities	4,707		5,798
Nevada Power Company [Member] | Gain on Property Sales [Member]
Regulatory liabilities
Receiving Regulatory Treatment - Earning a Return	0	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	27,300
Total regulatory liabilities	27,300		32,844
Nevada Power Company [Member] | Other Regulatory Liabilities [Member]
Regulatory liabilities
Remaining Amortization Period	Various thru 2018
Receiving Regulatory Treatment - Earning a Return	639	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	1,508	[3]
Total regulatory liabilities	2,147		4,216
Nevada Power Company [Member] | Energy Efficiency Program Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	29,808	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	29,808		0
Nevada Power Company [Member] | Energy Efficiency Implementation Regulatory Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	6,790	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	6,790		0
Nevada Power Company [Member] | Loss on Reacquired Debt [Member]
Regulatory assets
Remaining Amortization Period	Term of Related Debt
Receiving Regulatory Recovery - Earning a Return	37,821	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	37,821		39,958
Nevada Power Company [Member] | Deferred Income Tax Charges Assets [Member]
Regulatory assets
Remaining Amortization Period	Various
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	169,211
Pending Regulatory Review	0
Total regulatory assets	169,211		178,060
Nevada Power Company [Member] | Merger Costs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2044
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	161,833
Pending Regulatory Review	0
Total regulatory assets	161,833		168,212
Nevada Power Company [Member] | Lenzie Generating Station [Member]
Regulatory assets
Remaining Amortization Period	2042
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	65,139
Pending Regulatory Review	0
Total regulatory assets	65,139		67,351
Nevada Power Company [Member] | Mohave Generating Station and Deferred Costs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2017
Receiving Regulatory Recovery - Earning a Return	6,931	[1]
Receiving Regulatory Recovery - Not Earning a Return	10,545
Pending Regulatory Review	4,230	[4]
Total regulatory assets	21,706		24,160
Nevada Power Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	58,368	[4]
Total regulatory assets	58,368		60,797
Nevada Power Company [Member] | Conservation Programs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2017
Receiving Regulatory Recovery - Earning a Return	99,671	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	7,511	[3]
Total regulatory assets	107,182		133,889
Nevada Power Company [Member] | Ely Energy Center [Member]
Regulatory assets
Remaining Amortization Period	2017
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	19,503
Pending Regulatory Review	22,815	[4]
Total regulatory assets	42,318		46,373
Nevada Power Company [Member] | Legacy Meters [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	61,420	[4]
Total regulatory assets	61,420		21,777
Nevada Power Company [Member] | Renewable Energy Programs Regulatory Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	9,495	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	9,495		10,694
Nevada Power Company [Member] | Peabody Coal Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	18,305
Pending Regulatory Review	0
Total regulatory assets	18,305		17,899
Nevada Power Company [Member] | Deferred Rate Increase [Member]
Regulatory assets
Remaining Amortization Period	2013
Receiving Regulatory Recovery - Earning a Return	8,550	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	8,550		12,177
Nevada Power Company [Member] | Other Costs [Member]
Regulatory assets
Remaining Amortization Period	2017
Receiving Regulatory Recovery - Earning a Return	9,578	[1]
Receiving Regulatory Recovery - Not Earning a Return	14,319
Pending Regulatory Review	5,292	[3],[4]
Total regulatory assets	29,189		34,050
Nevada Power Company [Member] | Regulatory Assets Subtotal - excluding pensions [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	185,522	[1]
Receiving Regulatory Recovery - Not Earning a Return	458,855
Pending Regulatory Review	159,636
Total regulatory assets	804,013		852,989
Nevada Power Company [Member] | Pension Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	136,682	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	136,682		108,528
Nevada Power Company [Member] | Energy Efficiency Program Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	4,174	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	4,174		25,250
Nevada Power Company [Member] | Energy Efficiency Implementation Rate Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	9,302	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	9,302		12,342
Sierra Pacific Power Company [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	235,684	[1]
Receiving Regulatory Recovery - Not Earning a Return	203,097
Pending Regulatory Review	30,242
Total regulatory assets	469,023		469,298
Regulatory liabilities
Receiving Regulatory Treatment - Earning a Return	216,788	[1]
Receiving Regulatory Treatment - Not Earning a Return	10,435
Pending Regulatory Treatment	64
Total regulatory liabilities	227,287		211,308
Sierra Pacific Power Company [Member] | Cost of Removal [Member]
Regulatory liabilities
Remaining Amortization Period	Various
Receiving Regulatory Treatment - Earning a Return	204,426	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	204,426		189,940
Sierra Pacific Power Company [Member] | Deferred Income Tax Charges [Member]
Regulatory liabilities
Remaining Amortization Period	Various
Receiving Regulatory Treatment - Earning a Return	0	[1]
Receiving Regulatory Treatment - Not Earning a Return	10,435
Pending Regulatory Treatment	0
Total regulatory liabilities	10,435		11,635
Sierra Pacific Power Company [Member] | Gain on Property Sales [Member]
Regulatory liabilities
Remaining Amortization Period	2013
Receiving Regulatory Treatment - Earning a Return	2,222	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	2,222		4,444
Sierra Pacific Power Company [Member] | Renewable Energy Programs Regulatory Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	460	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	460		0
Sierra Pacific Power Company [Member] | Other Regulatory Liabilities [Member]
Regulatory liabilities
Remaining Amortization Period	Various thru 2043
Receiving Regulatory Treatment - Earning a Return	4,761	[1]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	64	[3]
Total regulatory liabilities	4,825		5,289
Sierra Pacific Power Company [Member] | Energy Efficiency Program Liability [Member]
Regulatory liabilities
Remaining Amortization Period	2014
Receiving Regulatory Treatment - Earning a Return	4,919	[1],[2]
Receiving Regulatory Treatment - Not Earning a Return	0
Pending Regulatory Treatment	0
Total regulatory liabilities	4,919		0
Sierra Pacific Power Company [Member] | Loss on Reacquired Debt [Member]
Regulatory assets
Remaining Amortization Period	Term of Related Debt
Receiving Regulatory Recovery - Earning a Return	29,090	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	29,090		32,450
Sierra Pacific Power Company [Member] | Deferred Income Tax Charges Assets [Member]
Regulatory assets
Remaining Amortization Period	Various
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	100,482
Pending Regulatory Review	0
Total regulatory assets	100,482		105,255
Sierra Pacific Power Company [Member] | Merger Costs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2046
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	95,352
Pending Regulatory Review	0
Total regulatory assets	95,352		100,456
Sierra Pacific Power Company [Member] | Pinon Pine [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2029
Receiving Regulatory Recovery - Earning a Return	25,805	[1]
Receiving Regulatory Recovery - Not Earning a Return	3,837
Pending Regulatory Review	0
Total regulatory assets	29,642		34,393
Sierra Pacific Power Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	8,191	[4]
Total regulatory assets	8,191		7,094
Sierra Pacific Power Company [Member] | Conservation Programs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2013
Receiving Regulatory Recovery - Earning a Return	10,575	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	4,799	[3]
Total regulatory assets	15,374		24,558
Sierra Pacific Power Company [Member] | Ely Energy Center [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	11,544	[4]
Total regulatory assets	11,544		11,593
Sierra Pacific Power Company [Member] | Legacy Meters [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	0	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	2,692	[4]
Total regulatory assets	2,692		0
Sierra Pacific Power Company [Member] | Renewable Energy Programs Regulatory Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	14,208	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	14,208		18,898
Sierra Pacific Power Company [Member] | Other Costs [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2031
Receiving Regulatory Recovery - Earning a Return	11,873	[1]
Receiving Regulatory Recovery - Not Earning a Return	3,426
Pending Regulatory Review	3,016	[3],[4]
Total regulatory assets	18,315		23,593
Sierra Pacific Power Company [Member] | Regulatory Assets Subtotal - excluding pensions [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	95,416	[1]
Receiving Regulatory Recovery - Not Earning a Return	203,097
Pending Regulatory Review	30,242
Total regulatory assets	328,755		365,139
Sierra Pacific Power Company [Member] | Pension Costs [Member]
Regulatory assets
Receiving Regulatory Recovery - Earning a Return	140,268	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	140,268		104,159
Sierra Pacific Power Company [Member] | Energy Efficiency Program Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	570	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	570		5,129
Sierra Pacific Power Company [Member] | Energy Efficiency Implementation Rate Asset [Member]
Regulatory assets
Remaining Amortization Period	Various thru 2014
Receiving Regulatory Recovery - Earning a Return	3,295	[1]
Receiving Regulatory Recovery - Not Earning a Return	0
Pending Regulatory Review	0
Total regulatory assets	$ 3,295		$ 1,720

[1] Earning a return includes either a carrying charge on the asset/liability balance, or a return as a component of rate base.

[2] Liability balance represents amounts that have been overcollected.

[3] Assets which are allowed to earn a carrying charge until included in rates. Reference Note 1, Summary of Significant Accounting Policies, Equity Carrying Charges

[4] Pending regulatory treatment includes either amounts which have prior regulatory precedent or have been approved and are subject to prudency review.