COMMON STOCK AND OTHER PAID-IN CAPITAL (Details) (USD $)	12 Months Ended			3 Months Ended									12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2013 Parent Company [Member]	Dec. 31, 2012 Parent Company [Member]	Sep. 30, 2012 Parent Company [Member]	Jun. 30, 2012 Parent Company [Member]	Mar. 31, 2012 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Sep. 30, 2011 Parent Company [Member]	Jun. 30, 2011 Parent Company [Member]	Mar. 31, 2011 Parent Company [Member]	Dec. 31, 2012 Nevada Power Company [Member]	Dec. 31, 2011 Nevada Power Company [Member]	Dec. 31, 2012 Sierra Pacific Power Company [Member]	Dec. 31, 2011 Sierra Pacific Power Company [Member]	Dec. 31, 2012 Non Employee Director Stock Plan [Member]	Dec. 31, 2011 Non Employee Director Stock Plan [Member]	Dec. 31, 2010 Non Employee Director Stock Plan [Member]	Dec. 31, 2012 Common Stock Investment Plan [Member]	Dec. 31, 2012 Employee Stock Purchase Plan [Member]
Warrants and Rights Note Disclosure [Abstract]
Period from adoption that rights plan shall expire, if plan is adopted without prior shareholder approval (in years)	one year
Stock Ownership Plans [Abstract]
Shares of common stock reserved for issuance under the Stock Plans (in shares)	14,050,162
Maximum employee percentage deduction for ESPP purchases (in hundredths)																					15.00%
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date																					85.00%
Non-Employee Director Stock [Abstract]
Annual retainer for non-employee directors	$ 135,000
Minimum amount of retainer to be paid in stock	75,000
Granted shares to non-employee directors (in shares)																	43,808	49,002	65,933
Share based compensation granted to non-employee directors																	748,248	745,879	829,074
Common Stock Investment Plan [Abstract]
Minimum initial purchase for new investors																				250
Minimum purchase amount for existing shareholders																				50
Dividend reinvestment increments (in hundredths)																				10.00%
Dividends Payable [Line Items]
Dividends Declared Per Share of Common Stock	$ 0.64	$ 0.49	$ 0.45	$ 0.19	$ 0.17	$ 0.17	$ 0.17	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.12
Dividends [Abstract]
Declaration date				Feb. 07, 2013									Feb. 07, 2013		Feb. 07, 2013
Dividends Payable, Date to be Paid, Day, Month and Year				Mar. 20, 2013
Dividends Payable, Date of Record, Day, Month and Year				Mar. 05, 2013
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries													184,000,000	99,000,000	20,000,000	114,000,000
Dividend declared to parent company													50,000,000
Common stock repurchaed (shares)	1,100,000
Common stock repurchased	$ (19,931,000)