DEBT COVENANT AND OTHER RESTRICTIONS, Dividends (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended							3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	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]	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]
Dividends [Abstract]
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries				$ 184.0	$ 99.0	$ 20.0	$ 114.0
Dividend declaration date				Feb. 07, 2013		Feb. 07, 2013		Feb. 07, 2013
Dividend declared to parent company				$ 50.0
Common Stock, Dividends, Per Share, Declared	$ 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 Payable, Date of Record, Day, Month and Year								Mar. 05, 2013