INCOME TAXES (BENEFITS) (Details4) (USD $) In Millions, unless otherwise specified							12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Sierra Pacific Power Company [Member]	Dec. 31, 2011 Sierra Pacific Power Company [Member]	Dec. 31, 2012 Nevada Power Company [Member]	Dec. 31, 2011 Nevada Power Company [Member]	Dec. 31, 2012 Research [Member]	Dec. 31, 2012 Research [Member] Sierra Pacific Power Company [Member]	Dec. 31, 2012 Research [Member] Nevada Power Company [Member]	Dec. 31, 2012 General Business [Member]	Dec. 31, 2012 General Business [Member] Nevada Power Company [Member]	Dec. 31, 2012 Internal Revenue Service (IRS) [Member]	Dec. 31, 2012 Internal Revenue Service (IRS) [Member] Sierra Pacific Power Company [Member]	Dec. 31, 2012 Internal Revenue Service (IRS) [Member] Nevada Power Company [Member]
Operating loss and Tax Credit carryfowards [Line Items]
Deferred tax asset, Net operating loss carryforward												$ 369.3	$ 56.4	$ 253.3
Deferred tax asset, Tax credit carryforward							13.6	4.7	8.9	2.0	2.0
Deferred tax asset, Total net operating loss and tax credits	384.9	470.8	61.1	62.5	264.2	353.7
Valuation allowance, Net operating loss carryforward												0	0	0
Valuation allowance, Tax credit carryforward							0	0	0	1.5	1.5
Valuation allowance, Total net operating loss and tax credits	1.5		0		1.5
Net deferred tax asset, Net operating loss carryforward												369.3	56.4	253.3
Net deferred tax asset, Tax credit carryforward							13.6	4.7	8.9	0.5	0.5
Net deferred tax asset, Total net operating loss and tax credits	383.4		61.1		262.7
Expiration period, Net operating loss carryforward												2028-2032	2028-2032	2028-2032
Expiration period, Tax credit carryforward							2028-2032	2028-2032	2028-2032	2013-2017	2013-2017
Gross NOL carryover												$ 1,100.0	$ 161.1	$ 723.7