INCOME TAXES (BENEFITS) (Details4) (USD $) In Millions, unless otherwise specified							12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Sierra Pacific Power Company [Member]	Dec. 31, 2010 Sierra Pacific Power Company [Member]	Dec. 31, 2011 Nevada Power Company [Member]	Dec. 31, 2010 Nevada Power Company [Member]	Dec. 31, 2011 Research [Member]	Dec. 31, 2011 Research [Member] Sierra Pacific Power Company [Member]	Dec. 31, 2011 Research [Member] Nevada Power Company [Member]	Dec. 31, 2011 General Business [Member]	Dec. 31, 2011 General Business [Member] Nevada Power Company [Member]	Dec. 31, 2011 Internal Revenue Service (IRS) [Member]	Dec. 31, 2011 Internal Revenue Service (IRS) [Member] Sierra Pacific Power Company [Member]	Dec. 31, 2011 Internal Revenue Service (IRS) [Member] Nevada Power Company [Member]
Operating loss and Tax Credit carryfowards [Line Items]
Deferred tax asset, Net operating loss carryforward												$ 456.5	$ 58.1	$ 343.7
Deferred tax asset, Tax credit carryforward							12.6	4.4	8.3	1.7	1.7
Deferred tax asset, Total net operating loss and tax credits	470.8	173.8	62.5	46.3	353.7	82.5
Valuation allowance, Net operating loss carryforward												0	0	0
Valuation allowance, Tax credit carryforward							0	0	0	1.2	1.2
Valuation allowance, Total net operating loss and tax credits	1.2		0		1.2
Net deferred tax asset, Net operating loss carryforward												456.5	58.1	343.7
Net deferred tax asset, Tax credit carryforward							12.6	4.4	8.3	0.5	0.5
Net deferred tax asset, Total net operating loss and tax credits	469.6		62.5		352.5
Expiration period, Net operating loss carryforward												2024-2031	2024-2031	2024-2031
Expiration period, Tax credit carryforward							2024-2031	2024-2031	2024-2031	2012-2016	2012-2016
Gross NOL carryover												$ 1,300.0	$ 166.0	$ 982.0