COMMITMENTS AND CONTINGENCIES, Litigation Contingencies and Other Commitments (Details) (USD $)	9 Months Ended
	Sep. 30, 2012 MW
Capital Projects [Member]
ON Line TUA [Abstract]
Capacity of interconnection (in kV)	500
Utilities' aggregate share in transmission line project (in hundredths)	25.00%
GBT-South's share in the ON Line project (in hundredths)	75.00%
Nevada Power Company [Member]
Royalty claim [Abstract]
Damages sought in DC Lawsuit	$ 600,000,000
Minimum punitive damages sought in DC Lawsuit	1,000,000,000
% Owned (in hundredths)	11.00%
Nevada Power Company [Member] | Capital Projects [Member]
ON Line TUA [Abstract]
Capitalized construction costs	241,100,000
Sierra Pacific Power Company [Member]
Farad Dam [Abstract]
Number of hydro generating units sold	four
Total capacity of hydro generating units sold (in MW)	10.3
Proceeds from sale of hydro units	8,000,000
Capacity of the Farad Hydro generating unit (in MW)	2.8
Estimate to rebuild diversion dam of the Farad Hydro generating unit	20,000,000
Amount entitled to be recovered for costs incurred to date on Farad Dam	4,000,000
Duration to rebuild the Farad dam from the date of the Court's decision	three years
Replacement cost of Farad Dam	19,800,000
Cash Value Of Insurance	1,300,000
Sierra Pacific Power Company [Member] | Capital Projects [Member]
ON Line TUA [Abstract]
Capitalized construction costs	$ 12,700,000