COMMITMENTS AND CONTINGENCIES (Details) (USD $)	9 Months Ended
	Sep. 30, 2011
Litigation Contingencies [Abstract]
Proceeds from Sale of hydro units	$ 8,000,000
ON Line TUA [Abstract]
Capacity Of Interconnection	500
Utilities' aggregate share transmission line project	25.00%
GBT-South's share in the ON Line project (in hundredths)	75.00%
Capitalized construction costs	110,000,000
Total Estimated On Line Construction Costs	556,000,000
NPC [Member]
Environmental [Abstract]
Reclamation estimate of coal washing and load-out facility site	5,000,000
Litigation Contingencies [Abstract]
Damages sought in DC Lawsuit	600,000,000
Minimum punitive damages sought in DC Lawsuit	1,000,000,000
ON Line TUA [Abstract]
Capitalized construction costs	105,200,000
NPC [Member] | Navajo Generating Station [Member]
Investments in Generating Stations Involved in Litigation [Line Items]
Ownership interest in the generating stations (in hundredths)	11.00%
NPC [Member] | Mohave Generating Station [Member]
Investments in Generating Stations Involved in Litigation [Line Items]
Ownership interest in the generating stations (in hundredths)	14.00%
SPPC [Member]
Environmental [Abstract]
Third party ownership percentage in Valmy Generating Station (in hundredths)	50.00%
Litigation Contingencies [Abstract]
Number of hydro generating units sold	4
Total capacity of hydro generating units sold (in MW)	2.8
Capacity of the Farad Hydro generating unit (in MW)	10.3
Estimate to rebuild the diversion dam of the Farad Hydro generating unit	20,000,000
Amount entitled to recovered for costs incurred to date on Farad Dam	4,000,000
Duration period to rebuild the Farad dam from the date of the Court's decision	three
Amount of actual cash value entitled to if Farad Dam is not rebuilt	1,300,000
ON Line TUA [Abstract]
Capitalized construction costs	$ 4,800,000