COMMITMENTS AND CONTINGENCIES, Environmental (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Environmental [Abstract]
Regional Haze	$ 77.1
Nevada Power Company [Member]
Environmental [Abstract]
Reclamation estimate of coal washing and load-out facility site	4.0
Nevada Power Company [Member] | Navajo Generating Station [Member]
Environmental [Abstract]
Ownership interest in generating stations (in hundredths)	11.30%
Regional Haze	1,100.0
Sierra Pacific Power Company [Member] | Valmy Generating Station [Member]
Environmental [Abstract]
Ownership interest in generating stations (in hundredths)	50.00%
Mercury Air Toxic Standards Costs	$ 6.4