CONTINGENCIES AND COMMITMENTS (Litigation and Regulatory Citations in Connection with the Butte Fire) (Details) $ in Millions						1 Months Ended		3 Months Ended
	Mar. 30, 2018 contractor	Mar. 02, 2018 USD ($)	Feb. 20, 2018 USD ($)	Apr. 25, 2017 USD ($) citation	Apr. 13, 2017 USD ($)	Apr. 30, 2018 USD ($)	May 31, 2017 USD ($)	Mar. 31, 2018 USD ($) household contractor complaint plaintiff	May 23, 2016 contractor	Apr. 28, 2016 a fatality structure outbuilding home comercial_property
Loss Contingencies [Line Items]
Number of vegetation management contractors dismissed from complaints (contractor) | contractor	2
Butte Fire
Loss Contingencies [Line Items]
Number of acres burned (acre) | a										70,868
Number of fatalities caused by fire (fatality) | fatality										2
Number of homes destroyed by fire (home) | home										549
Number of outbuildings damaged by fire (outbuilding) | outbuilding										368
Number of commercial properties damaged by fire (commercial property) | comercial_property										4
Number of structures damaged (structure) | structure										44
Number of vegetation management contractors (contractor) | contractor								2	2
Number of complaints filed (complaint) | complaint								79
Number of plaintiffs (plaintiff) | plaintiff								3,770
Number of households represented in court (household) | household								2,000
Number of master complaints (complaint) | complaint								2
Fire fighting costs recovery requested					$ 87.0
Value of claims brought against the company							$ 190.0
Number of households with inestimable losses | household								600
Cumulative legal expenses incurred								$ 99.0
Legal expenses incurred								12.0
Coverage for third party liability								922.0
Probable insurance recoveries								922.0
Cumulative reimbursements from insurance policies								60.0
Reimbursements from insurance policies								7.0
Number of citations (citation) | citation				2
Value of citations issued				$ 8.3
Butte Fire | Minimum
Loss Contingencies [Line Items]
Probable loss to be incurred								$ 1,100.0
Butte Fire | County Of Calaveras
Loss Contingencies [Line Items]
Value of claims brought against company		$ 167.0	$ 85.0
Subsequent Event | Butte Fire
Loss Contingencies [Line Items]
Cumulative reimbursements from insurance policies						$ 31.0