CONTINGENCIES AND COMMITMENTS (Schedule of Loss Accrual) (Details) - Butte Fire - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingency Accrual [Roll Forward]
Loss accrual, beginning balance	$ 561	$ 690	$ 0
Accrued losses	0	350	750
Payments	(201)	(479)	(60)
Loss accrual, ending balance	360	$ 561	$ 690
Settlement agreements entered	783
Settlement agreement paid	$ 740