OTHER CONTINGENCIES AND COMMITMENTS (Interim Rate Relief Subject to Refund) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($) catastrophicEvent	Jul. 02, 2021 USD ($)	Jan. 08, 2021 USD ($)	Sep. 30, 2020 USD ($)	May 04, 2020 USD ($)	Aug. 07, 2019 USD ($)	Apr. 25, 2019 USD ($)	Mar. 30, 2018 USD ($) catastrophicEvent
Loss Contingencies [Line Items]
Expenses and capital expenditures, disallowed costs	$ 1,625.0
CEMA Interim Rate Relief
Loss Contingencies [Line Items]
Cost recovery							$ 373.0
Revised cost recovery, increase to revenue requirement			$ 5.6		$ 757.0	$ 669.0
CEMA Interim Rate Relief | Subsequent event
Loss Contingencies [Line Items]
Revised cost recovery, decrease to revenue requirement per audit		$ 2.4
CEMA Interim Rate Relief | Mid 2016 - Early 2017
Loss Contingencies [Line Items]
Cost recovery								$ 183.0
Number of catastrophic events | catastrophicEvent								7
CEMA Interim Rate Relief | 2016 to 2017
Loss Contingencies [Line Items]
Cost recovery								$ 405.0
WMCE Interim Rate Relief
Loss Contingencies [Line Items]
Number of catastrophic events | catastrophicEvent	10
Expenses and capital expenditures, disallowed costs				$ 1,180.0
Expenses and capital expenditures, capital expenditures				801.0
Cost recovery, increase to revenue requirement				$ 1,280.0
Approved interim rate relief	$ 447.0
Interim rate relief remaining	$ 868.0
Interim rate relief remaining, period	1 year
Approved interim rate relief, subject to refund	$ 447.0
WMCE Interim Rate Relief | Fire hazard prevention memorandum account
Loss Contingencies [Line Items]
Cost recovery	293.0
WMCE Interim Rate Relief | Fire risk and wildfire mitigation memorandum account
Loss Contingencies [Line Items]
Cost recovery	740.0
WMCE Interim Rate Relief | Catastrophic event memorandum account
Loss Contingencies [Line Items]
Cost recovery	$ 251.0