COMMITMENTS AND CONTINGENCIES (Narrative) (Details) $ in Thousands	1 Months Ended				3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017 item	Mar. 31, 2016 mi	May 31, 2007 entity mi	Sep. 30, 2020 item	Jun. 30, 2021 USD ($) item defendant	Dec. 31, 2020 USD ($)	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Asset retirement obligations | $						$ 286,435	$ 283,163	$ 285,401	$ 263,748	$ 263,445	$ 210,323
Number of groundwater extraction wells | item		2
Contingency loss | $						0
Lease liabilities | $						$ 487,962	$ 442,737		$ 443,725
Parent Company [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	15.00%						15.00%
Texas Brine [Member]
Loss Contingencies [Line Items]
Number of pipeline cases | item						3
Number of defendants | defendant						3
New York Water District Cases [Member]
Loss Contingencies [Line Items]
Number of cases | item						27
Cooperating Parties Group [Member]
Loss Contingencies [Line Items]
Number of other companies to perform a Remedial Investigation/ Feasibility Study related to the Lower Passaic River Clean-Up lawsuit | entity				70
Number of miles of the River used in the Remedial Investigation/Feasibility Study | mi				17
Number of miles for bank-to-bank dredging remedy | mi			8
Texas Brine and Occidental Chemical Co [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage							20.00%
Occidental Chemical Co [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	50.00%						30.00%
Texas Brine [Member]
Loss Contingencies [Line Items]
Judge ruled allocation of fault among defendants, percentage	35.00%						55.00%
Number of cases | item						2
LADWP [Member]
Loss Contingencies [Line Items]
Number of planned new treatment capabilities | item					2
Maximum [Member] | EPA [Member]
Loss Contingencies [Line Items]
Estimated implementation costs | $						$ 1,380,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Outstanding standby letters of credit | $						$ 57,285