RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES - Part 1 (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Assets	$ 110,498	$ 67,030
(Liabilities)	(349,018)	(231,537)
Derivative, Net Liability Position, Aggregate Fair Value	0
Cash posted - offsetting derivative net liability positions under master-netting arrangements	35,100
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	107,461	67,030
(Liabilities)	(345,980)	(231,537)
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	3,037	0
(Liabilities)	(3,038)	0
Natural Gas Pipelines
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	0	0
Other Current Assets [Member] \| Commodity contracts \| Financial contracts \| Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	107,461	64,858
(Liabilities)	(142,573)	(26,997)
Other Current Assets [Member] \| Commodity contracts \| Financial contracts \| Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	3,037	0
(Liabilities)	(3,038)	0
Other Current Liabilities [Member] \| Interest Rate Contracts \| Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	0	0
(Liabilities)	0	(90,161)
Other Deferred Credits \| Commodity contracts \| Financial contracts \| Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	0	1,591
(Liabilities)	0	(2,599)
Other Deferred Credits \| Interest Rate Contracts \| Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	0	581
(Liabilities)	$ (203,407)	(111,780)
Interest Rate Contracts \| LIBOR Based Interest Payments [Member] \| Cash Flow Hedging [Member] \| Forward contracts
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		$ 1,300,000

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

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