DERIVATIVES (Volumes of Outstanding Derivative Contracts, in Megawatt Hours Unless Otherwise Specified) (Details)	Jun. 30, 2020 MMBTU MWh	Dec. 31, 2019 MWh MMBTU
Forwards, Futures and Swaps | Natural Gas
Derivative [Line Items]
Contract Volume (mmbtu and mwh) | MMBTU	199,547,057	131,896,159
Forwards, Futures and Swaps | Electricity
Derivative [Line Items]
Contract Volume (mmbtu and mwh)	9,754,771	18,675,852
Options | Natural Gas
Derivative [Line Items]
Contract Volume (mmbtu and mwh) | MMBTU	33,810,000	14,720,000
Options | Electricity
Derivative [Line Items]
Contract Volume (mmbtu and mwh)	1,620,000	0
Congestion Revenue Rights | Electricity
Derivative [Line Items]
Contract Volume (mmbtu and mwh)	287,183,280	308,467,999