DERIVATIVES (Volumes of Outstanding Derivative Contracts) (Details)	Dec. 31, 2019 MMBTU MWh	Dec. 31, 2018 MMBTU MWh
Forwards and Swaps | Natural Gas (MMBtus)
Derivative [Line Items]
Contract Volume | MMBTU	131,896,159	177,750,349
Forwards and Swaps | Electricity (Megawatt-hours)
Derivative [Line Items]
Contract Volume | MWh	18,675,852	3,833,490
Options | Natural Gas (MMBtus)
Derivative [Line Items]
Contract Volume | MMBTU	14,720,000	13,735,405
Congestion revenue rights | Electricity (Megawatt-hours)
Derivative [Line Items]
Contract Volume | MWh	308,467,999	340,783,089