COMMITMENTS, GUARANTEES AND CONTINGENCIES - Clean Air Act and Climate Change (Details) T in Millions	12 Months Ended
	Dec. 31, 2020 phase T	Nov. 12, 2014
Loss Contingencies [Line Items]
Proposed reduction in power plants carbon pollution (percent)	90.00%
National Ambient Air Quality Standards
Loss Contingencies [Line Items]
Capping of SO2 Emissions Under CSAPR	2.4
Capping of NOx emissions under CSAPR	1.2
National Ambient Air Quality Standards | CSAPR
Loss Contingencies [Line Items]
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides | phase	2
Minimum | Climate Change
Loss Contingencies [Line Items]
Reduction in emissions (percent)		26.00%
Maximum | Climate Change
Loss Contingencies [Line Items]
Reduction in emissions (percent)		28.00%