CONTINGENCIES, COMMITMENTS, AND GUARANTEES - SPC Litigation (Details) - Southern Power - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019
Loss Contingencies [Line Items]
Construction contract payment withheld		$ 26
Gain on funds received in excess of initial replacement costs, net of allocation to noncontrolling interests, net of tax	$ 12
RE Roserock, LLC
Loss Contingencies [Line Items]
Noncontrolling ownership percentage held by parent		51.00%