ACQUISITIONS AND DISPOSITIONS - SPC Acquisitions and Dispositions Narrative (Details) $ in Millions						1 Months Ended			12 Months Ended
		Jan. 17, 2020 USD ($)	Jun. 13, 2019 USD ($) MW	Dec. 11, 2018 wind_farm investor	May 22, 2018	Dec. 31, 2018 USD ($) wind_farm investor	Sep. 30, 2018 operating_facility	May 31, 2018 USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019 USD ($) facility MW	Dec. 31, 2018 USD ($)		Dec. 31, 2017 USD ($)	May 31, 2019 MW
Business Acquisition [Line Items]
Construction work in progress						$ 7,254					$ 7,880	$ 7,254
Impairment charges											168	210		$ 0
Assets held for sale						393					188	393
Sale of noncontrolling interests												1,273
Gain (loss) on dispositions											(2,569)	(291)		(40)
Southern Power
Business Acquisition [Line Items]
Construction work in progress						$ 430					515	430
Impairment charges											$ 3	156		$ 0
Sale of noncontrolling interests	[1]											1,273
Number of wind facilities | operating_facility							8
Southern Power | Mankato
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW											385				385
Southern Power | Series of Business Acquisitions
Business Acquisition [Line Items]
Number of facilities under construction | facility											2
Construction work in progress											$ 417
Southern Power | Minimum | Series of Business Acquisitions
Business Acquisition [Line Items]
Aggregate construction costs											490
Southern Power | Maximum | Series of Business Acquisitions
Business Acquisition [Line Items]
Aggregate construction costs											535
Wind Generating Facility | Southern Power
Business Acquisition [Line Items]
Impairment charges												36
Assets held for sale											$ 17
Scenario, Forecast | Wind Generating Facility | Southern Power
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage									80.00%	100.00%
SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership					33.00%
Distribution made to limited partner, cash distributions paid, percentage											67.00%
SP Solar Holdings I, LP | SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership								33.00%
Proceeds from sale of equity method investments								$ 1,200
Sale of noncontrolling interests								511
SP Wind
Business Acquisition [Line Items]
Number of wind facilities | wind_farm				8		8
SP Wind | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership				100.00%
Number of financial investors | investor				3
Distribution made to limited partner, cash distributions paid, percentage											60.00%
SP Wind | Financial Investors
Business Acquisition [Line Items]
Distribution made to limited partner, cash distributions paid, percentage						40.00%					40.00%
Allocation of tax attributes to limited partner						99.00%
SP Wind | SP Wind | Southern Power
Business Acquisition [Line Items]
Proceeds from sale of equity method investments						$ 1,200
Number of financial investors | investor						3
Common stockholders' equity | Southern Power
Business Acquisition [Line Items]
Sale of noncontrolling interests								(410)				$ (417)	[1]
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Florida Plants | Southern Power
Business Acquisition [Line Items]
Cash proceeds from sale of business						$ 203
Asset impairment charge								119
After tax impairment charges								$ 89
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Nacogdoches Biomass-Fueled Facility | Southern Power
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW			115
Consideration for sale			$ 461
Gain (loss) on dispositions			23
Gain on dispositions, after tax			$ 88
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Mankato | Southern Power
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW											385
Subsequent Event | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Mankato | Southern Power
Business Acquisition [Line Items]
Consideration for sale		$ 663
Gain (loss) on dispositions		39
Gain on dispositions, after tax		$ 23

[1] See Note 15 under "Southern Power - Sales of Renewable Facility Interests" for additional information.