ACQUISITIONS AND DISPOSITIONS - Southern Power Narrative (Details) $ in Millions		1 Months Ended			3 Months Ended	12 Months Ended
	Jan. 17, 2020 USD ($)	Jun. 30, 2019 USD ($) MW	Dec. 31, 2018 USD ($) investor wind_farm	May 31, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2021	Dec. 31, 2020 USD ($) agreement	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) investor wind_farm operating_facility	Mar. 31, 2020 MW	May 31, 2019 MW
Business Acquisition [Line Items]
Construction work in progress							$ 8,697	$ 7,880
Impairment charges							0	168	$ 210
(Gain) loss on dispositions, net							65	2,569	291
Sale of noncontrolling interests							65		1,273
Purchase of membership interests from noncontrolling interests							60
Gain (loss) on dispositions							$ 66	2,588	301
Southern Power
Business Acquisition [Line Items]
Approximate nameplate capacity (in MW) | MW										300
Number of Power Purchase Agreements | agreement							2
Construction work in progress							$ 127	515
Impairment charges							0	3	156
(Gain) loss on dispositions, net							39	23	2
Sale of noncontrolling interests							65		$ 1,273
Purchase of membership interests from noncontrolling interests							60
Number of wind facilities | operating_facility									8
Gain (loss) on dispositions							39	24	$ 3
Southern Power | Series of Business Acquisitions
Business Acquisition [Line Items]
Construction work in progress							34
Southern Power | Minimum | Series of Business Acquisitions
Business Acquisition [Line Items]
Aggregate construction costs							392
Southern Power | Maximum | Series of Business Acquisitions
Business Acquisition [Line Items]
Aggregate construction costs							$ 460
SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership									33.00%
SP Wind | Southern Power
Business Acquisition [Line Items]
Sale of equity interest in limited partnership									100.00%
Wind Generating Facility | Southern Power
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage							100.00%
Impairment charges									$ 36
(Gain) loss on dispositions, net							$ 0	$ 17
Scenario, Forecast | Wind Generating Facility | Southern Power
Business Acquisition [Line Items]
Project qualification for production tax credits, percentage						80.00%
SP Solar Holdings I, LP | Southern Power
Business Acquisition [Line Items]
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]
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							$ (2)		$ (417)
Purchase of membership interests from noncontrolling interests				$ 410			$ (5)
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
Asset impairment charge, after tax					$ 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 (loss) 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
Consideration for sale	$ 663
Gain (loss) on dispositions	39
Gain (loss) on dispositions, after tax	$ 23