ACQUISITIONS AND DISPOSITIONS - GAS Acquisitions and Dispositions Narrative (Details) $ in Millions		1 Months Ended			6 Months Ended		12 Months Ended
	Jul. 01, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($) payment	May 31, 2019 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 31, 2022 USD ($)	Apr. 22, 2021 USD ($)
Business Acquisition [Line Items]
Gain (loss) on dispositions							$ 176	$ 66	$ 2,588
Impairment charges							2	0	168
Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions							127	22	0
Impairment charges							0	0	115
Southern Company Gas | Triton
Business Acquisition [Line Items]
Realized loss on disposal				$ 6
Realized gain on disposal, net of tax				7
Reversal of federal income tax valuation allowance				$ 13					13
Sequent | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Consideration for sale	$ 159
Gain (loss) on dispositions	121						121
Gain (loss) on dispositions, after tax	$ 92						92
Deferred tax expense, increase from change in appointment rate					$ 85	$ 85	$ 85
Pivotal LNG | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions									(24)
Gain (loss) on dispositions, after tax									$ (17)
Cash proceeds from sale of business			$ 178
Number of contingent milestone payments | payment			2
Contingent milestone payment, amount											$ 5
Pivotal LNG | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas | Scenario, Forecast
Business Acquisition [Line Items]
Contingent milestone payment, amount										$ 5
Jefferson Island | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas | Natural Gas Storage Facility
Business Acquisition [Line Items]
Gain (loss) on dispositions		$ 22
Gain (loss) on dispositions, after tax		16
Cash proceeds from sale of business		$ 33
Impairment charges								91
Impairment charges, after tax								$ 69