ACQUISITIONS AND DISPOSITIONS - GAS Acquisitions and Dispositions Narrative (Details)			1 Months Ended		3 Months Ended					12 Months Ended
	Feb. 07, 2020 USD ($) payment	May 29, 2019 USD ($)	Jul. 31, 2018 USD ($) utility	Jun. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Impairment charges					$ 0
Gain (loss) on dispositions										$ (2,569,000,000)	$ (291,000,000)	$ (40,000,000)
Southern Company Gas
Business Acquisition [Line Items]
Impairment charges					$ 0					115,000,000	42,000,000	0
Number of natural gas distribution utilities sold | utility			3
Gain (loss) on dispositions										0	$ (291,000,000)	$ 0
Southern Company Gas | Triton
Business Acquisition [Line Items]
Realized loss on disposal		$ 6,000,000
Realized gain on disposal, net of tax		7,000,000
Reversal of federal income tax valuation allowance		$ 13,000,000
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions, after tax						$ (15,000,000)	$ 40,000,000	$ (76,000,000)
Gain (loss) on dispositions						$ (27,000,000)	$ 353,000,000	$ (36,000,000)
Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business				$ 365,000,000
Gain (loss) on dispositions, after tax				(67,000,000)						(17,000,000)
Tax on sale of business				$ 34,000,000
Impairment charges									$ 42,000,000	42,000,000
Gain (loss) on dispositions										$ (24,000,000)
Elizabethtown Gas and Elkton Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Gain (loss) on dispositions, after tax			$ 0
Tax on sale of business			$ 205,000,000
Number of natural gas distribution utilities sold | utility			2
Proceeds from sale of oil and gas property and equipment			$ 1,700,000,000
Florida City Gas | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business			587,000,000
Gain (loss) on dispositions, after tax			16,000,000
Tax on sale of business			$ 103,000,000
Subsequent Event | Southern Company Gas | Pivotal LNG And Atlantic Coast Pipeline
Business Acquisition [Line Items]
Number of contingent milestone payments | payment	2
Contingent milestone payment, amount	$ 5,000,000
Subsequent Event | Pivotal Home Solutions | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Southern Company Gas
Business Acquisition [Line Items]
Cash proceeds from sale of business	$ 165,000,000