REGULATORY MATTERS - Schedule of SO Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions			12 Months Ended
	Jan. 01, 2020	Oct. 01, 2019	Dec. 31, 2019	Dec. 31, 2018
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 3,838	$ 720
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue			34 years
Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 3,507	2,378
Customer refund liability, current			105
Customer refund			$ 55
Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue			33 years
Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (1,874)	(1,872)
Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 810	(769)
Regulatory amortization period		5 years
Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Life of new issue			30 years
Deferred income tax credits
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (6,301)	(6,455)
Deferred tax liabilities			$ 778
Deferred income tax credits | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liability amortization period			6 years
Deferred income tax credits | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (3,078)	(3,080)
Deferred income tax credits | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(874)	(940)
Deferred income tax credits | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(1,960)	(2,027)
Other cost of removal obligations
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(2,084)	(2,297)
Other cost of removal obligations | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(1,606)	(1,585)
Other cost of removal obligations | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(412)	(497)
Customer refunds
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(285)	(293)
Customer refunds | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(229)	(165)
Customer refund liability, current			105	55
Over recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(205)	(47)
Over recovered regulatory clause revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(82)	(43)
Property damage reserves-liability
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(204)	(76)
Other regulatory liabilities
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (86)	(132)
Other regulatory liabilities | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory liability amortization period			20 years
Other regulatory liabilities | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (16)	(7)
Other regulatory liabilities | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (22)	(46)
Other regulatory liabilities | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			20 years
Other regulatory liabilities | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ (19)	(12)
Customer refunds - RSE portion | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			53	109
Customer refunds | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			110	100
Customer refunds | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			(56)	(142)
Retiree benefit plans
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			4,423	3,658
Regulatory asset			$ 23
Retiree benefit plans | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			15 years
Retiree benefit plans | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 1,516	1,295
Retiree benefit plans | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			13 years
Retiree benefit plans | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 167	161
Retiree benefit plans | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			15 years
Retiree benefit plans | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 1,131	947
Retiree benefit plans | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			14 years
Asset retirement obligations-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 4,381	2,933
Asset retirement obligations-asset | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			3,119	2,644
Asset retirement obligations-asset | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			1,043	147
Remaining net book value of retired assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 1,275	211
Remaining net book value of retired assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			18 years
Remaining net book value of retired assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 596	127
Remaining net book value of retired assets | Georgia Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			3 years
Remaining net book value of retired assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			18 years
Deferred income tax charges
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 803	799
Deferred income tax charges | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			80 years
Deferred income tax charges | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 523	522
Deferred tax liabilities			660
Deferred income tax charges | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 245	241
Regulatory amortization period			53 years
Deferred income tax charges | Alabama Power | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			53 years
Property damage reserves-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 410	416
Environmental remediation-asset
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			349	366
Loss on reacquired debt
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			323	346
Loss on reacquired debt | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			262	277
Loss on reacquired debt | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			52	56
Under recovered regulatory clause revenues
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			254	407
Under recovered regulatory clause revenues | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 72	90
Regulatory amortization period			6 years
Under recovered regulatory clause revenues | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 142	142
Vacation pay
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 186	182
Regulatory amortization period			1 year
Vacation pay | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 93	91
Regulatory amortization period			1 year
Vacation pay | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 11	11
Regulatory amortization period			1 year
Vacation pay | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 72	71
Regulatory amortization period			1 year
Long-term debt fair value adjustment
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 107	121
Long-term debt fair value adjustment | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 107	121
Long-term debt fair value adjustment | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			19 years
Other regulatory assets
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 492	581
Other regulatory assets | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			8 years
Other regulatory assets | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 50	120
Regulatory amortization period			24 months
Other regulatory assets | Southern Company Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 68	59
Other regulatory assets | Southern Company Gas | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			8 years
Other regulatory assets | Alabama Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Total regulatory assets (liabilities), net			$ 67	$ 57
Regulatory amortization period			12 months
Asset Group 1 | Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory amortization period			6 years
Subsequent Event | Major storms | Georgia Power
Schedule of Regulatory Assets and Liabilities [Line Items]
Recoveries for storm damage	$ 213