VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Millions		12 Months Ended
	May 29, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 50	$ 44	$ 43
Charged to Income		68	69	56
Charged to Other Accounts		0	(1)	0
Deductions		69	61	55
Reclassified to Held for Sale		0	1	0
Balance at End of Period		49	50	44
Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		100	148	22
Charged to Income		13	(38)	126
Charged to Other Accounts		0	0	0
Deductions		0	10	0
Reclassified to Held for Sale		0	0	0
Balance at End of Period		113	100	148
Alabama Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		10	9	10
Charged to Income		24	13	10
Charged to Other Accounts		0	0	0
Deductions		12	12	11
Balance at End of Period		22	10	9
Georgia Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2	3	3
Charged to Income		13	11	11
Charged to Other Accounts		0	0	0
Deductions		13	12	11
Balance at End of Period		2	2	3
Georgia Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		33	0	0
Charged to Income		(5)	39	0
Charged to Other Accounts		0	0	0
Deductions		0	6	0
Balance at End of Period		28	33	0
Mississippi Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1	1	0
Charged to Income		2	1	2
Charged to Other Accounts		0	0	0
Deductions		2	1	1
Balance at End of Period		1	1	1
Mississippi Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		32	124	0
Charged to Income		0	(92)	124
Charged to Other Accounts		0	0	0
Deductions		0	0	0
Balance at End of Period		32	32	124
Southern Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		22	10	0
Charged to Income		7	12	10
Charged to Other Accounts		0	0	0
Deductions		0	0	0
Balance at End of Period		29	22	10
Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		30	28	27
Charged to Income		29	33	28
Charged to Other Accounts		0	(1)	0
Deductions		41	30	27
Balance at End of Period		18	30	28
Southern Company Gas | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		12	11	19
Charged to Income		(8)	1	0
Charged to Other Accounts		0	0	0
Deductions		0	0	8
Balance at End of Period		4	$ 12	$ 11
Triton | Southern Company Gas
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Reversal of federal income tax valuation allowance	$ 13
State and Local Jurisdiction | Georgia Power
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance		28
State and Local Jurisdiction | Southern Company Gas
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation allowance		$ 5