Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 13	$ 44	$ 43	$ 13
Charged to Income			69	56	40
Charged to Other Accounts			(1)	0	(1)
Acquisitions			0	0	41
Deductions			61	55	50
Reclassified to Held for Sale			1	0	0
Balance at End of Period	$ 43		50	44	43
Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2	148	22	2
Charged to Income			(38)	126	0
Charged to Other Accounts			0	0	0
Acquisitions			0	0	20
Deductions			10	0	0
Reclassified to Held for Sale			0	0	0
Balance at End of Period	22		100	148	22
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	10
Charged to Income			13	10	11
Charged to Other Accounts			0	0	0
Deductions			12	11	11
Balance at End of Period	10		10	9	10
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	2
Charged to Income			11	11	15
Charged to Other Accounts			0	0	0
Deductions			12	11	14
Balance at End of Period	3		2	3	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		0	0	0	0
Charged to Income			39	0	0
Charged to Other Accounts			0	0	0
Deductions			6	0	0
Balance at End of Period	0		33	0	0
Mississippi Power | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	1	0	0
Charged to Income			1	2	1
Charged to Other Accounts			0	0	0
Deductions			1	1	1
Balance at End of Period	0		1	1	0
Mississippi Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	124	0	0
Charged to Income			(92)	124	0
Charged to Other Accounts			0	0	0
Deductions			0	0	0
Balance at End of Period	0		32	124	0
Southern Power | Tax valuation allowance (net state)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	10	0	0
Charged to Income			12	10	0
Charged to Other Accounts			0	0	0
Deductions			0	0	0
Balance at End of Period	0		22	10	0
Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	38		28	27
Charged to Income	9		33	28
Charged to Other Accounts	(1)		(1)	0
Deductions	19		30	27
Balance at End of Period	27	38	30	28	27
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	19		11	19
Charged to Income	0		1	0
Charged to Other Accounts	0		0	0
Deductions	0		0	8
Balance at End of Period	19	19	$ 12	$ 11	19
Predecessor | Southern Company Gas | Provision for uncollectible accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	38	29			29
Charged to Income		16
Charged to Other Accounts		2
Deductions		9
Balance at End of Period		38
Predecessor | 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	$ 19	19			$ 19
Charged to Income		0
Charged to Other Accounts		0
Deductions		0
Balance at End of Period		$ 19