Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 13,341	$ 43,429	$ 13,341	$ 18,253
Charged to Income			55,770	39,959	31,074
Charged to Other Accounts			(248)	(1,257)	0
Acquisitions			30	40,629	0
Deductions (Note)			54,605	49,243	35,986
Balance at End of Period	$ 43,429		44,376	43,429	13,341
SOUTHERN Co GAS | Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	37,663		27,316
Charged to Income	9,500		28,022
Charged to Other Accounts	(1,257)		(248)
Deductions (Note)	18,590		27,286
Balance at End of Period	27,316	37,663	27,804	27,316
SOUTHERN Co GAS | Income tax valuation
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	19,182		19,182
Charged to Income	0		0
Charged to Other Accounts	0		0
Deductions (Note)	0		7,910
Balance at End of Period	19,182	19,182	11,272	19,182
MISSISSIPPI POWER CO
Movement in Valuation Allowances and Reserves [Roll Forward]
Retail rate recovery					371,000
MISSISSIPPI POWER CO | Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		287	494	287	825
Charged to Income			1,377	1,295	(1,994)
Charged to Other Accounts			0	0	0
Deductions (Note)			1,279	1,088	(1,456)
Balance at End of Period	494		592	494	287
ALABAMA POWER CO | Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		9,597	10,487	9,597	9,143
Charged to Income			9,367	11,310	13,500
Charged to Other Accounts			0	0	0
Deductions (Note)			11,075	10,420	13,046
Balance at End of Period	10,487		8,779	10,487	9,597
GEORGIA POWER CO | Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2,147	2,836	2,147	6,076
Charged to Income			11,250	14,476	16,862
Charged to Other Accounts			0	0	0
Deductions (Note)			11,474	13,787	20,791
Balance at End of Period	2,836		2,612	2,836	2,147
GULF POWER CO | Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		775	732	775	2,087
Charged to Income			2,859	2,946	2,041
Charged to Other Accounts			0	0	0
Deductions (Note)			2,846	2,989	3,353
Balance at End of Period	732		$ 745	732	775
Predecessor | SOUTHERN Co GAS | Provision for uncollectible accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	37,663	29,142		29,142	35,069
Charged to Income		15,976			27,050
Charged to Other Accounts		1,608			3,017
Deductions (Note)		9,063			35,994
Balance at End of Period		37,663			29,142
Predecessor | SOUTHERN Co GAS | Income tax valuation
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 19,182	19,182		$ 19,182	19,637
Charged to Income		0			0
Charged to Other Accounts		0			0
Deductions (Note)		0			455
Balance at End of Period		$ 19,182			$ 19,182