Segment and Related Information - Financial Data for Business Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Operating revenues	$ 5,430	$ 4,459	$ 11,202	$ 8,451
Segment net income	(1,381)	623	(723)	1,112
Total assets	108,684		108,684		$ 109,697
Kemper IGCC
Segment Reporting Information [Line Items]
Pre-tax charge to income	3,000	81	3,100	134
After tax charge to income	2,100	50	2,200	83
Plant Scherer Unit 3
Segment Reporting Information [Line Items]
After tax charge to income			20
Loss on Plant Scherer Unit 3			33
Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,585	4,379	8,716	8,360
Segment net income	(1,360)	688	(859)	1,203
Total assets	85,889		85,889		86,994
Intersegment Eliminations | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	(101)	(109)	(206)	(212)
Segment net income	0	0	0	0
Total assets	(317)		(317)		(316)
Consolidation Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(37)	(45)	(79)	(81)
Segment net income	(2)	(4)	0	(7)
Total assets	(1,362)		(1,362)		(1,624)
Traditional Electric Operating Companies | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	4,157	4,115	7,943	7,884
Segment net income	(1,442)	599	(1,010)	1,064
Total assets	71,503		71,503		72,141
SOUTHERN POWER CO | Electric Utilities
Segment Reporting Information [Line Items]
Operating revenues	529	373	979	688
Segment net income	82	89	151	139
Total assets	14,703		14,703		15,169
SOUTHERN Co GAS | Natural Gas
Segment Reporting Information [Line Items]
Operating revenues	716		2,276
Segment net income	49		288
Total assets	21,809		21,809		21,853
All Other
Segment Reporting Information [Line Items]
Operating revenues	166	125	289	172
Segment net income	(68)	(61)	(152)	(84)
Total assets	2,348		2,348		2,474
SOUTHERN POWER CO
Segment Reporting Information [Line Items]
Operating revenues	529	373	979	688
Segment net income	82	89	151	139
Total assets	14,703		14,703		15,169
SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues	716		2,276
Segment net income	49		288
Total assets	21,809		21,809		21,853
SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	769		2,393
Segment net income	50		282
Total assets	23,720		23,720		24,875
SOUTHERN Co GAS | Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues	(56)		(122)
Segment net income	0		0
Total assets	(13,093)		(13,093)		(14,167)
SOUTHERN Co GAS | Gas distribution operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	603		1,783
Segment net income	54		171
Total assets	18,257		18,257		19,453
SOUTHERN Co GAS | Gas marketing services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	166		454
Segment net income	4		35
Total assets	2,093		2,093		2,084
SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	(12)		119
Segment net income	(17)		51
Total assets	989		989		1,127
Less Gross Gas Costs	1,666		3,510
SOUTHERN Co GAS | Gas Midstream Operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	12		37
Segment net income	9		25
Total assets	2,381		2,381		2,211
SOUTHERN Co GAS | All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	3		5
Segment net income	(1)		6
Total assets	11,182		11,182		$ 11,145
Predecessor | SOUTHERN Co GAS
Segment Reporting Information [Line Items]
Operating revenues		571		1,905
EBIT		(24)		328
Segment net income		(51)		131
Predecessor | SOUTHERN Co GAS | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		611		2,003
EBIT		30		388
Predecessor | SOUTHERN Co GAS | Intersegment Eliminations
Segment Reporting Information [Line Items]
Operating revenues		(42)		(102)
EBIT		1		0
Predecessor | SOUTHERN Co GAS | Gas distribution operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		547		1,575
EBIT		118		353
Predecessor | SOUTHERN Co GAS | Gas marketing services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		149		435
EBIT		29		109
Predecessor | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		(95)		(32)
EBIT		(112)		(68)
Less Gross Gas Costs		1,214		2,675
Predecessor | SOUTHERN Co GAS | Gas Midstream Operations | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		10		25
EBIT		(5)		(6)
Predecessor | SOUTHERN Co GAS | All Other | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		2		4
EBIT		(55)		(60)
Third Party Gross Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	1,531		3,370
Third Party Gross Revenues | Predecessor | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		1,061		2,500
Intercompany Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	123		259
Intercompany Revenues | Predecessor | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		58		143
Total Gross Revenues | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues	$ 1,654		$ 3,629
Total Gross Revenues | Predecessor | SOUTHERN Co GAS | Wholesale Gas Services | Operating Segments
Segment Reporting Information [Line Items]
Operating revenues		$ 1,119		$ 2,643