Segment and Related Information - Financial Data for Business Segments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) state	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) state utilitiy	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of States in which Entity Operates | state	4		4
Operating revenues	$ 6,264	$ 5,401	$ 14,715	$ 13,921
Segment net income (loss)	1,130	959	2,226	2,096
Total assets	106,362		106,362		$ 78,318
Kemper IGCC [Member]
Segment Reporting Information [Line Items]
Pre-Tax Charge To Income	88	150	222	182
After Tax Charge To Income	54	93	137	112
Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	5,619	5,390	13,979	13,887
Segment net income (loss)	1,194	976	2,391	2,093
Total assets	83,359		83,359		77,560
Intersegment Eliminations [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	(117)	(109)	(330)	(322)
Segment net income (loss)	0	0	0	0
Total assets	(440)		(440)		(397)
Consolidation Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues	(37)	(26)	(118)	(86)
Segment net income (loss)	(1)	1	(8)	0
Total assets	(1,156)		(1,156)		(1,061)
Southern Company Gas [Member] | Natural Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	543		543
Segment net income (loss)	4		4
Total assets	21,185		21,185
Traditional Operating Companies [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	5,236	5,098	13,120	13,123
Segment net income (loss)	1,018	874	2,076	1,912
Total assets	71,448		71,448		69,052
Southern Power [Member] | Electric Utilities [Member]
Segment Reporting Information [Line Items]
Operating revenues	500	401	1,189	1,086
Segment net income (loss)	176	102	315	181
Total assets	12,351		12,351		8,905
All Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	139	37	311	120
Segment net income (loss)	(67)	(18)	(161)	3
Total assets	2,974		$ 2,974		1,819
Southern Company Gas [Member]
Segment Reporting Information [Line Items]
Number of Reportable Segments | utilitiy			7
Operating revenues	543
Segment net income (loss)	4
Southern Power [Member]
Segment Reporting Information [Line Items]
Wholesale revenues, affiliates	110	104	$ 313	303
Operating revenues	500	$ 401	1,189	$ 1,086
Total assets	$ 12,351		$ 12,351		$ 8,905