Segment and Related Information - Financial Data for Business Segments (Details) (USD $)	3 Months Ended					9 Months Ended				12 Months Ended
	Sep. 30, 2014		Mar. 31, 2014	Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Number of States in which Entity Operates	4					4
Segment and Related Information (Textual) [Abstract]
Operating revenues	$ 5,339,000,000			$ 5,017,000,000		$ 14,450,000,000		$ 13,160,000,000
Financial data for business segments
Operating revenues	5,339,000,000			5,017,000,000		14,450,000,000		13,160,000,000
Segment net income (loss)	718,000,000	[1],[2]		852,000,000	[1],[2]	1,680,000,000	[1],[3]	1,230,000,000	[1],[3]
Total assets	67,654,000,000					67,654,000,000				64,546,000,000
Electric Utilities [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	5,327,000,000			5,005,000,000		14,408,000,000		13,120,000,000
Financial data for business segments
Operating revenues	5,327,000,000			5,005,000,000		14,408,000,000		13,120,000,000
Segment net income (loss)	722,000,000	[1],[2]		850,000,000	[1],[2]	1,685,000,000	[1],[3]	1,241,000,000	[1],[3]
Total assets	66,862,000,000					66,862,000,000				63,775,000,000
Traditional Operating Companies [Member] | Electric Utilities [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	5,007,000,000			4,744,000,000		13,594,000,000		12,430,000,000
Financial data for business segments
Operating revenues	5,007,000,000			4,744,000,000		13,594,000,000		12,430,000,000
Segment net income (loss)	658,000,000	[1],[2]		765,000,000	[1],[2]	1,557,000,000	[1],[3]	1,099,000,000	[1],[3]
Total assets	62,419,000,000					62,419,000,000				59,447,000,000
Southern Power [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	103,000,000			97,000,000		243,000,000		264,000,000
Financial data for business segments
Operating revenues	103,000,000			97,000,000		243,000,000		264,000,000
Southern Power [Member] | Electric Utilities [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	435,000,000			365,000,000		1,115,000,000		975,000,000
Financial data for business segments
Operating revenues	435,000,000			365,000,000		1,115,000,000		975,000,000
Segment net income (loss)	64,000,000	[1],[2]		85,000,000	[1],[2]	128,000,000	[1],[3]	142,000,000	[1],[3]
Total assets	4,609,000,000					4,609,000,000				4,429,000,000
Eliminations [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	(22,000,000)			(23,000,000)		(72,000,000)		(68,000,000)
Financial data for business segments
Operating revenues	(22,000,000)			(23,000,000)		(72,000,000)		(68,000,000)
Segment net income (loss)	(2,000,000)	[1],[2]		3,000,000	[1],[2]	(5,000,000)	[1],[3]	1,000,000	[1],[3]
Total assets	(512,000,000)					(512,000,000)				(306,000,000)
Eliminations [Member] | Electric Utilities [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	(115,000,000)			(104,000,000)		(301,000,000)		(285,000,000)
Financial data for business segments
Operating revenues	(115,000,000)			(104,000,000)		(301,000,000)		(285,000,000)
Segment net income (loss)	0	[1],[2]		0	[1],[2]	0	[1],[3]	0	[1],[3]
Total assets	(166,000,000)					(166,000,000)				(101,000,000)
All Other [Member]
Segment and Related Information (Textual) [Abstract]
Operating revenues	34,000,000			35,000,000		114,000,000		108,000,000
Financial data for business segments
Operating revenues	34,000,000			35,000,000		114,000,000		108,000,000
Segment net income (loss)	(2,000,000)	[1],[2]		(1,000,000)	[1],[2]	0	[1],[3]	(12,000,000)	[1],[3]
Total assets	1,304,000,000					1,304,000,000				1,077,000,000
Kemper Igcc [Member]
Financial data for business segments
Pre-tax charge to income	418,000,000		380,000,000	150,000,000		798,000,000		1,140,000,000		1,180,000,000
After tax charge to income	$ 258,100,000		$ 234,700,000	$ 92,600,000		$ 492,800,000		$ 704,000,000		$ 728,700,000

[1] After dividends on preferred and preference stock of subsidiaries.

[2] Segment net income (loss) for the traditional operating companies for the three months ended September 30, 2014 and September 30, 2013 includes a $418.0 million pre-tax charge ($258.1 million after tax) and a $150.0 million pre-tax charge ($92.6 million after tax), respectively, for estimated probable losses on the Kemper IGCC. See Note (B) under "Integrated Coal Gasification Combined Cycle – Kemper IGCC Schedule and Cost Estimate" herein for additional information.

[3] Segment net income (loss) for the traditional operating companies for the nine months ended September 30, 2014 and September 30, 2013 includes $798.0 million in pre-tax charges ($492.8 million after tax) and $1.14 billion in pre-tax charges ($704.0 million after tax), respectively, for estimated probable losses on the Kemper IGCC. See Note (B) under "Integrated Coal Gasification Combined Cycle – Kemper IGCC Schedule and Cost Estimate" herein for additional information.