Commitments - Textual (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended								12 Months Ended																	12 Months Ended				12 Months Ended															12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2010 Mississippi Power [Member]	Dec. 31, 2012 Mississippi Power [Member] Railcar	Dec. 31, 2011 Mississippi Power [Member]	Dec. 31, 2010 Mississippi Power [Member]	Dec. 31, 2001 Mississippi Power [Member]	Dec. 31, 2012 Gulf Power [Member]	Dec. 31, 2011 Gulf Power [Member]	Dec. 31, 2010 Gulf Power [Member]	Nov. 30, 2012 Gulf Power [Member]	Dec. 31, 2012 Georgia Power [Member]	Dec. 31, 2011 Georgia Power [Member]	Dec. 31, 2010 Georgia Power [Member]	Dec. 31, 2012 Southern Power [Member]	Dec. 31, 2011 Southern Power [Member]	Dec. 31, 2010 Southern Power [Member]	Dec. 31, 2012 Alabama Power [Member]	Dec. 31, 2011 Alabama Power [Member]	Dec. 31, 2010 Alabama Power [Member]	Dec. 31, 2012 Alabama Power and Georgia Power [Member]	Dec. 31, 2012 Purchased Power [Member]	Dec. 31, 2012 Purchased Power [Member] Gulf Power [Member]	Dec. 31, 2012 Purchased Power [Member] Alabama Power [Member]	Dec. 31, 2012 Barges and Rail Cars [Member]	Dec. 31, 2012 Barges and Rail Cars [Member] Mississippi Power [Member]	Dec. 31, 2012 Barges and Rail Cars [Member] Gulf Power [Member]	Dec. 31, 2012 Barges and Rail Cars [Member] Georgia Power [Member]	Dec. 31, 2012 Barges and Rail Cars [Member] Alabama Power [Member]	Dec. 31, 2011 Barges and Rail Cars [Member] Alabama Power [Member]	Dec. 31, 2010 Barges and Rail Cars [Member] Alabama Power [Member]	Dec. 31, 2012 Residual value of leased property [Member] Alabama Power [Member]	Dec. 31, 2012 Fuel Handling Equipment [Member] Mississippi Power [Member]	Dec. 31, 2011 Fuel Handling Equipment [Member] Mississippi Power [Member]	Dec. 31, 2010 Fuel Handling Equipment [Member] Mississippi Power [Member]	Dec. 31, 2012 Barge Transportation [Member] Mississippi Power [Member]	Dec. 31, 2011 Barge Transportation [Member] Mississippi Power [Member]	Dec. 31, 2010 Barge Transportation [Member] Mississippi Power [Member]	Dec. 31, 2012 Plant Watson [Member] Mississippi Power [Member]	Dec. 31, 2012 Plant Scholz [Member] Barges and Rail Cars [Member] Gulf Power [Member]	Dec. 31, 2012 Plants Crist and Smith [Member] Barges and Rail Cars [Member] Gulf Power [Member]	Dec. 31, 2012 Plant Daniel [Member] Mississippi Power [Member]	Dec. 31, 2012 Plant Daniel [Member] Gulf Power [Member]	Dec. 31, 2012 2018 [Member] Residual value of leased property [Member] Georgia Power [Member]	Dec. 31, 2012 Alabama Power [Member] Payment Guarantee [Member] Georgia Power [Member]	Dec. 31, 2012 Alabama Power [Member] Financial Guarantee [Member] Georgia Power [Member]	Dec. 31, 2012 MEAG Power [Member] Georgia Power [Member]	Dec. 31, 2012 Plant Daniel [Member] Barges and Rail Cars [Member] Gulf Power [Member]	Dec. 31, 2011 Plant Daniel [Member] Barges and Rail Cars [Member] Gulf Power [Member]	Dec. 31, 2010 Plant Daniel [Member] Barges and Rail Cars [Member] Gulf Power [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Capital Leases, Future Minimum Payments, Lesser Of Fair Value and Present Value													$ 149,000,000
Commitments (Textual) [Abstract]
Payments Pursuant to Long Term Service Agreements									8,119,000	8,007,000	6,011,000					63,932,000	57,969,000	41,598,000
Minimum contractual obligation																							3,503,000,000	741,800,000	408,000,000
Purchase obligation, 2013																							164,000,000	24,700,000	31,000,000
Purchase obligation, 2014																							200,000,000	52,900,000	37,000,000
Purchase obligation, 2015																							249,000,000	78,600,000	38,000,000
Purchase obligation, 2016																							258,000,000	78,700,000	39,000,000
Purchase obligation, 2017																							263,000,000	78,800,000	40,000,000
Purchase obligation, 2018 and thereafter																							2,369,000,000	428,100,000	223,000,000
Total charges for nuclear fuel included in fuel expense	5,057,000,000	6,262,000,000	6,699,000,000		411,226,000	490,415,000	501,830,000		544,936,000	662,283,000	742,322,000		2,051,000,000	2,789,000,000	3,102,000,000	426,257,000	454,790,000	391,535,000	1,503,000,000	1,679,000,000	1,851,000,000
Jointly Owned Utility Plant, Proportionate Ownership Share									50.00%										14.00%																													5.00%
Capacity Payments													50,000,000	52,000,000	55,000,000
Expense Under Purchase Power Agreements Accounted For As Operating Leases	171,000,000	199,000,000	180,000,000						24,600,000	25,100,000	25,100,000								33,000,000	33,000,000	30,000,000
Management fee					38,100,000
Term of management fee contract					40 years
Operating lease expenses	155,000,000	176,000,000	188,000,000		11,100,000	32,600,000	38,600,000		20,100,000	21,900,000	23,100,000		34,000,000	33,000,000	35,000,000	800,000	600,000	500,000	24,000,000	23,000,000	25,000,000									19,000,000	18,000,000	20,000,000		200,000	400,000	700,000	7,300,000	7,500,000	8,400,000
Number of Railcars Used Under Operating Lease					229
Operating leases, future minimum lease payments due	422,000,000								39,700,000				90,000,000						62,000,000							193,000,000		38,800,000	74,000,000																33,000,000
Operating leases, term of lease					10 years			10 years
Company's share of the leases					50.00%																																			100.00%			50.00%
Fuel cost recovery clause				3,500,000	3,600,000	2,600,000																																											3,600,000	2,600,000	3,500,000
Average Operating Leases Future Minimum Payments Due Current																											1,600,000
Average Operating Leases Future Minimum Payments Due In Three Years																											1,600,000
Average Operating Leases Future Minimum Payments Due In Two Years																											1,600,000
Leasing commitment, 2013	113,000,000								18,900,000				30,000,000			1,300,000			20,000,000			83,000,000				71,000,000		18,600,000	25,000,000				21,000,000	200,000			8,200,000												1,600,000
Leasing commitment, 2015	53,000,000								1,200,000				17,000,000			1,400,000			8,000,000							24,000,000		1,100,000	14,000,000				5,000,000	200,000			8,200,000				2,400,000	13,000,000							1,600,000
Leasing commitment, 2016	45,000,000								1,000,000				10,000,000			1,300,000			9,000,000							19,000,000		900,000	8,000,000				4,000,000																1,600,000
Leasing commitment, 2014	95,000,000								17,500,000				24,000,000			1,600,000			12,000,000							57,000,000		17,200,000	20,000,000				8,000,000	200,000			8,200,000				2,400,000	13,000,000							1,600,000
Leasing commitment, 2015																											1,600,000
Leasing commitment, 2016																											1,600,000
Leasing commitment, 2018 and thereafter	84,000,000								0				3,000,000			40,300,000			9,000,000							11,000,000		0	2,000,000				12,000,000
Pollution control revenue bonds, outstanding					82,700,000	82,700,000			309,000,000	309,000,000		13,000,000	1,800,000,000	1,800,000,000					1,200,000,000																									41,000,000		25,000,000
Senior Notes outstanding	17,400,000,000	15,900,000,000			1,100,000,000	630,000,000			945,000,000	936,400,000			7,900,000,000	6,400,000,000		1,300,000,000	1,300,000,000																														50,000,000
Leasing commitment, 2017	32,000,000								1,100,000				6,000,000			1,300,000			4,000,000							11,000,000		1,000,000	5,000,000				0																1,600,000
Deferred Capacity Expenses													$ 169,000,000	$ 216,000,000	$ 223,000,000