Retirement Benefits - Changes in Fair Value Measurement of Level 3 Pension Plan Assets (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Pension Plans [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	$ 6,722,000,000
Actual return on investments:
Total return on investments	1,010,000,000	256,000,000
Fair value of plan assets end of year	7,890,000,000	6,722,000,000
Pension Plans [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	1,099,000,000	1,002,000,000
Pension Plans [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	593,000,000	582,000,000
Other Postretirement Benefits [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	786,000,000
Actual return on investments:
Total return on investments	93,000,000	4,000,000
Fair value of plan assets end of year	817,000,000	786,000,000
Other Postretirement Benefits [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	40,000,000	39,000,000
Other Postretirement Benefits [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	21,000,000	23,000,000
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	1,437,000,000	1,367,000,000
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	782,000,000	674,000,000
Actual return on investments:
Related to investments held at year end	56,000,000	72,000,000
Related to investments sold during the year	3,000,000	20,000,000
Total return on investments	59,000,000	92,000,000
Purchases, sales, and settlements	0	16,000,000
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	841,000,000	782,000,000
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	582,000,000	638,000,000
Actual return on investments:
Related to investments held at year end	1,000,000	(12,000,000)
Related to investments sold during the year	41,000,000	47,000,000
Total return on investments	42,000,000	35,000,000
Purchases, sales, and settlements	(31,000,000)	(91,000,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	593,000,000	582,000,000
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Actual return on investments:
Fair value of plan assets end of year	51,000,000	53,000,000
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	30,000,000	26,000,000
Actual return on investments:
Related to investments held at year end	0	3,000,000
Related to investments sold during the year	0	1,000,000
Total return on investments	0	4,000,000
Purchases, sales, and settlements	0	0
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	30,000,000	30,000,000
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	23,000,000	23,000,000
Actual return on investments:
Related to investments held at year end	0	0
Related to investments sold during the year	1,000,000	2,000,000
Total return on investments	1,000,000	2,000,000
Purchases, sales, and settlements	(3,000,000)	(2,000,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	21,000,000	23,000,000
Gulf Power [Member] | Pension Plans [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	300,848,000
Actual return on investments:
Total return on investments	45,762,000	9,552,000
Fair value of plan assets end of year	347,458,000	300,848,000
Gulf Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	48,401,000	44,827,000
Gulf Power [Member] | Pension Plans [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	26,129,000	26,053,000
Gulf Power [Member] | Other Postretirement Benefits [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	14,747,000
Actual return on investments:
Total return on investments	2,131,000	514,000
Fair value of plan assets end of year	16,056,000	14,747,000
Gulf Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	2,175,000	2,123,000
Gulf Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	1,170,000	1,232,000
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	63,307,000	61,162,000
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	34,989,000	30,355,000
Actual return on investments:
Related to investments held at year end	1,918,000	3,021,000
Related to investments sold during the year	132,000	896,000
Total return on investments	2,050,000	3,917,000
Purchases, sales, and settlements	0	717,000
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	37,039,000	34,989,000
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	26,053,000	28,727,000
Actual return on investments:
Related to investments held at year end	44,000	(538,000)
Related to investments sold during the year	1,396,000	1,941,000
Total return on investments	1,440,000	1,403,000
Purchases, sales, and settlements	(1,364,000)	(4,077,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	26,129,000	26,053,000
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Actual return on investments:
Fair value of plan assets end of year	2,828,000	2,889,000
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	1,657,000	1,452,000
Actual return on investments:
Related to investments held at year end	107,000	129,000
Related to investments sold during the year	6,000	42,000
Total return on investments	113,000	171,000
Purchases, sales, and settlements	(103,000)	34,000
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	1,667,000	1,657,000
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	1,232,000	1,375,000
Actual return on investments:
Related to investments held at year end	(1,000)	(26,000)
Related to investments sold during the year	80,000	77,000
Total return on investments	79,000	51,000
Purchases, sales, and settlements	(156,000)	(194,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	1,155,000	1,232,000
Mississippi Power [Member] | Pension Plans [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	278,878,000
Actual return on investments:
Total return on investments	39,668,000	10,805,000
Fair value of plan assets end of year	348,933,000	278,878,000
Mississippi Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	48,606,000	41,553,000
Mississippi Power [Member] | Pension Plans [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	26,240,000	24,151,000
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	20,322,000
Actual return on investments:
Total return on investments	2,427,000	720,000
Fair value of plan assets end of year	21,842,000	20,322,000
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	2,434,000	2,371,000
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	1,307,000	1,377,000
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	63,576,000	56,697,000
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	32,434,000	27,976,000
Actual return on investments:
Related to investments held at year end	4,629,000	2,964,000
Related to investments sold during the year	133,000	830,000
Total return on investments	4,762,000	3,794,000
Purchases, sales, and settlements	0	664,000
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	37,196,000	32,434,000
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	24,151,000	26,475,000
Actual return on investments:
Related to investments held at year end	44,000	(498,000)
Related to investments sold during the year	3,415,000	1,951,000
Total return on investments	3,459,000	1,453,000
Purchases, sales, and settlements	(1,370,000)	(3,777,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	26,240,000	24,151,000
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Actual return on investments:
Fair value of plan assets end of year	3,165,000	3,228,000
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	1,851,000	1,625,000
Actual return on investments:
Related to investments held at year end	119,000	141,000
Related to investments sold during the year	7,000	47,000
Total return on investments	126,000	188,000
Purchases, sales, and settlements	(112,000)	38,000
Fair value of plan assets end of year	1,865,000	1,851,000
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	1,377,000	1,538,000
Actual return on investments:
Related to investments held at year end	(1,000)	(29,000)
Related to investments sold during the year	90,000	85,000
Total return on investments	89,000	56,000
Purchases, sales, and settlements	(173,000)	(217,000)
Fair value of plan assets end of year	1,293,000	1,377,000
Georgia Power [Member] | Pension Plans [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	2,545,000,000
Actual return on investments:
Total return on investments	377,000,000	76,000,000
Fair value of plan assets end of year	2,805,000,000	2,545,000,000
Georgia Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	391,000,000	379,000,000
Georgia Power [Member] | Pension Plans [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	211,000,000	220,000,000
Georgia Power [Member] | Other Postretirement Benefits [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	385,000,000
Actual return on investments:
Total return on investments	43,000,000	(4,000,000)
Fair value of plan assets end of year	382,000,000	385,000,000
Georgia Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	13,000,000	12,000,000
Georgia Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	7,000,000	7,000,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	511,000,000	517,000,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	296,000,000	258,000,000
Actual return on investments:
Related to investments held at year end	2,000,000	24,000,000
Related to investments sold during the year	1,000,000	8,000,000
Total return on investments	3,000,000	32,000,000
Purchases, sales, and settlements	0	6,000,000
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	299,000,000	296,000,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	220,000,000	245,000,000
Actual return on investments:
Related to investments held at year end	0	(5,000,000)
Related to investments sold during the year	2,000,000	14,000,000
Total return on investments	2,000,000	9,000,000
Purchases, sales, and settlements	(11,000,000)	(34,000,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	211,000,000	220,000,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Actual return on investments:
Fair value of plan assets end of year	17,000,000	16,000,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	9,000,000	8,000,000
Actual return on investments:
Related to investments held at year end	1,000,000	1,000,000
Related to investments sold during the year	0	0
Total return on investments	1,000,000	1,000,000
Purchases, sales, and settlements	0	0
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	10,000,000	9,000,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	7,000,000	8,000,000
Actual return on investments:
Related to investments held at year end	0	0
Related to investments sold during the year	0	0
Total return on investments	0	0
Purchases, sales, and settlements	0	(1,000,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	7,000,000	7,000,000
Alabama Power [Member] | Pension Plans [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	1,864,000,000
Actual return on investments:
Total return on investments	274,000,000	32,000,000
Fair value of plan assets end of year	2,062,000,000	1,864,000,000
Alabama Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	287,000,000	278,000,000
Alabama Power [Member] | Pension Plans [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	155,000,000	161,000,000
Alabama Power [Member] | Other Postretirement Benefits [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	317,000,000
Actual return on investments:
Total return on investments	39,000,000	5,000,000
Fair value of plan assets end of year	341,000,000	317,000,000
Alabama Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Actual return on investments:
Fair value of plan assets end of year	15,000,000	15,000,000
Alabama Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Actual return on investments:
Fair value of plan assets end of year	8,000,000	8,000,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	376,000,000	379,000,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	217,000,000	191,000,000
Actual return on investments:
Related to investments held at year end	2,000,000	16,000,000
Related to investments sold during the year	1,000,000	6,000,000
Total return on investments	3,000,000	22,000,000
Purchases, sales, and settlements	0	4,000,000
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	220,000,000	217,000,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	161,000,000	180,000,000
Actual return on investments:
Related to investments held at year end	0	(3,000,000)
Related to investments sold during the year	2,000,000	9,000,000
Total return on investments	2,000,000	6,000,000
Purchases, sales, and settlements	(8,000,000)	(25,000,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	155,000,000	161,000,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Actual return on investments:
Fair value of plan assets end of year	19,000,000	19,000,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	11,000,000	10,000,000
Actual return on investments:
Related to investments held at year end	0	1,000,000
Related to investments sold during the year	0	0
Total return on investments	0	1,000,000
Purchases, sales, and settlements	0	0
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	11,000,000	11,000,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Changes in the fair value measurement of the Level 3 items in the pension plan assets
Fair value of plan assets beginning of year	8,000,000	9,000,000
Actual return on investments:
Related to investments held at year end	0	0
Related to investments sold during the year	0	0
Total return on investments	0	0
Purchases, sales, and settlements	0	(1,000,000)
Transfers into/out of Level 3	0	0
Fair value of plan assets end of year	$ 8,000,000	$ 8,000,000