Retirement Benefits - Changes in Fair Value Measurement of Level 3 Pension Plan Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
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	$ 8,650,000
Actual return on investments:
Total return on investments	797,000	1,098,000
Fair value of plan assets end of year	9,647,000	8,650,000
Pension Plans [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	1,414,000	1,260,000
Pension Plans [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	570,000	571,000
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	898,000
Actual return on investments:
Total return on investments	54,000	129,000
Fair value of plan assets end of year	905,000	898,000
Other Postretirement Benefits [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	48,000	46,000
Other Postretirement Benefits [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	19,000	20,000
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	1,691,000	1,571,000
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	1,000,000	841,000
Actual return on investments:
Related to investments held at year end	79,000	74,000
Related to investments sold during the year	33,000	30,000
Total return on investments	112,000	104,000
Purchases, sales, and settlements	9,000	55,000
Fair value of plan assets end of year	1,121,000	1,000,000
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	571,000	593,000
Actual return on investments:
Related to investments held at year end	51,000	8,000
Related to investments sold during the year	(16,000)	51,000
Total return on investments	35,000	59,000
Purchases, sales, and settlements	(36,000)	(81,000)
Fair value of plan assets end of year	570,000	571,000
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Actual return on investments:
Fair value of plan assets end of year	56,000	56,000
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	36,000	30,000
Actual return on investments:
Related to investments held at year end	1,000	3,000
Related to investments sold during the year	0	1,000
Total return on investments	1,000	4,000
Purchases, sales, and settlements	0	2,000
Fair value of plan assets end of year	37,000	36,000
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	20,000	21,000
Actual return on investments:
Related to investments held at year end	1,000	0
Related to investments sold during the year	(1,000)	2,000
Total return on investments	0	2,000
Purchases, sales, and settlements	(1,000)	(3,000)
Fair value of plan assets end of year	19,000	20,000
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	2,256,000
Actual return on investments:
Total return on investments	207,000	285,000
Fair value of plan assets end of year	2,385,000	2,256,000
Alabama Power [Member] | Pension Plans [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	350,000	329,000
Alabama Power [Member] | Pension Plans [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	141,000	149,000
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	387,000
Actual return on investments:
Total return on investments	23,000	61,000
Fair value of plan assets end of year	391,000	387,000
Alabama Power [Member] | Other Postretirement Benefits [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	18,000	17,000
Alabama Power [Member] | Other Postretirement Benefits [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	7,000	7,000
Alabama Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	418,000	410,000
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	261,000	220,000
Actual return on investments:
Related to investments held at year end	6,000	19,000
Related to investments sold during the year	8,000	8,000
Total return on investments	14,000	27,000
Purchases, sales, and settlements	2,000	14,000
Fair value of plan assets end of year	277,000	261,000
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	149,000	155,000
Actual return on investments:
Related to investments held at year end	5,000	2,000
Related to investments sold during the year	(4,000)	13,000
Total return on investments	1,000	15,000
Purchases, sales, and settlements	(9,000)	(21,000)
Fair value of plan assets end of year	141,000	149,000
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	20,000	20,000
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	13,000	11,000
Actual return on investments:
Related to investments held at year end	0	1,000
Related to investments sold during the year	0	0
Total return on investments	0	1,000
Purchases, sales, and settlements	0	1,000
Fair value of plan assets end of year	13,000	13,000
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	7,000	8,000
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)
Fair value of plan assets end of year	7,000	7,000
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	3,055,000
Actual return on investments:
Total return on investments	285,000	387,000
Fair value of plan assets end of year	3,368,000	3,055,000
Georgia Power [Member] | Pension Plans [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	493,000	445,000
Georgia Power [Member] | Pension Plans [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	199,000	202,000
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	406,000
Actual return on investments:
Total return on investments	21,000	56,000
Fair value of plan assets end of year	401,000	406,000
Georgia Power [Member] | Other Postretirement Benefits [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	15,000	14,000
Georgia Power [Member] | Other Postretirement Benefits [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	6,000	6,000
Georgia Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	590,000	555,000
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	353,000	299,000
Actual return on investments:
Related to investments held at year end	23,000	25,000
Related to investments sold during the year	12,000	10,000
Total return on investments	35,000	35,000
Purchases, sales, and settlements	3,000	19,000
Fair value of plan assets end of year	391,000	353,000
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	202,000	211,000
Actual return on investments:
Related to investments held at year end	15,000	3,000
Related to investments sold during the year	(6,000)	17,000
Total return on investments	9,000	20,000
Purchases, sales, and settlements	(12,000)	(29,000)
Fair value of plan assets end of year	199,000	202,000
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	18,000	17,000
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	11,000	10,000
Actual return on investments:
Related to investments held at year end	1,000	1,000
Related to investments sold during the year	0	0
Total return on investments	1,000	1,000
Purchases, sales, and settlements	0	0
Fair value of plan assets end of year	12,000	11,000
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	6,000	7,000
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)
Fair value of plan assets end of year	6,000	6,000
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	381,941
Actual return on investments:
Total return on investments	33,512	49,076
Fair value of plan assets end of year	432,798	381,941
Gulf Power [Member] | Pension Plans [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	63,435	55,632
Gulf Power [Member] | Pension Plans [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	25,573	25,201
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	17,278
Actual return on investments:
Total return on investments	1,578	2,119
Fair value of plan assets end of year	18,087	17,278
Gulf Power [Member] | Other Postretirement Benefits [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	2,576	2,443
Gulf Power [Member] | Other Postretirement Benefits [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	1,039	1,108
Gulf Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	75,854	69,340
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	44,139	37,039
Actual return on investments:
Related to investments held at year end	4,263	3,357
Related to investments sold during the year	1,488	1,310
Total return on investments	5,751	4,667
Purchases, sales, and settlements	391	2,433
Fair value of plan assets end of year	50,281	44,139
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	25,201	26,129
Actual return on investments:
Related to investments held at year end	2,697	376
Related to investments sold during the year	(727)	2,282
Total return on investments	1,970	2,658
Purchases, sales, and settlements	(1,598)	(3,586)
Fair value of plan assets end of year	25,573	25,201
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	3,081	3,047
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	1,939	1,667
Actual return on investments:
Related to investments held at year end	27	108
Related to investments sold during the year	60	57
Total return on investments	87	165
Purchases, sales, and settlements	16	107
Fair value of plan assets end of year	2,042	1,939
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	1,108	1,155
Actual return on investments:
Related to investments held at year end	26	16
Related to investments sold during the year	(30)	104
Total return on investments	(4)	120
Purchases, sales, and settlements	(65)	(167)
Fair value of plan assets end of year	1,039	1,108
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	383,687
Actual return on investments:
Total return on investments	40,051	49,431
Fair value of plan assets end of year	443,463	383,687
Mississippi Power [Member] | Pension Plans [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	64,999	55,887
Mississippi Power [Member] | Pension Plans [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	26,203	25,316
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	23,057
Actual return on investments:
Total return on investments	1,814	2,379
Fair value of plan assets end of year	23,980	23,057
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Real Estate Investments [Member]
Actual return on investments:
Fair value of plan assets end of year	2,862	2,716
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Private Equity [Member]
Actual return on investments:
Fair value of plan assets end of year	1,154	1,231
Mississippi Power [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
Actual return on investments:
Fair value of plan assets end of year	77,723	69,657
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	44,341	37,196
Actual return on investments:
Related to investments held at year end	5,253	3,385
Related to investments sold during the year	1,525	1,316
Total return on investments	6,778	4,701
Purchases, sales, and settlements	401	2,444
Fair value of plan assets end of year	51,520	44,341
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	25,316	26,240
Actual return on investments:
Related to investments held at year end	3,269	378
Related to investments sold during the year	(745)	2,300
Total return on investments	2,524	2,678
Purchases, sales, and settlements	(1,637)	(3,602)
Fair value of plan assets end of year	26,203	25,316
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	3,423	3,387
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	2,156	1,865
Actual return on investments:
Related to investments held at year end	28	158
Related to investments sold during the year	67	64
Total return on investments	95	222
Purchases, sales, and settlements	18	69
Fair value of plan assets end of year	2,269	2,156
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	1,231	1,293
Actual return on investments:
Related to investments held at year end	28	18
Related to investments sold during the year	(33)	110
Total return on investments	(5)	128
Purchases, sales, and settlements	(72)	(190)
Fair value of plan assets end of year	$ 1,154	$ 1,231