Retirement Benefits - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	$ 0	$ 419,000
Other regulatory assets, deferred	4,334,000	2,495,000
Other current liabilities	(544,000)	(346,000)
Other regulatory liabilities, deferred	(398,000)	(479,000)
Employee benefit obligations	(2,432,000)	(1,461,000)
Accumulated OCI	(128,000)	(75,000)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	4,664,000	2,624,000
Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	419,000
Other regulatory assets, deferred	3,073,000	1,651,000
Other current liabilities	(42,000)	(40,000)
Employee benefit obligations	(1,177,000)	(509,000)
Accumulated OCI	134,000	64,000
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	55,000	80,000
Net (Gain) Loss	3,152,000	1,634,000
Prior Service Cost, Estimated	25,000
Net (Gain) Loss, Estimated	215,000
Pension Plans [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	4,000	5,000
Net (Gain) Loss	130,000	59,000
Prior Service Cost, Estimated	1,000
Net (Gain) Loss, Estimated	9,000
Pension Plans [Member] | Regulatory Assets [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	51,000	75,000
Net (Gain) Loss	3,022,000	1,575,000
Prior Service Cost, Estimated	24,000
Net (Gain) Loss, Estimated	206,000
Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	387,000	109,000
Other current liabilities	(4,000)	(4,000)
Other regulatory liabilities, deferred	(21,000)	(36,000)
Employee benefit obligations	(1,082,000)	(777,000)
Accumulated OCI	8,000	1,000
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	2,000	9,000
Net (Gain) Loss	372,000	65,000
Prior Service Cost, Estimated	4,000
Net (Gain) Loss, Estimated	17,000
Other Postretirement Benefits [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	0	0
Net (Gain) Loss	8,000	1,000
Prior Service Cost, Estimated	0
Net (Gain) Loss, Estimated	0
Other Postretirement Benefits [Member] | Regulatory Assets [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	2,000	9,000
Net (Gain) Loss	364,000	64,000
Prior Service Cost, Estimated	4,000
Net (Gain) Loss, Estimated	17,000
Alabama Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	276,000
Other regulatory assets, deferred	1,063,000	645,000
Other current liabilities	(80,000)	(41,000)
Other regulatory liabilities, deferred	(239,000)	(259,000)
Employee benefit obligations	(326,000)	(195,000)
Accumulated OCI	(29,000)	(26,000)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	738,000	92,000
Alabama Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	276,000
Other regulatory assets, deferred	827,000	476,000
Other current liabilities	(10,000)	(9,000)
Employee benefit obligations	(186,000)	(101,000)
Alabama Power [Member] | Pension Plans [Member] | Regulatory Assets [Member]
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	12,000	19,000
Net (Gain) Loss	815,000	457,000
Prior Service Cost, Estimated	6,000
Net (Gain) Loss, Estimated	(55,000)
Alabama Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	68,000	6,000
Other regulatory liabilities, deferred	(14,000)	(21,000)
Employee benefit obligations	(111,000)	(42,000)
Alabama Power [Member] | Other Postretirement Benefits [Member] | Regulatory Assets [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	54,000	(15,000)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	15,000	19,000
Net (Gain) Loss	39,000	(34,000)
Prior Service Cost, Estimated	4,000
Net (Gain) Loss, Estimated	2,000
Georgia Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	118,000
Other regulatory assets, deferred	1,753,000	1,113,000
Other current liabilities	(204,000)	(122,000)
Employee benefit obligations	(903,000)	(542,000)
Accumulated OCI	(8,000)	(5,000)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	2,529,000	1,886,000
Georgia Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	118,000
Other regulatory assets, deferred	1,102,000	610,000
Other current liabilities	(12,000)	(12,000)
Employee benefit obligations	(386,000)	(137,000)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	17,000	26,000
Net (Gain) Loss	1,085,000	584,000
Prior Service Cost, Estimated	9,000
Net (Gain) Loss, Estimated	76,000
Georgia Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	213,000	69,000
Employee benefit obligations	(469,000)	(316,000)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(5,000)	(4,000)
Net (Gain) Loss	218,000	73,000
Prior Service Cost, Estimated	0
Net (Gain) Loss, Estimated	11,000
Gulf Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	11,533
Other regulatory assets, deferred	416,028	340,415
Other current liabilities	(22,386)	(22,972)
Other regulatory liabilities, deferred	(48,556)	(56,051)
Employee benefit obligations	(120,752)	(76,338)
Accumulated OCI	(737)	(1,109)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	319,644	160,224
Gulf Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	11,533
Other regulatory assets, deferred	145,815	75,280
Other current liabilities	(1,307)	(1,183)
Employee benefit obligations	(54,487)	(20,039)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	3,286	4,401
Net (Gain) Loss	142,529	70,879
Prior Service Cost, Estimated	1,115
Net (Gain) Loss, Estimated	9,281
Gulf Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	6,100	0
Other current liabilities	(639)	(687)
Other regulatory liabilities, deferred	(4,290)	(6,984)
Employee benefit obligations	(59,668)	(50,418)
Gulf Power [Member] | Other Postretirement Benefits [Member] | Regulatory Assets [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	1,810	(6,984)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(2,137)	138
Net (Gain) Loss	3,947	(7,122)
Prior Service Cost, Estimated	25
Net (Gain) Loss, Estimated	0
Mississippi Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	385,410	200,620
Other current liabilities	(44,701)	(21,413)
Other regulatory liabilities, deferred	(63,681)	(144,992)
Employee benefit obligations	(147,536)	(94,430)
Accumulated OCI	(7,015)	(7,864)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Net Regulatory Assets	171,764	66,604
Mississippi Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Prepaid pension costs	0	5,698
Other regulatory assets, deferred	150,972	77,572
Other current liabilities	(2,337)	(2,134)
Employee benefit obligations	(65,029)	(25,556)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	3,030	4,118
Net (Gain) Loss	147,942	73,454
Prior Service Cost, Estimated	1,088
Net (Gain) Loss, Estimated	10,293
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	18,345	5,227
Other regulatory liabilities, deferred	(2,011)	(3,111)
Employee benefit obligations	(71,532)	(57,663)
Amounts related to defined benefit pension Plans that had not yet been recognized in net periodic pension cost along with estimated amortization
Prior Service Cost	(2,123)	(2,311)
Net (Gain) Loss	18,457	4,427
Prior Service Cost, Estimated	(188)
Net (Gain) Loss, Estimated	778
Net Regulatory Assets	$ 16,334	$ 2,116