Retirement Benefits - Amounts Recognized in Balance Sheets and Amounts in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	$ 4,989	$ 4,334
Other current liabilities	(590)	(374)
Other regulatory liabilities, deferred	(254)	(398)
Employee benefit obligations	(2,582)	(2,432)
Accumulated OCI	(130)	(128)
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	5,564	4,664
Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	2,998	3,073
Other current liabilities	(46)	(42)
Employee benefit obligations	(1,262)	(1,177)
Accumulated OCI	125	134
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	30	55
Net (Gain) Loss	3,093	3,152
Prior Service Cost, Estimated	14
Net (Gain) Loss, Estimated	151
Pension Plans [Member] | AOCI Attributable to Parent [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	3	4
Net (Gain) Loss	122	130
Prior Service Cost, Estimated	1
Net (Gain) Loss, Estimated	6
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	27	51
Net (Gain) Loss	2,971	3,022
Prior Service Cost, Estimated	13
Net (Gain) Loss, Estimated	145
Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	433	387
Other current liabilities	(4)	(4)
Other regulatory liabilities, deferred	(22)	(21)
Employee benefit obligations	(1,152)	(1,082)
Accumulated OCI	8	8
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	32	2
Net (Gain) Loss	387	372
Other Postretirement Benefits [Member] | AOCI Attributable to Parent [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	8
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	32	2
Net (Gain) Loss	379	364
Prior Service Cost, Estimated	6
Net (Gain) Loss, Estimated	14
Alabama Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	1,114	1,063
Other current liabilities	(39)	(40)
Other regulatory liabilities, deferred	(136)	(239)
Employee benefit obligations	(388)	(326)
Accumulated OCI	(32)	(29)
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	791	738
Alabama Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	822	827
Other current liabilities	(11)	(10)
Employee benefit obligations	(216)	(186)
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	6	12
Net (Gain) Loss	816	815
Prior Service Cost, Estimated	3
Net (Gain) Loss, Estimated	(40)
Alabama Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	95	68
Other regulatory liabilities, deferred	(13)	(14)
Employee benefit obligations	(142)	(111)
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	82	54
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	19	15
Net (Gain) Loss	63	39
Prior Service Cost, Estimated	4
Net (Gain) Loss, Estimated	2
Georgia Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	2,152	1,753
Other current liabilities	(143)	(172)
Employee benefit obligations	(949)	(903)
Accumulated OCI	(15)	(8)
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	2,933	2,529
Georgia Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	1,076	1,102
Other current liabilities	(13)	(12)
Employee benefit obligations	(406)	(386)
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	8	17
Net (Gain) Loss	1,068	1,085
Prior Service Cost, Estimated	5
Net (Gain) Loss, Estimated	55
Georgia Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	223	213
Employee benefit obligations	(496)	(469)
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	8	(5)
Net (Gain) Loss	215	218
Prior Service Cost, Estimated	1
Net (Gain) Loss, Estimated	9
Gulf Power [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	427	416
Other current liabilities	(40)	(22)
Other regulatory liabilities, deferred	(47)	(48)
Employee benefit obligations	(129)	(121)
Accumulated OCI	0	(1)
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	296	319
Gulf Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	142	146
Other current liabilities	(1)	(1)
Employee benefit obligations	(59)	(55)
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	3
Net (Gain) Loss	140	143
Prior Service Cost, Estimated	1
Net (Gain) Loss, Estimated	6
Gulf Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	10	6
Other current liabilities	(1)	(1)
Other regulatory liabilities, deferred	(5)	(4)
Employee benefit obligations	(63)	(59)
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	5	2
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	(2)
Net (Gain) Loss	5	4
Prior Service Cost, Estimated	0
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	525	385
Other current liabilities	(74)	(46)
Other regulatory liabilities, deferred	(71)	(64)
Employee benefit obligations	(153)	(148)
Accumulated OCI	(6)	(7)
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	667	172
Mississippi Power [Member] | Pension Plans [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	144	151
Other current liabilities	(3)	(2)
Employee benefit obligations	(67)	(65)
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	3
Net (Gain) Loss	142	148
Prior Service Cost, Estimated	1
Net (Gain) Loss, Estimated	7
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Amounts recognized in the consolidated balance sheets related to company's pension plans
Other regulatory assets, deferred	21	18
Other regulatory liabilities, deferred	(3)	(2)
Employee benefit obligations	(74)	(72)
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	(2)
Net (Gain) Loss	(18)	18
Prior Service Cost, Estimated	0
Net (Gain) Loss, Estimated	1
Net Regulatory Assets	$ (18)	$ 16