Retirement Benefits - Components of Accumulated OCI and Changes in Regulatory Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Postretirement Benefits [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	$ (387)	$ (372)
Reclassification adjustments
Amortization of prior service costs	21	6	$ 21
Net periodic benefit cost	64	47	63
Other Postretirement Benefits [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	366	73
Net (gain) loss	33	301
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(379)	(364)
Change in prior service costs	(33)	2
Reclassification adjustments
Amortization of prior service costs	(4)	(4)
Amortization of net gain (loss)	(17)	(2)
Total reclassification adjustments	(21)	(6)
Net periodic benefit cost	45	293
Ending Balance	411	366	73
Other Postretirement Benefits [Member] | AOCI Attributable to Parent [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	8	1
Net (gain) loss	0	7
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(8)	(8)
Change in prior service costs	0	0
Reclassification adjustments
Amortization of prior service costs	0	0
Amortization of net gain (loss)	0	0
Total reclassification adjustments	0	0
Net periodic benefit cost	0	7
Ending Balance	8	8	1
Pension Plan [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(3,093)	(3,152)
Reclassification adjustments
Amortization of prior service costs	25	26	27
Net periodic benefit cost	218	139	245
Pension Plan [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	3,073	1,651
Net (gain) loss	155	1,552
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(2,971)	(3,022)
Change in prior service costs		(1)
Reclassification adjustments
Amortization of prior service costs	(24)	(25)
Amortization of net gain (loss)	(206)	(106)
Total reclassification adjustments	(230)	(131)
Net periodic benefit cost	(75)	1,422
Ending Balance	2,998	3,073	1,651
Pension Plan [Member] | AOCI Attributable to Parent [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	134	64
Net (gain) loss	1	75
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(122)	(130)
Change in prior service costs		0
Reclassification adjustments
Amortization of prior service costs	(1)	(1)
Amortization of net gain (loss)	(9)	(4)
Total reclassification adjustments	(10)	(5)
Net periodic benefit cost	(9)	70
Ending Balance	125	134	64
Georgia Power [Member] | Other Postretirement Benefits [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(215)	(218)
Reclassification adjustments
Amortization of prior service costs	11	2	12
Net periodic benefit cost	28	17	26
Georgia Power [Member] | Other Postretirement Benefits [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	213	69
Net (gain) loss	9	146
Change in prior service costs	(12)	0
Reclassification adjustments
Amortization of net gain (loss)	(11)	(2)
Net periodic benefit cost	10	144
Ending Balance	223	213	69
Georgia Power [Member] | Pension Plan [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(1,068)	(1,085)
Reclassification adjustments
Amortization of prior service costs	9	10	10
Net periodic benefit cost	61	38	79
Georgia Power [Member] | Pension Plan [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	1,102	610
Net (gain) loss	59	543
Reclassification adjustments
Amortization of prior service costs	(9)	(10)
Amortization of net gain (loss)	(76)	(41)
Total reclassification adjustments	(85)	(51)
Net periodic benefit cost	(26)	492
Ending Balance	1,076	1,102	610
Alabama Power [Member] | Other Postretirement Benefits [Member]
Reclassification adjustments
Amortization of prior service costs	5	4	5
Net periodic benefit cost	5	4	7
Alabama Power [Member] | Other Postretirement Benefits [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	54	(15)
Net (gain) loss	25	73
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(63)	(39)
Change in prior service costs	(8)	0
Reclassification adjustments
Amortization of prior service costs	(3)	(4)
Amortization of net gain (loss)	(2)	0
Total reclassification adjustments	(5)	(4)
Net periodic benefit cost	28	69
Ending Balance	82	54	(15)
Alabama Power [Member] | Pension Plan [Member]
Reclassification adjustments
Amortization of prior service costs	6	7	7
Net periodic benefit cost	48	21	47
Alabama Power [Member] | Pension Plan [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	827	476
Net (gain) loss	56	389
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(816)	(815)
Reclassification adjustments
Amortization of prior service costs	(6)	(7)
Amortization of net gain (loss)	(55)	(31)
Total reclassification adjustments	(61)	(38)
Net periodic benefit cost	(5)	351
Ending Balance	822	827	476
Gulf Power [Member]
Reclassification adjustments
Amortization of prior service costs	1	1	1
Net periodic benefit cost	10	7	12
Gulf Power [Member] | Other Postretirement Benefits [Member]
Reclassification adjustments
Amortization of prior service costs	0	0	0
Net periodic benefit cost	3	3	3
Gulf Power [Member] | Other Postretirement Benefits [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	2	(7)
Net (gain) loss	1	11
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(5)	(4)
Change in prior service costs	(2)	2
Reclassification adjustments
Amortization of prior service costs	0	0
Amortization of net gain (loss)	0	0
Total reclassification adjustments	0	0
Net periodic benefit cost	3	9
Ending Balance	5	2	(7)
Gulf Power [Member] | Pension Plan [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(140)	(143)
Gulf Power [Member] | Pension Plan [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	146	75
Net (gain) loss	6	77
Reclassification adjustments
Amortization of prior service costs	(1)	(1)
Amortization of net gain (loss)	(9)	(5)
Total reclassification adjustments	(10)	(6)
Net periodic benefit cost	(4)	71
Ending Balance	142	146	75
Mississippi Power [Member]
Reclassification adjustments
Amortization of prior service costs	1	1	1
Net periodic benefit cost	12	7	13
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	18	(18)
Reclassification adjustments
Amortization of prior service costs	1	0	0
Net periodic benefit cost	4	3	4
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	16	2
Net (gain) loss	0	14
Change in prior service costs	(3)	0
Reclassification adjustments
Amortization of net gain (loss)	(1)	0
Total reclassification adjustments	(1)	0
Net periodic benefit cost	2	14
Ending Balance	18	16	2
Mississippi Power [Member] | Pension Plan [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	(142)	(148)
Mississippi Power [Member] | Pension Plan [Member] | Net Regulatory Assets/Liabilities [Member]
Changes in the Balance of AOCI and Regulatory Assets [Roll Forward]
Beginning Balance	151	78
Net (gain) loss	4	79
Reclassification adjustments
Amortization of prior service costs	(1)	(1)
Amortization of net gain (loss)	(10)	(5)
Total reclassification adjustments	(11)	(6)
Net periodic benefit cost	(7)	73
Ending Balance	$ 144	$ 151	$ 78