Retirement Benefits - Textual (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%	3.84%
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Total accumulated benefit obligation for the pension plans	$ 10,000,000,000	$ 8,100,000,000
Period over which company has elected to amortize changes in the market value of all plan assets	5 years
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	500,000,000
Expected postretirement trust contributions	0
Discount rate on net periodic benefit costs	4.17%	5.02%	4.26%	4.98%
Mortality Assumption Change	636,000,000
Projected benefit obligations	10,909,000,000	8,863,000,000	9,302,000,000
Total matching contributions	542,000,000	39,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	19,000,000
Discount rate on net periodic benefit costs	4.04%	4.85%	4.05%	4.88%
Mortality Assumption Change	92,000,000
Projected benefit obligations	1,986,000,000	1,682,000,000	1,872,000,000
Total matching contributions	39,000,000	39,000,000
Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%	3.84%
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Total accumulated benefit obligation for the pension plans	2,400,000,000	1,900,000,000
Period over which company has elected to amortize changes in the market value of all plan assets	5 years
Alabama Power [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Voluntary Contribution to Pension Plan	0
Expected postretirement trust contributions	0
Discount rate on net periodic benefit costs	4.18%	5.02%	4.27%	4.98%
Mortality Assumption Change	156,000,000
Projected benefit obligations	2,592,000,000	2,112,000,000	2,218,000,000
Total matching contributions	11,000,000	9,000,000
Alabama Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	2,000,000
Discount rate on net periodic benefit costs	4.04%	4.86%	4.06%	4.88%
Mortality Assumption Change	22,000,000
Projected benefit obligations	503,000,000	431,000,000	490,000,000
Total matching contributions	4,000,000	7,000,000
Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	17,000,000
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%	3.84%
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Period over which company has elected to amortize changes in the market value of all plan assets	5 years
Georgia Power [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	150,000,000
Expected postretirement trust contributions	0
Discount rate on net periodic benefit costs	4.18%	5.02%	4.27%	4.98%
Mortality Assumption Change	226,000,000
Total accumulated benefit obligation for the pension plans	3,500,000,000	2,900,000,000
Projected benefit obligations	3,781,000,000	3,116,000,000	3,312,000,000
Total matching contributions	162,000,000	12,000,000
Georgia Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate on net periodic benefit costs	4.03%	4.85%	4.04%	4.87%
Mortality Assumption Change	46,000,000
Projected benefit obligations	864,000,000	723,000,000	800,000,000
Total matching contributions	8,000,000	11,000,000
Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%	3.84%
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Period over which company has elected to amortize changes in the market value of all plan assets	5 years
Gulf Power [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate on net periodic benefit costs	4.18%	5.02%	4.27%	4.98%
Mortality Assumption Change	29,600,000
Total accumulated benefit obligation for the pension plans	438,000,000	353,000,000
Projected benefit obligations	490,561,000	395,328,000	413,501,000
Total matching contributions	31,251,000	1,134,000
Gulf Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	0
Discount rate on net periodic benefit costs	4.04%	4.86%	4.06%	4.88%
Mortality Assumption Change	2,600,000
Projected benefit obligations	78,501,000	68,579,000	75,395,000
Total matching contributions	2,846,000	2,381,000
Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%	3.84%
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Total accumulated benefit obligation for the pension plans	462,000,000	370,000,000
Period over which company has elected to amortize changes in the market value of all plan assets	5 years
Total matching contributions	4,600,000	4,100,000	3,900,000
Mississippi Power [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	33,000,000
Discount rate on net periodic benefit costs	4.17%	5.01%	4.26%	4.98%
Mortality Assumption Change	30,200,000
Projected benefit obligations	512,847,000	409,395,000	432,553,000
Total matching contributions	35,526,000	2,430,000
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate on net periodic benefit costs	4.03%	4.85%	4.04%	4.87%
Mortality Assumption Change	5,200,000
Projected benefit obligations	95,655,000	80,940,000	91,783,000
Total matching contributions	3,413,000	2,562,000
Employee Saving Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching limit of contribution by employer	85.00%
Maximum limit of contribution of employees base salary	6.00%
Total matching contributions	87,000,000	84,000,000	82,000,000
Employee Saving Plan [Member] | Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching limit of contribution by employer	85.00%
Maximum limit of contribution of employees base salary	6.00%
Total matching contributions	21,000,000	20,000,000	19,000,000
Employee Saving Plan [Member] | Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching limit of contribution by employer	85.00%
Maximum limit of contribution of employees base salary	6.00%
Total matching contributions	25,000,000	24,000,000	24,000,000
Employee Saving Plan [Member] | Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching limit of contribution by employer	85.00%
Maximum limit of contribution of employees base salary	6.00%
Total matching contributions	4,200,000	4,100,000	4,000,000
Employee Saving Plan [Member] | Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching limit of contribution by employer	85.00%
Maximum limit of contribution of employees base salary	6.00%
Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	10,300,000,000
Qualified Pension Plans [Member] | Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	2,500,000,000
Qualified Pension Plans [Member] | Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	3,600,000,000
Qualified Pension Plans [Member] | Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	30,000,000
Expected postretirement trust contributions	0
Projected benefit obligations	464,000,000
Qualified Pension Plans [Member] | Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	0
Projected benefit obligations	481,000,000
Non Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	617,000,000
Non Qualified Pension Plans [Member] | Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	123,000,000
Non Qualified Pension Plans [Member] | Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	165,000,000
Non Qualified Pension Plans [Member] | Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	26,000,000
Non Qualified Pension Plans [Member] | Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	$ 32,000,000