Retirement Benefits - Textual (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Total accumulated benefit obligation for the pension plans	$ 9,600,000,000	$ 10,000,000,000
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]
Expected postretirement trust contributions	$ 0
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 191,000,000
Projected benefit obligations	10,542,000,000	$ 10,909,000,000	$ 8,863,000,000
Total matching contributions	45,000,000	$ 542,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	$ 14,000,000
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 35,000,000
Projected benefit obligations	1,989,000,000	$ 1,986,000,000	$ 1,682,000,000
Total matching contributions	$ 39,000,000	39,000,000
Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Total accumulated benefit obligation for the pension plans	$ 2,300,000,000	$ 2,400,000,000
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]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 51,000,000
Projected benefit obligations	2,506,000,000	$ 2,592,000,000	$ 2,112,000,000
Total matching contributions	$ 12,000,000	$ 11,000,000
Alabama Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 9,000,000
Projected benefit obligations	505,000,000	$ 503,000,000	$ 431,000,000
Total matching contributions	1,000,000	$ 4,000,000
Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	$ 14,000,000
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]
Expected postretirement trust contributions	$ 0
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 66,000,000
Total accumulated benefit obligation for the pension plans	3,300,000,000	$ 3,500,000,000
Projected benefit obligations	3,615,000,000	3,781,000,000	$ 3,116,000,000
Total matching contributions	$ 14,000,000	$ 162,000,000
Georgia Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 17,000,000
Projected benefit obligations	854,000,000	$ 864,000,000	$ 723,000,000
Total matching contributions	$ 10,000,000	$ 8,000,000
Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
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]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 9,000,000
Total accumulated benefit obligation for the pension plans	424,000,000	$ 438,000,000
Projected benefit obligations	480,000,000	491,000,000	$ 395,000,000
Total matching contributions	1,000,000	$ 31,000,000
Gulf Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	$ 0
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 1,000,000
Projected benefit obligations	81,000,000	$ 78,000,000	$ 69,000,000
Total matching contributions	$ 3,000,000	3,000,000
Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual increase or decrease in assumed medical care cost trend rate	1.00%
Total accumulated benefit obligation for the pension plans	$ 447,000,000	462,000,000
Period over which company has elected to amortize changes in the market value of all plan assets	5 years
Total matching contributions	$ 5,000,000	$ 5,000,000	$ 4,000,000
Mississippi Power [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 9,000,000
Projected benefit obligations	500,000,000	$ 513,000,000	$ 409,000,000
Total matching contributions	$ 2,000,000	$ 36,000,000
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual salary increase on net periodic benefit costs	3.59%	3.59%	3.59%
Mortality Assumption Change	$ 2,000,000
Projected benefit obligations	97,000,000	$ 96,000,000	$ 81,000,000
Total matching contributions	$ 3,000,000	3,000,000
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	$ 92,000,000	87,000,000	84,000,000
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	$ 22,000,000	21,000,000	20,000,000
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	$ 26,000,000	25,000,000	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	$ 4,000,000	$ 4,000,000	$ 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	$ 10,000,000,000
Qualified Pension Plans [Member] | Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	2,400,000,000
Qualified Pension Plans [Member] | Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	3,500,000,000
Qualified Pension Plans [Member] | Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	0
Projected benefit obligations	457,000,000
Qualified Pension Plans [Member] | Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected postretirement trust contributions	0
Projected benefit obligations	470,000,000
Non Qualified Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	582,000,000
Non Qualified Pension Plans [Member] | Alabama Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	124,000,000
Non Qualified Pension Plans [Member] | Georgia Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	151,000,000
Non Qualified Pension Plans [Member] | Gulf Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	23,000,000
Non Qualified Pension Plans [Member] | Mississippi Power [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	$ 30,000,000