Income Taxes - Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State income tax, net of federal deduction	2.30%	2.50%	2.50%
Employee stock plans dividend deduction	(1.40%)	(1.60%)	(1.00%)
Non-deductible book depreciation	1.40%	1.50%	0.90%
AFUDC-Equity	(2.90%)	(2.60%)	(1.30%)
ITC basis difference	(1.60%)	(1.20%)	(0.30%)
Other	(0.30%)	(0.50%)	(0.20%)
Effective income tax rate	32.50%	33.10%	35.60%
Alabama Power [Member]
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State income tax, net of federal deduction	4.40%	4.00%	4.10%
Non-deductible book depreciation	1.10%	1.00%	0.90%
Difference in prior years' deferred and current tax rate	(0.10%)	(0.10%)	(0.10%)
AFUDC-Equity	(1.30%)	(0.90%)	(0.50%)
Other	(0.10%)	(0.10%)	(0.30%)
Effective income tax rate	39.00%	38.90%	39.10%
Georgia Power [Member]
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State income tax, net of federal deduction	2.20%	2.50%	1.60%
Non-deductible book depreciation	1.30%	1.30%	1.20%
AFUDC-Equity	(0.80%)	(0.60%)	(1.00%)
Other	(0.70%)	(0.40%)	(0.10%)
Effective income tax rate	37.00%	37.80%	36.70%
Gulf Power [Member]
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State income tax, net of federal deduction	3.50%	3.50%	3.30%
Non-deductible book depreciation	0.40%	0.50%	0.50%
Difference in prior years' deferred and current tax rate	(0.10%)	(0.20%)	(0.20%)
AFUDC-Equity	(1.80%)	(1.10%)	(0.90%)
Other	0.10%	(0.10%)	(0.20%)
Effective income tax rate	37.10%	37.60%	37.50%
Mississippi Power [Member]
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	(35.00%)	(35.00%)	35.00%
State income tax, net of federal deduction	(4.00%)	(3.70%)	1.30%
Non-deductible book depreciation	0.10%	0.10%	0.30%
AFUDC-Equity	(7.80%)	(5.00%)	(18.60%)
Other	0.10%	(0.10%)	(1.20%)
Effective income tax rate	(46.60%)	(43.70%)	16.80%
Southern Power [Member]
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State income tax, net of federal deduction	(6.00%)	2.20%	3.70%
Amortization of ITC	(4.30%)	(1.70%)	(1.00%)
ITC basis difference	(27.70%)	(14.50%)	(2.60%)
Other	1.10%	0.30%	(0.60%)
Effective income tax rate	(1.90%)	21.30%	34.50%