Income Taxes - Reconciliation of Federal Statutory Income Tax Rate (Details)	6 Months Ended		12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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			2.10%	1.90%	2.30%
Employee stock plans dividend deduction			(1.20%)	(1.20%)	(1.40%)
Non-deductible book depreciation			0.90%	1.20%	1.40%
AFUDC-Equity			(2.00%)	(2.20%)	(2.90%)
Amortization of ITC			(0.90%)	(0.50%)	(0.50%)
ITC basis difference			(5.00%)	(1.50%)	(1.60%)
Production tax credits			(1.20%)	(0.00%)	(0.00%)
Other			(0.40%)	0.20%	0.20%
Effective income tax rate			27.30%	32.90%	32.50%
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			4.20%	3.80%	4.40%
Non-deductible book depreciation			1.00%	1.20%	1.10%
AFUDC-Equity			(0.70%)	(1.60%)	(1.30%)
Other			(0.70%)	0.00%	(0.20%)
Effective income tax rate			38.80%	38.40%	39.00%
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			2.10%	2.50%	2.20%
Non-deductible book depreciation			0.80%	1.20%	1.30%
AFUDC-Equity			(0.80%)	(0.70%)	(0.80%)
Other			(0.40%)	(0.40%)	(0.70%)
Effective income tax rate			36.70%	37.60%	37.00%
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			3.40%	3.90%	3.50%
Non-deductible book depreciation			0.60%	0.50%	0.40%
Difference in prior years' deferred and current tax rate			(0.10%)	(0.10%)	(0.10%)
AFUDC-Equity			(0.00%)	(1.80%)	(1.80%)
Other			0.60%	(0.60%)	0.10%
Effective income tax rate			39.50%	36.90%	37.10%
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			5.70%	6.30%	4.00%
Non-deductible book depreciation			(0.70%)	(1.30%)	(0.10%)
AFUDC-Equity			28.50%	49.60%	7.80%
Other			0.00%	2.90%	(0.10%)
Effective income tax rate			68.50%	92.50%	46.60%
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			(9.10%)	(0.30%)	(6.00%)
Amortization of ITC			(20.60%)	(5.00%)	(4.30%)
ITC basis difference			(89.00%)	(21.50%)	(27.70%)
Production tax credits			(23.30%)	(0.60%)	(0.00%)
Noncontrolling interests			(6.20%)	(1.70%)	(0.30%)
Other			4.60%	2.50%	1.40%
Effective income tax rate			(108.60%)	8.40%	(1.90%)
Successor [Member] | Southern Company Gas [Member]
Reconciliation of federal statutory income tax rate to effective income tax rate
Federal statutory rate	35.00%
State income tax, net of federal deduction	4.00%
Other	1.00%
Effective income tax rate	40.00%
Predecessor [Member] | Southern Company Gas [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%		3.40%	3.80%
Other		(0.90%)		(2.00%)	(1.20%)
Effective income tax rate		37.60%		36.40%	37.60%