Retirement Benefits - Pension Plan and Other Postretirement Benefit Plan Assets (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Pension Plans [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Pension Plans [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	26.00%
Defined Benefit Plan Assets	30.00%	30.00%
Pension Plans [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	23.00%	23.00%
Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	23.00%
Defined Benefit Plan Assets	23.00%	27.00%
Pension Plans [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Pension Plans [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	14.00%
Defined Benefit Plan Assets	16.00%	14.00%
Pension Plans [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	6.00%	5.00%
Other Postretirement Benefits [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Other Postretirement Benefits [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	42.00%
Defined Benefit Plan Assets	38.00%	41.00%
Other Postretirement Benefits [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	21.00%
Defined Benefit Plan Assets	23.00%	23.00%
Other Postretirement Benefits [Member] | Domestic fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	24.00%
Defined Benefit Plan Assets	26.00%	26.00%
Other Postretirement Benefits [Member] | Global fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	4.00%
Defined Benefit Plan Assets	4.00%	3.00%
Other Postretirement Benefits [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	1.00%
Defined Benefit Plan Assets	1.00%	0.00%
Other Postretirement Benefits [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	5.00%
Defined Benefit Plan Assets	6.00%	5.00%
Other Postretirement Benefits [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	2.00%
Alabama Power [Member] | Pension Plans [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Alabama Power [Member] | Pension Plans [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	26.00%
Defined Benefit Plan Assets	30.00%	30.00%
Alabama Power [Member] | Pension Plans [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	23.00%	23.00%
Alabama Power [Member] | Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	23.00%
Defined Benefit Plan Assets	23.00%	27.00%
Alabama Power [Member] | Pension Plans [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Alabama Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	14.00%
Defined Benefit Plan Assets	16.00%	14.00%
Alabama Power [Member] | Pension Plans [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	6.00%	5.00%
Alabama Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Alabama Power [Member] | Other Postretirement Benefits [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	48.00%
Defined Benefit Plan Assets	45.00%	48.00%
Alabama Power [Member] | Other Postretirement Benefits [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	20.00%
Defined Benefit Plan Assets	20.00%	20.00%
Alabama Power [Member] | Other Postretirement Benefits [Member] | Domestic fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	24.00%
Defined Benefit Plan Assets	27.00%	26.00%
Alabama Power [Member] | Other Postretirement Benefits [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	1.00%
Defined Benefit Plan Assets	1.00%	0.00%
Alabama Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	4.00%
Defined Benefit Plan Assets	5.00%	4.00%
Alabama Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	2.00%
Georgia Power [Member] | Pension Plans [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Georgia Power [Member] | Pension Plans [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	26.00%
Defined Benefit Plan Assets	30.00%	30.00%
Georgia Power [Member] | Pension Plans [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	23.00%	23.00%
Georgia Power [Member] | Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	23.00%
Defined Benefit Plan Assets	23.00%	27.00%
Georgia Power [Member] | Pension Plans [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Georgia Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	14.00%
Defined Benefit Plan Assets	16.00%	14.00%
Georgia Power [Member] | Pension Plans [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	6.00%	5.00%
Georgia Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	40.00%
Defined Benefit Plan Assets	34.00%	38.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	21.00%
Defined Benefit Plan Assets	27.00%	26.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | Domestic fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	23.00%
Defined Benefit Plan Assets	25.00%	24.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | Global fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	8.00%	7.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	1.00%
Defined Benefit Plan Assets	0.00%	0.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	4.00%
Defined Benefit Plan Assets	4.00%	4.00%
Georgia Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	2.00%
Defined Benefit Plan Assets	2.00%	1.00%
Gulf Power [Member] | Pension Plans [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Gulf Power [Member] | Pension Plans [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	26.00%
Defined Benefit Plan Assets	30.00%	30.00%
Gulf Power [Member] | Pension Plans [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	23.00%	23.00%
Gulf Power [Member] | Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	23.00%
Defined Benefit Plan Assets	23.00%	27.00%
Gulf Power [Member] | Pension Plans [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Gulf Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	14.00%
Defined Benefit Plan Assets	16.00%	14.00%
Gulf Power [Member] | Pension Plans [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	6.00%	5.00%
Gulf Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Gulf Power [Member] | Other Postretirement Benefits [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	29.00%	29.00%
Gulf Power [Member] | Other Postretirement Benefits [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	24.00%
Defined Benefit Plan Assets	22.00%	22.00%
Gulf Power [Member] | Other Postretirement Benefits [Member] | Domestic fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	25.00%	29.00%
Gulf Power [Member] | Other Postretirement Benefits [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Gulf Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	14.00%
Defined Benefit Plan Assets	16.00%	14.00%
Gulf Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	6.00%	5.00%
Mississippi Power [Member] | Pension Plans [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Mississippi Power [Member] | Pension Plans [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	26.00%
Defined Benefit Plan Assets	30.00%	30.00%
Mississippi Power [Member] | Pension Plans [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	25.00%
Defined Benefit Plan Assets	23.00%	23.00%
Mississippi Power [Member] | Pension Plans [Member] | Fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	23.00%
Defined Benefit Plan Assets	23.00%	27.00%
Mississippi Power [Member] | Pension Plans [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Mississippi Power [Member] | Pension Plans [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	14.00%
Defined Benefit Plan Assets	16.00%	14.00%
Mississippi Power [Member] | Pension Plans [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	9.00%
Defined Benefit Plan Assets	6.00%	5.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	100.00%
Defined Benefit Plan Assets	100.00%	100.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Domestic Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	21.00%
Defined Benefit Plan Assets	24.00%	24.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member] | International Equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	20.00%
Defined Benefit Plan Assets	18.00%	19.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Fixed income [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	38.00%
Defined Benefit Plan Assets	38.00%	41.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Special situations [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	3.00%
Defined Benefit Plan Assets	2.00%	1.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Real estate investments [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	11.00%
Defined Benefit Plan Assets	13.00%	11.00%
Mississippi Power [Member] | Other Postretirement Benefits [Member] | Private equity [Member]
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Defined Benefit Plan Assets, Target	7.00%
Defined Benefit Plan Assets	5.00%	4.00%