Contingencies and Regulatory Matters - Textual - APC (Details) - ALABAMA POWER CO	1 Months Ended	12 Months Ended
	Apr. 30, 2016 MW	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($) MW	Feb. 17, 2017 USD ($)	Jan. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Claims awarded to companies related to nuclear fuel disposal litigation			$ 26,000,000
Adjusting point of weighted cost of equity		5.98%
Percent of basis points		0.07%
Rate adjustment period		2 years
Maximum percentage of rate RSE		4.00%
Maximum annual percentage of ratio R\rate		5.00%
Rate RSE refund liability						$ 73,000,000
Rate RSE increase					4.48%
Rate RSE increase amount					$ 245,000,000
Tax cuts and jobs act, anticipated retail revenue reduction, next twelve months		$ 250,000,000
Under recovered certified power purchase agreements		12,000,000				142,000,000
Over (under) recovered environmental clause		17,000,000				9,000,000
Over recovered fuel cost		25,000,000				$ 76,000,000
Minimum natural disaster reserve balance, triggering establishment charge		50,000,000
Natural disaster reserve, expected collection annually until reserve is restored		16,000,000
Natural disaster reserve authorized limit		$ 75,000,000
Maximum period for recovery deferred stock related operations and maintenance costs and any future reserve deficits		24 months
Maximum rate NDR charge per month, monthly nonresidential customer account		$ 10
Maximum rate NDR charge per month, monthly residential customer account		5
Natural disaster reserve		$ 38,000,000
Minimum
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted cost of equity		5.75%
Potential period for next depreciation study		2 years
Maximum
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted cost of equity		6.21%
Potential period for next depreciation study		4 years
Regulatory Assets [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Under recovered certified power purchase agreements		$ 69,000,000
Over (under) recovered environmental clause				$ (36,000,000)
Plant Gorgas Units 6 and 7
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units included in request for decertification of units | MW			200
Plant Barry Unit 3
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units included in request for decertification of units | MW			225
Plant Barry Units 1 And 2
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units included in request for decertification of units | MW			250
Plant Greene County Units 1 And 2
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units included in request for decertification of units | MW	300