Contingencies and Regulatory Matters - Narrative (Details)																	1 Months Ended						3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended									29 Months Ended	57 Months Ended	60 Months Ended	84 Months Ended
	Oct. 20, 2016 USD ($)	Oct. 12, 2016 USD ($)	Sep. 30, 2016 USD ($) state mi	Aug. 17, 2016 USD ($)	Jun. 09, 2016 USD ($)	Jun. 03, 2016	May 03, 2016 USD ($)	May 01, 2016 USD ($)	Mar. 31, 2016 USD ($) MW	Dec. 31, 2015 USD ($)	Dec. 05, 2015 USD ($)	Dec. 03, 2015	Jul. 07, 2015 USD ($)	Apr. 15, 2015 USD ($)	Jan. 01, 2014 USD ($)	Mar. 19, 2013	Jun. 30, 2019 USD ($)	Apr. 30, 2016 MW	Mar. 31, 2016 USD ($) MW	Sep. 30, 2015 USD ($)	Feb. 28, 2013 USD ($)	Jan. 31, 2013 USD ($)	Sep. 30, 2016 USD ($) state mi	Sep. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) clause state mi MW	Sep. 30, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2010	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Sep. 30, 2016 USD ($) state mi	Sep. 30, 2016 USD ($) state mi	Dec. 31, 2020 USD ($)	Dec. 31, 2022	Jan. 01, 2121	Aug. 31, 2016	Jul. 28, 2016 MW	May 17, 2016 USD ($)	Apr. 01, 2016 USD ($)	Mar. 09, 2016 USD ($)	Jan. 05, 2016 USD ($)
Loss Contingencies [Line Items]
Maximum borrowing capacity			$ 8,445,000,000																				$ 8,445,000,000			$ 8,445,000,000											$ 8,445,000,000	$ 8,445,000,000
Construction work in progress			$ 10,069,000,000							$ 9,082,000,000													$ 10,069,000,000			$ 10,069,000,000				$ 9,082,000,000							$ 10,069,000,000	$ 10,069,000,000
Number of States in which Entity Operates | state			4																				4			4											4	4
Allowance for equity funds used during construction																							$ 52,000,000	$ 60,000,000		$ 150,000,000	$ 163,000,000
Other Regulatory Assets Current			$ 414,000,000							402,000,000													414,000,000			414,000,000				402,000,000							$ 414,000,000	$ 414,000,000
Scenario, Forecast [Member] | Customers [Member]
Loss Contingencies [Line Items]
Percentage basis net merger savings																																								60.00%
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Pre-tax charge to income																							88,000,000	150,000,000		222,000,000	182,000,000
After tax charge to income																							54,000,000	93,000,000		137,000,000	112,000,000
Georgia Power [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			23,000,000																				23,000,000			23,000,000											23,000,000	23,000,000
Capacity of renewable resources approved for procurement | MW																																											1,200
Capacity of renewable resources approved for self-build | MW																																											200
Rate ECR increase (decrease)																																												(15.00%)
Approved increase (decrease) in annual billings based on fuel cost recovery rate																																												$ (313,000,000)
Accrual under alternate rate plan																										30,000,000
Additional construction capital costs										3,300,000,000															$ 141,000,000
Percentage of proportionate share owed in consortium agreement																																				45.70%
Maximum borrowing capacity			1,750,000,000																				1,750,000,000			$ 1,750,000,000											1,750,000,000	1,750,000,000
Increase (decrease) in projected certified construction capital costs																										5.00%
Estimated in-service capital cost																																			$ 4,418,000,000
Amendment to estimated In-service capital cost																					$ 4,800,000,000
Retail rate of return on common equity																																10.95%
Construction work in progress			4,888,000,000							4,775,000,000													4,888,000,000			$ 4,888,000,000				4,775,000,000							4,888,000,000	4,888,000,000
Allowance for equity funds used during construction																										36,000,000	24,000,000
Other Regulatory Assets Current			115,000,000							123,000,000													115,000,000			115,000,000				123,000,000							115,000,000	115,000,000
Georgia Power [Member] | Other Current Liabilities [Member]
Loss Contingencies [Line Items]
Over recovered fuel balance			125,000,000																				125,000,000			125,000,000											125,000,000	125,000,000
Georgia Power [Member] | Other deferred credits and liabilities [Member]
Loss Contingencies [Line Items]
Over recovered fuel balance										116,000,000																				116,000,000
Georgia Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Capacity of renewable resources considered for renewable commercial and industrial program | MW																																											200
Storm restoration costs			155,000,000																				155,000,000			155,000,000											155,000,000	155,000,000
Additional construction capital costs																																				$ 114,000,000
Georgia Power [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Storm restoration costs			130,000,000																				130,000,000			130,000,000											130,000,000	130,000,000
Georgia Power [Member] | Intercession City Combustion Turbine [Member]
Loss Contingencies [Line Items]
Capacity of units approved for decertification | MW																																											143
Jointly owned utility plant, proportionate ownership share																																										33.00%
Georgia Power [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
Additional construction capital costs																													$ 5,440,000,000
Amendment to estimated In-service capital cost																													5,680,000,000
Percent of basis points																																							0.95%		0.30%
Requested rate increase (decrease) amount																												$ 70,000,000											$ (325,000,000)
Requested rate increase (decrease) amount, reduction in net income																																							$ (115,000,000)
Georgia Power [Member] | Scenario, Forecast [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Cost recovery, new nuclear																	$ 99,000,000
Georgia Power [Member] | Plant Mitchell Units 3, 4A, and 4B [Member]
Loss Contingencies [Line Items]
Capacity of units approved for decertification | MW																																											217
Georgia Power [Member] | Plant Kraft Unit 1 [Member]
Loss Contingencies [Line Items]
Capacity of units approved for decertification | MW																																											17
Georgia Power [Member] | Plant Vogtle Units 3 And 4 [Member]
Loss Contingencies [Line Items]
Maximum borrowing capacity																																														$ 920,000,000
Estimated in-service capital cost														$ 5,000,000,000
Construction work in progress			3,800,000,000																				3,800,000,000			3,800,000,000											3,800,000,000	3,800,000,000
Construction financing costs			1,200,000,000
Georgia Power [Member] | Plant Vogtle Units 3 And 4 [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Project settlement cost to be capitalized										350,000,000																				350,000,000
Project settlement cost to be capitalized, amount paid to date			256,000,000																				256,000,000			$ 256,000,000											256,000,000	256,000,000
Georgia Power [Member] | Plant Vogtle Units 3 And 4 [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
Construction financing costs																	22,000,000												2,400,000,000
Monthly Operational Readiness Costs																	$ 2,000,000
Georgia Power [Member] | Plant Vogtle Unit 3 [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Period Of Additional Current Schedule Pressure																										4 months
Georgia Power [Member] | Plant Vogtle Unit 3 [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Period Of Additional Current Schedule Pressure																										3 months
Gulf Power [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			46,000,000																				46,000,000			$ 46,000,000											46,000,000	46,000,000
Regulatory assets									$ 63,000,000										$ 63,000,000
Maximum borrowing capacity			280,000,000																				280,000,000			$ 280,000,000											280,000,000	280,000,000
Public utilities, approved return on equity percentage																										10.25%
Construction work in progress			64,000,000							48,000,000													64,000,000			$ 64,000,000				48,000,000							64,000,000	64,000,000
Reduction in depreciation expense																										$ 0				20,100,000	$ 8,400,000	$ 62,500,000
Number of regulatory clauses | clause																										4
Other Regulatory Assets Current			62,000,000							90,000,000													62,000,000			$ 62,000,000				90,000,000							62,000,000	62,000,000
Gulf Power [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount																												(41,000,000)
Gulf Power [Member] | Plant Scherer Unit 3 [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount																												14,000,000	11,000,000
Gulf Power [Member] | Plant Smith Units 1 and 2 [Member]
Loss Contingencies [Line Items]
Capacity of units approved for decertification | MW									357										357
Southern Company Gas [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			433,000,000																				433,000,000			433,000,000											433,000,000	433,000,000
Maximum borrowing capacity			2,000,000,000																				2,000,000,000			2,000,000,000											2,000,000,000	2,000,000,000
Infrastructure Improvement Program, Annual Investment Amount																										110,000,000
Infrastructure Improvement Program, Petitioned Annual Investment Amount																										44,000,000
Southern Company Gas [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Infrastructure Improvement Program, Annual Investment Amount																										250,000,000
Southern Company Gas [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Infrastructure Improvement Program, Annual Investment Amount																										10,000,000
Nicor Gas [Member]
Loss Contingencies [Line Items]
Loss contingency damages sought																				$ 300,000
Maximum borrowing capacity			700,000,000																				700,000,000			700,000,000											700,000,000	700,000,000
Mississippi Power [Member]
Loss Contingencies [Line Items]
Increase in base rate under cost based electric tariff due to settlement								$ 7,000,000
Over recovered fuel cost			58,000,000							71,000,000													58,000,000			58,000,000				71,000,000							58,000,000	58,000,000
Approved increase (decrease) in fuel rates amount				$ 18,000,000			$ (2,000,000)
Approved increase (decrease) in annual billings based on fuel cost recovery rate				$ (51,000,000)																																											$ (120,000,000)
Maximum borrowing capacity			175,000,000																				175,000,000			175,000,000											175,000,000	175,000,000
Construction work in progress			2,525,000,000							2,254,000,000													2,525,000,000			$ 2,525,000,000				2,254,000,000							2,525,000,000	2,525,000,000
Annual PEP filing rate increase amount																																													$ 5,000,000
Approved rate increase (decrease) percentage															3.00%	15.00%
Plant capacity under coal gasification combined cycle technology (in MWs) | MW																										582
Costs associated with CCP12 grant funds																																	$ 245,000,000
Settlement agreement collection amount to mitigate rate impact year two															$ 156,000,000
Allowance for equity funds used during construction																							31,000,000	29,000,000		$ 90,000,000	82,000,000
Retail rate recovery													$ 342,000,000
Carrying costs associated with retail rate recovery													$ 29,000,000
Other Regulatory Assets Current			118,000,000							95,000,000													118,000,000			118,000,000				95,000,000							118,000,000	118,000,000
Regulatory liabilities			7,000,000																				7,000,000			7,000,000											7,000,000	7,000,000
Mississippi Power [Member] | Construction in Progress [Member]
Loss Contingencies [Line Items]
Estimate of possible loss			2,630,000,000																				2,630,000,000			2,630,000,000											2,630,000,000	2,630,000,000
Mississippi Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Approved rate increase (decrease) percentage				2.00%
Costs due to extension of in-service date																										35,000,000
Mississippi Power [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Costs due to extension of in-service date																										25,000,000
Mississippi Power [Member] | MRA Revenue [Member]
Loss Contingencies [Line Items]
Over recovered fuel cost			17,000,000							24,000,000													17,000,000			17,000,000				24,000,000							17,000,000	17,000,000
Approved increase (decrease) in fuel rates amount																										(11,000,000)
Mississippi Power [Member] | MB Revenue [Member]
Loss Contingencies [Line Items]
Over recovered fuel cost			1,000,000							1,000,000													1,000,000			1,000,000				1,000,000							1,000,000	1,000,000
Approved increase (decrease) in fuel rates amount																										(1,000,000)
Mississippi Power [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
AFUDC cost																													$ 11,000,000
Approved increase (decrease) in fuel rates amount																												$ 22,000,000
Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Period of amortization of regulatory assets									36 months
Regulatory assets			$ 105,000,000																				$ 105,000,000			$ 105,000,000											$ 105,000,000	$ 105,000,000
Pipeline Infrastructure (in miles) | mi			61																				61			61											61	61
Estimated cost																										$ 5,300,000,000							2,880,000,000
Costs associated with CCP12 grant funds																										(140,000,000)
Pre-tax charge to income																							$ 88,000,000			222,000,000												$ 2,630,000,000
After tax charge to income																							$ 54,000,000			137,000,000												$ 1,630,000,000
Monthly charge of allowance for equity funds used during construction																										15,000,000
Monthly cost regulatory assets deferred																										$ 3,000,000
Allowance for equity funds used during construction																																					$ 352,000,000
Purchase of interest			100.00%									15.00%											100.00%			100.00%											100.00%	100.00%
Maximum cap construction cost																										$ 6,530,000,000
Period Of Commercial Operations Established By Discovery Docket																										5 years
Other Regulatory Assets Current			$ 105,000,000																				$ 105,000,000			$ 105,000,000											$ 105,000,000	$ 105,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Cost Estimate Extension [Member]
Loss Contingencies [Line Items]
Estimated cost																							$ 53,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Post In-Service Costs [Member]
Loss Contingencies [Line Items]
Estimated cost																										78,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Current Estimate [Member]
Loss Contingencies [Line Items]
Estimated cost																										5,520,000,000
Costs associated with CCP12 grant funds																										(140,000,000)
Maximum cap construction cost																										6,820,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | In-Service Asset Proposal [Member]
Loss Contingencies [Line Items]
Approved increase (decrease) in fuel rates amount											$ 126,000,000															$ 159,000,000
Public utilities, approved return on equity percentage												9.225%
Public utilities approved equity capital structure percentage												49.733%
Customer refund																			$ 11,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Denbury Onshore, Contractor [Member]
Loss Contingencies [Line Items]
Long-term contract for purchase of percentage of carbon dioxide captured from plant			70.00%			100.00%																	70.00%			70.00%											70.00%	70.00%
Mississippi Power [Member] | Kemper IGCC [Member] | Treetop Midstream Services, LLC, Contractor [Member]
Loss Contingencies [Line Items]
Long-term contract for purchase of percentage of carbon dioxide captured from plant			30.00%																				30.00%			30.00%											30.00%	30.00%
Mississippi Power [Member] | Kemper IGCC [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Loss contingency damages sought					$ 100,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Property, Plant and Equipment [Member]
Loss Contingencies [Line Items]
Estimated cost																										$ 3,700,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Other Property And Investments [Member]
Loss Contingencies [Line Items]
Estimated cost																										6,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Fossil Fuel Stock [Member]
Loss Contingencies [Line Items]
Estimated cost																										81,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Materials And Supplies [Member]
Loss Contingencies [Line Items]
Estimated cost																										46,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Other regulatory assets, current [Member]
Loss Contingencies [Line Items]
Estimated cost																										33,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Other regulatory assets, deferred [Member]
Loss Contingencies [Line Items]
Estimated cost																										177,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Other current assets [Member]
Loss Contingencies [Line Items]
Estimated cost																										4,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Other deferred charges and assets [Member]
Loss Contingencies [Line Items]
Estimated cost																										9,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Current Assets [Member]
Loss Contingencies [Line Items]
Regulatory assets			$ 33,000,000																				$ 33,000,000			$ 33,000,000											$ 33,000,000	$ 33,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Estimated cost																																	2,880,000,000
Amortization period of regulatory assets and liabilities																										10 years
Mississippi Power [Member] | Kemper IGCC [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Amortization period of regulatory assets and liabilities																										2 years
Mississippi Power [Member] | Electricity Generation Plant, Non-Nuclear [Member]
Loss Contingencies [Line Items]
Estimated cost																						$ 2,400,000,000											$ 2,400,000,000
Alternate financing																																$ 1,000,000,000
Mississippi Power [Member] | Electricity Generation Plant, Non-Nuclear [Member] | Denbury Onshore, Contractor [Member]
Loss Contingencies [Line Items]
Long-term contract for purchase of carbon dioxide term						16 years
Mississippi Power [Member] | Mine [Member]
Loss Contingencies [Line Items]
Term of management fee contract																																		40 years
Alabama Power [Member]
Loss Contingencies [Line Items]
Maximum borrowing capacity			1,335,000,000																				1,335,000,000			$ 1,335,000,000											1,335,000,000	1,335,000,000
Construction work in progress			473,000,000							801,000,000													473,000,000			473,000,000				801,000,000							473,000,000	473,000,000
Allowance for equity funds used during construction																							7,000,000	$ 14,000,000		23,000,000	$ 43,000,000
Other Regulatory Assets Current			73,000,000							$ 115,000,000													73,000,000			73,000,000				$ 115,000,000							73,000,000	73,000,000
Alabama Power [Member] | Plant Greene County Units 1 And 2 [Member]
Loss Contingencies [Line Items]
Capacity of units ceased using coal | MW																		300
Georgia Power And Atlanta Gas Light Company [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
Percentage basis net merger savings																																								40.00%
Storm Costs [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Regulatory assets			94,000,000																				94,000,000			94,000,000											94,000,000	94,000,000
Subsequent Event [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Estimate of possible loss	$ 240,000,000
Public utilities, approved return on equity percentage	10.00%
Subsequent Event [Member] | Gulf Power [Member]
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage		11.00%
Requested rate increase (decrease) amount		$ 106,800,000
Location One [Member] | Southern Company Gas [Member]
Loss Contingencies [Line Items]
Environmental remediation liability			$ 5,000,000																				$ 5,000,000			$ 5,000,000											$ 5,000,000	$ 5,000,000
Infrastructure Program [Member] | Southern Company Gas [Member]
Loss Contingencies [Line Items]
Number of States in which Entity Operates | state			6																				6			6											6	6
Infrastructure Program [Member] | Southern Company Gas [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Program Duration Period																										10 years
Infrastructure Program [Member] | Southern Company Gas [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Program Duration Period																										4 years