Contingencies and Regulatory Matters - Textual - Regulatory Matters (Details)																		1 Months Ended						3 Months Ended		6 Months Ended	12 Months Ended										14 Months Ended	48 Months Ended	84 Months Ended	90 Months Ended
	Feb. 21, 2017 USD ($)	Feb. 14, 2017 USD ($)	Jan. 01, 2017 USD ($)	Dec. 31, 2016 USD ($) utility	Dec. 20, 2016 USD ($)	Dec. 13, 2016	Dec. 06, 2016 USD ($) $ / KWH_Kilowatt_hour	Dec. 05, 2016 USD ($)	Oct. 12, 2016 USD ($)	Sep. 01, 2016 USD ($)	Aug. 17, 2016 USD ($)	Aug. 01, 2016 USD ($)	Jul. 28, 2016 MW	Mar. 09, 2016 USD ($) mi	Jan. 01, 2016 USD ($)	Jan. 01, 2015 USD ($)	Jan. 01, 2013	Dec. 31, 2016 USD ($) utility $ / KWH_Kilowatt_hour	Jul. 31, 2016 USD ($)	Nov. 30, 2015 $ / KWH_Kilowatt_hour	Oct. 31, 2015 USD ($)	Sep. 30, 2015 USD ($) station mi	Apr. 30, 2015 MW	Dec. 31, 2016 USD ($) utility	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) utility	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) $ / KWH_Kilowatt_hour	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) utility rate_plan_filing $ / KWH_Kilowatt_hour	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) MW	Dec. 31, 2013 USD ($) Customer mi	Dec. 31, 2012 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($) MW	Sep. 30, 2015 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2022	Jun. 30, 2016 USD ($)	Jan. 01, 2121	Jan. 01, 2021	Jun. 30, 2019 USD ($)	Oct. 01, 2017 $ / item	Feb. 17, 2017 USD ($)	Feb. 03, 2017 USD ($)	Dec. 01, 2016 USD ($)	Nov. 30, 2016 USD ($)	Oct. 01, 2016 $ / item	Aug. 31, 2016	Aug. 29, 2016 USD ($)	Jun. 17, 2016 USD ($)	May 17, 2016 USD ($)	May 03, 2016 USD ($)	Mar. 31, 2016 MW	Jan. 05, 2016 USD ($)	Oct. 01, 2015 $ / item	Feb. 28, 2015 USD ($)	Sep. 30, 2014
Schedule of Regulatory Assets and Liabilities [Line Items]
Other Regulatory Assets Current				$ 581,000,000														$ 581,000,000						$ 581,000,000		$ 581,000,000				$ 581,000,000	$ 580,000,000
Line of Credit Facility, Maximum Borrowing Capacity				8,443,000,000														8,443,000,000						8,443,000,000		8,443,000,000				8,443,000,000
Construction in Progress, Gross				8,977,000,000														8,977,000,000						8,977,000,000		8,977,000,000				8,977,000,000	9,082,000,000
Other Cost of Removal Obligations				2,748,000,000														2,748,000,000						2,748,000,000		2,748,000,000				$ 2,748,000,000	1,162,000,000
Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Performance Evaluation Plan, Number Of Filings Per Calendar Year | rate_plan_filing																														2
Other Regulatory Assets Current				115,000,000														115,000,000						115,000,000		115,000,000				$ 115,000,000	95,000,000
Over Recovered Fuel Cost																															71,000,000
Approved Increase (Decrease) in Annual Billing Based on Fuel Cost Recovery Rate											$ (51,000,000)																																													$ (120,000,000)
Storm Restoration Costs				0														0						0		0				0
Line of Credit Facility, Maximum Borrowing Capacity				173,000,000														173,000,000						173,000,000		173,000,000				173,000,000
Construction in Progress, Gross				2,545,000,000														2,545,000,000						2,545,000,000		2,545,000,000				2,545,000,000	2,254,000,000
Other Cost of Removal Obligations				$ 170,000,000														$ 170,000,000						$ 170,000,000		$ 170,000,000				$ 170,000,000	165,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount											$ 18,000,000
Annual PEP Lookback Refund To Customers																																	$ 5,000,000
Annual PEP Filing Rate Increase																																	1.90%
Annual PEP Filing Rate Increase Amount																																	$ 15,000,000
Anticipates of Elimination Adjustment will Result in Additional Revenues																																	$ 3,000,000
Gain Contingency, Surcharge Revenue																															5,000,000
Required Customers For Energy Efficiency Programs | Customer																																	25,000
Required Period For Filing Quick Start Plans																																	6 months
PSC Retail Rate Increase (Decrease)																																																$ 1,000,000				$ (1,000,000)		$ (2,000,000)
Regulatory amortization period																			5 years
Percentage Of PSC Retail Rate Increase (Decrease)																																																				(0.07%)
System Restoration Rider Rate																					0.00%
Psc approved annual property damage reserve accrual																					$ 3,000,000
Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Adjusting Point Of Weighted Cost Of Equity				5.98%														5.98%						5.98%		5.98%				5.98%
Percent Of Basis Points Increase (Decrease)				(0.07%)														(0.07%)						(0.07%)		(0.07%)				(0.07%)																	(0.07%)
Other Regulatory Assets Current				$ 149,000,000														$ 149,000,000						$ 149,000,000		$ 149,000,000				$ 149,000,000	182,000,000
Rate Adjustment Period																														2 years
Maximum Percentage of Rate RSE																														4.00%
Maximum Annual Percentage of Ratio Rate																														5.00%
Rate RSE Increase																																															4.48%
Rate RSE Increase Amount																																															$ 245,000,000
Rate RSE Refund Liability				73,000,000														73,000,000						73,000,000		73,000,000				$ 73,000,000
Under Recovered Certified Power Purchase Agreements				142,000,000														142,000,000						142,000,000		142,000,000				142,000,000	99,000,000
Over (Under) Recovered Environmental Clause				9,000,000														$ 9,000,000						9,000,000		9,000,000				$ 9,000,000
Current Billing Rates Under Rate ECR in Terms of Per Units | $ / KWH_Kilowatt_hour							0.02015																							0.05910
Future Stated Rates Under Rate Ecr Factor In Terms Of Per Units | $ / KWH_Kilowatt_hour																		0.02030		0.02681
Over Recovered Fuel Cost				76,000,000														$ 76,000,000						76,000,000		76,000,000				$ 76,000,000	238,000,000
Rate ECR Increase Decrease							(0.15%)
Rate ECR Increase Decrease Amount							$ (8,000,000)
Maximum Period for Recovery Deferred Storm Related Operations and Maintenance Costs and Any Future Reserve Deficits																														24 months
Maximum Rate NDR Charge Per Month, Monthly Nonresidential Customer Account				10														10						10		10				$ 10
Maximum Rate NDR Charge Per Month, Monthly Residential Customer Account				5														5						5		5				5
Old Natural Disaster Reserve Authorized Limit				$ 75,000,000														$ 75,000,000						$ 75,000,000		$ 75,000,000				$ 75,000,000
Jointly Owned Utility Plant, Proportionate Ownership Share				14.00%														14.00%						14.00%		14.00%				14.00%
Line of Credit Facility, Maximum Borrowing Capacity				$ 1,335,000,000														$ 1,335,000,000						$ 1,335,000,000		$ 1,335,000,000				$ 1,335,000,000
Construction in Progress, Gross				491,000,000														491,000,000						491,000,000		491,000,000				491,000,000	801,000,000
Percent Of Designated Customer Value Benchmark Survey																																																											33.30%
Other Cost of Removal Obligations				$ 684,000,000														$ 684,000,000						$ 684,000,000		$ 684,000,000				$ 684,000,000	722,000,000
Amortization of regulatory assets																																$ 123,000,000
Regulatory liability amortization																																120,000,000
Non-nuclear Outage Costs																																95,000,000
Compliance And Pension Costs																																28,000,000
Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Percent Of Basis Points Increase (Decrease)				(0.25%)														(0.25%)						(0.25%)		(0.25%)				(0.25%)
Other Regulatory Assets Current				$ 44,000,000														$ 44,000,000						$ 44,000,000		$ 44,000,000				$ 44,000,000	$ 90,000,000
Retail Rate Of Return On Common Equity																															10.25%
Public Utilities, Approved Return on Equity, Percentage									11.00%																					10.25%
Regulatory asset																																																			$ 63,000,000
Line of Credit Facility, Maximum Borrowing Capacity				280,000,000														280,000,000						280,000,000		280,000,000				$ 280,000,000
Construction in Progress, Gross				51,000,000														51,000,000						51,000,000		51,000,000				51,000,000	$ 48,000,000
Base Revenue In Year One																																	$ 35,000,000
Base Revenue In Year Two																																	$ 20,000,000
Other Cost of Removal Obligations				249,000,000														249,000,000						249,000,000		249,000,000				249,000,000	233,000,000
Reduction In Depreciation Expense																														$ 0	20,100,000	8,400,000
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 106,800,000
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue																														10.00%
Purchased Power Over (Under) Recovered Balance Percentage																														10.00%
Cost of Project One				316,000,000														316,000,000						316,000,000		316,000,000				$ 316,000,000
Period of Establishment of Conservation Goals, in Years																														5 years
Period Numeric Conservation Goals Cover, in Years																														10 years
Psc approved annual property damage reserve accrual				$ 3,500,000														$ 3,500,000						$ 3,500,000		$ 3,500,000				$ 3,500,000
Gulf Power and Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share				50.00%														50.00%						50.00%		50.00%				50.00%
Cost of Project One				$ 653,000,000														$ 653,000,000						$ 653,000,000		$ 653,000,000				$ 653,000,000
Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Portion of Actual Earnings Above Approved ROE Band Refunded to Customers																	66.67%													66.67%
Other Regulatory Assets Current				193,000,000														193,000,000						193,000,000		193,000,000				$ 193,000,000	$ 213,000,000
Increase (Decrease) in Base Tariff Rate															$ 49,000,000	$ 107,000,000
Increase (Decrease) In ECCR Tariff															75,000,000	23,000,000
Increase (Decrease) In Demand Side Management Tariff															3,000,000	3,000,000
Increase (Decrease) In Municipal Franchise Fee Tariff															13,000,000	3,000,000
Increase (Decrease) in Revenue to be Received from Base Rate Change															$ 140,000,000	136,000,000
Retail Rate Of Return On Common Equity																	10.95%																10.95%
Public Utilities, Approved Return on Equity, Percentage															10.00%
Revenue Subject To Refund																														11,000,000
Capacity Of Units Included in Application Request By Subsidiaries For Future Period Requests | MW													1,200
Capacity of Renewable Resources Approved For Self-build | MW													200
Approved Increase (Decrease) in Annual Billing Based on Fuel Cost Recovery Rate															$ (350,000,000)																																						$ (313,000,000)
Adjustment To Fuel Cost Recovery Rate If Under Recovered Fuel Balance Exceeds Budget Thereafter																														$ 200,000,000
Required Period For Options And Hedges																														48 months	24 months
Over Recovered Fuel Balance				84,000,000														84,000,000						84,000,000		84,000,000				$ 84,000,000	$ 116,000,000
Storm Restoration Costs				121,000,000														121,000,000						121,000,000		121,000,000				121,000,000
Accrual Under Alternate Rate Plan																														30,000,000
Electric Generating Capacity in Mega Watts Under Consortium Agreement | MW																																				1,100
Liquidated Damages, Percentage																																				10.00%
Additional Construction Capital Costs					$ 3,300,000,000																					222,000,000														$ 3,700,000,000
Percentage of proportionate share owed in consortium agreement																																				45.70%
Line of Credit Facility, Maximum Borrowing Capacity				1,750,000,000														1,750,000,000						1,750,000,000		1,750,000,000				$ 1,750,000,000
Estimated In-service Capital Cost																																			$ 4,418,000,000
NCCR Tariff															$ 19,000,000	$ 27,000,000																368,000,000
Increase (Decrease) In Projected Certified Construction Capital Costs																														5.00%
Loss Contingency, Estimate of Possible Loss					$ 240,000,000
Construction in Progress, Gross				4,939,000,000														4,939,000,000						4,939,000,000		4,939,000,000				$ 4,939,000,000	4,775,000,000
Portion of Actual Earnings Above Approved ROE Band Retained by Subsidiary Company																	33.33%													33.33%
Regulatory liability amortization																														$ 14,000,000	$ 14,000,000	$ 14,000,000
Southern Company Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 2,000,000,000														$ 2,000,000,000						$ 2,000,000,000		$ 2,000,000,000				$ 2,000,000,000
Number of natural gas distribution utilities | utility				7														7						7		7				7
Nicor Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 700,000,000														$ 700,000,000						$ 700,000,000		$ 700,000,000				$ 700,000,000
Loss Contingency, Damages Sought, Value																						$ 300,000
Elizabethtown Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Business Combination, Regulatory Approval Requirements, Required Rate Credit Payments to Customers																								$ 400,000	$ 17,500,000
Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Period to File Subsequent Rate Request						60 days
Minimum [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Potential Period For Next Depreciation Study																														3 years
Minimum [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Period For Quick Start Plans To Be In Effect																																	2 years
Minimum [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted Cost Of Equity				5.75%														5.75%						5.75%		5.75%				5.75%
Minimum [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Percent Of Basis Points Increase (Decrease)				(0.75%)														(0.75%)						(0.75%)		(0.75%)				(0.75%)
Retail Rate Of Return On Common Equity																															9.25%
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue																														10.00%
Minimum [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail Rate Of Return On Common Equity																	10.00%
Liquidated Damages, Monetary Amount																																				$ 920,000,000
Maximum [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Potential Period For Next Depreciation Study																														5 years
Maximum [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Period For Quick Start Plans To Be In Effect																																	3 years
Public Utilities, Approved Rate Increase (Decrease), Percentage											2.00%
Maximum [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Weighted Cost Of Equity				6.21%														6.21%						6.21%		6.21%				6.21%
Rate RSE Increase																																															3.52%
Maximum [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail Rate Of Return On Common Equity																															11.25%
Maximum [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail Rate Of Return On Common Equity																	12.00%
Capacity of Renewable Resources Considered For Renewable Commercial and Industrial Program | MW													200
Liquidated Damages, Monetary Amount																																				930,000,000
Additional Construction Capital Costs																																				$ 114,000,000
Maximum [Member] | Nicor Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Infrastructure Investment, Annual Customer Rate Increase																																	4.00%
Regulatory Clause Revenues, under-recovered [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (Under) Recovered Fuel Balance				$ 15,000,000														$ 15,000,000						$ 15,000,000		$ 15,000,000				$ 15,000,000
Over (Under) Recovered Environmental Cost				8,000,000														8,000,000						8,000,000		8,000,000				8,000,000	$ 0
Under Recovered Energy Conservation Costs				4,000,000														4,000,000						4,000,000		4,000,000				4,000,000
Other regulatory liabilities current [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (Under) Recovered Fuel Balance																															18,000,000
Over Recovered Energy Conservation Costs																															4,000,000
Regulatory Assets [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Under Recovered Certified Power Purchase Agreements				69,000,000														69,000,000						69,000,000		69,000,000				69,000,000
Over Recovered Regulatory Clause Revenues, Current [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Over Recovered Fuel Balance																															10,000,000
Other deferred credits and liabilities [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Over Recovered Fuel Balance																															106,000,000
Storm damage reserves | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Storm Restoration Costs				116,000,000														116,000,000						116,000,000		116,000,000				116,000,000
Scenario, Forecast [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																													$ 22,000,000
Scenario, Forecast [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Future Stated Rates Under Rate Ecr Factor In Terms Of Per Units | $ / KWH_Kilowatt_hour																												0.05910
Scenario, Forecast [Member] | Georgia Power And Atlanta Gas Light Company [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Percentage Basis, Net Merger Savings																																							40.00%
Scenario, Forecast [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Percent Of Basis Points Increase (Decrease)																																						0.95%			3.00%	3.00%
Customer Refund																													40,000,000
Additional Construction Capital Costs																																						$ 5,440,000,000
Increase (Decrease) in Basis Points																																						(8,000,000)
Amendment To Estimated In-service Capital Cost																																						$ 5,680,000,000
Scenario, Forecast [Member] | Maximum [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Cost Recovery, New Nuclear																																											$ 99,000,000
Plant Sweatt Units 1 And 2 [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Unit Conversion To Non-fossil Fuel Source | MW																																80
Plant Watson Units 4 And 5 [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Unit Conversion To Non-fossil Fuel Source | MW																																750
Plant Scherer Unit 3 [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																														12,000,000
Plant Scherer Unit 3 [Member] | Scenario, Forecast [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount																													14,000,000
Public Utilities, Approved Rate Incremental Increase (Decrease), Amount																													$ 2,000,000
Plant Gorgas Units 6 and 7 [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request For Decertification Of Units | MW																							200
Plant Barry Units 1 And 2 [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request For Decertification Of Units | MW																							250
Plant Barry Unit 3 [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request For Decertification Of Units | MW																							225
Plant Greene County Units 1 And 2 [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Unit Conversion To Non-fossil Fuel Source | MW																																200
Regulatory asset				17,000,000														17,000,000						17,000,000		17,000,000				17,000,000
Plant Greene County Units 1 And 2 [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request For Decertification Of Units | MW																							300
Plant Mitchell Units 3, 4A, and 4B [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request For Decertification Of Units | MW													217
Plant Kraft Unit 1 [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request For Decertification Of Units | MW													17
Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Construction in Progress, Gross				3,900,000,000														$ 3,900,000,000						$ 3,900,000,000		$ 3,900,000,000				3,900,000,000
Construction Financing Costs				$ 1,300,000,000
Production Tax Credit , Amount Per Unit, Net Present Value																														$ 400,000,000
Plant Vogtle Units 3 And 4 [Member] | Scenario, Forecast [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Monthly Financing Costs																											$ 30,000,000
Construction Financing Costs																											2,500,000,000
Monthly Operational Readiness Costs																											$ 6,000,000
Plant Smith Units 1 and 2 [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Approved For Decertification | MW																																																							357
Plant Watson [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset																			$ 41,000,000
Customers [Member] | Scenario, Forecast [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Percentage Basis, Net Merger Savings																																							60.00%
Subsequent Event [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Requested Revenue Requirement Increase (Decrease), Amount		$ 18,000,000
System Restoration Rider Rate																																														0.00%
Psc approved annual property damage reserve accrual																																														$ 4,000,000
Subsequent Event [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount			$ (41,000,000)
Subsequent Event [Member] | Maximum [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage		2.00%
Subsequent Event [Member] | Regulatory Assets [Member] | Alabama Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (Under) Recovered Environmental Clause																																													$ (36,000,000)
Subsequent Event [Member] | Scenario, Forecast [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Requested Revenue Requirement Increase (Decrease), Amount																												$ 27,000,000
Plant Daniel Units 1 and 2 [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share				50.00%														50.00%						50.00%		50.00%				50.00%
Plant Daniel Units 1 and 2 [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share				50.00%														50.00%						50.00%		50.00%				50.00%
Intercession City Combustion Turbine [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity Of Units Included In Request To Sell | MW													143
Jointly Owned Utility Plant, Proportionate Ownership Share																																																		33.00%
Storm Costs [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulatory asset				$ 206,000,000														$ 206,000,000						$ 206,000,000		$ 206,000,000				$ 206,000,000
Property Damage Reserves Liability [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Other Regulatory Assets Current				30,000,000														30,000,000						30,000,000		30,000,000				30,000,000	30,000,000
Regulatory asset				206,000,000														206,000,000						206,000,000		206,000,000				206,000,000	92,000,000
Illinois Commission Staff [Member] | Nicor Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss Contingency, Damages Sought, Value																																$ 18,000,000
Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity																															920,000,000
Settlement Agreement [Member] | Gulf Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Other Cost of Removal Obligations				$ 62,500,000														$ 62,500,000						$ 62,500,000		$ 62,500,000				$ 62,500,000
Citizens Utility Board (CUB) [Member] | Nicor Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss Contingency, Damages Sought, Value																																$ 22,000,000
Pending Litigation [Member] | Southern Company Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of natural gas distribution utilities | utility				1														1						1		1				1
Pending Litigation [Member] | Minimum [Member] | Southern Company Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Loss Contingency, Estimate of Possible Loss				$ 11,000,000														$ 11,000,000						$ 11,000,000		$ 11,000,000				$ 11,000,000
Pending Litigation [Member] | Plant Vogtle Units 3 And 4 [Member] | Georgia Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Project Settlement Cost To Be Capitalized				350,000,000														350,000,000						350,000,000		350,000,000				350,000,000
Project Settlement Cost To Be Capitalized, Amount Paid To Date				$ 263,000,000														$ 263,000,000						$ 263,000,000		$ 263,000,000				$ 263,000,000
Capital Projects Associated with Infrastructure Improvement Programs [Member] | Southern Company Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of natural gas distribution utilities | utility				6														6						6		6				6
Regulatory Infrastructure Program [Member] | Nicor Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																																9 years
Infrastructure Program [Member] | Minimum [Member] | Southern Company Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																														4 years
Infrastructure Program [Member] | Maximum [Member] | Southern Company Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																														10 years
STRIDE [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																																	4 years
STRIDE [Member] | i-SRP [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period												4 years
Infrastructure Replacement Program, Petitioned Investment Amount (more than)												$ 177,000,000
Approved Infrastructure Replacement Program																																	$ 445,000,000
Infrastructure Replacement Program, Cost Recovery Period																																	10 years
Infrastructure Programs, Plan Filing Frequency																																	3 years
STRIDE [Member] | i-SRP [Member] | Subsequent Event [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period	4 years
Infrastructure Replacement Program, Petitioned Investment Amount (more than)	$ 177,000,000
STRIDE [Member] | i-CGP [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Approved Infrastructure Replacement Program																																	$ 91,000,000
STRIDE [Member] | i-VPR [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Approved Infrastructure Replacement Program																																	$ 275,000,000
Regulated Operations, Natural Gas Pipeline Length, Approved for Replacement | mi																																	756
Regulated Operations, Natural Gas Pipeline Length, Considered for Replacement | mi																																	3,300
STRIDE [Member] | i-VPR [Member] | Minimum [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulated Operations, Period For Replacement																																	15 years
STRIDE [Member] | i-VPR [Member] | Maximum [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Regulated Operations, Period For Replacement																																	20 years
AIR [Member] | Elizabethtown Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																																	4 years				1 year
Fair Value Inputs, Discount Rate																																	6.65%
Public Utilities, Requested Revenue Requirement Increase (Decrease), Amount								$ 20,000,000		$ 19,000,000
Approved Infrastructure Replacement Program																																$ 15,000,000	$ 115,000,000
Public Utilities, Requested Return on Equity, Percentage										10.25%
Safety, Modernization and Reliability Tariff (SMART) Plan [Member] | Elizabethtown Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Infrastructure Replacement Program, Petitioned Investment Amount (more than)																						$ 1,100,000,000															$ 1,100,000,000
Regulated Operations, Natural Gas Pipeline Length, Considered for Replacement | mi																						630
Regulated Operations, Number of Regulator Stations, Considered for Replacement | station																						240
Regulated Operations, Rider Surcharge, Recovery Period																						10 years
Safety, Modernization and Reliability Tariff (SMART) Plan [Member] | Subsequent Event [Member] | Elizabethtown Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Infrastructure Replacement Program, Petitioned Investment Amount (more than)	$ 1,100,000,000
SAVE [Member] | Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																																		5 years
Regulated Operations, Natural Gas Pipeline Length, Approved for Replacement | mi														200
Approved Infrastructure Replacement Program, Allowed Amount To Exceed				$ 2,000,000														$ 2,000,000						$ 2,000,000		$ 2,000,000				$ 2,000,000
SAVE [Member] | Maximum [Member] | Virginia Natural Gas
Schedule of Regulatory Assets and Liabilities [Line Items]
Approved Infrastructure Replacement Program, Amount Per Year																																		$ 25,000,000
Approved Infrastructure Replacement Program																																		$ 105,000,000
Approved Infrastructure Replacement Program, Allowed Amount To Exceed														$ 5,000,000
Approved Infrastructure Replacement Program, Approved Investment Amount, Current Fiscal Year														30,000,000
Approved Infrastructure Replacement Program, Approved Investment Amount, Year Two														35,000,000
Approved Infrastructure Replacement Program, Approved Investment Amount, Year Three														35,000,000
Approved Infrastructure Replacement Program, Approved Investment Amount, Year Four														35,000,000
Approved Infrastructure Replacement Program, Approved Investment Amount, Year Five														35,000,000
Approved Infrastructure Replacement Program, Approved Investment Amount, Year Six														$ 35,000,000
SAFE [Member] | Florida City Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																						10 years
Approved Infrastructure Replacement Program																						$ 105,000,000															$ 105,000,000
energySMART [Member] | Nicor Gas [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Program Duration Period																																3 years
Approved Infrastructure Replacement Program																																$ 93,000,000
Retail [Member] | Mississippi Power [Member]
Schedule of Regulatory Assets and Liabilities [Line Items]
Under Recovered Fuel Cost				37,000,000														37,000,000						37,000,000		37,000,000				37,000,000
Proposed Change in Annual Revenues				$ 55,000,000														$ 55,000,000						$ 55,000,000		$ 55,000,000				$ 55,000,000
Favorable Regulatory Action [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Gain Contingency, Surcharge Revenue																					15,000,000
Litigation Settlement, Amount																					$ 144,000,000
Gain Contingency, Unrecorded Amount, Alternative Phased-In Increase | $ / item																																																	0.81								0.82
Favorable Regulatory Action [Member] | Scenario, Forecast [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Gain Contingency, Unrecorded Amount, Alternative Phased-In Increase | $ / item																																												0.81
True Up Recovery [Member] | Atlanta Gas Light
Schedule of Regulatory Assets and Liabilities [Line Items]
Gain Contingency, Unrecorded Amount																																																										$ 178,000,000
Interest Expense																															1,000,000
Selling, General and Administrative Expense																															$ 5,000,000