Contingencies and Regulatory Matters - Narrative (Details)														1 Months Ended			3 Months Ended		6 Months Ended			12 Months Ended										38 Months Ended	48 Months Ended	90 Months Ended	102 Months Ended
	Jul. 01, 2017 USD ($)	Jun. 30, 2017 USD ($) MW	Jun. 09, 2017 USD ($)	May 04, 2017 USD ($)	Apr. 04, 2017 intervenor	Mar. 31, 2017 USD ($)	Mar. 27, 2017	Mar. 10, 2017 USD ($)	Feb. 21, 2017 USD ($)	Dec. 20, 2016 USD ($)	May 01, 2016 USD ($)	Mar. 31, 2016	Jan. 01, 2016	Apr. 28, 2017 USD ($)	Sep. 30, 2016 USD ($)	Jan. 31, 2016 USD ($)	Jun. 30, 2017 USD ($) MW	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) clause MW	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2018	Aug. 31, 2018	Dec. 31, 2017 USD ($)	Mar. 31, 2017	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Jun. 30, 2017 USD ($) MW	Dec. 31, 2020 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) MW	Jan. 01, 2121	Aug. 01, 2017	Jul. 06, 2017 USD ($)	Jun. 23, 2017 USD ($)	May 31, 2017 USD ($)	May 01, 2017	Mar. 07, 2017 USD ($)	Feb. 17, 2017 USD ($)	Aug. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Lawsuit deferral period							30 days
Maximum borrowing capacity		$ 8,168,000,000															$ 8,168,000,000		$ 8,168,000,000													$ 8,168,000,000			$ 8,168,000,000
Stockholders' equity, including portion attributable to noncontrolling interest		(25,241,000,000)															(25,241,000,000)	$ (23,446,000,000)	(25,241,000,000)	$ (26,612,000,000)	$ (23,446,000,000)					$ (26,612,000,000)	$ (21,982,000,000)					(25,241,000,000)		$ (23,446,000,000)	(25,241,000,000)
Property, plant and equipment, gross		101,021,000,000															101,021,000,000		101,021,000,000	98,416,000,000						98,416,000,000						101,021,000,000			101,021,000,000
SOUTHERN POWER CO
Loss Contingencies [Line Items]
Maximum borrowing capacity		750,000,000															750,000,000		750,000,000													750,000,000			750,000,000					$ 600,000,000
Stockholders' equity, including portion attributable to noncontrolling interest		(5,814,000,000)															(5,814,000,000)		(5,814,000,000)	(5,675,000,000)						(5,675,000,000)						(5,814,000,000)			(5,814,000,000)
Wholesale revenues, non-affiliates																	436,000,000	264,000,000	783,000,000		480,000,000
Property, plant and equipment, gross		13,731,000,000															13,731,000,000		13,731,000,000	12,728,000,000						12,728,000,000						13,731,000,000			13,731,000,000
GEORGIA POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability		12,000,000															12,000,000		$ 12,000,000	17,000,000						17,000,000						12,000,000			12,000,000
Cost recovery, new nuclear																																										$ 50,000,000
Percentage of Proportionate share owed in consortium agreement																															45.70%
Liquidated damages, percentage																			40.00%												10.00%
Maximum borrowing capacity		1,750,000,000															1,750,000,000		$ 1,750,000,000													1,750,000,000			1,750,000,000
Weekly payment of services under contract agreement														$ 5,400,000
Estimated in-service capital cost																														$ 4,418,000,000
Financing costs collected, net of tax																			1,400,000,000
Additional construction capital costs										$ 3,300,000,000										222,000,000														$ 3,700,000,000
Estimate of possible loss										$ 240,000,000
Retail rate of return on common equity																													10.95%
Public utilities, approved return on equity percentage													10.00%
Financing costs incurred																																			1,400,000,000
Estimated cancellation costs																																			400,000,000
Wholesale revenues, non-affiliates																	40,000,000	40,000,000	79,000,000		82,000,000
Property, plant and equipment, gross		34,410,000,000															34,410,000,000		34,410,000,000	33,841,000,000						33,841,000,000						34,410,000,000			34,410,000,000
GEORGIA POWER CO | Minimum
Loss Contingencies [Line Items]
Estimated financing costs																																			3,100,000,000
GEORGIA POWER CO | Maximum
Loss Contingencies [Line Items]
Estimated financing costs																																			3,500,000,000
GEORGIA POWER CO | Other current liabilities
Loss Contingencies [Line Items]
Over recovered fuel balance		61,000,000															61,000,000		61,000,000													61,000,000			61,000,000
GEORGIA POWER CO | Other deferred credits and liabilities
Loss Contingencies [Line Items]
Over recovered fuel balance																				84,000,000						84,000,000
GULF POWER CO
Loss Contingencies [Line Items]
Environmental remediation liability		51,000,000															51,000,000		51,000,000	44,000,000						44,000,000						51,000,000			51,000,000
Maximum borrowing capacity		$ 280,000,000															$ 280,000,000		$ 280,000,000													$ 280,000,000			$ 280,000,000
Retail rate of return on common equity		10.25%															10.25%		10.25%													10.25%			10.25%
Reduction in depreciation expense																			$ 34,000,000							0	$ 20,100,000	$ 8,400,000	$ 62,500,000
Wholesale revenues, non-affiliates																	$ 12,000,000	15,000,000	30,000,000		31,000,000
Loss on Plant Scherer Unit 3																	0	0	$ 33,000,000		0
Number of regulatory clauses | clause																			4
Property, plant and equipment, gross		$ 5,156,000,000															$ 5,156,000,000		$ 5,156,000,000	5,140,000,000						5,140,000,000						$ 5,156,000,000			$ 5,156,000,000
GULF POWER CO | Minimum
Loss Contingencies [Line Items]
Retail rate of return on common equity		9.25%															9.25%		9.25%													9.25%			9.25%
GULF POWER CO | Maximum
Loss Contingencies [Line Items]
Retail rate of return on common equity		11.25%															11.25%		11.25%													11.25%			11.25%
SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability		$ 416,000,000															$ 416,000,000		$ 416,000,000	426,000,000						426,000,000						$ 416,000,000			$ 416,000,000
Maximum borrowing capacity		1,900,000,000															1,900,000,000		1,900,000,000													1,900,000,000			1,900,000,000
Stockholders' equity, including portion attributable to noncontrolling interest		(9,242,000,000)															(9,242,000,000)		(9,242,000,000)	(9,109,000,000)						(9,109,000,000)						(9,242,000,000)			(9,242,000,000)
Property, plant and equipment, gross		14,850,000,000															14,850,000,000		14,850,000,000	14,508,000,000						14,508,000,000						14,850,000,000			14,850,000,000
MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Gain contingency, surcharge revenue																										5,000,000
Increase in base rate under cost based electric tariff due to settlement											$ 7,000,000
AFUDC cost																			22,000,000
Fuel cost recovery		14,000,000															14,000,000		14,000,000	37,000,000						37,000,000						14,000,000			14,000,000
Maximum borrowing capacity		113,000,000															113,000,000		113,000,000													113,000,000			113,000,000
Wholesale revenues, non-affiliates																	62,000,000	60,000,000	124,000,000		120,000,000
Maximum annual percentage increase in revenue				2.00%																																					2.00%
Maximum annual increase in revenue				$ 18,000,000
Deferred revenue				$ 26,000,000
Property, plant and equipment, gross		4,826,000,000															4,826,000,000		4,826,000,000	4,865,000,000						4,865,000,000						4,826,000,000			4,826,000,000
ALABAMA POWER CO
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
Wholesale revenues, non-affiliates																	68,000,000	$ 67,000,000	133,000,000		$ 130,000,000
Property, plant and equipment, gross		26,466,000,000															26,466,000,000		26,466,000,000	26,031,000,000						26,031,000,000						26,466,000,000			26,466,000,000
ALABAMA POWER CO | Regulatory assets, deferred
Loss Contingencies [Line Items]
Over (under) recovered environmental clause																																											$ 36,000,000
Atlanta Gas Light
Loss Contingencies [Line Items]
Public utilities, approved return on equity percentage									10.75%
Approved increase (decrease) in fuel rates amount									$ 20,000,000
Elizabethtown Gas
Loss Contingencies [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 13,000,000													$ 19,000,000
Test year duration																									12 months
Public utilities, requested return on equity, percentage		9.60%													10.25%
Public utilities, property, plant and equipment, accumulated depreciation		$ 3,000,000															3,000,000		3,000,000													3,000,000			3,000,000
Nicor Gas
Loss Contingencies [Line Items]
Maximum borrowing capacity		700,000,000															700,000,000		700,000,000													700,000,000			700,000,000					700,000,000
Public utilities, requested rate increase (decrease), amount								$ 208,000,000
Public utilities, requested return on equity, percentage								10.70%
Statutory time limit								11 months
Virginia Natural Gas
Loss Contingencies [Line Items]
Public utilities, requested return on equity, percentage						10.25%
Florida City Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, petitioned investment amount		7,000,000															7,000,000		7,000,000													7,000,000			7,000,000
RE Roserock, LLC | SOUTHERN POWER CO
Loss Contingencies [Line Items]
Ownership percentage by parent																											51.00%
Loss Contingency, Payments																			26,000,000
Location One | SOUTHERN Co GAS
Loss Contingencies [Line Items]
Environmental remediation liability		5,000,000															5,000,000		5,000,000													5,000,000			5,000,000
Kemper Igcc [Member] | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Estimated Cost Incurred After in Service Date																																								$ 175,000,000
Period of amortization of regulatory assets												36 months
AFUDC cost																																493,000,000
Plant Vogtle Units 3 And 4
Loss Contingencies [Line Items]
Guarantor obligations			$ 3,680,000,000.00
Plant Vogtle Units 3 And 4 | GEORGIA POWER CO
Loss Contingencies [Line Items]
Liquidated damages, monetary amount																			1,700,000,000												$ 920,000,000
Liquidated damages, monetary amount Received, based on percentage of ownership																															$ 420,000,000
Maximum borrowing capacity																$ 920,000,000
Guarantor obligations			$ 1,700,000,000.0
Requested rate increase (decrease) amount																			400,000,000
Plant Scherer Unit 3
Loss Contingencies [Line Items]
Loss on Plant Scherer Unit 3																			$ 33,000,000
Plant Scherer Unit 3 | GULF POWER CO
Loss Contingencies [Line Items]
Number of intervenors | intervenor					3
Plant Smith Units 1 and 2 | GULF POWER CO
Loss Contingencies [Line Items]
Capacity of units included in request for decertification of units | MW																			357
Plant Scherer Unit Three | GULF POWER CO
Loss Contingencies [Line Items]
Loss on Plant Scherer Unit 3																			$ 32,500,000
MRA Revenue | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Fuel cost recovery		7,000,000															7,000,000		7,000,000	$ 13,000,000						$ 13,000,000						7,000,000			7,000,000
Westinghouse | Plant Vogtle Units 3 And 4 | GEORGIA POWER CO
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed																60 days
Vogtle Owners | Interim Assessment Agreement
Loss Contingencies [Line Items]
Loss Contingency, Payments																			552,000,000
Estimate of possible loss		650,000,000															650,000,000		650,000,000													650,000,000			650,000,000
Vogtle Owners | Removal of Subcontractor Liens
Loss Contingencies [Line Items]
Loss Contingency, Payments																			354,000,000
Estimate of possible loss		400,000,000															400,000,000		400,000,000													400,000,000			400,000,000
Vogtle Owners | GEORGIA POWER CO | Interim Assessment Agreement
Loss Contingencies [Line Items]
Estimate of possible loss		297,000,000															297,000,000		297,000,000													297,000,000			297,000,000
Vogtle Owners | GEORGIA POWER CO | Removal of Subcontractor Liens
Loss Contingencies [Line Items]
Estimate of possible loss		183,000,000															183,000,000		183,000,000													183,000,000			183,000,000
Vogtle Owners | Plant Vogtle Units 3 And 4 | GEORGIA POWER CO
Loss Contingencies [Line Items]
Period of notice required in the event letters of credit are not renewed			30 days
Restatement Adjustment | Toshiba
Loss Contingencies [Line Items]
Stockholders' equity, including portion attributable to noncontrolling interest																																							$ 5,000,000,000
Scenario, Forecast | GEORGIA POWER CO
Loss Contingencies [Line Items]
Additional construction capital costs																																	$ 5,440,000,000
Percent of basis points																																	0.95%			0.30%
Increase (decrease) in basis points																																	$ (8,000,000)
Amendment to estimated in-service capital cost																																	$ 5,680,000,000
Scenario, Forecast | GULF POWER CO
Loss Contingencies [Line Items]
Overall net customer impact from rate case settlement agreement																								$ 54,300,000
Increase (decrease) in revenue to be received from base rate change	$ 62,000,000
Wholesale revenues, non-affiliates																								$ 7,700,000
Retail regulatory equity ratio	0.525
Scenario, Forecast | Virginia Natural Gas
Loss Contingencies [Line Items]
Test year duration																							12 months
FFB Loan | GEORGIA POWER CO
Loss Contingencies [Line Items]
Maximum borrowing capacity		$ 2,600,000,000.0															$ 2,600,000,000.0		$ 2,600,000,000.0													$ 2,600,000,000.0			$ 2,600,000,000.0
Retirement Of Plant | Scenario, Forecast | GULF POWER CO
Loss Contingencies [Line Items]
Regulatory asset, amortization period																						15 years
Plant Scherer Unit Three | GULF POWER CO
Loss Contingencies [Line Items]
Electric generating units, capacity | MW		205															205		205													205			205
SAVE Program | Virginia Natural Gas
Loss Contingencies [Line Items]
Infrastructure replacement program, petitioned investment amount		$ 44,000,000															$ 44,000,000		$ 44,000,000													$ 44,000,000			$ 44,000,000
Regulated operation, allowable cost recovery						$ 13,000,000
Approved infrastructure replacement program		14,000,000															14,000,000		14,000,000													14,000,000			14,000,000
Regulatory Infrastructure Program | Nicor Gas
Loss Contingencies [Line Items]
Program duration period																												9 years
Property, plant and equipment, gross		75,000,000															75,000,000		75,000,000													75,000,000			75,000,000
STRIDE | Atlanta Gas Light
Loss Contingencies [Line Items]
Approved infrastructure replacement program		94,000,000															94,000,000		$ 94,000,000													94,000,000			94,000,000
Integrated System Reinforcement Program | Atlanta Gas Light
Loss Contingencies [Line Items]
Infrastructure replacement program, petitioned investment amount																																												$ 177,000,000
Integrated System Reinforcement Program | Atlanta Gas Light | Minimum
Loss Contingencies [Line Items]
Program duration period																			4 years
Aging Infrastructure Replacement Program | Elizabethtown Gas
Loss Contingencies [Line Items]
Approved infrastructure replacement program		$ 12,000,000															$ 12,000,000		$ 12,000,000													$ 12,000,000			$ 12,000,000
Subsequent Event | SOUTHERN POWER CO
Loss Contingencies [Line Items]
Ownership percentage by parent																																					100.00%
Subsequent Event | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
Percentage of PSC retail rate increase																																						0.85%
PSC retail rate increase (decrease)																																						$ 8,000,000
Subsequent Event | Energy Efficiency Cost Rider | MISSISSIPPI POWER CO
Loss Contingencies [Line Items]
PSC retail rate increase (decrease)																																						$ 2,000,000