Contingencies and Regulatory Matters - Narrative (Details)									1 Months Ended			3 Months Ended		6 Months Ended	12 Months Ended								51 Months Ended	84 Months Ended
	May. 01, 2016 USD ($)	Apr. 08, 2016 USD ($)	Dec. 03, 2015 USD ($)	Jul. 07, 2015 USD ($)	Jun. 30, 2015 USD ($)	Apr. 15, 2015 USD ($)	Jan. 01, 2014 USD ($)	Mar. 19, 2013	Dec. 31, 2015 USD ($)	Feb. 28, 2013 USD ($)	Jan. 31, 2013 USD ($)	Mar. 31, 2016 USD ($) clause mi MW	Mar. 31, 2015 USD ($)	Dec. 31, 2015 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 ($)	Dec. 31, 2008 USD ($)	Mar. 31, 2016 USD ($) mi	Dec. 31, 2022	Apr. 14, 2016 USD ($)	Apr. 01, 2016 USD ($)	Feb. 01, 2016 USD ($)	Jan. 13, 2016 USD ($)	Jan. 05, 2016 USD ($)	Jul. 10, 2015 USD ($)	Oct. 06, 2014
Loss Contingencies [Line Items]
Maximum Borrowing Capacity												$ 6,495,000,000											$ 6,495,000,000
Construction in Progress, Gross									$ 9,082,000,000			9,406,000,000		$ 9,082,000,000		$ 9,082,000,000							9,406,000,000
Other Regulatory Assets Deferred									4,989,000,000			4,957,000,000		4,989,000,000		4,989,000,000							4,957,000,000
Projected Balance Of Regulatory Assets									402,000,000			394,000,000		402,000,000		402,000,000							394,000,000
Kemper IGCC [Member]
Loss Contingencies [Line Items]
Pre-Tax Charge To Income												53,000,000	$ 9,000,000
After Tax Charge To Income												33,000,000	$ 6,000,000
Georgia Power [Member]
Loss Contingencies [Line Items]
Environmental Exit Costs, Assets Previously Disposed, Liability for Remediation												28,000,000											28,000,000
Additional Construction Capital Costs					$ 3,100,000,000							5,440,000,000		160,000,000
Percentage of Proportionate Share Owed in Consortium Agreement																						45.70%
Maximum Borrowing Capacity												$ 1,750,000,000											1,750,000,000
Increase (Decrease) In Projected Certified Construction Capital Costs												5.00%
Estimated In-service Capital Cost																					$ 4,400,000,000
Amendment To Estimated In-service Capital Cost										$ 4,800,000,000
Delay Of Estimated In-service Date						18 months
Construction in Progress, Gross									4,775,000,000			$ 4,817,000,000		4,775,000,000		4,775,000,000							4,817,000,000
Other Regulatory Assets Deferred									2,152,000,000			2,138,000,000		2,152,000,000		2,152,000,000							2,138,000,000
Projected Balance Of Regulatory Assets									123,000,000			126,000,000		123,000,000		123,000,000							126,000,000
Georgia Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Additional Construction Capital Costs																						$ 114,000,000
Georgia Power [Member] | Other Current Liabilities [Member]
Loss Contingencies [Line Items]
Over Recovered Fuel Balance												177,000,000											177,000,000
Georgia Power [Member] | Other deferred credits and liabilities [Member]
Loss Contingencies [Line Items]
Over Recovered Fuel Balance									116,000,000					116,000,000		116,000,000
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
Monthly Operational Readiness Costs						$ 10,000,000
Monthly Financing Costs												27,000,000
Construction Financing Costs												2,400,000,000
Construction in Progress, Gross												3,700,000,000											3,700,000,000
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		350,000,000
Project Settlement Cost To Be Capitalized, Amount Paid To Date									241,000,000					241,000,000		241,000,000
Gulf Power [Member]
Loss Contingencies [Line Items]
Environmental Exit Costs, Assets Previously Disposed, Liability for Remediation												46,000,000											46,000,000
Maximum Borrowing Capacity												280,000,000											280,000,000
Construction in Progress, Gross									48,000,000			57,000,000		48,000,000		48,000,000							57,000,000
Reduction In Depreciation Expense																		$ 62,500,000
Reduction In Depreciation Expense Year One												$ 5,600,000				20,100,000	$ 8,400,000
Number Of Regulatory Clauses | clause												4
Other Regulatory Assets Deferred									427,000,000			$ 420,000,000		427,000,000		427,000,000							420,000,000
Projected Balance Of Regulatory Assets									90,000,000			90,000,000		90,000,000		90,000,000							90,000,000
Mississippi Power [Member]
Loss Contingencies [Line Items]
Ownership Percentage in Project One																			50.00%
Over Recovered Fuel Cost									71,000,000			80,000,000		71,000,000		71,000,000							80,000,000
Approved Increase (Decrease) in Annual Billing Based on Fuel Cost Recovery Rate																											$ (36,000,000)		$ (120,000,000)
Maximum Borrowing Capacity												205,000,000											205,000,000
Construction in Progress, Gross									2,254,000,000			$ 2,400,000,000		2,254,000,000		2,254,000,000							$ 2,400,000,000
Annual PEP Filing Rate Increase Amount																										$ 5,000,000
Plant Capacity Under Coal Gasification Combined Cycle Technology (in MWs) | MW												582
Co Two Pipeline Infrastructure (in miles) | mi												61											61
Costs associated with CCP12 grant funds																			$ 245,000,000
Other Property And Investments												$ 6,000,000											$ 6,000,000
Lignite Mining Costs												75,000,000											75,000,000
Materials, Supplies, and Other												45,000,000											45,000,000
Cost deferred in other regulatory assets												22,000,000											22,000,000
Other Regulatory Assets Deferred									525,000,000			520,000,000		525,000,000		525,000,000							520,000,000
Other deferred charges and assets												11,000,000											11,000,000
Increase Retail Rates In Year One								15.00%
Increase Retail Rates In Year Two							3.00%
Settlement Agreement Collection Amount To Mitigate Rate Impact Year Two							$ 156,000,000
Retail Rate Recovery				$ 342,000,000
Carrying Costs Associated With Retail Rate Recovery				$ 29,000,000
Projected Balance Of Regulatory Assets									95,000,000			101,000,000		95,000,000		95,000,000							101,000,000
Regulatory Liabilities												$ 3,000,000											$ 3,000,000
Percentage of Carbon Dioxide Captured from Project												70.00%											70.00%
Percentage of Contract to Purchase Carbon Dioxide from Project												30.00%											30.00%
Mississippi Power [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Costs Due To Extension Of In-service Date												$ 25,000,000
Mississippi Power [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Costs Due To Extension Of In-service Date												35,000,000
Mississippi Power [Member] | Construction in Progress [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss												2,470,000,000											$ 2,470,000,000
Mississippi Power [Member] | MRA Revenue [Member]
Loss Contingencies [Line Items]
Over Recovered Fuel Cost									24,000,000			25,000,000		$ 24,000,000		$ 24,000,000							25,000,000
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] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Estimated Cost												4,990,000,000							$ 2,880,000,000
Costs associated with CCP12 grant funds												0
Other Regulatory Assets Deferred												196,000,000											196,000,000
Pre-Tax Charge To Income												53,000,000											2,470,000,000
After Tax Charge To Income												33,000,000											$ 1,520,000,000
Monthly Charge Of Allowance For Equity Funds Used During Construction												14,000,000
Monthly Cost Regulatory Assets Deferred												$ 2,000,000
Purchase of Interest												100.00%											100.00%								15.00%
Maximum Cap Construction Cost												$ 6,240,000,000
Regulatory Assets												120,000,000											$ 120,000,000
Projected Balance Of Regulatory Assets												98,000,000											98,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Current Estimate [Member]
Loss Contingencies [Line Items]
Estimated Cost												5,350,000,000
Costs associated with CCP12 grant funds												(140,000,000)
Maximum Cap Construction Cost												$ 6,580,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | In-Service Asset Proposal [Member]
Loss Contingencies [Line Items]
PSC Retail Rate Increase (Decrease)			$ 126,000,000																											$ 159,000,000
Public Utilities, Approved Equity Capital Structure, Percentage			49.733%
Public Utilities, Approved Return on Equity, Percentage			9.225%
Customer Refund									$ 11,000,000
Period to File Subsequent Rate Request			18 months
Mississippi Power [Member] | Kemper IGCC [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Amortization Period of Regulatory Assets and Liabilities												2 years
Mississippi Power [Member] | Kemper IGCC [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Amortization Period of Regulatory Assets and Liabilities												10 years
Mississippi Power [Member] | Kemper IGCC [Member] | Property, Plant and Equipment [Member]
Loss Contingencies [Line Items]
Estimated Cost												$ 3,610,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Other current assets [Member]
Loss Contingencies [Line Items]
Estimated Cost												1,000,000
Mississippi Power [Member] | Kemper IGCC [Member] | Current Assets [Member]
Loss Contingencies [Line Items]
Regulatory Assets												$ 22,000,000											$ 22,000,000
Mississippi Power [Member] | Mine [Member]
Loss Contingencies [Line Items]
Term of Management Fee Contract																				40 years
Subsequent Event [Member] | Georgia Power [Member]
Loss Contingencies [Line Items]
Rate ECR Increase Decrease																									15.00%
Approved Increase (Decrease) in Annual Billing Based on Fuel Cost Recovery Rate																									$ (313,000,000)
Subsequent Event [Member] | Mississippi Power [Member]
Loss Contingencies [Line Items]
Increase in Base Rate Under Cost Based Electric Tariff Due to Settlement	$ 7,000,000
Increase (Decrease) in Revenue to be Received from Base Rate Change															$ 5,000,000
AFUDC Cost															$ 6,000,000
Subsequent Event [Member] | Mississippi Power [Member] | Kemper IGCC [Member]
Loss Contingencies [Line Items]
Government Grants Received		$ 137,000,000
Scenario, Forecast [Member] | Georgia Power And Atlanta Gas Light Company [Member]
Loss Contingencies [Line Items]
Percentage Basis, Net Merger Savings																								40.00%
Customers [Member] | Scenario, Forecast [Member]
Loss Contingencies [Line Items]
Percentage Basis, Net Merger Savings																								60.00%