Financing - Long-Term Debt Narrative (Details) - USD ($)	1 Months Ended			2 Months Ended
	Nov. 30, 2018	May 31, 2018	Mar. 31, 2018	Feb. 19, 2019	Jan. 31, 2019	Dec. 31, 2018	Oct. 31, 2018	Aug. 31, 2018	Jul. 31, 2018	Jun. 30, 2018	Apr. 30, 2018	Jan. 31, 2018
Floating Rate Bank Term Loan Agreement | Notes Payable to Banks
Debt Disclosure [Line Items]
Debt instrument, face amount			$ 900,000,000
Senior Notes | Series 2018A Floating Rate Senior Notes due February 14, 2020
Debt Disclosure [Line Items]
Debt instrument, face amount								$ 750,000,000
Senior Notes | Subsequent Event
Debt Disclosure [Line Items]
Repayments of debt				$ 1,200,000,000
Senior Notes | Subsequent Event | Series 2018A Floating Rate Senior Notes due February 14, 2020
Debt Disclosure [Line Items]
Debt instrument, face amount				750,000,000
Debt instrument, repurchase amount				504,000,000
Senior Notes | Subsequent Event | Senior Notes 1.85% Due July 1, 2019
Debt Disclosure [Line Items]
Debt instrument, face amount				1,000,000,000
Debt instrument, repurchase amount				$ 522,000,000
Fixed stated interest rate of debt obligation				1.85%
Senior Notes | Subsequent Event | Series 2014B 2.15% Senior Notes Due September 1, 2019
Debt Disclosure [Line Items]
Debt instrument, face amount				$ 350,000,000
Debt instrument, repurchase amount				$ 180,000,000
Fixed stated interest rate of debt obligation				2.15%
Alabama Power | Senior Notes | Series 2018A Floating Rate Senior Notes
Debt Disclosure [Line Items]
Debt instrument, face amount										$ 500,000,000
Fixed stated interest rate of debt obligation										4.30%
Alabama Power | Senior Notes | Series 2008B 5.40% Senior Notes due June 1, 2018
Debt Disclosure [Line Items]
Fixed stated interest rate of debt obligation											5.40%
Debt instrument, repurchased face amount											$ 250,000,000
Alabama Power | Municipal bonds | The Industrial Development Board Of The City Of Mobile, Alabama Pollution Control Revenue Bonds (Alabama Power Company Plant Barry Project), Series 2008
Debt Disclosure [Line Items]
Debt instrument, face amount							$ 120,000,000
Alabama Power | Maturity December 1, 2018 | SEGCO
Debt Disclosure [Line Items]
Guarantee of unsecured senior notes	$ 100,000,000					$ 100,000,000
Georgia Power | Senior Notes
Debt Disclosure [Line Items]
Repayments of debt		$ 902,000,000
Georgia Power | Senior Notes | Series 2007A 5.65% Senior Notes
Debt Disclosure [Line Items]
Debt instrument, face amount		250,000,000
Debt instrument, repurchase amount		$ 89,000,000
Fixed stated interest rate of debt obligation		5.65%
Georgia Power | Senior Notes | Series 2009A 5.95% Senior Notes
Debt Disclosure [Line Items]
Debt instrument, face amount		$ 500,000,000
Debt instrument, repurchase amount		$ 326,000,000
Fixed stated interest rate of debt obligation		5.95%
Georgia Power | Senior Notes | Series 2010B 5.40% Senior Notes
Debt Disclosure [Line Items]
Debt instrument, face amount		$ 600,000,000
Debt instrument, repurchase amount		$ 335,000,000
Fixed stated interest rate of debt obligation		5.40%
Georgia Power | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1995
Debt Disclosure [Line Items]
Debt instrument, face amount						105,000,000
Georgia Power | Municipal bonds | Development Authority of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Bowen Project), First Series 1997
Debt Disclosure [Line Items]
Debt instrument, face amount						173,000,000
Georgia Power | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Fifth Series 1994
Debt Disclosure [Line Items]
Debt instrument, face amount						55,000,000
Georgia Power | Municipal bonds | Development Authority of Burke County (Georgia) Pollution Control Revenue Bnds (Georgia Power Company Plant Vogtle Project), Second Series 2008
Debt Disclosure [Line Items]
Debt instrument, face amount						65,000,000
Georgia Power | Municipal bonds | Development Authority Of Bartow County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2013
Debt Disclosure [Line Items]
Debt instrument, face amount						72,000,000
Georgia Power | Municipal bonds | Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), First Series 2018 Due November 1, 2052
Debt Disclosure [Line Items]
Debt instrument, face amount						$ 108,000,000
Georgia Power | Municipal bonds | Subsequent Event
Debt Disclosure [Line Items]
Debt instrument, repurchased face amount				$ 108,000,000
Georgia Power | Municipal bonds | Subsequent Event | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project) First Series 1992
Debt Disclosure [Line Items]
Debt instrument, repurchased face amount					$ 13,000,000
Georgia Power | Municipal bonds | Subsequent Event | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Eighth Series 1994
Debt Disclosure [Line Items]
Debt instrument, repurchased face amount					20,000,000
Georgia Power | Municipal bonds | Subsequent Event | Development Authority of Burke County (Georgia) Pollution Control Revenue Bonds (Georgia Power Company Plant Vogtle Project), Second Series 1995
Debt Disclosure [Line Items]
Debt instrument, repurchased face amount					$ 75,000,000
Georgia Power | Notes Payable to Banks | Floating Rate Bank Term Loan Agreement 3
Debt Disclosure [Line Items]
Debt instrument, face amount												$ 100,000,000
Mississippi Power
Debt Disclosure [Line Items]
Fixed stated interest rate of debt obligation						7.13%
Mississippi Power | Senior Notes | Series 2018A Floating Rate Senior Notes
Debt Disclosure [Line Items]
Debt instrument, face amount			300,000,000
Mississippi Power | Senior Notes | Series 2018B 3.95% Senior Notes
Debt Disclosure [Line Items]
Debt instrument, face amount			$ 300,000,000
Fixed stated interest rate of debt obligation			3.95%
Mississippi Power | Senior Notes | Series G 5.40% Senior Notes Due July 1, 2035
Debt Disclosure [Line Items]
Fixed stated interest rate of debt obligation							5.40%
Debt instrument, repurchased face amount							$ 30,000,000
Mississippi Power | Senior Notes | Series 2009A 5.55% Senior Notes Due March 1, 2019
Debt Disclosure [Line Items]
Fixed stated interest rate of debt obligation							5.55%
Debt instrument, repurchased face amount							$ 125,000,000
Mississippi Power | Municipal bonds | Pollution Control Revenue Bonds
Debt Disclosure [Line Items]
Debt instrument, repurchase amount									$ 43,000,000
Mississippi Power | Unsecured Term Loan | Unsecured Term Loan
Debt Disclosure [Line Items]
Repayments of debt			$ 900,000,000
Southern Power | Floating Rate Bank Term Loan Agreement | Notes Payable to Banks
Debt Disclosure [Line Items]
Debt instrument, face amount		$ 100,000,000
Debt instrument, repurchased face amount		$ 420,000,000
SEGCO | Senior Notes | Series 2013A Senior Notes
Debt Disclosure [Line Items]
Repayments of debt	$ 100,000,000
Scenario, Forecast | Senior Notes | Series 2018A Floating Rate Senior Notes due February 14, 2020
Debt Disclosure [Line Items]
Fixed stated interest rate of debt obligation				1.85%