Cover Page - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2020
Jan. 31, 2021
Jun. 30, 2020
Document Information [Line Items]   
Document Type10-K  
Document Annual Reporttrue  
Document Period End DateDec. 31, 2020  
Current Fiscal Year End Date--12-31  
Document Transition Reportfalse  
Entity File Number1-3526  
Entity Registrant NameThe Southern Company  
Entity Tax Identification Number58-0690070  
Entity Incorporation, State or Country CodeDE  
Entity Address, Address Line One30 Ivan Allen Jr. Boulevard, N.W.  
Entity Address, City or TownAtlanta  
Entity Address, State or ProvinceGA  
Entity Address, Postal Zip Code30308  
City Area Code404  
Local Phone Number506-5000  
Entity Well-known Seasoned IssuerYes  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryLarge Accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
ICFR Auditor Attestation Flagtrue  
Entity Shell Companyfalse  
Entity Public Float  $ 54.8
Entity Common Stock, Shares Outstanding (in shares) 1,056,609,660 
Documents Incorporated by Reference
Documents incorporated by reference: specified portions of The Southern Company's Definitive Proxy Statement on Schedule 14A relating to the 2021 Annual Meeting of Stockholders are incorporated by reference into PART III. In addition, specified portions of Alabama Power Company's Definitive Proxy Statement on Schedule 14A relating to its 2021 Annual Meeting of Shareholders are incorporated by reference into PART III.
Each of Georgia Power Company, Mississippi Power Company, Southern Power Company, and Southern Company Gas meets the conditions set forth in General Instructions I(1)(a) and (b) of Form 10-K and is therefore filing this Form 10-K with the reduced disclosure format specified in General Instructions I(2)(b), (c), and (d) of Form 10-K.
This combined Form 10-K is separately filed by The Southern Company, Alabama Power Company, Georgia Power Company, Mississippi Power Company, Southern Power Company, and Southern Company Gas. Information contained herein relating to any individual registrant is filed by such registrant on its own behalf. Each registrant makes no representation as to information relating to the other registrants.
  
Entity Central Index Key0000092122  
Amendment Flagfalse  
Document Fiscal Year Focus2020  
Document Fiscal Period FocusFY  
Common Stock, par value $5 per share   
Document Information [Line Items]   
Title of 12(b) SecurityCommon Stock, par value $5 per share  
Trading SymbolSO  
Security Exchange NameNYSE  
Series 2016A 5.25% Junior Subordinated Notes due 2076   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2016A 5.25% Junior Subordinated Notes due 2076  
Trading SymbolSOJB  
Security Exchange NameNYSE  
Series 2017B 5.25% Junior Subordinated Notes due 2077   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2017B 5.25% Junior Subordinated Notes due 2077  
Trading SymbolSOJC  
Security Exchange NameNYSE  
2019 Series A Corporate Units   
Document Information [Line Items]   
Title of 12(b) Security2019 Series A Corporate Units  
Trading SymbolSOLN  
Security Exchange NameNYSE  
Series 2020A 4.95% Junior Subordinated Notes due 2080   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2020A 4.95% Junior Subordinated Notes due 2080  
Trading SymbolSOJD  
Security Exchange NameNYSE  
Series 2020C 4.20% Junior Subordinated Notes due 2060   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2020C 4.20% Junior Subordinated Notes due 2060  
Trading SymbolSOJE  
Security Exchange NameNYSE  
Alabama Power   
Document Information [Line Items]   
Entity File Number1-3164  
Entity Registrant NameAlabama Power Company  
Entity Tax Identification Number63-0004250  
Entity Incorporation, State or Country CodeAL  
Entity Address, Address Line One600 North 18th Street  
Entity Address, City or TownBirmingham  
Entity Address, State or ProvinceAL  
Entity Address, Postal Zip Code35203  
City Area Code205  
Local Phone Number257-1000  
Entity Well-known Seasoned IssuerYes  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
ICFR Auditor Attestation Flagfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 30,537,500 
Entity Central Index Key0000003153  
Alabama Power | 5.00% Series Class A Preferred Stock   
Document Information [Line Items]   
Title of 12(b) Security5.00% Series Class A Preferred Stock  
Trading SymbolALP PR Q  
Security Exchange NameNYSE  
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.20% Series   
Document Information [Line Items]   
Title of 12(g) Security4.20% Series  
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.52% Series   
Document Information [Line Items]   
Title of 12(g) Security4.52% Series  
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.60% Series   
Document Information [Line Items]   
Title of 12(g) Security4.60% Series  
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.64% Series   
Document Information [Line Items]   
Title of 12(g) Security4.64% Series  
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.72% Series   
Document Information [Line Items]   
Title of 12(g) Security4.72% Series  
Alabama Power | Preferred Stock, Cumulative, $100 Par Value, 4.92% Series   
Document Information [Line Items]   
Title of 12(g) Security4.92% Series  
Georgia Power   
Document Information [Line Items]   
Entity File Number1-6468  
Entity Registrant NameGeorgia Power Company  
Entity Tax Identification Number58-0257110  
Entity Incorporation, State or Country CodeGA  
Entity Address, Address Line One241 Ralph McGill Boulevard, N.E.  
Entity Address, City or TownAtlanta  
Entity Address, State or ProvinceGA  
Entity Address, Postal Zip Code30308  
City Area Code404  
Local Phone Number506-6526  
Entity Well-known Seasoned IssuerYes  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
ICFR Auditor Attestation Flagfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 9,261,500 
Entity Central Index Key0000041091  
Georgia Power | Series 2017A 5.00% Junior Subordinated Notes due 2077   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2017A 5.00% Junior Subordinated Notes due 2077  
Trading SymbolGPJA  
Security Exchange NameNYSE  
Mississippi Power   
Document Information [Line Items]   
Entity File Number001-11229  
Entity Registrant NameMississippi Power Company  
Entity Tax Identification Number64-0205820  
Entity Incorporation, State or Country CodeMS  
Entity Address, Address Line One2992 West Beach Boulevard  
Entity Address, City or TownGulfport  
Entity Address, State or ProvinceMS  
Entity Address, Postal Zip Code39501  
City Area Code228  
Local Phone Number864-1211  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
ICFR Auditor Attestation Flagfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 1,121,000 
Entity Central Index Key0000066904  
Southern Power   
Document Information [Line Items]   
Entity File Number001-37803  
Entity Registrant NameSouthern Power Company  
Entity Tax Identification Number58-2598670  
Entity Incorporation, State or Country CodeDE  
Entity Address, Address Line One30 Ivan Allen Jr. Boulevard, N.W.  
Entity Address, City or TownAtlanta  
Entity Address, State or ProvinceGA  
Entity Address, Postal Zip Code30308  
City Area Code404  
Local Phone Number506-5000  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
ICFR Auditor Attestation Flagfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 1,000 
Entity Central Index Key0001160661  
Southern Power | Series 2016A 1.000% Senior Notes due 2022   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2016A 1.000% Senior Notes due 2022  
Trading SymbolSO/22B  
Security Exchange NameNYSE  
Southern Power | Series 2016B 1.850% Senior Notes due 2026   
Document Information [Line Items]   
Title of 12(b) SecuritySeries 2016B 1.850% Senior Notes due 2026  
Trading SymbolSO/26A  
Security Exchange NameNYSE  
Southern Company Gas   
Document Information [Line Items]   
Entity File Number1-14174  
Entity Registrant NameSouthern Company Gas  
Entity Tax Identification Number58-2210952  
Entity Incorporation, State or Country CodeGA  
Entity Address, Address Line OneTen Peachtree Place, N.E.  
Entity Address, City or TownAtlanta  
Entity Address, State or ProvinceGA  
Entity Address, Postal Zip Code30309  
City Area Code404  
Local Phone Number584-4000  
Entity Well-known Seasoned IssuerNo  
Entity Voluntary FilersNo  
Entity Current Reporting StatusYes  
Entity Interactive Data CurrentYes  
Entity Filer CategoryNon-accelerated Filer  
Entity Small Businessfalse  
Entity Emerging Growth Companyfalse  
ICFR Auditor Attestation Flagfalse  
Entity Shell Companyfalse  
Entity Common Stock, Shares Outstanding (in shares) 100 
Entity Central Index Key0001004155  

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