v3.26.1
Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Details) - USD ($)
$ in Millions
Jun. 30, 2026
Dec. 31, 2025
Assets:    
Derivatives $ 35 $ 72
Cash equivalents 1,786  
Other investments 10  
Total 5,060  
Liabilities:    
Derivatives 434 321
Contingent consideration 12  
Other 24  
Total 470  
Collateral already posted, assets, aggregate fair value 18  
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 1,768  
Total 3,050  
Liabilities:    
Contingent consideration 0  
Other 0  
Total 11  
Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 18  
Total 1,781  
Liabilities:    
Contingent consideration 0  
Other 13  
Total 436  
Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Other investments 10  
Total 18  
Liabilities:    
Contingent consideration 12  
Other 11  
Total 23  
Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Total 211  
Energy-related derivatives    
Assets:    
Derivatives 69  
Liabilities:    
Derivatives 166  
Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 8  
Liabilities:    
Derivatives 11  
Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 61  
Liabilities:    
Derivatives 155  
Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
Interest rate derivatives    
Assets:    
Derivatives 5  
Liabilities:    
Derivatives 205  
Interest rate derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
Interest rate derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 5  
Liabilities:    
Derivatives 205  
Interest rate derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
Domestic equity    
Assets:    
Investments in trusts 1,323  
Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 1,030  
Domestic equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 293  
Domestic equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Foreign equity    
Assets:    
Investments in trusts 455  
Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 199  
Foreign equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 256  
Foreign equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
U.S. Treasury and government agency securities    
Assets:    
Investments in trusts 410  
Investments, available-for-sale: 13  
U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 1  
U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 410  
Investments, available-for-sale: 12  
U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Municipal bonds    
Assets:    
Investments in trusts 31  
Investments, available-for-sale: 2  
Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Municipal bonds | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 31  
Investments, available-for-sale: 2  
Municipal bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Pooled funds – fixed income    
Assets:    
Investments in trusts 4  
Pooled funds – fixed income | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
Pooled funds – fixed income | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 4  
Pooled funds – fixed income | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Corporate bonds    
Assets:    
Investments in trusts 533  
Investments, available-for-sale: 4  
Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Corporate bonds | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 533  
Investments, available-for-sale: 4  
Corporate bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Mortgage- and asset-backed securities    
Assets:    
Investments in trusts 110  
Investments, available-for-sale: 3  
Mortgage- and asset-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Mortgage- and asset-backed securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 110  
Investments, available-for-sale: 3  
Mortgage- and asset-backed securities | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Investments, available-for-sale: 0  
Private equity    
Assets:    
Investments in trusts 202  
Private equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
Private equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 0  
Private equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Private equity | Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Investments in trusts 202  
Cash and cash equivalents    
Assets:    
Investments in trusts 1  
Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 1  
Cash and cash equivalents | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 0  
Cash and cash equivalents | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Other    
Assets:    
Investments in trusts 46  
Other investments 53  
Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 33  
Other investments 10  
Other | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 4  
Other investments 35  
Other | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Other investments 8  
Other | Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Investments in trusts 9  
Foreign currency derivatives    
Liabilities:    
Derivatives 63  
Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Liabilities:    
Derivatives 0  
Foreign currency derivatives | Significant Other Observable Inputs (Level 2)    
Liabilities:    
Derivatives 63  
Foreign currency derivatives | Significant Unobservable Inputs (Level 3)    
Liabilities:    
Derivatives 0  
ALABAMA POWER CO    
Assets:    
Derivatives 11 6
Cash equivalents 58  
Other investments 35  
Total 1,761  
Liabilities:    
Derivatives 58 31
Collateral already posted, assets, aggregate fair value 0  
ALABAMA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 40  
Other investments 0  
Total 822  
ALABAMA POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 18  
Other investments 35  
Total 728  
ALABAMA POWER CO | Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Other investments 0  
Total 0  
ALABAMA POWER CO | Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Total 211  
ALABAMA POWER CO | Energy-related derivatives    
Assets:    
Derivatives 27  
Liabilities:    
Derivatives 58  
ALABAMA POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
ALABAMA POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 27  
Liabilities:    
Derivatives 58  
ALABAMA POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
ALABAMA POWER CO | Domestic equity    
Assets:    
Investments in trusts 851  
ALABAMA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 569  
ALABAMA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 282  
ALABAMA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Foreign equity    
Assets:    
Investments in trusts 199  
ALABAMA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 199  
ALABAMA POWER CO | Foreign equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Foreign equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | U.S. Treasury and government agency securities    
Assets:    
Investments in trusts 16  
ALABAMA POWER CO | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 16  
ALABAMA POWER CO | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Municipal bonds    
Assets:    
Investments in trusts 1  
ALABAMA POWER CO | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Municipal bonds | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 1  
ALABAMA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Corporate bonds    
Assets:    
Investments in trusts 319  
ALABAMA POWER CO | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Corporate bonds | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 319  
ALABAMA POWER CO | Corporate bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Mortgage- and asset-backed securities    
Assets:    
Investments in trusts 28  
ALABAMA POWER CO | Mortgage- and asset-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Mortgage- and asset-backed securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 28  
ALABAMA POWER CO | Mortgage- and asset-backed securities | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Private equity    
Assets:    
Investments in trusts 202  
ALABAMA POWER CO | Private equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Private equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Private equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Private equity | Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Investments in trusts 202  
ALABAMA POWER CO | Other    
Assets:    
Investments in trusts 25  
ALABAMA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 14  
ALABAMA POWER CO | Other | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 2  
ALABAMA POWER CO | Other | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Other | Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Investments in trusts 9  
GEORGIA POWER CO    
Assets:    
Derivatives 3 4
Cash equivalents 11  
Total 1,482  
Liabilities:    
Derivatives 48 33
GEORGIA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 11  
Total 491  
GEORGIA POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 0  
Total 991  
GEORGIA POWER CO | Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Total 0  
GEORGIA POWER CO | Energy-related derivatives    
Assets:    
Derivatives 14  
Liabilities:    
Derivatives 48  
GEORGIA POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
GEORGIA POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 14  
Liabilities:    
Derivatives 48  
GEORGIA POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
GEORGIA POWER CO | Domestic equity    
Assets:    
Investments in trusts 462  
GEORGIA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 461  
GEORGIA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 1  
GEORGIA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Foreign equity    
Assets:    
Investments in trusts 254  
GEORGIA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Foreign equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 254  
GEORGIA POWER CO | Foreign equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | U.S. Treasury and government agency securities    
Assets:    
Investments in trusts 394  
GEORGIA POWER CO | U.S. Treasury and government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 394  
GEORGIA POWER CO | U.S. Treasury and government agency securities | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Municipal bonds    
Assets:    
Investments in trusts 30  
GEORGIA POWER CO | Municipal bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Municipal bonds | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 30  
GEORGIA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Corporate bonds    
Assets:    
Investments in trusts 214  
GEORGIA POWER CO | Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Corporate bonds | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 214  
GEORGIA POWER CO | Corporate bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Mortgage- and asset-backed securities    
Assets:    
Investments in trusts 82  
GEORGIA POWER CO | Mortgage- and asset-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Mortgage- and asset-backed securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 82  
GEORGIA POWER CO | Mortgage- and asset-backed securities | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Other    
Assets:    
Investments in trusts 21  
GEORGIA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 19  
GEORGIA POWER CO | Other | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 2  
GEORGIA POWER CO | Other | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
MISSISSIPPI POWER CO    
Assets:    
Derivatives 1 1
Cash equivalents 1  
Total 15  
MISSISSIPPI POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 1  
Total 1  
MISSISSIPPI POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 0  
Total 14  
MISSISSIPPI POWER CO | Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Total 0  
MISSISSIPPI POWER CO | Energy-related derivatives    
Assets:    
Derivatives 14  
Liabilities:    
Derivatives 40  
MISSISSIPPI POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
MISSISSIPPI POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 14  
Liabilities:    
Derivatives 40  
MISSISSIPPI POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
SOUTHERN POWER CO    
Assets:    
Derivatives 2 21
Cash equivalents 162  
Total 175  
Liabilities:    
Derivatives 4 1
Contingent consideration 12  
Other 24  
Total 40  
Collateral already posted, assets, aggregate fair value 0  
SOUTHERN POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 162  
Total 162  
Liabilities:    
Contingent consideration 0  
Other 0  
Total 0  
SOUTHERN POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 0  
Total 3  
Liabilities:    
Contingent consideration 0  
Other 13  
Total 17  
SOUTHERN POWER CO | Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Total 10  
Liabilities:    
Contingent consideration 12  
Other 11  
Total 23  
SOUTHERN POWER CO | Energy-related derivatives    
Assets:    
Derivatives 3  
Liabilities:    
Derivatives 4  
SOUTHERN POWER CO | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
SOUTHERN POWER CO | Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 3  
Liabilities:    
Derivatives 4  
SOUTHERN POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
SOUTHERN POWER CO | Other    
Assets:    
Derivatives 10  
SOUTHERN POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
SOUTHERN POWER CO | Other | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 0  
SOUTHERN POWER CO | Other | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 10  
SOUTHERN Co GAS    
Assets:    
Derivatives 17 28
Cash equivalents 200  
Total 228  
Liabilities:    
Derivatives 78 79
Total 78  
Collateral already posted, assets, aggregate fair value 18 $ 33
SOUTHERN Co GAS | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 200  
Total 209  
Liabilities:    
Total 11  
SOUTHERN Co GAS | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 0  
Total 19  
Liabilities:    
Total 67  
SOUTHERN Co GAS | Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Total 0  
Liabilities:    
Total 0  
SOUTHERN Co GAS | Energy-related derivatives    
Assets:    
Derivatives 11  
Liabilities:    
Derivatives 16  
SOUTHERN Co GAS | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 8  
Liabilities:    
Derivatives 11  
SOUTHERN Co GAS | Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 3  
Liabilities:    
Derivatives 5  
SOUTHERN Co GAS | Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
SOUTHERN Co GAS | Interest rate derivatives    
Liabilities:    
Derivatives 62  
SOUTHERN Co GAS | Interest rate derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Liabilities:    
Derivatives 0  
SOUTHERN Co GAS | Interest rate derivatives | Significant Other Observable Inputs (Level 2)    
Liabilities:    
Derivatives 62  
SOUTHERN Co GAS | Interest rate derivatives | Significant Unobservable Inputs (Level 3)    
Liabilities:    
Derivatives 0  
SOUTHERN Co GAS | Domestic equity    
Assets:    
Non-qualified deferred compensation trusts 10  
SOUTHERN Co GAS | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Domestic equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Non-qualified deferred compensation trusts 10  
SOUTHERN Co GAS | Domestic equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Foreign equity    
Assets:    
Non-qualified deferred compensation trusts 2  
SOUTHERN Co GAS | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Foreign equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Non-qualified deferred compensation trusts 2  
SOUTHERN Co GAS | Foreign equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Pooled funds – fixed income    
Assets:    
Non-qualified deferred compensation trusts 4  
SOUTHERN Co GAS | Pooled funds – fixed income | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Pooled funds – fixed income | Significant Other Observable Inputs (Level 2)    
Assets:    
Non-qualified deferred compensation trusts 4  
SOUTHERN Co GAS | Pooled funds – fixed income | Significant Unobservable Inputs (Level 3)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Cash and cash equivalents    
Assets:    
Non-qualified deferred compensation trusts 1  
SOUTHERN Co GAS | Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Non-qualified deferred compensation trusts 1  
SOUTHERN Co GAS | Cash and cash equivalents | Significant Other Observable Inputs (Level 2)    
Assets:    
Non-qualified deferred compensation trusts 0  
SOUTHERN Co GAS | Cash and cash equivalents | Significant Unobservable Inputs (Level 3)    
Assets:    
Non-qualified deferred compensation trusts $ 0