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Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value (Details) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Assets:    
Derivatives $ 37 $ 72
Cash equivalents 501  
Other investments 10  
Total 3,583  
Liabilities:    
Derivatives 326 267
Contingent consideration 11  
Other 24  
Total 436  
Collateral already posted, assets, aggregate fair value 22  
Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 486  
Total 1,625  
Liabilities:    
Contingent consideration 0  
Other 0  
Total 9  
Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 15  
Total 1,736  
Liabilities:    
Contingent consideration 0  
Other 13  
Total 405  
Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Other investments 10  
Total 18  
Liabilities:    
Contingent consideration 11  
Other 11  
Total 22  
Net Asset Value as a Practical Expedient (NAV)    
Assets:    
Total 204  
Energy-related derivatives    
Assets:    
Derivatives 78  
Liabilities:    
Derivatives 160  
Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 2  
Liabilities:    
Derivatives 9  
Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 76  
Liabilities:    
Derivatives 151  
Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
Interest rate derivatives    
Assets:    
Derivatives 7  
Liabilities:    
Derivatives 191  
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 7  
Liabilities:    
Derivatives 191  
Interest rate derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
Domestic equity    
Assets:    
Investments in trusts 1,143  
Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 884  
Domestic equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 259  
Domestic equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
Foreign equity    
Assets:    
Investments in trusts 408  
Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 177  
Foreign equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 231  
Foreign equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
U.S. Treasury and government agency securities    
Assets:    
Investments in trusts 390  
Investments, available-for-sale: 14  
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: 2  
U.S. Treasury and government agency securities | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 390  
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 50  
Investments, available-for-sale: 1  
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 50  
Investments, available-for-sale: 1  
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 529  
Investments, available-for-sale: 3  
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 529  
Investments, available-for-sale: 3  
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 108  
Investments, available-for-sale: 4  
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 108  
Investments, available-for-sale: 4  
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 195  
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 195  
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 75  
Other investments 57  
Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 63  
Other investments 10  
Other | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 3  
Other investments 39  
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    
Assets:    
Derivatives 5  
Liabilities:    
Derivatives 50  
Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
Foreign currency derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 5  
Liabilities:    
Derivatives 50  
Foreign currency derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
ALABAMA POWER CO    
Assets:    
Derivatives 2 6
Cash equivalents 24  
Other investments 39  
Total 1,596  
Liabilities:    
Derivatives 25 18
Collateral already posted, assets, aggregate fair value 0  
ALABAMA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 9  
Other investments 0  
Total 701  
ALABAMA POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 15  
Other investments 39  
Total 691  
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 204  
ALABAMA POWER CO | Energy-related derivatives    
Assets:    
Derivatives 25  
Liabilities:    
Derivatives 48  
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 25  
Liabilities:    
Derivatives 48  
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 750  
ALABAMA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 502  
ALABAMA POWER CO | Domestic equity | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 248  
ALABAMA POWER CO | Domestic equity | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
ALABAMA POWER CO | Foreign equity    
Assets:    
Investments in trusts 177  
ALABAMA POWER CO | Foreign equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 177  
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 15  
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 15  
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 317  
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 317  
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 30  
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 30  
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 195  
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 195  
ALABAMA POWER CO | Other    
Assets:    
Investments in trusts 23  
ALABAMA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 13  
ALABAMA POWER CO | Other | Significant Other Observable Inputs (Level 2)    
Assets:    
Investments in trusts 1  
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 4 4
Cash equivalents 8  
Total 1,411  
Liabilities:    
Derivatives 28 19
GEORGIA POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 8  
Total 440  
GEORGIA POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 0  
Total 971  
GEORGIA POWER CO | Significant Unobservable Inputs (Level 3)    
Assets:    
Cash equivalents 0  
Total 0  
GEORGIA POWER CO | Energy-related derivatives    
Assets:    
Derivatives 25  
Liabilities:    
Derivatives 49  
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 25  
Liabilities:    
Derivatives 49  
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 383  
GEORGIA POWER CO | Domestic equity | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 382  
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 229  
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 229  
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 375  
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 375  
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 49  
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 49  
GEORGIA POWER CO | Municipal bonds | Significant Unobservable Inputs (Level 3)    
Assets:    
Investments in trusts 0  
GEORGIA POWER CO | Corporate bonds    
Assets:    
Investments in trusts 212  
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 212  
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 78  
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 78  
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 52  
GEORGIA POWER CO | Other | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Investments in trusts 50  
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
Liabilities:    
Derivatives 20 14
MISSISSIPPI POWER CO | Energy-related derivatives    
Assets:    
Derivatives 19  
Liabilities:    
Derivatives 38  
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 19  
Liabilities:    
Derivatives 38  
MISSISSIPPI POWER CO | Energy-related derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
Liabilities:    
Derivatives 0  
SOUTHERN POWER CO    
Assets:    
Derivatives 8 21
Total 19  
Liabilities:    
Derivatives 2 1
Contingent consideration 11  
Other 24  
Total 38  
Collateral already posted, assets, aggregate fair value 0  
SOUTHERN POWER CO | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Total 0  
Liabilities:    
Contingent consideration 0  
Other 0  
Total 0  
SOUTHERN POWER CO | Significant Other Observable Inputs (Level 2)    
Assets:    
Total 9  
Liabilities:    
Contingent consideration 0  
Other 13  
Total 16  
SOUTHERN POWER CO | Significant Unobservable Inputs (Level 3)    
Assets:    
Total 10  
Liabilities:    
Contingent consideration 11  
Other 11  
Total 22  
SOUTHERN POWER CO | Energy-related derivatives    
Assets:    
Derivatives 4  
Liabilities:    
Derivatives 3  
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 4  
Liabilities:    
Derivatives 3  
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 POWER CO | Foreign currency derivatives    
Assets:    
Derivatives 5  
SOUTHERN POWER CO | Foreign currency derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 0  
SOUTHERN POWER CO | Foreign currency derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 5  
SOUTHERN POWER CO | Foreign currency derivatives | Significant Unobservable Inputs (Level 3)    
Assets:    
Derivatives 0  
SOUTHERN Co GAS    
Assets:    
Derivatives 15 28
Cash equivalents 121  
Total 143  
Liabilities:    
Derivatives 65 65
Total 77  
Collateral already posted, assets, aggregate fair value 22 $ 33
SOUTHERN Co GAS | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Cash equivalents 121  
Total 124  
Liabilities:    
Total 9  
SOUTHERN Co GAS | Significant Other Observable Inputs (Level 2)    
Assets:    
Cash equivalents 0  
Total 19  
Liabilities:    
Total 68  
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 5  
Liabilities:    
Derivatives 22  
SOUTHERN Co GAS | Energy-related derivatives | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Derivatives 2  
Liabilities:    
Derivatives 9  
SOUTHERN Co GAS | Energy-related derivatives | Significant Other Observable Inputs (Level 2)    
Assets:    
Derivatives 3  
Liabilities:    
Derivatives 13  
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 55  
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 55  
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