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RETIREMENT BENEFITS - Fair Values of Pension Plan and Other Postretirement Benefit Plan Assets (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Pension plans    
Assets:    
Plan assets $ 15,826 $ 14,621
Liabilities:    
Derivatives (1) (33)
Total $ 15,825 $ 14,588
Target Allocation   100.00%
Actual Allocation   100.00%
Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 42.00% 41.00%
Pension plans | Domestic equity    
Assets:    
Plan assets $ 3,100 $ 2,930
Pension plans | International equity    
Assets:    
Plan assets $ 3,403 $ 2,991
Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 31.00%
Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 1,994 $ 1,780
Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 75 48
Pension plans | Corporate bonds    
Assets:    
Plan assets 1,859 1,715
Pension plans | Pooled funds    
Assets:    
Plan assets 850 792
Pension plans | Cash equivalents and other    
Assets:    
Plan assets 242 255
Pension plans | Real estate investments    
Assets:    
Plan assets $ 1,891 $ 1,924
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 12.00% 13.00%
Pension plans | Special situations    
Assets:    
Plan assets $ 258 $ 237
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Pension plans | Private equity    
Assets:    
Plan assets $ 1,829 $ 1,797
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 11.00% 12.00%
Pension plans | Private Credit    
Assets:    
Plan assets $ 265 $ 152
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00%  
Pension plans | Infrastructure    
Assets:    
Plan assets $ 60  
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00%  
Other postretirement benefit plans    
Assets:    
Plan assets $ 1,249 $ 1,139
Liabilities:    
Derivatives   (1)
Total   $ 1,138
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Other postretirement benefit plans | Equity    
Liabilities:    
Target Allocation 60.00% 61.00%
Actual Allocation 63.00% 62.00%
Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 206 $ 192
Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 165 $ 137
Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 29.00%
Actual Allocation 27.00% 28.00%
Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 61 $ 54
Other postretirement benefit plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 2 1
Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 53 48
Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 106 99
Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 13 16
Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 520 478
Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 55 $ 54
Liabilities:    
Target Allocation 4.00% 4.00%
Actual Allocation 4.00% 5.00%
Other postretirement benefit plans | Special situations    
Assets:    
Plan assets $ 7 $ 6
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 1.00%
Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 52 $ 50
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 4.00% 4.00%
Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets $ 7 $ 4
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00%  
Other postretirement benefit plans | Infrastructure    
Assets:    
Plan assets $ 2  
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 0.00%  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 5,022 $ 4,670
Liabilities:    
Derivatives (1) 0
Total 5,021 4,670
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 2,216 2,095
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 2,219 1,959
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 237 255
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 350 361
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private Credit    
Assets:    
Plan assets 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans    
Assets:    
Plan assets 185 175
Liabilities:    
Derivatives   0
Total   175
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 98 94
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 63 54
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 13 16
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 11 11
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets 0  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Infrastructure    
Assets:    
Plan assets 0  
Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 6,851 6,202
Liabilities:    
Derivatives 0 (33)
Total 6,851 6,169
Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 884 835
Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 1,184 1,032
Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 1,994 1,780
Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 75 48
Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 1,859 1,715
Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 850 792
Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 5 0
Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Pension plans | Private Credit    
Assets:    
Plan assets 0  
Significant Other Observable Inputs (Level 2) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans    
Assets:    
Plan assets 952 861
Liabilities:    
Derivatives   (1)
Total   860
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 108 98
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 102 83
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 61 54
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 2 1
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 53 48
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 106 99
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 520 478
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets 0  
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Infrastructure    
Assets:    
Plan assets 0  
Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 3,953 3,749
Liabilities:    
Derivatives 0 0
Total 3,953 3,749
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments    
Assets:    
Plan assets 1,541 1,563
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 258 237
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 1,829 1,797
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 265 152
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 60  
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 112 103
Liabilities:    
Derivatives   0
Total   103
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 0 0
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 44 43
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 7 6
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 52 50
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets 7 $ 4
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Infrastructure    
Assets:    
Plan assets 2  
Alabama Power    
Liabilities:    
Target Allocation   100.00%
Actual Allocation   100.00%
Alabama Power | Pension plans    
Assets:    
Plan assets $ 3,856 $ 3,555
Liabilities:    
Derivatives   (8)
Total   $ 3,547
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Alabama Power | Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 42.00% 41.00%
Alabama Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 753 $ 712
Alabama Power | Pension plans | International equity    
Assets:    
Plan assets $ 830 $ 727
Alabama Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 31.00%
Alabama Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 486 $ 433
Alabama Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 18 12
Alabama Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 453 417
Alabama Power | Pension plans | Pooled funds    
Assets:    
Plan assets 207 193
Alabama Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 59 62
Alabama Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 461 $ 468
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 12.00% 13.00%
Alabama Power | Pension plans | Special situations    
Assets:    
Plan assets $ 63 $ 57
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Alabama Power | Pension plans | Private equity    
Assets:    
Plan assets $ 446 $ 437
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 11.00% 12.00%
Alabama Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 65 $ 37
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00%  
Alabama Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 15  
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00%  
Alabama Power | Other postretirement benefit plans    
Assets:    
Plan assets $ 454 $ 418
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Alabama Power | Other postretirement benefit plans | Equity    
Liabilities:    
Target Allocation 68.00% 68.00%
Actual Allocation 69.00% 68.00%
Alabama Power | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 25 $ 24
Alabama Power | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 28 $ 25
Alabama Power | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 23.00% 23.00%
Actual Allocation 23.00% 24.00%
Alabama Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 17 $ 14
Alabama Power | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 15 14
Alabama Power | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 11 11
Alabama Power | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 2 2
Alabama Power | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 320 294
Alabama Power | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 16 $ 16
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 3.00% 4.00%
Alabama Power | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets $ 2 $ 2
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 1.00%
Alabama Power | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 15 $ 15
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 3.00% 3.00%
Alabama Power | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets $ 2 $ 1
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 0.00%
Alabama Power | Other postretirement benefit plans | Infrastructure    
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation   0.00%
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 1,222 $ 1,135
Liabilities:    
Derivatives   0
Total   1,135
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 538 509
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 541 476
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 58 62
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 85 88
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private Credit    
Assets:    
Plan assets 0  
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans    
Assets:    
Plan assets 41 38
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 18 17
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 18 16
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 2 2
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 3 3
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 1,669 1,509
Liabilities:    
Derivatives   (8)
Total   1,501
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 215 203
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 289 251
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 486 433
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 18 12
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 453 417
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 207 193
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 1 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private Credit    
Assets:    
Plan assets 0  
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans    
Assets:    
Plan assets 381 349
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 7 7
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 10 9
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 17 14
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 15 14
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 11 11
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 320 294
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 965 911
Liabilities:    
Derivatives   0
Total   911
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments    
Assets:    
Plan assets 376 380
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 63 57
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 446 437
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 65 37
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 15  
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 32 31
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 0 0
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 13 13
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 2 2
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 15 15
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets 2 $ 1
Georgia Power    
Liabilities:    
Target Allocation   100.00%
Actual Allocation   100.00%
Georgia Power | Pension plans    
Assets:    
Plan assets $ 4,884 $ 4,538
Liabilities:    
Derivatives   (10)
Total   $ 4,528
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Georgia Power | Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 42.00% 41.00%
Georgia Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 956 $ 911
Georgia Power | Pension plans | International equity    
Assets:    
Plan assets $ 1,050 $ 928
Georgia Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 31.00%
Georgia Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 615 $ 552
Georgia Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 23 15
Georgia Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 574 532
Georgia Power | Pension plans | Pooled funds    
Assets:    
Plan assets 262 246
Georgia Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 75 79
Georgia Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 584 $ 597
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 12.00% 13.00%
Georgia Power | Pension plans | Special situations    
Assets:    
Plan assets $ 80 $ 73
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Georgia Power | Pension plans | Private equity    
Assets:    
Plan assets $ 564 $ 558
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 11.00% 12.00%
Georgia Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 82 $ 47
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 1.00%
Georgia Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 19 $ 0
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00% 0.00%
Georgia Power | Other postretirement benefit plans    
Assets:    
Plan assets $ 458 $ 420
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Georgia Power | Other postretirement benefit plans | Equity    
Liabilities:    
Target Allocation 59.00% 59.00%
Actual Allocation 60.00% 59.00%
Georgia Power | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 61 $ 59
Georgia Power | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 68 $ 57
Georgia Power | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 35.00% 35.00%
Actual Allocation 32.00% 33.00%
Georgia Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 17 $ 14
Georgia Power | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 15 14
Georgia Power | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 51 48
Georgia Power | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 8 10
Georgia Power | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 201 184
Georgia Power | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 17 $ 17
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 3.00% 4.00%
Georgia Power | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets $ 2 $ 2
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 1.00%
Georgia Power | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 15 $ 15
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 3.00% 3.00%
Georgia Power | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets $ 2  
Liabilities:    
Actual Allocation 1.00%  
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 1,549 $ 1,451
Liabilities:    
Derivatives   0
Total   1,451
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 683 652
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 685 608
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 73 79
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 108 112
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private Credit    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans    
Assets:    
Plan assets 84 82
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 54 52
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 18 16
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 8 10
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 4 4
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 2,114 1,924
Liabilities:    
Derivatives   (10)
Total   1,914
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 273 259
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 365 320
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 615 552
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 23 15
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 574 532
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 262 246
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 2 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private Credit    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans    
Assets:    
Plan assets 342 308
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 7 7
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 50 41
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 17 14
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 15 14
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 51 48
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 201 184
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 1,221 1,163
Liabilities:    
Derivatives   0
Total   1,163
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments    
Assets:    
Plan assets 476 485
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 80 73
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 564 558
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 82 47
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 19 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 32 30
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 13 13
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 2 2
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 15 15
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets 2  
Mississippi Power | Pension plans    
Assets:    
Plan assets $ 720 667
Liabilities:    
Derivatives   (2)
Total   $ 665
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Mississippi Power | Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 42.00% 41.00%
Mississippi Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 140 $ 135
Mississippi Power | Pension plans | International equity    
Assets:    
Plan assets $ 155 $ 136
Mississippi Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 31.00%
Mississippi Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 91 $ 81
Mississippi Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 3 2
Mississippi Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 85 78
Mississippi Power | Pension plans | Pooled funds    
Assets:    
Plan assets 39 36
Mississippi Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 11 12
Mississippi Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 86 $ 87
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 12.00% 13.00%
Mississippi Power | Pension plans | Special situations    
Assets:    
Plan assets $ 12 $ 11
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Mississippi Power | Pension plans | Private equity    
Assets:    
Plan assets $ 83 $ 82
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 11.00% 12.00%
Mississippi Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 12 $ 7
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 1.00%
Mississippi Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 3 $ 0
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00% 0.00%
Mississippi Power | Other postretirement benefit plans    
Assets:    
Plan assets $ 26 $ 23
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Mississippi Power | Other postretirement benefit plans | Equity    
Liabilities:    
Target Allocation 34.00% 34.00%
Actual Allocation 34.00% 32.00%
Mississippi Power | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 4 $ 4
Mississippi Power | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 5 $ 4
Mississippi Power | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 43.00% 43.00%
Actual Allocation 43.00% 44.00%
Mississippi Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 7 $ 7
Mississippi Power | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 3 2
Mississippi Power | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 1 1
Mississippi Power | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 1 1
Mississippi Power | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 2 $ 2
Liabilities:    
Target Allocation 10.00% 10.00%
Actual Allocation 10.00% 11.00%
Mississippi Power | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets $ 0 $ 0
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 2.00% 2.00%
Mississippi Power | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 3 $ 2
Liabilities:    
Target Allocation 7.00% 7.00%
Actual Allocation 9.00% 10.00%
Mississippi Power | Other postretirement benefit plans | Private Credit    
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 1.00%
Mississippi Power | Other postretirement benefit plans | Infrastructure    
Liabilities:    
Target Allocation 1.00% 1.00%
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 228 $ 214
Liabilities:    
Derivatives   0
Total   214
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 100 97
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 101 89
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 11 12
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 16 16
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private Credit    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans    
Assets:    
Plan assets 7 7
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 3 3
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 3 3
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 1 1
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 312 282
Liabilities:    
Derivatives   (2)
Total   280
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 40 38
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 54 47
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 91 81
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 3 2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 85 78
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 39 36
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private Credit    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans    
Assets:    
Plan assets 14 12
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 1 1
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 2 1
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 7 7
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 3 2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 1 1
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Mississippi Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 180 171
Liabilities:    
Derivatives   0
Total   171
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments    
Assets:    
Plan assets 70 71
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 12 11
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 83 82
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 12 7
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 3 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 5 4
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 2 2
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 3 2
Southern Power | Pension plans    
Assets:    
Plan assets $ 206 $ 188
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Southern Power | Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 42.00% 41.00%
Southern Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 41 $ 38
Southern Power | Pension plans | International equity    
Assets:    
Plan assets $ 44 $ 38
Southern Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 31.00%
Southern Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 26 $ 23
Southern Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 1 1
Southern Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 24 22
Southern Power | Pension plans | Pooled funds    
Assets:    
Plan assets 11 10
Southern Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 3 3
Southern Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 25 $ 25
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 12.00% 13.00%
Southern Power | Pension plans | Special situations    
Assets:    
Plan assets $ 3 $ 3
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Southern Power | Pension plans | Private equity    
Assets:    
Plan assets $ 24 $ 23
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 11.00% 12.00%
Southern Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 3 $ 2
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 1.00%
Southern Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 1 $ 0
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00% 0.00%
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 66 $ 60
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 29 27
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 29 25
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 3 3
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 5 5
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private Credit    
Assets:    
Plan assets 0 0
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 89 80
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 12 11
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 15 13
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 26 23
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 1 1
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 24 22
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 11 10
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments    
Assets:    
Plan assets 0 0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Private Credit    
Assets:    
Plan assets 0 0
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 51 48
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments    
Assets:    
Plan assets 20 20
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 3 3
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 24 23
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 3 2
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 1 0
Southern Company Gas | Pension plans    
Assets:    
Plan assets $ 1,060 983
Liabilities:    
Derivatives   (2)
Total   $ 981
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Southern Company Gas | Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 42.00% 41.00%
Southern Company Gas | Pension plans | Domestic equity    
Assets:    
Plan assets $ 207 $ 198
Southern Company Gas | Pension plans | International equity    
Assets:    
Plan assets $ 228 $ 201
Southern Company Gas | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 31.00%
Southern Company Gas | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 134 $ 120
Southern Company Gas | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 5 3
Southern Company Gas | Pension plans | Corporate bonds    
Assets:    
Plan assets 125 115
Southern Company Gas | Pension plans | Pooled funds    
Assets:    
Plan assets 57 53
Southern Company Gas | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 16 17
Southern Company Gas | Pension plans | Real estate investments    
Assets:    
Plan assets $ 126 $ 129
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 12.00% 13.00%
Southern Company Gas | Pension plans | Special situations    
Assets:    
Plan assets $ 17 $ 16
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Southern Company Gas | Pension plans | Private equity    
Assets:    
Plan assets $ 123 $ 121
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 11.00% 12.00%
Southern Company Gas | Pension plans | Private Credit    
Assets:    
Plan assets $ 18 $ 10
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00%  
Southern Company Gas | Pension plans | Infrastructure    
Assets:    
Plan assets $ 4  
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00%  
Southern Company Gas | Other postretirement benefit plans    
Assets:    
Plan assets $ 153 $ 138
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Southern Company Gas | Other postretirement benefit plans | Equity    
Liabilities:    
Target Allocation 72.00% 72.00%
Actual Allocation 74.00% 73.00%
Southern Company Gas | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 84 $ 77
Southern Company Gas | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 30 $ 24
Southern Company Gas | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 26.00% 26.00%
Actual Allocation 24.00% 25.00%
Southern Company Gas | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 1 $ 1
Southern Company Gas | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 1 1
Southern Company Gas | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 34 32
Southern Company Gas | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 1 1
Southern Company Gas | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 1 $ 1
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 1.00%
Southern Company Gas | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 1 $ 1
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 1.00%
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 336 $ 315
Liabilities:    
Derivatives   0
Total   315
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 148 142
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 149 132
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 16 17
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 23 24
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Private Credit    
Assets:    
Plan assets 0  
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans    
Assets:    
Plan assets 3 3
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 1 1
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 1 1
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 1 1
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 459 416
Liabilities:    
Derivatives   (2)
Total   414
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 59 56
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 79 69
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 134 120
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 5 3
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 125 115
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 57 53
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Real estate investments    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Special situations    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Private equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Private Credit    
Assets:    
Plan assets 0  
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans    
Assets:    
Plan assets 148 133
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 83 76
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 29 23
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 1 1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 1 1
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 34 32
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 0 0
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 265 252
Liabilities:    
Derivatives   0
Total   252
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Domestic equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | International equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Corporate bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Pooled funds    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Real estate investments    
Assets:    
Plan assets 103 105
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 17 16
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 123 121
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 18 10
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 4  
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 2 2
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 0
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets 1 1
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 1 $ 1