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RETIREMENT BENEFITS - Fair Values of Pension Plan and Other Postretirement Benefit Plan Assets (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Pension plans    
Assets:    
Plan assets $ 14,621 $ 14,760
Liabilities:    
Derivatives (33)  
Total $ 14,588  
Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 41.00% 40.00%
Pension plans | Domestic equity    
Assets:    
Plan assets $ 2,930 $ 2,730
Pension plans | International equity    
Assets:    
Plan assets $ 2,991 $ 2,999
Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 32.00%
Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 1,780 $ 1,973
Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 48 44
Pension plans | Corporate bonds    
Assets:    
Plan assets 1,715 1,724
Pension plans | Pooled funds    
Assets:    
Plan assets 792 777
Pension plans | Cash equivalents and other    
Assets:    
Plan assets 255 429
Pension plans | Real estate investments    
Assets:    
Plan assets $ 1,924 $ 2,053
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 13.00% 14.00%
Pension plans | Special situations    
Assets:    
Plan assets $ 237 $ 245
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Pension plans | Private equity    
Assets:    
Plan assets $ 1,797 $ 1,761
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 12.00% 12.00%
Pension plans | Private Credit    
Assets:    
Plan assets $ 152 $ 25
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 1.00%  
Pension plans | Infrastructure    
Assets:    
Plan assets $ 0  
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00%  
Other postretirement benefit plans    
Assets:    
Plan assets $ 1,139 $ 1,096
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 61.00% 60.00%
Actual Allocation 62.00% 61.00%
Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 192 $ 172
Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 137 $ 135
Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 29.00% 30.00%
Actual Allocation 28.00% 28.00%
Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 54 $ 57
Other postretirement benefit plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 1 2
Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 48 47
Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 99 92
Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 16 23
Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 478 456
Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 54 $ 57
Liabilities:    
Target Allocation 4.00% 4.00%
Actual Allocation 5.00% 6.00%
Other postretirement benefit plans | Special situations    
Assets:    
Plan assets $ 6 $ 6
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 1.00% 1.00%
Other postretirement benefit plans | Private equity    
Assets:    
Plan assets $ 50 $ 48
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 4.00% 4.00%
Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets $ 4 $ 1
Liabilities:    
Target Allocation 1.00% 1.00%
Actual Allocation 0.00%  
Other postretirement benefit plans | Infrastructure    
Assets:    
Plan assets $ 0  
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 $ 4,670 $ 4,646
Liabilities:    
Derivatives 0  
Total 4,670  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 2,095 1,959
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 1,959 1,947
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 255 371
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 361 369
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 175 170
Liabilities:    
Derivatives 0  
Total 175  
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 94 85
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 54 53
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 16 21
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 6,202 6,399
Liabilities:    
Derivatives (33)  
Total 6,169  
Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 835 771
Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 1,032 1,052
Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 1,780 1,973
Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 48 44
Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 1,715 1,724
Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 792 777
Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 58
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 861 825
Liabilities:    
Derivatives 1  
Total 860  
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 98 87
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 83 82
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 54 57
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 1 2
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 48 47
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 99 92
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 0 2
Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 478 456
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 3,749 3,715
Liabilities:    
Derivatives 0  
Total 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 1,563 1,684
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 237 245
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 1,797 1,761
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 152 25
Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 103 101
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 43 46
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Special situations    
Assets:    
Plan assets 6 6
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private equity    
Assets:    
Plan assets 50 48
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets 4 1
Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Infrastructure    
Assets:    
Plan assets $ 0  
Alabama Power    
Liabilities:    
Target Allocation 100.00%  
Actual Allocation 100.00%  
Alabama Power | Pension plans    
Assets:    
Plan assets $ 3,555 $ 3,579
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 41.00% 40.00%
Alabama Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 712 $ 663
Alabama Power | Pension plans | International equity    
Assets:    
Plan assets $ 727 $ 727
Alabama Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 32.00%
Alabama Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 433 $ 479
Alabama Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 12 11
Alabama Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 417 418
Alabama Power | Pension plans | Pooled funds    
Assets:    
Plan assets 193 188
Alabama Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 62 104
Alabama Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 468 $ 497
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 13.00% 14.00%
Alabama Power | Pension plans | Special situations    
Assets:    
Plan assets $ 57 $ 59
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Alabama Power | Pension plans | Private equity    
Assets:    
Plan assets $ 437 $ 427
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 12.00% 12.00%
Alabama Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 37 $ 6
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 1.00%  
Alabama Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 0  
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00%  
Alabama Power | Other postretirement benefit plans    
Assets:    
Plan assets $ 418 $ 402
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% 67.00%
Actual Allocation 68.00% 66.00%
Alabama Power | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 24 $ 22
Alabama Power | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 25 $ 25
Alabama Power | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 23.00% 23.00%
Actual Allocation 24.00% 23.00%
Alabama Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 14 $ 16
Alabama Power | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 14 14
Alabama Power | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 11 8
Alabama Power | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 2 3
Alabama Power | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 294 280
Alabama Power | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 16 $ 17
Liabilities:    
Target Allocation 3.00% 4.00%
Actual Allocation 4.00% 6.00%
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% 4.00%
Alabama Power | Other postretirement benefit plans | Private Credit    
Liabilities:    
Target Allocation   1.00%
Alabama Power | Other postretirement benefit plans | Infrastructure    
Liabilities:    
Target Allocation   1.00%
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 1,135 $ 1,127
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 509 476
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 476 472
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 62 90
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 88 89
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 38 38
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 17 16
Alabama Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 16 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 3
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 1,509 1,552
Liabilities:    
Derivatives (8)  
Total 1,501  
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 203 187
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 251 255
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 433 479
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 12 11
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 417 418
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 193 188
Alabama Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 14
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 349 333
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 7 6
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 9 9
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 14 16
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 14 14
Alabama Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 11 8
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 294 280
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 911 900
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 380 408
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 57 59
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 437 427
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 37 6
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
Alabama Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 31 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 14
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
Georgia Power    
Liabilities:    
Target Allocation 100.00% 100.00%
Actual Allocation 100.00% 100.00%
Georgia Power | Pension plans    
Assets:    
Plan assets $ 4,538 $ 4,615
Liabilities:    
Derivatives (10)  
Total $ 4,528  
Target Allocation 100.00%  
Actual Allocation 100.00%  
Georgia Power | Pension plans | Equity    
Liabilities:    
Target Allocation 41.00% 41.00%
Actual Allocation 41.00% 40.00%
Georgia Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 911 $ 852
Georgia Power | Pension plans | International equity    
Assets:    
Plan assets $ 928 $ 938
Georgia Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 32.00%
Georgia Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 552 $ 617
Georgia Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 15 14
Georgia Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 532 539
Georgia Power | Pension plans | Pooled funds    
Assets:    
Plan assets 246 243
Georgia Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 79 134
Georgia Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 597 $ 642
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 13.00% 14.00%
Georgia Power | Pension plans | Special situations    
Assets:    
Plan assets $ 73 $ 77
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Georgia Power | Pension plans | Private equity    
Assets:    
Plan assets $ 558 $ 551
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 12.00% 12.00%
Georgia Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 47 $ 8
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 1.00% 0.00%
Georgia Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 0 $ 0
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00% 0.00%
Georgia Power | Other postretirement benefit plans    
Assets:    
Plan assets $ 420 $ 409
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% 58.00%
Actual Allocation 59.00% 57.00%
Georgia Power | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 59 $ 53
Georgia Power | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 57 $ 56
Georgia Power | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 35.00% 35.00%
Actual Allocation 33.00% 35.00%
Georgia Power | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 14 $ 16
Georgia Power | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 14 14
Georgia Power | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 48 47
Georgia Power | Other postretirement benefit plans | Cash equivalents and other    
Assets:    
Plan assets 10 13
Georgia Power | Other postretirement benefit plans | Trust-owned life insurance    
Assets:    
Plan assets 184 176
Georgia Power | Other postretirement benefit plans | Real estate investments    
Assets:    
Plan assets $ 17 $ 18
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 4.00% 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 $ 14
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 3.00% 3.00%
Georgia Power | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets   $ 0
Liabilities:    
Target Allocation   1.00%
Actual Allocation   0.00%
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 1,451 $ 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 652 611
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 608 609
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 79 116
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 112 115
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 82 80
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 52 47
Georgia Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 16 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 10 13
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 | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets   0
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans    
Assets:    
Plan assets 1,924 2,001
Liabilities:    
Derivatives (10)  
Total 1,914  
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 259 241
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 320 329
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 552 617
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 15 14
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 532 539
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 246 243
Georgia Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 18
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 308 299
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 7 6
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 41 40
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 14 16
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Corporate bonds    
Assets:    
Plan assets 14 14
Georgia Power | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Pooled funds    
Assets:    
Plan assets 48 47
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 184 176
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 | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets   0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans    
Assets:    
Plan assets 1,163 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 485 527
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 73 77
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 558 551
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 47 8
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 30 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 14
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 14
Georgia Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans | Private Credit    
Assets:    
Plan assets   0
Mississippi Power    
Liabilities:    
Target Allocation 100.00%  
Actual Allocation 100.00%  
Mississippi Power | Pension plans    
Assets:    
Plan assets $ 667 $ 675
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 41.00% 40.00%
Mississippi Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 135 $ 124
Mississippi Power | Pension plans | International equity    
Assets:    
Plan assets $ 136 $ 137
Mississippi Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 32.00%
Mississippi Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 81 $ 90
Mississippi Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 2 2
Mississippi Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 78 79
Mississippi Power | Pension plans | Pooled funds    
Assets:    
Plan assets 36 36
Mississippi Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 12 20
Mississippi Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 87 $ 94
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 13.00% 14.00%
Mississippi Power | Pension plans | Special situations    
Assets:    
Plan assets $ 11 $ 11
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Mississippi Power | Pension plans | Private equity    
Assets:    
Plan assets $ 82 $ 81
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 12.00% 12.00%
Mississippi Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 7 $ 1
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 1.00% 0.00%
Mississippi Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 0 $ 0
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00% 0.00%
Mississippi Power | Other postretirement benefit plans    
Assets:    
Plan assets $ 23 $ 24
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 32.00% 33.00%
Mississippi Power | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 4 $ 4
Mississippi Power | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 4 $ 4
Mississippi Power | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 43.00% 43.00%
Actual Allocation 44.00% 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 2 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 $ 3
Liabilities:    
Target Allocation 10.00% 10.00%
Actual Allocation 11.00% 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 $ 2 $ 2
Liabilities:    
Target Allocation 7.00% 7.00%
Actual Allocation 10.00% 10.00%
Mississippi Power | Other postretirement benefit plans | Private Credit    
Liabilities:    
Target Allocation   3.00%
Mississippi Power | Other postretirement benefit plans | Infrastructure    
Liabilities:    
Target Allocation   1.00%
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans    
Assets:    
Plan assets $ 214 $ 212
Liabilities:    
Derivatives 0  
Total 214  
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 97 89
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 89 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 12 17
Mississippi Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 16 17
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 8
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 1
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 282 293
Liabilities:    
Derivatives (2)  
Total 280  
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 38 35
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 47 48
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 81 90
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 2 2
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 78 79
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 36 36
Mississippi Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 3
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 12 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 1 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 2 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 171 170
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 71 77
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 11 11
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 82 81
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 7 1
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Mississippi Power | Net Asset Value as a Practical Expedient (NAV) | Other postretirement benefit plans    
Assets:    
Plan assets 4 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 2 2
Southern Power | Pension plans    
Assets:    
Plan assets $ 188 $ 187
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 41.00% 40.00%
Southern Power | Pension plans | Domestic equity    
Assets:    
Plan assets $ 38 $ 34
Southern Power | Pension plans | International equity    
Assets:    
Plan assets $ 38 $ 38
Southern Power | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 32.00%
Southern Power | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 23 $ 25
Southern Power | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 1 1
Southern Power | Pension plans | Corporate bonds    
Assets:    
Plan assets 22 22
Southern Power | Pension plans | Pooled funds    
Assets:    
Plan assets 10 10
Southern Power | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 3 6
Southern Power | Pension plans | Real estate investments    
Assets:    
Plan assets $ 25 $ 26
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 13.00% 14.00%
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 $ 23 $ 22
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 12.00% 12.00%
Southern Power | Pension plans | Private Credit    
Assets:    
Plan assets $ 2 $ 0
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 1.00% 0.00%
Southern Power | Pension plans | Infrastructure    
Assets:    
Plan assets $ 0 $ 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 $ 60 $ 59
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 27 24
Southern Power | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 25 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 5
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 80 82
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 11 10
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 13 13
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 23 25
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 22 22
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 10 10
Southern Power | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 1
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 48 46
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 21
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 23 22
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 2 0
Southern Power | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 0 0
Southern Company Gas | Pension plans    
Assets:    
Plan assets $ 983 $ 989
Liabilities:    
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 41.00% 40.00%
Southern Company Gas | Pension plans | Domestic equity    
Assets:    
Plan assets $ 198 $ 182
Southern Company Gas | Pension plans | International equity    
Assets:    
Plan assets $ 201 $ 201
Southern Company Gas | Pension plans | Fixed income    
Liabilities:    
Target Allocation 30.00% 30.00%
Actual Allocation 31.00% 32.00%
Southern Company Gas | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets $ 120 $ 132
Southern Company Gas | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 3 3
Southern Company Gas | Pension plans | Corporate bonds    
Assets:    
Plan assets 115 116
Southern Company Gas | Pension plans | Pooled funds    
Assets:    
Plan assets 53 52
Southern Company Gas | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 17 29
Southern Company Gas | Pension plans | Real estate investments    
Assets:    
Plan assets $ 129 $ 138
Liabilities:    
Target Allocation 12.00% 12.00%
Actual Allocation 13.00% 14.00%
Southern Company Gas | Pension plans | Special situations    
Assets:    
Plan assets $ 16 $ 16
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 2.00% 2.00%
Southern Company Gas | Pension plans | Private equity    
Assets:    
Plan assets $ 121 $ 118
Liabilities:    
Target Allocation 9.00% 9.00%
Actual Allocation 12.00% 12.00%
Southern Company Gas | Pension plans | Private Credit    
Assets:    
Plan assets $ 10 $ 2
Liabilities:    
Target Allocation 3.00% 3.00%
Actual Allocation 1.00%  
Southern Company Gas | Pension plans | Infrastructure    
Assets:    
Plan assets $ 0  
Liabilities:    
Target Allocation 2.00% 2.00%
Actual Allocation 0.00%  
Southern Company Gas | Other postretirement benefit plans    
Assets:    
Plan assets $ 138 $ 127
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 73.00% 72.00%
Southern Company Gas | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets $ 77 $ 69
Southern Company Gas | Other postretirement benefit plans | International equity    
Assets:    
Plan assets $ 24 $ 24
Southern Company Gas | Other postretirement benefit plans | Fixed income    
Liabilities:    
Target Allocation 26.00% 26.00%
Actual Allocation 25.00% 26.00%
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 32 29
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 $ 315 $ 310
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Domestic equity    
Assets:    
Plan assets 142 130
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | International equity    
Assets:    
Plan assets 132 130
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 17 25
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension plans | Real estate investments    
Assets:    
Plan assets 24 25
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 5
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 1 2
Southern Company Gas | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 1 2
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 416 430
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Domestic equity    
Assets:    
Plan assets 56 52
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | International equity    
Assets:    
Plan assets 69 71
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | U.S. Treasury, government, and agency bonds    
Assets:    
Plan assets 120 132
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Mortgage- and asset-backed securities    
Assets:    
Plan assets 3 3
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Corporate bonds    
Assets:    
Plan assets 115 116
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Pooled funds    
Assets:    
Plan assets 53 52
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Pension plans | Cash equivalents and other    
Assets:    
Plan assets 0 4
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 133 120
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | Domestic equity    
Assets:    
Plan assets 76 67
Southern Company Gas | Significant Other Observable Inputs (Level 2) | Other postretirement benefit plans | International equity    
Assets:    
Plan assets 23 22
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 32 29
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 252 249
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 105 113
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Special situations    
Assets:    
Plan assets 16 16
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private equity    
Assets:    
Plan assets 121 118
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Private Credit    
Assets:    
Plan assets 10 2
Southern Company Gas | Net Asset Value as a Practical Expedient (NAV) | Pension plans | Infrastructure    
Assets:    
Plan assets 0  
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