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Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Liabilities:    
Weather derivative premium $ 11 $ 4
Collateral already posted, aggregate fair value 193 62
Energy-related derivatives    
Liabilities:    
Collateral already posted, aggregate fair value 6 8
Recurring    
Assets:    
Interest rate derivatives 1 14
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value 129  
Nuclear decommissioning trusts:    
Cash equivalents 1,455 1,172
Other investments 10 10
Total 3,995 3,471
Liabilities:    
Interest rate derivatives 38 29
Contingent consideration 22 18
Total 816 735
Recurring | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 772 662
Recurring | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 286 216
Recurring | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 251 92
Recurring | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 68 73
Recurring | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 336 332
Recurring | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 57 183
Recurring | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 29 20
Recurring | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 31 26
Recurring | Energy-related derivatives    
Assets:    
Derivatives 570 671
Liabilities:    
Energy-related derivatives 733 630
Recurring | Foreign currency derivatives    
Liabilities:    
Foreign currency derivatives 23 58
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Interest rate derivatives 0 0
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value 0  
Nuclear decommissioning trusts:    
Cash equivalents 1,455 1,172
Other investments 9 9
Total 2,587 2,189
Liabilities:    
Interest rate derivatives 0 0
Contingent consideration 0 0
Total 480 345
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 690 589
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 62 48
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 21 22
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 19 11
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives 331 338
Liabilities:    
Energy-related derivatives 480 345
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign currency derivatives    
Liabilities:    
Foreign currency derivatives 0 0
Recurring | Significant Other Observable Inputs (Level 2)    
Assets:    
Interest rate derivatives 1 14
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value 129  
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Other investments 0 0
Total 1,378 1,261
Liabilities:    
Interest rate derivatives 38 29
Contingent consideration 0 0
Total 314 372
Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 82 73
Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 224 168
Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 251 92
Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 68 73
Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 315 310
Recurring | Significant Other Observable Inputs (Level 2) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 57 183
Recurring | Significant Other Observable Inputs (Level 2) | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Other Observable Inputs (Level 2) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 12 15
Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives 239 333
Liabilities:    
Energy-related derivatives 253 285
Recurring | Significant Other Observable Inputs (Level 2) | Foreign currency derivatives    
Liabilities:    
Foreign currency derivatives 23 58
Recurring | Significant Unobservable Inputs (Level 3)    
Assets:    
Interest rate derivatives 0 0
Foreign Currency Derivative Instruments Not Designated as Hedging Instruments, Asset at Fair Value 0  
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Other investments 1 1
Total 1 1
Liabilities:    
Interest rate derivatives 0 0
Contingent consideration 22 18
Total 22 18
Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
Recurring | Significant Unobservable Inputs (Level 3) | Foreign currency derivatives    
Liabilities:    
Foreign currency derivatives 0 0
ALABAMA POWER CO    
Assets:    
Derivatives 4 20
Liabilities:    
Energy-related derivatives 10 9
ALABAMA POWER CO | Recurring    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts, NAV 29 20
Cash equivalents 349 262
Total 1,255 1,072
ALABAMA POWER CO | Recurring | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 523 457
ALABAMA POWER CO | Recurring | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 121 95
ALABAMA POWER CO | Recurring | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 24 21
ALABAMA POWER CO | Recurring | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 181 168
ALABAMA POWER CO | Recurring | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 18 19
ALABAMA POWER CO | Recurring | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 29 20
Nuclear decommissioning trusts, NAV 29 20
ALABAMA POWER CO | Recurring | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 6 10
ALABAMA POWER CO | Recurring | Energy-related derivatives    
Assets:    
Derivatives 4 20
Liabilities:    
Energy-related derivatives 10 9
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Nuclear decommissioning trusts:    
Cash equivalents 349 262
Total 880 717
Liabilities:    
Interest rate derivatives   0
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 442 385
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 62 48
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 21 22
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 6 0
ALABAMA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0  
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2)    
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 346 335
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 81 72
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 59 47
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 24 21
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 160 146
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 18 19
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 10
ALABAMA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives 4 20
Liabilities:    
Energy-related derivatives 10 9
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3)    
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 0 0
Liabilities:    
Interest rate derivatives   0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
ALABAMA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0  
GEORGIA POWER CO    
Assets:    
Derivatives 6 46
Liabilities:    
Energy-related derivatives (24) 11
GEORGIA POWER CO | Recurring    
Assets:    
Interest rate derivatives   2
Nuclear decommissioning trusts:    
Cash equivalents 690 860
Total 1,625  
Liabilities:    
Energy-related derivatives 24 11
GEORGIA POWER CO | Recurring | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 249 205
GEORGIA POWER CO | Recurring | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 166 121
GEORGIA POWER CO | Recurring | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 227 71
GEORGIA POWER CO | Recurring | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 68 73
GEORGIA POWER CO | Recurring | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 155 164
GEORGIA POWER CO | Recurring | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 40 164
GEORGIA POWER CO | Recurring | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 24 16
GEORGIA POWER CO | Recurring | Energy-related derivatives    
Assets:    
Derivatives 6 44
Liabilities:    
Energy-related derivatives 19 8
GEORGIA POWER CO | Recurring | Interest rate derivatives    
Liabilities:    
Energy-related derivatives 5 3
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Interest rate derivatives   0
Nuclear decommissioning trusts:    
Cash equivalents 690 215
Total 950  
Liabilities:    
Energy-related derivatives 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 248 204
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 12 11
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
GEORGIA POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivatives    
Liabilities:    
Energy-related derivatives 0 0
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2)    
Assets:    
Interest rate derivatives   2
Nuclear decommissioning trusts:    
Cash equivalents 0 645
Total 675  
Liabilities:    
Energy-related derivatives 24 11
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 1 1
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 166 121
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 227 71
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 68 73
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 155 164
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 40 164
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 12 5
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives 6 44
Liabilities:    
Energy-related derivatives 19 8
GEORGIA POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Interest rate derivatives    
Liabilities:    
Energy-related derivatives 5 3
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3)    
Assets:    
Interest rate derivatives   0
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 0  
Liabilities:    
Energy-related derivatives 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Domestic equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Foreign equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | U.S. Treasury and government agency securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Municipal bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Corporate bonds    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Mortgage- and asset-backed securities    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Other    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
GEORGIA POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Interest rate derivatives    
Liabilities:    
Energy-related derivatives 0 0
GULF POWER CO    
Assets:    
Derivatives 0 5
Liabilities:    
Energy-related derivatives 21 29
GULF POWER CO | Recurring    
Nuclear decommissioning trusts:    
Cash equivalents 21 20
Total   25
GULF POWER CO | Recurring | Energy-related derivatives    
Assets:    
Derivatives   5
Liabilities:    
Energy-related derivatives 21 29
GULF POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Nuclear decommissioning trusts:    
Cash equivalents 21 20
Total   20
GULF POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives   0
Liabilities:    
Energy-related derivatives 0 0
GULF POWER CO | Recurring | Significant Other Observable Inputs (Level 2)    
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total   5
GULF POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives   5
Liabilities:    
Energy-related derivatives 21 29
GULF POWER CO | Recurring | Significant Unobservable Inputs (Level 3)    
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total   0
GULF POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives   0
Liabilities:    
Energy-related derivatives 0 0
MISSISSIPPI POWER CO    
Assets:    
Derivatives 3 7
Liabilities:    
Energy-related derivatives 9 11
MISSISSIPPI POWER CO | Recurring    
Nuclear decommissioning trusts:    
Cash equivalents 224 206
Total 227 212
MISSISSIPPI POWER CO | Recurring | Energy-related derivatives    
Assets:    
Derivatives 2 3
Liabilities:    
Energy-related derivatives 9 10
MISSISSIPPI POWER CO | Recurring | Interest rate derivatives    
Assets:    
Interest rate derivatives 1 3
MISSISSIPPI POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Nuclear decommissioning trusts:    
Cash equivalents 224 206
Total 224 206
MISSISSIPPI POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
MISSISSIPPI POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate derivatives    
Assets:    
Interest rate derivatives 0 0
MISSISSIPPI POWER CO | Recurring | Significant Other Observable Inputs (Level 2)    
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 3 6
MISSISSIPPI POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives 2 3
Liabilities:    
Energy-related derivatives 9 10
MISSISSIPPI POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Interest rate derivatives    
Assets:    
Interest rate derivatives 1 3
MISSISSIPPI POWER CO | Recurring | Significant Unobservable Inputs (Level 3)    
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 0 0
MISSISSIPPI POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
MISSISSIPPI POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Interest rate derivatives    
Assets:    
Interest rate derivatives 0 0
SOUTHERN POWER CO | Recurring    
Assets:    
Interest rate derivatives   1
Nuclear decommissioning trusts:    
Cash equivalents 21 628
Total 153 650
Liabilities:    
Contingent consideration 22 18
Total 58 81
SOUTHERN POWER CO | Recurring | Energy-related derivatives    
Assets:    
Derivatives 3 21
Liabilities:    
Energy-related derivatives 13 5
SOUTHERN POWER CO | Recurring | Foreign currency derivatives    
Assets:    
Derivatives 129  
Liabilities:    
Foreign currency derivatives 23 58
SOUTHERN POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)    
Assets:    
Interest rate derivatives   0
Nuclear decommissioning trusts:    
Cash equivalents 21 628
Total 21 628
Liabilities:    
Contingent consideration 0 0
Total 0 0
SOUTHERN POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
SOUTHERN POWER CO | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign currency derivatives    
Assets:    
Derivatives 0  
Liabilities:    
Foreign currency derivatives 0 0
SOUTHERN POWER CO | Recurring | Significant Other Observable Inputs (Level 2)    
Assets:    
Interest rate derivatives   1
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 132 22
Liabilities:    
Contingent consideration 0 0
Total 36 63
SOUTHERN POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives 3 21
Liabilities:    
Energy-related derivatives 13 5
SOUTHERN POWER CO | Recurring | Significant Other Observable Inputs (Level 2) | Foreign currency derivatives    
Assets:    
Derivatives 129  
Liabilities:    
Foreign currency derivatives 23 58
SOUTHERN POWER CO | Recurring | Significant Unobservable Inputs (Level 3)    
Assets:    
Interest rate derivatives   0
Nuclear decommissioning trusts:    
Cash equivalents 0 0
Total 0 0
Liabilities:    
Contingent consideration 22 18
Total 22 18
SOUTHERN POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives 0 0
Liabilities:    
Energy-related derivatives 0 0
SOUTHERN POWER CO | Recurring | Significant Unobservable Inputs (Level 3) | Foreign currency derivatives    
Assets:    
Derivatives 0  
Liabilities:    
Foreign currency derivatives 0 0
SOUTHERN Co GAS    
Assets:    
Derivatives 554  
Liabilities:    
Energy-related derivatives 581  
Weather derivative premium 11 4
Collateral already posted, aggregate fair value 193 62
SOUTHERN Co GAS | Energy-related derivatives    
Liabilities:    
Collateral already posted, aggregate fair value 6  
SOUTHERN Co GAS | Recurring | Energy-related derivatives    
Assets:    
Derivatives 554  
Liabilities:    
Energy-related derivatives 660  
SOUTHERN Co GAS | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives 331  
Liabilities:    
Energy-related derivatives 479  
SOUTHERN Co GAS | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives 223  
Liabilities:    
Energy-related derivatives 181  
SOUTHERN Co GAS | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives 0  
Liabilities:    
Energy-related derivatives 0  
Predecessor | SOUTHERN Co GAS    
Assets:    
Derivatives   660
Liabilities:    
Energy-related derivatives   569
Predecessor | SOUTHERN Co GAS | Energy-related derivatives    
Liabilities:    
Collateral already posted, aggregate fair value   8
Predecessor | SOUTHERN Co GAS | Recurring | Energy-related derivatives    
Assets:    
Derivatives   577
Liabilities:    
Energy-related derivatives   569
Predecessor | SOUTHERN Co GAS | Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Energy-related derivatives    
Assets:    
Derivatives   338
Liabilities:    
Energy-related derivatives   345
Predecessor | SOUTHERN Co GAS | Recurring | Significant Other Observable Inputs (Level 2) | Energy-related derivatives    
Assets:    
Derivatives   239
Liabilities:    
Energy-related derivatives   224
Predecessor | SOUTHERN Co GAS | Recurring | Significant Unobservable Inputs (Level 3) | Energy-related derivatives    
Assets:    
Derivatives   0
Liabilities:    
Energy-related derivatives   0
Nuclear Decommissioning Trusts | Recurring    
Nuclear decommissioning trusts:    
Total 29 20
Nuclear Decommissioning Trusts | Recurring | Private equity    
Nuclear decommissioning trusts:    
Nuclear decommissioning trusts, NAV $ 29 $ 20