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Segment and Related Information - Schedule of Gas Revenues (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Segment Reporting Information [Line Items]      
Total operating revenues $ 8,397 $ 7,775  
Other segment items 4,665 4,193  
Depreciation and amortization(b) 1,420 1,286  
Earnings from equity method investments 50 32  
Interest expense(c) 778 714  
Income taxes (benefit) 228 280  
Consolidated Net Income Attributable to Southern Company 1,356 1,334  
Total assets 157,031   $ 155,720
SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues 2,191 1,839  
Other segment items 1,357 1,069  
Depreciation and amortization(b) 183 169  
Earnings from equity method investments 46 39  
Interest expense(c) 105 92  
Income taxes (benefit) 145 130  
Consolidated Net Income Attributable to Southern Company 447 418  
Total assets 27,551   27,387
Operating Segments      
Segment Reporting Information [Line Items]      
Total operating revenues 8,213 7,594  
Other segment items 4,515 4,043  
Depreciation and amortization(b) 1,403 1,268  
Earnings from equity method investments 45 37  
Interest expense(c) 471 434  
Income taxes (benefit) 305 355  
Consolidated Net Income Attributable to Southern Company 1,564 1,531  
Total assets 155,141   153,416
Operating Segments | SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues 2,193 1,839  
Other segment items 1,360 1,072  
Depreciation and amortization(b) 182 168  
Earnings from equity method investments 46 39  
Interest expense(c) 101 92  
Income taxes (benefit) 155 139  
Consolidated Net Income Attributable to Southern Company 441 407  
Total assets 29,396   28,615
Operating Segments | Gas distribution operations | SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues 1,900 1,570  
Other segment items 1,177 905  
Depreciation and amortization(b) 179 164  
Earnings from equity method investments 0 0  
Interest expense(c) 91 82  
Income taxes (benefit) 116 104  
Consolidated Net Income Attributable to Southern Company 337 315  
Total assets 26,111   25,391
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues 8 8  
Other segment items 0 1  
Depreciation and amortization(b) 1 1  
Earnings from equity method investments 46 39  
Interest expense(c) 9 9  
Income taxes (benefit) 11 9  
Consolidated Net Income Attributable to Southern Company 33 27  
Total assets 1,517   1,475
Operating Segments | Gas marketing services | SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues 285 261  
Other segment items 183 166  
Depreciation and amortization(b) 2 3  
Earnings from equity method investments 0 0  
Interest expense(c) 1 1  
Income taxes (benefit) 28 26  
Consolidated Net Income Attributable to Southern Company 71 65  
Total assets 1,768   1,749
All Other      
Segment Reporting Information [Line Items]      
Total operating revenues 218 229  
Other segment items 190 208  
Depreciation and amortization(b) 17 18  
Earnings from equity method investments 5 (4)  
Interest expense(c) 307 280  
Income taxes (benefit) (77) (75)  
Consolidated Net Income Attributable to Southern Company (214) (206)  
Total assets 2,684   2,829
All Other | SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues 2 4  
Other segment items 1 1  
Depreciation and amortization(b) 1 1  
Earnings from equity method investments 0 0  
Interest expense(c) 4 0  
Income taxes (benefit) (10) (9)  
Consolidated Net Income Attributable to Southern Company 6 11  
Total assets 11,276   10,643
Eliminations      
Segment Reporting Information [Line Items]      
Total operating revenues (34) (48)  
Other segment items (40) (58)  
Depreciation and amortization(b) 0 0  
Earnings from equity method investments 0 (1)  
Interest expense(c) 0 0  
Income taxes (benefit) 0 0  
Consolidated Net Income Attributable to Southern Company 6 9  
Total assets (794)   (525)
Eliminations | SOUTHERN Co GAS      
Segment Reporting Information [Line Items]      
Total operating revenues (4) (4)  
Other segment items (4) (4)  
Depreciation and amortization(b) 0 0  
Earnings from equity method investments 0 0  
Interest expense(c) 0 0  
Income taxes (benefit) 0 0  
Consolidated Net Income Attributable to Southern Company 0 $ 0  
Total assets $ (13,121)   $ (11,871)