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Segment and Related Information - Schedule of Gas Revenues (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
Jun. 30, 2025
Mar. 31, 2025
Sep. 30, 2024
Jun. 30, 2024
Mar. 31, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
Segment Reporting Information [Line Items]                  
Total operating revenues $ 7,823     $ 7,274     $ 22,572 $ 20,383  
Other segment items 3,564     3,491     11,377 10,146  
Depreciation and amortization 1,422     1,210     4,030 3,537  
Earnings from equity method investments 33     31     76 107  
Interest expense(e) 755     692     2,343 2,050  
Income taxes (benefit) 404     377     973 890  
Consolidated Net Income Attributable to Southern Company 1,711     1,535     3,925 3,867  
Total assets 153,248           153,248   $ 145,180
SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues 734     682     3,552 3,220  
Other segment items 464     421     2,133 1,866  
Depreciation and amortization 176     162     517 475  
Earnings from equity method investments 31     34     93 110  
Interest expense(e) 94     84     277 250  
Income taxes (benefit) 6     11     169 184  
Consolidated Net Income Attributable to Southern Company 25 $ 106 $ 418 38 $ 108 $ 409 549 555  
Total assets 26,926           26,926   26,177
Operating Segments                  
Segment Reporting Information [Line Items]                  
Total operating revenues 7,662     7,104     22,040 19,913  
Other segment items 3,396     3,329     10,886 9,700  
Depreciation and amortization 1,404     1,193     3,978 3,484  
Earnings from equity method investments 33     36     97 114  
Interest expense(e) 458     433     1,343 1,293  
Income taxes (benefit) 489     447     1,246 1,101  
Consolidated Net Income Attributable to Southern Company 1,948     1,738     4,684 4,449  
Total assets 151,312           151,312   143,382
Operating Segments | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues 734     677     3,549 3,210  
Other segment items 460     417     2,129 1,859  
Depreciation and amortization 175     161     516 474  
Earnings from equity method investments 31     34     93 110  
Interest expense(e) 100     84     282 257  
Income taxes (benefit) (5)     6     159 178  
Consolidated Net Income Attributable to Southern Company 35     43     556 552  
Total assets 28,335           28,335   27,336
Operating Segments | Gas distribution operations | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues 668     616     3,122 2,828  
Other segment items 409     366     1,842 1,612  
Depreciation and amortization 171     156     502 459  
Earnings from equity method investments 0     0     0 0  
Interest expense(e) 89     75     252 229  
Income taxes (benefit) (13)     (2)     109 125  
Consolidated Net Income Attributable to Southern Company 12     21     417 403  
Total assets 25,200           25,200   24,067
Operating Segments | Gas Pipeline Investments | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues 8     8     24 24  
Other segment items 1     1     3 3  
Depreciation and amortization 1     1     4 4  
Earnings from equity method investments 31     34     93 110  
Interest expense(e) 10     8     28 26  
Income taxes (benefit) 7     8     20 24  
Consolidated Net Income Attributable to Southern Company 20     24     62 77  
Total assets 1,468           1,468   1,573
Operating Segments | Gas marketing services | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues 58     53     403 358  
Other segment items 50     50     284 244  
Depreciation and amortization 3     4     10 11  
Earnings from equity method investments 0     0     0 0  
Interest expense(e) 1     1     2 2  
Income taxes (benefit) 1     0     30 29  
Consolidated Net Income Attributable to Southern Company 3     (2)     77 72  
Total assets 1,667           1,667   1,696
Operating Segments | All Other | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Consolidated Net Income Attributable to Southern Company       (5)          
All Other                  
Segment Reporting Information [Line Items]                  
Total operating revenues 202     215     656 598  
Other segment items 209     203     611 548  
Depreciation and amortization 18     17     52 53  
Earnings from equity method investments 0     (5)     (21) (8)  
Interest expense(e) 297     261     1,000 769  
Income taxes (benefit) (85)     (70)     (273) (211)  
Consolidated Net Income Attributable to Southern Company (237)     (201)     (755) (569)  
Total assets 2,397           2,397   2,371
All Other | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues 1     6     11 19  
Other segment items 5     5     12 16  
Depreciation and amortization 1     1     1 1  
Earnings from equity method investments 0     0     0 0  
Interest expense(e) (6)     0     (5) (7)  
Income taxes (benefit) 11     5     10 6  
Consolidated Net Income Attributable to Southern Company (10)           (7) 3  
Total assets 10,845           10,845   10,047
Eliminations                  
Segment Reporting Information [Line Items]                  
Total operating revenues (41)     (45)     (124) (128)  
Other segment items (41)     (41)     (120) (102)  
Depreciation and amortization 0     0     0 0  
Earnings from equity method investments 0     0     0 1  
Interest expense(e) 0     (2)     0 (12)  
Income taxes (benefit) 0     0     0 0  
Consolidated Net Income Attributable to Southern Company 0     (2)     (4) (13)  
Total assets (461)           (461)   (573)
Eliminations | SOUTHERN Co GAS                  
Segment Reporting Information [Line Items]                  
Total operating revenues (1)     (1)     (8) (9)  
Other segment items (1)     (1)     (8) (9)  
Depreciation and amortization 0     0     0 0  
Earnings from equity method investments 0     0     0 0  
Interest expense(e) 0     0     0 0  
Income taxes (benefit) 0     0     0 0  
Consolidated Net Income Attributable to Southern Company 0     $ 0     0 $ 0  
Total assets $ (12,254)           $ (12,254)   $ (11,206)