| Assets | — | — |
| Current assets | — | — |
| Cash and cash equivalents | 103a | 227a |
| Restricted cash and cash equivalents | 75a | 21a |
| Accounts receivable and accrued revenue, less allowance of $23 in 2024 and $21 in 2023 | 1,049a | 933a |
| Accounts receivable - related parties | 14a | 11a |
| Inventories at average cost | — | — |
| Gas in underground storage | 435a | 587a |
| Materials and supplies | 299a | 267a |
| Generating plant fuel stock | 35a | 84a |
| Deferred property taxes | 448a | 426a |
| Regulatory assets | 229a | 203a |
| Prepayments and other current assets | 103a | 80a |
| Total current assets | 2,790a | 2,839a |
| Plant, property, and equipment | — | — |
| Plant, property, and equipment, gross | 34,932a | 33,135a |
| Less accumulated depreciation and amortization | 9,569a | 9,007a |
| Plant, property, and equipment, net | 25,363a | 24,128a |
| Construction work in progress | 2,098a | 944a |
| Total plant, property, and equipment | 27,461a | 25,072a |
| Other non-current assets | — | — |
| Regulatory assets | 3,569a | 3,683a |
| Accounts receivable | 20a | 22a |
| Investments | 69a | 76a |
| Postretirement benefits | 1,627a | 1,468a |
| Other | 384a | 357a |
| Total other non-current assets | 5,669a | 5,606a |
| Total assets | 35,920a | 33,517a |
| Liabilities and equity | — | — |
| Current liabilities | — | — |
| Current portion of long-term debt and finance leases | 1,195a | 980a |
| Notes payable | 65a | 93a |
| Accounts payable | 1,085a | 802a |
| Accounts payable - related parties | 8a | 7a |
| Accrued rate refunds | 38a | 54a |
| Accrued interest | 156a | 142a |
| Accrued taxes | 654a | 612a |
| Regulatory liabilities | 111a | 56a |
| Other current liabilities | 209a | 149a |
| Total current liabilities | 3,521a | 2,895a |
| Non-current liabilities | — | — |
| Long-term debt | 15,194a | 14,508a |
| Non-current portion of finance leases | 112a | 62a |
| Regulatory liabilities | 4,067a | 3,894a |
| Postretirement benefits | 96a | 106a |
| Asset retirement obligations | 728a | 771a |
| Deferred investment tax credit | 122a | 126a |
| Deferred income taxes | 2,925a | 2,615a |
| Other non-current liabilities | 407a | 415a |
| Total non-current liabilities | 23,651a | 22,497a |
| Equity | — | — |
| Common stockholders’ equity | — | — |
| Common stock, authorized 350.0 shares in both periods; outstanding 298.8 shares in 2024 and 294.4 shares in 2023 | 3a | 3a |
| Other paid-in capital | 6,009a | 5,705a |
| Accumulated other comprehensive loss | -41a | -46a |
| Retained earnings | 2,035a | 1,658a |
| Total common stockholders’ equity | 8,006a | 7,320a |
| Cumulative redeemable perpetual preferred stock, Series C, authorized 9.2 depositary shares; outstanding 9.2 depositary shares in both periods | 224a | 224a |
| Total stockholders’ equity | 8,230a | 7,544a |
| Noncontrolling interests | 518a | 581a |
| Total equity | 8,748a | 8,125a |
| Total liabilities and equity | 35,920a | 33,517a |
| Cash and cash equivalents | 44a | 35a |
| Restricted cash and cash equivalents | 75a | 21a |
| Accounts receivable and accrued revenue, less allowance of $23 in 2024 and $21 in 2023 | 1,019a | 909a |
| Accounts and notes receivable - related parties | 17a | 11a |
| Gas in underground storage | 435a | 587a |
| Materials and supplies | 291a | 257a |
| Generating plant fuel stock | 30a | 80a |
| Deferred property taxes | 448a | 426a |
| Regulatory assets | 229a | 203a |
| Prepayments and other current assets | 86a | 65a |
| Total current assets | 2,674a | 2,594a |
| Plant, property, and equipment, gross | 33,434a | 31,723a |
| Less accumulated depreciation and amortization | 9,310a | 8,796a |
| Plant, property, and equipment, net | 24,124a | 22,927a |
| Construction work in progress | 1,766a | 845a |
| Total plant, property, and equipment | 25,890a | 23,772a |
| Regulatory assets | 3,569a | 3,683a |
| Accounts receivable | 26a | 28a |
| Accounts and notes receivable - related parties | 92a | 95a |
| Postretirement benefits | 1,514a | 1,367a |
| Other | 323a | 313a |
| Total other non-current assets | 5,524a | 5,486a |
| Total assets | 34,088a | 31,852a |
| Current portion of long-term debt and finance leases | 456a | 731a |
| Notes payable | 65a | 93a |
| Accounts payable | 917a | 764a |
| Accounts payable - related parties | 12a | 13a |
| Accrued rate refunds | 38a | 54a |
| Accrued interest | 130a | 110a |
| Accrued taxes | 678a | 614a |
| Regulatory liabilities | 111a | 56a |
| Other current liabilities | 185a | 128a |
| Total current liabilities | 2,592a | 2,563a |
| Long-term debt | 10,818a | 10,037a |
| Long-term debt - related parties | 823a | 424a |
| Non-current portion of finance leases | 69a | 39a |
| Regulatory liabilities | 4,067a | 3,894a |
| Postretirement benefits | 70a | 77a |
| Asset retirement obligations | 694a | 739a |
| Deferred investment tax credit | 122a | 126a |
| Deferred income taxes | 3,053a | 2,789a |
| Other non-current liabilities | 349a | 364a |
| Total non-current liabilities | 20,065a | 18,489a |
| Common stockholder’s equity | — | — |
| Common stock, authorized 125.0 shares; outstanding 84.1 shares in both periods | 841a | 841a |
| Other paid-in capital | 8,174a | 7,759a |
| Accumulated other comprehensive loss | -11a | -15a |
| Retained earnings | 2,390a | 2,178a |
| Total common stockholder’s equity | 11,394a | 10,763a |
| Cumulative preferred stock, $4.50 series, authorized 7.5 shares; outstanding 0.4 shares in both periods | 37a | 37a |
| Total equity | 11,431a | 10,800a |
| Total liabilities and equity | 34,088a | 31,852a |