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Supplemental Information (Tables) | 12 Months Ended
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Dec. 31, 2025
Supplemental Information [Abstract] |
Schedule of Cash and Cash Equivalents Including Restricted Cash | The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of December 31, 2025 and 2024:
| December 31, 2025 |  |  | December 31, 2024
Ameren | Ameren Missouri | Ameren Illinois |  |  | Ameren | Ameren Missouri | Ameren Illinois
“Cash and cash equivalents” | $ | 13 |  | $ | 6 |  | $ | 3 |  |  |  | $ | 7 |  | $ | — |  | $ | — |
Restricted cash included in “Other current assets” | 63 |  | 54 |  | 5 |  |  |  | 15 |  | 7 |  | 6 |
Restricted cash included in “Other assets” | 336 |  | — |  | 336 |  |  |  | 296 |  | — |  | 296 |
Restricted cash included in “Nuclear decommissioning trust fund” | 8 |  | 8 |  | — |  |  |  | 10 |  | 10 |  | — |
Total cash, cash equivalents, and restricted cash | $ | 420 |  | $ | 68 |  | $ | 344 |  |  |  | $ | 328 |  | $ | 17 |  | $ | 302 |
Schedule of Accounts, Notes, Loans and Financing Receivable | The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the years ended December 31, 2025 and 2024:
| December 31, 2025 |  |  | December 31, 2024
| Ameren Missouri |  | Ameren Illinois(a) | Ameren |  |  | Ameren Missouri | Ameren Illinois(a) | Ameren
Beginning balance at January 1 | $ | 12 |  |  | $ | 18 |  | $ | 30 |  |  |  | $ | 12 |  | $ | 18 |  | $ | 30 |
Bad debt expense | 17 |  |  | 34 |  | 51 |  |  |  | 11 |  | 28 |  | 39 |
Charged to other accounts(b) | — |  |  | 7 |  | 7 |  |  |  | — |  | 8 |  | 8 |
Net write-offs | (12) |  |  | (37) |  | (49) |  |  |  | (11) |  | (36) |  | (47) |
Ending balance at December 31 | $ | 17 |  |  | $ | 22 |  | $ | 39 |  |  |  | $ | 12 |  | $ | 18 |  | $ | 30 |
(a)Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. (b)Amounts associated with the allowance for doubtful accounts related to receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
Schedule of Supplemental Balance Sheet Information Related to Operating Leases | The following table provides supplemental balance sheet information related to operating leases as of December 31, 2025 and 2024:
| December 31, 2025 | December 31, 2024 |  |
| Ameren |  | Ameren Missouri | Ameren |  | Ameren Missouri |  |
Other assets | $ | 76 |  |  | $ | 70 |  | $ | 72 |  |  | $ | 69 |  |  |
Other current liabilities | 3 |  |  | 2 |  | 5 |  |  | 4 |  |  |
Other deferred credits and liabilities | 73 |  |  | 68 |  | 67 |  |  | 65 |  |  |
Weighted average remaining operating lease term | 28 years |  | 29 years | 29 years |  | 30 years |  |
Weighted average discount rate(a) | 5.3 | % |  | 5.3 | % | 5.3 | % |  | 5.3 | % |  |
(a)As an implicit rate is not readily determinable under most of our lease agreements, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. We use an implicit rate when readily determinable.
Schedule of Maturity of Operating Lease Liabilities | The following table presents Ameren’s and Ameren Missouri’s remaining maturities of operating lease liabilities as of December 31, 2025:
| Ameren |  | Ameren Missouri
2026 | $ | 6 |  |  | $ | 5 |
2027 | 6 |  |  | 5 |
2028 | 6 |  |  | 5 |
2029 | 6 |  |  | 5 |
2030 | 5 |  |  | 4 |
Thereafter | 129 |  |  | 127 |
Total lease payments | $ | 158 |  |  | $ | 151 |
Less imputed interest | 82 |  |  | 81 |
Total | $ | 76 |  |  | $ | 70 |
Schedule of Inventories | The following table presents the components of inventories for each of the Ameren Companies at December 31, 2025 and 2024:
| December 31, 2025 |  |  | December 31, 2024
| Ameren Missouri | Ameren Illinois | Ameren |  |  | Ameren Missouri | Ameren Illinois | Ameren
Fuel(a) | $ | 101 |  | $ | — |  | $ | 101 |  |  |  | $ | 113 |  | $ | — |  | $ | 113 |
Natural gas stored underground | 10 |  | 88 |  | 98 |  |  |  | 9 |  | 82 |  | 91 |
Materials, supplies, and other | 381 |  | 190 |  | 575 |  |  |  | 392 |  | 162 |  | 558 |
Total inventories | $ | 492 |  | $ | 278 |  | $ | 774 |  |  |  | $ | 514 |  | $ | 244 |  | $ | 762 |
(a)Consists of coal, oil, and propane.
Schedule of Asset Retirement Obligations | The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2025 and 2024:
| December 31, 2025 |  |  | December 31, 2024
| Ameren Missouri |  | Ameren Illinois |  | Ameren |  |  |  | Ameren Missouri |  | Ameren Illinois |  | Ameren |
Beginning balance at January 1 | $ | 823 |  | (a) | $ | 4 |  | (b) | $ | 827 |  | (a) |  |  | $ | 787 |  |  | $ | 4 |  |  | $ | 791 |  |
Liabilities incurred | — |  |  | — |  |  | — |  |  |  |  | 21 |  | (c) | — |  |  | 21 |  | (c)
Liabilities settled | (10) |  |  | — |  |  | (10) |  |  |  |  | (13) |  |  | — |  |  | (13) |  |
Accretion(d) | 36 |  | (d) | — |  |  | 36 |  | (d) |  |  | 35 |  |  | — |  |  | 35 |  |
Change in estimates | — |  |  | 1 |  |  | 1 |  |  |  |  | (7) |  |  | — |  |  | (7) |  |
Ending balance at December 31 | $ | 849 |  | (a)(e) | $ | 5 |  | (b) | $ | 854 |  | (a)(e) |  |  | $ | 823 |  | (a)(e) | $ | 4 |  | (b) | $ | 827 |  | (a)(e)
(a)Balance included $5 million and $5 million in “Other current liabilities” on the balance sheet as of December 31, 2025 and 2024, respectively. (b)Included in “Other deferred credits and liabilities” on the balance sheet. (c)In 2024, Ameren and Ameren Missouri recorded an ARO related to decommissioning for the Cass County, Boomtown, and Huck Finn energy centers. In addition, as a result of the 2024 CCR Rule, Ameren and Ameren Missouri recorded an increase to their AROs associated with CCR storage facilities. See Note 14 – Commitments and Contingencies for additional information. (d)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities. (e)The balance included an ARO related to the decommissioning of the Callaway Enter Center of $678 million and $648 million as of December 31, 2025 and 2024, respectively.
Schedule of Excise Taxes | The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the years ended December 31, 2025, 2024, and 2023:
| 2025 |  | 2024 |  | 2023 |
Ameren Missouri | $ | 189 |  |  | $ | 169 |  |  | $ | 166 |  |
Ameren Illinois | 140 |  |  | 130 |  |  | 121 |  |
Ameren | $ | 329 |  |  | $ | 299 |  |  | $ | 287 |  |
Schedule of Rates and Amounts For Allowance for Funds Used During Construction | The following table presents the average rate that was applied to eligible construction work in progress and the amounts of allowance for funds used during construction capitalized in 2025, 2024, and 2023:
| 2025 |  | 2024 |  | 2023 |
Average rate: |  |  |  |  |  |
Ameren Missouri | 7 | % |  | 6 | % |  | 6 | % |
Ameren Illinois | 7 | % |  | 6 | % |  | 6 | % |
Ameren: |  |  |  |  |  |
Allowance for equity funds used during construction | $ | 88 |  |  | $ | 76 |  |  | $ | 54 |  |
Allowance for borrowed funds used during construction | 52 |  |  | 56 |  |  | 48 |  |
Total Ameren | $ | 140 |  |  | $ | 132 |  |  | $ | 102 |  |
Ameren Missouri: |  |  |  |  |  |
Allowance for equity funds used during construction | $ | 56 |  |  | $ | 58 |  |  | $ | 30 |  |
Allowance for borrowed funds used during construction | 36 |  |  | 39 |  |  | 27 |  |
Total Ameren Missouri | $ | 92 |  |  | $ | 97 |  |  | $ | 57 |  |
Ameren Illinois: |  |  |  |  |  |
Allowance for equity funds used during construction | $ | 30 |  |  | $ | 17 |  |  | $ | 19 |  |
Allowance for borrowed funds used during construction | 15 |  |  | 15 |  |  | 17 |  |
Total Ameren Illinois | $ | 45 |  |  | $ | 32 |  |  | $ | 36 |  |
Schedule of Earnings Per Share, Basic and Diluted | The following table reconciles the weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the years ended December 31, 2025, 2024, and 2023:
| 2025 |  | 2024 |  | 2023
Weighted-average Common Shares Outstanding – Basic | 270.5 |  |  | 266.8 |  |  | 262.8 |
Assumed settlement of performance share units and restricted stock units | 0.9 |  |  | 0.5 |  |  | 0.6 |
Dilutive effect of forward sale agreements | 0.8 |  |  | 0.1 |  |  | — |
Weighted-average Common Shares Outstanding – Diluted(a) | 272.2 |  |  | 267.4 |  |  | 263.4 |
(a)There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations as calculated using the treasury stock method for the years ended December 31, 2025, 2024, and 2023 related to performance share units and restricted stock units. Outstanding forward sale agreements as of December 31, 2025 and 2024 that were anti-dilutive for the years ended December 31, 2025 and 2024, respectively, were excluded from the earnings per diluted share calculation as calculated using the treasury stock method. The outstanding forward sale agreements as of December 31, 2023, were anti-dilutive for the year ended December 31, 2023, and excluded from the earnings per diluted share calculation as calculated using the treasury stock method. For additional information about the outstanding forward sale agreements, see Note 5 – Long-term Debt and Equity Financings.
Schedule of Cash Flow, Supplemental Disclosures | The following table presents the total income taxes paid, net of refunds, including production and investment tax credit sale proceeds, for the years ended December 31, 2025, 2024, and 2023:
| Ameren Missouri(a) |  | Ameren Illinois(a) |  | Ameren
2025 |  | 2024 |  |  | 2023 |  | 2025 |  | 2024 |  | 2023 |  | 2025 |  | 2024 |  | 2023
Federal(b) | $ | (350) |  |  | $ | (131) |  |  |  | $ | (24) |  |  | $ | 79 |  |  | $ | (25) |  |  | $ | 76 |  |  | $ | (309) |  |  | $ | (92) |  |  | $ | (37) |
State |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Illinois | — |  |  | — |  |  |  | — |  |  | 39 |  |  | (21) |  |  | 26 |  |  | 34 |  |  | (12) |  |  | 28 |
Missouri | (9) |  |  | (5) |  |  |  | 5 |  |  | — |  |  | — |  |  | — |  |  | (37) |  |  | 12 |  |  | (15) |
Total taxes paid | $ | (359) |  |  | $ | (136) |  |  |  | $ | (19) |  |  | $ | 118 |  |  | $ | (46) |  |  | $ | 102 |  |  | $ | (312) |  |  | $ | (92) |  |  | $ | (24) |
(a)Amounts represent income tax paid, net of refunds, to Ameren (parent), pursuant to the tax allocation agreement. See Note 1 – Summary of Significant Accounting Policies – Income Taxes for additional information. (b)Includes production and investment tax credit sale proceeds for Ameren and Ameren Missouri of $314 million, $95 million, and $49 million for the years ended December 31, 2025, 2024, and 2023, respectively. The following table provides noncash financing and investing activity excluded from the statements of cash flows for the years ended December 31, 2025, 2024, and 2023:
| December 31, 2025 |  | December 31, 2024 |  | December 31, 2023
Ameren | Ameren Missouri |  | Ameren Illinois |  | Ameren | Ameren Missouri | Ameren Illinois |  | Ameren | Ameren Missouri | Ameren Illinois
Investing |  |  |  |  |  |  |  |  |  |  |  |
Accrued capital expenditures, including nuclear fuel expenditures | $ | 622 |  | $ | 355 |  |  | $ | 210 |  |  | $ | 480 |  | $ | 303 |  | $ | 157 |  |  | $ | 518 |  | $ | 270 |  | $ | 212 |
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund | 160 |  | 160 |  |  | — |  |  | 165 |  | 165 |  | — |  |  | 167 |  | 167 |  | — |
Return of investment in industrial development revenue bonds(a) | — |  | — |  |  | — |  |  | — |  | — |  | — |  |  | 240 |  | 240 |  | — |
Financing |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock for stock-based compensation | $ | 25 |  | $ | — |  |  | $ | — |  |  | $ | 16 |  | $ | — |  | $ | — |  |  | $ | 40 |  | $ | — |  | $ | — |
Issuance of common stock under the DRPlus | 7 |  | — |  |  | — |  |  | 7 |  | — |  | — |  |  | 7 |  | — |  | — |
Termination of a financing agreement(a) | — |  | — |  |  | — |  |  | — |  | — |  | — |  |  | 240 |  | 240 |  | — |
(a)In January 2023, Ameren Missouri and Audrain County mutually agreed to terminate a financing obligation agreement related to the CT energy center in Audrain County, which was scheduled to expire in December 2023. No cash was exchanged in connection with the termination of the agreement as the $240 million principal amount of the financing obligation due from Ameren Missouri was equal to the amount of bond service payments due to Ameren Missouri.

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