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Supplemental Information (Tables) | 12 Months Ended
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Dec. 31, 2023
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, 2023 and 2022:
| December 31, 2023 |  |  | December 31, 2022
Ameren | Ameren Missouri | Ameren Illinois |  |  | Ameren | Ameren Missouri | Ameren Illinois
Cash and cash equivalents | $ | 25 |  | $ | — |  | $ | — |  |  |  | $ | 10 |  | $ | — |  | $ | — |
Restricted cash included in “Other current assets” | 13 |  | 5 |  | 5 |  |  |  | 13 |  | 5 |  | 6 |
Restricted cash included in “Other assets” | 229 |  | — |  | 229 |  |  |  | 185 |  | — |  | 185 |
Restricted cash included in “Nuclear decommissioning trust fund” | 5 |  | 5 |  | — |  |  |  | 8 |  | 8 |  | — |
Total cash, cash equivalents, and restricted cash | $ | 272 |  | $ | 10 |  | $ | 234 |  |  |  | $ | 216 |  | $ | 13 |  | $ | 191 |
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, 2023 and 2022:
| December 31, 2023 |  |  | December 31, 2022
| Ameren Missouri |  | Ameren Illinois(a) | Ameren |  |  | Ameren Missouri | Ameren Illinois(a) | Ameren
Beginning balance at January 1 | $ | 13 |  |  | $ | 18 |  | $ | 31 |  |  |  | $ | 13 |  | $ | 16 |  | $ | 29 |
Bad debt expense | 11 |  |  | 40 |  | 51 |  |  |  | 9 |  | 25 |  | 34 |
Charged to other accounts(b) | — |  |  | 5 |  | 5 |  |  |  | — |  | 4 |  | 4 |
Net write-offs | (12) |  |  | (45) |  | (57) |  |  |  | (9) |  | (27) |  | (36) |
Ending balance at December 31 | $ | 12 |  |  | $ | 18 |  | $ | 30 |  |  |  | $ | 13 |  | $ | 18 |  | $ | 31 |
(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 Inventories | The following table presents the components of inventories for each of the Ameren Companies at December 31, 2023 and 2022:
| December 31, 2023 |  |  | December 31, 2022
| Ameren Missouri | Ameren Illinois | Ameren |  |  | Ameren Missouri | Ameren Illinois | Ameren
Fuel(a) | $ | 109 |  | $ | — |  | $ | 109 |  |  |  | $ | 79 |  | $ | — |  | $ | 79 |
Natural gas stored underground | 8 |  | 87 |  | 95 |  |  |  | 10 |  | 120 |  | 130 |
Materials, supplies, and other | 391 |  | 138 |  | 529 |  |  |  | 345 |  | 113 |  | 458 |
Total inventories | $ | 508 |  | $ | 225 |  | $ | 733 |  |  |  | $ | 434 |  | $ | 233 |  | $ | 667 |
(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, 2023 and 2022:
| December 31, 2023 |  |  | December 31, 2022
| Ameren Missouri |  | Ameren Illinois |  | Ameren |  |  |  | Ameren Missouri |  | Ameren Illinois |  | Ameren |
Beginning balance at January 1 | $ | 782 |  | (a) | $ | 4 |  | (b) | $ | 786 |  | (a) |  |  | $ | 760 |  |  | $ | 4 |  |  | $ | 764 |  |
Liabilities incurred | — |  |  | — |  |  | — |  |  |  |  | 1 |  |  | — |  |  | 1 |  |
Liabilities settled | (10) |  |  | — |  |  | (10) |  |  |  |  | (4) |  |  | — |  |  | (4) |  |
Accretion(c) | 33 |  |  | — |  |  | 33 |  |  |  |  | 32 |  |  | — |  |  | 32 |  |
Change in estimates | (18) |  |  | — |  |  | (18) |  |  |  |  | (7) |  |  | — |  |  | (7) |  |
Ending balance at December 31 | $ | 787 |  | (a)(d) | $ | 4 |  | (b) | $ | 791 |  | (a)(d) |  |  | $ | 782 |  | (a) | $ | 4 |  | (b) | $ | 786 |  | (a)
(a)Balance included $19 million and $23 million in “Other current liabilities” on the balance sheet as of December 31, 2023 and 2022, respectively. (b)Included in “Other deferred credits and liabilities” on the balance sheet. (c)Accretion expense attributable to Ameren Missouri was recorded as a decrease to regulatory liabilities. (d)The balance as of December 31, 2023, included an ARO related to the decommissioning of the Callaway Enter Center of $619 million.
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, 2023, 2022, and 2021:
| 2023 |  | 2022 |  | 2021 |
Ameren Missouri | $ | 166 |  |  | $ | 162 |  |  | $ | 150 |  |
Ameren Illinois | 121 |  |  | 133 |  |  | 125 |  |
Ameren | $ | 287 |  |  | $ | 295 |  |  | $ | 275 |  |
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 2023, 2022, and 2021:
| 2023 |  | 2022 |  | 2021 |
Average rate: |  |  |  |  |  |
Ameren Missouri | 6 | % |  | 5 | % |  | 6 | % |
Ameren Illinois | 6 | % |  | 5 | % |  | 5 | % |
Ameren: |  |  |  |  |  |
Allowance for equity funds used during construction | $ | 54 |  |  | $ | 43 |  |  | $ | 43 |  |
Allowance for borrowed funds used during construction | 48 |  |  | 26 |  |  | 17 |  |
Total Ameren | $ | 102 |  |  | $ | 69 |  |  | $ | 60 |  |
Ameren Missouri: |  |  |  |  |  |
Allowance for equity funds used during construction | $ | 30 |  |  | $ | 24 |  |  | $ | 26 |  |
Allowance for borrowed funds used during construction | 27 |  |  | 13 |  |  | 10 |  |
Total Ameren Missouri | $ | 57 |  |  | $ | 37 |  |  | $ | 36 |  |
Ameren Illinois: |  |  |  |  |  |
Allowance for equity funds used during construction | $ | 19 |  |  | $ | 18 |  |  | $ | 17 |  |
Allowance for borrowed funds used during construction | 17 |  |  | 12 |  |  | 7 |  |
Total Ameren Illinois | $ | 36 |  |  | $ | 30 |  |  | $ | 24 |  |
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, 2023, 2022, and 2021:
| 2023 |  | 2022 |  | 2021
Weighted-average Common Shares Outstanding – Basic | 262.8 |  |  | 258.4 |  |  | 256.3 |
Assumed settlement of performance share units and restricted stock units | 0.6 |  |  | 1.0 |  |  | 1.3 |
Dilutive effect of forward sale agreements | — |  |  | 0.1 |  |  | — |
Weighted-average Common Shares Outstanding – Diluted(a) | 263.4 |  |  | 259.5 |  |  | 257.6 |
(a)There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations for the years ended December 31, 2023, 2022, and 2021 related to performance share units and restricted stock units. 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.
Schedule of Cash Flow, Supplemental Disclosures | The following table provides noncash financing and investing activity excluded from the statements of cash flows for the years ended December 31, 2023, 2022, and 2021:
| December 31, 2023 |  | December 31, 2022 |  | December 31, 2021
Ameren | Ameren Missouri |  | Ameren Illinois |  | Ameren | Ameren Missouri | Ameren Illinois |  | Ameren | Ameren Missouri | Ameren Illinois
Investing |  |  |  |  |  |  |  |  |  |  |  |
Accrued capital expenditures, including nuclear fuel expenditures | $ | 518 |  | $ | 270 |  |  | $ | 212 |  |  | $ | 441 |  | $ | 243 |  | $ | 181 |  |  | $ | 524 |  | $ | 301 |  | $ | 215 |
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund | 167 |  | 167 |  |  | — |  |  | (218) |  | (218) |  | — |  |  | 163 |  | 163 |  | — |
Return of investment in industrial development revenue bonds(a) | 240 |  | 240 |  |  | — |  |  | — |  | — |  | — |  |  | — |  | — |  | — |
Financing |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock for stock-based compensation | $ | 40 |  | $ | — |  |  | $ | — |  |  | $ | 31 |  | $ | — |  | $ | — |  |  | $ | 33 |  | $ | — |  | $ | — |
Issuance of common stock under the DRPlus | 7 |  | — |  |  | — |  |  | 8 |  | — |  | — |  |  | — |  | — |  | — |
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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