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Related Party Transactions | 12 Months Ended
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Dec. 31, 2025
Related Party Transactions [Abstract] |
RELATED PARTY TRANSACTIONS | RELATED-PARTY TRANSACTIONS In the normal course of business, Ameren Missouri and Ameren Illinois engage in affiliate transactions. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between Ameren’s subsidiaries are reported as affiliate transactions on their individual financial statements, but those transactions are eliminated in consolidation for Ameren’s consolidated financial statements. Below are the material related-party agreements. Electric Power Supply Agreements Ameren Illinois must acquire capacity and energy sufficient to meet its obligations to customers. Ameren Illinois uses periodic RFP processes, administered by the IPA and approved by the ICC, to contract capacity and energy on behalf of its customers. Ameren Missouri participates in the RFP process and has been a winning supplier for certain periods. Capacity Supply Agreements In procurement events in 2021, Ameren Missouri contracted to supply a portion of Ameren Illinois’ capacity requirements for $2 million from June 2022 through May 2023. Energy Product Agreements Based on the outcome of an IPA-administered procurement event in 2021, Ameren Missouri and Ameren Illinois have entered into an energy product agreement by which Ameren Missouri agreed to sell, and Ameren Illinois agreed to purchase, 136,000 MWhs at an average price of $37 per MWh from January 2022 through September 2023. Interconnection Agreements Ameren Missouri and Ameren Illinois are parties to an interconnection agreement that governs the connection of their respective transmission lines and other facilities used for the distribution of power. These agreements have no contractual expiration date, but may be terminated by either party with three years’ notice. Ameren Missouri and ATXI are parties to an interconnection agreement that governs the connection of the High Prairie Energy Center to an ATXI transmission line that allows Ameren Missouri to distribute power generated from the High Prairie Energy Center. Ameren Missouri and Ameren Illinois are parties to interconnection agreements that govern the connection of the Cass County and Boomtown energy centers to Ameren Illinois transmission lines that allows Ameren Missouri to distribute power generated from the Cass County and Boomtown energy centers. Support Services Agreements Ameren Services provides support services to its affiliates. The costs of support services including wages, employee benefits, professional services, and other expenses, are based on, or are an allocation of, actual costs incurred. The support services agreement can be terminated at any time by the mutual agreement of Ameren Services and that affiliate or by either party with 60 days’ notice before the end of a calendar year. In addition, Ameren Missouri and Ameren Illinois provide affiliates with access to their facilities for administrative purposes and with use of other assets. The costs of the rent and facility services and other assets are based on, or are an allocation of, actual costs incurred. Ameren Missouri and Ameren Illinois also provide storm-related and miscellaneous support services to each other on an as-needed basis. Ameren Missouri and Ameren Illinois had long-term receivables included in “Other assets” from Ameren Services of $36 million and $38 million, respectively, as of December 31, 2025, and $29 million and $32 million, respectively, as of December 31, 2024, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans. Transmission Services Ameren Missouri and Ameren Illinois each receives transmission services from ATXI for their respective retail loads. Electric Transmission Maintenance and Construction Agreements ATXI entered into separate agreements with Ameren Missouri and Ameren Illinois in which Ameren Missouri or Ameren Illinois, as applicable, may perform certain maintenance and construction services related to ATXI’s electric transmission assets. Money Pool See Note 4 – Short-term Debt and Liquidity for a discussion of affiliate borrowing arrangements. Long-Term Debt, Net - Related Parties In November 2024, December 2024, and June 2025, Ameren (parent) purchased senior secured notes and first mortgage bonds issued by Ameren Missouri, and first mortgage bonds issued by Ameren Illinois. See Note 5 – Long-term Debt and Equity Financings for additional information. Tax Allocation Agreement See Note 1 – Summary of Significant Accounting Policies for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of December 31, 2025 and 2024:
| 2025 |  |  | 2024
| Ameren Missouri | Ameren Illinois |  |  | Ameren Missouri | Ameren Illinois
Income taxes payable to parent(a) | $ | — |  | $ | 4 |  |  |  | $ | — |  | $ | 32 |
Income taxes receivable from parent(b) | 3 |  | 7 |  |  |  | 28 |  | — |
(a)Included in “Accounts payable – affiliates” on the balance sheet. (b)Included in “Accounts receivable – affiliates” on the balance sheet. Capital Contributions The following table presents cash capital contributions received from Ameren (parent) by Ameren Missouri and Ameren Illinois for the years ended December 31, 2025, 2024, and 2023:
| 2025 |  | 2024 |  | 2023 |
Ameren Missouri(a) | $ | 28 |  |  | $ | 476 |  |  | $ | — |  |
Ameren Illinois(a) | 2 |  |  | 36 |  |  | 91 |  |
(a)Includes capital contributions made as a result of the tax allocation agreement. Effects of Related-party Transactions on the Statement of Income The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the years ended December 31, 2025, 2024, and 2023. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity.
Agreement | Income Statement Line Item |  |  |  | Ameren Missouri |  | Ameren Illinois
Ameren Missouri power supply agreements | Operating Revenues |  | 2025 | $ | — |  | $ | (a)
with Ameren Illinois |  |  | 2024 |  | — |  |  | (a)
|  |  | 2023 |  | 2 |  |  | (a)
Ameren Missouri and Ameren Illinois | Operating Revenues |  | 2025 |  | 31 |  |  | 1 |
rent and facility services |  |  | 2024 |  | 31 |  |  | 1 |
|  |  | 2023 |  | 32 |  |  | (b)
Ameren Illinois interconnection agreement | Operating Revenues |  | 2025 |  | (a) |  | 1 |
with Ameren Missouri |  |  | 2024 |  | (a) |  | (b)
|  |  | 2023 |  | (a) |  | — |
Ameren Missouri and Ameren Illinois | Operating Revenues |  | 2025 |  | 1 |  |  | 5 |
miscellaneous support services |  |  | 2024 |  | 2 |  |  | 2 |
|  |  | 2023 |  | (b) |  | 2 |
Total Operating Revenues |  |  | 2025 | $ | 32 |  | $ | 7 |
|  |  | 2024 |  | 33 |  |  | 3 |
|  |  | 2023 |  | 34 |  |  | 2 |
Ameren Illinois power supply | Purchased Power |  | 2025 | $ | (a) | $ | — |
agreements with Ameren Missouri |  |  | 2024 |  | (a) |  | — |
|  |  | 2023 |  | (a) |  | 2 |
Ameren Missouri interconnection agreement | Purchased Power |  | 2025 |  | 1 |  |  | (a)
with Ameren Illinois |  |  | 2024 |  | (b) |  | (a)
|  |  | 2023 |  | — |  |  | (a)
Ameren Missouri and Ameren Illinois | Purchased Power |  | 2025 |  | 10 |  |  | 2 |
transmission services from ATXI |  |  | 2024 |  | 9 |  |  | 2 |
|  |  | 2023 |  | 2 |  |  | 1 |
Total Purchased Power |  |  | 2025 | $ | 11 |  | $ | 2 |
|  |  | 2024 |  | 9 |  |  | 2 |
|  |  | 2023 |  | 2 |  |  | 3 |
Ameren Missouri and Ameren Illinois | Other Operations and |  | 2025 | $ | (b) | $ | 3 |
rent and facility services | Maintenance |  | 2024 |  | 1 |  |  | 1 |
|  |  | 2023 |  | (b) |  | 3 |
Ameren Services support services | Other Operations and |  | 2025 |  | 177 |  |  | 164 |
agreement | Maintenance |  | 2024 |  | 169 |  |  | 158 |
|  |  | 2023 |  | 148 |  |  | 138 |
Total Other Operations and |  |  | 2025 | $ | 177 |  | $ | 167 |
Maintenance Expenses |  |  | 2024 |  | 170 |  |  | 159 |
|  |  | 2023 |  | 148 |  |  | 141 |
Money pool borrowings (advances) | (Interest Charges) |  | 2025 | $ | (1) |  | $ | 1 |
| Other Income, Net |  | 2024 |  | (4) |  |  | (b)
|  |  | 2023 |  | (b) |  | (b)
Long-term debt, net - related parties | (Interest Charges) |  | 2025 | $ | (3) |  | $ | (b)
|  |  | 2024 |  | (b) |  | (b)
|  |  | 2023 |  | (a) |  | (a)
(a)Not applicable. (b)Amount less than $1 million.

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- Definition The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480990/946-20-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480990/946-20-50-5 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480990/946-20-50-6 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477968/946-235-50-2 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 235 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477968/946-235-50-2 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(g)(3)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(c)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(e)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 850 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/850/tableOfContent Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-6 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-1 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 850 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483326/850-10-50-1 + Details
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