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Related Party Transactions
 9 Months Ended
Sep. 30, 2025
Related Party Transactions [Abstract]  
RELATED PARTY TRANSACTIONS RELATED-PARTY TRANSACTIONS
In the ordinary course of business, Ameren Missouri and Ameren Illinois have engaged in, and may in the future 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. For a discussion of material related-party agreements and money pool agreements, see Note 13 – Related-party Transactions and Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of the Form 10-K.
Support Services Agreements
Ameren Missouri and Ameren Illinois had long-term receivables included in “Other assets” from Ameren Services of $18 million and $20 million, respectively, as of September 30, 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.
Tax Allocation Agreement
See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of the Form 10-K 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 September 30, 2025, and December 31, 2024:
September 30, 2025December 31, 2024
Ameren MissouriAmeren IllinoisAmeren MissouriAmeren Illinois
Income taxes payable to parent(a)
$3$67$—$32
Income taxes receivable from parent(b)
2—28—
(a)Included in “Accounts payable – affiliates” on the balance sheet.
(b)Included in “Accounts receivable – affiliates” on the balance sheet.
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 three and nine months ended September 30, 2025 and 2024:
Three MonthsNine Months
AgreementIncome Statement
Line Item		Ameren
Missouri		Ameren
Illinois		Ameren
Missouri		Ameren
Illinois
Ameren Missouri and Ameren IllinoisOperating Revenues2025$8 $(b)$23 $1 
rent and facility services
20248 (b)23 (b)
Ameren Missouri and Ameren Illinois miscellaneousOperating Revenues2025$1 $(b)$1 $5 
support services20241 (b)2 1 
Total Operating Revenues2025$9 $(b)$24 $6 
20249 (b)25 1 
Ameren Missouri and Ameren IllinoisPurchased Power2025$2 $1 $7 $2 
transmission services from ATXI20243 1 7 2 
Ameren Missouri and Ameren IllinoisOther Operations and Maintenance2025$(b)$(b)$(b)$3 
rent and facility services
2024(b)(b)(b)(b)
Ameren Services support servicesOther Operations and Maintenance2025$42 $39 $130 $119 
agreement
202441 38 122 115 
Total Other Operations and2025$42 $39 $130 $122 
Maintenance202441 38 122 115 
Money pool interest(Interest Charges)/Other Income, Net2025$(b)$(b)$(b)$(b)
2024(b)(b)(3)(2)
Long-term debt, net - related parties(Interest Charges)2025$(1)$(b)$(2)$(b)
2024— — — — 
(a)Not applicable.
(b)Amount less than $1 million.