v3.26.3
Retirement Benefits
 9 Months Ended
Sep. 30, 2026
Retirement Benefits [Abstract]  
RETIREMENT BENEFITS RETIREMENT BENEFITS
The following table presents the components of the net periodic benefit cost (income) incurred for Ameren’s pension and postretirement benefit plans for the three and nine months ended September 30, 2026 and 2025:
Pension BenefitsPostretirement Benefits
Three MonthsNine MonthsThree MonthsNine Months
20262025202620252026202520262025
Service cost(a)
$22 $21 $62 $62 $2 $3 $7 $8 
Non-service cost components:
Interest cost56 58 169 175 10 11 33 33 
Expected return on plan assets(b)
(63)(76)(197)(227)(24)(24)(71)(71)
Amortization of:(b)
Prior service cost (credit)— — — — (1)(1)(3)(3)
Actuarial (gain) loss3 (9)8 (26)(7)(9)(23)(27)
Total non-service cost components(c)
$(4)$(27)$(20)$(78)$(22)$(23)$(64)$(68)
Net periodic benefit cost (income)(d)
$18 $(6)$42 $(16)$(20)$(20)$(57)$(60)
(a)Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.
(b)Prior service cost (credit) is amortized on a straight-line basis over the average future service of active participants benefiting under a plan amendment. Net actuarial gains or losses subject to amortization are amortized over 10 years. Expected return on plan assets is based on a market-related value of assets that recognizes asset (gains) losses over 4 years.
(c)Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 5 – Other Income, Net for additional information.
(d)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
Ameren Missouri and Ameren Illinois are responsible for their respective share of Ameren’s pension and other postretirement costs. The following table presents the respective share of net periodic pension and other postretirement benefit costs (income) incurred for the three and nine months ended September 30, 2026 and 2025:
Pension BenefitsPostretirement Benefits
Three MonthsNine MonthsThree MonthsNine Months
20262025202620252026202520262025
Ameren Missouri(a)
$7 $(4)$18 $(11)$(6)$(7)$(17)$(21)
Ameren Illinois10 (1)22 (3)(14)(13)(40)(39)
Other1 (1)2 (2)(b)(b)(b)(b)
Ameren(a)
$18 $(6)$42 $(16)$(20)$(20)$(57)$(60)
(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
(b)Amount less than $1 million.