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Retirement Benefits (Tables)
 9 Months Ended
Sep. 30, 2018
Defined Benefit Plan [Abstract]  
Components Of Net Periodic Benefit Cost
The following table presents the components of the net periodic benefit cost (income), prior to capitalization, incurred for Ameren’s pension and postretirement benefit plans for the three and nine months ended September 30, 2018 and 2017:
 
Pension Benefits
 
Postretirement Benefits
 
Three Months
 
Nine Months
 
Three Months
 
Nine Months
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Service cost(a)
$
25

 
$
24

 
$
75

 
$
70

 
$
6

 
$
6

 
$
16

 
$
16

Non-service cost components:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Interest cost
42

 
44

 
126

 
134

 
10

 
12

 
30

 
35

Expected return on plan assets
(68
)
 
(65
)
 
(206
)
 
(196
)
 
(20
)
 
(19
)
 
(58
)
 
(56
)
Amortization of:
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Prior service benefit
—

 
(1
)
 
—

 
(1
)
 
(1
)
 
(2
)
 
(3
)
 
(4
)
Actuarial loss (gain)
17

 
14

 
51

 
41

 
(2
)
 
(2
)
 
(5
)
 
(5
)
Total non-service cost components(b)
(9
)
 
(8
)
 
(29
)
 
(22
)
 
(13
)
 
(11
)
 
(36
)
 
(30
)
Net periodic benefit cost (income)
$
16

 
$
16

 
$
46

 
$
48

 
$
(7
)
 
$
(5
)
 
$
(20
)
 
$
(14
)
(a)
Service cost, net of capitalization, is reflected in “Operating Expenses – Other operations and maintenance” on Ameren’s statement of income.
(b)
2018 amounts and the non-capitalized portion of 2017’s non-service cost components, as discussed above, are reflected in “Other Income, Net” on Ameren’s statement of income. See Note 5 – Other Income, Net for additional information.
Summary Of Benefit Plan Costs Incurred
Ameren Missouri and Ameren Illinois are responsible for their respective shares of Ameren’s pension and 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, 2018 and 2017:
 
Pension Benefits
 
Postretirement Benefits
 
Three Months
 
Nine Months
 
Three Months
 
Nine Months
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Ameren Missouri(a)
$
6

 
$
6

 
$
17

 
$
18

 
$
(1
)
 
$
(1
)
 
$
(1
)
 
$
(3
)
Ameren Illinois
11

 
10

 
30

 
30

 
(6
)
 
(3
)
 
(19
)
 
(10
)
Other
(1
)
 
—

 
(1
)
 
—

 
—

 
(1
)
 
—

 
(1
)
Ameren(a)
$
16

 
$
16

 
$
46

 
$
48

 
$
(7
)
 
$
(5
)
 
$
(20
)
 
$
(14
)

(a)
Does not include the impact of the regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates.