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Retirement Benefits (Tables)
 12 Months Ended
Dec. 31, 2023
Summary Of Benefit Liability Recorded
The following table presents the net benefit liability/(asset) recorded on the balance sheets as of December 31, 2023 and 2022:
20232022
Ameren(a)
$(551)$(377)
Ameren Missouri(a)
(142)(84)
Ameren Illinois(a)
(351)(263)
(a)Liabilities associated with pension and other postretirement benefits are recorded in “Other current liabilities” and “Other deferred credits and liabilities” on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets.
Funded Status Of Benefit Plans and Amounts Included In Regulatory Assets and AOCI The following table presents the funded status of Ameren’s pension and postretirement benefit plans as of December 31, 2023 and 2022. It also provides the amounts included in regulatory assets or liabilities and accumulated OCI at December 31, 2023 and 2022, that have not been recognized in net periodic benefit costs.
20232022
Pension
Benefits		Postretirement
Benefits		Pension
Benefits		Postretirement
Benefits
Accumulated benefit obligation at end of year$4,102 $(a)$3,911 $(a)
Change in benefit obligation:
Net benefit obligation at beginning of year$4,061 $838 $5,457 $1,129 
Service cost79 12 128 20 
Interest cost221 45 163 34 
Participant contributions— 7 — 8 
Actuarial (gain) loss170 17 (1,425)(289)
Benefits paid(273)(63)(262)(64)
Net benefit obligation at end of year4,258 856 4,061 838 
Change in plan assets:
Fair value of plan assets at beginning of year4,027 1,249 5,745 1,558 
Actual return on plan assets514 197 (1,461)(255)
Employer contributions4 3 5 2 
Participant contributions— 7 — 8 
Benefits paid(273)(63)(262)(64)
Fair value of plan assets at end of year4,272 1,393 4,027 1,249 
Funded status – deficiency (surplus)(14)(537)34 (411)
Accrued benefit cost (asset) at December 31$(14)$(537)$34 $(411)
Amounts recognized in the balance sheet consist of:
Noncurrent asset$(44)$(537)$— $(411)
Current liability(b)
2 — 3 — 
Noncurrent liability(c)
28 — 31 — 
Net liability (asset) recognized$(14)$(537)$34 $(411)
Amounts recognized in regulatory assets or liabilities consist of:
Net actuarial gain$(10)$(311)$(107)$(268)
Prior service credit— (25)— (29)
Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial (gain) loss22 (4)15 (4)
Total$12 $(340)$(92)$(301)
(a)Not applicable.
(b)Included in “Other current liabilities” on Ameren’s consolidated balance sheet.
(c)Included in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.
Assumptions Used To Determine Benefit Obligations
The following table presents the assumptions used to determine our benefit obligations at December 31, 2023 and 2022:
Pension BenefitsPostretirement Benefits
2023202220232022
Discount rate at measurement date5.25 %5.55 %5.25 %5.55 %
Increase in future compensation3.50 
(a)
3.50 
(a)
3.50 
(a)
3.50 
(a)
Cash balance pension plan interest crediting rate5.50 5.00 
(b)
(c)(c)
Medical cost trend rate (initial)(d)
(c)(c)(e)(e)
Medical cost trend rate (ultimate)(d)
(c)(c)5.00 5.00 
(a)As of December 31, 2023, increase in future compensation is 4.00% in 2024, and 3.50% thereafter. As of December 31, 2022, increase in future compensation was 4.50% for 2023, 4.00% in 2024, and 3.50% thereafter.
(b)Cash balance pension plan interest crediting rate was 5.50% for 2023 and 2024, and 5.00% thereafter.
(c)Not applicable.
(d)Initial and ultimate medical cost trend rate for certain Medicare-eligible participants was 2.50% at December 31, 2023 and 2022.
(e)Initial medical cost trend rates of 6.93% and 7.25% for pre-Medicare plan participants and 6.50% and 6.75% for post-Medicare plan participants at December 31, 2023 and 2022, respectively, trend down to the ultimate rate by 2030, with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.
Schedule Of Cash Contributions Made To Benefit Plans
The following table presents the cash contributions made to our defined benefit retirement plans and to our postretirement plan during 2023, 2022, and 2021:
Pension BenefitsPostretirement Benefits
202320222021202320222021
Ameren Missouri$1 $1 $22 $2 $1 $1 
Ameren Illinois2 3 28 1 1 1 
Ameren Services1 1 10 — — — 
Ameren$4 $5 $60 $3 $2 $2 
Target Allocation Of The Plans' Asset Categories
The following table presents our target allocations and our pension and postretirement plans’ asset categories as of December 31, 2023 and 2022:
Asset
Category
Target Allocation
2023
Percentage of Plan Assets at December 31,
20232022
Pension Plan:
Cash and cash equivalents
0% – 5%
1 %1 %
Equity securities:
U.S. large-capitalization
11% – 21%
15 %15 %
U.S. small- and mid-capitalization
3% – 13%
8 %8 %
Global
10% – 20%
16 %12 %
International
6% – 16%
12 %16 %
Total equity
45% – 55%
51 %51 %
Debt securities
35% – 45%
35 %
(a)
35 %
(a)
Diversified credit
0% – 10%
7 %7 %
Real estate
0% – 10%
6 %6 %
Private equity
0% – 5%
(b)(b)
Total 100 %100 %
Postretirement Plans:
Cash and cash equivalents
0% – 7%
1 %2 %
Equity securities:
U.S. large-capitalization
23% – 33%
32 %29 %
U.S. small- and mid-capitalization
3% – 13%
8 %8 %
Global
9% – 19%
15 %10 %
International
5% – 15%
8 %13 %
Total equity
55% – 65%
63 %60 %
Debt securities
33% – 43%
36 %38 %
Total 100 %100 %
(a)Includes interest rate futures derivative instruments.
(b)Less than 1% of plan assets.
Components Of Net Periodic Benefit Cost
The following table presents the components of the net periodic benefit cost (income) of Ameren’s pension and postretirement benefit plans during 2023, 2022, and 2021:
Pension BenefitsPostretirement Benefits
202320222021202320222021
Service cost(a)
$79 $128 $134 $12 $20 $23 
Non-service cost components:
Interest cost221 163 152 45 34 33 
Expected return on plan assets(b)
(333)(320)(297)(91)(85)(80)
Amortization of(b):
Prior service credit— — — (4)(4)(4)
Actuarial (gain) loss(115)25 73 (45)(19)(6)
Total non-service cost components(c)
$(227)$(132)$(72)$(95)$(74)$(57)
Net periodic benefit cost (income)(d)
$(148)$(4)$62 $(83)$(54)$(34)
(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 is amortized on a straight-line basis over the average future service of active participants benefiting under the plan amendment. Net actuarial gains or losses related to the net benefit obligation subject to amortization are amortized on a straight-line basis over 10 years. The difference between the actual and expected return on plan assets is amortized over 4 years.
(c)Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 6 – 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 rates.
Summary Of Benefit Plan Costs Incurred
The Ameren Companies are responsible for their share of the pension and postretirement benefit costs (income). The following table presents the pension and postretirement benefit costs (income) incurred for the years ended December 31, 2023, 2022, and 2021:
Pension CostsPostretirement Costs
202320222021202320222021
Ameren Missouri(a)
$(76)$(3)$29 $(30)$(14)$(4)
Ameren Illinois(62)3 34 (54)(41)(31)
Other(10)(4)(1)1 1 1 
Ameren$(148)$(4)$62 $(83)$(54)$(34)
(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.
Schedule Of Expected Payments From Qualified Trust And Company Funds
The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2023, are as follows:
Pension BenefitsPostretirement Benefits
Paid from
Qualified
Trust Funds		Paid from
Company
Funds		Paid from
Qualified
Trust Funds		Paid from
Company
Funds
2024$277 $3 $56 $3 
2025281 3 58 3 
2026287 3 58 3 
2027290 3 58 3 
2028293 2 58 3 
2029 – 20331,488 13 289 15 
Assumptions Used To Determine Net Periodic Benefit Cost
The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2023, 2022, and 2021:
Pension BenefitsPostretirement Benefits
202320222021202320222021
Discount rate at measurement date5.55 %3.00 %2.75 %5.55 %3.00 %2.75 %
Expected return on plan assets6.75 6.50 6.50 6.75 6.50 6.50 
Increase in future compensation3.50 
(a)
3.50 3.50 3.50 
(a)
3.50 3.50 
Cash balance pension plan interest crediting rate5.00 
(b)
5.00 5.00 (c)(c)(c)
Medical cost trend rate (initial)(d)
(c)(c)(c)(e)5.00 5.00 
Medical cost trend rate (ultimate)(d)
(c)(c)(c)5.00 5.00 5.00 
(a)Increase in future compensation is 4.50% for 2023, 4.00% in 2024, and 3.50% thereafter for the year ended December 31, 2023.
(b)Cash balance pension plan interest crediting rate is 5.50% for 2023 and 2024, and 5.00% thereafter for the year ended December 31, 2023.
(c)Not applicable.
(d)Initial and ultimate medical cost trend rate for certain Medicare-eligible participants is 2.50% for the year ended December 31, 2023 and 3.00% for the years ended December 31, 2022 and 2021.
(e)Initial medical cost trend rates of 7.25% for pre-Medicare plan participants and 6.75% for post-Medicare plan participants trend down to the ultimate rate by 2030, with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.
Schedule Of Matching Contributions The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to each of the Ameren Companies for the years ended December 31, 2023, 2022, and 2021:
202320222021
Ameren Missouri$27 $23 $21 
Ameren Illinois21 19 16 
Other1 1 1 
Ameren$49 $43 $38 
Pension Benefits  
Target Allocation Of The Plans' Asset Categories
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plans’ assets measured at fair value and NAV as of December 31, 2023 and 2022:
December 31, 2023December 31, 2022
Level 1Level 2NAVTotalLevel 1Level 2NAVTotal
Cash and cash equivalents$— $— $90 $90 $— $— $172 $172 
Equity securities:
U.S. large-capitalization— — 663 663 — — 658 658 
U.S. small- and mid-capitalization353 — — 353 321 — — 321 
International316 — 229 545 266 — 395 661 
Global— — 721 721 — — 493 493 
Debt securities:
Corporate bonds— 479 — 479 — 397 — 397 
Municipal bonds— 43 — 43 — 41 — 41 
U.S. Treasury and agency securities— 994 — 994 — 859 — 859 
Diversified credit— — 305 305 — — 281 281 
Other49 13 — 62 (3)7 — 4 
Real estate— — 248 248 — — 271 271 
Private equity— — — — — — 1 1 
Total$718 $1,529 $2,256 $4,503 $584 $1,304 $2,271 $4,159 
Less: Medical benefit assets(a)
(196)(172)
Plus: Net receivables (payables)(b)
(35)40 
Fair value of pension plans’ assets$4,272 $4,027 
(a)Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(b)Net of receivables related to pending securities sales and payables related to pending securities purchases.
Postretirement Benefits  
Target Allocation Of The Plans' Asset Categories
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans’ assets measured at fair value and NAV as of December 31, 2023 and 2022:
December 31, 2023December 31, 2022
Level 1Level 2NAVTotalLevel 1Level 2NAVTotal
Cash and cash equivalents$10 $— $— $10 $14 $— $— $14 
Equity securities:
U.S. large-capitalization302 — 81 383 221 — 87 308 
U.S. small- and mid-capitalization96 — — 96 92 — — 92 
International51 — 49 100 43 — 98 141 
Global— — 174 174 — — 110 110 
Debt securities:
Municipal bonds— 161 — 161 — 123 — 123 
Other— — 271 271 — — 287 287 
Total$459 $161 $575 $1,195 $370 $123 $582 $1,075 
Plus: Medical benefit assets(a)
196 172 
Plus: Net receivables(b)
  2 2 
Fair value of postretirement benefit plans’ assets  $1,393 $1,249 
(a)Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(b)Net of receivables related to pending securities sales and payables related to pending securities purchases.