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Stock-Based Compensation | 12 Months Ended
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Dec. 31, 2025
Share-Based Payment Arrangement [Abstract] |
STOCK-BASED COMPENSATION | STOCK-BASED COMPENSATION The 2022 Omnibus Incentive Compensation Plan is Ameren’s long-term incentive plan available for eligible employees and directors. It provides for a maximum of 8.8 million common shares to be available for grant to eligible employees and directors. At December 31, 2025, there were 7.3 million common shares remaining for grant. Awards may be restricted stock, restricted stock units, stock options (incentive stock options and nonqualified stock options), stock appreciation rights, performance awards, cash-based awards and other stock-based awards. Ameren used newly issued shares to fulfill its stock-based compensation obligations for 2025, 2024, and 2023, and intends to use newly issued shares to fulfill its stock-based compensation obligations for 2026. The following table summarizes Ameren’s outstanding performance share unit and restricted stock unit activity for the year ended December 31, 2025:
| Performance Share Units – Market Condition(a) |  | Performance Share Units – Performance Condition(b) |  | Restricted Stock Units
| Share Units |  | Weighted-average Fair Value per Share Unit |  | Share Units |  | Weighted-average Fair Value per Share Unit |  | Stock Units |  | Weighted-average Fair Value per Stock Unit
Outstanding at January 1, 2025(c) | 808,950 |  |  | $ | 77.73 |  |  | 120,997 |  |  | $ | 79.09 |  |  | 395,520 |  |  | $ | 79.73 |
Granted | 245,464 |  |  | 123.19 |  |  | 40,408 |  |  | 96.66 |  |  | 132,931 |  |  | 97.33 |
Forfeitures | (80,469) |  |  | 87.56 |  |  | (13,337) |  |  | 82.09 |  |  | (47,305) |  |  | 83.77 |
Dividend equivalents(d) | 22,947 |  |  | 87.13 |  |  | 3,452 |  |  | 82.34 |  |  | 10,968 |  |  | 82.72 |
Vested and distributed | (217,017) |  |  | 92.75 |  |  | (34,980) |  |  | 87.85 |  |  | (119,601) |  |  | 87.95 |
Outstanding at December 31, 2025(c) | 779,875 |  |  | $ | 87.12 |  |  | 116,540 |  |  | $ | 82.31 |  |  | 372,513 |  |  | $ | 82.95 |
(a)The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions. Compensation cost on nonforfeited awards is recognized regardless of whether Ameren achieves the specified market conditions. (b)The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. Compensation cost is recognized ratably over the requisite service period only for awards for which it is probable that the performance condition will be satisfied. (c)Outstanding awards include awards that vest on a pro-rata basis due to attainment of retirement eligibility by employees, but have not yet been distributed. In these cases, the pro-rata basis awards have not yet been distributed as the entire performance period has not been completed. The number of shares issued for retirement-eligible employees will vary depending on actual performance over the three-year performance period. (d)Dividend equivalents represent the right to receive shares measured by the dividend payable with respect to the corresponding number of outstanding share units. Dividend equivalents will accrue and be reinvested in additional share units throughout the performance period. Performance Share Units – Market Condition A market condition performance share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, certain specified market conditions have been met and if the individual remains employed by Ameren through the required vesting period. The vesting period for share units awarded extends beyond the three-year performance period to the payout date, which is approximately 38 months after the grant date. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis over the three-year performance period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions. The fair value of each share unit is based on a Monte Carlo simulation. The Monte Carlo simulation is used to estimate expected share payout based on Ameren’s TSR for a three-year performance period relative to the designated peer group beginning January 1st of the award year. The simulation can produce a greater or lesser fair value for the share unit than the applicable closing common share price because it includes the weighted payout scenarios in which an increase or decrease in the share price has occurred and/or in which the payout is above 100% due to Ameren’s projected TSR performance. The key assumptions used to calculate fair value also include a three-year risk-free rate, Ameren’s common stock volatility, and volatility for the peer group. The following table presents the fair value of each share unit along with the significant assumptions used to calculate the fair value of each share unit for the years ended December 31, 2025, 2024, and 2023:
| 2025 | 2024 | 2023
Fair value of share units awarded | $123.19 | $56.73 | $91.07
Three-year risk-free rate | 4.23% | 4.25% | 4.19%
Ameren’s common stock volatility(a) | 21% | 21% | 26%
Volatility range for the peer group(a) | 19% – 24% | 19% – 23% | 24% – 32%
(a)Based on a historical period that is equal to the remaining term of the performance period as of the grant date. In addition to the market condition performance share units described above, there are an immaterial number of market condition performance share units with different vesting conditions and target payout percentages. Performance Share Units – Performance Condition A performance condition share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, Ameren has met the specified performance condition and if the individual remains employed by Ameren through the required vesting period. The vesting period for share units awarded extends beyond the three-year performance period to the payout date, which is approximately 38 months after the grant date. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis over the three-year performance period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual performance conditions achieved. The specified performance condition in each award year is based on Ameren’s clean energy transition. The grant-date fair value for an individual outcome of a performance condition is determined by Ameren’s closing common share price on the grant date. Restricted Stock Units Restricted stock units vest and entitle an employee to receive shares of Ameren common stock (plus accumulated dividends) if the individual remains employed with Ameren through the payment date of the awards. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis. The payout date of the awards is approximately 38 months after the grant date. The fair value of each restricted stock unit is determined by Ameren’s closing common share price on the grant date. Stock-Based Compensation Expense The following table presents the stock-based compensation expense for the years ended December 31, 2025, 2024, and 2023:
| 2025 |  | 2024 |  | 2023
Ameren Missouri | $ | 8 |  |  | $ | 8 |  |  | $ | 6 |
Ameren Illinois | 4 |  |  | 4 |  |  | 4 |
Other(a) | 16 |  |  | 16 |  |  | 16 |
Ameren | 28 |  |  | 28 |  |  | 26 |
Less: Income tax benefit | 7 |  |  | 7 |  |  | 7 |
Stock-based compensation expense, net | $ | 21 |  |  | $ | 21 |  |  | $ | 19 |
(a)Represents compensation expense for employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above. Ameren settled performance share units and restricted stock units of $38 million, $24 million, and $60 million for the years ended December 31, 2025, 2024, and 2023, respectively. There were no significant stock-based compensation costs capitalized during the years ended December 31, 2025, 2024, and 2023. As of December 31, 2025, total compensation cost of $43 million related to outstanding awards not yet recognized is expected to be recognized over a weighted-average period of 23 months. For the years ended December 31, 2025, 2024, and 2023, excess tax benefits (deficiencies) associated with the settlement of stock-based compensation awards reduced (increased) income tax expense by $1 million, $(1) million, and $6 million, respectively.

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