Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Summary Of Nonvested Shares Related To Long-Term Incentive Plan

The following table summarizes Ameren’s nonvested performance share unit and restricted stock unit activity for the year ended December 31, 2021:

	Performance Share Units – Market Condition(a)			Performance Share Units – Performance Condition(b)			Restricted Stock Units
	Share Units	Weighted-average Fair Value per Share Unit		Shares	Weighted-average Fair Value per Share Unit		Stock Units	Weighted-average Fair Value per Stock Unit
Nonvested at January 1, 2021(c)	464,139	$	73.34	31,896	$	76.66	303,695	$	68.52
Granted	266,081	87.11		42,672	78.11		129,723	78.17
Forfeitures	(21,143)	80.77		(2,449)	77.55		(10,209)	74.88
Vested and undistributed(d)	(186,792)	77.91		(15,134)	77.27		(87,427)	73.13
Vested and distributed	(93,499)	62.88		—	—		(87,597)	56.38
Performance share adjustment	—	—		(13,881)	77.54		—	—
Nonvested at December 31, 2021(e)	428,786	$	81.81	43,104	$	77.54	248,185	$	75.97

(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. The performance share adjustment represents the change in the probability that a performance condition will be satisfied.

(c)Does not include 366,243 market condition performance share units, 7,607 performance shares based on Ameren’s clean energy transition, and 160,034 restricted stock units that were vested and undistributed.

(d)Vested and undistributed units are awards that vest on a pro-rata basis due to attainment of retirement eligibility by certain employees, but have not yet been distributed. For vested and undistributed performance share units, the number of shares issued for retirement-eligible employees will vary depending on actual performance over the three-year performance period.

(e)Does not include 357,575 market condition performance share units, 22,739 performance shares based on Ameren’s clean energy transition, and 164,000 restricted stock units that were vested and undistributed.

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award

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, 2021, 2020, and 2019:

	2021	2020	2019
Fair value of share units awarded	$87.11	$82.49	$67.42
Three-year risk-free rate	0.17%	1.62%	2.46%
Ameren’s common stock volatility(a)	28%	15%	17%
Volatility range for the peer group(a)	26% – 36%	14% – 28%	15% – 25%

(a)Based on a historical period that is equal to the remaining term of the performance period as of the grant date.

The following table presents the stock-based compensation expense for the years ended December 31, 2021, 2020, and 2019:

	2021		2020		2019
Ameren Missouri	$	5	$	5	$	4
Ameren Illinois	3		3		3
Other(a)	14		13		13
Ameren	22		21		20
Less: Income tax benefit	6		6		5
Stock-based compensation expense, net	$	16	$	15	$	15

(a)Represents compensation expense for employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above.