Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure of Compensation Related Costs, Share-based Payments [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, 2019:

	Performance Share Units				Restricted Stock Units
	Share Units		Weighted-average Fair Value per Share Unit		Stock Units		Weighted-average Fair Value per Stock Unit
Nonvested at January 1, 2019(a)	682,811		$	56.58	155,253		$	57.38
Granted	304,384		67.42		132,526		65.89
Forfeitures	(35,120	)	64.40		(11,802	)	62.75
Vested and undistributed(b)	(235,275	)	62.28		(53,297	)	61.99
Vested and distributed	(176,923	)	44.13		(2,403	)	54.30
Nonvested at December 31, 2019(c)	539,877		$	63.79	220,277		$	61.13

(a) Does not include 619,783 performance share units and 26,557 restricted stock units that were vested and undistributed.

(b) 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.

(c)

Does not include 503,283 of performance share units and 79,854 of restricted stock units that were vested and undistributed.

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

The following table presents the stock-based compensation expense for the years ended December 31, 2019, 2018, and 2017:

	2019		2018		2017
Ameren Missouri	$	4	$	4	$	4
Ameren Illinois	3		3		2
Other(a)	13		13		12
Ameren	20		20		18
Less income tax benefit	5		6		7
Stock-based compensation expense, net	$	15	$	14	$	11

(a)

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

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, 2019, 2018, and 2017:

	2019	2018	2017
Fair value of share units awarded	$67.42	$62.88	$59.16
Three-year risk-free rate	2.46%	1.98%	1.47%
Ameren’s common stock volatility(a)	17%	17%	19%
Volatility range for the peer group(a)	15% – 25%	15% – 23%	15% – 21%

(a)

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