Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary Of Nonvested Shares Related To Long-Term Incentive Plan

A summary of nonvested shares at December 31, 2014, and changes during the year ended December 31, 2014, under the 2006 Incentive Plan and the 2014 Incentive Plan are presented below:

	Performance Share Units
	Share Units		Weighted-average Fair Value per Share Unit
Nonvested at January 1, 2014	1,218,544		$	33.23
Granted(a)	688,323		38.90
April Grants(b)	38,559		50.34
Unearned or forfeited(c)	(97,432	)	34.42
Earned and vested(d)	(685,617	)	36.12
Nonvested at December 31, 2014	1,162,377		$	35.35

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2014 under the 2006 Incentive Plan and the 2014 Incentive Plan.

(b) In April 2014, certain executive officers were granted additional share units under the 2006 Incentive Plan and the 2014 Incentive Plan. The significant assumptions used to calculate fair value included a prorated three-year risk-free rate ranging from 0.76% to 0.79%, volatility of 12% to 18% for the peer group, and Ameren’s attainment of a three-year average earnings per share threshold during the performance period.

(c) Includes share units granted in 2012 that were not earned based on performance provisions of the award grants.

(d) Includes share units granted in 2012 that vested as of December 31, 2014, that were earned pursuant to the provisions of the award grants.