Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Summary of Nonvested Shares Related To Long-Term Incentive Plan) (Details) (Performance Shares, USD $)	1 Months Ended		6 Months Ended
	Apr. 30, 2014		Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Three-year risk-free rate			0.78%
Volatility rate, minimum	12.00%		12.00%
Volatility rate, maximum	18.00%		18.00%
Share Units
Share Units, Nonvested as of January 1, 2014			1,218,544
Share Units, Granted	38,559	[1]	683,591	[2]
Share Units, Forfeitures			(65,847)
Share Units, Vested			(116,297)	[3]
Share Units, Nonvested as of March 31, 2014			1,758,550
Weighted-average Fair Value per Unit at Grant Date
Weighted-average Fair Value per Unit, Nonvested as of January 1, 2014			$ 33.23
Weighted-average Fair Value per Unit, Grants	$ 50.34	[1]	$ 38.90	[2]
Weighted-average Fair Value per Unit, Forfeitures			$ 33.82
Weighted-average Fair Value per Unit, Vested			$ 38.81	[3]
Weighted-average Fair Value per Unit, Nonvested as of March 31, 2014			$ 35.42
Performance period			3 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Three-year risk-free rate	0.76%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Three-year risk-free rate	0.79%

[1] 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.

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

[3] Share units vested due to the attainment of retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.