Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Footnote) (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Debt instrument, interest rate, maximum	18.00%
Series 1992 Due 2022 [Member] | Union Electric Company [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate during period	0.34%	0.47%
Series A 1998 Due 2033 [Member] | Union Electric Company [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate during period	0.69%	0.71%
Series B 1998 Due 2033 [Member] | Union Electric Company [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate during period	0.68%	0.73%
Series C 1998 Due 2033 [Member] | Union Electric Company [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate during period	0.69%	0.74%
Series B-1 1993 Due 2028 [Member] | Ameren Illinois Company [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate during period	0.28%	0.59%