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Long-Term Debt And Equity Financings (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Jun. 30, 2011 Ameren Illinois Company [Member]	Sep. 30, 2011 Senior Unsecured Notes 8.875% Due 2014 [Member]
Debt Instrument [Line Items]
Common stock, shares issued	0.6	1.8
Common stock, value of shares issued	$ 17	$ 49	$ 60
Amount of senior notes matured and retired				$ 150
Interest rate on senior secured notes				6.625%
Excess in indebtedness upon default of maturity					25