Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Parenthetical) (Details)	12 Months Ended																						12 Months Ended																				12 Months Ended
	Dec. 31, 2011 Senior Unsecured Notes 8.875% Due 2014 [Member]	Dec. 31, 2011 Senior Secured Notes 5.25% Due 2012 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 4.65% Due 2013 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.50% Due 2014 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 4.75% Due 2015 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.40% Due 2016 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.40% Due 2017 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.00% Due 2018 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.10% Due 2018 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.70% Due 2019 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.10% Due 2019 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.00% Due 2020 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.50% Due 2034 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 5.30% Due 2037 [Member] Union Electric Company [Member]	Dec. 31, 2011 Senior Secured Notes 8.45% Due 2039 [Member] Union Electric Company [Member]	Dec. 31, 2011 Series 1992 Due 2022 [Member] Union Electric Company [Member]	Dec. 31, 2011 Series 1993 5.45% Due 2028 [Member] Union Electric Company [Member]	Dec. 31, 2011 Series A 1998 Due 2033 [Member] Union Electric Company [Member]	Dec. 31, 2011 Series B 1998 Due 2033 [Member] Union Electric Company [Member]	Dec. 31, 2011 Series C 1998 Due 2033 [Member] Union Electric Company [Member]	Sep. 30, 2010 Series 7.69% Due 2036 [Member]	Jun. 30, 2011 Senior Secured Notes 6.625% Due 2011 [Member]	Dec. 31, 2011 Senior Secured Notes 6.625% Due 2011 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 8.875% Due 2013 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.20% Due 2016 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.25% Due 2016 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.125% Due 2017 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.25% Due 2018 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 9.75% Due 2018 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.125% Due 2028 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.70% Due 2036 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Secured Notes 6.70% Due 2036 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series1992 B 6.20% Due 2012 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series A 2000 5.50% Due 2014 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series1993 5.90% Due 2023 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series1994A 5.70% Due 2024 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series C-1 1993 5.95% Due 2026 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series C-2 1993 5.70% Due 2026 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series B-1 1993 Due 2028 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series1998A 5.40% Due 2028 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Series1998B 5.40% Due 2028 [Member] Ameren Illinois Company [Member]	Nov. 30, 2010 Senior Notes Series D 8.35% Due 2010 [Member]	Dec. 31, 2011 Senior Notes Series F 7.95% Due 2032 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Notes Series H 7.00% Due 2018 [Member] Ameren Illinois Company [Member]	Dec. 31, 2011 Senior Notes Series I 6.30% Due 2020 [Member] Ameren Illinois Company [Member]
Debt Instrument [Line Items]
Long-term debt interest rate	8.875%	5.25%	4.65%	5.50%	4.75%	5.40%	6.40%	6.00%	5.10%	6.70%	5.10%	5.00%	5.50%	5.30%	8.45%		5.45%				7.69%	6.625%	6.625%	8.875%	6.20%	6.25%	6.125%	6.25%	9.75%	6.125%	6.70%	6.70%	6.20%	5.50%	5.90%	5.70%	5.95%	5.70%		5.40%	5.40%	8.35%	7.95%	7.00%	6.30%
Long-term debt maturity date	2014	2012	2013	2014	2015	2016	2017	2018	2018	2019	2019	2020	2034	2037	2039	2022	2028	2033	2033	2033			2011	2013	2016	2016	2017	2018	2018	2028	2036	2036	2012	2014	2023	2024	2026	2026	2028	2028	2028		2032	2018	2020