Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		May 31, 2014	Jan. 31, 2014		Oct. 31, 2013	May 15, 2014
Debt Instrument [Line Items]
Less: Maturities due within one year	$ (120,000,000)		$ (534,000,000)
Long-term Debt, Net	6,120,000,000		5,504,000,000
Parent Company
Debt Instrument [Line Items]
Less: Maturities due within one year	0		(425,000,000)
Parent Company | 8.875% Senior unsecured notes due 2014
Debt Instrument [Line Items]
Debt instrument face amount			425,000,000
Long-term debt interest rate	8.875%				8.875%
Long-term debt maturity date	2014
Union Electric Company
Debt Instrument [Line Items]
Long-term debt, gross	4,005,000,000		3,764,000,000
Less: Unamortized discount and premium	6,000,000		7,000,000
Less: Maturities due within one year	(120,000,000)		(109,000,000)
Long-term Debt, Net	3,879,000,000		3,648,000,000
Union Electric Company | City Of Bowling Green Capital Lease Peno Creek Ct
Debt Instrument [Line Items]
Capital lease obligations	54,000,000		59,000,000
Long-term debt maturity date	2022
Union Electric Company | Audrain County Capital Lease Audrain County Ct
Debt Instrument [Line Items]
Capital lease obligations	240,000,000		240,000,000
Long-term debt maturity date	2023
Ameren Illinois Company
Debt Instrument [Line Items]
Debt instrument face amount						1,000,000	[1]
Fair-market value adjustments			4,000,000
Long-term debt, gross	2,246,000,000		1,863,000,000
Less: Unamortized discount and premium	5,000,000		7,000,000
Less: Maturities due within one year			0
Long-term Debt, Net	2,241,000,000		1,856,000,000
Secured Debt | Union Electric Company | 4.65% Senior secured notes due 2013
Debt Instrument [Line Items]
Long-term debt interest rate								4.65%
Secured Debt | Union Electric Company | 5.50% Senior secured notes due 2014
Debt Instrument [Line Items]
Debt instrument face amount	0	[2]	104,000,000	[2]
Long-term debt interest rate	5.50%								5.50%
Long-term debt maturity date	2014
Secured Debt | Union Electric Company | 4.75% Senior secured notes due 2015
Debt Instrument [Line Items]
Debt instrument face amount	114,000,000	[2]	114,000,000	[2]
Long-term debt interest rate	4.75%
Long-term debt maturity date	2015
Secured Debt | Union Electric Company | 5.40% Senior secured notes due 2016
Debt Instrument [Line Items]
Debt instrument face amount	260,000,000	[2]	260,000,000	[2]
Long-term debt interest rate	5.40%
Long-term debt maturity date	2016
Secured Debt | Union Electric Company | 6.40% Senior secured notes due 2017
Debt Instrument [Line Items]
Debt instrument face amount	425,000,000	[2]	425,000,000	[2]
Long-term debt interest rate	6.40%
Long-term debt maturity date	2017
Secured Debt | Union Electric Company | 6.00% Senior secured notes due 2018
Debt Instrument [Line Items]
Debt instrument face amount	179,000,000	[2],[3]	179,000,000	[2],[3]
Long-term debt interest rate	6.00%
Long-term debt maturity date	2018
Secured Debt | Union Electric Company | 5.10% Senior secured notes due 2018
Debt Instrument [Line Items]
Debt instrument face amount	199,000,000	[2]	199,000,000	[2]
Long-term debt interest rate	5.10%
Long-term debt maturity date	2018
Secured Debt | Union Electric Company | 6.70% Senior secured notes due 2019
Debt Instrument [Line Items]
Debt instrument face amount	329,000,000	[2],[3]	329,000,000	[2],[3]
Long-term debt interest rate	6.70%
Long-term debt maturity date	2019
Secured Debt | Union Electric Company | 5.10% Senior secured notes due 2019
Debt Instrument [Line Items]
Debt instrument face amount	244,000,000	[2]	244,000,000	[2]
Long-term debt interest rate	5.10%
Long-term debt maturity date	2019
Secured Debt | Union Electric Company | 5.00% Senior secured notes due 2020
Debt Instrument [Line Items]
Debt instrument face amount	85,000,000	[2]	85,000,000	[2]
Long-term debt interest rate	5.00%
Long-term debt maturity date	2020
Secured Debt | Union Electric Company | Senior Secured Notes350 Due2024 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	350,000,000	[2]
Long-term debt interest rate	3.50%
Long-term debt maturity date	2024
Secured Debt | Union Electric Company | 5.50% Senior secured notes due 2034
Debt Instrument [Line Items]
Debt instrument face amount	184,000,000	[2]	184,000,000	[2]
Long-term debt interest rate	5.50%
Long-term debt maturity date	2034
Secured Debt | Union Electric Company | 5.30% Senior secured notes due 2037
Debt Instrument [Line Items]
Debt instrument face amount	300,000,000	[2]	300,000,000	[2]
Long-term debt interest rate	5.30%
Long-term debt maturity date	2037
Secured Debt | Union Electric Company | 8.45% Senior secured notes due 2039
Debt Instrument [Line Items]
Debt instrument face amount	350,000,000	[2],[3]	350,000,000	[2],[3]
Long-term debt interest rate	8.45%
Long-term debt maturity date	2039
Secured Debt | Union Electric Company | 3.90% Senior secured notes due 2042
Debt Instrument [Line Items]
Debt instrument face amount	485,000,000	[2],[3]	485,000,000	[2],[3]
Long-term debt interest rate	3.90%
Long-term debt maturity date	2042
Secured Debt | Ameren Illinois Company | Senior Secured Notes 8.875% Due 2013
Debt Instrument [Line Items]
Long-term debt interest rate			8.875%
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.20% Due 2016
Debt Instrument [Line Items]
Debt instrument face amount	54,000,000	[4]	54,000,000	[4]
Long-term debt interest rate	6.20%
Long-term debt maturity date	2016
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.25% Due 2016
Debt Instrument [Line Items]
Debt instrument face amount	75,000,000	[5]	75,000,000	[5]
Long-term debt interest rate	6.25%
Long-term debt maturity date	2016
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.125% Due 2017
Debt Instrument [Line Items]
Debt instrument face amount	250,000,000	[5],[6]	250,000,000	[5],[6]
Long-term debt interest rate	6.125%
Long-term debt maturity date	2017
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.25% Due 2018
Debt Instrument [Line Items]
Debt instrument face amount	144,000,000	[5],[6]	144,000,000	[5],[6]
Long-term debt interest rate	6.25%
Long-term debt maturity date	2018
Secured Debt | Ameren Illinois Company | Senior Secured Notes 9.75% Due 2018
Debt Instrument [Line Items]
Debt instrument face amount	313,000,000	[5],[6]	313,000,000	[5],[6]
Long-term debt interest rate	9.75%
Long-term debt maturity date	2018
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 2.70%, Due 2022
Debt Instrument [Line Items]
Debt instrument face amount	400,000,000	[5],[6]	400,000,000	[5],[6]
Long-term debt interest rate	2.70%
Long-term debt maturity date	2022
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 3 Point 25, Due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	300,000,000	[5],[6]
Long-term debt interest rate	3.25%
Long-term debt maturity date	2025
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.125% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	60,000,000	[5]	60,000,000	[5]
Long-term debt interest rate	6.125%
Long-term debt maturity date	2028
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.70% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	61,000,000	[5]	61,000,000	[5]
Long-term debt interest rate	6.70%
Long-term debt maturity date	2036
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.70% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	42,000,000	[4]	42,000,000	[4]
Long-term debt interest rate	6.70%
Long-term debt maturity date	2036
Secured Debt | Ameren Illinois Company | Senior Secured Notes 4.80% Due 2043
Debt Instrument [Line Items]
Debt instrument face amount	280,000,000	[5]	280,000,000	[5]
Long-term debt interest rate	4.80%		4.80%
Long-term debt maturity date	2043
Secured Debt | Ameren Illinois Company | Senior Secured Notes430 Due2044 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	250,000,000	[5]
Long-term debt interest rate	4.30%
Long-term debt maturity date	2044
Secured Debt | Ameren Illinois Company | Series 1993 5.90% Due 2023
Debt Instrument [Line Items]
Debt instrument face amount	1,000,000	[7]
Long-term debt interest rate	5.90%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1992 Series due 2022
Debt Instrument [Line Items]
Debt instrument face amount	47,000,000	[8],[9]	47,000,000	[8],[9]
Long-term debt maturity date	2022
Debt instrument, interest rate, maximum	18.00%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1993 5.45% Series due 2028
Debt Instrument [Line Items]
Debt instrument face amount	1,000,000	[7]
Long-term debt interest rate	5.45%							5.45%
Long-term debt maturity date	2028
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series A due 2033
Debt Instrument [Line Items]
Debt instrument face amount	60,000,000	[8],[9]	60,000,000	[8],[9]
Long-term debt maturity date	2033
Debt instrument, interest rate, maximum	18.00%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series B due 2033
Debt Instrument [Line Items]
Debt instrument face amount	50,000,000	[8],[9]	50,000,000	[8],[9]
Long-term debt maturity date	2033
Debt instrument, interest rate, maximum	18.00%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series C due 2033
Debt Instrument [Line Items]
Debt instrument face amount	50,000,000	[8],[9]	50,000,000	[8],[9]
Long-term debt maturity date	2033
Debt instrument, interest rate, maximum	18.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series 1993 5.90% Due 2023
Debt Instrument [Line Items]
Debt instrument face amount	1,000,000	[10],[7]	32,000,000	[10]
Long-term debt interest rate	5.90%
Long-term debt maturity date	2023
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series 1994 A 5.70% Due 2024
Debt Instrument [Line Items]
Debt instrument face amount	1,000,000	[1]	36,000,000	[1]
Long-term debt interest rate	5.70%
Long-term debt maturity date	2024
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series C-1 1993 5.95% Due 2026
Debt Instrument [Line Items]
Debt instrument face amount			35,000,000	[11]
Long-term debt interest rate	5.95%
Long-term debt maturity date	2026
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series C-2 1993 5.70% Due 2026
Debt Instrument [Line Items]
Debt instrument face amount			8,000,000	[11]
Long-term debt interest rate	5.70%
Long-term debt maturity date	2026
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series B-1 1993 Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	17,000,000	[11],[8]	17,000,000	[11],[8]
Long-term debt maturity date	2028
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series1998A 5.40% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount			19,000,000	[1]
Long-term debt interest rate	5.40%
Long-term debt maturity date	2028
Redemption price, percentage	100.00%
Environmental Improvement And Pollution Control Revenue Bonds | Ameren Illinois Company | Series1998B 5.40% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount			$ 33,000,000	[1]
Long-term debt interest rate	5.40%
Long-term debt maturity date	2028
Redemption price, percentage	100.00%

[1] These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy. Less than $1 million principal amount of the bonds remain outstanding.

[2] These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri senior secured notes currently outstanding, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.

[3] Ameren Missouri has agreed, during the life of these notes, not to optionally redeem, purchase or otherwise retire in full its first mortgage bonds. Ameren Missouri has also agreed to prevent a first mortgage bond release date from occurring as long as any of the 8.45% senior secured notes due 2039 and any of the 3.90% senior secured notes due 2042 remain outstanding.

[4] hese notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture. The notes have a fall-away lien provision, and Ameren Illinois could cause these notes to become unsecured at any time by redeeming the pollution control bonds 5.90% Series 1993 due 2023 (of which less than $1 million remains outstanding). Ameren Illinois may resecure these notes if it chooses.

[5] These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois senior secured notes currently outstanding, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2024.

[6] Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.

[7] These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.

[8] The interest rates, and the periods during which such rates apply, vary depending on our selection of defined rate modes. Maximum interest rates could reach 18% depending on the series of bonds. The average interest rates for 2014 and 2013 were as follows: 2014 2013Ameren Missouri 1992 Series due 20220.10% 0.17%Ameren Missouri 1998 Series A due 20330.26% 0.34%Ameren Missouri 1998 Series B due 20330.27% 0.33%Ameren Missouri 1998 Series C due 20330.26% 0.34%Ameren Illinois 1993 Series B-1 due 20280.21% 0.14%

[9] These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri's senior secured notes. The bonds are also backed by an insurance guarantee policy.

[10] These bonds are first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture and are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.

[11] The bonds are callable at 100% of par value.