Long-Term Debt And Equity Financings (Narrative) (Details) (USD $)	12 Months Ended					12 Months Ended							12 Months Ended	3 Months Ended				3 Months Ended				3 Months Ended					3 Months Ended					1 Months Ended	0 Months Ended					0 Months Ended						0 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 31, 2013 DRPlus	Dec. 31, 2011 DRPlus	Dec. 31, 2011 401 (K)	Dec. 31, 2013 Union Electric Company	Dec. 31, 2012 Union Electric Company	Jan. 31, 2014 Ameren Illinois Company		Dec. 31, 2013 Ameren Illinois Company	Dec. 31, 2012 Ameren Illinois Company	Dec. 31, 2013 Ameren Missouri and Ameren Illinois	Dec. 31, 2013 Senior Secured Notes 4.80% Due 2043 Ameren Illinois Company Secured Debt		Dec. 31, 2012 Senior Secured Notes 4.80% Due 2043 Ameren Illinois Company Secured Debt		Dec. 31, 2013 Senior Secured Notes 8.875% Due 2013 Ameren Illinois Company Secured Debt		Dec. 31, 2012 Senior Secured Notes 8.875% Due 2013 Ameren Illinois Company Secured Debt		Dec. 31, 2013 1993 5.45% Series due 2028 Union Electric Company Environmental Improvement And Pollution Control Revenue Bonds		Oct. 31, 2013 1993 5.45% Series due 2028 Union Electric Company Environmental Improvement And Pollution Control Revenue Bonds	Dec. 31, 2012 1993 5.45% Series due 2028 Union Electric Company Environmental Improvement And Pollution Control Revenue Bonds		Dec. 31, 2013 4.65% Senior secured notes due 2013 Union Electric Company Secured Debt		Oct. 31, 2013 4.65% Senior secured notes due 2013 Union Electric Company Secured Debt	Dec. 31, 2012 4.65% Senior secured notes due 2013 Union Electric Company Secured Debt		Nov. 30, 2012 Series1992 B 6.20% Due 2012 Ameren Illinois Company Environmental Improvement And Pollution Control Revenue Bonds	Aug. 20, 2012 Senior Secured Notes, 2.70%, Due 2022 Ameren Illinois Company Secured Debt	Dec. 31, 2013 Senior Secured Notes, 2.70%, Due 2022 Ameren Illinois Company Secured Debt		Dec. 31, 2012 Senior Secured Notes, 2.70%, Due 2022 Ameren Illinois Company Secured Debt		Sep. 11, 2012 3.90% Senior secured notes due 2042 Union Electric Company Secured Debt	Dec. 31, 2013 3.90% Senior secured notes due 2042 Union Electric Company Secured Debt		Dec. 31, 2012 3.90% Senior secured notes due 2042 Union Electric Company Secured Debt		Sep. 20, 2012 3.90% Senior secured notes due 2042 Union Electric Company Secured Debt	Sep. 20, 2012 5.25% Senior secured notes due 2012 Union Electric Company Secured Debt	Aug. 27, 2012 Series A 2000 5.50% Due 2014 Ameren Illinois Company Environmental Improvement And Pollution Control Revenue Bonds	Dec. 31, 2013 Minimum Ameren Illinois Company	Jan. 31, 2014 Subsequent Event Ameren Illinois Company Environmental Improvement And Pollution Control Revenue Bonds
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized	100,000,000						7,500,000.0				2,600,000.0
Preferred stock, par value	$ 0.01						$ 1
Preferred stock, shares outstanding	0
Common stock, shares authorized	400,000,000	400,000,000		4,000,000	6,000,000		150,000,000	150,000,000			45,000,000	45,000,000
Common stock, shares issued		0	2,200,000			2,200,000
Common stock, value of shares issued			$ 65,000,000			$ 65,000,000
Debt instrument face amount									1,000,000	[1]				280,000,000	[2]	0	[2]		[3]	150,000,000	[3]	1,000,000	[4]		44,000,000	[4]		[5]		200,000,000	[5]		400,000,000	400,000,000	[2],[6]	400,000,000	[2],[6]	485,000,000	485,000,000	[5],[7]	485,000,000	[5],[7]	485,000,000
Long-term debt interest rate														4.80%				8.875%				5.45%		5.45%			4.65%		4.65%			6.20%	2.70%	2.70%				3.90%	3.90%				3.90%	5.25%	5.50%
Proceeds from issuance of secured debt														276,000,000																			397,000,000					478,000,000
Redemptions of long-term debt																		150,000,000				44,000,000					200,000,000					1,000,000												173,000,000	51,000,000		163,000,000
Bonds interest rate assumption													6.00%
Dividend rate on preferred shares, percentage													7.00%
Excess in indebtedness upon default of maturity	$ 25,000,000
Common stock equity to capitalization ratio											55.00%																																			30.00%

[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.

[2] 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 mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.

[3] These 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 will remain secured only as long as any series of first mortgage bonds issued under the CILCO 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 CILCO first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2023.

[4] 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.

[5] 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 first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.

[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] 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.