Long-Term Debt And Equity Financings (Aggregate Principal Amount of Senior Notes) (Details) (USD $)	12 Months Ended			12 Months Ended	0 Months Ended						0 Months Ended						0 Months Ended						0 Months Ended						0 Months Ended						0 Months Ended
	Dec. 31, 2013 Ameren Illinois Company	Jan. 31, 2014 Ameren Illinois Company		Dec. 31, 2013 Ameren Illinois Company 2.70% Senior Notes Due 2022	Aug. 27, 2012 Ameren Illinois Company Secured Debt Senior Secured Notes 9.75% Due 2018		Dec. 31, 2013 Ameren Illinois Company Secured Debt Senior Secured Notes 9.75% Due 2018		Dec. 31, 2012 Ameren Illinois Company Secured Debt Senior Secured Notes 9.75% Due 2018		Aug. 27, 2012 Ameren Illinois Company Secured Debt Senior Secured Notes 6.25% Due 2018		Dec. 31, 2013 Ameren Illinois Company Secured Debt Senior Secured Notes 6.25% Due 2018		Dec. 31, 2012 Ameren Illinois Company Secured Debt Senior Secured Notes 6.25% Due 2018		Sep. 20, 2012 Union Electric Company Secured Debt 6.00% Senior secured notes due 2018		Dec. 31, 2013 Union Electric Company Secured Debt 6.00% Senior secured notes due 2018		Dec. 31, 2012 Union Electric Company Secured Debt 6.00% Senior secured notes due 2018		Sep. 20, 2012 Union Electric Company Secured Debt 6.70% Senior secured notes due 2019		Dec. 31, 2013 Union Electric Company Secured Debt 6.70% Senior secured notes due 2019		Dec. 31, 2012 Union Electric Company Secured Debt 6.70% Senior secured notes due 2019		Sep. 20, 2012 Union Electric Company Secured Debt 5.10% Senior secured notes due 2018		Dec. 31, 2013 Union Electric Company Secured Debt 5.10% Senior secured notes due 2018		Dec. 31, 2012 Union Electric Company Secured Debt 5.10% Senior secured notes due 2018		Sep. 20, 2012 Union Electric Company Secured Debt 5.10% Senior secured notes due 2019		Dec. 31, 2013 Union Electric Company Secured Debt 5.10% Senior secured notes due 2019		Dec. 31, 2012 Union Electric Company Secured Debt 5.10% Senior secured notes due 2019		Dec. 31, 2013 Union Electric Company Secured Debt 3.90% Senior secured notes due 2042		Dec. 31, 2012 Union Electric Company Secured Debt 3.90% Senior secured notes due 2042		Sep. 20, 2012 Union Electric Company Secured Debt 3.90% Senior secured notes due 2042	Sep. 11, 2012 Union Electric Company Secured Debt 3.90% Senior secured notes due 2042	Sep. 20, 2012 Maximum Union Electric Company Secured Debt 5.10% Senior secured notes due 2018
Debt Instrument [Line Items]
Payments of Debt Issuance Costs				$ 21,000,000
Long-term debt interest rate				2.70%	9.75%		9.75%				6.25%		6.25%				6.00%		6.00%				6.70%		6.70%				5.10%		5.10%				5.10%		5.10%				3.90%				3.90%	3.90%
Amortization of Financing Costs	15,000,000
Principal Amount Repurchased					87,000,000						194,000,000						71,000,000						121,000,000						1,000,000	[1]					56,000,000
Premium Plus Accrued and Unpaid Interest					36,000,000	[2]					47,000,000	[2]					19,000,000	[3]					35,000,000	[3]											12,000,000	[3]											1,000,000
Principal Amount Outstanding After Tender Offer		$ 1,000,000	[4]	$ 400,000,000	$ 313,000,000		$ 313,000,000	[5],[6]	$ 313,000,000	[5],[6]	$ 144,000,000		$ 144,000,000	[5],[6]	$ 144,000,000	[5],[6]	$ 179,000,000		$ 179,000,000	[7],[8]	$ 179,000,000	[7],[8]	$ 329,000,000		$ 329,000,000	[7],[8]	$ 329,000,000	[7],[8]	$ 199,000,000	[1]	$ 199,000,000	[8]	$ 199,000,000	[8]	$ 244,000,000		$ 244,000,000	[8]	$ 244,000,000	[8]	$ 485,000,000	[7],[8]	$ 485,000,000	[7],[8]	$ 485,000,000	$ 485,000,000

[1] Amount is less than $1 million.

[2] Premiums paid in the amount of $21 million in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $400 million 2.70% senior secured notes due 2022. Premiums of $15 million were expensed in 2013 as a result of disallowances in the ICC's December 2013 electric and natural gas rate orders. See Note 2 – Rate and Regulatory Matters for further information regarding the disallowances

[3] The premiums paid in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $485 million 3.90% senior secured notes due 2042.

[4] 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.

[5] 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.

[6] 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.

[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.

[8] 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.