Long-Term Debt and Equity Financings (Schedule of Debt Redemptions) (Details) (Ameren Illinois Company, USD $)				0 Months Ended					0 Months Ended																													1 Months Ended
	Jan. 31, 2014		Dec. 31, 2013 2.70% Senior Notes Due 2022	Aug. 27, 2012 Secured Debt Senior Secured Notes 9.75% Due 2018	Dec. 31, 2013 Secured Debt Senior Secured Notes 9.75% Due 2018		Dec. 31, 2012 Secured Debt Senior Secured Notes 9.75% Due 2018		Aug. 27, 2012 Secured Debt Senior Secured Notes 6.25% Due 2018	Dec. 31, 2013 Secured Debt Senior Secured Notes 6.25% Due 2018		Dec. 31, 2012 Secured Debt Senior Secured Notes 6.25% Due 2018		Dec. 31, 2013 Environmental Improvement And Pollution Control Revenue Bonds Series 1993 5.90% Due 2023		Dec. 31, 2012 Environmental Improvement And Pollution Control Revenue Bonds Series 1993 5.90% Due 2023		Dec. 31, 2013 Environmental Improvement And Pollution Control Revenue Bonds Series 1994 A 5.70% Due 2024		Dec. 31, 2012 Environmental Improvement And Pollution Control Revenue Bonds Series 1994 A 5.70% Due 2024		Dec. 31, 2013 Environmental Improvement And Pollution Control Revenue Bonds Series C-1 1993 5.95% Due 2026		Dec. 31, 2012 Environmental Improvement And Pollution Control Revenue Bonds Series C-1 1993 5.95% Due 2026		Dec. 31, 2013 Environmental Improvement And Pollution Control Revenue Bonds Series C-2 1993 5.70% Due 2026		Dec. 31, 2012 Environmental Improvement And Pollution Control Revenue Bonds Series C-2 1993 5.70% Due 2026		Dec. 31, 2013 Environmental Improvement And Pollution Control Revenue Bonds Series1998A 5.40% Due 2028		Dec. 31, 2012 Environmental Improvement And Pollution Control Revenue Bonds Series1998A 5.40% Due 2028		Dec. 31, 2013 Environmental Improvement And Pollution Control Revenue Bonds Series1998B 5.40% Due 2028		Dec. 31, 2012 Environmental Improvement And Pollution Control Revenue Bonds Series1998B 5.40% Due 2028		Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds	Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds Series 1993 5.90% Due 2023		Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds Series 1994 A 5.70% Due 2024		Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds Series C-1 1993 5.95% Due 2026	Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds Series C-2 1993 5.70% Due 2026	Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds Series1998A 5.40% Due 2028	Jan. 31, 2014 Subsequent Event Environmental Improvement And Pollution Control Revenue Bonds Series1998B 5.40% Due 2028
Debt Instrument [Line Items]
Redemptions of long-term debt				$ 87,000,000					$ 194,000,000																													$ 163,000,000	$ 32,000,000	[1]	$ 36,000,000	[1]	$ 35,000,000	$ 8,000,000	$ 19,000,000	$ 33,000,000
Debt instrument face amount	$ 1,000,000	[2]	$ 400,000,000	$ 313,000,000	$ 313,000,000	[3],[4]	$ 313,000,000	[3],[4]	$ 144,000,000	$ 144,000,000	[3],[4]	$ 144,000,000	[3],[4]	$ 32,000,000	[5]	$ 32,000,000	[5]	$ 36,000,000	[2]	$ 36,000,000	[2]	$ 35,000,000	[6]	$ 35,000,000	[6]	$ 8,000,000	[6]	$ 8,000,000	[6]	$ 19,000,000	[2]	$ 19,000,000	[2]	$ 33,000,000	[2]	$ 33,000,000	[2]

[1] Less than $1 million principal amount of the bonds remain outstanding as of January 31, 2014.

[2] 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.

[3] 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.

[4] 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.

[5] 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.

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