Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
2012	$ 179,000,000
2013	355,000,000
2014	585,000,000
2015	120,000,000
2016	395,000,000
Thereafter	5,232,000,000
Total	6,866,000,000
Unamortized discount and premium	1,000,000
Parent Company [Member]
Unamortized discount and premium	1,000,000	2,000,000
Union Electric Company [Member]
Unamortized discount and premium	5,000,000	6,000,000
Ameren Illinois Company [Member]
Unamortized discount and premium	8,000,000	9,000,000
Ameren Energy Generating Company [Member]
Unamortized discount and premium	1,000,000	1,000,000
Ameren Missouri [Member]
Unamortized discount and premium	$ 5,000,000

The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

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-Section 45

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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