Divestiture Transactions and Discontinued Operations (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			3 Months Ended					1 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2013 New Ameren Energy Resources Company, LLC	Mar. 31, 2014 New Ameren Energy Resources Company, LLC	Mar. 14, 2013 New Ameren Energy Resources Company, LLC	Mar. 31, 2014 Notes Payable, Other Payables [Member] New Ameren Energy Resources Company, LLC	Dec. 31, 2013 Notes Payable, Other Payables [Member] New Ameren Energy Resources Company, LLC	Jan. 31, 2014 Elgin, Gibson City and Grand Tower Energy Centers	Dec. 31, 2013 Elgin, Gibson City and Grand Tower Energy Centers	Mar. 31, 2014 Ameren Energy Marketing Company [Member]	Mar. 31, 2014 Guarantee Type, Other [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Escrow Deposit, Reserve Period	2 years
Proceeds from Sales of Business, Affiliate and Productive Assets									$ 168.0	$ 137.5
Proceeds from Asset Sale Held in Escrow									17
Impairment of assets to be disposed of				155
Discontinued operations deferred tax expense				98
Discontinued operations deferred tax benefit				63
Loss from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	1	199
Asset retirement obligations	373		369
Range of possible loss maximum					34.0
Other deferred credits and liabilities	554		538		29
Accounts and wages payable	559		806		5
Notes, Loans and Financing Receivable, Net, Noncurrent							27	18
Buyer's indemnification guarantee obligation						25
Guarantees Outstanding	184										171	13
Guarantees, Maximum Exposure											17
Letters of Credit Outstanding, Amount	$ 9