Divestiture Transactions and Discontinued Operations (Components of Assets and Liabilities on Consolidated Balance Sheet) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset retirement obligations	$ 369		$ 349
Current assets of discontinued operations
Cash and cash equivalents			25		7
Accounts receivable and unbilled revenue	5		102
Materials and supplies	5		135
Mark-to-market derivative assets			102
Property and plant, net	142		748
Accumulated deferred income taxes, net	13	[1]	395	[1]
Other assets			104
Total current assets of discontinued operations	165		1,611		3,721
Current liabilities of discontinued operations
Accounts payable and other current obligations	5		141
Mark-to-market derivative liabilities			63
Long-term debt, net			824
Asset retirement obligations	40	[2]	97	[2]
Pension and other postretirement benefits			40
Other liabilities			28
Total current liabilities of discontinued operations	45		1,193
Accumulated other comprehensive income (loss)		[3]	19	[3]
Noncontrolling Interest		[4]	8	[4]
Electric Energy Inc
Current liabilities of discontinued operations
Percentage of EEI not owned by Ameren			20.00%
Shutdown Of Meredosia And Hutsonville Energy Centers [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset retirement obligations	$ 31		$ 26

[1] (a)The December 31, 2013 balance primarily consists of deferred income tax assets related to the abandoned Meredosia and Hutsonville energy centers.

[2] (b)Includes AROs associated with the abandoned Meredosia and Hutsonville energy centers of $31 million and $26 million at December 31, 2013, and 2012, respectively.

[3] (c)Accumulated other comprehensive income related to discontinued operations included in “Accumulated other comprehensive loss” on Ameren’s December 31, 2012, consolidated balance sheet. This balance related to New AER assets and liabilities that were realized or removed from Ameren’s consolidated balance sheet either before or at the December 2, 2013 closing of the New AER divestiture.

[4] (d)The 20% ownership interest of EEI not owned by Ameren was included in “Noncontrolling interests” on Ameren’s December 31, 2012, consolidated balance sheet. This noncontrolling interest was removed from Ameren’s consolidated balance sheet at the December 2, 2013 closing of the New AER divestiture.