Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative Instrument Detail [Abstract]
Counterparty letters of credit held as collateral	$ 1	$ 1

Counterparty letters of credit held as collateral.

No definition available.

Name:	aee_LettersOfCreditHeldAsCollateral
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant