Fair Value Measurements (Narrative) (Details) (USD $) In Millions	6 Months Ended	12 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Fair Value Measurements
Loss recognized related to valuation adjustments for counterparty default risk	$ 1
Gain recognized related to valuation adjustments for counter party default risk		1
Valuation adjustments related to derivative contracts	$ 1		$ 2

Name:

aee_GainLossRecognizedRelatedToValuationAdjustmentsForCounterpartyDefaultRisk

Namespace Prefix:

aee

Data Type:

xbrli:monetaryItemType

Balance Type:

debit

Period Type:

duration