Derivative Financial Instruments (Potential Loss On Counterparty Exposures) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Concentration Risk [Line Items]
Potential loss on counterparty exposures related to derivative contracts	$ 5aee_DerivativePotentialLoss
Union Electric Company
Concentration Risk [Line Items]
Potential loss on counterparty exposures related to derivative contracts	$ 5

Potential loss on counterparty exposures related to derivative instruments, including NPNS contracts, after consideration of all collateral held and application of master trading and netting agreements.

No definition available.

Name:	aee_DerivativePotentialLoss
Namespace Prefix:	aee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant