Commitments And Contingencies (Pumped-Storage Hydroelectric Facility Breach) (Detail) - Union Electric Company $ in Millions	Jun. 30, 2015 USD ($)
Loss Contingencies [Line Items]
Insurance settlements receivable	$ 41
Insurance Claim	$ 53

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration