Commitments and Contingencies (Other Commitments - Fuel Supply Contracts) (Details) (Midwest Generation LLC, Coal Supply Agreements, USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Jul. 31, 2013 Subsequent Event
Long-term Purchase Commitment [Line Items]
Purchase commitments, remainder of 2013	$ 162	$ 35
Purchase commitments, 2014	150
Total commitments under existing agreements	$ 312

Minimum amount of purchase arrangement maturing in the remainder of the fiscal year following the latest fiscal year ended. Includes, but is not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

No definition available.

Name:	eme_PurchaseObligationFutureMinimumPaymentsRemainderofFiscalYear
Namespace Prefix:	eme_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant