Summary of Significant Accounting Policies (Purchased Emission Allowances, Exemptions and Offsets) (Details) (Other Long-Term Assets, USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Other Long-Term Assets
Indefinite-lived Intangible Assets [Line Items]
Purchased emission allowances, Noncurrent	$ 16	$ 76

This element represents the emission allowances purchased, which are included in other long-term assets of the consolidated balance sheet.

No definition available.

Name:	eme_EmissionAllowancesPurchasedNoncurrent
Namespace Prefix:	eme_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant