This element represents the standby letter of credit by the entity.

No definition available.

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

- Definition

Standby Letters of Credit Expiring After Ten Years

+ References

No definition available.

+ Details

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

- Definition

This element represents aggregated standby letters of credit issued under credit facilities and scheduled to expire in ninety six months or less.

+ References

No definition available.

+ Details

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

- Definition

Standby Letters of Credit Expiring within Five Years

+ References

No definition available.

+ Details

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

- Definition

Standby Letters of Credit Expiring within Nine Years

+ References

No definition available.

+ Details

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

- Definition

This element represents aggregated standby letters of credit issued under credit facilities and scheduled to expire in twelve months or less.

+ References

No definition available.

+ Details

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

- Definition

Standby Letters of Credit Expiring within Six Years

+ References

No definition available.

+ Details

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

- Definition

Standby Letters of Credit Expiring within Ten Years

+ References

No definition available.

+ Details

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

- Definition

This element represents aggregated standby letters of credit issued under credit facilities and scheduled to expire in twenty four months or less.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Cash and equivalents whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

+ Details

Name:	us-gaap_RestrictedCashAndCashEquivalentsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Debt and Credit Agreements (Credit Facilities and Letters of Credit) (Details) (Letter of Credit, USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2013 Walnut Creek Project	Apr. 30, 2013 Other EME Subsidiaries	Sep. 17, 2013 Mountain Wind Power I Project	Sep. 17, 2013 Mountain Wind Power II Project	Sep. 30, 2013 Terminated
Line of Credit Facility [Line Items]
Standby letters of credit	$ 169	$ 22				$ 0
Standby letters of credit expiring in 2013	2
Standby letters of credit expiring in 2014	57
Standby letters of credit expiring in 2017	17
Standby letters of credit expiring in 2018	9
Standby letters of credit expiring in 2020	27
Standby letters of credit expiring in 2021	18
Standby letters of credit expiring in 2022	13
Standby letters of credit expiring in 2023	26
Cash collateral	22
Credit facility, maximum borrowing capacity			$ 75	$ 10	$ 16