Related Party Transactions (Details) (USD $) In Millions	3 Months Ended	9 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Sep. 30, 2010
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties	$ 0.3		$ 0.3		$ 1.9
Accounts Payable, Related Parties, Current and Noncurrent	17.5		17.5		9.2
WGEServices
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties	1.2		1.2		2.3
Related Party Transaction, Revenues from Transactions with Related Party	3.0	4.2	20.5	20.2
Related Party Purchased Receivables			$ 0.4

Amount for accounts payable to related parties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph k
-Subparagraph 1
-Article 4

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 2
-Subparagraph d

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 17
-Article 7

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 3
-Article 7

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph k
-Subparagraph 1
-Article 4

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 2
-Subparagraph d

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 3
-Subparagraph a
-Article 5

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenues, net of returns and allowances, realized from sales and other transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 57
-Paragraph 2
-Subparagraph c

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The purchased amount of receivables of a related party

+ Details

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Namespace Prefix:	wgl
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration