Concentrations of Credit Risk - Additional Information (Details) customer in Millions, $ in Millions	12 Months Ended
Sep. 30, 2020 USD ($) customer State counterparty
Concentration Risk [Line Items]
Number of large counterparties for which credit risk is disclosed \| counterparty	5
Number of counterparties with investment-grade rating \| counterparty	4
Utility Companies And Their Marketing Affiliates
Concentration Risk [Line Items]
Accounts receivable \| $	$ 73.0
Five Largest Counterparties
Concentration Risk [Line Items]
Accounts receivable \| $	$ 35.7
Gas Utility
Concentration Risk [Line Items]
Number of customer serves \| customer	1.7
Number of state serves across multiple rate classes \| State	3

Number of large counterparties in terms of net accounts receivable exposure for which credit risk is reported.

No definition available.

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- Definition

Number of counterparties, investment-grade rated or owned by investment-grade rated integrated utilities.

+ References

No definition available.

+ Details

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- Definition

Number of customer serves.

+ References

No definition available.

+ Details

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- Definition

Number of state serves across multiple rate classes.

+ References

No definition available.

+ Details

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- 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.

+ References

No definition available.

+ Details

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- Definition

This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(5))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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