Summary of Significant Accounting Policies - Narrative (Details) - USD ($)	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Alternative Revenue Program [Line Items]
Composite depreciation rate for regulated property, plant and equipment	3.00%	3.00%	3.10%
Asset retirement obligations	$ 18,400,000	$ 20,300,000
Asset retirement costs	12,800,000	14,400,000
Cash held in margin accounts	$ 0	$ 0
Pipeline and Storage
Alternative Revenue Program [Line Items]
Regulatory mechanism threshold	75.00%
Rate case revenue benchmark	$ 69,400,000

Alternative Revenue Program [Line Items]

No definition available.

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- Definition

Asset retirement costs recorded as a component of property, plant and equipment that will be depreciated over the remaining life of the underlying associated assets.

+ References

No definition available.

+ Details

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- Definition

Amount of cash pledged as collateral against derivative liabilities.

+ References

No definition available.

+ Details

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- Definition

Rate case revenue benchmark as set in the APT rate case filing and part of our regulatory mechanism. This revenue benchmark is used in calculating the total revenue to be billed or returned to customers.

+ References

No definition available.

+ Details

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- Definition

APT has a regulatory mechanism that requires that we share with its tariffed customers a set percentage, as determined through the rate case filings, of the difference between the total non-tariffed revenues earned during a test period and a revenue benchmark.

+ References

No definition available.

+ Details

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Composite depreciation rate for public utility plants in service.

+ References

No definition available.

+ Details

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