Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
Sep. 30, 2023 USD ($) plan	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Alternative Revenue Program [Line Items]
Number of asset management plans under management \| plan	2
Composite depreciation rate for regulated property, plant and equipment	3.00%	3.00%	3.00%
Impairment of long-lived assets	$ 0	$ 0	$ 0
Derivative, cash collateral	0	$ 0
Self-insured retention	$ 1,000,000
Pipeline and Storage
Alternative Revenue Program [Line Items]
Regulatory mechanism threshold (in percent)	75.00%	75.00%	75.00%
Rate case revenue benchmark	$ 69,400,000

Alternative Revenue Program [Line Items]

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- Definition

Amount of cash pledged as collateral against derivative liabilities.

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- Definition

Number of Asset Management Plans Under Management

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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.

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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.

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- Definition

Self Insured Retention Deductible

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- Definition

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482099/360-10-50-2

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482130/360-10-45-4

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- Definition

Composite depreciation rate for public utility plants in service.

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