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Business Segment Information - Schedule of Long-Lived Assets by Geographical Areas (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023
--- | --- | --- | ---
United States |  |  |
Revenues from External Customers and Long-Lived Assets [Line Items] |  |  |
Long-lived assets | $ 8,308,377 | $ 7,963,851 | $ 7,865,832

X
- Definition Amount of long-lived assets, including all non-current assets and property, plant and equipment. + References No definition available. + Details
Name: | nfg_NoncurrentAssets1
Namespace Prefix: | nfg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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
Name: | us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |