Accelerated AMT Credit Refund Received Under CARES Act

No definition available.

Name:	nfg_AcceleratedAMTCreditRefundReceivedUnderCARESAct
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

First Installment of AMT Credit Refunds

+ References

No definition available.

+ Details

Name:	nfg_FirstInstallmentOfAMTCreditRefunds
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Income Taxes [Line Items]

+ References

No definition available.

+ Details

Name:	nfg_IncomeTaxesLineItems
Namespace Prefix:	nfg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Regulatory assets representing future amounts collectible from customers corresponding to additional deferred income taxes not previously recorded because of ratemaking practices.

+ References

No definition available.

+ Details

Name:	nfg_RecoverableFutureTaxes
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reversal of estimate for potential sequestration of AMT credit refunds under 2017 Tax Reform Act.

+ References

No definition available.

+ Details

Name:	nfg_ReversalofEstimateForPotentialSequestrationofAMTCreditRefundsUnder2017TaxReformAc
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Noncurrent regulatory liability representing the reduction of previously recorded deferred income taxes associated with rate-regulated activities that are expected to be refundable to customers as of the end of the period.

+ References

No definition available.

+ Details

Name:	nfg_TaxesRefundableToCustomers
Namespace Prefix:	nfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319

+ Details

Name:	us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32559-109319

+ Details

Name:	us-gaap_TaxCreditCarryforwardAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 10B
-URI http://asc.fasb.org/extlink&oid=123427490&loc=SL37586934-109318

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319

+ Details

Name:	us-gaap_UnrecognizedTaxBenefits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=nfg_DeferredIncomeTaxesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TaxCreditCarryforwardAxis=nfg_AlternativeMinimumTaxCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2018
Income Taxes [Line Items]
First Installment of AMT Credit Refunds Received			$ 42,500
Accelerated AMT Credit Refund Received Under CARES Act			42,500
Taxes Refundable to Customers		$ 354,089	357,508
Recoverable Future Taxes		121,992	118,310
Reversal of estimate for potential sequestration of AMT credit refunds	$ 5,000
Valuation Allowance	0	57,645	63,205	$ 5,000
Unrecognized Tax Benefits	$ 0	0	0
Deferred Income Taxes [Member]
Income Taxes [Line Items]
Taxes Refundable to Customers		354,100	357,500
Recoverable Future Taxes		$ 122,000	$ 118,300
Alternative Minimum Tax Credit [Member]
Income Taxes [Line Items]
Tax Credit Carryforwards				$ 85,000