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Data Type:	xbrli:monetaryItemType
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The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income or regulatory assets and regulatory liabilities as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan.

No definition available.

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Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.

No definition available.

Name:	nfg_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeRegulatoryAssetRegulatoryLiabilityNetPriorServiceCostCreditBeforeTax
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

The amounts in accumulated other comprehensive income and regulatory assets and regulatory liabilities related to gains and losses that are not recognized immediately and are expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

No definition available.

Name:	nfg_DefinedBenefitPlanAmortizationOfNetGainsLossesExpectedToBeRecognizedNextYear
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Data Type:	xbrli:monetaryItemType
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The amounts in accumulated other comprehensive income or regulatory assets and liabilities related to prior service cost or credit expected to be recognized as components of net periodic benefit cost over the next fiscal year that follows the most recent annual statement of financial position presented.

No definition available.

Name:	nfg_DefinedBenefitPlanAmortizationOfNetPriorServiceCostCreditExpectedToBeRecognizedInNextFiscalYear
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Data Type:	xbrli:monetaryItemType
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The aggregate amount in accumulated other comprehensive income or regulatory assets and regulatory liabilities expected to be recognized as a component of net periodic benefit cost over the fiscal year that follows the most recent annual statement of financial position presented (including the net gain or loss, net prior service cost or credit, and net transition asset or obligation).

No definition available.

Name:	nfg_DefinedBenefitPlanAmountsThatWillBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossOrRegulatoryAssetRegulatoryLiabilityInNextFiscalYear
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Data Type:	xbrli:monetaryItemType
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The pretax cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that occurred during the period. The cost has not yet been recognized in net periodic benefit cost. A plan amendment includes provisions that grant increased (decreased) benefits based on services rendered in prior periods.

No definition available.

Name:	nfg_OtherComprehensiveIncomeRegulatoryAssetRegulatoryLiabilityDefinedBenefitPlanNetPriorServiceCostCreditArisingDuringPeriodBeforeTax
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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Amounts recognized in other comprehensive income (but not yet recognized in net periodic benefit cost), including the net gain (loss) and net prior service cost (credit), or regulatory assets and regulatory liabilities arising during the period. Also includes reclassification adjustments out of other comprehensive income as a result of being recognized as components of net periodic benefit cost for the period.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Pretax change in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan, that has not been recognized in net periodic benefit cost.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Before tax amount of the income statement impact or change in regulatory assets and regulatory liabilities of the reclassification adjustment for actuarial gain (loss) recognized as a component of net periodic benefit cost.

No definition available.

Name:	nfg_OtherComprehensiveIncomeRegulatoryAssetRegulatoryLiabilityReclassificationOfDefinedBenefitPlansNetGainLossRecognizedInNetPeriodicBenefitCostBeforeTax
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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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.

No definition available.