Name:	fnb_AssumptionForFairValueOnSecuritizationDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesAnnualizedConstantPrepaymentRate
Namespace Prefix:	fnb_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

Sensitivity Analysis Of Fair Value Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities Impact Of One Point Zero Percent Adverse Change In Prepayment Speed

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfOnePointZeroPercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity analysis of fair value of interests continued to be held by transferor servicing assets or liabilities impact of one point zero percent favorable change in prepayment speed.

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfOnePointZeroPercentFavorableChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity Analysis Of Fair Value Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities Impact Of Three Point Zero Percent Adverse Change In Prepayment Speed

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfThreePointZeroPercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity Analysis Of Fair Value Of Interests Continued To Be Held By Transferor Servicing Assets Or Liabilities Impact Of Two Point Zero Percent Adverse Change In Prepayment Speed

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfTwoPointZeroPercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity analysis of fair value of interests continued to be held by transferor servicing assets or liabilities impact of two point zero percent favorable change in prepayment speed.

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfTwoPointZeroPercentFavorableChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity analysis of fair value of interests continued to be held by transferor servicing assets or liabilities impact of zero point five zero percent adverse change in prepayment speed.

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfZeroPointFiveZeroPercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity analysis of fair value of interests continued to be held by transferor servicing assets or liabilities impact of zero point five zero percent favorable change in prepayment speed.

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfZeroPointFiveZeroPercentFavorableChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity analysis of fair value of interests continued to be held by transferor servicing assets or liabilities impact of zero point two five percent adverse change in prepayment speed.

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfZeroPointTwoFivePercentAdverseChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Sensitivity analysis of fair value of interests continued to be held by transferor servicing assets or liabilities impact of zero point two five percent favorable change in prepayment speed.

No definition available.

Name:	fnb_SensitivityAnalysisOfFairValueOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesImpactOfZeroPointTwoFivePercentFavorableChangeInPrepaymentSpeed
Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-4

Name:	us-gaap_AssumptionForFairValueAsOfBalanceSheetDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Discount rate which is used to value residual cash flows generated by financial assets of the securitization, asset-backed financing arrangement, or similar transfer for initial fair value measurement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-3

Name:	us-gaap_AssumptionForFairValueOnSecuritizationDateOfInterestsContinuedToBeHeldByTransferorServicingAssetsOrLiabilitiesDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Weighted average life of securitized assets for initial fair value measurement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-3