Name:	fnb_AnnuityEquivalentOfContributionToDefinedContributionPlanDeductedFromMonthlyBenefitOfBasicRetirementPlan
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Data Type:	num:percentItemType
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Period Type:	duration

Consecutive period of highest average monthly cash compensation used to determine the basic benefit under the company's basic retirement plan.

No definition available.

Name:	fnb_DefinedBenefitPlanAssumptionsConsecutivePeriodOfHighestAverageCompensation
Namespace Prefix:	fnb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Period prior to retirement used to determine the highest average monthly salary used to determine the basic benefit under the company's basic retirement plan.

No definition available.

Name:	fnb_DefinedBenefitPlanAssumptionsConsecutiveTermOfEmployment
Namespace Prefix:	fnb_
Data Type:	xbrli:durationItemType
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Period Type:	duration

Percentage of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

Name:	fnb_DefinedContributionPlanEmployerDiscretionaryContributionPercentage
Namespace Prefix:	fnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Disclosure Retirement Plans [Abstract]

No definition available.

Name:	fnb_DisclosureRetirementPlansAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Number of supplemental non-qualified retirement plans sponsored by the entity.

No definition available.

Name:	fnb_NumberOfSupplementalNonQualifiedRetirementPlans
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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Percentage of compensation at the end of the year representing an automatic contribution that the company makes into the defined contribution plan.

No definition available.

Name:	fnb_PercentageForEmployeeAutomaticContribution
Namespace Prefix:	fnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The amount of the cost recognized during the period for defined contribution plans.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

Name:	us-gaap_DefinedContributionPlanCostRecognized
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage employer matches of the employee's percentage contribution matched.

No definition available.