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Commitments, Credit Risk and Contingencies - Additional Information (Detail)	Mar. 31, 2014
Commitments And Contingencies Disclosure [Abstract]
Percentage of Commitments to extend credit dependent upon the financial condition of the customers	76.10%

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- Definition

Rate of commitments to extend credit dependent on financial condition

+ References

No definition available.

+ Details

Name:	fnb_RateOfCommitmentsToExtendCreditDependentOnFinancialCondition
Namespace Prefix:	fnb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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- Details

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