Commitments, Credit Risk and Contingencies - Additional Information (Detail)	Sep. 30, 2013
Commitments And Contingencies Disclosure [Abstract]
Percentage of Commitments to extend credit dependent upon the financial condition of the customers	78.30%

Rate of commitments to extend credit dependent on financial condition

No definition available.

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