Junior Subordinated Debt (Narrative) (Detail)	Dec. 31, 2012
Subordinated Borrowing [Line Items]
Number of unconsolidated subsidiary trusts	4
Percent of the common equity of each Trust owned by the Corporation	100.00%

Percentage Of Each Trust Common Equity Owned By Corporation

No definition available.

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