Fair Value Measurements (Details) - EBP 002 - USD ($)	Dec. 31, 2025	Dec. 31, 2024
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	$ 585,743,136	$ 520,560,705
Level 1
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	585,743,136	520,560,705
Level 2
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
Level 3
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
F.N.B. Corporation common stock
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	117,165,090	119,345,286
F.N.B. Corporation common stock \| Level 1
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	117,165,090	119,345,286
F.N.B. Corporation common stock \| Level 2
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
F.N.B. Corporation common stock \| Level 3
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
Money market fund
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	10,843	9,928
Money market fund \| Level 1
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	10,843	9,928
Money market fund \| Level 2
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
Money market fund \| Level 3
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
Mutual fund investments
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	468,567,203	401,205,491
Mutual fund investments \| Level 1
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	468,567,203	401,205,491
Mutual fund investments \| Level 2
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	0	0
Mutual fund investments \| Level 3
EBP, Investment, Fair Value and NAV [Line Items]
Investments, at fair value:	$ 0	$ 0

Fair value of investment, excluding plan interest in master trust, held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)). Includes, but is not limited to, derivative, investment measured at net asset value per share as practical expedient, and insurance contract not meeting fully-benefit responsive investment criteria.

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+ Details

- Definition

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.

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