INCOME TAXES - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Amount
Statutory federal tax rate	$ 141
State and local income taxes, net of federal income tax effect	10
Tax credits:
Renewable energy investment tax credits	(37)
LIHTC	(21)
Other tax credits	(5)
Non-taxable or non-deductible items:
Tax-exempt interest	(9)
Cash surrender value on BOLI	(4)
Tax credit cost amortization, net of tax benefits	20
FDIC premium disallowance	7
Other non-taxable or non-deductible items	3
Other	(1)
Total income taxes	$ 104	$ 90	$ 99
Percent
Statutory federal tax rate	21.00%	21.00%	21.00%
State taxes, net of federal benefit	1.60%	1.50%	1.90%
Tax credits:
Renewable energy investment tax credits	(5.60%)
LIHTC	(3.20%)
Other tax credits	(0.70%)
Non-taxable or non-deductible items:
Tax-exempt interest	(1.30%)	(1.50%)	(1.60%)
Cash surrender value on BOLI	(0.60%)	(0.60%)	(0.50%)
Tax credit cost amortization, net of tax benefits	2.90%	3.20%	2.30%
Tax credits		(9.00%)	(7.30%)
FDIC premium disallowance	1.10%	1.30%	1.00%
Other non-taxable or non-deductible items	0.40%
Other items	(0.10%)	0.40%	0.10%
Effective tax rate	15.50%	16.30%	16.90%

Effective Income Tax Rate Reconciliation, Cash Surrender Value Of Life Insurance, Amount

No definition available.

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Namespace Prefix:	fnb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the cash surrender value of life insurance policies.

+ References

No definition available.