BORROWINGS - Junior Subordinated Debt Trusts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 72	$ 67
Trust Preferred Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	77
Common Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	3
F.N.B. Statutory Trust II
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
Interest Rate	2.48%
F.N.B. Statutory Trust II | LIBOR
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.65%
F.N.B. Statutory Trust II | Trust Preferred Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
F.N.B. Statutory Trust II | Common Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	1
Yadkin Valley Statutory Trust I
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
Interest Rate	2.15%
Yadkin Valley Statutory Trust I | LIBOR
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.32%
Yadkin Valley Statutory Trust I | Trust Preferred Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 25
Yadkin Valley Statutory Trust I | Common Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	1
FNB Financial Services Capital Trust I
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 23
Interest Rate	2.46%
FNB Financial Services Capital Trust I | LIBOR
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.46%
FNB Financial Services Capital Trust I | Trust Preferred Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 25
FNB Financial Services Capital Trust I | Common Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	1
Patapsco Statutory Trust I
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 5
Interest Rate	2.31%
Patapsco Statutory Trust I | LIBOR
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.48%
Patapsco Statutory Trust I | Trust Preferred Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 5
Patapsco Statutory Trust I | Common Securities
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 0