BORROWINGS - Junior Subordinated Debt Trusts (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 66	$ 66
London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Basis spread on variable rate	2.40%
Trust Preferred Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 72
Common Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	3
F.N.B. Statutory Trust II [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
Interest Rate	1.96%
F.N.B. Statutory Trust II [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.65%
F.N.B. Statutory Trust II [Member] | Trust Preferred Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
F.N.B. Statutory Trust II [Member] | Common Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	1
Yadkin Valley Statutory Trust I [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
Interest Rate	1.63%
Yadkin Valley Statutory Trust I [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.32%
Yadkin Valley Statutory Trust I [Member] | Trust Preferred Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 25
Yadkin Valley Statutory Trust I [Member] | Common Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	1
FNB Financial Services Capital Trust I [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 22
Interest Rate	1.77%
FNB Financial Services Capital Trust I [Member] | London Interbank Offered Rate (LIBOR) [Member]
Subordinated Borrowing [Line Items]
Basis spread on variable rate	1.46%
FNB Financial Services Capital Trust I [Member] | Trust Preferred Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 25
FNB Financial Services Capital Trust I [Member] | Common Securities [Member]
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 1