BORROWINGS - Junior Subordinated Debt Trusts (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Subordinated Borrowing [Line Items]
Junior subordinated debt	$ 66	$ 111
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	3.77%
F.N.B. Statutory Trust II [Member] | 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	3.44%
Yadkin Valley Statutory Trust I [Member] | 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	3.56%
FNB Financial Services Capital Trust I [Member] | 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