What type of faith in the Trinity? Do you mean believing in the Trinity? Because even Satan believes. Knows. So faith cannot be just believing in the Trinity. It must be another faith. A saving faith. Otherwise it seems Satan could be saved. And we all know that isn't so.
I said faith - I never mentioned belief. Faith has a different connotation than belief.
Faith has its roots in the Latin word fides - Trust is among its nuanced meanings.
Faith in the Trinity means trusting in its saving power. Is that what you meant by (a) saving faith? If so, that is what I meant, as well.