about how much of the american fleet was destroyed from the bombing of pearl harbor?

Virtually all the heavy ships, cruisers and battle wagons were destroyed or rendered inoperable. The carriers luckily were out at sea. The outcome of the war would probably have been different had those carriers been in port.

Actually the term "destroyed" isn't quite accurate. The Arizona was destroyed - most of the other ships were raised and repaired. It took time, but the Japanese strike didn't destroy the shipyard or repair docks. The harbor was shallow enough to allow salvage. Something like 80% of the ships were returned to service before the end of the war.

Immediately after the attack, the situation looked terrible, but within months ships were returning to duty, it took longer to repair some than others.

It was indeed good fortune that the carriers were out at sea when the attack happened. It's doubly fortunate that the planned third attack wave of the Japanese wasn't carried out. That would have targeted the repair docks and the fuel storage areas.