This bears repeating!
Also, the point of derivatives is often to insure against some unfavorable market event. If JP Morgan Chase can't pay up, the innocent counter-party gets screwed. Like wrecking your car and then finding out the insurance company can't pay your claim.
Big mortgage lenders like Fannie Mae and Freddi Mac borrow short and lend long, but use derivatives to hedge the risk of rising interest rates. But if the hedge is no good, then they're quickly in trouble and Uncle Sam will have to bail them out.