it's a hundred to one that
It is extremely unlikely that (something will happen or be the case). They say they're working toward a solution, but with congress deadlocked the way they are, I reckon it's a hundred to one that they pass any legislation on the issue.
it’s a hundred, etc. to one that somebody/something will (not) do something
it is almost certain that somebody/something will (not) do something: It’s a hundred to one that the train will be late.It’s a million to one that she’ll finish before us. She always does.