Again, based on the other states that I'm familiar with (and not MT specifically), you would enter 0 there too. The software needs those two numbers (income double taxed and tax paid on the double taxed income) to calculated the credit for tax paid to the other state. You're not claiming that on the MT return.
If you claim it, at all, you will claim it on the ID return. That said, that credit is unusual for a situation where you moved from one state to the other. Your MT source income most likely stopped when you moved.
