Detroit credit rating upgraded 2 notches by Moody's, now investment grade

[mwilbert]

I don't have too much knowledge in this area but does a better credit rating allow for any existing debt to be refinanced?

Not in general. The market price of the existing debt presumably will already have risen as the credit quality of the issuer improved, so it will tend to be just as expensive as the new debt, so there would be no benefit to paying it off by issuing new debt. It's the owner of the existing debt who gets the benefit of the improvement in the borrowers credit, not the issuer of that debt.

Some debt is "callable", which means that it has terms that allow the borrower to repay the debt early, usually at a modest premium. If your credit rating has gone up substantially, or if interest rates have fallen for other reasons, so that the old debt has a significantly higher interest rate than new debt, it can be a good idea to pay off the old expensive debt, refinancing it with new cheaper debt.