As I understand it they have already borrowed around $1B, and now because of the lower interest rate, they are able to secure a bigger loan that they'll use to pay back the original and then still have a bucket of cash, at a lower interest.
I don't know about the US, but here in Denmark it has been a common "trick" in mortgage financing as the interest rate dropped over the last couple of decades.
But as with all taking on debt to pay off debt, it's like wetting yourself.