Thanks, all. Not a silly question about the refundable vs non-refundable; I should have mentioned that upfront. It was a non-refundable ticket, which is why I'm fairly certain it won't be a full refund, based on my research. However, it seems that United should communincate this once I issued my initial refund request.
How can I determine whether or not I have the credit (minus the $150 change fee)? Again, I spoke to several agents and no one mentioned this. I also checked my acct on United.com (as I fly United every few weeks) and there's no indication of a credit.
Thanks!