Thank you for getting back to us, @DarcyS.
Allow me to fill you in on everything about the posting of bill payments on a report.
The report will show payments depending on the accounting method you use. Since the full payment is showing in October, the accounting method you use for your Profit and Loss report may be accrual. The accrual method shows your completed and pending transactions on your financial reports. While the cash method shows only completed transactions, like the date when you completely finished paying your bills.
You'll want to change the accounting method on your Profit and Loss report to show the full payment in December. I've attached a screenshot below of your visual reference.

I'm adding this article to know more about the common accounting terms: Learn common accounting terms.
Please let me know if you need clarification about this, or there's anything else I can do for you. I'll be standing by for your response. Have a great day.