A company chose to report its bonds payable @ fair value, due to credit migration, bonds payable decreased. What will the company record (gain or loss)? Where?

I found this in my notes (title). Apparently the correct response i that the company will record a gain in OCI. I do get the “gain” part, since it is a liability bein reduced, however, i don’t get the “recorded in OCI” part.

To me, OCI can include the below:
Unrealized gains/losses from Available for sale securities
Unrealized gains/losses from hedging instruments
Adjustments for minimum pension liability
Adjustments from foreign exchange translations

Where does “bonds payable” fit in the list above?

Thanks guys.