Like Greg, I experienced a merger of equals (2 years ago). I had BSA/Security/Fraud in my legacy bank, as did my counterpart from the other institution. Upon merging we realigned our duties, leaving Security/Fraud at my desk and BSA at my counterpart's desk.
Like Greg, we learned that there is value in examining the policies and procedures of both organizations and incorporating items from each into the merged program. In doing this, be sure to aim for the processes that are truly the best fit. This can only be done by spending time with the policies and procedures of the new-to-you half of the merger, and learning the reasons why certain things are the way they are.
During our merger, we learned that even though our respective footprints were near each other, our markets and histories were vastly different. Our individual programs had grown to address the challenges, demographics, and risks associated with the communities we served. Like Greg suggested, learning these will require a lot of listening.
Learning where each bank is coming from will also help you effectively communicate program and procedural changes to your frontline team. They will be overwhelmed with changes to processes, systems, and expectations, so the clearer a road map you can provide them, the easier it will be to get everyone on the same page and moving forward in the same direction.