Combine 8 cups water, apple cider, salt, brown sugar, onion, garlic, orange slices, rosemary, peppercorns, and bay leaves in a large pot. Bring to a simmer over medium heat, stirring until salt and sugar dissolve, about 5 minutes.

Remove from heat, stir in the remaining 8 cups cold water, and pour brine into a nonreactive container. Add ice cubes or place in an ice bath and stir occasionally until cool, about 20 minutes.

Once cold, submerge turkey in the brine, breast side down. Add a little more water if needed to cover. Cover tightly and refrigerate for 12 to 24 hours.