Русско-англо-русский юридический словарь

The principal parties to any reinsurance contract are the reinsurer, who assumes the subject risk in return for premium, and the ‘reinsured’, who may also be referred to as the ‘reassured’, or the ‘cedant’. (LexisNexis)

The company that purchases the reinsurance policy is called a "ceding company" or "cedent" or "cedant" under most arrangements. (Wikipedia)