Sullivan & Cromwell and Davis Polk & Wardwell have the lead roles on an upcoming Tokyo initial public offering of Japanese conglomerate SoftBank Group Corp.’s domestic telecommunications business that seeks to raise $21 billion.

The proposed listing of subsidiary SoftBank Corp., slated for Dec. 19 on the Tokyo Stock Exchange, will be the largest the world has seen since Chinese e-commerce giant Alibaba Group Holding Ltd.’s $25 billion listing on the New York Stock Exchange in 2014.