Sullivan & Cromwell and Davis Polk & Wardwell have won the lead roles on the Tokyo initial public offering (IPO) of Japanese conglomerate SoftBank Group's domestic telecoms business, a listing which is aiming to raise $21bn.

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

The billions raised will fund SoftBank's future investments and help lower the company's ballooning debt, which, as of end of September, was about $158bn.

Sullivan & Cromwell Tokyo partners Keiji Hatano and Izumi Akai are representing SoftBank on the listing. In 2016, the New York firm advised SoftBank on a $10bn sale of shares in Alibaba.

Mori Hamada & Matsumoto is advising the issuer on Japanese law led by Tokyo partner Taro Omoto. The Japanese firm, alongside Morrison & Foerster, previously advised SoftBank on its $20bn acquisition of American mobile carrier Sprint Nextel in 2012.

Davis Polk Tokyo partner Jon Gray is representing a group of underwriters led by Nomura Holdings, Goldman Sachs Japan, Mizuho Securities, Deutsche Bank, JP Morgan and SMBC Nikko Securities. In 2016, the US firm, alongside Slaughter and May, advised UK chip designer ARM on its $31bn sale to SoftBank.

Anderson Mori & Tomotsune is serving as Japanese counsel for the banks.

Japanese entrepreneur Masayoshi Son started SoftBank as a telecom carrier but has transformed the company into a global tech investor over the years. In addition to famously being an early investor in Alibaba, in 2016, Son's SoftBank established, in cooperation with a Saudi Arabian sovereign fund, a $100bn Vision Fund for technology investment around the world. Vision Fund portfolio companies include ARM, Indian e-commerce company Flipkart and shared office space provider WeWork Companies Inc.