"With the IPO of SoftBank's Japan operations, the various parts of the company can continue to grow independently", company head Masayoshi Son said.
Analysts put the unit's total value from $55B to $60B, which means a minority portion sale could raise nearly $20B.
SoftBank also owns stakes in Chinese e-commerce giant Alibaba and the silicon specialist Arm, and the IPO will be important in raising cash for more investments, including into companies like Wag, which matches dog owners with dog walkers in what Son called the "dog version of Uber". They plan to make more transparent how the planned $100bn Vision Fund will benefit SoftBank and how its start-up investments are valued, said the person, asking not to be identified because the matter is private. Since its inception, the fund has invested more than US$40 billion into late-stage tech startups and digital companies, in line with Son's vision for a future world which is interconnected and powered by artificial intelligence and the Internet of things.
SoftBank Group, Yahoo Japan and retailer Aeon will jointly operate an online retail website in an effort to compete with rivals such as Amazon.com in the Japanese market, according to an official at one of the companies. But what were initially dismissed as idle boasts of massive investments to come, made by a figure very aware of the power of public relations, seem to be coming to fruition - much to the delight of the swathe of investors keen to capitalize alongside "Masa", as he is known. A year ago it bought a 15 percent stake in ride-sharing giant Uber - which sources said was worth $7.7 billion - while it also has piled cash into Uber's Chinese rival Didi Chuxing.
Stocks ride rollercoaster for gains to end brutal week
The Dow Jones industrial average has dropped 500 points, as stocks fell sharply during a patch of continued market volatility. The market, now in its second-longest bull run of all time, had not seen a correction for two years, an unusually long time.
Quarterly sales rose 3.9% to 2.4 trillion yen ($22 billion).
The reinsurer's shares closed at 90.18 Swiss francs on Wednesday. "I set out to make a conglomeration of No. 1 companies".
"Swiss Re has a strong balance sheet and pays a high dividend yield - above 5 percent - which I think they can keep up", Stefan Schuermann at Bank Vontobel in Zurich said.
SoftBank also owns the SoftBank Hawks baseball club, which won last year's Japan Series, this country's equivalent of the World Series.
One such company he mentioned is Wag, a USA venture that connects dog owners with dog walkers online, which Son called the "dog version of Uber".