Government-owned Japan Post Holdings Co Ltd [IPO-JAPP.T] said it plans to list in the second half of the next business year and its bank and insurance units will go public at the same time, in what could be the biggest IPO of Japanese state enterprises in two decades.

The Japan Post group, one of the world's biggest financial institutions with net assets of some 13.8 trillion yen ($115 billion), also said it plans to eventually cut its stakes in the two units to around 50 percent. Japan Post Bank Co Ltd is the nation's biggest bank and Japan Post Insurance Co is its biggest insurance company.

Japan Post President Taizo Nishimuro declined to comment on the potential scale of the offering, saying that would be determined by market conditions at the time of the IPO.

The government has said in the past it expects to raise around 1 trillion yen ($8.3 billion) in the first of multiple rounds of sales, basing its assumption on the results of previous share offers of state-owned companies. Funds raised will finance reconstruction projects for areas hit by the 2011 earthquake and tsunami.

"Listing all three companies at the same time is the best way to do this fairly," Nishimuro told a news conference on Friday.

According to the Nikkei business daily, the government plans to initially list 10 percent of outstanding shares for each of the three companies.

The group's other main unit - the national postal service with more than 20,000 post offices - will not be listed. It has seen steep declines in earnings over the past decade with the growth of e-mail and web billing.

The offering is expected to be huge but the market should be able to absorb it, said Mitsushige Akino, chief fund manager at Ichiyoshi Asset Management.

"If the market is doing well, the IPO will be welcome. It's going to depend on price but I expect the bookbuilding process to go well," he said.

The privatization of Japan Post was first made into law in 2005 under then Prime Minister Junichiro Koizumi but it has been a highly divisive issue with members of both ruling and main opposition parties fiercely objecting to it.