The merger of Cushman with Chicago-based DTZ, owned by private equity group TPG, PAG Asia Capital and Ontario Teachers' Pension Plan, will create one of the world's largest real estate services companies, Exor said in a statement on Monday.
The proceeds will help Exor pay for any future acquisitions as it seeks to diversify a portfolio which also includes controlling stakes in carmaker Fiat Chrysler and tractor maker CNH Industrial.
Last month Exor made a $6.4 billion all-cash offer for PartnerRe to try to trump a bid by Axis Capital Holdings as it seeks to branch out into financial services with its steadier and higher returns.
Even though PartnerRe rejected Exor's offer, the Italian company said it remained fully committed to its bid at the proposed terms.
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However, sources told Reuters last week that Exor would consider raising its offer at a board meeting on Tuesday, when it is also due to release first-quarter results.
"We believe there is some scope for Exor to raise its offer even though we continue to view the bid for PartnerRe as opportunistic and Exor unlikely to take part in a bidding war," UBS analyst Philippe Houchois said in a note.
The closing of the Cushman transaction is expected in the fourth quarter of this year, subject to regulatory approvals.
Cushman & Wakefield reported adjusted core earnings of $175.4 million last year.
Exor shares were down 0.24 percent at 42.26 euros, compared with a 0.6 percent fall in Milan's blue-chip index.