Aon has combined with rival Willis Towers Watson for around $80 billion. – Credits: Bloomberg.

Three U.S. firms and a Magic Circle firm have won places advising on the merger of insurance giants Aon and Willis Towers Watson, creating a company with an expected combined $80 billion value.

London-headquartered insurance companies Aon and Willis Towers Watson announced their merger Monday, in a $30 billion deal.

Freshfields Bruckhaus Deringer, Latham & Watkins, and Arthur Cox are advising Aon while Weil Gotshal & Manges, Skadden Arps Slate Meagher & Flom and Matheson advised Willis Towers Watson.

Freshfields is advising Aon and its board with a team led by London-based M&A partner Julian Long, antitrust partner Martin McElwee, employment partner Andrew Murphy and finance regulation partner James Smethurst.

Latham & Watkins is acting for the company with a corporate team led by Orange County and New York partner Charles Ruck, Chicago partner Bradley Faris, with further assistance from Orange County partner Daniel Rees.

The firm is also advising on antitrust matters with Washington D.C. partners Marc Williamson and Michael Egge, as well as Brussels partners Lars Kjolbye and Hector Armengod leading the team.

On tax matters, Latham called on London partner Sean Finn, Washington D.C. partner Nicholas DeNovio, and Los Angeles partner Laurence Stein. The firm also deployed U.S.-based teams to advise on intellectual property, securities, benefits and compensation, finance, compliance and export control matters.

Aon provides risk, retirement and health solution. It employs 50,000 across 120 countries. Willis Towers Watson designs and delivers solutions to manage risk and benefits. It has 45,000 employees and serves clients in more than 140 countries, according to a statement.

The announcement comes a year after Aon issued a statement stating that it did not intend to pursue a business combination with Willis Towers Watson.

Irish firm Arthur Cox also advised Aon, with a Dublin-based team headed by corporate partners Cian McCourt, Brian O'Gorman, Stephen Hegarty, and was supported by tax partners Ailish Finnerty and Fintan Clancy.

On the other side, Weil Gotshal fielded a team advising Willis Towers led by New York M&A partners Michael J. Aiello, Matthew Gilroy, and Amanda Fenster, as well as London M&A partner David Avery-Gee. The team was also supported by Washington D.C. tax partners Joseph M. Pari and Devon Bodoh, as well as New York-based executive compensation and benefits partners Paul Wessel and Amy Rubin.

Meanwhile, Skadden also advised the company on antitrust and regulatory matters in New York, according to a person close to the matter. The team included New York-based M7A partners Joseph Coco, Todd Freed and Blair Thetford.

According to a statement, Matheson advised Willis Towers Watson on the merger.

Last summer, Aon named Darren Zeidel as its new general counsel after decade-long predecessor Peter Lieb became the company's chief executive officer's "special legal adviser". Lieb is due to retire in December.