Aon plc

What does Aon do?

Aon is the world's largest insurance broker by revenue. It advises clients on risk, places insurance and reinsurance, and consults on health, benefits, and retirement through its Risk Capital and Human Capital segments.

Is Aon publicly traded?

Yes. Aon plc trades on the New York Stock Exchange under ticker AON. It is domiciled in Dublin, Ireland.

Who founded Aon?

Aon was formed in 1982 by the merger of Ryan Insurance Group, founded by Patrick Ryan, and Combined International Corporation, founded by W. Clement Stone. Patrick Ryan led the combined company.

Where is Aon headquartered?

Aon is legally domiciled in Dublin, Ireland, at 15 George's Quay. Its principal operating centers are Chicago and London.

Who owns Aon?

Aon is publicly owned. Vanguard, BlackRock, and State Street are among the largest institutional shareholders. No controlling shareholder exists.

What is Aon's revenue?

Aon reported total revenue of $17.2 billion for fiscal 2025, split between $11.3 billion in Risk Capital and $5.9 billion in Human Capital.

Aon was created in 1982 by the merger of Ryan Insurance Group, founded by Patrick Ryan in 1964, and Combined International Corporation, founded by W. Clement Stone in 1919. Ryan became CEO and built the combined company into an acquisition machine.

The modern shape came from two large deals. Aon acquired the brokerage operations of Alexander & Alexander in 1997 and the reinsurance broker Benfield in 2008. The 2010 acquisition of Hewitt Associates for $4.9 billion added the human capital consulting business that now generates a third of revenue.

The company changed its name from Combined International to Aon in 1987, using the Gaelic word for one. It moved its domicile to London in 2012 and to Dublin in 2020. Greg Case has been CEO since 2005.

A proposed $30 billion merger with Willis Towers Watson collapsed in July 2021 after US Department of Justice opposition, costing Aon a $1 billion termination fee that it paid to Willis. The abandoned deal remains the largest failed insurance brokerage combination.

In 2024 and 2025 Aon completed the acquisition of NFP, a middle-market broker, for approximately $13.4 billion, its largest completed deal. The FY2025 results showed $17.2 billion in revenue, up 9% year over year. In 2026 Aon was reported to be pursuing USI Insurance Services, the large privately held broker, a deal that would extend its middle-market push further. That transaction had not been announced as of October 1, 2026.

Aon publishes an annual ESG report aligned with GRI and SASB frameworks and discloses through CDP. The firm has set a net-zero operations commitment and reports progress on renewable energy use in offices. It is not B Corp certified, and its sustainability posture is typical of professional services firms: material but not product-linked.

The 2021 collapse of the Willis Towers Watson merger is the dominant regulatory event in recent history. The Department of Justice sued to block the $30 billion combination on antitrust grounds, arguing the merged firm would control too much commercial risk brokerage. Aon abandoned the deal rather than litigate, paying the $1 billion termination fee.

Aon has also faced periodic fiduciary and error-and-omission claims typical of a large broker, none material at the group level. The firm is regulated across dozens of jurisdictions, and compliance costs are a standing feature of its filings.