Aon is abandoning its $24 billion takeover attempt of Willis Towers

Thomson Reuters

The US Bank Tower and the AON Corporation building are pictured as part of the Los Angeles, California skyline

• Aon is abandoning its potential transaction with Willis Towers Watson.
• The preliminary transaction would have been an all-share deal valuing Willis at $24 billion.
• Watch Aon and Willis Towers Watson trade live.

In a quick reversal, Aon is abandoning its $23.5 billion takeover attempt of Willis Towers Watson. Because Willis is an Irish company, Aon was forced to disclose its interest Tuesday due to Irish takeover regulations.

"As a result of media speculation, those regulations required Aon to make the disclosure at a very early stage in the consideration of a potential all-share business combination," Aon said in a press release out Wednesday. "Aon today confirms that it does not intend to pursue this business combination."

After calling off the all-share deal Wednesday, stock prices from both companies returned to preannouncement levels. Willis Tower shares were trading down 5% and Aon was up 6%.

Aon and Willis are two of the largest traded insurance brokers, which connect buyers and sellers of insurance. Research analysts indicated that any potential transaction may face regulatory issues given the market share of both companies.