Looking to diversify it services portfolio, Chicago-based Aon Corp. is acquiring New York-based Hewitt Associates Inc. for $4.9 billion in cash and stock.

With the purchase, Aon acquires a HR consulting and outsourcing firm with more than 3,000 clients across the globe. The companies predict immediate synergies, noting their combined client base will provide significant cross-sell opportunities to leverage Hewitt's predominantly large corporate client base with Aon's largely middle market client base. Upon the close of the transaction, Aon will integrate Hewitt with its existing consulting and outsourcing operations, Aon Consulting, and operate the segment globally under the newly created Aon Hewitt brand.

"This agreement reflects our ongoing efforts to ensure that Aon's associates, capabilities and technology remain at the forefront of our industry, providing distinctive client value," Aon CEO Greg Case said in a statement. "As we continue to grow our business, this merger will give us a broader portfolio of innovative products and services focused on what we believe are two of the most important topics in the global economy today—risk and people."

The companies say that Aon Hewitt will have revenues of $4.3 billion annually and field a team of 29,000 associates globally.  Russ Fradin, chairman and CEO of Hewitt, will have the same titles at Aon Hewitt, reporting to Case.

"We are extremely excited to join forces with another iconic global brand to form the leading human capital services enterprise," Fradin said. "This combination allows us to provide even more services for our clients and greater opportunities for our associates.  

The transaction is expected to close by mid-November, subject to customary closing conditions, regulatory approvals, as well as approval by both Aon and Hewitt stockholders.