Greg Case, president and CEO of Aon, said: "Through these divestitures, we have further simplified our global organisation and successfully executed our strategy to exit the lower margin and more capital intensive insurance underwriting business.

"Our core assets will now be more strategically aligned as we expand our capabilities to better serve our risk brokerage and consulting clients.

"At the same time, the increased share repurchase programme reflects our ongoing belief in the underlying positive momentum of the business and is an effective use of capital to maximise long-term shareholder value."

The purchase price is subject to adjustment to reflect certain changes to CICA's net worth through the closing of the transaction.

CICA has diversified premium of approximately 66 percent domestic and 33 percent international and will provide diversification to ACE's premium base in a business where expertise already exists.

Meanwhile AM Best believes that ACE management's challenges will be less of business integration than the long term execution issues associated with maintaining an expensive captive distribution force, sensitive lapse rates and regulatory scrutiny.

The ratings agency believes that ACE maintains sufficient capital to fund the acquisition and, further, that reinvestment in profitable, cash producing and complementary businesses is more beneficial on a long-term basis than alternate capital management possibilities.

AM Best has also revised the under review status to positive implications from negative for the financial strength rating of A (excellent) and issuer credit ratings of "a" of CICA and Combined Life Insurance Company of New York.