Ace Ltd., a global insurance company with North American headquarters in Philadelphia, said today it had agreed to buy Combined Insurance Co. of America and some of its subsidiaries from Aon Corp. for $2.4 billion in cash, doubling its personal accident and supplemental health insurance business.

Ace, which is headquartered in Bermuda and has corporate offices in New York, said Combined Insurance has 4 million policyholders and a sales force of nearly 7,000. Combined Insurance is based in Glenview, Ill.

Ace's shares at 10:20 a.m. were up 59 cents, or 1 percent, to $60.10 on the New York Stock Exchange. Ace employs 2,300 in the Philadelphia region.