NEW YORK (Bloomberg) -- Marsh & McLennan Cos., the world's largest insurance broker, said first-quarter profit fell 36 percent after its flagship unit lost US customers and the company reported lower gains from asset sales. Shares headed for their biggest drop in seven months.

Net income dropped to $268 million, or 47 cents a share, from $416 million, or 75 cents, a year earlier, New York-based Marsh & McLennan said in a statement today. Marsh, which offers insurance broking and captive management services in Bermuda, announced a plan to buy back $500 million in shares.

The company lost brokerage clients at Marsh Inc., its biggest division, after chief executive Michael Cherkasky replaced 25 of the 65 US office managers. Bringing in better-performing leadership is worth the short-term cost, Cherkasky said in a conference call. Revenue fell for an 11th straight quarter at the unit, dropping by less than 1 percent to $1.14 billion.