NEW YORK (CNN/Money) - Marsh & McLennan CEO Jeffrey Greenberg stepped down Monday, and the company promised to overhaul its business practices -- just 11 days after the world's largest insurance broker was accused by New York Attorney General Eliot Spitzer of rigging bids in the insurance market.

Jeff Greenberg quit as CEO.

The New York City-based insurance broker said it named Michael Cherkasky, chief executive of Marsh's risk and insurance services unit, to succeed Greenberg, 53.

The company also said it plans to announce "significant reforms" to its business Tuesday. Mostly, this means Marsh will receive compensation for its services from only one party -- its clients, the company said in a statement.

"I am committed to managing the company through this challenging period," Cherkasky said in the statement. "I will be working closely with the leadership and colleagues of MMC's operating companies and with our board members to make sure that our business model and processes provide the best service to our clients," he added.

Greenberg's resignation came after Spitzer sued Marsh on Oct. 14 and called for changes in Marsh's top management, saying: "The leadership of that company is not a leadership I will talk to and not a leadership I will negotiate with."

Marsh (Research) shares jumped 9 percent in after-hours trading Monday as investors welcomed the news.

But industry analysts said that the change at the top may not mean the end of the struggles facing Marsh & McLennan.

"The markets will like (Greenberg) leaving, but I think there is a lot more involved in Spitzer's case than just getting rid of (him),'' David Jordan, chief investment officer of the First Focus Funds, told Reuters. "I would think there's still more bad news for Marsh down the road."

The company's stock lost about 40 percent of its value after Spitzer filed civil charges accusing it of steering unsuspecting clients to certain insurers in exchange for lucrative payoffs.

Reports that Marsh board members were meeting with Spitzer's office and that Greenberg would depart quickly have swirled since the middle of last week.

Greenberg is part of an insurance family dynasty, and once was expected to take over AIG, the world's largest insurer by market value, from his father Maurice "Hank" Greenberg. Jeffrey Greenberg's brother Evan is chief executive of Ace Ltd., a Bermuda-based insurer.

But Jeffrey Greenberg quit AIG to join Marsh & McLennan in 1995, and in 1999 he became chief executive. Until recently, he had generally received high marks for his stewardship.

In Spitzer's suit, Marsh was accused of rigging bids and colluding with AIG and other insurers to fix prices. All three of Marsh's divisions have been probed by the New York attorney general's office in the past year.

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J.P. Morgan analyst David Sheusi has written that regulators might extract more than $2 billion in penalties for the alleged wrongful practices, more than the $1.4 billion that Spitzer won last year from 10 Wall Street banks for biased stock research.

AIG, which is under investigation by the Securities and Exchange Commission and Justice Department on other matters, said Monday that it told its lawyers to seek a "prompt resolution" of those probes.

Cherkasky, who was Spitzer's former boss as investigations chief for the New York County district attorney, was named chief executive of the company's Marsh Inc. risk and insurance services unit earlier this month.  

-- from staff and wire reports