The move is another in a series of management changes that started soon after GM emerged from bankruptcy protection in July of 2009. The company has had four CEOs in less than two years, and it recently changed its top executives in sales, marketing, product development and engineering.
Shares of GM fell 85 cents, or 2.6 percent, to $31.40 in afternoon trading Thursday, below the November initial public offering price of $33. The Dow Jones industrial average was down 209 points, or 1.7 percent.
Itay Michaeli, auto analyst with Citi Investment Research, blamed most of Thursday's stock drop on the broader market decline, but said Liddell's departure would have an impact.
"To see a major management change just when you thought there would be no more management changes is going to rattle things a little bit," he said.
In 2009, Liddell said he was leaving Microsoft with an eye on taking a higher position, and Whitacre even told reporters that Liddell would be a candidate to replace him. When Akerson got the job, that led to speculation that Liddell was unhappy about being passed over.
Liddell has held the CFO job at three companies: GM, Microsoft and International Paper.
He said he has not looked for another job while at GM, but indicated Thursday that a CEO post might be in the offing.
"I have a number of interesting ideas which I have in the back of my mind, but none of them have CFO on it," he said during the conference call.
Under Liddell, GM posted four straight profitable quarters and began to repair accounting troubles that had plagued it for years. He joined the company in January 2010 with a reputation as a problem solver.
GM's stock stayed above the IPO price until late February when it posted fourth-quarter earnings that were below the three previous quarters, and unrest in the Middle East drove up oil prices.
Akerson said Liddell was a major contributor to GM during a pivotal time in company history.
"He guided the company's IPO process and established a good financial foundation for the future," he said.
Ammann, 38, joined GM as treasurer in March of 2010. Before GM, he was managing director and head of industrial investment banking for Morgan Stanley. His replacement will be announced later.
Ammann told reporters that he is committed to GM for the long term, and he agrees with Liddell's financial strategies. Investors, he said, could expect "more of the same."
Some industry analysts wonder if Liddell's departure was prompted by GM's decision in the past two months to raise incentives — such as low-interest loans and lease deals — moves that could hurt GM's bottom line in the first quarter.
But Liddell said his leaving has nothing to do with the company's first-quarter performance, and Akerson said the company was off to a fast start for the quarter.
GM had been plagued with financial reporting problems heading into and emerging from bankruptcy protection. Going into its IPO last year, the company said weaknesses in its financial controls meant many of its numbers could not be considered reliable.
Steven Rattner, former head of the government's autos task force, has said that GM had the weakest finance operation that task force members had seen in a major company.
But just two weeks ago, when GM released its 2010 earnings, the company said those problems had been fixed.
GM reported net income of $4.7 billion last year, fueled by strong sales in China and the U.S. as the global auto market began to recover. It was the company's best performance since earning $6 billion in 1999 during the height of the pickup truck and SUV sales boom.
GM accepted nearly $50 billion in government help to help it survive in 2009. But the company has since made an impressive recovery with global sales growing 12 percent last year.
The company must still pay back more of its rescue aid. GM's owners, the U.S. Treasury Department, the Canadian (federal) and Ontario governments and a union health care trust fund, sold common stock in the November IPO. The U.S. government got $13.5 billion from the sale and will have to sell its remaining shares for $53 each to break even on its aid to GM.
AP Auto Writer Sharon Silke Carty in Detroit contributed to this report.