General Motors Co. has begun to work on the U.S. regulatory filing needed for an initial public offering but does not expect to have that ready in the next two weeks, Chief Executive Ed Whitacre said on Thursday.

“We are working on an S-1,” Whitacre told Reuters, referring to the U.S. Securities and Exchange Commission registration statement required for a securities offering.

“It’s a very thick document. We’ve begun to work on it,” Whitacre said.

“I don’t know when we are going to be able to file it because we still have a lot to do. It’s not in the way, way out there, but we still have a lot to do,” he added.

It was the first time that the top U.S. automaker has confirmed that it was readying an IPO, an event that would mark its return as a public company and reduce the U.S. government’s majority ownership.

Whitacre, who was attending an auto industry event sponsored by the Center for Automotive Research, said the filing would not be ready within the next two weeks.

GM, which went through a restructuring in bankruptcy a year ago supported by $50 billion in U.S. taxpayer money, will report second-quarter results next week.

The automaker has been lining up bankers for a stock offering expected to rank as one of the largest IPOs and to give the U.S. Treasury an opportunity to reduce its 61 percent ownership stake.

People with knowledge of the process, who could not be named because the preparations remain private, had said that GM’s target was to complete the regulatory paperwork for an IPO by the middle of August.