WASHINGTON, Feb 25 (Reuters) - Pinnacle Airlines Corp., an indirect subsidiary of Northwest Airlines Corp. (NWAC), the No. 4 U.S. airline, on Monday filed to offer as much as $400 million in stock in an initial public offering. Details such as the size and price of proposed IPO were not provided in a preliminary prospectus filed with the U.S. Securities and Exchange Commission. Those details are expected in future filings. Pinnacle said NWA Inc, a unit of Northwest, will offer all of the shares of common stock it holds in the Memphis, Tennessee-based company, will not receive any proceeds from the IPO. NWA will hold 13 percent of Pinnacle's outstanding common stock after the offering, Pinnacle said.