General Motors said it had no comment on a report saying it plans to double its stake in Fiat SpA's money-losing car unit to 40%, Dow Jones reported. Dow Jones said that Italian newspaper Milano Finanza said on Thursday that the deal would raise up to €2.5 billion for Fiat Auto while Fiat SpA would maintain its 40% stake in the car unit, with the remaining 20% open to new investors.