SOUTHFIELD, Mich. — Detroit's three carmakers all reported surprisingly robust August sales, powered by pickups and sport utility vehicles, suggesting US consumers are undeterred by the marked decline in global stock markets.

Ford and Fiat Chrysler Automobiles reported surprising sales increases, while General Motors Co. posted a small decline, after cutting back low-margin sales to rental fleets. But GM executives boosted their full-year outlook for the market by 300,000 vehicles.

America's love affair with new trucks shows that the economy is still a standout as Europe's recovery ambles along and China is slowing. Not even a 6.6 percent drop in the Dow Jones Industrial Average last month has kept consumers from dealerships. Auto stocks fell much less on Tuesday than those of other sectors.

"The market is down but consumers don't seem to care, they seemed to shrug it off," said Jeff Schuster, senior vice president of forecasting for research firm LMC Automotive in Troy, Michigan. "If the market stabilizes we should have a really robust September."

GM's 0.7 percent decline beat analysts' forecast, leading the company to say that sales this year may reach 17.3 million, up from an original forecast of as many as 17 million cars and light trucks. The Detroit-based automaker projected a 17.5 million annualized selling rate for August. Analysts had estimated the pace would be 17.3 million.

Ford's light-vehicle deliveries increased 5.6 percent and Fiat Chrysler's rose 1.7 percent. Both were projected to report decreases.

Fiat Chrysler's North American unit sold 201,672 vehicles in the United States last month, the second time this year that the group topped 200,000.