OMAHA, Neb. - Billionaire Warren Buffett wants investors to be wary of the high fees Wall Street routinely charges because of the damage they do to investment returns, and he emphasized his confident outlook in the U.S. economy.

Buffett devoted a section of his annual letter to Berkshire Hathaway shareholders Saturday to explaining again the benefits low-cost index funds have over most other investments.

He says he estimates that wealthy investors who use high-priced advisers have wasted over $100 billion over the past decade.

Buffett again praised the country's market system for its ability to allow Americans to continue building "mind-boggling amounts" of wealth.

Buffett devoted most of his letter to detailing the evolution of Berkshire and the performance of the Omaha, Nebraska-based company last year. His annual letters are always well read.