Warren Buffett has regularly endorsed a low-cost S&P 500 index fund as the best option for non-professional investors that want exposure to U.S. stocks. Consequently, his decision to sell Berkshire's S&P 500 index funds begs the question: Has Buffett lost confidence in the U.S. stock market or the American economy?

Warren Buffett's Berkshire Hathaway on Saturday reported fourth-quarter operating earnings that surged more than 70% year-over-year.

U.S. stock indexes are drifting Monday following their sharp losses from last week, with the S&P 500 up 0.1% in afternoon trading.