Berkshire Hathaway upped its holdings of the five big Japanese trading houses, according to regulatory filings on Monday.

The S&P 500 index (SNPINDEX: ^GSPC) has followed the Nasdaq Composite (NASDAQINDEX: ^IXIC) into correction territory, with both having fallen 10% from their peaks. Warren Buffett's advice to buy an S&P 500 index fund is still a good idea,

Warren Buffett's Berkshire Hathaway raised its holdings in five Japanese trading houses, in its latest investments in Japan's top commodity firms that began nearly five years ago.