Shares of Bank of America Corp. dropped 0.47% to $44.34 Friday, on what proved to be an all-around rough trading session for the stock market, with the S&P 500 Index falling 1.11% to 5,970.84 and Dow Jones Industrial Average falling 0.

Both are substantial investments in Berkshire's portfolio. The Bank of America investment is one of the largest, with a $34 billion market value representing a 9.99% stake in the megabank. Ally is a smaller bank, but Berkshire owns 9.5% of it, an investment worth just over $1 billion.

Shares of Bank of America Corp. inched 0.38% higher to $44.55 Thursday, on what proved to be an all-around mixed trading session for the stock market, with the Dow Jones Industrial Average rising 0.07% to 43,