Berkshire Hathaway ( BRK.A 0.98%) ( BRK.B 0.98%) stock is down big since Warren Buffett announced that he would be stepping down as chief executive officer (but remain chairman) by the end of the year. Here's why the sell-off is a buying opportunity for investors looking for an ultra-reliable blue chip stock to hold for years to come.

Famed investor Warren Buffett is donating $6 billion worth of his company's stock to five foundations, bringing the total he has given to them since 2006 to roughly $60 billion, based on their value when received.