Buffett also leaves Abel and Berkshire Hathaway with a tremendous stockpile of cash. Buffett began selling stocks last year ahead of the market sell-off, while also ending the company's buyback program. Together with increased operating profits, Berkshire ended the first quarter with a whopping $347.7 billion in cash on its balance sheet.

"You're losing one of the most esteemed investors one could argue of all time," a source said of investors' reaction to Buffett's plan to step down.