Buffett tops up 'excellent' US blue chips on Berkshire Hathaway

Added $4.7bn to 2015 earnings

Warren Buffett, chief executive of Berkshire Hathaway, has increased his exposure to four 'excellent' US blue-chip stocks, including American Express and IBM.

In his annual letter to shareholders, Buffett (pictured) said he had increased exposure to his 'Big Four' investments; American Express, Coca-Cola, IBM and Wells Fargo. IBM and Wells Fargo were increased...