Berkshire Hathaway is a holding company built by Warren Buffett around a simple structure: insurance operations generate float, and that float funds a sprawling collection of businesses and stock holdings. Wholly owned subsidiaries include GEICO, the BNSF railroad, Berkshire Hathaway Energy and dozens of manufacturing, service and retail brands. On top sits a large portfolio of publicly traded shares. The B shares, created in 1996, make the company accessible to ordinary investors, and Berkshire is often treated as a diversified proxy for the American economy.