Top global miner BHP Billiton (BHP.AX)(BLT.L) will spin off a roughly $16 billion company to shareholders, mostly offloading assets acquired in its 2001 merger with Billiton, as it looks to focus on its strongest businesses. Chief Executive Andrew Mackenzie, in the top job for just over a year, said the move to simplify BHP to its “four pillars” of iron ore, copper, coal and petroleum would rev up growth in cash flow and boost returns.