MIDLAND, Mich. (AP) — The longtime chief executive of Dow Chemical, who led the company through the financial crisis, a merger with rival DuPont and the planned disassembly of the entire enterprise, is stepping down. Andrew Liveris announced two years ago he'd retire by mid-2017, but that was delayed until the company named a successor to head its materials-science division, one of three companies that DowDupont will divide itself into.