The president of Humana has announced his retirement and will step down within the next 18 months.Mike McCallister says he’s been thinking about retiring for some time. He has worked for Humana for 38 years; he’s been Humana’s CEO for nearly 12 years and has been board chair since 2010. But he says he’s confident in his replacement, Bruce Broussard.Broussard was the former CEO of McKresson Specialty Health in San Francisco. His position with Humana will become official in December when he becomes board chair while McCallister remains CEO.McCallister says he’s confident Broussard will continue Humana’s success over the past decade.The company also announced that Chief Operating Officer James E. Murray is being promoted to Executive Vice President and Chief Operating Officer.