Two months after being named to the top job at UnitedHealth Group, Chief Executive Andrew Witty announced Wednesday his first major leadership changes within the Minnetonka-based health care giant, including a new CEO at UnitedHealthcare, which is the nation's largest health insurer.

Brian Thompson is now chief executive at the company's insurance division. For several years, Thompson ran the Medicare business at UnitedHealthcare including Medicare Advantage plans where seniors opt to receive benefits from the federal program through private managed-care companies.

Enrollment in Medicare Advantage plans at UnitedHealthcare grew by more than 13% over the past year, and now stands at more than 7.2 million seniors, according to a report last month from Pennsylvania-based research firm Mark Farrah Associates. The growth expanded UnitedHealthcare's nation-leading share of the lucrative Medicare insurance market.

"Brian's experience, relationships and values make him especially well-suited to help UnitedHealthcare improve how health care works for consumers, physicians, employers, governments and our other partners, leading to continued and sustained long-term growth," Witty said in a prepared statement.

The chief executive position at UnitedHealthcare opened as Witty was named chief executive in February, and Dirk McMahon, the insurance division's previous CEO, was elevated to president and chief operating officer for the parent company.

In addition to the health insurance unit, UnitedHealth Group operates a large health-services business called Optum that manages pharmaceutical benefits within health plans and provides consulting services in health care data and IT.

Optum also runs a fast-growing division that provides patient care through clinics, surgery centers and facilities for urgent care.

Also on Wednesday, Witty announced a series of moves involving other top executives within the company.

Dan Schumacher, who is currently president and chief operating officer at Optum, is taking a new position as UnitedHealth Group's chief strategy and growth officer, reporting directly to Witty. John Prince, who runs the pharmaceutical benefits management (PBM) business, will succeed Schumacher as the Optum president.

Heather Cianfrocco will become chief executive of the PBM, which is called OptumRx.

Witty, meanwhile, will shed the title of Optum's CEO at some point soon, with a new chief executive being appointed for the division.

Christopher Snowbeck • 612-673-4744

Twitter: @chrissnowbeck