The shift came after Mr. Witty signaled to the board that he was considering leaving, according to people with knowledge of the matter. Mr. Witty, who served on the UnitedHealth board before joining the company as an executive, is well-regarded by the board, which didn’t want to lose him, according to these people.
Mr. Wichmann stepped down voluntarily, these people said.
See this article: https://www.wsj.com/articles/unitedhealth-group-names-andrew-witty-as-chief-executive-11612443921