Citigroup (C) is shuffling a handful of senior executive positions. In a note to employees, CEO Vikram Pandit and President and Chief Operating Officer John Havens said William Mills will return stateside to become chief executive for North America. "Many of us on the operating committee have thought for some time that we need a CEO for this region to provide the same focus on clients, regulators and expenses that the other regions have developed," Pandit and Havens said of Mills appointment. Mills has 35 years of investment banking experience and most recently led Citi operations for Europe, the Middle East and Africa. Pandit and Havens said "mobility and challenging new assignments for our people are at the core of our history and key strengths of any well- managed business, especially one with our global footprint." Mike Corbat will fill Mills' post at CEO for EMEA. He had been leading Citi Holdings for several years. Mark Mason will move to CEO of Citi Holdings, replacing Corbat. Mason had been operating chief of the holdings unit. Manuel Medina-Mora was named chief executive of global consumer banking. He had held a similar post for the Americas. Javier Arrigunaga will become CEO of Mexico. He had been with Banamex since 2002 and spent a dozen years at Mexico's central bank prior to that. Francisco Aristeguieta will assume the CEO post for Citi's Latin American operations. Aristeguieta has been with the banking giant for 17 years, mostly in Venezuela. Alberto Verme was named chairman of the EMEA Banking unit. He has been with Citi since 1994, most recently with Mills, focusing on Eastern Europe and the Middle East. Stephen Bird becomes CEO of the Asia Pacific region, and Shirish Apte will move to co-chairman of Asia Pacific Banking. The new assignments are effective Jan. 1. Write to Jason Philyaw. Follow him on Twitter: @jrphilyaw.