DETROIT (Reuters) - Compensation for Mary Barra, who will become General Motors Co <GM.N> chief executive on January 15, has not yet been determined, the automaker said in a U.S. regulatory filing on Thursday.

Barra, who is 51 but will turn 52 by the time she takes over as CEO, had total compensation of about $4.9 million in 2012, including a $750,000 cash salary, according to the filing.

Barra was unanimously selected on December 7 by GM's board of directors to succeed the current CEO, Dan Akerson, who is retiring. Akerson said he pushed up plans to retire by at least half a year in order to help his wife battle cancer.

Akerson's total compensation for 2012 was about $11.1 million, including a cash salary of $1.7 million.