NEW YORK — General Motors Corp. (GM) agreed to sell its Allison Transmission commercial and military business to two private equity firms for about $5.6 billion.

The sales agreement with The Carlyle Group and Onex Corp. covers substantially all of Allison, including seven manufacturing facilities in Indianapolis and its worldwide distribution network and sales offices. A production facility in Baltimore will remain with GM.

Allison designs and manufactures automatic transmissions for medium- and heavy-duty commercial vehicles, including school buses. Its annual revenue is more than $2 billion.