The majority of auto makers use 3rd party suppliers for the vast majority of their components. In some cases it might be a joint partnership (eg: Ford has a joint factory with Getrag), or it might be a completely independent company, or a quasi-independent subsidiary (MOPAR, a lot of the Sprawling Toyota conglomerate). You’ll note that above transmission is a ZF designed baseline with extremely minor tweaks, then built in GM factories. Similar is the FCA produced 9 speed that’s the infamous ZF dog - gear design. Mercedes hasn’t been Daimler-Chrysler since before the recession; although FCA is still using early 2000s Mercedes platforms to underpin their rear drive cars and SUVs.