You know, I really have no idea.
Here's how it stands now, I think: ZeniMax Media is our publisher; they giveth and taketh the monies. We're Bethesda Game Studios; we make-a the games. There are a number of other companies owned by ZeniMax, namely id Software, Splash Damage, Arkane Studios, all of whom also make-a the games. An anology to planets orbiting a sun would not be remiss, replacing gravity with cash money. Well, it might be a little remiss.
It's a tree! ZeniMax is the trunk, it has six major branches, and Socrates200X is a leaf!
ZeniMax Media is an entertainment company comprising of six divisions:
1. Bethesda Softworks: publishers of games by Bethesda Game Studios, Obsidian, id software, Arkane, inXile, Splash Damage, Rebellion, HeadFirst, A2M and others. Bethesda commissions and licences new games, organises publicity and distribution, and has a sizeable in-house QA department. Bethesda does not own id software; Zenimax does.
2. Vir2L Studios: a mobile/handheld game design company
3. ZeniMax online Studios: MMO online game developer
4. id software: developers of Quake, Doom, Wolfenstein etc
5. Bethesda Game Studios: developers of Elder Scrolls and Fallout games
6. Arkane Studios: developers of Arx Fatalis
(Tango Gameworks should probably be added to this as a seventh branch.)