Took a wee bit of time to search and put this together. Thought it was kinda interesting. I don’t think it’s really complete yet, whoever wants to add anything in…feel free.
The following is a list of most of the automakers and the companies that they either own, own major shares, or are currently in joint ventures with.
GM > Buick, Cadillac, Chevrolet, GM Daewoo, GMC, Holden, Hummer, Opel, Pontiac, Saab, Saturn and Vauxhall
Collaborations Toyota, DaimlerChrysler (in turn is with Mercedes-Benz), BMW, Suzuki, Shanghai Automotive Inudstry Corp. of China, AvtoVaz(Russia), Renault, Fiat & recently UzAvtosanoa(Uzbekistan)
Ford > Volvo, Mazda(owns 1/3), and smaller holding’s in Aston Martin
Tata Motors > Daewoo (trucking unit), Jaguar and Land Rover
Fiat > Ferrari, Iveco, and Maserati, Abarth, Alfa Romeo, and Lancia
Volkswagen > Audi, Bentley, Skoda, Lamborghini, Bugatti, SEAT, Scania
Toyota > Lexus, Scion, Daihatsu (holdings), Fuji Heavy Industries, Isuzu Motors, Yamaha (other various technology holdings as well, Toyota is considered one of the largest conglomerates in the world)
Honda > Acura, other holdings are into motorcycles, robots, jets, ATV, electrical generators, (many non automotive holdings)
Nissan > Datsun (discontinued) Renault (alliance) Infiniti
Mazda > Amati (never materialized, was created to compete against the japanese luxury line)
Mitsubishi another Japanese conglomerate (started off as a shipping company, went into coal mining to banking, insurance, paper, steel, glass and obviously automotive.
BMW > Mini (Austin), Rolls-Royce
lastly,
Daimlerchrylser & Mercedes-Benz, has some holdings in non-automotive industries (motorcycles, etc…)