Music, movies, TV networks, video games and theme parks fall under his leadership.
Mr. Diller will serve as co-CEO with Vivendi Universal's chairman, Jean-Rene Fourtou.
Mr. Diller last year sold assets such as USA Network to Vivendi and took on the post of CEO of VU Entertainment, which included movies, theme parks and some TV. Now, that role has been expanded on an interim basis.
A company spokeswoman said "interim" refers to the next several months.