I work for a games publisher that has some (heavy) ties to Hollywood and i have it on good authority that it’s definitely more like 30%.
Screenwriters are great and all that, but they're eminently fungible, whereas folk like Cruise are not.
I'd suggest it's more like 5%-10% upfront. What they get on residuals may be a lot higher, but that assumes the film covers its costs, which in Hollywood can mean anything.
Not any more. Case law has basically ripped the old “Hollywood accounting” to shreds. I’m not saying profits and losses can’t be manipulated, but you can’t get away with the dirty tricks used 20 years ago, and firms are held to somewhat higher standards.