My employer for my current day job (~70k employees) pretty much says this in their 17 page contract. It was a big warning sign for me when considering the offer, but I know that many other major corporations do this.

As a result, I have to take extra care not to "release" anything I create on the side, which is frustrating because I have always enjoyed working on side projects. Realistically though, it's unlikely for the company to claim ownership over any of these petty/small projects; but I'm sure if you released something that gained a lot of traction, especially something that competes with them, they would pounce on it.