To be exceptionally wealthy; to have large amounts of money to spend. "It" refers to money, with the image being that of one literally rolling around in piles of cash. Usually used in the continuous tense ("rolling in it"). I wouldn't worry too much about the Smiths. They're rolling in it. It sickens me to see these politicians rolling in it while so many of us struggle to keep a roof over our heads.

Exceptionally wealthy; having large amounts of money to spend. "It" refers to money, with the image being that of one literally rolling around in piles of cash. I hear her father is rolling in it, so I wouldn't be too worried about her future. Once we get this plan underway, we'll be rolling in it in no time!