be rolling in it

To be exceptionally wealthy. "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! These companies are all rolling in it, so they can afford the very best legal teams in the world. What hope does an ordinary guy like me have against them in a court of law?

be rolling (in it or in money)

be very rich. informal

Rolling in (i.e. ‘turning over and over in’) here has the sense of ‘luxuriating in’. The idea of wallowing in riches has been current since the late 16th century.