rouler sur l'or

to be rolling in money, to be rolling in it, to be loaded, to be minted (to be extremely well-off financially)

“C'est, à ce qu'on assure, un fameux lapin! il roule sur l'or! il mène avec lui trois maîtresses et son cuisinier!” — From what I hear, he's a regular dog; he's rolling in money; he's taking three mistresses and a cook along with him.