You need to finish a game with you player's grand wealth total coming to more than $2,000,000. This can be tricky to get. Fortunately, you can use the "Home Button" trick to redo any turn where your player loses money.
Play a multiplayer game with two players. Take both of them to college and try to get the Doctor career, as it is the highest paying. Then just play the game. Anytime you land on a space where you lose money or lose you job, redo the turn. Also, anytime the other player lands on a blue space that would sue you, redo the turn as well. With these tips, you should have no problem getting this achievement. You can try to get $2,000,000 with either of the players.