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This achievement unlocks when all players escape the heist with over $1 million total heist money.
Best done on hot coffee, but you have to make sure you grab the Senator's briefcase, as this is the prime objective of the map. It's also been reported in the comments that this might have to be done on the first round.
Once that's done, and everyone escapes alive, your achievement will unlock.
This will NOT unlock if you just escape with a little money, the main objective of the map must be collected.