In an ideal/a perfect world
Definition 1 of 1
Pro Tip 1/3Hypothetical Context
The phrase often suggests a hypothetical or non-realistic situation used for comparison. 
In an ideal world, I'd have a private jet to avoid traffic.
Pro Tip 2/3Expressing Desire
Use it to express what you wish would happen, knowing that it's unlikely or impractical. 
In a perfect world, all children would have access to free education.
Pro Tip 3/3Contrasting Reality
It's often used to contrast an imperfect current situation with a desirable, but unreachable, alternative. 
In an ideal world, we would not need to work overtime.