The most famous document in the history of religious toleration has three problems: it is not an edict, it was not issued at Milan, and it may not be a single document at all. Constantine and Licinius met at Milan in early 313 and agreed a policy. What survives is the instruction sent afterwards to provincial governors, preserved in Latin by Lactantius and in Greek by Eusebius, both of whom quote a letter of Licinius issued in the East.
The substance is nevertheless real and generous. It grants to Christians and to everyone else the free power to follow whatever religion each chooses, so that whatever divinity is in the heavenly seat may be favourable to the emperors and to their subjects. And it orders the restitution of property taken from Christian congregations, at public expense where it had passed into private hands, which is the provision that actually cost something.
The wording is worth reading closely for what it does not do. It establishes no religion, names no orthodoxy, and grants nothing to Christians that it does not grant to everyone. Whatever Constantine's personal convictions by this date, the policy expressed here is a general freedom of worship, and the atlas records it as such rather than as the moment the empire became Christian, which is a later and different event.