For a minor that is traveling unaccompanied without an adult then the person under 18 flying alone doesn't need any extra ID.
When you're traveling as a minor without an adult the only person who will need to show ID is the adult dropping off the minor at the airport and picking up the minor.
The adult dropping off or picking up the minor at the airport will need to have their name listed on the flight reservation.
If you're under 18 and flying with your parents then you don't need to show additional ID and only your parents or the other adult will need to show ID.
If the child is under 14 days old then they may need a birth certificate or other proof of the child's age.
If the child is under 2 years old and plans to fly free on the parents lap then they need Identification as well such as a birth certificate to prove they're under 2 years of age.