Sure you can delete them from your Macs and iOS devices, but what if you’ve got a few over the past few years and you don’t use them anymore?
You can't delete them as such, but you can "empty" them. See http://www.wikihow.com/Delete-an-Apple-ID for details.
Some lines from a forum:
You can't. Once an Apple ID exists Apple will absolutely not under any circumstances delete it or merge it with another Apple ID. Since iCloud accounts are affiliated with Apple IDs, once you create an iCloud account, said account cannot be removed or merged with a different iCloud account either. The only thing you can do is simply not use one of the Apple ID and/or iCloud accounts.
Go to https://www.icloud.com/ and login with the associated appleID and password and delete off all the contents.