I teleported around 16,777,216 but the message came weird in the chat.
it will say something like 1.6477554E7 (example).

The reason this happens is because when you put the I coordinate the game thinks is too high and displays it weird in the chat.

Reproduce by:

• Spawn a pig
• name him Pigman
• type /tp @e[type=Pig,name=Pigman] ~ ~ ~6000000
  be careful or you may teleport yourself