What's This White "Smoke?"

Originally Posted by OldGuy

If I start my Z when it's not been driven overnight or longer, clouds of white smoke (vapor) are emitted from both tailpipes as it idles during warm-up. I'm sure it's not oil burning and it seems to diminish when the car has warmed up. I assume this is nothing to worry about but can someone explain what is happening to cause this and reassure me that its not harming the car? The car has 399 miles on it.