1 Bitcoin = $1,000,000 USD
21 Million Bitcoins = $21,000,000,000,000 ($21 Trillion USD)
The value of Bitcoin is never going to be that high, I think that we have to stay realistic and not speculate about things that we know are not going to happen.
I would be a great thing if the value would be that high but it is impossible to think that it will happen.