Sorry but I have to chime in on this.
The video game industry as a whole took in 11.7 billion in 2008. This is the total for all games. Now an online game can easily make $200k - $500k a year, but not in the millions of millions. I've been a gamer for 27 years, so I know the market and industry of most types of games.
With that said, you can't say "I have a billion dollar idea, let's make it". You didn't even give any details on it. You will need to build a coding manual and stick to it instead of whatever comes to your head at the moment. For a project like this, be prepared to pay an upwards of $50,000 - $75,000 for programming, not including the graphics.