There is 12,577,500 bitcoin in circulation right now.
So with roughly that much bitcoin multiplied to $1,000,000 USD would would make the total value of all the bitcoin $12,577,500,000,000.
Thats twelve trillion ,five hundred seventy seven billion ,five hundred million.
There was approximately $1.27 trillion in circulation as of March 26, 2014, of which $1.22 trillion was in Federal Reserve notes.
"source -
http://www.federalreserve.gov/faqs/currency_12773.htm"
I'm not sure total USD in circulation is a good valuation point for Bitcoin. First there is an international aspect, BTC is not restricted to USA. Second the $1.27 trillion represents dollars in circulation. But one dollar can be exchanged twice, thrice or multiple times. A much better indicator I think is gross domestic product (or gross national product) because this represents the total market value of goods produced domestically (at a national level respectively) per year.
And for the optimists, since BTC is international why not take the foreign exchange market as a reference point. According to Bank for International Settlements, trading in foreign exchange markets averaged $5.3 trillion per day in April 2013. Again that's per day! Can you imagine what would happen if only a fraction of these transactions would be done in BTC?