Is this a troll question? Ofcourse btc is not bigger than usd that would be crazyness and btc would be way higher in price right now than it is.
Bitcoin is bit but not that big yet by far. We need more advertisement around the whole digital currency idea for it to get more big.
Bitcoin obviously cannot cross USD in terms of success and popularity though it is way higher than it in terms of value or price.
Bitcoin still needs a lot of time to reach where USD is now, and for reaching there bitcoin would have to face a lot of problems.