Soros has had massive short positions on the US dollar.
Given its fall over the past 18 months and, especially in the last six, Soros may have doubled the billions he already had.
Soros has made his billions looking for asset balances that are out of kilter from reality (US$ vs Euro) for instance. He is much maligned for making a killing off of the collapse of the British pound a number of years ago. But who do you blame when a government intervenes in a market to prop up its currency and maintain a value contrary to the equilibrium free-market value? The speculator who sees the opportunity and takes advantage or the government that tries to manipulate the market in a sustained fashion over a long period of time?
And while his friends in the media are beginning to talk down the dollar, he's cashing in and going long. He gains on both the up and the down.