Still on course for near double-digit losses against the dollar in 2015, the euro is on track for a solid victory of about 4 percent during the month of December. Much of the euro's December dominance stems from the European Central Bank's milder policy prescriptions than markets had anticipated.The euro next year would face significant downside risk if the 19-nation economy fails to meaningfully turn the corner, which would likely hasten another round of ECB stimulus.

The dollar is paying the price for being the year's top performer as the few still at their trading desk are liquidating some of their winnings to realize profit. Not many expect the dollar's December decline to lead to a lasting New Years hangover, however. Still, the dollar's fate over the coming year will be squarely in the hands of the world's biggest economy. Improving economic health would translate into higher Federal Reserve borrowing rates which would ultimately buoy the buck against its lower yielding peers.