An "overnight" change in the value of a currency is a devaluation, not a depreciation.
Probably the biggest overnight devaluation ever was the January 31, 1934, devaluation of the dollar from $20 per ounce to $35 per ounce, a 40% devaluation. The money supply was about $8 billion plus at least another $12 billion in gold-backed bonds. So, perhaps the total erasure was 40% of $20 billion or $8 billion dollars, worth 400 million ounces of gold (before the devaluation). As of right now 400 million ounces of gold would be worth $480 billion dollars (2014).
If the U.S. government was to pull a stunt like this today, it would result in a loss of about $12 trillion to people around the world.
Another biggie on this list is the Gorbachev erasure. In 1989, the Soviet Union under Gorbachev invalidated all 50 and 100 ruble notes. There is no telling how much cash the Soviet citizens had squirreled away, but it could easily have been 100 billion dollars.