Just like international development money in Europe has been moved to pay for handling refugees from war locally and military action in Syria, it is a risk that this pledge just becomes recycled money from this previous pot of money. (International development funds were about $130BN in 2014.) And countries like the Netherlands and Finland have been cutting back their spending recently, quite dramatically, if they just spend what they used to spend they could claim they have done their part already, without actually adding anything.
(They will add $100 billion, not million.)