For nothing is impossible with God.But in TNIV this verse has been changed to:
For no word from God will ever fail.Why the change? Is it justified? The main issue is apparently with the Greek rema, which usually means "word" but sometimes, and especially in Luke's writings (also 1:65, 2:15,19,51; Acts 5:32, 10:37) has a weaker meaning "thing, happening, affair". So the NIV interpretation can certainly be jusitified. But then in Luke 1:38, 2:17,29,50, 5:5, 7:1, 9:45×2, 18:34, 20:26, 24:8,11; Acts 2:14, 5:20, 6:11,13, 10:22,44, 11:14,16, 13:42, 16:38, 26:25, 28:25 rema clearly refers to spoken words. It is most telling that 1:38 in the sense of spoken words immediately follows the ambiguous 1:37, although there must be a rapid shift in sense in 2:15,17,19 and 2:50,51.
The slight problem I see with the TNIV interpretation is that adunateo would normally mean "be impossible" rather than "fail". In fact this verb is found elsewhere in the New Testament only in Matthew 17:20, but the related adjective adunatos is more common. The meaning is almost always "impossible", although in Acts 14:8 and Romans 15:1 it means more like "weak, powerless".
So, literally the verse is "With God every word/matter will not be impossible". I would take this to mean something like "Nothing that God says he will do will be impossible for him to carry out". And the TNIV rendering effectively says the same thing.
But, lest anyone think that TNIV is weakening God by denying that he can do all things, that he is almighty, see Matthew 19:26 TNIV:
... with God all things are possible.