NFL contracts arent guaranteed. Most of the time when players sign big, long term deals like this, they never see the entire thing.
As details come out, we find that this contract has $32M guaranteed at signing, and a total $52M guaranteed (of the so called "$120M").
So if we break it down, it turns out we can get out of the contract after 3 or 4 years. It's essentially a 3 year/$52M contract, or 4 year/$70M contract. $17M/yr for a premier pass rusher is about right.