While not all the details are known at this point, we do have some. The offer was at least double what he was offered last offseason (he was offered $66 million) and is said to run between 6 and 9 years. Given that he is only two days away from having two full years of service time, he would have qualified for early arb next offseason as a Super Two player and been five years away from free agency (at the age of 29).
It looks like the Cubs are buying out all the arb years plus at least one of free agency. If it runs just the 6 years, that would put it at a 6-year $132 million contract. I could easily see it, though, having a couple of option years attached at the end with some pretty hefty paydays that could push it close to $200 million for 7 or 8 years.
This makes a ton of sense to lock in a long-term contract before the upcoming lockout. If he can get his guaranteed money now, he will be sitting pretty regardless of how this upcoming Collective Bargaining agreement comes out.