The sum is the only reason I'm kinda doubting this rumor. Still... Minecraft is the biggest gaming phenomenon in years, and the train doesn't seem to be slowing in the slightest, so there's a huge amount of value there.
That said, it's not as simple as the title question says. MS couldn't get 20 new AAA games from anywhere with $2 billion because they don't have the manpower themselves and getting so many from other sources would be very difficult. And what IPs would they be? When would they get them? Nope, too difficult.
EDIT: And just for the record, if it was possible, I'd say 20 new AAA games for sure. I'm just pointing out why it's not really a fair comparison.