Per IDC:

[T]he iPad Pro was the clear winner this season as it was the top selling detachable, surpassing notable entries from Microsoft and other PC vendors. It's also important to note that the transition towards detachable tablets has presented positive opportunities for both Apple and Microsoft. However, Google's recent foray into this space has been rather lackluster as the Android platform will require a lot more refinement to achieve any measurable success.

The introduction of the iPad Pro didn't seem to do much to improve Apple's overall tablet sales, so it's a little surprising to see that it still outsold the Surface which is supposed to be selling quite well. I think this is an exciting space, and I see a lot of Macs and PCs getting just a little nervous.