Naruto merged his half of Kurama with the other half after he defeated Sasuke, giving Naruto ALL of the nine-tails Chakra, both Yin and Yang.
If you need a refresher:
http://naruto.wikia.com/wiki/Kurama Go down to the Kaguya Ootosuki Strikes section, in the very last paragraph it details how Sasuke had absorbed both halves of Kurama, and then after Naruto managed to beat him anyways, that the original Sage of the Six Paths encouraged Kurama to rejoin with Naruto to look after him(This was done after the 8-tails rejoined Killer B).