If you are on Windows 8.1 you have to do this. android - ADB Driver and Windows 8.1 - Stack Overflow It worked for me.
I remember when I was on Win7 64 bit you can't use MTP (Media Device), but Camera (PTP) worked.
I wish my adb would detect it. I've installed my USB drivers 3 times now, and it is just making me more angry and not working.
Posted via THE Nexus 6!