The Nexus 6P USB driver can be downloaded below as it uses the Google USB driver. You can follow the install instructions below as soon as you connect your mobile phone to your computer. The installation process and USB driver is the same as the Nexus 6 as well as the Nexus 9 USB driver. Simply download the file below and install the driver from there with easy to understand instructions,
Nexus 6P USB Driver
First you will need to download the Google USB driver from this website and extract the file to a directory onto your computer. Remember where you extracted the files as you will need to know where to find it later. This does not install like the Samsung USB driver. The file is normally called (latest_usb_driver_windows.zip). Now you will need to open your device manager in order to update the driver for the device which would normally be showing an error.
1. Click Start menu and right-click on Computer.
2. Click Manage.
3. Click Device Manager in left pane.
4. In Device Manager window, expand categories and locate the device
5. Right-click on the device name and select Update Driver Software
6. Click on Browse to find the location of the downloaded driver file.
7. Find the files you had just extracted for the Google USB driver and click on the .inf file;
8. Click on Next button to install the driver.