[STM32L082] Powering the USB section of the chip

I do not want to use the USB part of the STM32L082. According to the Ref Manual RM0376 page 140 there is no explicit mention that the VCC_USB can be tied to GND if not in use. So what would be the thing to do (and reduce the power even further): GND or 3.0-3.6V?

Please advise?