If you keep the current low enough (<0.5 mA) the clamping diodes of the Arduino pin will take care of it. So even the 100V spikes can be handled while normally 12V gives a 5V output. The problem is that the resistors are getting quite large so better use a separate clamping diode:
This circuit goes from 0-3.8V output for 0-12V input, so you can measure a bit over 12V as well.