Voltage divider for a voltage range spanning negative voltages
You can use a voltage divider. The grounds must be common, and any difference in potential will lead to errors. With your resistor values, the source must be able to drive a 6200 ohm load.
The ratio of the resistors is 1200/6200 so a +/-10V input will give you (nominally) about +/-1.935V. The resistor tolerances will affect what  you actually get. 1% tolerance values (E96 series) that are close are 4.99K and 1.21K and even if the resistors are worst-case off it will still be less than 2V for 10V in.
If you were looking for an exact ratio you would take the 1M\$\Omega\$ input resistance into account, but it's around 0.1% effect.
For example, if you used a perfect 4.99K\$\Omega\$ resistor, the exact value of the other resistor for 10V-&gt;2V would be 1247.5\$\Omega\$ not considering the 1M\$\Omega\$ and 1249.06\$\Omega\$ taking the input loading into effect, or about -0.12% less.
To adjust the resistor for the loading the equation is:
Rnew = 1/(1/Rold - 1/Rload)