On a Windows 10 VM set to 2 GB of RAM, Windows idles at about 1.1 GB.
On a 16 GB Windows it uses about 7.5 GB. All of that seems to swap out or go away somewhere if I get busy with Visual Studio.
On a 64 GB Windows it seems to idle at about 9.6 GB used. Of course, this one isn't a purely work machine and has Steam, Origin, Ubisoft's thing, etc, etc.
So Windows 10 is pretty variable. I imagine it has something to do with running various services in parallel.