normally you just right click a file and select properties, there is a line that says "opens with" and a change option. click change and navigate to python.exe. should now open to python and not try to run the file itself.
or am i misunderstanding what you mean by "edit with idle". does that open the file some other way? you'd need to identify the exe file being used for that command if it is different, then just select that one as default to open with.