With AutoCAD 2014 you now have the ability to use the FILLET or CHAMFER commands on a polyline that is “self-intersecting.” When the “radius” of a FILLET is set to <0> or when there is no angle set to a CHAMFER, these tools can be used to clean intersections by trimming or extending objects at their intersections. But since a polyline is a single object, this hasn’t been possible without the help of an add-on like a lisp routine or .NET application.
Here are a few posts that describe how to do use FILLET or CHAMFER to clean intersections:
The great thing is that there is no change to how the FILLET or CHAMFER command works to use this new ability. Simply use the FILLET or CHAMFER command as normal and the ability to select 2 different segments of a polyline are now available.
Below is an example of how AutoCAD 2013 did not have this feature: