In addition to the aforementioned contextual action, which I find pretty tedious for every inherited item, you can also set ReSharper to “pull” the default comments when implementing a base class or interface.
To do this, from the ReSharper main menu, go to Options | Code Editing | Member Generation | Other Options Options | Code Editing | Member Generation | Other Options Options | Code Editing | Member Generation | Other Options inside here, you will see the option of copying XML documentation from overridden members, if you check this option, ReSharper will automatically copy all the legacy documentation for you.

source share