DOC: level argument description in _binop

Author: toobaz

pandas/core/series.py

@@ -1512,7 +1512,7 @@ def _binop(self, other, func, level=None, fill_value=None):
         fill_value : float or object
             Value to substitute for NA/null values. If both Series are NA in a
             location, the result will be NA regardless of the passed fill value
-        level : int or name
+        level : int or level name, default None
             Broadcast across a level, matching Index values on the
             passed MultiIndex level