SELECT name, SUM(mb)
  FROM (
    SELECT 
      nvl2(l.segment_name, l.TABLE_NAME, s.segment_name) name,
      ROUND(bytes / 1024 / 1024) mb
    FROM user_segments s, user_lobs l
    WHERE s.segment_name = l.segment_name(+)
      AND ROUND(bytes / 1024 / 1024) > 0
    ORDER BY 1, 2)
  GROUP BY name
  ORDER BY 1;

NAME    SEGMENT_TYPE  MB
--------------  ------------  ----------
AKT_CA_KAT_UNQ	INDEX	      3
AKT_GLP_RG_UNQ	INDEX	      2
AKTUELLES	TABLE	      17