CREATE TABLE TST_SUMMARY
  (
  SUMMARY_ID NUMBER PRIMARY KEY,
  TYPE NUMBER,
  TRANS_DATE DATE,
  TOTAL_AMOUNT NUMBER
  );

CREATE SEQUENCE SEQ_TEST START WITH 1
NOCACHE
NOCYCLE;

CREATE OR REPLACE TRIGGER TRG_TEST
BEFORE INSERT ON TST_SUMMARY FOR EACH ROW
BEGIN
    SELECT  SEQ_TEST.NEXTVAL INTO :NEW.SUMMARY_ID FROM DUAL;
END;


CREATE TABLE TST_DETAIL
  (
  DETAIL_ID NUMBER,
  AMOUNT NUMBER,
  TRANS_DATE DATE,
  FK_SUMMARY_ID NUMBER REFERENCES TST_SUMMARY,
  PRIMARY KEY (DETAIL_ID, TRANS_DATE)  
  );


INSERT ALL
  INTO TST_DETAIL VALUES (1,1001.5,TO_DATE('01-12-2014','DD-MM-YYYY'),NULL)
  INTO TST_DETAIL VALUES (2,2000.5,TO_DATE('01-12-2014','DD-MM-YYYY'),NULL)
  INTO TST_DETAIL VALUES (3,3009.9,TO_DATE('01-12-2014','DD-MM-YYYY'),NULL)
  INTO TST_DETAIL VALUES (4,4000.1,TO_DATE('01-12-2014','DD-MM-YYYY'),NULL)
  INTO TST_DETAIL VALUES (5,9001.9,TO_DATE('05-12-2014','DD-MM-YYYY'),NULL)
  INTO TST_DETAIL VALUES (6,1009.1,TO_DATE('05-12-2014','DD-MM-YYYY'),NULL)
SELECT * FROM DUAL;

INSERT INTO TST_SUMMARY(TYPE, TRANS_DATE, TOTAL_AMOUNT )  
  (SELECT 4, TRANS_DATE, SUM(AMOUNT) FROM TST_DETAIL GROUP BY  TRANS_DATE);

--BUT I DONT KNOW HOW TO UPDATE THE DETAIL TABLE (DETAIL.FK_SUMMARY_ID) 

1. This will put a heavy strain on your system.  If you ever try this with large detail tables you will end up with lots of updating which will burden your logging system and auditing system and replication system and pretty much anything else that needs to monitor in some way what happens to your data.

2. It may be an untenable design anyway.  As soon as you develop a second summary that requires use of detail rows that were summed up into the first summary you will have detail rows that participate in multiple summaries.  What do you update your detail row with then?  Now you are faced with needed to add new "association" tables to fix it.