You can use the RETURNING CLAUSE in your insert command.
It should look like this:
INSERT INTO customer (col1, col2, ...) VALUES (val1, val2, ...) RETURNING id
Another option is to use the INSERT ALL syntax, something like this:
INSERT ALL INTO customer (id, col1, col2, ...) VALUES (your_seq.nextval ,val1, val2, ...) INTO customer_details (cust_id, col1, col2, ...) VALUES (your_seq.currval ,val1, val2, ...) select * from dual;