could you tell me those four customer's details and their ID?
SELECT T1.customer_details ,  T1.customer_id FROM Customers AS T1 JOIN Customer_Policies AS T2 ON T1.Customer_id   =   T2.Customer_id GROUP BY T1.customer_id HAVING count ( * )   >  1
four customers' details refers to SELECT customer_details; their ID refers to customer_id; customers having more than one policy refers to GROUP BY customer_id HAVING COUNT(*) > 1;