List the details of the customers who do not have any policies.
CREATE TABLE Customer_Policies (customer_id VARCHAR); CREATE TABLE Customers (customer_details VARCHAR, customer_id VARCHAR); CREATE TABLE Customers (customer_details VARCHAR)
[SQL] SELECT customer_details FROM Customers EXCEPT SELECT T1.customer_details FROM Customers AS T1 JOIN Customer_Policies AS T2 ON T1.customer_id = T2.customer_id [/SQL]