CREATE TABLE Customer_Policies (customer_id VARCHAR)
CREATE TABLE Customers (customer_details VARCHAR, customer_id VARCHAR)

List the details of the customers who do not have any policies.
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
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"