Unused Column in Oracle

CREATE TABLE cust_details (
    cust_id               NUMBER,
    cust_name             VARCHAR2(100),
    cust_address          VARCHAR2(255),
    cust_account_number   NUMBER 
);

insert into cust_details values(1,'SCOTT','500,1A,california',11111111);
insert into cust_details values(2,'KING','120,1B,california',22222222);
insert into cust_details values(3,'JAMES','400,1A,california',33333333);
insert into cust_details values(4,'JHON','300,1A,california',44444444);

commit;

desc cust_details;

select * 
from cust_details;

alter table cust_details set unused(cust_account_number);

select * 
from cust_details;

desc cust_details;

select * 
from USER_TAB_COLUMNS 
where table_name = 'CUST_DETAILS';

alter table cust_details drop unused columns;