You can use the below script to do the same. I've excluded system db's since the same can't be removed.

set nocount on

declare @dbname as varchar(80)

declare @server_name as varchar(20)

select @server_name = @@servername

declare rs_cursor CURSOR for select name from master.dbo.sysdatabases where name not in ('model','master','msdb','tempdb','alert_db','mssecurity')

open rs_cursor

Fetch next from rs_cursor into @dbname

IF @@FETCH_STATUS <> 0

PRINT 'No database to backup...Please check your script!!!'

WHILE @@FETCH_STATUS = 0

BEGIN

print 'sp_detach_db ' + @dbname

print 'go'

print 'print ''Detach of ' + upper(@dbname) + ' database successfully completed'''

print 'go'

PRINT ' '

FETCH NEXT FROM rs_cursor INTO @dbname

END

CLOSE rs_cursor

deallocate rs_cursor

print ' '

print 'print ''SERVER NAME : ' + upper(@server_name) + '--> All databases successfully detached'''

Copy the above script and execute it, you will get the output as detach script . Copy the output and execut it. All the user db's will be detached!!!!

If you face any problem let me know