I would recommend idling this achievement unless you want to play 80 hours of terrorist hunts. To idle this achievement you need three xboxes and three gold accounts to do it. Setup a attack & defend match on any map on a dummy account that you don't want to earn xp on. Make the time for the match 20 minutes and make sure that dedicated host is on or else the matches won't start up while your gone. Join the game with your main account and dummy account and make sure that the account that you want to earn xp on is on defenders so that you get the maximum amount of xp per match. Once you get two accounts in the game the match should start and you can go away from your xbox. In an eight hour session you will earn roughly 40,000 xp. You need 675,000 to reach the rank of elite.