Not getting value through call back in Enber js

I am new to Ember JS and any UI framework. Facing below issue so kindly suggest.

I user object (json) having it's group ids (array). Using group Ids I need to pull the group name and details. Using below code to get the details.

Asynchronous call is going through and fetching the data but I an not getting in nameGroup variable.

var nameGroupName = _.filter(user.userGroups, function(group){
     return groupService.GroupDetails(group).then(function(result) {
       return result.name;
     });
});

Kindly suggest.