Angular JS filter not equals

The syntax is just a little off, try:

<li class="list-group-item"
    ng-repeat="question in newSection.Questions | filter:{ Id: '!-1'}"
    ng-mouseenter="hover = true" ng-mouseleave="hover = false">

    <div href="#" editable-text="question.Text">{{question.Text}}</div>
</li>

See a little JSFiddle: http://jsfiddle.net/U3pVM/3845/

Edit:

Example with variables:

<script> var invalidId = '-1'; </script>
<li class="list-group-item"
    ng-repeat="question in newSection.Questions | filter:{ Id: '!' + invalidId}"
    ng-mouseenter="hover = true" ng-mouseleave="hover = false">

    <div href="#" editable-text="question.Text">{{question.Text}}</div>
</li>