How can you pass a bound variable to an ng-click function?

I have a simple delete button that will accept a string or number but won't accept an ng-model variable ( not sure if that's the correct terminology ).

<button class="btn btn-danger" ng-click="delete('{{submission.id}}')">delete</button>

Which generates:

<button class="btn btn-danger" ng-click="delete('503a9742d6df30dd77000001')">delete</button>

However, nothing happens when I click. If I hard code a variable then it works just fine. I assume I'm just not doing things the "Angular" way, but I'm not sure what that way is :)

Here's my controller code:

$scope.delete = function ( id ) {
    alert( 'delete ' + id );
}