Pluck id (integer) cast to string !

While plucking from a database, I get id as strings.

$alphabets = new Alphabet();
return $alphabets->pluck('name', 'id');

Output

{
    "1": "Apple",
    "2": "Ball",
    "3": "Cat"
}

Expected

{
    1: "Apple",
    2: "Ball",
    3: "Cat"
}

But, when I reverse ID and name,

return $alphabets->pluck('id', 'name');

I get id as integer.

{
    "Apple": 1,
    "Ball": 2,
    "Cat": 3
}

I'm not sure what's happening behind the scene. But how can I get ID in integer ? Actually, Old flash session doesn't set value because of 1 vs "1".

 {!! Form::select('alphabet', $alphabets, null, ['class' => 'form-control', 'multiple' => true]) !!}