How do I include the id field in a django form?

I'm trying to create a simple form that pulls up a record by asking its ID in the form.

views.py

class Bill(models.Model):
    """
    Represents a single purchase made by a customer at a business.
    """
    business = models.ForeignKey(Businesses)
    customer = models.ForeignKey(User, blank=True, null=True)
    charge = models.ForeignKey(Charge, blank=True, null=True)
    amount = models.IntegerField(verbose_name='Purchase amount (in cents)',
                                 validators=[MinValueValidator(0)])
    tip = models.IntegerField(verbose_name='Tip amount (in cents)',
                                 validators=[MinValueValidator(0)])
    comments = models.CharField(max_length=255, blank=True, null=True)
    timestamp = models.DateTimeField(auto_now_add=True)

forms.py

from django import forms from django.forms import ModelForm from transactions.models import Bill

class BillSelectForm(ModelForm):
    class Meta:
        model = Bill
        fields = ('id',)

views.py

@login_required(login_url='/sign-in/')
def select_bill(request):
    """
    Finds a bill based on its ID number.
    """
    if request.method == 'POST':
        form = BillSelectForm(request.POST)
        if form.is_valid():
            pass
            # look up db for id number
            # go to bill view page if id found AND bill not paid
            # go back to same page and create message saying wrong bill

    else:
        form = BillSelectForm()

    return render(request, 'bill_select.html', {'form': form})

However, on the template, when I use {{ form.as_p }}, I'm seeing nothing at all. Thoughts?