They are not listed on your bill. Your PDF bill simply says that the price of your plan includes the discount.
Which plan do you have? How many lines on your account. Simply by looking at the available plans and the price of each depending on how many lines are on your account, you can tell if you are getting the discount. Regardless, as I said previously your PDF bill will state the discount if you are currently getting it.
Reading thru the following thread may help you understand a bit better:
@menace11 Being able to check your discount every once in a while is a great thing to do to make sure you're getting the best price possible. The great news is that the automatic payment discount is already included in the price of your plan, and you can be sure you're getting the discount as long as you've got your payment method set up with a debit card or checking account. If you have a question more specific to your account, please send us a Private Note and we'd be happy to further assist.