It is impossible to transfer BTC from one address to another without paying fees,  that too now the fees being too high even if you need to transfer small amounts you need to pay high fees larger than amount you are transferring. If you have two of the accounts in coinbase exchange you can do it literally for free by just inserting the mail id. If there was no fees, people would just spam bitcoin transaction I think lightning network will help us out by minimizing the fees to large extent and making it free of cost for paying only once in the beginning and in the end while withdrawing funds by setting up a payment channel. Hope LN strikes soon.