The basic “Car Rental Loss” coverage is included for free on your amex card if you waive the collision insurance with the rental agency. The “Premium Car Rental Coverage” is an extended benefit on the amex card that you must opt-in to. This costs ~$20 for each car rental reservation.
https://www.reddit.com/r/amex/comments/14km60g/thank_god_for_amex_car_rental_insurance/