You may be able to transfer airline miles into Marriott points, but you should really check with the airline site as you cannot make this request within the Marriott site. This is true of most loyalty programs, i.e., the request to convert is with the "host" program. I have not heard of any rental car conversions as these usually earn miles/points directly into the airline/hotel member's account. No hotel programs allow conversion between hotel awards - counter-intuitive to say the least. NOTE: It is NOT advised to convert between programs as the conversion factor/ratio diminishes the value of the original points/miles after conversion fees and bad "exchange rates."