CAR has canned reports that provide this info, it logs inbound and outbound calls, you cannot choose to just have one.
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/service/7_1_2/car/CAR/cardvgat.html
CAR is provided with basic reporting, which you cannot adjust, if you require something with more details/info, you would require a 3rd party billing solution.
HTH
java
if this helps, please rate