Offline charging for sessions over a 3GPP network and a WLAN access network

A system comprising:

• a charging system operable to receive a first accounting request for a session from a first network element that manages a session for a communication device, and to receive a second accounting request for a data flow occurring during the session from a second network element that manages the data flow during the session, wherein at least one of the accounting requests includes a session charging identifier for the session and a data flow charging identifier for the data flow;
• the charging system is further operable to generate a first Charging Data Record (CDR) for the session based on the first accounting request, to generate a second CDR for the data flow based on the second accounting request, and to insert the session charging identifier and the data flow charging identifier in at least one of the CDRs;
• the charging system is further operable to correlate the first and second CDRs based on the session charging identifier and the data flow charging identifier inserted in the at least one of the CDRs to generate a consolidated CDR, and to transmit the consolidated CDR to a billing system.