What is the difference between a travel agency’s itinerary and an airline’s itinerary?

The content is different and the functions are different.

The travel agency’s itinerary includes: departure and destination, itinerary arrangements, hotel reservation information, transportation arrangements, tour guide contact information, etc. The airline's itinerary includes: flight information, passenger information, baggage regulations, boarding gate and boarding time, etc.

A travel agency's itinerary is a detailed itinerary provided by the travel agency for tour groups or individual tourists. The airline's itinerary is a document provided by the airline to passengers, detailing the passenger's flight information and related services.