Exactly. The carrier is responsible to verify you have any required documents for entry into any country they fly you to. Passport, visa, etc. The airline is responsible and they get the fine if they fly anybody that doesn't have their required documents. Of course in addition to that, an airline can request whatever they want to at check in. As for going to the gate, even if it's an Intl flight, the nice folks checking your ID should not be looking for any of that.........strictly satisfying the requirement of a government issued photo ID........