Although the CBP website clearly states for Global entry on arrival all you need is your passport this was in fact untrue on arriva at ORD. My mum was asked for a proof of address which could be a driver license or utility bill. As she doesn’t drive and we didn’t carry a utility bill she did not get approvedZ the CBP agent did however say she can email it to him within 30days and she will be approved. If she doesn’t she will need to reapply again. So be warned guys bring a proof address just in case.