Cross subsidisation doesn't have to be cash either. Sometimes it's as simple as (say) giving some amaaaaaazing people a newly refurbished hangar. Sometimes it's the inefficiencies that creep into your business because you can't access your tarmac area that was set aside for you as a result of giving up said hangar because amaaaaaaazing people you gave the hangar to keep leaving another aeroplane in said tarmac area.
This then causes a delay to that aircraft arriving on to its bay, delay to premium domestic services, etc.
There is no way of allocating those sorts of things on the balance sheet. That doesn't mean they don't happen and it is certainly a way that either Qantas 'subsidises' Jetstar or Jetstar drags on Qantas.