It probably is 100% all the way. Yet what about the small magnetic field that is generated since it is AC. Does that cause a miniscule loss in the form of a magnetic field? So could someone argue that it is .000001 % inefficient?
If the field does not do work, it is not going to "consume" energy any differently than the electric field. As for 0.000001% inefficient, I'll save the arguments for the sake of arguing to others.