Electric bill for reactive power
There are a couple of factors to consider. 

1) Old-style wall-wart chargers use a transformer that runs at line frequency (50 or 60 Hz). High-quality line-frequency transformers do present a large reactive load to the AC Mains. 

Unfortunately, most wall-wart chargers do NOT use high-quality transformers. They usually run very close (or into) saturation and thus run warm or even hot. That heat shows up on your power bill as energy consumed. 

2) Modern chargers use a switch-mode power supply. These can be extremely efficient when idling. 

Bottom line is: If the charger is running warm, it is consuming energy and that usage will show up on your power bill.