Predicting bond type

The classic example of using first ionization energies to predict bond type is that of NaCl:

$\ce{Na + Cl → Na^+ + Cl^- → NaCl}$

Sodium has a first ionization energy of $\SI[per-mode=symbol]{495.8}{\kilo\joule\per\mole}.$Chlorine has a first ionization energy of $\SI[per-mode=symbol]{1251.1}{\kilo\joule\per\mole}.$Based on the difference in ionization energy, what type of bond exists when NaCl is formed?