  We compute the super-Hubble evolution of non-Gaussianity of primordial
curvature perturbations in two-field inflation models by employing two
formalisms: delta N and covariant formalisms. Although two formalisms treat the
evolution of fluctuations radically different, we show that the formulas of
f_{NL} parameter agree quantitatively with each other within 1 % accuracy. We
analytically find that the amplitude of f_{NL} decays no faster than a^{-3} as
the inflationary trajectory reaches to the adiabatic limit for generic
potentials.
