This work studies the capacity region of ergodic fading Gaussian interference channels, where only one of the users is subject to interference from the other user, and that channel state information is not available at transmitters (no CSIT). In particular, inner and outer bounds of the capacity region are obtained. The inner bound is achieved by artificially creating layers in the signaling of the interference-free user. The outer bound is developed by characterizing the trade-off between the rate gain of the interference-free user and the rate loss of the other user due to interference. Furthermore, the gap between the inner and outer bounds is no more than 12.772 bits per channel use per user, regardless of the signal-to-noise ratios and fading statistics.