  The next generation weak lensing surveys (i.e., LSST, Euclid and WFIRST) will
require exquisite control over systematic effects. In this paper, we address
shear calibration and present the most realistic forecast to date for
LSST/Euclid/WFIRST and CMB lensing from a stage 4 CMB experiment (CMB S4). We
use the CosmoLike code to simulate a joint analysis of all the two-point
functions of galaxy density, galaxy shear and CMB lensing convergence. We
include the full Gaussian and non-Gaussian covariances and explore the
resulting joint likelihood with Monte Carlo Markov Chains. We constrain shear
calibration biases while simultaneously varying cosmological parameters, galaxy
biases and photometric redshift uncertainties. We find that CMB lensing from
CMB S4 enables the calibration of the shear biases down to 0.2% - 3% in 10
tomographic bins for LSST (below the ~0.5% requirements in most tomographic
bins), down to 0.4% - 2.4% in 10 bins for Euclid and 0.6% - 3.2% in 10 bins for
WFIRST. For a given lensing survey, the method works best at high redshift
where shear calibration is otherwise most challenging. This self-calibration is
robust to Gaussian photometric redshift uncertainties and to a reasonable level
of intrinsic alignment. It is also robust to changes in the beam and the
effectiveness of the component separation of the CMB experiment, and slowly
dependent on its depth, making it possible with third generation CMB
experiments such as AdvACT and SPT-3G, as well as the Simons Observatory.
