Electroneutral blends of oppositely and uniformly charged flexible polymers spontaneously microsegregate, recapitulating phases formed in block copolymer melts. The length scale of the pattern is controlled by the charge density and the thermodynamic incompatibility of two species, with the molecular weight of the chains entering as a small correction. We calculate the disordered phase spinodal in the random phase approximation and determine the microphase diagrams numerically for the disordered-cylindrical-lamellar phases in a two-dimensional self-consistent lattice model. The mesophases are intrinsically characterized by spontaneous charge separation, so the morphology and orientation of the patterned phases are quite sensitive to externally applied electric fields.