We present a simple device architecture that allows all-electrical detection of plasmons in a graphene waveguide. The key principle of our electrical plasmon detection scheme is the nonlinear nature of the hydrodynamic equations of motion that describe transport in graphene at room temperature and in a wide range of carrier densities. These nonlinearities yield a dc voltage in response to the oscillating field of a propagating plasmon. For illustrative purposes, we calculate the dc voltage arising from the propagation of the lowest-energy modes in a fully analytical fashion. Our device architecture for all-electrical plasmon detection paves the way for the integration of graphene plasmonic waveguides in electronic circuits.