This article proposes a power system state estimation (PSSE) capable of dealing with distribution and transmission networks. The proposed approach combines decoupled techniques, complex per unit (cpu) system, and a switching branch representation to meet the increasing complexity of state estimation issue when associated with the emerging electrical systems. The result is an efficient tool that can easily deal with distributed generation, closed loop, or meshed operation and manoeuvres in distribution systems (DS) keeping the efficiency and ability of the fast decoupled estimator to process transmission systems (TS). Results obtained with several simulations carried out on two distribution test systems, a 136-node Brazilian feeder and a 907-node European feeder, and on the IEEE 14-bus TS, demonstrate the effectiveness of the proposed methodology.