Conventional planning and optimization of cellular mobile networks for supporting the peak-time user demand leads to substantial wastage of electrical energy. Infrastructure sharing among geographically collocated networks is considered promising for energy efficient operation of future cellular systems. Therefore, this paper proposes a generalized energy-efficient cooperation framework for sharing BSs between two cellular radio-access networks (RANs) serving the same geographical area. Previous works have the constraint of cooperation only among the collocated BSs belonging to different RANs, while the proposed framework is free from such limitation. To the best of our knowledge, this paper is the first for developing cooperation mechanisms among the non-collated BSs. Independent Poisson point process is used for modeling the near realistic random locations of both BSs and user equipment (UEs). Under the proposed framework, BSs belonging to different RANs dynamically share each others traffic and thus allow some BSs to switch into low power sleep mode for saving energy. During this BS switching through traffic-sharing, connection continuity (no drop of the existing calls) is maintained throughout the network. A generalized optimization problem for maximizing energy savings is formulated. Due to the high complexity of the optimization problem, heuristically guided algorithms differing in BS selection and UE association policies are proposed. More specifically, two different BSs selection schemes and three separate UE association policies are integrated in the algorithms. Performance of the proposed inter-RAN cooperation framework is evaluated using extensive simulations demonstrating a substantial energy savings and gain in energy efficiency. Impact of different network parameters, such as BS selection and UE association policies, BS and UE densities, BS power profile and SINR requirements for connection continuity on the system performance is thoroughly investigated and analyzed.