This paper presents a process model for the management of architectural decisions in enterprise architecture planning. First, decisions are made at the enterprise level, with strategic business considerations on the enterprise information, systems and technology strategy and governance issues. The next step is to define the domains, to then go on with domain architecture decisions. At the systems level, the enterprise and domain architecture decisions are collected and converted into architecture descriptions accurate in precision, form and detail to be given as input to the information systems development process, following the architectural planning. The model is derived from previous work and empirical findings in three large organizations, where the enterprise architecture and enterprise systems have been developed. This case study contributes with considerations on the domains, their definition, and produces refinements to an enterprise architecture process model presented before. For the development of the model, the "living system" paradigm is followed.