Structuring test plan is different from different company & people. In general, one should note that test plan depends upon :
People (Available man power / team)
Projects (Distribution of team across different project)
Priority of the project(How much priority / What priority we are giving to the project at what time)
Above all, documentation & Sign off from Concern team(s).
In my experience, it depends upon people and how your dealing with different set of people.