As HarryB mentioned His answer. Their are 2 types of admins,
Farm Admin: there are bit of confusion about the farm admin account, that it has full control on the farm and can access everything. That's not true, it can access everything from back-end expect from the Contents. If you want to access to content then you can add farm Admin account into the policy of Web for the desired web application then farm admin can access everything inside the Web app.
Members of the Farm Administrators group have Full Control permissions
to and responsibility for all servers in the server farm. Members can
perform all administrative tasks in Central Administration for the
server or server farm. They can assign administrators to manage
service applications, which are instances of shared services. This
group does not have access to individual sites or their content.
Site colelction AdminsThese administrators have the Full Control permission level on all Web sites in a site collection. They have Full Control access to all site content in that site collection, even if they do not have explicit permissions on that site. They can audit all site content and receive any administrative message. A primary and a secondary site collection administrator can be specified during the creation of a site collection.
Choose administrators and owners for the administration hierarchy in SharePoint 2013