If there is an IMS, would that mean that the different systems will also share processes, documentation, procedures, and policies?

Yes definately different has different procedures but it can be imapct thorught IMS.

some processes and documentation have the same procedures, but differ in data and information that filled with.

Polices can also share some points, but not all.

yes, business impact is covered

Yes, Sure IMS is a complete Business application if i can say, in other meaning IMS is a Terms and procedures

An integrated management system (IMS) combines all related components of a business into one system for easier management and operations. Quality (QMS), Environmental (EMS), and Safety (OHSMS) management systems are often combined and managed as an IMS.

Advantages of an Integrated Management Systems

• Consistent objectives, planning, and document management
• Implementation and Operation of the system cost less.
• Easier internal audits
• No Redundancies, reducing the chance of conflict.

This could only be shared processes as long the clause number standard has the same requirement standard, meaning the correspondence between them matches the same 

There can be a number of processes(departments) based upon the business requirements & of an organisation. Ideally the processes are the unique ones while there can be a number of  procedures linked to these processes,some of whom may be common while others can be distinguished ones based on the requirements of the induvudial standards.

Ideally the company should function on the basis of a common vision & policy to attain the goals defined in these processes.