Interface Documentation

Hi all,
We are currently in the process of implementing a new financial system which needs to interfaces with several other business systems to process payments. i.e. the source system interfaces with new target financial system to send instruction on people/businesses that need to be paid.  I want to make sure that the details regarding these interfaces are suitably documented.
What I am struggling with in this regard is what we should be documenting.  Some research highlights different expectations and requirements e.g. interface strategies, interface designs, interface control documents, interface specification etc.

My question is what documents should we be creating for the new system as a whole, what documents we should be creating for each specific interface and what kind of information should be included in each?

Some thoughts I have had that we should be recording are:
•      Mapping tables
•      Validations
•      Ownership & Responsibilities
•      Security requirements
•      Data fields being interfaced
•      Interface method
•      Timings
•      How the interface will be processed
•      Reconciliations

TIA