A Level Subject Content for teaching from 2017
GCE Subject Level Guidance from DfE, this guidance is intended to help awarding organisations understand how to comply with the GCE subject-level conditions and requirements for mathematics. The guidance includes further information on the use of Technology and large Data sets.
For a change of specification as well as clear specifications, comparison and mapping documentation are always very useful.
From MEI, a summary which applies to all specifications:
Changes to AS/A Level Mathematics & Further Mathematics.
Also from the Further Maths Support Programme, see this very useful comparison of the applied mathematics content with the current mdules.
Stuart Price (right-click once you have followed the link and you will be able to save the image) has very helpfully mapped legacy A Level questions to the Further Mathematics Core specification.