What is the difference between mindfulness and detachment?
'Mindfulness' means 'to remember' to apply/practise the Buddhist teachings. It does not mean 'bringing one's attention to experiences occurring in the present moment' (as written by a person in Wikipedia). 

For example, if I wish to stalk and assassinate (murder) another person using a rifle, I must meticulously bringing my attention to experiences occurring in the present moment. Yet murdering a person in the present moment is not practising the Buddhist teachings. 

In summary, for the 'trainee' of the higher path, the mind must continuously remember to not attach to any experience. Therefore, to practise non-attachment requires mindfulness, as written in the suttas: 


  His mindfulness... is maintained to the extent of knowledge &amp; remembrance. And he remains independent, not clinging to anything in
  the world. 
  
  MN 10