Idle? That's fine (4)
I believe the answer is:
eric
This clue is a double definition.
'idle?' is the first definition.
(I've seen this before)
'fine' is the second definition.
(I've seen this before)
'that's' acts as a link.
(Other definitions for eric that I've seen before include "One of pair once popular" , "---- Roberts, actor brother of Julia" , "--, or Little by Little (Dean Farrar)" , "-- Idle; -- Morecambe" , "Man" .)