Cleaner bank retains papers (6)
I believe the answer is:
tidier
'cleaner' is the definition.
('tidy' can be similar in meaning to 'clean')
'bank retains papers' is the wordplay.
'bank' becomes 'tier' (both can mean a row of similar things).
'retains' indicates putting letters inside.
'papers' becomes 'ID' (identification papers).
'tier' placed around 'id' is 'TIDIER'.
(Other definitions for tidier that I've seen before include "More neat and orderly" , "More trim" , "Trigger" , "More methodical" , "not so disorderly" .)