Invoice is charged to Society keeping all the banks afloat presumably (8)
I believe the answer is:
billions
'all the banks afloat presumably' is the definition.
I can't tell whether this definition defines the answer.
'invoice is charged to society' is the wordplay.
'invoice' becomes 'bill' ('bill' can be a synonym of 'invoice').
'is charged' becomes 'ion' (I've seen this in other clues).
'to society' becomes 's' (common abbreviation in names of organisations).
'bill'+'ion'+'s'='BILLIONS'
'keeping' acts as a link.
Can you help me to learn more?
(Other definitions for billions that I've seen before include "Millions of millions" , "No bills I turn into vast sums" .)