RichThesaurus
never in a million years
vs
never in a month of Sundays
never in a million years
adv
Absolutely not.
never in a month of Sundays
adv
At no time whatsoever.
How often have the words
never in a million years
and
never in a month of Sundays
occurred in a corpus of books?
(source:
Google Ngram Viewer
)