to a fault
to a fault {adv. phr.}
So very well that it is in a way bad; to the point of being rather foolish; too well; too much.
Aunt May wants everything in her house to be exactly right; she is neat to a fault.
Mary acts her part to a fault.
John carries thoroughness to a fault; he spends many hours writing his reports.
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Source: A Dictionary of American Idioms
