This expression means to be very easy. It might come from the fact, while not being easy to make, pies are generally thought to be easy to eat. The saying refers to 'pie' as something pleasant. 'Pie' in this sense is archetypally American. The phrase was coined in the nineteenth century in the United States. The usage first comes in the saying 'as nice as pie'. The earliest example of the actual expression is from 1887.

Übersetzung:

kinderleicht sein

Gegenteil(e)

The opposite of "as easy as pie" is "it took some doing".

Synonym(e):

You could also say: to be as easy as falling off a log.