(as) easy as ABC
Extremely easy, simple, or intuitive; requiring very little skill or effort. After so many years as an accountant, doing taxes is as easy as ABC for me. Don't worry, after some lessons and a bit of practice, driving is easy as ABC!
as easy (or simple) as ABC
extremely easy or straightforward. From the 15th to the 17th century, a child's first spelling and reading book was commonly called an ABC , and this led to the development of its metaphorical use, ‘the basic elements or rudiments of something’.