Nothing is that simple
Lambda is a calculated value, calculated from co, c02 02 (possibly hc i can't remember) and various constants
in the uk we use the brettschneider method of calculation, which if you really wanted to see you could google

in the equation low Co helps get a good lambda value, but high Co2 is very important as is low oxygen content

so various conditions affect the lambda readings, including burn quality
and lambda can vary from the engine to the exhaust tip, for example a leak will raise O2 content and therefore increase the lambda shown on a gas analyser

when you see a car being MoT'd and Co=0, and lambda = 1.00 it will have a cat fitted, which requires lambda=1.00 ideally, and the CO content is removed by the cat even though it's present at the exhaust ports

i could go on, as it's my job every day but i don't want to be boring
but yes ,you could say generally low idle Co will give a better idle lambda reading