I did what I suppose you would call CC with DS when he was about 13 months.
It was when I thought he was old enough to understand what was happening - I can;t really explain it but I thought he would "get it".
Instead of BF to sleep or when he woke at night, I would settle him in his cot, gently pat and ssh for a minute or two, tell him it was sleepy time and tiptoe out of the room. If he started crying, I would go back in again almost immediately, and resettle him (not picking him up, just pat & sssh).
I would leave again and if he started crying again, leave it a minute or two before going back in.
I never had to go in more than twice and he would be settled & off to sleep within 5-10 minutes each time.
If he was distressed in any way I would stay with him, offer him a B/F or lie with him.
After a week or two he started settling by himslef and apart from when he is ill he has never cried during the night since, and goes happily to bed at night or for a nap.
Only you know your own child but at 20 months I would have thought you could try something similar?
It doesn;t mean leaving them screaming for hours, alone and distressed