These days, I prefer to use
tmux as a terminal multiplexer over screen. However, sometimes I work on systems that only have screen terminal multiplexer available.

Recenly, I ended up spawning a screen while I was already inside another screen. I then had to detach the nested screen. Normally, I would just press

ctrl-a d

This didn’t work - it just detached the outer screen.

The trick is to press:

ctrl-a a d

This will detach the inner screen while leaving the parent screen attached.