To delete all containers including its volumes use,
docker rm -vf $(docker ps -a -q)
To delete all the images,
docker rmi -f $(docker images -a -q)
Remember, you should remove all the containers before removing all the images from which those containers were created.
In case you are working on Windows (Powershell),
$images = docker images -a -q
foreach ($image in $images) { docker image rm $image -f }
Based on the comment from CodeSix, one liner for Window's Powershell,
docker images -a -q | % { docker image rm $_ -f }