If you encounter problems while detaching a volume through the Amazon EC2 console, it can be helpful to use the describe-volumes CLI command to diagnose the issue. For more information, see describe-volumes.. If your volume stays in the detaching state, you can force the detachment by choosing Force Detach.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-detaching-volume.html

