OP - I could have written this myself about my DH!
Horrific work environment, abusive, stressful. DH came home depressed, anxious, angry - you name it. He walked in to his bosses office one day and told his boss to shove it and quit.

At first, he told potential employers the truth - but eventually realized he was shooting himself in the foot! they saw him as a liability...a loose canon etc. Employers are afraid of "hero employees"...the ones that stand up for themselves. So DH changed his story - then and only then did he start to get call-backs for 2nd interviews. His story went something like this:

"I left my previous employer because I was offered a consulting opportunity I could not turn down - it was an opportunity of a life-time where I was going to be able to learn (insert new skill here) . My previous employer was great,it was a great company etc. but the work was no longer challenging so I chose to leave..." You get the idea.

The truth, that is exactly what you told us. The transfer to another department would not be seen as his fault, although some bad employers like to put people in positions where they know they would quit. Good luck.

He's a CPA who was transferred into another role in his company where he had no background, skills, or interest. In other words, a bad fit. He was coming to work with his eyelid fluttering and chest tightening so he walked in and said, "I'm leaving" and did. On one hand I am glad he did not have a heart attack but because he quit, no employment. He feels that with year end he will at least get consulting work so the unemployment is a moot point. What does he tell potential employers?