Does the law require automotive insurance companies to provide owners with a detailed breakdown of actual cash value data for total loss cases?

Generally speaking, the law does not require an insurance company to provide the sort of detailed breakdown you describe, but the law absolutely imposes on the insurance company an obligation to act in good faith during the settlement process, so if they unreasonably refuse to explain in detail how they arrived at the actual cash value they offered, they risk being found in violation of their obligation to process your claim in good faith. The sad reality of modern insurance practice is for them to pay as little as possible as late as possible, and some insurance companies can really be nasty about it. A good strategy in your negotiations with the insurance company is to make them think you're going to engage the services of a public insurance adjuster to negotiate with them on your behalf.  Public insurance adjusters are in the business of putting the screws on insurance companies to keep them honest during the adjustment process.  They often employ experts who used to work for insurance companies and know how the game works from the inside. They get paid on a contingent fee basis.  In other words, they get paid a percentage of what they recover for you from the insurance company. Some of them are snakes in the grass, but if you get one of the reputable ones they more than pay for themselves, because the amount they recover for you is so much more than what you were likely to get for yourself both you and they come out ahead. The thing is, your insurance company knows that the game is going to change dramatically for them if a public insurance adjuster gets involved and calls them on all of their bull@#$%, so they're much more likely to give you a fair deal if you put the fear in them that you're thinking about getting a public insurance adjuster involved. Don't let the insurance company think you're going to solicit a public insurance adjuster.  Make them think public insurance adjusters are approaching you because they think you've got a good claim that's worth pursuing.