Can anyone Explain All of Allstate's Different Writing Companies to Me?

I see dec pages and ID cards with so many different writing companies for Allstate, I'm just curious what to make of them. I know Northbrook is nonstandard, and Allstate P&C is their newest company for standard business, but I've seen auto cards with Allstate Indemnity, Allstate Ins. Co, Allstate F&C, is there some additional tiering represented among these companies, or have they just changed their product that many times over the past few years?
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