I know this is a lame answer, but honestly? It depends. My first job was at a large insurer where I did data analytics for the claims processing units, so I have a pretty detailed understanding of how claims processing works at that company. Since becoming a consultant, I have gained insight into claims processing at a variety of other insurers, and the most obvious consistency I have seen among all of them is that each one is unique. Even within a single company, different subunits may operate very differently. For example, a unit devoted to processing claims for individual commercial policies may work differently from another unit processing small group commercial policies.
There are a lot of reasons for this variation: internal policies, provider practices, company investment in technology, corporate structure (mergers and acquisitions can create terrific patchworks of operations), type of
insurer, type of claim, etc. Technology is an especially important driver with the advent of electronic claims submission and even real-time adjudication of claims. Some insurers have made great advances with auto-adjudication programs and can process a large number of claims that way. Some insurers haven't. But this too will change rapidly across the industry over the coming years. Analytics is also an especially rapidly developing area in claims processing. Like many industries, insurers are beginning to realize and harness the power of "big data" available. But often antiquated systems and lack of internal expertise makes this process very slow.
That being said, I often refer new hires to the AMA's excellent Follow That Claim. It is oriented towards physicians, but it gives a good overview of the overall claims process. But keep in mind that there really isn't a one size fits all approach.