A brewing battle over how to treat more than $5.5 trillion in assets on company books is pitting investors against businesses, investment advisers against academics and even banks against their own trade association.

At issue is an accounting term known as goodwill, which is the premium a company pays when it buys another for more than the value of its net assets. An unprecedented five-year boom in mergers and acquisitions has added urgency over how to account for the financial concept.

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