Let’s say international conglomerate FooCo decides to acquire a widget factory to get in on that sweet sweet widget-manufacturing action. How much should they pay for the factory? One thing you can do is add up the value of all their assets: buildings, machines, inventory, delivery contracts, money owed to them from customers, and so on. Then you subtract their liabilities: debts, payroll, money they owe to suppliers, etc. Let’s say all that adds up to $10 million.
The factory owners will probably not sell it to you for $10 million, however. For one thing, they know you’re going to earn profit from the factory as long as it produces and sells widgets, and that’s worth something. For another, they know that you really want to get in the widget game, and they have a widget factory, and that means they can sell at a premium. They also know that their factory has a reputation as the best widget maker, and FooCo will be acquiring that as well. All of these “intangible” assets, which can’t really be accounted in any reasonable way, constitute “goodwill.”
So if FooCo buys the factory for $12 million, they can account for the acquisition as a factory worth $10 million plus $2 million in “goodwill.”
Goodwill is required to be accounted for separately from tangible assets, so that people reading the books understand what is actually being accounted for in things that can be valued and added up vs. the far more nebulous concept of goodwill.
Years later, the market for widgets crashes, and nobody is interested in buying them anymore. The factory sells fewer and fewer widgets and earns less and less profit for FooCo. The fact that the factory is now earning substantially less money than in the past means that the premium that FooCo paid - the extra $2 million - is now too high. Another way to look at is: if FooCo were to sell the factory now (assuming all its tangible assets were worth the same, which they wouldn’t be, but ignore that) they would not get $12 million for it, and might not even get $10 million.
That difference in value is a goodwill impairment, basically an acknowledgement that you would not be able to get that much of a premium over tangible assets if you sold the thing. (There are many other things that can decrease the value of an asset, goodwill impairment is just one. In real life, the factory machines and buildings would also depreciate as they got older.)
So, Sony:
In 1989, in a series of transactions, Sony acquired Columbia Pictures and related assets, which after a series of reorganizations and other acquisitions, eventually became part of the massive Sony Pictures Entertainment, an American subsidiary of Sony.
Sony paid a large premium over the book value of Columbia’s tangible assets, and recorded several billion dollars of goodwill for Columbia Pictures on their balance sheets.
One of the most profitable arms of the SPE subsidiary had been their home video sales, but the market for home video (sales and rental) has imploded in recent years. Because that part of the business is earning substantially less money, Sony has to record a goodwill impairment of $962 million to show investors that the intangible assets SPE (cash flow from future home video sales, plus other stuff, I assume) are now not worth as much.