Century Link comes along and looks at the value of all the copper in the ground and says that they will pay $1B for it even though on the books it has zero book value. That excess paid becomes good will on Century Link because they paid more for it than book value.
Goodwill is essentially what happens when you pay over book value for an asset.
It's quite common in telecom, because telecom infrastructure investments are generally depreciated over 10 years, but the capital assets still have some value even after they've been depreciated for tax purposes. If they were still listed as capital assets they could be depreciated, so they have to be booked as an asset somewhere.
There are of course a lot of companies that have extremely valuable brands and IP, but those tend to trade at pretty fair market valuations and don't have an unusually high percentage of goodwill relative to the rest of their assets.
In the case of CenturyLink, that would be a major red flag to me.
In some cases, there is additional value created by an acquisition that can justify that added value, but in many cases it's just a way to justify an irrational overvaluation on a balance sheet.
For example, the last time I looked CTL had lost about $2 billion in market cap after this deal was announced. That's the market saying "you overpaid for this company" or, as I prefer to say "your goodwill valuation is BS."
Wrong. For example "Hewlett-Packard purchased Autonomy for $11 billion in 2011. The purchase price represented a greater than 65 percent premium over the price at which Autonomy was trading at the time of the announcement. Hewlett-Packard recorded $6.9 billion of goodwill and $4.3 billion of other intangible assets in connection with the acquisition."
Thanks for helping me make my point.