Meaning of headline "Goldman Stunned by Op-Ed Loses $2.2 Billion for Shareholders"

What does this headline mean?

Goldman Stunned by Op-Ed Loses $2.2 Billion for Shareholders

I am not sure what "Op-Ed loses" means in this context.

As choster noted, the "Goldman Stunned by Op-Ed Loses $2.2 Billion for Shareholders" headline is an abbreviated form of "Goldman Sachs, stunned by an op-ed article, has lost $2.2 billion in shareholder value." (The subject headline appears at, for example, pharmagossip and findlaw; it appears as "Goldman Roiled by Op-Ed Loses $2.2B for Shareholders" at bloomberg.)

Note, however, that Op-Ed does not stand for "opinion-editorial" as suggested in some previous answers; it stands for "opposite the editorial page", as noted in wikipedia and in thefreedictionary; that is the page where opposition opinions most often appear.

I take this to be a newspaper headline. Newspaper editors create some terrible constructions in their efforts to be informative while saving space in headlines, resulting in concepts like the crash blossom

More explicitly written, this headline would read Goldman Sachs, stunned by an op-ed article, has lost $2.2 billion in shareholder value.

An op-ed is an opinion-editorial article, one that argues for a position on a topic rather than reporting news about it. The op-ed in this specific case was a searing attack on the organization's practices penned by a Goldman employee and published in the New York Times.

Op-ed is short for either opinion-editorial or opposite the editorial (page) depending on who you ask.

In either case, the headline refers to this op-ed piece, and purports that Goldman lost $2.2 billion as a result of its publication.

I think it's poor phrasing by the headline writer at The San Francisco Chronicle. The verb to stun normally means to render senseless, or (particularly, in the passive) to be shocked. But none of the definitions given in that Merriam-Webster link apply here.

Technically speaking, the headline actually uses it in OED sense 4: To break or crush with heavy blows. Goldman Sachs Group was attacked (stunned) by an op-ed (not a true "Editorial Opinion", but an article by a named writer appearing on the page opposite the "Editorial Leader", so to some extent endorsed by the paper's editorial board).

Many readers won't be familiar with this usage, so they'll understand the headline as meaning that Goldman were stunned/astonished to have lost $2.2 billion, but won't quite be able to parse it. What it actually means is...

A [very negative] Op-Ed knocked Goldman so hard the value of their shares went down by $2.2 billion.

Perhaps the headline writer was using stun as a metaphoric substitute for hit by a stun grenade.