What is the grammatical term for the following idiom?

When there is a group or list of specific items, its components are curiously pluralized when reciting them in one sentence.

For instance,when a person discusses the qualities of blue-chip stocks, he might say, "I'm talking about your IBMs, your Procter and Gambles, your General Electrics."

In referring to Hall of Fame baseball players, one might say, "Just compare your Ruths, your Gehrigs, your Cobbs, your Killebrews, to today's players."

Why is the "intrusive s", or inappropriate plural form, so often heard and seen? After all, we are only talking about one IBM company, one Babe Ruth ....

Plurals are used in that sentence because the things being listed ARE plural, not singular. The fact that it's a list isn't really important.

"I'm talking about your IBMs, your Procter and Gambles, your General Electrics"... means "I'm talking about all of the companies that do work or in other ways similar to: IBM, Procter and Gamble, and General Electric."

The use of "your" is just to say "these companies are yours in that they are part of your social identity", and isn't really meaningful.

Raku is right in that this is "pars pro toto" (and less specifically, an example of synecdoche) because "IBMs" is used to refer to the whole set of companies similar to IBM in some ways.

As a similar example not in a list, someone might say:

"All of these Einsteins are blowing the rest of us out of the water."

Here, Einsteins are just a bunch of smart people.

IMHO this is a "pars pro toto" idiom where you mention a part (lat. "pars") for ("pro") the whole ("toto").

The plural is used to express generalization. The speaker is not really talking about the single company IBM, the single baseball player Gehrig, but the whole set of companies and famous players. He is just mentioning the part (company, player) to speak about the whole (companies, famous players).

Pluralizing the single parts also has the effect of augmenting the effect of mentioning powerful representatives of the whole. This makes the speaker sound more convincing, which is, in general, the aim of every stylistic device.

Mark's metonymy is also present here. So I think it's a combination of multiple stylistic devices.