Learn English – There has to be vs there have to be

The correct use changes depending on the sentence:

Do you have any idea how to do this?
Do you have any idea what to do?
Do you have any ideas for me?
Do you have any ideas for how to do this?

It seems that, if the singular or plural noun (idea) is directly connected by a subordinating conjuction (how / what / where / which / that), you use the singular; if it's modified by a prepositional phrase (for...) or by nothing at all, you use the plural.

Without using all that grammar jargon, I'd say use the singular if it's followed by how, what, that, who, whom, whose, which, etc, and use the plural otherwise.

In ordinary usage, nouns like "milk" and "water" are uncountable.  There are times, however, when such words do have a countable sense.  For example, cows produce a different milk than goats.  If I want to compare those two milks, then I'm using the word "milk" in a countable sense and phrases like "a different milk" and "those two milks" are natural and sensible. 

In financial contexts, it is natural and sensible to talk about different countable monies.  The USD and the Euro are two different monies.  Taxable income and tax-free income are two different monies. 

Strictly speaking, it isn't necessary to force a countable sense onto an uncountable noun.  It is just as natural and sensible to talk about "two types of milk" or "two kinds of money", which allows "milk" and "money" to retain their ordinary, uncountable meanings.  Your cited definition includes the phrase "as used in financial contexts".  A better phrasing might be "as used in financial jargon".