As a noun, ideal refers to (1) a conception of something in its absolute perfection, or (2) an honorable or worthy principle or aim. It is not conventionally a variant or synonym of idea, though it is sometimes colloquially used this way.
However, this ideal isn’t always reached by governments that want their thumbs on the economy and, more particularly, the revenue it represents. [Small Business Trends]
The pluralistic ideal that many communities strive for is an unattainable goal. [New Voices]
We have failed those ideals, utterly and spectacularly, more than a few times in our relatively short history. [Bellingham Herald]