Note: As a jurisdiction is not specified, this answer assumes United States law throughout. OP's profile says they are in California, so this is hopefully correct.
Copyright law
You cannot transfer a copyright in an idea, because ideas are expressly excluded from copyright protection in 17 USC 102(b). So you can't have such a copyright in the first place.
By itself, this does not invalidate the provision, because the provision is not exclusive to copyright and explicitly extends to any and all forms of ownership.
Patent law
Patents do not explicitly exempt ideas in 35 USC 101, but they do require that patentable subject matter be a "new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof" - and it's hard to argue that an "idea" fits any of those criteria per se. However, if the idea is precise and detailed enough to enable a "person of ordinary skill in the art" to actually build it, then it might well qualify for patent protection (subject to the restrictions in sections 102, 103, and the rest of the whole of US patent law - see particularly Alice v. CLS Bank and its progeny in the CAFC).
Trade secrets
Under 18 USC 1839(3), trade secrets are much broader than patents or copyrights and can include "all forms and types of financial, business, scientific, technical, economic, or engineering information, including..." and it then goes on to list many different types of information in greater detail. While the word "idea" is not specifically listed, I think it would be difficult to argue that ideas can never be trade secrets given how expansive this wording is. As with patents, there are other requirements which must also be satisfied, particularly relating to the economic value of the information as well as its secrecy. If an idea is highly vague, has never been written down, has been shared or published in some form, and/or is worthless, then it's probably not eligible for protection.
Chattels
The wording of this contract seems to include both physical property and intellectual property:
Contractor agrees that all of the work product produced under this Agreement, including without limitation all notes, designs, specifications, technical information, ideas, processes, … or modifications, and other data relating to the work done under this Agreement by Contractor, and all Intellectual Property with respect to the work product (collectively, the “Work Product”), is solely and exclusively the property of CUSTOMER and Contractor hereby conveys, transfers and assigns all Intellectual Property in the Work Product to CUSTOMER.
This is not one provision, it's two separate provisions stuck together:
- One provision requiring the contractor to physically hand over all of the "work product" to the customer.
- A second provision stating that the customer also owns the intellectual property.
Therefore, if the contractor is in physical possession of an "idea" (which has been written down or recorded in some other tangible medium), then the customer can demand either a copy or the original (depending on how the rest of the contract is worded and the surrounding circumstances), because such writings are the chattel property of the customer under the terms of this contract. Chattel property rights do not have the sorts of scope limitations which we find in intellectual property rights, so it is entirely fair and valid for a contract to demand this.
