It isn't possible to know on the facts given whether you have a patentable idea. The judicial position on this is that:
'You cannot patent an idea, which you have simply conceived or have suggested no way of carrying out, but the invention consists in thinking of or conceiving something and suggesting a way of doing it'.
(LJ Buckley, per Hicton's Patent Syndicate (1909))
As the above post succinctly surmises, you must not make a prior disclosure of your 'idea' (But note that telling somone about idea X wouldn't matter as neither of you could patent it if you cannot carry it out.)
As you state you have 'only' an idea, it is imperative that you know exactly how it would work! If given the materials right now, you could construct it, then write down how to do it and you're almost there. For example, I cannot patent a time machine if all I do is think 'wouldn't it be great if...'
If you have say, a blueprint, you must still satisfy some quite strict criteria regarding 'inventive step' and 'the state of the art', but I won't go into that unless you repost and you do have the necessary plans.
Good luck!