I agree with Eoin. If you have not done so you NEED to talk w. your lawyer before you say anything about this idea. You contract will say something about the IP you product during this time. I have been in exactly your position, and it may be that all related IP you produce is owned by them, or only IP you deliver, etc. you need to understand what actions on your part cause them to own the IP.
Quite possibly once they can prove you produced it while in their employ, they own it. in that case you are risking never being able to do it, if you present it.
IF you can present it w/o them owning it, then I think there is little reason to be heavy handed when presenting it. Simply say "this is a great idea, and I definitely want to do it." Later if they fail to make motion on the idea, you can start saying, "well this is a good idea, and I want to pursue it one way or another." Ultimately you will not cause bad blood, if you gave them every option to move with it, before you took it elsewhere.
have you actually found that mythical AI idea that is actually marketable (grin)