Wanna tell my husband.

Mareike
On a show it was talking about couples having crazy fantasies but never telling the other person what those are. My husband was like "I think I know all of yours" but he has no idea!!! 
For example, I think it's hot to imagine that he's getting a blow job from another girl while he's going down on me. But I don't want that to really happen! 
But there are also some role playing ideas that I would totally wanna try, but they might be a little out there. 
How can I bring this up best, and get him to be open about maybe some fantasies he has been keeping?