1
general::
Truly, seriously, as in No kidding, I really did lose my wallet. [Colloquial; first half of 1900s]
American Heritage Idioms
2
general::
Phrase(s): No kidding!
1. Inf. You are not kidding me, are you? (An expression of mild surprise.) • Jane: I got elected vice president. Bill: No kidding! That’s great! 2. Inf. Everyone already knows that! Did you just find that out? (Sarcastic.) • Sue: It looks like taxes will be increasing. Tom: No kidding! What do you expect? • Alice: I’m afraid I’m putting on a little weight. Jane: No kidding!
McGrawhill's American Idioms And Phrasal Verbs