have the first idea

have the first idea (third-person singular simple present has the first idea, present participle having the first idea, simple past and past participle had the first idea)

1. (chiefly in the negative) To have any knowledge (about something); have a clue.
   • 2011, Gregory Dark, Susie and the Snow-it-alls, →ISBN:

     Do you have the first idea of the worry you've caused me?

   • 2011, Tom Clempson, One Seriously Messed-Up Week, →ISBN:

     We were meant to get a replacement teacher but we usually just get the occasional Part-Timer or maybe a P.E. teacher whose football has been rained off – neither of whom have the first idea about what they're supposed to be teaching us.

   • 2013, Lucy Hepburn, 2 Busy 4 Love, →ISBN:

     Like you would have the first idea how to get to Newark Airport.

   • 2014, Tamar Cohen, The Broken, →ISBN, page 128:

     I think if you had the first idea how shitty this looks to me, you'd never have done it in the first place.”

2. Used other than figuratively or idiomatically: see have,‎ first,‎ idea.
   • 1817, The Edinburgh Observer: Or, Town and Country Magazine:

     The best instruments known are also due to the genius of Newton; it was he who had the first idea of adapting mirrors to those which serve to measure these distances.

   • 2011, Brian Boyd, Stalking Nabokov, →ISBN, page 387:

     I knew that Nabokov had had the first idea for the novel almost four years before his death and that when he still had more than fourteen months to live Véra had reported that he was “about half way” to completion.

This is usually used in the negative. That is, most commonly one speaks of not having the first idea about something.