Mariah Carey just became the HIGHEST PAID JUDGE in reality television ... because her one-year deal with "American Idol" is worth close to $18 MILLION ... this according to sources connected to "Idol."
Carey's deal dwarfs the contract Jennifer Lopez signed when she joined the judge's table -- J.Lo only scored a measly $12 mil for her first year on the show.
Carey also blows past Britney Spears ... who's making $15 million on "X Factor."
Somewhere ... Nick Cannon is smiling.
Mariah has since tweeted about joining the show ... saying, "It's gonna be so much fun working on American Idol. As a singer-songwriter, I'm excited to help find and nurture new talent. LYM! – MC”