US Bureau of Labor Statistics (BTS.gov) said 124,000 in the U.S. in 2018. That's all commercial pilots. If you limit it to the largest U.S. airline and cargo operators it's 75,000. DL, AA, UA, SW, JB, NK, AK, FX, UPS. Regional airlines is frequently mentioned as approx. 18,000. So all airline size job totals, to include regional airlines, might be 100,000?
IATA might have overall aircraft or passenger counts (ASM/RSM) for the entire world. Figure out what percentage the U.S. has of the totals and using the numbers I provided might give you a reasonable estimate for your question.