Sorry, I couldn't find pricing data for that day. The closing price for Citigroup (C) on December 31, 2018 was $40.70. It was up 0.2% for the day. The latest price is $102.52.
DATE
OPEN
HIGH
LOW
CLOSE
VOLUME
December 31 2018
$40.64
$41.18
$40.18
$40.70
19,317,510
Daily pricing data for Citigroup dates back to 10/30/1986, and may be incomplete.