Take context from the input text and decide on the accurate relationship between 'Banamex' and 'Citigroup' from the options provided.
Options: subsidiary, member of, operator, founded by

Thu, Jul 23, 2015, 00:04 BST - UK Markets open in 7 hrs 56 mins Citigroup shuts Banamex USA, pays $140 mn in fines AFP – 40 minutes ago View Photo
operator