The 6 largest U.S. banks spent $70.2 billion in 2013 on regulatory compliance, up from $34.7 billion in 2007. A growing army of rule enforcers are forcing striking changes on banks’ internal cultures. At one midsize bank in the U.S., a compliance officer was reprimanded after complaining about an individual regulator to a colleague in the bathroom, only to find out the regulator had been in a stall.