American International Group, MGIC Investment, Genworth Financial and Radian Group have been served with subpoenas by the Consumer Financial Protection Bureau, the firms said in public filings last week, as the bureau is apparently probing to determine if the mortgage insurance companies transferred billions in M.I. premiums to the banks that made the mortgages. PHH Corp. made a similar disclosure back in January. The CFPB’s subpoenas, known as Civil Investigative Demands, indicate that the bureau’s enforcement...