Taxpayer Exposure Mitigation Act of 2017 This bill amends the National Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973 to limit the required purchase of flood insurance in certain circumstances to only residential properties (currently, the requirement applies to all types of property). It also requires the Federal Emergency Management Agency (FEMA) to annually transfer a portion of the risk from the National Flood Insurance Program (NFIP) to private reinsurance or capital markets. The amount of transferred risk must be based on a probable maximum loss target for NFIP established by FEMA each fiscal year. The bill amends the Biggert-Waters Flood Insurance Reform Act of 2012 to require FEMA to establish standards for the development of alternative flood insurance rate maps by local and state governments. FEMA must consider recommendations made by the Technical Mapping Advisory Council when establishing these standards. FEMA must approve the use of these alternative maps under NFIP.