Reforming Executive Guidance Act of 2017 or the REG Act of 2017 This bill requires guidance documents of federal agencies to be considered rules that are subject to the congressional review process. A "guidance document" is a statement of general applicability and future effect, other than a regulatory action, issued by a federal agency that sets forth: (1) a policy on a statutory, regulatory, or technical issue; or (2) an interpretation of a statutory or regulatory issue. The bill modifies the definition of rule to include significant guidance for purposes of rulemaking. A "significant guidance document" is guidance that may reasonably be anticipated to: (1) lead to an annual effect of at least $100 million on, or adversely affect in a material way, the economy, productivity, competition, employment, the environment, public health or safety, or governmental entities or communities; (2) create a serious inconsistency, or otherwise interfere, with an action taken or planned by another federal agency; (3) materially alter the budgetary impact of any entitlement, grant, user fees, or loan programs or the rights or obligations of recipients; or (4) raise novel legal or policy issues arising out of legal mandates.