Financial Stability Oversight Council Improvement Act of 2017 (Sec. 2) This bill amends the Financial Stability Act of 2010 to require the Financial Stability Oversight Council, in determining whether a nonbank financial company shall be designated as systemically important and consequently be supervised by the Federal Reserve Board and subject to prudential standards, to consider the appropriateness of imposing such standards as opposed to other forms of regulation to mitigate identified risks to U.S. financial stability. The bill revises procedural requirements related to council determinations of systemic importance. Specifically, the council must: (1) provide an opportunity, during an annual reevaluation of such a determination for a nonbank financial company, for the company to submit written materials to, and meet with, the council in order to contest the determination; (2) every five years, upon request by a nonbank financial company, reevaluate such a determination and hold a vote on whether to rescind it; and (3) undertake certain procedures for initial evaluations. (Sec. 4) The bill amends the Federal Reserve Act to lower the maximum allowable amount of surplus funds of the Federal Reserve banks.