Keeping America's Pension Promises Act This bill repeals the elimination of the pension anti-cutback provisions under the Multiemployer Pension Reform Act of 2014. The anti-cutback provisions prohibit reductions in pension benefits to participants in multiemployer pension plans. The bill amends the Employee Retirement Income Security Act of 1974 (ERISA), with respect to partitions of eligible multiemployer plans, to modify the procedures and allow plan sponsors to petition the Pension Benefit Guaranty Corporation (PBGC) for a partition of additional financially-troubled pension plans. The PBGC must establish a legacy fund to cover the administrative and benefit costs resulting from a partition. The Department of the Treasury must transfer amounts to the fund that are equal to the increase in revenues as a result of specified provisions of this bill that amend the Internal Revenue Code. The provisions amend the Internal Revenue Code to impose a .03% excise tax on certain trading transactions with respect to securities. The bill amends the federal bankruptcy code to assign first claim priority to pension obligations under ERISA.