21st Century Glass-Steagall Act of 2017 This bill amends the Federal Deposit Insurance Act, the Bank Holding Company Act of 1956, the Home Owner's Loan Act, the International Banking Act of 1978, the federal bankruptcy code, and other laws to: limit affiliations between an insured depository institution and any insurance company, securities entity, or swaps entity ; restrict the authority of a national banking association to purchase or sell investment securities or stock, invest in certain structured or synthetic products, control or hold an interest in financial subsidiaries, or otherwise engage in nonbanking activities; restrict the authority of a federal savings association to invest in, redeem, or hold shares or certificates issued by an open-end management investment company; limit the authority of a financial holding company to engage in nonfinancial activities; disallow certain foreign banks from engaging in nonbanking activities in the United States; repeal bankruptcy code provisions related to the contractual right to liquidate, terminate, or accelerate certain types of financial instruments; and establish various enforcement and penalty provisions.