Litigation and Regulatory Matters	3 Months Ended
Litigation and Regulatory Matters	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Litigation and Regulatory Matters	Litigation and Regulatory Matters The following supplements, and should be read together with, the disclosure in Note 30, "Litigation and Regulatory Matters," in our 2023 Form 10-K. Only those matters with significant updates and new matters since our disclosure in our 2023 Form 10-K are reported herein. In addition to the matters described below and in our 2023 Form 10-K, in the ordinary course of business, we are routinely named as defendants in, or as parties to, various legal actions and proceedings relating to activities of our current and/or former operations. These legal actions and proceedings may include claims for substantial or indeterminate compensatory or punitive damages, or for injunctive relief. In the ordinary course of business, we also are subject to governmental and regulatory examinations, information-gathering requests, investigations and proceedings (both formal and informal), certain of which may result in adverse judgments, settlements, fines, penalties, injunctions or other relief. In connection with formal and informal inquiries by these regulators, we receive numerous requests, subpoenas and orders seeking documents, testimony and other information in connection with various aspects of our regulated activities. Due to the inherent unpredictability of legal matters, including litigation, governmental and regulatory matters, particularly where the damages sought are substantial or indeterminate or when the proceedings or investigations are in the early stages, we cannot determine with any degree of certainty the timing or ultimate resolution of such matters or the eventual loss, fines, penalties or business impact, if any, that may result. We establish reserves for litigation, governmental and regulatory matters when those matters present loss contingencies that are both probable and can be reasonably estimated. Once established, reserves are adjusted from time to time, as appropriate, in light of additional information. The actual costs of resolving litigation and regulatory matters, however, may be substantially higher than the amounts reserved for those matters. Some of our exposure may be offset by applicable insurance coverage. We do not consider the possible availability of insurance coverage in determining the amounts of any accruals (although we record the amount of related insurance recoveries that are deemed probable up to the amount of the accrual). For the legal matters disclosed below, including litigation and governmental and regulatory matters, as well as for the legal matters disclosed in Note 30, "Litigation and Regulatory Matters," in our 2023 Form 10-K, as to which a loss in excess of accrued liability is reasonably possible in future periods and for which there is sufficient currently available information on the basis of which management believes it can make a reliable estimate, we believe a reasonable estimate could be as much as $100 million for HUSI. The legal matters underlying this estimate of possible loss will change from time to time and actual results may differ significantly from this current estimate. Given the substantial or indeterminate amounts sought in certain of these matters, and the inherent unpredictability of such matters, an adverse outcome in certain of these matters could have a material adverse effect on our consolidated financial statements in any particular quarterly or annual period. Precious Metals Fix Matters Platinum and Palladium Fix Litigation In April 2024, a settlement in principle was reached with the plaintiffs to resolve the Platinum and Palladium Fix Litigation. The settlement in principle remains subject to finalization of the documentation and court approval. The financial impact of the settlement is not material. Mortgage Securitization Trust Litigation The First Department affirmed dismissal of the Zittman case, and Zittman has filed a motion seeking reconsideration or, in the alternative, leave to appeal to the New York State Court of Appeals. First Citizens Litigation Defendants filed a motion to dismiss in August 2023. In January 2024, the court denied defendants' motion in part and granted it in part and directed plaintiff to amend its complaint to specify its allegations as to each defendant. In February 2024, First Citizens filed its amended complaint. In March 2024, defendants filed a motion to dismiss portions of the amended complaint. Anti-Terrorism Act Cases Charlotte Freeman, et al. v. HSBC Holdings plc, et al. Plaintiffs filed a motion to vacate the judgment against them in February 2024.