Contingent Liabilities	6 Months Ended
Contingent Liabilities	Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingent Liabilities	CONTINGENT LIABILITIES Legal Proceedings and Regulatory Matters As previously reported in the Corporation's Form 10-K for the year ended December 31, 2020 and Form 10-Q for the period ended March 31, 2021, the Bank appealed a court's decision in Butte Local Development v. Masters Group v. Comerica Bank, for lender liability. On July 6, 2021, the Montana Supreme Court affirmed in part, reversed in part the trial court's judgment in favor of Masters. The court reduced the amount of the award by $8 million. Additionally, in second quarter 2021, the Corporation agreed to a proposed settlement in connection with a class action lawsuit filed in the U.S. District Court in California and a related Trustee claim pending in the U.S. Bankruptcy Court in Delaware. Upon final settlement and court approval, the Corporation expects to be released from any liability for additional litigation or claims. The estimated net impact of this settlement, including the Corporation's insurance coverage, was $15 million and included in other noninterest expenses. The Corporation has accrued the estimated probable loss for these two matters within accrued expenses and other liabilities. The Corporation and certain of its subsidiaries are subject to various other pending or threatened legal proceedings arising out of the normal course of business or operations. The Corporation believes it has meritorious defenses to the claims asserted against it in its other currently outstanding legal proceedings and, with respect to such legal proceedings, intends to continue to defend itself vigorously, litigating or settling cases according to management’s judgment as to what is in the best interests of the Corporation and its shareholders. Settlement may result from the Corporation's determination that it may be more prudent financially to settle, rather than litigate, and should not be regarded as an admission of liability. Further, from time to time, the Corporation is also subject to examinations, inquiries and investigations by regulatory authorities in areas including, but not limited to, compliance, risk management and consumer protection, which could lead to administrative or legal proceedings or settlements. Remedies in these proceedings or settlements may include fines, penalties, restitution or alterations in the Corporation's business practices and may result in increased operating expenses or decreased revenues. On at least a quarterly basis, the Corporation assesses its potential liabilities and contingencies in connection with outstanding legal proceedings and regulatory matters utilizing the latest information available. On a case-by-case basis, accruals are established for those legal claims and regulatory matters for which it is probable that a loss will be incurred and the amount of such loss can be reasonably estimated. The actual costs of resolving these claims and regulatory matters may be substantially higher or lower than the amounts accrued. Based on current knowledge, and after consultation with legal counsel, management believes current accruals are adequate, and the amount of any incremental liability arising from these matters is not expected to have a material adverse effect on the Corporation’s consolidated financial condition, results of operations or cash flows. For matters where a loss is not probable, the Corporation has not established an accrual. The Corporation believes the estimate of the aggregate range of reasonably possible losses, in excess of established accruals, for all legal proceedings and regulatory matters in which it is involved is from zero to approximately $48 million at June 30, 2021. This estimated aggregate range of reasonably possible losses is based upon currently available information for those legal proceedings and regulatory matters in which the Corporation is involved, taking into account the Corporation’s best estimate of such losses for those legal cases and regulatory matters for which such estimate can be made. For certain legal cases and regulatory matters, the Corporation does not believe that an estimate can currently be made. The Corporation’s estimate involves significant judgment, given the varying stages of the legal proceedings and regulatory matters (including the fact many are currently in preliminary stages), the existence in certain legal proceedings of multiple defendants (including the Corporation) whose share of liability has yet to be determined, the numerous yet-unresolved issues in many of the legal proceedings and regulatory matters (including issues regarding class certification and the scope of many of the claims) and the attendant uncertainty of the various potential outcomes of such legal proceedings and regulatory matters. Accordingly, the Corporation’s estimate will change from time to time, and actual losses may be more or less than the current estimate. In the event of unexpected future developments, it is possible the ultimate resolution of these matters, if unfavorable, may be material to the Corporation's consolidated financial condition, results of operations or cash flows. For information regarding income tax contingencies, refer to Note 11.