Commitments and Contingencies	12 Months Ended
Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	18. COMMITMENTS AND CONTINGENCIES Legal Proceedings Durand Litigation On March 12, 2007, a putative class action suit captioned Jennifer A. Durand v. The Hanover Insurance Group, Inc., and The Allmerica Financial Cash Balance Pension Plan, was filed in the United States District Court for the Western District of Kentucky. The named plaintiff, a former employee of the Company’s former life insurance and annuity business who received a lump sum distribution from the Company’s Cash Balance Plan (the “Plan”) at or about the time of her separation from the Company, claims that she and others similarly situated did not receive the appropriate lump sum distribution because in computing the lump sum, the Company and the Plan understated the accrued benefit in the calculation. The plaintiff claims that the Plan underpaid her distributions and those of similarly situated participants by failing to pay an additional so-called “whipsaw” amount reflecting the present value of an estimate of future interest credits from the date of the lump sum distribution to each participant’s retirement age of 65 (“whipsaw claim”). The plaintiff filed an Amended Complaint adding two new named plaintiffs and additional claims on December 11, 2009. Two of the three new claims set forth in the Amended Complaint were dismissed by the District Court, which action was upheld in November 2015 by the U.S. Court of Appeals, Sixth Circuit. The District Court, however, did allow to stand the new claim in the Amended Complaint for breach of fiduciary duty and failure to meet notice requirements arising under the Employee Retirement Income Security Act of 1974 (“ERISA”) from the various interest crediting and lump sum distribution matters of which plaintiffs complain, but only as to plaintiffs’ “whipsaw” claim that remained in the case. On December 17, 2013, the Court entered an order certifying a class to bring “whipsaw” and related breach of fiduciary duty claims consisting of all persons who received a lump sum distribution between March 1, 1997 and December 31, 2003. On February 16, 2018, the Court entered an order limiting the claims of those participants who received lump sum distributions prior to March 13, 2002 to alleged violations of ERISA’s disclosure requirements and breaches of fiduciary duty. Subsequently, the parties entered into settlement discussions and have reached a settlement, which the Court preliminarily approved on December 18, 2018. The Court will consider whether to give final approval to the settlement at a hearing on March 22, 2019. Provided the Court approves the settlement, the Company does not believe the resulting settlement amount will be material to the Company’s financial position or have a material effect on its results of operations. Other Matters The Company has been named a defendant in various other legal proceedings arising in the normal course of business. In addition, the Company is involved, from time to time, in examinations, investigations and proceedings by governmental and self-regulatory agencies. The potential outcome of any such action or regulatory proceedings in which the Company has been named a defendant or the subject of an inquiry or investigation, and its ultimate liability, if any, from such action or regulatory proceedings, is difficult to predict at this time. The ultimate resolutions of such proceedings are not expected to have a material effect on its financial position, although they could have a material effect on the results of operations for a particular quarter or annual period. Residual Markets The Company is required to participate in residual markets in various states, which generally pertain to high risk insureds, disrupted markets or lines of business or geographic areas where rates are regarded as excessive. The results of the residual markets are not subject to the predictability associated with the Company’s own managed business, and are significant to both the personal and commercial automobile lines of business.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

18. COMMITMENTS AND CONTINGENCIES

Legal Proceedings

Durand Litigation

On March 12, 2007, a putative class action suit captioned Jennifer A. Durand v. The Hanover Insurance Group, Inc., and The Allmerica Financial Cash Balance Pension Plan, was filed in the United States District Court for the Western District of Kentucky. The named plaintiff, a former employee of the Company’s former life insurance and annuity business who received a lump sum distribution from the Company’s Cash Balance Plan (the “Plan”) at or about the time of her separation from the Company, claims that she and others similarly situated did not receive the appropriate lump sum distribution because in computing the lump sum, the Company and the Plan understated the accrued benefit in the calculation. The plaintiff claims that the Plan underpaid her distributions and those of similarly situated participants by failing to pay an additional so-called “whipsaw” amount reflecting the present value of an estimate of future interest credits from the date of the lump sum distribution to each participant’s retirement age of 65 (“whipsaw claim”).

The plaintiff filed an Amended Complaint adding two new named plaintiffs and additional claims on December 11, 2009. Two of the three new claims set forth in the Amended Complaint were dismissed by the District Court, which action was upheld in November 2015 by the U.S. Court of Appeals, Sixth Circuit. The District Court, however, did allow to stand the new claim in the Amended Complaint for breach of fiduciary duty and failure to meet notice requirements arising under the Employee Retirement Income Security Act of 1974 (“ERISA”) from the various interest crediting and lump sum distribution matters of which plaintiffs complain, but only as to plaintiffs’ “whipsaw” claim that remained in the case. On December 17, 2013, the Court entered an order certifying a class to bring “whipsaw” and related breach of fiduciary duty claims consisting of all persons who received a lump sum distribution between March 1, 1997 and December 31, 2003.

On February 16, 2018, the Court entered an order limiting the claims of those participants who received lump sum distributions prior to March 13, 2002 to alleged violations of ERISA’s disclosure requirements and breaches of fiduciary duty. Subsequently, the parties entered into settlement discussions and have reached a settlement, which the Court preliminarily approved on December 18, 2018. The Court will consider whether to give final approval to the settlement at a hearing on March 22, 2019. Provided the Court approves the settlement, the Company does not believe the resulting settlement amount will be material to the Company’s financial position or have a material effect on its results of operations.

Other Matters

The Company has been named a defendant in various other legal proceedings arising in the normal course of business. In addition, the Company is involved, from time to time, in examinations, investigations and proceedings by governmental and self-regulatory agencies. The potential outcome of any such action or regulatory proceedings in which the Company has been named a defendant or the subject of an inquiry or investigation, and its ultimate liability, if any, from such action or regulatory proceedings, is difficult to predict at this time. The ultimate resolutions of such proceedings are not expected to have a material effect on its financial position, although they could have a material effect on the results of operations for a particular quarter or annual period.

Residual Markets

The Company is required to participate in residual markets in various states, which generally pertain to high risk insureds, disrupted markets or lines of business or geographic areas where rates are regarded as excessive. The results of the residual markets are not subject to the predictability associated with the Company’s own managed business, and are significant to both the personal and commercial automobile lines of business.