The Hanover Insurance Group, Inc. (THG) 10-Q 29 Apr 20 2020 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 27, 2020
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Registrant Name	HANOVER INSURANCE GROUP, INC.
Entity Central Index Key	0000944695
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		37,997,945
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	1-13754
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3263626
Entity Address, Address Line One	440 Lincoln Street
Entity Address, City or Town	Worcester
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01653
City Area Code	508
Local Phone Number	855-1000
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Common Stock, $.01 Par Value [Member]
Document Information [Line Items]
Title of 12(b) Security	Common Stock, $.01 par value
Trading Symbol	THG
Security Exchange Name	NYSE
7 5/8% Senior Debentures Due 2025 [Member]
Document Information [Line Items]
Title of 12(b) Security	7 5/8% Senior Debentures due 2025
Trading Symbol	THG
Security Exchange Name	NYSE
6.35% Subordinated Debentures Due 2053 [Member]
Document Information [Line Items]
Title of 12(b) Security	6.35% Subordinated Debentures due 2053
Trading Symbol	THGA
Security Exchange Name	NYSE

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Revenues
Premiums		$ 1,141,400,000	$ 1,095,100,000
Net investment income		69,600,000	70,200,000
Net realized and unrealized investment gains (losses):
Net realized gains (losses) from sales and other		3,100,000	(400,000)
Net change in fair value of equity securities		(136,200,000)	48,600,000
Impairment losses on investments		(28,500,000)	0
Total net realized and unrealized investment gains (losses)		(161,600,000)	48,200,000
Fees and other income		6,800,000	6,000,000
Total revenues		1,056,200,000	1,219,500,000
Losses and expenses
Losses and loss adjustment expenses		728,200,000	699,600,000
Amortization of deferred acquisition costs		236,900,000	229,500,000
Interest expense		9,400,000	9,400,000
Other operating expenses		135,600,000	132,400,000
Total losses and expenses		1,110,100,000	1,070,900,000
Income (loss) from continuing operations before income taxes		(53,900,000)	148,600,000
Income tax expense (benefit):
Current		21,300,000	12,200,000
Deferred		(36,500,000)	13,800,000
Total income tax expense (benefit)		(15,200,000)	26,000,000
Income (loss) from continuing operations		(38,700,000)	122,600,000
Discontinued operations (net of taxes):
Net income (loss)		$ (40,000,000)	$ 122,400,000
Basic:
Income (loss) from continuing operations		$ (1.01)	$ 3.02
Net income (loss) per share		$ (1.04)	$ 3.01
Weighted average shares outstanding		38.3	40.6
Diluted:
Income (loss) from continuing operations		$ (1.01)	$ 2.98
Net income (loss) per share		$ (1.04)	$ 2.97
Weighted average shares outstanding	[1]	38.3	41.2
Chaucer [Member]
Discontinued operations (net of taxes):
Sale of business			$ 900,000
Loss from discontinued operations			$ (300,000)
Basic:
Sale of business			$ 0.02
Loss from discontinued operations			(0.01)
Diluted:
Sale of business			0.02
Loss from discontinued operations			$ (0.01)
Life [Member]
Discontinued operations (net of taxes):
Loss from discontinued operations		$ (1,300,000)	$ (800,000)
Basic:
Loss from discontinued operations		$ (0.03)	$ (0.02)
Diluted:
Loss from discontinued operations		$ (0.03)	$ (0.02)
[1]	Excludes 0.6 million shares due to antidilution that resulted from the Company having losses from continuing operations and net losses for the quarter ended March 31, 2020.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (40)	$ 122.4
Available-for-sale securities:
Net appreciation (depreciation) during the period	(83.2)	115
Change in unrealized gains recognized in other comprehensive income		1.4
Total available-for-sale securities	(83.2)	116.4
Pension and postretirement benefits:
Net change in net actuarial loss	1.2	2.3
Cumulative foreign currency translation adjustment:
Amount recognized as cumulative foreign currency translation during the period		0.1
Total other comprehensive income (loss), net of tax	(82)	118.8
Comprehensive income (loss)	$ (122)	$ 241.2

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets
Fixed maturities, at fair value (amortized cost of $6,493.7 and $6,452.2)	$ 6,625	$ 6,687.1
Equity securities, at fair value	447	575.7
Other investments	755.5	733.2
Total investments	7,827.5	7,996
Cash and cash equivalents	143.9	215.7
Accrued investment income	51.5	53
Premiums and accounts receivable, net	1,271	1,260.4
Reinsurance recoverable on paid and unpaid losses and unearned premiums	1,820.4	1,814
Deferred acquisition costs	465.7	467.4
Deferred income tax asset	3.2
Goodwill	178.8	178.8
Other assets	417.3	402.4
Assets of discontinued businesses	98.1	102.8
Total assets	12,277.4	12,490.5
Liabilities
Loss and loss adjustment expense reserves	5,724.9	5,654.4
Unearned premiums	2,421	2,416.7
Expenses and taxes payable	512	627.7
Deferred income tax liability		51.8
Reinsurance premiums payable	58.5	53.4
Debt	707.5	653.4
Liabilities held-for-sale and discontinued businesses	116.9	116.9
Total liabilities	9,540.8	9,574.3
Commitments and contingencies
Shareholders’ Equity
Preferred stock, par value $0.01 per share; 20.0 million shares authorized; none issued
Common stock, par value $0.01 per share; 300.0 million shares authorized; 60.5 million shares issued	0.6	0.6
Additional paid-in capital	1,861.6	1,837.3
Accumulated other comprehensive income	70.6	152.6
Retained earnings	2,344.9	2,410.9
Treasury stock at cost (22.5 million and 22.1 million shares)	(1,541.1)	(1,485.2)
Total shareholders’ equity	2,736.6	2,916.2
Total liabilities and shareholders’ equity	$ 12,277.4	$ 12,490.5

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 6,493.7	$ 6,452.2
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	60,500,000	60,500,000
Treasury stock, shares	22,500,000	22,100,000

Consolidated Statements of Shar

Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Net Unrealized Appreciation (Depreciation) on Investments [Member]	Defined Benefit Pension and Postretirement Plans [Member]	Cumulative Foreign Currency Translation Adjustment [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income, Net of Tax [Member]
Balance at beginning of period at Dec. 31, 2018		$ 0.6	$ 1,871.8	$ (27.2)	$ (88.6)	$ (0.7)	$ 2,182.3
Balance at beginning of period at Dec. 31, 2018								$ (983.5)
Cumulative effect of accounting change, net of taxes at Dec. 31, 2018							(1.5)
Balance at beginning of period, as adjusted at Dec. 31, 2018							2,180.8
Net income (loss)	$ 122.4						122.4
Shares purchased at cost								(200)
Settlement and prepayment of accelerated share repurchases and other			(50.1)
Net appreciation (depreciation) on available-for-sale securities	116.4			116.4
Net amount recognized as net periodic benefit					2.3
Amount recognized as cumulative foreign currency translation during the period	0.1					0.1
Adoption of Accounting Standards Update | Accounting Standards Update No. 2017-08 [Member]				1.5
Dividends to shareholders							(24.5)
Net shares reissued at cost under employee stock-based compensation plans								5.7
Balance at end of period at Mar. 31, 2019	2,927	0.6	1,821.7	90.7	(86.3)	$ (0.6)	2,278.7		$ 3.8
Balance at end of period at Mar. 31, 2019								(1,177.8)
Balance at beginning of period at Dec. 31, 2019	2,916.2	0.6	1,837.3	216	(63.4)		2,410.9
Balance at beginning of period at Dec. 31, 2019	(1,485.2)							(1,485.2)
Cumulative effect of accounting change, net of taxes at Dec. 31, 2019							(0.9)
Balance at beginning of period, as adjusted at Dec. 31, 2019							2,410
Net income (loss)	(40)						(40)
Shares purchased at cost								(59.2)
Settlement and prepayment of accelerated share repurchases and other			24.3
Net appreciation (depreciation) on available-for-sale securities	(83.2)			(83.2)
Net amount recognized as net periodic benefit					1.2
Dividends to shareholders							(25.1)
Net shares reissued at cost under employee stock-based compensation plans								3.3
Balance at end of period at Mar. 31, 2020	2,736.6	$ 0.6	$ 1,861.6	$ 132.8	$ (62.2)		$ 2,344.9		$ 70.6
Balance at end of period at Mar. 31, 2020	$ (1,541.1)							$ (1,541.1)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash Flows From Operating Activities
Net income	$ (40)	$ 122.4
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized and unrealized investment (gains) losses	162.4	(48.4)
Gain on sale of Chaucer-related Irish entity		(0.9)
Net amortization and depreciation	5.1	6.9
Stock-based compensation expense	5	4.2
Amortization of defined benefit plan costs	1.5	2.8
Deferred income tax expense (benefit)	(36.7)	13.8
Change in deferred acquisition costs	1.7	2.7
Change in premiums receivable, net of reinsurance premiums payable	(5.5)	(4.3)
Change in loss, loss adjustment expense and unearned premium reserves	75	99.2
Change in reinsurance recoverable	(6.4)	(28.2)
Change in expenses and taxes payable	(112.7)	(88)
Other, net	(12.8)	(45)
Net cash provided by operating activities	36.6	37.2
Cash Flows From Investing Activities
Proceeds from disposals and maturities of fixed maturities	316.3	193.1
Proceeds from disposals of equity securities and other investments	73.2	28.1
Purchase of fixed maturities	(376.5)	(483.4)
Purchase of equity securities and other investments	(109.7)	(37.6)
Capital expenditures	(3.2)	(3.9)
Net cash proceeds from sale of Chaucer-related Irish entity, partially offset by cash transferred		24.4
Net cash used in investing activities	(99.9)	(279.3)
Cash Flows From Financing Activities
Proceeds from exercise of employee stock options	3	5
Proceeds from short-term borrowings	54
Change in cash collateral related to securities lending program		6.7
Dividends paid to shareholders	(24.8)	(217)
Repurchases of common stock	(34.9)	(250)
Repayment of debt		(151.1)
Other financing activities	(5.8)	(4.2)
Net cash used in financing activities	(8.5)	(610.6)
Net change in cash and cash equivalents	(71.8)	(852.7)
Net change in cash related to discontinued operations		0.5
Cash and cash equivalents, beginning of period	215.7	1,020.7
Cash and cash equivalents, end of period	$ 143.9	$ 168.5

Basis of Presentation and Princ

Basis of Presentation and Principles of Consolidation	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	1. Basis of Presentation and Principles of Consolidation The accompanying unaudited consolidated financial statements of The Hanover Insurance Group, Inc. and its subsidiaries (“THG” or the “Company”) have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and with the requirements of Form 10-Q. Certain financial information that is provided in annual financial statements, but is not required in interim reports, has been omitted. The interim consolidated financial statements of THG include the accounts of The Hanover Insurance Company (“Hanover Insurance”) and Citizens Insurance Company of America, THG’s principal property and casualty companies; and other insurance and non-insurance subsidiaries. These legal entities conduct their operations through several business segments discussed in Note 9 – “Segment Information”. The interim consolidated financial statements also include the Company’s discontinued operations, consisting of the Company’s accident and health and former life insurance businesses, as well as the Company’s former Chaucer business. All intercompany accounts and transactions have been eliminated. The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amount of revenues and expenses during the reporting period. Actual results could differ from those estimates. In the opinion of the Company’s management, the accompanying interim consolidated financial statements reflect all adjustments, consisting of normal recurring items, necessary for a fair presentation of the financial position and results of operations. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the full year. These financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (“SEC”) on February 24, 2020.

New Accounting Pronouncements

New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2020
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	2. New Accounting Pronouncements Recently Implemented Standards In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASC Update No. 2016-13, (Topic 326) Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (“ASC Update No. 2016-13”) Codification Improvements to Topic 326, Financial Instruments – Credit Losses In 2019 and 2020, the FASB has issued several updates to ASC Update No. 2016-13, including the issuance in April 2019, ASC Update 2019-04, Codification Improvements to Topic 326, Financial Instruments – Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments Financial Instruments – Credit Losses (Topic 326): Targeted Transition Relief, Codification Improvements to Topic 326, Financial Instruments – Credit Losses Financial Instruments – Credit Losses (Topic 326) and Leases (Topic 842) – Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 119 and Update to SEC Section on Effective Date Related to Accounting Standards Update No. 2016-02, Leases (Topic 842) In August 2018, the FASB issued ASC Update No. 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract . This ASC update requires the capitalization of implementation costs incurred in a hosting arrangement that is a service contract consistent with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The guidance also requires an entity to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting agreement, and apply impairment guidance consistent with long-lived assets. ASC Update No. 2018-15 also provides specific guidelines related to the presentation of these capitalized implementation costs and related expenses in the financial statements. The updated guidance is effective for interim and annual periods beginning after December 15, 2019, and should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. Early adoption is permitted, including interim periods. The Company implemented this guidance prospectively, effective January 1, 2020, and it did not have a material impact on its financial position or results of operations. In August 2018, the FASB issued ASC Update No. 2018-13 (Topic 820) Fair Value Measurement, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In January 2017, the FASB issued ASC Update No. 2017-04, (Topic 350) Intangibles – Goodwill and Other: Simplifying the Test for Goodwill Impairment Recently Issued Standards In January 2020, the FASB issued ASC Update No. 2020-01 Investments – Equity Securities (Topic 321), Investments – Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) In December 2019, the FASB issued ASC Update No. 2019-12 Income Taxes (Topic 740) – Simplifying the Accounting for Income Taxes Income Taxes In August 2018, the FASB issued ASC Update No. 2018-14 (Topic 715-20) Compensation – Retirement Benefits – Defined Benefit Plans – General – Disclosure Framework – Changes to the Disclosure Requirements for the Defined Benefit Plans. This ASC update modifies disclosures related to defined benefit pension or other postretirement plans. This ASC update removes the disclosure of amounts in accumulated other comprehensive income expected to be recognized over the next fiscal year and the effects of a one percentage point change of health care cost trends on net periodic benefit costs and postretirement benefit obligations and clarifies the specific requirements of disclosures related to the project benefit obligation and accumulated benefit obligation. This ASC Update also adds disclosures related to weighted average crediting rates for cash balance plans and requires disclosure of an explanation of any significant gains and losses related to changes in benefit obligations for the period. The amendments in this ASC update are effective for fiscal years ending after December 15, 2020, and should be applied on a retrospective basis to all periods presented. Early adoption is permitted. Implementing this guidance is not expected to have an impact on the Company’s financial position or results of operations as the update is disclosure related.

Investments

Investments	3 Months Ended
	Mar. 31, 2020
Investments Debt And Equity Securities [Abstract]
Investments	3. Investments A. Fixed maturities The amortized cost and fair value of available-for-sale fixed maturities were as follows: March 31, 2020 Amortized Cost, Allowance net of Allowance Gross Gross Amortized for Credit for Credit Unrealized Unrealized (in millions) Cost Losses Losses Gains Losses Fair Value U.S. Treasury and government agencies $ 265.9 $ — $ 265.9 $ 20.3 $ — $ 286.2 Foreign government 4.2 — 4.2 0.3 — 4.5 Municipal 833.8 — 833.8 35.3 1.4 867.7 Corporate 3,749.0 6.2 3,742.8 81.5 60.0 3,764.3 Residential mortgage-backed 913.5 — 913.5 43.5 0.1 956.9 Commercial mortgage-backed 661.3 — 661.3 20.3 2.1 679.5 Asset-backed 66.0 — 66.0 0.4 0.5 65.9 Total fixed maturities $ 6,493.7 $ 6.2 $ 6,487.5 $ 201.6 $ 64.1 $ 6,625.0 December 31, 2019 Gross Gross OTTI Amortized Unrealized Unrealized Unrealized (in millions) Cost Gains Losses Fair Value Losses U.S. Treasury and government agencies $ 342.0 $ 9.1 $ 1.3 $ 349.8 $ — Foreign government 15.7 0.4 — 16.1 — Municipal 807.1 27.6 1.2 833.5 — Corporate 3,653.5 161.6 3.9 3,811.2 3.0 Residential mortgage-backed 905.4 17.1 1.1 921.4 — Commercial mortgage-backed 666.4 25.6 0.1 691.9 — Asset-backed 62.1 1.1 — 63.2 — Total fixed maturities $ 6,452.2 $ 242.5 $ 7.6 $ 6,687.1 $ 3.0 As of December 31, 2019, other-than-temporary impairments (“OTTI”) unrealized losses in the table above represents OTTI recognized in accumulated other comprehensive income (“AOCI”). This amount excludes net unrealized gains on impaired securities relating to changes in the value of such securities subsequent to the impairment measurement date of $4.2 million. The Company deposits funds with various state and governmental authorities. For a discussion of the Company’s deposits with state and governmental authorities, see also Note 3 – “Investments” of the Notes to Consolidated Financial Statements in the Company’s 2019 Annual Report on Form 10-K. The amortized cost and fair value by maturity periods for fixed maturities are shown in the following table. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties, or the Company may have the right to put or sell the obligations back to the issuers. March 31, 2020 Amortized Cost, net of Allowance for Fair (in millions) Credit Losses Value Due in one year or less $ 354.0 $ 355.8 Due after one year through five years 1,871.0 1,897.6 Due after five years through ten years 2,258.1 2,290.7 Due after ten years 363.6 378.6 4,846.7 4,922.7 Mortgage-backed and asset-backed securities 1,640.8 1,702.3 Total fixed maturities $ 6,487.5 $ 6,625.0 B. Fixed maturity securities in an unrealized loss position The following tables provide information about the Company’s available-for-sale fixed maturity securities that were in an unrealized loss position at March 31, 2020 and December 31, 2019 including the length of time the securities have been in an unrealized loss position: March 31, 2020 12 months or less Greater than 12 months Total Gross Gross Gross Unrealized Fair Unrealized Fair Unrealized Fair (in millions) Losses Value Losses Value Losses Value Investment grade: Municipal $ 1.4 $ 62.7 $ — $ 0.6 $ 1.4 $ 63.3 Corporate 49.0 1,145.7 — — 49.0 1,145.7 Residential mortgage-backed 0.1 3.3 — 1.4 0.1 4.7 Commercial mortgage-backed 2.1 111.5 — — 2.1 111.5 Asset-backed 0.5 21.3 — — 0.5 21.3 Total investment grade 53.1 1,344.5 — 2.0 53.1 1,346.5 Below investment grade: Corporate 11.0 144.2 — — 11.0 144.2 Total fixed maturities $ 64.1 $ 1,488.7 $ — $ 2.0 $ 64.1 $ 1,490.7 December 31, 2019 12 months or less Greater than 12 months Total Gross Gross Gross Unrealized Fair Unrealized Fair Unrealized Fair (in millions) Losses Value Losses Value Losses Value Investment grade: U.S. Treasury and government agencies $ 1.3 $ 73.0 $ — $ 9.3 $ 1.3 $ 82.3 Municipal 1.1 72.5 0.1 5.6 1.2 78.1 Corporate 0.7 86.5 0.1 4.7 0.8 91.2 Residential mortgage-backed 0.7 69.2 0.4 34.4 1.1 103.6 Commercial mortgage-backed 0.1 40.6 — 0.9 0.1 41.5 Asset-backed — — — 1.7 — 1.7 Total investment grade 3.9 341.8 0.6 56.6 4.5 398.4 Below investment grade: Corporate 2.2 27.1 0.9 9.0 3.1 36.1 Total fixed maturities $ 6.1 $ 368.9 $ 1.5 $ 65.6 $ 7.6 $ 434.5 The Company views gross unrealized losses on fixed maturities as non-credit related and through its assessment of unrealized losses has determined that these securities will recover, allowing the Company to realize the anticipated long-term economic value. The Company currently does not intend to sell nor does it expect to be required to sell these securities before recovery of their amortized cost. The Company employs a systematic methodology to evaluate declines in fair value below amortized cost for fixed maturity securities. In determining impairments , the Company evaluates several factors and circumstances, including the issuer’s overall financial condition; the issuer’s credit and financial strength ratings; the issuer’s financial performance, including earnings trends and asset quality; any specific events which may influence the operations of the issuer; the general outlook for market conditions in the industry or geographic region in which the issuer operates; and the degree to which the fair value of an issuer’s securities i s below the Company’s amortized cost. The Company also considers any factors that might raise doubt about the issuer’s ability to make contractual payments as they come due and whether the Company expects to recover the entire amortized cost basis of the security. C. Proceeds from sales The proceeds from sales of available-for-sale securities and gross realized gains and gross realized losses on those sales were as follows: Three Months Ended March 31, 2020 2019 Proceeds from Gross Gross Proceeds from Gross Gross (in millions) Sales Gains Losses Sales Gains Losses Fixed maturities, excluding held-for-sale (Chaucer) $ 66.0 $ 2.7 $ 0.4 $ 60.1 $ 1.0 $ 1.5 Fixed maturities, held-for-sale — — — 0.3 — — Total fixed maturities $ 66.0 $ 2.7 $ 0.4 $ 60.4 $ 1.0 $ 1.5 D. Impairments For the three months ended March 31, 2020, the Company recognized $28.5 million of impairments, consisting primarily of $22.2 million on fixed maturities and $4.8 million on mortgage loans. Impairments on fixed maturities included $16.0 million categorized as intend-to-sell and $6.2 million of credit-related losses. As such, the Company recorded an allowance for credit losses of $6.2 million on corporate fixed maturities at March 31, 2020. In addition, the Company increased its allowance for credit losses on mortgage loans by $4.8 million in the first quarter of 2020, to $6.1 million as of March 31, 2020. For the three months ended March 31, 2019, the Company recognized no impairments. The methodology and significant inputs used to measure the amount of credit losses on fixed maturities in 2020 were as follows: Corporate bonds – the Company utilized a financial model that derives expected cash flows based on probability-of-default factors by credit rating, asset duration and loss-given-default factors based on security type. These factors are based on historical data provided by an independent third-party rating agency. In addition, other market data relevant to the realizability of contractual cash flows may be considered, including current conditions and reasonable and supportable forecasts. Mortgage loans – the Company utilized a model that estimates expected losses based on mortgage risk rating and risk factors based on property type, such as office, retail, lodging, multi-family and industrial. Expected loss ratios are based on historical data provided by an independent third-party rating agency. The risk factors, based on property characteristics and metrics including the geographic market, are predominantly driven by loan-to-value and debt service coverage ratios. An adjustment to ratings may be made to reflect current conditions and to incorporate reasonable and supportable forecasts, such as volatility of cash flows and valuation. E. Equity securities Equity securities are carried at fair value and all increases or decreases in fair value are reported in net realized and unrealized investment gains (losses) on the Consolidated Statements of Income. The following table provides pre-tax net realized and unrealized gains (losses) on equity securities: Three Months Ended March 31, (in millions) 2020 2019 Net gains (losses) recognized during the period $ (136.2 ) $ 48.6 Less: net gains (losses) recognized on equity securities sold during the period (0.6 ) 1.1 Net unrealized gains (losses) recognized during the period on equity securities still held $ (135.6 ) $ 47.5

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value	4. Fair Value Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability, i.e., exit price, in an orderly transaction between market participants. The Company emphasizes the use of observable market data whenever available in determining fair value. Fair values presented for certain financial instruments are estimates which, in many cases, may differ significantly from the amounts that could be realized upon immediate liquidation. A hierarchy of the three broad levels of fair value is as follows, with the highest priority given to Level 1 as these are the most observable, and the lowest priority given to Level 3: Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 – Quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data, including model-derived valuations. Level 3 – Unobservable inputs that are supported by little or no market activity. When more than one level of input is used to determine fair value, the financial instrument is classified as Level 2 or 3 according to the lowest level input that has a significant impact on the fair value measurement. The following methods and assumptions were used to estimate the fair value of each class of financial instruments and have not changed since last year. Fixed Maturities Level 1 securities generally include U.S. Treasury issues and other securities that are highly liquid and for which quoted market prices are available. Level 2 securities are valued using pricing for similar securities and pricing models that incorporate observable inputs including, but not limited to yield curves and issuer spreads. Level 3 securities include issues for which little observable data can be obtained, primarily due to the illiquid nature of the securities, and for which significant inputs used to determine fair value are based on the Company’s own assumptions. The Company utilizes a third party pricing service for the valuation of the majority of its fixed maturity securities and receives one quote per security. When quoted market prices in an active market are available, they are provided by the pricing service as the fair value and such values are classified as Level 1. Since fixed maturities other than U.S. Treasury securities generally do not trade on a daily basis, the pricing service prepares estimates of fair value for those securities using pricing techniques based on a market approach. Inputs into the fair value pricing common to all asset classes include: benchmark U.S. Treasury security yield curves; reported trades of identical or similar fixed maturity securities; broker/dealer quotes of identical or similar fixed maturity securities and structural characteristics such as maturity date, coupon, mandatory principal payment dates, frequency of interest and principal payments, and optional redemption features. Inputs into the fair value applications that are unique by asset class include, but are not limited to: • U.S. government agencies – determination of direct versus indirect government support and whether any contingencies exist with respect to the timely payment of principal and interest. • Foreign government – estimates of appropriate market spread versus underlying related sovereign treasury curve(s) dependent on liquidity and direct or contingent support. • Municipals – overall credit quality, including assessments of the level and variability of: sources of payment such as income, sales or property taxes, levies or user fees; credit support such as insurance; state or local economic and political base; natural resource availability; and susceptibility to natural or man-made catastrophic events such as hurricanes, earthquakes or acts of terrorism. • Corporate fixed maturities – overall credit quality, including assessments of the level and variability of: economic sensitivity; liquidity; corporate financial policies; management quality; regulatory environment; competitive position; ownership; restrictive covenants; and security or collateral. • Residential mortgage-backed securities – estimates of prepayment speeds based upon: historical prepayment rate trends; underlying collateral interest rates; geographic concentration; vintage year; borrower credit quality characteristics; interest rate and yield curve forecasts; government or monetary authority support programs; tax policies; and delinquency/default trends. • Commercial mortgage-backed securities – overall credit quality, including assessments of the value and supply/demand characteristics of: collateral type such as office, retail, residential, lodging, or other; geographic concentration by region, state, metropolitan statistical area and locale; vintage year; historical collateral performance including defeasance, delinquency, default and special servicer trends; and capital structure support features. • Asset-backed securities – overall credit quality, including assessments of the underlying collateral type such as credit card receivables, auto loan receivables and equipment lease receivables; geographic diversification; vintage year; historical collateral performance including delinquency, default and casualty trends; economic conditions influencing use rates and resale values; and contract structural support features. Generally, all prices provided by the pricing service, except actively traded securities with quoted market prices, are reported as Level 2. The Company holds privately placed fixed maturity securities and certain other fixed maturity securities that do not have an active market and for which the pricing service cannot provide fair values. The Company determines fair values for these securities using either matrix pricing utilizing the market approach or broker quotes. The Company will use observable market data as inputs into the fair value techniques, as discussed in the determination of Level 2 fair values, to the extent it is available, but is also required to use a certain amount of unobservable judgment due to the illiquid nature of the securities involved. Unobservable judgment reflected in the Company’s matrix model accounts for estimates of additional spread required by market participants for factors such as issue size, credit stress, structural complexity, high bond coupon or other unique features. These matrix-priced securities are reported as Level 2 or Level 3, depending on the significance of the impact of unobservable judgment on the security’s value. Additionally, the Company may obtain non-binding broker quotes which are reported as Level 3. Equity Securities Level 1 consists of publicly traded securities, including exchange traded funds, valued at quoted market prices. Level 2 includes securities that are valued using pricing for similar securities and pricing models that incorporate observable inputs. Level 3 consists of common or preferred stock of private companies for which observable inputs are not available. The Company utilizes a third party pricing service for the valuation of the majority of its equity securities and receives one quote for each equity security. When quoted market prices in an active market are available, they are provided by the pricing service as the fair value and such values are classified as Level 1. The Company holds certain equity securities that have been issued by privately-held entities that do not have an active market and for which the pricing service cannot provide fair values. Generally, the Company estimates fair value for these securities based on the issuer’s book value and market multiples and reports them as Level 3. Additionally, the Company may obtain non-binding broker quotes which are reported as Level 3. Other Investments Other investments primarily include mortgage participations and limited partnerships not subject to the equity method of accounting. The fair values of limited partnerships not subject to the equity method of accounting are based on the net asset value (“NAV”) provided by the general partner adjusted for recent financial information and are excluded from the fair value hierarchy. The estimated fair values of the financial instruments were as follows: March 31, 2020 December 31, 2019 Carrying Fair Carrying Fair (in millions) Value Value Value Value Financial Assets carried at: Fair Value through AOCI: Fixed maturities $ 6,625.0 $ 6,625.0 $ 6,687.1 $ 6,687.1 Fair Value through Net Income: Equity securities 447.0 447.0 575.7 575.7 Other investments 185.6 185.6 187.1 187.1 Amortized Cost/Cost: Other investments 463.5 473.7 443.3 463.7 Cash and cash equivalents 143.9 143.9 215.7 215.7 Total financial instruments $ 7,865.0 $ 7,875.2 $ 8,108.9 $ 8,129.3 Financial Liabilities carried at: Amortized Cost: Debt $ 707.5 $ 741.8 $ 653.4 $ 722.1 The Company has processes designed to ensure that the values received from its third party pricing service are accurately recorded, that the data inputs and valuation approaches and techniques utilized are appropriate and consistently applied, and that the assumptions are reasonable and consistent with the objective of determining fair value. The Company performs a review of the fair value hierarchy classifications and of prices received from its pricing service on a quarterly basis. The Company reviews the pricing services’ policies describing its methodology, processes, practices and inputs, including various financial models used to value securities. Also, the Company reviews the portfolio pricing, including a process for which securities with changes in prices that exceed a defined threshold are verified to independent sources, if available. If upon review, the Company is not satisfied with the validity of a given price, a pricing challenge would be submitted to the pricing service along with supporting documentation for its review. The Company does not adjust quotes or prices obtained from the pricing service unless the pricing service agrees with the Company’s challenge. During 20 20 and 2019 , the Company did not adjust any prices received from its pricing service. Changes in the observability of valuation inputs may result in a reclassification of certain financial assets or liabilities within the fair value hierarchy. As previously discussed, the Company utilizes a third-party pricing service for the valuation of the majority of its fixed maturities and equity securities. The pricing service has indicated that it will only produce an estimate of fair value if there is objectively verifiable information to produce a valuation. If the pricing service discontinues pricing an investment, the Company will use observable market data to the extent it is available, but may also be required to make assumptions for market based inputs that are unavailable due to market conditions. The following tables provide, for each hierarchy level, the Company’s investment assets that were measured at fair value on a recurring basis. March 31, 2020 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 286.2 $ 151.2 $ 135.0 $ — Foreign government 4.5 — 4.5 — Municipal 867.7 — 856.3 11.4 Corporate 3,764.3 — 3,763.8 0.5 Residential mortgage-backed 956.9 — 956.9 — Commercial mortgage-backed 679.5 — 667.7 11.8 Asset-backed 65.9 — 65.9 — Total fixed maturities 6,625.0 151.2 6,450.1 23.7 Equity securities 447.0 444.9 — 2.1 Other investments 3.5 — — 3.5 Total investment assets at fair value $ 7,075.5 $ 596.1 $ 6,450.1 $ 29.3 December 31, 2019 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 349.8 $ 157.9 $ 191.9 $ — Foreign government 16.1 — 16.1 — Municipal 833.5 — 821.4 12.1 Corporate 3,811.2 — 3,810.6 0.6 Residential mortgage-backed 921.4 — 921.4 — Commercial mortgage-backed 691.9 — 679.2 12.7 Asset-backed 63.2 — 63.2 — Total fixed maturities 6,687.1 157.9 6,503.8 25.4 Equity securities 575.7 573.6 — 2.1 Other investments 3.5 — — 3.5 Total investment assets at fair value $ 7,266.3 $ 731.5 $ 6,503.8 $ 31.0 Limited partnerships measured at fair value using NAV based on an ownership interest in partners’ capital have not been included in the hierarchy tables. At March 31, 2020 and December 31, 2019, the fair values of these investments were $182.1 million and $183.6 million, respectively, approximately 2% of total investment assets. The following tables provide, for each hierarchy level, the Company’s estimated fair values of financial instruments that were not carried at fair value: March 31, 2020 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 143.9 $ 143.9 $ — $ — Other investments 473.7 — 4.1 469.6 Total financial instruments $ 617.6 $ 143.9 $ 4.1 $ 469.6 Liabilities: Debt $ 741.8 $ — $ 741.8 $ — December 31, 2019 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 215.7 $ 215.7 $ — $ — Other investments 463.7 — 2.1 461.6 Total financial instruments $ 679.4 $ 215.7 $ 2.1 $ 461.6 Liabilities: Debt $ 722.1 $ — $ 722.1 $ — The tables below provide reconciliation for all assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3). Fixed Maturities (in millions) Municipal Corporate Commercial mortgage- backed Total Equity and Other Total Assets Three Months Ended March 31, 2020 Balance January 1, 2020 $ 12.1 $ 0.6 $ 12.7 $ 25.4 $ 5.6 $ 31.0 Total gains (losses): Included in other comprehensive income-net appreciation (depreciation) on available-for-sale securities 0.1 — (0.4 ) (0.3 ) — (0.3 ) Sales (0.8 ) (0.1 ) (0.5 ) (1.4 ) — (1.4 ) Balance March 31, 2020 $ 11.4 $ 0.5 $ 11.8 $ 23.7 $ 5.6 $ 29.3 Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the period $ 0.1 $ — $ (0.4 ) $ (0.3 ) $ — $ (0.3 ) Three Months Ended March 31, 2019 Balance January 1, 2019 $ 21.1 $ 0.8 $ 13.1 $ 35.0 $ 4.6 $ 39.6 Total gains: Included in total net realized and unrealized investment gains 0.1 — — 0.1 — 0.1 Included in other comprehensive income-net depreciation on available-for-sale securities 0.2 — 0.2 0.4 — 0.4 Sales: (0.9 ) (0.1 ) (0.5 ) (1.5 ) — (1.5 ) Balance March 31, 2019 $ 20.5 $ 0.7 $ 12.8 $ 34.0 $ 4.6 $ 38.6 There were no transfers between Level 2 and Level 3, and there were no Level 3 liabilities held by the Company for the three months ended March 31, 2020 and 2019. The following table provides quantitative information about the significant unobservable inputs used by the Company in the fair value measurements of Level 3 assets. Where discounted cash flows were used in the valuation of fixed maturities, the internally-developed discount rate was adjusted by the significant unobservable inputs shown in the table. March 31, 2020 December 31, 2019 Valuation Significant Fair Range Fair Range (in millions) Technique Unobservable Inputs Value (Wtd Average) Value (Wtd Average) Fixed maturities: Municipal Discounted cash flow Discount for: Small issue size Credit stress Above-market coupon $ 11.4 0.7 - 6.8% (4.4%) 0.6 - 3.4% (2.7%) 0.5% (0.5%) $ 12.1 0.7 - 6.8% (4.3%) — 0.5% (0.5%) Corporate Discounted cash flow Discount for: Small issue size Above-market coupon 0.5 2.5% (2.5%) 0.3% (0.3%) 0.6 2.5% (2.5%) 0.3% (0.3%) Commercial mortgage-backed Discounted cash flow Discount for: Small issue size Credit stress Above-market coupon Lease structure 11.8 1.9 - 3.1% (2.7%) 1.7 - 6.0% (2.3%) 0.5% (0.5%) 0.3% (0.3%) 12.7 1.9 - 3.1% (2.7%) — 0.5% (0.5%) 0.3% (0.3%) Equity securities Market comparables Net tangible asset market multiples 2.1 1.0X (1.0X) 2.1 1.0X (1.0X) Other Discounted cash flow Discount rate 3.5 18.0% (18.0%) 3.5 18.0% (18.0%) The weighted average of the unobservable inputs was weighted by the relative fair value of the fixed maturity securities to which the inputs were applied. Each unobservable input is based on the Company’s subjective opinion and therefore inherently contains a degree of uncertainty. Significant increases (decreases) in any of the above inputs in isolation would result in a significantly lower (higher) fair value measurement. There were no interrelationships between these inputs which might magnify or mitigate the effect of changes in unobservable inputs on the fair value measurement.

Debt and Credit Arrangements

Debt and Credit Arrangements	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Debt and Credit Arrangements	5. Debt and Credit Arrangements Debt consists of the following: (in millions) March 31, 2020 December 31, 2019 Senior debentures maturing April 15, 2026 $ 375.0 $ 375.0 Senior debentures maturing October 15, 2025 62.6 62.6 Subordinated debentures maturing March 30, 2053 175.0 175.0 Subordinated debentures maturing February 3, 2027 50.1 50.1 Short-term borrowings 54.0 — Total principal debt 716.7 662.7 Unamortized debt issuance costs (9.2 ) (9.3 ) Total $ 707.5 $ 653.4 The Company had $54.0 million of short-term advances from the Federal Home Loan Bank (“FHLB”) outstanding at March 31, 2020, which will be repaid in the second quarter of 2020. At March 31, 2020, the Company was in compliance with the covenants associated with its debt indentures and credit arrangements.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	6. Income Taxes Income tax expense for the three months ended March 31, 2020 and 2019 has been computed using estimated annual effective tax rates. These rates are revised, if necessary, at the end of each successive interim period to reflect current estimates of the annual effective tax rates. The tax provision was comprised of a U.S. federal income tax benefit of $15.2 million and an expense of $26.0 million for the three months ended March 31, 2020 and 2019, respectively. The Company or its subsidiaries files income tax returns in the U.S. federal jurisdiction and various state jurisdictions, and have previously filed in foreign jurisdictions. The Company and its subsidiaries are subject to U.S. federal and state income tax examinations and foreign examinations for years after 2015.

Pension Plans

Pension Plans	3 Months Ended
	Mar. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Pension Plans	7. Pension Plans The components of net periodic pension cost for the defined benefit pension plans included in the Company’s results of operations are as follows: Three Months Ended March 31, 2020 2019 (in millions) Pension Plans Interest cost $ 4.6 $ 5.3 Expected return on plan assets (5.6 ) (5.8 ) Recognized net actuarial loss 1.5 2.8 Net periodic pension cost $ 0.5 $ 2.3

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Other Comprehensive Income (Loss)	8. Other Comprehensive Income (Loss) The following tables provide changes in other comprehensive income (loss). Three Months Ended March 31, 2020 2019 Tax Tax Benefit Net of Benefit Net of (in millions) Pre-Tax (Expense) Tax Pre-Tax (Expense) Tax Unrealized gains (losses) on available-for-sale securities: Unrealized gains (losses) arising during period $ (122.4 ) $ 25.6 $ (96.8 ) $ 152.0 $ (32.0 ) $ 120.0 Amount of realized gains (losses) from sales and other (3.1 ) (1.2 ) (4.3 ) 0.3 (3.9 ) (3.6 ) Impairment losses on investments 22.7 (4.8 ) 17.9 — — — Net unrealized gains (losses) (102.8 ) 19.6 (83.2 ) 152.3 (35.9 ) 116.4 Pension and postretirement benefits: Amortization of net actuarial losses (gains) recognized as net periodic benefit cost 1.5 (0.3 ) 1.2 2.9 (0.6 ) 2.3 Cumulative foreign currency translation adjustment: Foreign currency translation recognized during the period — — — 0.1 — 0.1 Other comprehensive income (loss) $ (101.3 ) $ 19.3 $ (82.0 ) $ 155.3 $ (36.5 ) $ 118.8 Reclassifications out of accumulated other comprehensive income were as follows: Three Months Ended March 31, (in millions) 2020 2019 Amount Reclassified from Details about Accumulated Other Accumulated Other Affected Line Item in the Statement Comprehensive Income Components Comprehensive Income Where Net Income (Loss) is Presented Unrealized gains (losses) on available-for- sale securities $ 3.1 $ (0.3 ) Net realized gains (losses) from sales and other (22.2 ) — Impairment losses on investments (19.1 ) (0.3 ) Total before tax 5.9 3.9 Tax benefit (13.2 ) 3.6 Continuing operations; net of tax (0.4 ) — Discontinued operations - life businesses (13.6 ) 3.6 Net of tax Amortization of defined benefit pension and postretirement actuarial losses (1.5 ) (2.9 ) Loss adjustment expenses and other operating expenses (1) 0.3 0.6 Tax benefit (1.2 ) (2.3 ) Continuing operations; net of tax Total reclassifications for the period $ (14.8 ) $ 1.3 Benefit (expense) reflected in income (loss), net of tax (1) The amount reclassified from accumulated other comprehensive income for the pension and postretirement benefits was allocated approximately 40% to loss adjustment expenses and 60% to other operating expenses for the three months ended March 31, 2020 and 2019.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2020
Segment Reporting [Abstract]
Segment Information	9. Segment Information The Company’s primary business operations include insurance products and services provided through three operating segments: Commercial Lines, Personal Lines and Other. Commercial Lines includes commercial multiple peril, commercial automobile, workers’ compensation, and other commercial coverages, such as management and professional liability, marine, Hanover Programs, specialty industrial and commercial property, monoline general liability and surety. Personal Lines includes personal automobile, homeowners and other personal coverages. Included in the Other segment are Opus Investment Management, Inc., which markets investment management services to institutions, pension funds and other organizations; earnings on holding company assets; holding company and other expenses, including certain costs associated with retirement benefits due to the Company’s former life insurance employees and agents; and, a run-off voluntary property and casualty pools business. The separate financial information is presented consistent with the way results are regularly evaluated by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company reports interest expense related to debt separately from the earnings of its operating segments. This consists primarily of interest on the Company’s senior and subordinated debentures. Management evaluates the results of the aforementioned segments based on operating income before taxes, excluding interest expense on debt. Operating income before taxes excludes certain items which are included in net income, such as net realized and unrealized investment gains and losses. Such gains and losses are excluded since they are determined by interest rates, financial markets and the timing of sales. Also, operating income before taxes excludes net gains and losses on disposals of businesses, gains and losses related to the repayment of debt, discontinued operations, costs to acquire businesses, restructuring costs, the cumulative effect of accounting changes and certain other items. Although the items excluded from operating income before taxes may be important components in understanding and assessing the Company’s overall financial performance, management believes that the presentation of operating income before taxes enhances an investor’s understanding of the Company’s results of operations by highlighting net income attributable to the core operations of the business. However, operating income before taxes should not be construed as a substitute for income before income taxes or income from continuing operations, and operating income should not be construed as a substitute for net income. Summarized below is financial information with respect to the Company’s business segments. Three Months Ended March 31, (in millions) 2020 2019 Operating revenues: Commercial Lines $ 724.7 $ 698.7 Personal Lines 488.5 465.2 Other 4.6 7.4 Total 1,217.8 1,171.3 Net realized and unrealized investment gains (losses) (161.6 ) 48.2 Total revenues $ 1,056.2 $ 1,219.5 Operating income (loss) before interest expense and income taxes: Commercial Lines: Underwriting income $ 10.4 $ 36.7 Net investment income 46.4 44.3 Other expense (2.2 ) (0.8 ) Commercial Lines operating income 54.6 80.2 Personal Lines: Underwriting income 44.1 5.7 Net investment income 20.3 19.7 Other income 0.5 1.4 Personal Lines operating income 64.9 26.8 Other: Underwriting loss (3.3 ) (0.3 ) Net investment income 2.9 6.2 Other expense (2.0 ) (3.1 ) Other operating income (loss) (2.4 ) 2.8 Operating income before interest expense and income taxes 117.1 109.8 Interest on debt (9.4 ) (9.4 ) Operating income before income taxes 107.7 100.4 Non-operating items: Net realized and unrealized investment gains (losses) (161.6 ) 48.2 Income (loss) from continuing operations before income taxes $ (53.9 ) $ 148.6 The following table provides identifiable assets for the Company’s business segments and discontinued operations: March 31, 2020 December 31, 2019 (in millions) Identifiable Assets Property and Casualty Companies $ 12,179.3 $ 12,387.7 Assets of discontinued businesses 98.1 102.8 Total $ 12,277.4 $ 12,490.5 The Company reviews the assets of its Property and Casualty Companies collectively and does not allocate them between the Commercial Lines, Personal Lines and Other segments.

Stock-based Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	10. Stock-based Compensation As of March 31, 2020, there were 2,761,668 shares and 2,352,110 shares available for grant under The Hanover Insurance Group 2014 Long-Term Incentive Plan and The Hanover Insurance Group 2014 Employee Stock Purchase Plan, respectively. Compensation cost for the Company’s stock-based awards and the related tax benefits were as follows: Three Months Ended March 31, (in millions) 2020 2019 Stock-based compensation expense $ 5.0 $ 4.2 Tax benefit (1.1 ) (0.9 ) Stock-based compensation expense, net of taxes $ 3.9 $ 3.3 Stock Options Information on the Company’s stock option activity for the three months ended March 31, 2020 and 2019 is summarized below. Three Months Ended March 31, 2020 2019 (in whole shares and dollars) Shares Weighted Average Exercise Price Shares Weighted Average Exercise Price Outstanding, beginning of period 1,121,559 $ 87.88 1,099,076 $ 85.75 Granted 240,705 118.54 232,568 95.05 Exercised (35,918 ) 79.40 (64,017 ) 75.98 Forfeited or cancelled — — (3,141 ) 95.39 Outstanding, end of period 1,326,346 93.67 1,264,486 87.93 Restricted Stock Units The Company currently issues time-based, market-based and performance-based restricted stock units to eligible employees, all of which generally vest after 3 years of continued employment. The following tables summarize activity information about employee restricted stock units: Three Months Ended March 31, 2020 2019 (in whole shares and dollars) Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value Time-based restricted stock units: Outstanding, beginning of period 335,166 $ 109.55 332,481 $ 97.28 Granted 136,634 118.60 144,072 117.51 Vested (78,773 ) 85.44 (99,855 ) 83.25 Forfeited (2,861 ) 112.24 (8,687 ) 97.14 Outstanding, end of period 390,166 117.56 368,011 109.01 Performance-based and market-based restricted stock units: Outstanding, beginning of period 86,252 $ 110.70 69,838 $ 95.58 Granted 54,415 105.10 42,119 117.68 Vested (36,499 ) 80.26 (10,089 ) 82.74 Forfeited — — — — Outstanding, end of period 104,168 118.45 101,868 105.99 In the first three months of 2020 and 2019, the Company granted market-based awards totaling 34,911 and 23,924, respectively, to certain members of senior management, which are included in the table above as performance and market-based restricted stock activity. The vesting of these stock units is based on the relative total shareholder return (“TSR”) of the Company. This metric is generally based on relative TSR for a three-year The Company also granted performance-based restricted stock units in 2020 and 2019, totaling 19,504 and 18,195, respectively, which are based upon the Company’s achievement of return on equity objectives. These units have the potential to range from 0% to 150% of the shares disclosed, which varies based on grant year and individual participation level. Increases above the 100% target level are reflected as granted in the period in which performance-based stock unit goals are achieved. Decreases below the 100% target level are reflected as forfeited. There were no performance-based awards that vested in 2020 or 2019.

Earnings Per Share and Sharehol

Earnings Per Share and Shareholders' Equity Transactions	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share and Shareholders' Equity Transactions	11. Earnings Per Share and Shareholders’ Equity Transactions The following table provides weighted average share information used in the calculation of the Company’s basic and diluted earnings per share: Three Months Ended March 31, (in millions, except per share data) 2020 2019 Basic shares used in the calculation of earnings per share 38.3 40.6 Dilutive effect of securities (1): Employee stock options — 0.3 Non-vested stock grants — 0.3 Diluted shares used in the calculation of earnings per share 38.3 41.2 Per share effect of dilutive securities on income (loss) from continuing operations and net income (loss) $ — $ (0.04 ) (1) Excludes 0.6 million shares due to antidilution that resulted from the Company having losses from continuing operations and net losses for the quarter ended March 31, 2020. Diluted earnings per share for the three months ended March 31, 2020 and 2019 excludes 0.4 million and 0.2 million, respectively, of common shares issuable under the Company’s stock compensation plans because their effect would be antidilutive. T he Board of Directors authorized a stock repurchase program which provides for aggregate repurchases of up to $900 million, including a $300 million increase to the program that was authorized on December 5, 2019. Under the repurchase authorization, the Company may repurchase, from time to time, common stock in amounts, at prices and at such times as the Company deems appropriate, subject to market conditions and other considerations. Repurchases may be executed using open market purchases, privately negotiated transactions, accelerated repurchase programs or other transactions. The Company is not required to purchase any specific number of shares or to make purchases by any certain date under this program. On December 9, 2019, pursuant to the terms of an accelerated share repurchase (“ASR”) agreement (the “December 2019 ASR”) the Company paid $150.0 million in exchange for an initial delivery of approximately 0.9 million shares of common stock. On February 26, 2020, the Company received approximately 0.2 million of its common stock shares as final settlement of shares repurchased under the December 2019 ASR.

Liabilities for Outstanding Cla

Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2020
Insurance [Abstract]
Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses	12. Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses Reserve Rollforward and Prior Year Development The Company regularly updates its reserve estimates as new information becomes available and further events occur which may impact the resolution of unsettled claims. Reserve adjustments are reflected in results of operations as adjustments to losses and loss adjustment expenses (“LAE”). Often these adjustments are recognized in periods subsequent to the period in which the underlying policy was written and loss event occurred. These types of subsequent adjustments are described as “prior years’ loss reserves”. Such development can be either favorable or unfavorable to the Company’s financial results and may vary by line of business. In this section, all amounts presented include catastrophe losses and LAE, unless otherwise indicated. The table below provides a reconciliation of the gross beginning and ending reserve for unpaid losses and loss adjustment expenses. Three Months Ended March 31, (in millions) 2020 2019 Gross loss and LAE reserves, beginning of period $ 5,654.4 $ 5,304.1 Reinsurance recoverable on unpaid losses 1,574.8 1,472.6 Net loss and LAE reserves, beginning of period 4,079.6 3,831.5 Net incurred losses and LAE in respect of losses occurring in: Current year 730.2 712.8 Prior years (2.0 ) (13.2 ) Total incurred losses and LAE 728.2 699.6 Net payments of losses and LAE in respect of losses occurring in: Current year 174.6 175.3 Prior years 484.4 459.1 Total payments 659.0 634.4 Net reserve for losses and LAE, end of period 4,148.8 3,896.7 Reinsurance recoverable on unpaid losses 1,576.1 1,484.9 Gross reserve for losses and LAE, end of period $ 5,724.9 $ 5,381.6 As a result of continuing trends in the Company’s business, reserves including catastrophes have been re-estimated for all prior accident years and were decreased by $2.0 million and $13.2 million in 2020 and 2019, respectively. 2020 For the three months ended March 31, 2020, net favorable loss and LAE development was $2.0 million. Lower than expected losses in the workers’ compensation line, other commercial lines and homeowners line were partially offset by higher than expected losses in the commercial and personal automobile lines, commercial multiple peril line, and in the Company’s run-off voluntary assumed property and casualty reinsurance pools business. Within other commercial lines, lower than expected losses in the Company’s marine line and specialty industrial and commercial property lines were partially offset by higher than expected losses in the general liability lines. The higher than expected losses in the Company’s run-off voluntary assumed property and casualty reinsurance pools business was based on an updated third-party actuarial study received in the first quarter of 2020 for the legacy Excess and Casualty Reinsurance Association (“ECRA”) pool that primarily consists of asbestos and environmental exposures. 2019 For the three months ended March 31, 2019, net favorable loss and LAE development was $13.2 million, primarily as a result of favorable catastrophe development due to the sale of subrogation rights on certain 2017 and 2018 California wildfires . In addition, higher than expected losses in the Company’s personal and commercial automobile lines were substantially offset by lower than expected losses in the Company’s workers’ compensation and commercial multiple peril lines.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Legal Proceedings The Company has been named a defendant in various 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 quarterly 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 .

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events On April 10, 2020, the Company announced that it will return 15% of April and May personal automobile premiums to its eligible Personal Lines customers in all of THG’s markets, providing financial relief during the outbreak of the novel coronavirus, also known as COVID-19, and subsequent global pandemic. The Company’s decision to return a portion of premium payments to its customers is a recognition of the impact of government-mandated stay-at-home measures, which are reducing the number of vehicles on the roads and miles driven, and consequently, the number of claims filed. The Company estimates that this premium refund will be approximately $30 million, which will be recognized in the second quarter of 2020. Pending regulatory approvals, the Company will credit April in-force policies in May, and May in-force policies in June.

New Accounting Pronouncements (

New Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements Recently Implemented Standards In June 2016, the Financial Accounting Standards Board (“FASB”) issued ASC Update No. 2016-13, (Topic 326) Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (“ASC Update No. 2016-13”) Codification Improvements to Topic 326, Financial Instruments – Credit Losses In 2019 and 2020, the FASB has issued several updates to ASC Update No. 2016-13, including the issuance in April 2019, ASC Update 2019-04, Codification Improvements to Topic 326, Financial Instruments – Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments Financial Instruments – Credit Losses (Topic 326): Targeted Transition Relief, Codification Improvements to Topic 326, Financial Instruments – Credit Losses Financial Instruments – Credit Losses (Topic 326) and Leases (Topic 842) – Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 119 and Update to SEC Section on Effective Date Related to Accounting Standards Update No. 2016-02, Leases (Topic 842) In August 2018, the FASB issued ASC Update No. 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract . This ASC update requires the capitalization of implementation costs incurred in a hosting arrangement that is a service contract consistent with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The guidance also requires an entity to expense the capitalized implementation costs of a hosting arrangement that is a service contract over the term of the hosting agreement, and apply impairment guidance consistent with long-lived assets. ASC Update No. 2018-15 also provides specific guidelines related to the presentation of these capitalized implementation costs and related expenses in the financial statements. The updated guidance is effective for interim and annual periods beginning after December 15, 2019, and should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. Early adoption is permitted, including interim periods. The Company implemented this guidance prospectively, effective January 1, 2020, and it did not have a material impact on its financial position or results of operations. In August 2018, the FASB issued ASC Update No. 2018-13 (Topic 820) Fair Value Measurement, Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement In January 2017, the FASB issued ASC Update No. 2017-04, (Topic 350) Intangibles – Goodwill and Other: Simplifying the Test for Goodwill Impairment Recently Issued Standards In January 2020, the FASB issued ASC Update No. 2020-01 Investments – Equity Securities (Topic 321), Investments – Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815) In December 2019, the FASB issued ASC Update No. 2019-12 Income Taxes (Topic 740) – Simplifying the Accounting for Income Taxes Income Taxes In August 2018, the FASB issued ASC Update No. 2018-14 (Topic 715-20) Compensation – Retirement Benefits – Defined Benefit Plans – General – Disclosure Framework – Changes to the Disclosure Requirements for the Defined Benefit Plans. This ASC update modifies disclosures related to defined benefit pension or other postretirement plans. This ASC update removes the disclosure of amounts in accumulated other comprehensive income expected to be recognized over the next fiscal year and the effects of a one percentage point change of health care cost trends on net periodic benefit costs and postretirement benefit obligations and clarifies the specific requirements of disclosures related to the project benefit obligation and accumulated benefit obligation. This ASC Update also adds disclosures related to weighted average crediting rates for cash balance plans and requires disclosure of an explanation of any significant gains and losses related to changes in benefit obligations for the period. The amendments in this ASC update are effective for fiscal years ending after December 15, 2020, and should be applied on a retrospective basis to all periods presented. Early adoption is permitted. Implementing this guidance is not expected to have an impact on the Company’s financial position or results of operations as the update is disclosure related.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2020
Investments Debt And Equity Securities [Abstract]
Schedule of Available-for-sale Fixed Maturities Reconciliation	The amortized cost and fair value of available-for-sale fixed maturities were as follows: March 31, 2020 Amortized Cost, Allowance net of Allowance Gross Gross Amortized for Credit for Credit Unrealized Unrealized (in millions) Cost Losses Losses Gains Losses Fair Value U.S. Treasury and government agencies $ 265.9 $ — $ 265.9 $ 20.3 $ — $ 286.2 Foreign government 4.2 — 4.2 0.3 — 4.5 Municipal 833.8 — 833.8 35.3 1.4 867.7 Corporate 3,749.0 6.2 3,742.8 81.5 60.0 3,764.3 Residential mortgage-backed 913.5 — 913.5 43.5 0.1 956.9 Commercial mortgage-backed 661.3 — 661.3 20.3 2.1 679.5 Asset-backed 66.0 — 66.0 0.4 0.5 65.9 Total fixed maturities $ 6,493.7 $ 6.2 $ 6,487.5 $ 201.6 $ 64.1 $ 6,625.0 December 31, 2019 Gross Gross OTTI Amortized Unrealized Unrealized Unrealized (in millions) Cost Gains Losses Fair Value Losses U.S. Treasury and government agencies $ 342.0 $ 9.1 $ 1.3 $ 349.8 $ — Foreign government 15.7 0.4 — 16.1 — Municipal 807.1 27.6 1.2 833.5 — Corporate 3,653.5 161.6 3.9 3,811.2 3.0 Residential mortgage-backed 905.4 17.1 1.1 921.4 — Commercial mortgage-backed 666.4 25.6 0.1 691.9 — Asset-backed 62.1 1.1 — 63.2 — Total fixed maturities $ 6,452.2 $ 242.5 $ 7.6 $ 6,687.1 $ 3.0
Investments Classified by Contractual Maturity Date	The amortized cost and fair value by maturity periods for fixed maturities are shown in the following table. Actual maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties, or the Company may have the right to put or sell the obligations back to the issuers. March 31, 2020 Amortized Cost, net of Allowance for Fair (in millions) Credit Losses Value Due in one year or less $ 354.0 $ 355.8 Due after one year through five years 1,871.0 1,897.6 Due after five years through ten years 2,258.1 2,290.7 Due after ten years 363.6 378.6 4,846.7 4,922.7 Mortgage-backed and asset-backed securities 1,640.8 1,702.3 Total fixed maturities $ 6,487.5 $ 6,625.0
Schedule of Unrealized Loss on Investments	The following tables provide information about the Company’s available-for-sale fixed maturity securities that were in an unrealized loss position at March 31, 2020 and December 31, 2019 including the length of time the securities have been in an unrealized loss position: March 31, 2020 12 months or less Greater than 12 months Total Gross Gross Gross Unrealized Fair Unrealized Fair Unrealized Fair (in millions) Losses Value Losses Value Losses Value Investment grade: Municipal $ 1.4 $ 62.7 $ — $ 0.6 $ 1.4 $ 63.3 Corporate 49.0 1,145.7 — — 49.0 1,145.7 Residential mortgage-backed 0.1 3.3 — 1.4 0.1 4.7 Commercial mortgage-backed 2.1 111.5 — — 2.1 111.5 Asset-backed 0.5 21.3 — — 0.5 21.3 Total investment grade 53.1 1,344.5 — 2.0 53.1 1,346.5 Below investment grade: Corporate 11.0 144.2 — — 11.0 144.2 Total fixed maturities $ 64.1 $ 1,488.7 $ — $ 2.0 $ 64.1 $ 1,490.7 December 31, 2019 12 months or less Greater than 12 months Total Gross Gross Gross Unrealized Fair Unrealized Fair Unrealized Fair (in millions) Losses Value Losses Value Losses Value Investment grade: U.S. Treasury and government agencies $ 1.3 $ 73.0 $ — $ 9.3 $ 1.3 $ 82.3 Municipal 1.1 72.5 0.1 5.6 1.2 78.1 Corporate 0.7 86.5 0.1 4.7 0.8 91.2 Residential mortgage-backed 0.7 69.2 0.4 34.4 1.1 103.6 Commercial mortgage-backed 0.1 40.6 — 0.9 0.1 41.5 Asset-backed — — — 1.7 — 1.7 Total investment grade 3.9 341.8 0.6 56.6 4.5 398.4 Below investment grade: Corporate 2.2 27.1 0.9 9.0 3.1 36.1 Total fixed maturities $ 6.1 $ 368.9 $ 1.5 $ 65.6 $ 7.6 $ 434.5
Schedule of Realized Gain (Loss)	The proceeds from sales of available-for-sale securities and gross realized gains and gross realized losses on those sales were as follows: Three Months Ended March 31, 2020 2019 Proceeds from Gross Gross Proceeds from Gross Gross (in millions) Sales Gains Losses Sales Gains Losses Fixed maturities, excluding held-for-sale (Chaucer) $ 66.0 $ 2.7 $ 0.4 $ 60.1 $ 1.0 $ 1.5 Fixed maturities, held-for-sale — — — 0.3 — — Total fixed maturities $ 66.0 $ 2.7 $ 0.4 $ 60.4 $ 1.0 $ 1.5
Schedule of Pre-tax Net Realized and Unrealized Gains (Losses) on Equity Securities	Three Months Ended March 31, (in millions) 2020 2019 Net gains (losses) recognized during the period $ (136.2 ) $ 48.6 Less: net gains (losses) recognized on equity securities sold during the period (0.6 ) 1.1 Net unrealized gains (losses) recognized during the period on equity securities still held $ (135.6 ) $ 47.5

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	The estimated fair values of the financial instruments were as follows: March 31, 2020 December 31, 2019 Carrying Fair Carrying Fair (in millions) Value Value Value Value Financial Assets carried at: Fair Value through AOCI: Fixed maturities $ 6,625.0 $ 6,625.0 $ 6,687.1 $ 6,687.1 Fair Value through Net Income: Equity securities 447.0 447.0 575.7 575.7 Other investments 185.6 185.6 187.1 187.1 Amortized Cost/Cost: Other investments 463.5 473.7 443.3 463.7 Cash and cash equivalents 143.9 143.9 215.7 215.7 Total financial instruments $ 7,865.0 $ 7,875.2 $ 8,108.9 $ 8,129.3 Financial Liabilities carried at: Amortized Cost: Debt $ 707.5 $ 741.8 $ 653.4 $ 722.1
Fair Value, Investment Assets Measured on Recurring Basis	The following tables provide, for each hierarchy level, the Company’s investment assets that were measured at fair value on a recurring basis. March 31, 2020 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 286.2 $ 151.2 $ 135.0 $ — Foreign government 4.5 — 4.5 — Municipal 867.7 — 856.3 11.4 Corporate 3,764.3 — 3,763.8 0.5 Residential mortgage-backed 956.9 — 956.9 — Commercial mortgage-backed 679.5 — 667.7 11.8 Asset-backed 65.9 — 65.9 — Total fixed maturities 6,625.0 151.2 6,450.1 23.7 Equity securities 447.0 444.9 — 2.1 Other investments 3.5 — — 3.5 Total investment assets at fair value $ 7,075.5 $ 596.1 $ 6,450.1 $ 29.3 December 31, 2019 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 349.8 $ 157.9 $ 191.9 $ — Foreign government 16.1 — 16.1 — Municipal 833.5 — 821.4 12.1 Corporate 3,811.2 — 3,810.6 0.6 Residential mortgage-backed 921.4 — 921.4 — Commercial mortgage-backed 691.9 — 679.2 12.7 Asset-backed 63.2 — 63.2 — Total fixed maturities 6,687.1 157.9 6,503.8 25.4 Equity securities 575.7 573.6 — 2.1 Other investments 3.5 — — 3.5 Total investment assets at fair value $ 7,266.3 $ 731.5 $ 6,503.8 $ 31.0
Estimated Fair Values of Financial Instruments Not Carried at Fair Value	The following tables provide, for each hierarchy level, the Company’s estimated fair values of financial instruments that were not carried at fair value: March 31, 2020 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 143.9 $ 143.9 $ — $ — Other investments 473.7 — 4.1 469.6 Total financial instruments $ 617.6 $ 143.9 $ 4.1 $ 469.6 Liabilities: Debt $ 741.8 $ — $ 741.8 $ — December 31, 2019 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 215.7 $ 215.7 $ — $ — Other investments 463.7 — 2.1 461.6 Total financial instruments $ 679.4 $ 215.7 $ 2.1 $ 461.6 Liabilities: Debt $ 722.1 $ — $ 722.1 $ —
Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)	The tables below provide reconciliation for all assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3). Fixed Maturities (in millions) Municipal Corporate Commercial mortgage- backed Total Equity and Other Total Assets Three Months Ended March 31, 2020 Balance January 1, 2020 $ 12.1 $ 0.6 $ 12.7 $ 25.4 $ 5.6 $ 31.0 Total gains (losses): Included in other comprehensive income-net appreciation (depreciation) on available-for-sale securities 0.1 — (0.4 ) (0.3 ) — (0.3 ) Sales (0.8 ) (0.1 ) (0.5 ) (1.4 ) — (1.4 ) Balance March 31, 2020 $ 11.4 $ 0.5 $ 11.8 $ 23.7 $ 5.6 $ 29.3 Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the period $ 0.1 $ — $ (0.4 ) $ (0.3 ) $ — $ (0.3 ) Three Months Ended March 31, 2019 Balance January 1, 2019 $ 21.1 $ 0.8 $ 13.1 $ 35.0 $ 4.6 $ 39.6 Total gains: Included in total net realized and unrealized investment gains 0.1 — — 0.1 — 0.1 Included in other comprehensive income-net depreciation on available-for-sale securities 0.2 — 0.2 0.4 — 0.4 Sales: (0.9 ) (0.1 ) (0.5 ) (1.5 ) — (1.5 ) Balance March 31, 2019 $ 20.5 $ 0.7 $ 12.8 $ 34.0 $ 4.6 $ 38.6
Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3	The following table provides quantitative information about the significant unobservable inputs used by the Company in the fair value measurements of Level 3 assets. Where discounted cash flows were used in the valuation of fixed maturities, the internally-developed discount rate was adjusted by the significant unobservable inputs shown in the table. March 31, 2020 December 31, 2019 Valuation Significant Fair Range Fair Range (in millions) Technique Unobservable Inputs Value (Wtd Average) Value (Wtd Average) Fixed maturities: Municipal Discounted cash flow Discount for: Small issue size Credit stress Above-market coupon $ 11.4 0.7 - 6.8% (4.4%) 0.6 - 3.4% (2.7%) 0.5% (0.5%) $ 12.1 0.7 - 6.8% (4.3%) — 0.5% (0.5%) Corporate Discounted cash flow Discount for: Small issue size Above-market coupon 0.5 2.5% (2.5%) 0.3% (0.3%) 0.6 2.5% (2.5%) 0.3% (0.3%) Commercial mortgage-backed Discounted cash flow Discount for: Small issue size Credit stress Above-market coupon Lease structure 11.8 1.9 - 3.1% (2.7%) 1.7 - 6.0% (2.3%) 0.5% (0.5%) 0.3% (0.3%) 12.7 1.9 - 3.1% (2.7%) — 0.5% (0.5%) 0.3% (0.3%) Equity securities Market comparables Net tangible asset market multiples 2.1 1.0X (1.0X) 2.1 1.0X (1.0X) Other Discounted cash flow Discount rate 3.5 18.0% (18.0%) 3.5 18.0% (18.0%)

Debt and Credit Arrangements (T

Debt and Credit Arrangements (Tables)	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Schedule of Debt	Debt consists of the following: (in millions) March 31, 2020 December 31, 2019 Senior debentures maturing April 15, 2026 $ 375.0 $ 375.0 Senior debentures maturing October 15, 2025 62.6 62.6 Subordinated debentures maturing March 30, 2053 175.0 175.0 Subordinated debentures maturing February 3, 2027 50.1 50.1 Short-term borrowings 54.0 — Total principal debt 716.7 662.7 Unamortized debt issuance costs (9.2 ) (9.3 ) Total $ 707.5 $ 653.4

Pension Plans (Tables)

Pension Plans (Tables)	3 Months Ended
	Mar. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Components of Net Periodic Pension Cost	The components of net periodic pension cost for the defined benefit pension plans included in the Company’s results of operations are as follows: Three Months Ended March 31, 2020 2019 (in millions) Pension Plans Interest cost $ 4.6 $ 5.3 Expected return on plan assets (5.6 ) (5.8 ) Recognized net actuarial loss 1.5 2.8 Net periodic pension cost $ 0.5 $ 2.3

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Changes in Other Comprehensive Income (Loss)	The following tables provide changes in other comprehensive income (loss). Three Months Ended March 31, 2020 2019 Tax Tax Benefit Net of Benefit Net of (in millions) Pre-Tax (Expense) Tax Pre-Tax (Expense) Tax Unrealized gains (losses) on available-for-sale securities: Unrealized gains (losses) arising during period $ (122.4 ) $ 25.6 $ (96.8 ) $ 152.0 $ (32.0 ) $ 120.0 Amount of realized gains (losses) from sales and other (3.1 ) (1.2 ) (4.3 ) 0.3 (3.9 ) (3.6 ) Impairment losses on investments 22.7 (4.8 ) 17.9 — — — Net unrealized gains (losses) (102.8 ) 19.6 (83.2 ) 152.3 (35.9 ) 116.4 Pension and postretirement benefits: Amortization of net actuarial losses (gains) recognized as net periodic benefit cost 1.5 (0.3 ) 1.2 2.9 (0.6 ) 2.3 Cumulative foreign currency translation adjustment: Foreign currency translation recognized during the period — — — 0.1 — 0.1 Other comprehensive income (loss) $ (101.3 ) $ 19.3 $ (82.0 ) $ 155.3 $ (36.5 ) $ 118.8
Reclassifications Out of Accumulated Other Comprehensive Income	Reclassifications out of accumulated other comprehensive income were as follows: Three Months Ended March 31, (in millions) 2020 2019 Amount Reclassified from Details about Accumulated Other Accumulated Other Affected Line Item in the Statement Comprehensive Income Components Comprehensive Income Where Net Income (Loss) is Presented Unrealized gains (losses) on available-for- sale securities $ 3.1 $ (0.3 ) Net realized gains (losses) from sales and other (22.2 ) — Impairment losses on investments (19.1 ) (0.3 ) Total before tax 5.9 3.9 Tax benefit (13.2 ) 3.6 Continuing operations; net of tax (0.4 ) — Discontinued operations - life businesses (13.6 ) 3.6 Net of tax Amortization of defined benefit pension and postretirement actuarial losses (1.5 ) (2.9 ) Loss adjustment expenses and other operating expenses (1) 0.3 0.6 Tax benefit (1.2 ) (2.3 ) Continuing operations; net of tax Total reclassifications for the period $ (14.8 ) $ 1.3 Benefit (expense) reflected in income (loss), net of tax (1) The amount reclassified from accumulated other comprehensive income for the pension and postretirement benefits was allocated approximately 40% to loss adjustment expenses and 60% to other operating expenses for the three months ended March 31, 2020 and 2019.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2020
Segment Reporting [Abstract]
Financial Information with Respect to Business Segments	Summarized below is financial information with respect to the Company’s business segments. Three Months Ended March 31, (in millions) 2020 2019 Operating revenues: Commercial Lines $ 724.7 $ 698.7 Personal Lines 488.5 465.2 Other 4.6 7.4 Total 1,217.8 1,171.3 Net realized and unrealized investment gains (losses) (161.6 ) 48.2 Total revenues $ 1,056.2 $ 1,219.5 Operating income (loss) before interest expense and income taxes: Commercial Lines: Underwriting income $ 10.4 $ 36.7 Net investment income 46.4 44.3 Other expense (2.2 ) (0.8 ) Commercial Lines operating income 54.6 80.2 Personal Lines: Underwriting income 44.1 5.7 Net investment income 20.3 19.7 Other income 0.5 1.4 Personal Lines operating income 64.9 26.8 Other: Underwriting loss (3.3 ) (0.3 ) Net investment income 2.9 6.2 Other expense (2.0 ) (3.1 ) Other operating income (loss) (2.4 ) 2.8 Operating income before interest expense and income taxes 117.1 109.8 Interest on debt (9.4 ) (9.4 ) Operating income before income taxes 107.7 100.4 Non-operating items: Net realized and unrealized investment gains (losses) (161.6 ) 48.2 Income (loss) from continuing operations before income taxes $ (53.9 ) $ 148.6
Identifiable Assets by Business Segment	The following table provides identifiable assets for the Company’s business segments and discontinued operations: March 31, 2020 December 31, 2019 (in millions) Identifiable Assets Property and Casualty Companies $ 12,179.3 $ 12,387.7 Assets of discontinued businesses 98.1 102.8 Total $ 12,277.4 $ 12,490.5

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Compensation Cost and Related Tax Benefits	Compensation cost for the Company’s stock-based awards and the related tax benefits were as follows: Three Months Ended March 31, (in millions) 2020 2019 Stock-based compensation expense $ 5.0 $ 4.2 Tax benefit (1.1 ) (0.9 ) Stock-based compensation expense, net of taxes $ 3.9 $ 3.3
Summary of Stock Option Plan Activity	Information on the Company’s stock option activity for the three months ended March 31, 2020 and 2019 is summarized below. Three Months Ended March 31, 2020 2019 (in whole shares and dollars) Shares Weighted Average Exercise Price Shares Weighted Average Exercise Price Outstanding, beginning of period 1,121,559 $ 87.88 1,099,076 $ 85.75 Granted 240,705 118.54 232,568 95.05 Exercised (35,918 ) 79.40 (64,017 ) 75.98 Forfeited or cancelled — — (3,141 ) 95.39 Outstanding, end of period 1,326,346 93.67 1,264,486 87.93
Summary of Restricted Stock Activity	The following tables summarize activity information about employee restricted stock units: Three Months Ended March 31, 2020 2019 (in whole shares and dollars) Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value Time-based restricted stock units: Outstanding, beginning of period 335,166 $ 109.55 332,481 $ 97.28 Granted 136,634 118.60 144,072 117.51 Vested (78,773 ) 85.44 (99,855 ) 83.25 Forfeited (2,861 ) 112.24 (8,687 ) 97.14 Outstanding, end of period 390,166 117.56 368,011 109.01 Performance-based and market-based restricted stock units: Outstanding, beginning of period 86,252 $ 110.70 69,838 $ 95.58 Granted 54,415 105.10 42,119 117.68 Vested (36,499 ) 80.26 (10,089 ) 82.74 Forfeited — — — — Outstanding, end of period 104,168 118.45 101,868 105.99

Earnings Per Share and Shareh_2

Earnings Per Share and Shareholders' Equity Transactions (Tables)	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Information Regarding Basic and Diluted Earnings Per Share	The following table provides weighted average share information used in the calculation of the Company’s basic and diluted earnings per share: Three Months Ended March 31, (in millions, except per share data) 2020 2019 Basic shares used in the calculation of earnings per share 38.3 40.6 Dilutive effect of securities (1): Employee stock options — 0.3 Non-vested stock grants — 0.3 Diluted shares used in the calculation of earnings per share 38.3 41.2 Per share effect of dilutive securities on income (loss) from continuing operations and net income (loss) $ — $ (0.04 ) (1) Excludes 0.6 million shares due to antidilution that resulted from the Company having losses from continuing operations and net losses for the quarter ended March 31, 2020.

Liabilities for Outstanding C_2

Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2020
Insurance [Abstract]
Schedule of Liability for Unpaid Losses and Loss Adjustment Expenses	The table below provides a reconciliation of the gross beginning and ending reserve for unpaid losses and loss adjustment expenses. Three Months Ended March 31, (in millions) 2020 2019 Gross loss and LAE reserves, beginning of period $ 5,654.4 $ 5,304.1 Reinsurance recoverable on unpaid losses 1,574.8 1,472.6 Net loss and LAE reserves, beginning of period 4,079.6 3,831.5 Net incurred losses and LAE in respect of losses occurring in: Current year 730.2 712.8 Prior years (2.0 ) (13.2 ) Total incurred losses and LAE 728.2 699.6 Net payments of losses and LAE in respect of losses occurring in: Current year 174.6 175.3 Prior years 484.4 459.1 Total payments 659.0 634.4 Net reserve for losses and LAE, end of period 4,148.8 3,896.7 Reinsurance recoverable on unpaid losses 1,576.1 1,484.9 Gross reserve for losses and LAE, end of period $ 5,724.9 $ 5,381.6

Investments (Schedule of Availa

Investments (Schedule of Available-for-sale Fixed Maturities Reconciliation) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,493.7	$ 6,452.2
Amortized Cost, net of Allowance for Credit Losses	6,487.5
Fair Value	6,625	6,687.1
U.S. Treasury and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	265.9	342
Amortized Cost, net of Allowance for Credit Losses	265.9
Gross Unrealized Gains	20.3	9.1
Gross Unrealized Loss		1.3
Fair Value	286.2	349.8
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4.2	15.7
Amortized Cost, net of Allowance for Credit Losses	4.2
Gross Unrealized Gains	0.3	0.4
Fair Value	4.5	16.1
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	833.8	807.1
Amortized Cost, net of Allowance for Credit Losses	833.8
Gross Unrealized Gains	35.3	27.6
Gross Unrealized Loss	1.4	1.2
Fair Value	867.7	833.5
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,749	3,653.5
Allowance for Credit Losses	6.2
Amortized Cost, net of Allowance for Credit Losses	3,742.8
Gross Unrealized Gains	81.5	161.6
Gross Unrealized Loss	60	3.9
Fair Value	3,764.3	3,811.2
OTTI Unrealized Losses		3
Residential Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	913.5	905.4
Amortized Cost, net of Allowance for Credit Losses	913.5
Gross Unrealized Gains	43.5	17.1
Gross Unrealized Loss	0.1	1.1
Fair Value	956.9	921.4
Commercial Mortgage-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	661.3	666.4
Amortized Cost, net of Allowance for Credit Losses	661.3
Gross Unrealized Gains	20.3	25.6
Gross Unrealized Loss	2.1	0.1
Fair Value	679.5	691.9
Asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66	62.1
Amortized Cost, net of Allowance for Credit Losses	66
Gross Unrealized Gains	0.4	1.1
Gross Unrealized Loss	0.5
Fair Value	65.9	63.2
Fixed Maturities Including Held For Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,493.7	6,452.2
Allowance for Credit Losses	6.2
Amortized Cost, net of Allowance for Credit Losses	6,487.5
Gross Unrealized Gains	201.6	242.5
Gross Unrealized Loss	64.1	7.6
Fair Value	$ 6,625	6,687.1
OTTI Unrealized Losses		$ 3

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Schedule of Investments [Line Items]
Net unrealized gains on impaired securities			$ 4,200,000
Impairment on investments	$ 28,500,000	$ 0
Impairments on fixed maturities included intend to sell	16,000,000
Impairments on fixed maturities credit related losses	6,200,000
Corporate Fixed Maturities [Member]
Schedule of Investments [Line Items]
Allowance for credit losses	6,200,000
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Impairment on investments	22,200,000
Mortgage Loans [Member]
Schedule of Investments [Line Items]
Impairment on investments	4,800,000
Allowance for credit losses increase amount	4,800,000
Allowance for credit losses	$ 6,100,000

Investments (Investments Classi

Investments (Investments Classified by Contractual Maturity Date) (Details) $ in Millions	Mar. 31, 2020USD ($)
Available-for-sale Securities, Debt Maturities [Abstract]
Due in one year or less, Amortized Cost, net of Allowance for Credit Losses	$ 354
Due after one year through five years, Amortized Cost, net of Allowance for Credit Losses	1,871
Due after five years through ten years, Amortized Cost, net of Allowance for Credit Losses	2,258.1
Due after ten years, Amortized Cost, net of Allowance for Credit Losses	363.6
Gross fixed maturities, Amortized Cost, net of Allowance for Credit Losses	4,846.7
Mortgage-backed and asset-backed securities, Amortized Cost, net of Allowance for Credit Losses	1,640.8
Total fixed maturities, Amortized Cost, net of Allowance for Credit Losses	6,487.5
Due in one year or less, Fair Value	355.8
Due after one year through five years, Fair Value	1,897.6
Due after five years through ten years, Fair Value	2,290.7
Due after ten years, Fair Value	378.6
Gross fixed maturities, Fair Value	4,922.7
Mortgage-backed and asset-backed securities, Fair Value	1,702.3
Fixed maturities, Fair Value	$ 6,625

Investments (Schedule of Unreal

Investments (Schedule of Unrealized Loss on Investments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	$ 64.1	$ 6.1
12 months or less, Fair Value	1,488.7	368.9
Greater than 12 months, Gross Unrealized Losses		1.5
Greater than 12 months, Fair Value	2	65.6
Total, Gross Unrealized Losses	64.1	7.6
Total, Fair Value	1,490.7	434.5
Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	53.1	3.9
12 months or less, Fair Value	1,344.5	341.8
Greater than 12 months, Gross Unrealized Losses		0.6
Greater than 12 months, Fair Value	2	56.6
Total, Gross Unrealized Losses	53.1	4.5
Total, Fair Value	1,346.5	398.4
U.S. Treasury and Government Agencies [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		1.3
12 months or less, Fair Value		73
Greater than 12 months, Fair Value		9.3
Total, Gross Unrealized Losses		1.3
Total, Fair Value		82.3
Municipal [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	1.4	1.1
12 months or less, Fair Value	62.7	72.5
Greater than 12 months, Gross Unrealized Losses		0.1
Greater than 12 months, Fair Value	0.6	5.6
Total, Gross Unrealized Losses	1.4	1.2
Total, Fair Value	63.3	78.1
Corporate [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	49	0.7
12 months or less, Fair Value	1,145.7	86.5
Greater than 12 months, Gross Unrealized Losses		0.1
Greater than 12 months, Fair Value		4.7
Total, Gross Unrealized Losses	49	0.8
Total, Fair Value	1,145.7	91.2
Corporate [Member] | Below Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	11	2.2
12 months or less, Fair Value	144.2	27.1
Greater than 12 months, Gross Unrealized Losses		0.9
Greater than 12 months, Fair Value		9
Total, Gross Unrealized Losses	11	3.1
Total, Fair Value	144.2	36.1
Residential Mortgage-Backed [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.1	0.7
12 months or less, Fair Value	3.3	69.2
Greater than 12 months, Gross Unrealized Losses		0.4
Greater than 12 months, Fair Value	1.4	34.4
Total, Gross Unrealized Losses	0.1	1.1
Total, Fair Value	4.7	103.6
Commercial Mortgage-Backed [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	2.1	0.1
12 months or less, Fair Value	111.5	40.6
Greater than 12 months, Fair Value		0.9
Total, Gross Unrealized Losses	2.1	0.1
Total, Fair Value	111.5	41.5
Asset-backed [Member] | Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.5
12 months or less, Fair Value	21.3
Greater than 12 months, Fair Value		1.7
Total, Gross Unrealized Losses	0.5
Total, Fair Value	$ 21.3	$ 1.7

Investments (Schedule of Realiz

Investments (Schedule of Realized Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fixed Maturities Excluding Held-For-Sale Chaucer [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	$ 66	$ 60.1
Gross Gains	2.7	1
Gross Losses	0.4	1.5
Fixed Maturities Held-For-Sale [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales		0.3
Fixed Maturities Including Held For Sale [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	66	60.4
Gross Gains	2.7	1
Gross Losses	$ 0.4	$ 1.5

Investments (Schedule of Pre-ta

Investments (Schedule of Pre-tax Net Realized and Unrealized Gains (Losses) on Equity Securities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Net gains (losses) recognized during the period	$ (136.2)	$ 48.6
Less: net gains (losses) recognized on equity securities sold during the period	(0.6)	1.1
Net unrealized gains (losses) recognized during the period on equity securities still held	$ (135.6)	$ 47.5

Fair Value (Fair Value of Finan

Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Carrying Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 143.9	$ 215.7
Total financial instruments	7,865	8,108.9
Carrying Value [Member] | Income Approach Valuation Technique [Member] | Fair Value Through AOCI [Member] | Debt Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	6,625	6,687.1
Carrying Value [Member] | Income Approach Valuation Technique [Member] | Fair Value Through Net Income [Member] | Other Investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	185.6	187.1
Carrying Value [Member] | Income Approach Valuation Technique [Member] | Fair Value Through Net Income [Member] | Equity Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	447	575.7
Carrying Value [Member] | Cost Approach Valuation Technique [Member] | Amortized Cost/Cost [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	143.9	215.7
Debt	707.5	653.4
Carrying Value [Member] | Cost Approach Valuation Technique [Member] | Amortized Cost/Cost [Member] | Other Investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	463.5	443.3
Estimated Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	143.9	215.7
Total financial instruments	7,875.2	8,129.3
Debt	741.8	722.1
Estimated Fair Value [Member] | Income Approach Valuation Technique [Member] | Fair Value Through AOCI [Member] | Debt Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	6,625	6,687.1
Estimated Fair Value [Member] | Income Approach Valuation Technique [Member] | Fair Value Through Net Income [Member] | Other Investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	185.6	187.1
Estimated Fair Value [Member] | Income Approach Valuation Technique [Member] | Fair Value Through Net Income [Member] | Equity Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	447	575.7
Estimated Fair Value [Member] | Cost Approach Valuation Technique [Member] | Amortized Cost/Cost [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	143.9	215.7
Debt	741.8	722.1
Estimated Fair Value [Member] | Cost Approach Valuation Technique [Member] | Amortized Cost/Cost [Member] | Other Investments [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Fair value of investments	$ 473.7	$ 463.7

Fair Value (Fair Value,Investme

Fair Value (Fair Value,Investment Assets Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	$ 6,625	$ 6,687.1
Equity securities	447	575.7
Other investments	755.5	733.2
Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	4.5	16.1
Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	867.7	833.5
Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	3,764.3	3,811.2
Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	956.9	921.4
Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	679.5	691.9
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	2.1	2.1
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	6,625	6,687.1
Equity securities	447	575.7
Other investments	3.5	3.5
Total investment assets at fair value, excluding held-for-sale	7,075.5	7,266.3
Fair Value, Measurements, Recurring [Member] | U.S. Treasury And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	286.2	349.8
Fair Value, Measurements, Recurring [Member] | Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	4.5	16.1
Fair Value, Measurements, Recurring [Member] | Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	867.7	833.5
Fair Value, Measurements, Recurring [Member] | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	3,764.3	3,811.2
Fair Value, Measurements, Recurring [Member] | Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	956.9	921.4
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	679.5	691.9
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	65.9	63.2
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	151.2	157.9
Equity securities	444.9	573.6
Total investment assets at fair value, excluding held-for-sale	596.1	731.5
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Treasury And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	151.2	157.9
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	6,450.1	6,503.8
Total investment assets at fair value, excluding held-for-sale	6,450.1	6,503.8
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	135	191.9
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	4.5	16.1
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	856.3	821.4
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	3,763.8	3,810.6
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	956.9	921.4
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	667.7	679.2
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	65.9	63.2
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	23.7	25.4
Equity securities	2.1	2.1
Other investments	3.5	3.5
Total investment assets at fair value, excluding held-for-sale	29.3	31
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	11.4	12.1
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	0.5	0.6
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	$ 11.8	$ 12.7

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Fair Value Measurements [Line Items]
Investments measured at net asset value based on an ownership interest in partners'	2.00%		2.00%
Transfer between Level 2 and Level 3	$ 0	$ 0
Fair Value Measured Using NAV [Member] | Limited Partnerships Interest [Member]
Fair Value Measurements [Line Items]
Investments measured at fair value using net asset value	182,100,000		$ 183,600,000
Level 3 [Member]
Fair Value Measurements [Line Items]
Investments measured at fair value using net asset value	3,500,000		$ 3,500,000
Liabilities held	$ 0	$ 0

Fair Value (Estimated Fair Valu

Fair Value (Estimated Fair Values of Financial Instruments Not Carried at Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Equity securities	$ 447	$ 575.7
Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Equity securities	2.1	2.1
Other investments	3.5	3.5
Carrying Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	143.9	215.7
Estimated Fair Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	143.9	215.7
Other investments	473.7	463.7
Total financial instruments	617.6	679.4
Debt	741.8	722.1
Estimated Fair Value [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash and cash equivalents	143.9	215.7
Total financial instruments	143.9	215.7
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other investments	4.1	2.1
Total financial instruments	4.1	2.1
Debt	741.8	722.1
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other investments	469.6	461.6
Total financial instruments	$ 469.6	$ 461.6

Fair Value (Fair Value on Recur

Fair Value (Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 31	$ 39.6
Included in other comprehensive income-net appreciation (depreciation) on available-for-sale securities	(0.3)	0.4
Included in total net realized and unrealized investment gains		0.1
Sales	(1.4)	(1.5)
Ending Balance	29.3	38.6
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the period	(0.3)
Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	12.1	21.1
Included in other comprehensive income-net appreciation (depreciation) on available-for-sale securities	0.1	0.2
Included in total net realized and unrealized investment gains		0.1
Sales	(0.8)	(0.9)
Ending Balance	11.4	20.5
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the period	0.1
Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	0.6	0.8
Sales	(0.1)	(0.1)
Ending Balance	0.5	0.7
Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	12.7	13.1
Included in other comprehensive income-net appreciation (depreciation) on available-for-sale securities	(0.4)	0.2
Sales	(0.5)	(0.5)
Ending Balance	11.8	12.8
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the period	(0.4)
Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	25.4	35
Included in other comprehensive income-net appreciation (depreciation) on available-for-sale securities	(0.3)	0.4
Included in total net realized and unrealized investment gains		0.1
Sales	(1.4)	(1.5)
Ending Balance	23.7	34
Change in unrealized gains (losses) for the period included in other comprehensive income for assets held at the end of the period	(0.3)
Equity Securities and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	5.6	4.6
Ending Balance	$ 5.6	$ 4.6

Fair Value (Schedule of Additio

Fair Value (Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Fair Value [Line Items]
Fair Value	$ 6,625	$ 6,687.1
Equity securities, at fair value	447	575.7
Level 3 [Member]
Fair Value [Line Items]
Equity securities, at fair value	$ 2.1	$ 2.1
Equity Securities, FV-NI, Valuation Technique [Extensible List]	us-gaap:MarketApproachValuationTechniqueMember	us-gaap:MarketApproachValuationTechniqueMember
Equity Securities, FV-NI, Measurement Input [Extensible List]	thg:MeasurementInputNetTangibleAssetMarketMultipleMember	thg:MeasurementInputNetTangibleAssetMarketMultipleMember
Fair Value	$ 3.5	$ 3.5
Alternative Investment, Valuation Technique [Extensible List]	us-gaap:ValuationTechniqueDiscountedCashFlowMember	us-gaap:ValuationTechniqueDiscountedCashFlowMember
Alternative Investment, Measurement Input [Extensible List]	us-gaap:MeasurementInputDiscountRateMember	us-gaap:MeasurementInputDiscountRateMember
Fair value measurement market multiples	1	1
Level 3 [Member] | Weighted Average [Member]
Fair Value [Line Items]
Fair value measurement market multiples	1	1
Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Range	0.180	0.180
Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member]
Fair Value [Line Items]
Range	0.180	0.180
Municipal [Member]
Fair Value [Line Items]
Fair Value	$ 867.7	$ 833.5
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Fair Value	$ 11.4	$ 12.1
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.50%	0.50%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Minimum [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.70%	0.70%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Minimum [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.60%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Maximum [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	6.80%	6.80%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Maximum [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	3.40%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	4.40%	4.30%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	2.70%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.50%	0.50%
Corporate [Member]
Fair Value [Line Items]
Fair Value	$ 3,764.3	$ 3,811.2
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Fair Value	$ 0.5	$ 0.6
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	2.50%	2.50%
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.30%	0.30%
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	2.50%	2.50%
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.30%	0.30%
Commercial Mortgage-Backed [Member]
Fair Value [Line Items]
Fair Value	$ 679.5	$ 691.9
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Fair Value	$ 11.8	$ 12.7
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.50%	0.50%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount For Lease Structure [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.30%	0.30%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Minimum [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	1.90%	1.90%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Minimum [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	1.70%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Maximum [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	3.10%	3.10%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Maximum [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	6.00%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	2.70%	2.70%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	2.30%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.50%	0.50%
Commercial Mortgage-Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount For Lease Structure [Member]
Fair Value [Line Items]
Significant Unobservable Inputs	0.30%	0.30%

Debt and Credit Arrangements (S

Debt and Credit Arrangements (Schedule of Debt) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Short-term borrowings	$ 54
Total principal debt	716.7	$ 662.7
Unamortized debt issuance costs	(9.2)	(9.3)
Total	707.5	653.4
Senior debentures maturing April 15, 2026 [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 375	$ 375
Maturity date	Apr. 15, 2026	Apr. 15, 2026
Senior debentures maturing October 15, 2025 [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 62.6	$ 62.6
Maturity date	Oct. 15, 2025	Oct. 15, 2025
Subordinated debentures maturing March 30, 2053 [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 175	$ 175
Maturity date	Mar. 30, 2053	Mar. 30, 2053
Subordinated debentures maturing February 3, 2027 [Member]
Debt Instrument [Line Items]
Long-term borrowings	$ 50.1	$ 50.1
Maturity date	Feb. 3, 2027	Feb. 3, 2027

Debt and Credit Arrangements (N

Debt and Credit Arrangements (Narrative) (Details) $ in Millions	Mar. 31, 2020USD ($)
Debt Instrument [Line Items]
Short-term advances	$ 54
Federal Home Loan Bank [Member]
Debt Instrument [Line Items]
Short-term advances	$ 54

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Federal income tax expense	$ 15.2	$ 26

Pension Plans (Components of Ne

Pension Plans (Components of Net Periodic Pension Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Defined Benefit Plan, Type [Extensible List]	us-gaap:PensionPlansDefinedBenefitMember	us-gaap:PensionPlansDefinedBenefitMember
Interest cost	$ 4.6	$ 5.3
Expected return on plan assets	(5.6)	(5.8)
Recognized net actuarial loss	1.5	2.8
Net periodic pension cost	$ 0.5	$ 2.3

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) (Changes in Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Equity [Abstract]
Unrealized gains (losses) arising during period, Pre-Tax	$ (122.4)	$ 152
Amount of realized gains (losses) from sales and other, Pre-Tax	(3.1)	0.3
Impairment losses on investments, Pre-Tax	22.7
Net unrealized gains (losses), Pre-Tax	(102.8)	152.3
Amortization of net actuarial losses (gains) recognized as net periodic benefit cost, Pre-Tax	1.5	2.9
Foreign currency translation recognized during the period, Pre-Tax		0.1
Other comprehensive income (loss), Pre-Tax	(101.3)	155.3
Unrealized gains (losses) arising during period, Tax Benefit (Expense)	25.6	(32)
Amount of realized gains (losses) from sales and other, Tax Benefit (Expense)	(1.2)	(3.9)
Impairment losses on investments, Tax Benefit (Expense)	(4.8)
Net unrealized gains, Tax Benefit (Expense)	19.6	(35.9)
Amortization of net actuarial losses (gains) recognized as net periodic benefit cost, Tax Benefit (Expense)	(0.3)	(0.6)
Other comprehensive income (loss), Tax Benefit (Expense)	19.3	(36.5)
Unrealized gains (losses) arising during period, Net of Tax	(96.8)	120
Amount of realized gains (losses) from sales and other, Net of Tax	(4.3)	(3.6)
Impairment losses on investments, Net of Tax	17.9
Total available-for-sale securities	(83.2)	116.4
Amortization of net actuarial losses (gains) recognized as net periodic benefit cost, Net of Tax	1.2	2.3
Foreign currency translation recognized during the period, Net of Tax		0.1
Total other comprehensive income (loss), net of tax	$ (82)	$ 118.8

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	$ 3.1	$ (0.4)
Income (loss) from continuing operations before income taxes	(53.9)	148.6
Loss adjustment expenses and other operating expenses	(728.2)	(699.6)
Tax benefit	15.2	(26)
Income (loss) from continuing operations	(38.7)	122.6
Net income (loss)	(40)	122.4
Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - life businesses	(1.3)	(0.8)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(14.8)	1.3
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	3.1	(0.3)
Impairment losses on investments	(22.2)
Income (loss) from continuing operations before income taxes	(19.1)	(0.3)
Tax benefit	5.9	3.9
Income (loss) from continuing operations	(13.2)	3.6
Net income (loss)	(13.6)	3.6
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member] | Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - life businesses	(0.4)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined Benefit Pension and Postretirement Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss adjustment expenses and other operating expenses	(1.5)	(2.9)
Tax benefit	0.3	0.6
Income (loss) from continuing operations	$ (1.2)	$ (2.3)

Other Comprehensive Income (L_5

Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income) (Parenthetical) (Details) - Defined Benefit Pension and Postretirement Plans [Member]	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Comprehensive Income (Loss) [Line Items]
Loss adjustment expenses	40.00%	40.00%
Percentage of other operating expenses	60.00%	60.00%

Segment Information (Narrative)

Segment Information (Narrative) (Details)	3 Months Ended
	Mar. 31, 2020segment
Segment Reporting [Abstract]
Operating segments	3

Segment Information (Financial

Segment Information (Financial Information with Respect to Business Segments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 1,217.8	$ 1,171.3
Net realized and unrealized investment gains (losses)	(161.6)	48.2
Total revenues	1,056.2	1,219.5
Net investment income	69.6	70.2
Operating income (loss) before interest expense and income taxes	117.1	109.8
Interest on debt	(9.4)	(9.4)
Operating income before income taxes	107.7	100.4
Income (loss) from continuing operations before income taxes	(53.9)	148.6
Commercial Lines [Member]
Segment Reporting Information [Line Items]
Operating revenues	724.7	698.7
Underwriting income (loss)	10.4	36.7
Net investment income	46.4	44.3
Other income (expense)	(2.2)	(0.8)
Operating income (loss) before interest expense and income taxes	54.6	80.2
Personal Lines [Member]
Segment Reporting Information [Line Items]
Operating revenues	488.5	465.2
Underwriting income (loss)	44.1	5.7
Net investment income	20.3	19.7
Other income (expense)	0.5	1.4
Operating income (loss) before interest expense and income taxes	64.9	26.8
Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	4.6	7.4
Underwriting income (loss)	(3.3)	(0.3)
Net investment income	2.9	6.2
Other income (expense)	(2)	(3.1)
Operating income (loss) before interest expense and income taxes	$ (2.4)	$ 2.8

Segment Information (Identifiab

Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Identifiable assets	$ 12,277.4	$ 12,490.5
Identifiable assets	98.1	102.8
Property and Casualty Companies [Member]
Segment Reporting Information [Line Items]
Identifiable assets	12,179.3	12,387.7
Assets of Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 98.1	$ 102.8

Stock-based Compensation (Narra

Stock-based Compensation (Narrative) (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Time-based, Market-based and Performance-based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Market-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Granted, Shares	34,911	23,924
Increase as grant in period, percentage	100.00%
Market-Based Restricted Stock Units [Member] | 2019 Grants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	13,532
Market-Based Restricted Stock Units [Member] | 2020 Grants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares		5,820
Performance-Based and Market-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	54,415	42,119
Vested, Shares	36,499	10,089
Performance-Based and Market-Based Restricted Stock Units [Member] | Minimum [Member] | Senior management [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance metric, potential range	0.00%
Performance-Based and Market-Based Restricted Stock Units [Member] | Maximum [Member] | Senior management [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance metric, potential range	150.00%
Performance-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	19,504	18,195
Vested, Shares	0	0
Performance-Based Restricted Stock Units [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance metric, potential range	0.00%
Performance-Based Restricted Stock Units [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance metric, potential range	150.00%
2014 Stock Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant	2,761,668
ESPP Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant	2,352,110

Stock-based Compensation (Compe

Stock-based Compensation (Compensation Cost and Related Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based compensation expense	$ 5	$ 4.2
Tax benefit	(1.1)	(0.9)
Stock-based compensation expense, net of taxes	$ 3.9	$ 3.3

Stock-based Compensation (Summa

Stock-based Compensation (Summary of Stock Option Activity) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Shares
Outstanding, beginning of period, Shares	1,121,559	1,099,076
Granted, Shares	240,705	232,568
Exercised, Shares	(35,918)	(64,017)
Forfeited or cancelled, Shares		(3,141)
Outstanding, end of period, Shares	1,326,346	1,264,486
Weighted Average Exercise Price
Outstanding, beginning of period, Weighted Average Exercise Price	$ 87.88	$ 85.75
Granted, Weighted Average Exercise Price	118.54	95.05
Exercised, Weighted Average Exercise Price	79.40	75.98
Forfeited or cancelled, Weighted Average Exercise Price		95.39
Outstanding, end of period, Weighted Average Exercise Price	$ 93.67	$ 87.93

Stock-based Compensation (Sum_2

Stock-based Compensation (Summary of Restricted Stock Activity) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Time-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	335,166	332,481
Granted, Shares	136,634	144,072
Vested, Shares	(78,773)	(99,855)
Forfeited, Shares	(2,861)	(8,687)
Outstanding, end of period, Shares	390,166	368,011
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 109.55	$ 97.28
Granted, Weighted Average Grant Date Fair Value	118.60	117.51
Vested, Weighted Average Grant Date Fair Value	85.44	83.25
Forfeited, Weighted Average Grant Date Fair Value	112.24	97.14
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 117.56	$ 109.01
Performance-Based and Market-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	86,252	69,838
Granted, Shares	54,415	42,119
Vested, Shares	(36,499)	(10,089)
Outstanding, end of period, Shares	104,168	101,868
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 110.70	$ 95.58
Granted, Weighted Average Grant Date Fair Value	105.10	117.68
Vested, Weighted Average Grant Date Fair Value	80.26	82.74
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 118.45	$ 105.99

Earnings Per Share and Shareh_3

Earnings Per Share and Shareholders' Equity Transactions (Information Regarding Basic and Diluted Earnings Per Share) (Details) - $ / shares shares in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic shares used in the calculation of earnings per share		38.3	40.6
Diluted shares used in the calculation of earnings per share	[1]	38.3	41.2
Per share effect of dilutive securities on income (loss) from continuing operations and net income (loss)			$ (0.04)
Employee Stock Option [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of securities	[1]		0.3
Non-Vested Stock Grants [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of securities	[1]		0.3
[1]	Excludes 0.6 million shares due to antidilution that resulted from the Company having losses from continuing operations and net losses for the quarter ended March 31, 2020.

Earnings Per Share and Shareh_4

Earnings Per Share and Shareholders' Equity Transactions (Information Regarding Basic and Diluted Earnings Per Share) (Parenthetical) (Details) shares in Millions	3 Months Ended
	Mar. 31, 2020shares
Earnings Per Share [Abstract]
Antidilutive securities excluded from calculation of earnings per share	0.6

Earnings Per Share and Shareh_5

Earnings Per Share and Shareholders' Equity Transactions (Narrative) (Details) - USD ($) shares in Millions	Feb. 26, 2020	Dec. 09, 2019	Dec. 05, 2019	Mar. 31, 2020	Mar. 31, 2019
Class Of Stock [Line Items]
Antidilutive securities excluded from calculation of earnings per share				0.6
Accelerated Share Repurchase Agreement [Member]
Class Of Stock [Line Items]
Increase in repurchases common stock, authorized			$ 300,000,000
December 2019 Accelerated Share Repurchase Agreement [Member]
Class Of Stock [Line Items]
Amount paid by company		$ 150,000,000
Initial delivery of shares of common stock received		0.9
Final settlement of repurchase shares of common shares received	0.2
Maximum [Member] | Accelerated Share Repurchase Agreement [Member]
Class Of Stock [Line Items]
Repurchases common stock, authorized				$ 900,000,000
Stock Compensation Plans [Member]
Class Of Stock [Line Items]
Antidilutive securities excluded from calculation of earnings per share				0.4	0.2

Liabilities for Outstanding C_3

Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Schedule of Liability for Unpaid Losses and Loss Adjustment Expenses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Insurance [Abstract]
Gross loss and LAE reserves, beginning of period	$ 5,654.4	$ 5,304.1
Reinsurance recoverable on unpaid losses, beginning of period	1,574.8	1,472.6
Net loss and LAE reserves, beginning of period	4,079.6	3,831.5
Net incurred losses and LAE in respect of losses occurring in current year	730.2	712.8
Net incurred losses and LAE in respect of losses occurring in prior years	(2)	(13.2)
Total incurred losses and LAE	728.2	699.6
Net payments of losses and LAE in respect of losses occurring in current year	174.6	175.3
Net payments of losses and LAE in respect of losses occurring in prior years	484.4	459.1
Total payments	659	634.4
Net reserve for losses and LAE, end of period	4,148.8	3,896.7
Reinsurance recoverable on unpaid losses, end of period	1,576.1	1,484.9
Gross reserve for losses and LAE, end of period	$ 5,724.9	$ 5,381.6

Liabilities for Outstanding C_4

Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Insurance [Abstract]
(Favorable) unfavorable loss and LAE development	$ (2)	$ (13.2)

Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Apr. 10, 2020
Scenario Forecast [Member]
Subsequent Event [Line Items]
Refund of insurance premium amount	$ 30
Subsequent Event [Member] | Personal Lines [Member]
Subsequent Event [Line Items]
Percentage of premium return to eligible customers		15.00%