The Hanover Insurance Group, Inc. (THG) 10-Q 2 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	THG
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		40,701,200

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues
Premiums	$ 1,095.1	$ 1,042.5
Net investment income	70.2	66
Net realized and unrealized investment gains (losses):
Net realized gains (losses) from sales and other	(0.4)	0.6
Net change in fair value of equity securities	48.6	(22.9)
Net other–than–temporary impairment losses on investments recognized in earnings		(0.6)
Total net realized and unrealized investment gains (losses)	48.2	(22.9)
Fees and other income	6	5.9
Total revenues	1,219.5	1,091.5
Losses and expenses
Losses and loss adjustment expenses	699.6	670.9
Amortization of deferred acquisition costs	229.5	218.7
Interest expense	9.4	11.3
Other operating expenses	132.4	131.5
Total losses and expenses	1,070.9	1,032.4
Income from continuing operations before income taxes	148.6	59.1
Income tax expense:
Current	12.2	(5.7)
Deferred	13.8	14.3
Total income tax expense	26	8.6
Income from continuing operations	122.6	50.5
Discontinued operations:
Net income	$ 122.4	$ 67.7
Basic:
Income from continuing operations	$ 3.02	$ 1.19
Net income per share	$ 3.01	$ 1.59
Weighted average shares outstanding	40.6	42.5
Diluted:
Income from continuing operations	$ 2.98	$ 1.17
Net income per share	$ 2.97	$ 1.57
Weighted average shares outstanding	41.2	43.1
Chaucer [Member]
Revenues
Premiums		$ 221.1
Net investment income		16.4
Net realized and unrealized investment gains (losses):
Total revenues	$ 2.9	239.4
Losses and expenses
Losses and loss adjustment expenses		115
Amortization of deferred acquisition costs		69.3
Interest expense		1.1
Other operating expenses		32.2
Total losses and expenses		216.5
Discontinued operations:
Gain from sale of business, net of taxes	0.9
Income (loss) from discontinued operations	$ (0.3)	$ 17.3
Basic:
Gain from sale of business, net of taxes	$ 0.02
Income (loss) from discontinued operations	(0.01)	$ 0.40
Diluted:
Gain from sale of business, net of taxes	0.02
Income (loss) from discontinued operations	$ (0.01)	$ 0.40
Life [Member]
Discontinued operations:
Income (loss) from discontinued operations	$ (0.8)	$ (0.1)
Basic:
Income (loss) from discontinued operations	$ (0.02)
Diluted:
Income (loss) from discontinued operations	$ (0.02)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 122.4	$ 67.7
Available-for-sale securities:
Net appreciation (depreciation) during the period	115	(123.9)
Change in other-than-temporary impairment losses recognized in other comprehensive income	1.4	0.4
Total available-for-sale securities	116.4	(123.5)
Pension and postretirement benefits:
Net change in net actuarial loss and prior service cost	2.3	(2.3)
Cumulative foreign currency translation adjustment:
Amount recognized as cumulative foreign currency translation during the period	0.1	(0.5)
Total other comprehensive income (loss), net of tax	118.8	(126.3)
Comprehensive income (loss)	$ 241.2	$ (58.6)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets
Fixed maturities, at fair value (amortized cost of $6,492.7 and $6,245.9)	$ 6,559.4	$ 6,161.5
Equity securities, at fair value	504.7	464.4
Other investments	680.4	661.5
Total investments	7,744.5	7,287.4
Cash and cash equivalents	168.5	1,020.7
Accrued investment income	54	53.2
Premiums and accounts receivable, net	1,179.4	1,176.7
Reinsurance recoverable on paid and unpaid losses and unearned premiums	1,663.2	1,648.6
Deferred acquisition costs	449.5	450.8
Deferred income taxes	0.9	50.6
Goodwill	178.8	178.8
Other assets	417.4	371.6
Assets held-for-sale and discontinued businesses	103.6	103.9
Total assets	11,983.4	12,399.7
Liabilities
Loss and loss adjustment expense reserves	5,381.6	5,304.1
Unearned premiums	2,287.8	2,277.8
Expenses and taxes payable	556.9	909.8
Reinsurance premiums payable	46.8	37.3
Debt	653	777.9
Liabilities held-for-sale and discontinued businesses	118.3	115.9
Total liabilities	9,056.4	9,445
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	1,821.7	1,871.8
Accumulated other comprehensive income (loss)	3.8	(116.5)
Retained earnings	2,278.7	2,182.3
Treasury stock at cost (19.8 million and 18.2 million shares)	(1,177.8)	(983.5)
Total shareholders’ equity	2,927	2,954.7
Total liabilities and shareholders’ equity	11,983.4	12,399.7
Assets Held-for-Sale [Member]
Assets
Assets held-for-sale and discontinued businesses	23.6	57.4
Liabilities
Liabilities held-for-sale and discontinued businesses	$ 12	$ 22.2

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 6,492.7	$ 6,245.9
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	19,800,000	18,200,000

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 (Loss), net of tax [Member]
Balance at beginning of period at Dec. 31, 2017		$ 0.6	$ 1,857	$ 205.4	$ (79.5)	$ (18.3)	$ 1,975
Balance at beginning of period at Dec. 31, 2017								$ (942.5)
Cumulative effect of accounting change, net of taxes at Dec. 31, 2017							104.3
Balance at beginning of period, as adjusted at Dec. 31, 2017							2,079.3
Net income	$ 67.7						67.7
Shares purchased at cost								(13.6)
Prepaid repurchase of common stock and other			1.3
Net appreciation (depreciation) on available-for-sale securities	(123.5)			(123.5)
Net amount recognized as net periodic benefit (expense)	(2.3)				(2.3)
Amount recognized as cumulative foreign currency translation during the period	(0.5)					(0.5)
Adoption of Accounting Standards Update | Accounting Standards Update No. 2017-08 and No. 2016-01 and No. 2018-02 [Member]				(81.6)
Adoption of Accounting Standards Update | Accounting Standards Update No. 2018-02 [Member]					(16.2)	(3.9)
Dividends to shareholders							(22.9)
Net shares reissued at cost under employee stock-based compensation plans								6.6
Balance at end of period at Mar. 31, 2018	2,913.1	0.6	1,858.3	0.3	(98)	(22.7)	2,124.1		$ (120.4)
Balance at end of period at Mar. 31, 2018								(949.5)
Balance at beginning of period at Dec. 31, 2018	2,954.7	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)							(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	122.4						122.4
Shares purchased at cost								(200)
Prepaid repurchase of common stock and other			(50.1)
Net appreciation (depreciation) on available-for-sale securities	116.4			116.4
Net amount recognized as net periodic benefit (expense)	2.3				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 and No. 2016-01 and No. 2018-02 [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)							$ (1,177.8)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash Flows From Operating Activities
Net income	$ 122.4	$ 67.7
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized and unrealized investment gains	(48.4)	23.4
Gain on sale of Chaucer-related Irish entity	(0.9)
Net amortization and depreciation	6.9	6.9
Stock-based compensation expense	4.2	3
Amortization of defined benefit plan costs	2.8	2.5
Deferred income tax (benefit) expense	13.8	(7.4)
Change in deferred acquisition costs	2.7	(3.9)
Change in premiums receivable, net of reinsurance premiums payable	(4.3)	6.2
Change in loss, loss adjustment expense and unearned premium reserves	99.2	127.4
Change in reinsurance recoverable	(28.2)	(86.4)
Change in expenses and taxes payable	(88)	(69.1)
Other, net	(45)	(38.9)
Net cash provided by operating activities	37.2	31.4
Cash Flows From Investing Activities
Proceeds from disposals and maturities of fixed maturities	193.1	295.3
Proceeds from disposals of equity securities and other investments	28.1	21.8
Purchase of fixed maturities	(483.4)	(418.2)
Purchase of equity securities and other investments	(37.6)	(39.8)
Capital expenditures	(3.9)	(3.5)
Net cash proceeds from sale of Chaucer-related Irish entity, offset by cash transferred	24.4
Net cash used in investing activities	(279.3)	(144.4)
Cash Flows From Financing Activities
Proceeds from exercise of employee stock options	5	6.3
Proceeds from debt borrowings, net		33
Change in cash collateral related to securities lending program	6.7	(8.2)
Dividends paid to shareholders	(217)	(22.9)
Repurchases of common stock	(250)	(13.6)
Repayment of debt	(151.1)
Other financing activities	(4.2)	(2.2)
Net cash used in financing activities	(610.6)	(7.6)
Effect of exchange rate changes on cash		2.2
Net change in cash and cash equivalents	(852.7)	(118.4)
Net change in cash related to discontinued operations	0.5	(44.1)
Cash and cash equivalents, beginning of period	1,020.7	297.9
Cash and cash equivalents, end of period	$ 168.5	$ 135.4

Basis of Presentation and Princ

Basis of Presentation and Principles of Consolidation	3 Months Ended
	Mar. 31, 2019
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 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 Chaucer Holdings Limited (“Chaucer”), a United Kingdom (“U.K.”) domiciled specialist insurance underwriting group which operates through the Society and Corporation of Lloyd’s (“Lloyds”), and the international insurance and non-insurance subsidiaries, which collectively constituted the former Chaucer segment. On December 28, 2018, the Company completed the sale of Chaucer to China Reinsurance (Group) Corporation (“China Re”), and subsequently completed the sales of the Chaucer-related Irish and Australian entities on February 14, 2019 and April 10, 2019, respectively. Discontinued operations also include the Company’s accident and health and former life insurance businesses. 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, 2019 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 22, 2019.

New Accounting Pronouncements

New Accounting Pronouncements	3 Months Ended
	Mar. 31, 2019
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	2. New Accounting Pronouncements Recently Implemented Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Codification (“ASC”) Update No. 2016-02, (Topic 842) Leases Leases Targeted Improvements In March 2019, the FASB issued ASC Update No. 2019-01, Leases (Topic 842) – Codification Improvements Accounting Changes and Error Corrections In March 2017, the FASB issued ASC Update No. 2017-08, (Subtopic 310-20) Receivables – Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities Recently Issued Standards 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 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. 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 In June 2016, the FASB issued ASC Update No. 2016-13, (Topic 326) Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments – Credit Losses

Discontinued Operations Chaucer

Discontinued Operations Chaucer Business	3 Months Ended
	Mar. 31, 2019
Chaucer [Member]
Discontinued Operations Chaucer Business	3. Discontinued Operations – Chaucer Business On December 28, 2018, the Company completed the sale of its former subsidiary, Chaucer, to China Re. On February 14, 2019, the Company completed the sale of its Chaucer-related Irish entity for total proceeds of $28 million and on April 10, 2019, finalized the sale of the Australian entities for total proceeds of $13 million, completing the transfer of all Chaucer-related companies. Collectively, these entities constituted the Chaucer business in 2018 and prior, whereas just the Irish and Australian Chaucer-related entities comprised the Chaucer business reported in the Company’s results in 2019, until their respective sales to China Re. Three months ended March 31, 2019 Revenues from the Chaucer business were $2.9 million during the first quarter of 2019 and operating losses in this business totaled $0.3 million during that period. Three months ended March 31, 2018 The following table summarizes the results of Chaucer’s operations for the three months ended March 31, 2018: Three Months Ended March 31, (in millions) 2018 Revenues Net premiums earned $ 221.1 Net investment income 16.4 Other income 1.9 239.4 Losses and operating expenses Losses and LAE 115.0 Amortization of deferred acquisition costs 69.3 Other expenses 32.2 216.5 Income from Chaucer business before income taxes and other items (previously presented as Chaucer's operating income) 22.9 Other items: Interest expense (1.1 ) Net realized and unrealized investment losses (0.5 ) Other income 0.2 Income from Chaucer business before income taxes 21.5 Income tax expense (4.2 ) Income from Chaucer business, net of income taxes $ 17.3 Total assets held-for-sale were $23.6 million at March 31, 2019 and $57.4 million at December 31, 2018. Total liabilities held-for-sale were $12.0 million at March 31, 2019 and $22.2 million at December 31, 2018. Assets and liabilities held-for-sale decreased in the quarter due to the aforementioned sale of the Chaucer-related Irish entity. These balances are reflected in the Consolidated Balance Sheets under the caption “Assets held-for-sale” and “Liabilities held-for-sale”, respectively. The following table details the cash flows associated with the Chaucer business for the three months ended March 31, 2018: Three Months Ended March 31, (in millions) 2018 Net cash used in operating activities $ (5.9 ) Net cash provided by investing activities $ 47.7

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	4. Income Taxes Income tax expense for the three months ended March 31, 2019 and 2018 has been computed using estimated annual effective tax rates. The prior year’s rate reflects the recomputed income to exclude the Chaucer business. 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 U.S. federal income tax expense of $26.0 million and $8.6 million for the three months ended March 31, 2019 and 2018, respectively. The tax provision recorded in discontinued operations related to the Chaucer business for the three months ended March 31, 2018 was comprised of a $5.9 million U.S. federal income tax expense and a $1.7 million foreign income tax benefit. The Company or its subsidiaries files income tax returns in the U.S. federal jurisdiction and various state jurisdictions, as well as foreign jurisdictions. The Company and its subsidiaries are subject to U.S. federal and state income tax examinations and foreign examinations for years after 2014.

Investments

Investments	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Investments	5. Investments A. Fixed maturities The amortized cost and fair value of available-for-sale fixed maturities were as follows: March 31, 2019 Gross Gross OTTI Amortized Unrealized Unrealized Unrealized (in millions) Cost Gains Losses Fair Value Losses U.S. Treasury and government agencies $ 404.5 $ 4.7 $ 2.5 $ 406.7 $ — Foreign government 7.3 0.1 — 7.4 — Municipal 848.1 20.8 3.4 865.5 — Corporate 3,635.7 66.3 27.4 3,674.6 4.8 Residential mortgage-backed 819.2 6.8 6.1 819.9 — Commercial mortgage-backed 684.9 9.4 2.4 691.9 — Asset-backed 93.0 0.6 0.2 93.4 — Total fixed maturities $ 6,492.7 $ 108.7 $ 42.0 $ 6,559.4 $ 4.8 December 31, 2018 Gross Gross OTTI Amortized Unrealized Unrealized Unrealized (in millions) Cost Gains Losses Fair Value Losses U.S. Treasury and government agencies $ 414.7 $ 2.4 $ 7.2 $ 409.9 $ — Foreign government 7.3 0.1 — 7.4 — Municipal 879.0 16.6 9.8 885.8 — Corporate 3,476.6 26.1 92.0 3,410.7 6.6 Residential mortgage-backed 728.4 2.7 14.7 716.4 — Commercial mortgage-backed 648.4 1.7 9.8 640.3 — Asset-backed 91.5 0.2 0.7 91.0 — Fixed maturities, excluding held-for-sale (Chaucer) 6,245.9 49.8 134.2 6,161.5 6.6 Fixed maturities, held-for-sale 24.9 — 0.4 24.5 — Total fixed maturities $ 6,270.8 $ 49.8 $ 134.6 $ 6,186.0 $ 6.6 Other-than-temporary impairments (“OTTI”) unrealized losses in the tables above represent 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 $7.4 million as of both March 31, 2019 and December 31, 2018. 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 2018 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, 2019 Amortized Fair (in millions) Cost Value Due in one year or less $ 249.2 $ 250.9 Due after one year through five years 1,969.6 2,001.6 Due after five years through ten years 2,407.4 2,423.2 Due after ten years 269.4 278.5 4,895.6 4,954.2 Mortgage-backed and asset-backed securities 1,597.1 1,605.2 Total fixed maturities $ 6,492.7 $ 6,559.4 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, 2019 and December 31, 2018 including the length of time the securities have been in an unrealized loss position: March 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 $ — $ — $ 2.5 $ 158.4 $ 2.5 $ 158.4 Foreign governments — — — 0.8 — 0.8 Municipal — 9.7 3.4 192.3 3.4 202.0 Corporate 0.9 15.3 19.7 993.2 20.6 1,008.5 Residential mortgage-backed — 2.1 6.1 352.6 6.1 354.7 Commercial mortgage-backed — 0.3 2.4 226.7 2.4 227.0 Asset-backed — — 0.2 31.9 0.2 31.9 Total investment grade 0.9 27.4 34.3 1,955.9 35.2 1,983.3 Below investment grade: Corporate 0.3 17.1 6.5 75.7 6.8 92.8 Total fixed maturities $ 1.2 $ 44.5 $ 40.8 $ 2,031.6 $ 42.0 $ 2,076.1 December 31, 2018 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 $ 1.1 $ 66.0 $ 6.1 $ 210.9 $ 7.2 $ 276.9 Foreign governments — 2.0 — 0.8 — 2.8 Municipal 0.8 110.0 9.0 248.0 9.8 358.0 Corporate 30.0 1,277.9 43.9 781.6 73.9 2,059.5 Residential mortgage-backed 2.6 201.2 12.1 323.7 14.7 524.9 Commercial mortgage-backed 3.4 293.0 6.4 175.5 9.8 468.5 Asset-backed 0.4 42.3 0.3 18.0 0.7 60.3 Total investment grade 38.3 1,992.4 77.8 1,758.5 116.1 3,750.9 Below investment grade: Municipal — — — 0.9 — 0.9 Corporate 8.1 185.6 10.0 54.0 18.1 239.6 Total below investment grade 8.1 185.6 10.0 54.9 18.1 240.5 Fixed maturities, excluding held-for-sale (Chaucer) 46.4 2,178.0 87.8 1,813.4 134.2 3,991.4 Fixed maturities, held-for-sale 0.1 4.0 0.3 18.0 0.4 22.0 Total fixed maturities $ 46.5 $ 2,182.0 $ 88.1 $ 1,831.4 $ 134.6 $ 4,013.4 The Company views gross unrealized losses on fixed maturities as being temporary since it is its assessment that these securities will recover in the near term, allowing the Company to realize the anticipated long-term economic value. The Company employs a systematic methodology to evaluate declines in fair value below amortized cost for fixed maturity securities. In determining OTTI, 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 length of time and the degree to which the fair value of an issuer’s securities remains 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, 2019 2018 Proceeds from Gross Gross Proceeds from Gross Gross (in millions) Sales Gains Losses Sales Gains Losses Fixed maturities, excluding held-for-sale (Chaucer) $ 60.1 $ 1.0 $ 1.5 $ 57.1 $ 0.2 $ 1.7 Fixed maturities, held-for-sale 0.3 — — 70.7 0.4 0.6 Total fixed maturities $ 60.4 $ 1.0 $ 1.5 $ 127.8 $ 0.6 $ 2.3 D. Other-than-temporary impairments For the three months ended March 31, 2019, the Company recognized no OTTI. For the three months ended March 31, 2018, total OTTI from continuing operations was $0.9 million, consisting primarily of fixed maturities. Of this amount, $0.6 million was recognized in earnings and the remaining $0.3 million was recorded as unrealized losses in AOCI. The methodology and significant inputs used to measure the amount of credit losses on fixed maturities in 2018 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 and 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. The following table provides rollforwards of the cumulative amounts related to the Company’s credit loss portion of the OTTI losses on fixed maturity securities from continuing operations for which the non-credit portion of the loss is included in other comprehensive income. Three Months Ended March 31, (in millions) 2019 2018 Credit losses as of the beginning of the period $ 3.8 $ 3.6 Credit losses on securities for which an OTTI was not previously recognized — 0.2 Reductions for securities sold, matured or called (0.5 ) (0.7 ) Credit losses as of the end of the period $ 3.3 $ 3.1 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 from continuing operations: Three Months Ended March 31, (in millions) 2019 2018 Net gains (losses) recognized during the period $ 48.6 $ (22.9 ) Less: net gains recognized on equity securities sold during the period 1.1 0.5 Net unrealized gains (losses) recognized during the period on equity securities still held $ 47.5 $ (23.4 )

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value	6. 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 are 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; delinquency/default trends; and, in the case of non-agency collateralized mortgage obligations, severity of loss upon default and length of time to recover proceeds following default. • 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, 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 provided by the general partner adjusted for recent financial information and are excluded from the fair value hierarchy. The estimated fair value of the financial instruments were as follows: March 31, 2019 December 31, 2018 Carrying Fair Carrying Fair (in millions) Value Value Value Value Financial Assets carried at: Fair Value through AOCI: Fixed maturities $ 6,559.4 $ 6,559.4 $ 6,161.5 $ 6,161.5 Fair Value through Net Income: Equity securities 504.7 504.7 464.4 464.4 Other investments 180.3 180.3 175.0 175.0 Amortized Cost/Cost: Other investments 421.5 425.7 414.4 418.9 Cash and cash equivalents 168.5 168.5 1,020.7 1,020.7 Total financial instruments, excluding held-for-sale 7,834.4 7,838.6 8,236.0 8,240.5 Financial instruments, held-for-sale (Chaucer) 2.8 2.8 27.8 27.8 Total financial instruments $ 7,837.2 $ 7,841.4 $ 8,263.8 $ 8,268.3 Financial Liabilities carried at: Amortized Cost: Debt $ 653.0 $ 694.2 $ 777.9 $ 825.0 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 2019 and 2018, 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, 2019 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 406.7 $ 159.3 $ 247.4 $ — Foreign government 7.4 — 7.4 — Municipal 865.5 — 845.0 20.5 Corporate 3,674.6 — 3,673.9 0.7 Residential mortgage-backed, U.S. agency backed 817.2 — 817.2 — Residential mortgage-backed, non-agency 2.7 — 2.7 — Commercial mortgage-backed 691.9 — 679.1 12.8 Asset-backed 93.4 — 93.4 — Total fixed maturities 6,559.4 159.3 6,366.1 34.0 Equity securities 504.7 503.6 — 1.1 Other investments 3.5 — — 3.5 Total investment assets at fair value $ 7,067.6 $ 662.9 $ 6,366.1 $ 38.6 December 31, 2018 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 409.9 $ 154.9 $ 255.0 $ — Foreign government 7.4 — 7.4 — Municipal 885.8 — 864.7 21.1 Corporate 3,410.7 — 3,409.9 0.8 Residential mortgage-backed, U.S. agency backed 713.7 — 713.7 — Residential mortgage-backed, non-agency 2.7 — 2.7 — Commercial mortgage-backed 640.3 — 627.2 13.1 Asset-backed 91.0 — 91.0 — Total fixed maturities 6,161.5 154.9 5,971.6 35.0 Equity securities 464.4 463.3 — 1.1 Other investments 3.5 — — 3.5 Total investment assets at fair value, excluding held-for-sale (Chaucer) 6,629.4 618.2 5,971.6 39.6 Investment assets, held-for-sale 24.5 5.7 18.8 — Total investment assets at fair value $ 6,653.9 $ 623.9 $ 5,990.4 $ 39.6 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, 2019 and December 31, 2018, the fair values of these investments were $176.8 million and $171.5 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, 2019 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 168.5 $ 168.5 $ — $ — Other investments 425.7 — 1.8 423.9 Total financial instruments, excluding held-for-sale 594.2 168.5 1.8 423.9 Financial instruments, held-for-sale (Chaucer) 2.8 2.8 — — Total financial instruments $ 597.0 $ 171.3 $ 1.8 $ 423.9 Liabilities: Debt $ 694.2 $ — $ 694.2 $ — December 31, 2018 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 1,020.7 $ 1,020.7 $ — $ — Other investments 418.9 — 8.7 410.2 Total financial instruments, excluding held-for-sale 1,439.6 1,020.7 8.7 410.2 Financial instruments, held-for-sale (Chaucer) 3.3 3.3 — — Total financial instruments $ 1,442.9 $ 1,024.0 $ 8.7 $ 410.2 Liabilities: Debt $ 825.0 $ — $ 825.0 $ — The table below provide a 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, 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 appreciation 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 Three Months Ended March 31, 2018 Balance January 1, 2018, excluding held-for-sale (Chaucer) $ 24.6 $ 0.9 $ 14.2 $ 39.7 $ 4.7 $ 44.4 Total gains (losses): 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 (0.5 ) — (0.2 ) (0.7 ) — (0.7 ) Sales (1.1 ) (0.1 ) (0.5 ) (1.7 ) — (1.7 ) Balance March 31, 2018, excluding held-for-sale (Chaucer) $ 23.1 $ 0.8 $ 13.5 $ 37.4 $ 4.7 $ 42.1 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, 2019 and 2018. 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, 2019 December 31, 2018 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 $ 20.5 0.7 - 6.8% (3.3%) 1.3% (1.3%) 0.3 - 0.5% (0.5%) $ 21.1 0.7 - 6.8% (3.4%) 1.3% (1.3%) 0.3 - 0.5% (0.5%) Corporate Discounted cash flow Discount for: Small issue size Above-market coupon 0.7 2.5% (2.5%) 0.3% (0.3%) 0.8 2.5% (2.5%) 0.3% (0.3%) Commercial mortgage-backed Discounted cash flow Discount for: Small issue size Above-market coupon Lease structure 12.8 1.9 - 3.1% (2.7%) 0.5% (0.5%) 0.3% (0.3%) 13.1 1.9 - 3.1% (2.7%) 0.5% (0.5%) 0.3% (0.3%) Equity securities Market comparables Net tangible asset market multiples 1.1 1.0X (1.0X) 1.1 1.0X (1.0X) Other Discounted cash flow Discount rate 3.5 18.0% (18.0%) 3.5 18.0% (18.0%) 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.

Pension and Other Postretiremen

Pension and Other Postretirement Benefit Plans	3 Months Ended
	Mar. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Pension and Other Postretirement Benefit Plans	7. Pension and Other Postretirement Benefit Plans The components of net periodic pension cost for defined benefit pension and other postretirement benefit plans included in the Company’s results of operations are as follows: Three Months Ended March 31, 2019 2018 2019 2018 (in millions) Pension Plans Postretirement Plans Service cost - benefits earned during the period $ — $ — $ — $ — Interest cost 5.3 4.9 0.1 0.1 Expected return on plan assets (5.8 ) (5.2 ) — — Recognized net actuarial loss 2.8 2.5 — 0.1 Amortization of prior service cost — — — (0.1 ) Net periodic pension cost $ 2.3 $ 2.2 $ 0.1 $ 0.1

Other Comprehensive Income

Other Comprehensive Income	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Other Comprehensive Income	8. Other Comprehensive Income The following tables provide changes in other comprehensive income (loss). Three Months Ended March 31, 2019 2018 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 $ 152.0 $ (32.0 ) $ 120.0 $ (153.7 ) $ 32.1 $ (121.6 ) Amount of realized gains (losses) from sales and other 0.3 (3.9 ) (3.6 ) 0.2 (2.5 ) (2.3 ) Portion of other-than-temporary impairment losses recognized in earnings — — — 0.5 (0.1 ) 0.4 Net unrealized gains (losses) 152.3 (35.9 ) 116.4 (153.0 ) 29.5 (123.5 ) Pension and postretirement benefits: Net change in net actuarial loss and prior service cost 2.9 (0.6 ) 2.3 (2.9 ) 0.6 (2.3 ) Cumulative foreign currency translation adjustment: Foreign currency translation recognized during the period 0.1 — 0.1 (0.6 ) 0.1 (0.5 ) Other comprehensive income (loss) $ 155.3 $ (36.5 ) $ 118.8 $ (156.5 ) $ 30.2 $ (126.3 ) Reclassifications out of accumulated other comprehensive income were as follows: Three Months Ended March 31, (in millions) 2019 2018 Amount Reclassified from Details about Accumulated Other Accumulated Other Affected Line Item in the Statement Comprehensive Income Components Comprehensive Income Where Net Income is Presented Unrealized gains on available-for-sale securities $ (0.3 ) $ — Net realized losses from sales and other — (0.6 ) Net other-than-temporary impairment losses on investments recognized in earnings (0.3 ) (0.6 ) Total before tax 3.9 2.7 Tax benefit 3.6 2.1 Continued operations; net of tax — (0.2 ) Discontinued operations - Chaucer business 3.6 1.9 Net of tax Amortization of defined benefit pension and postretirement plans (2.9 ) (2.5 ) Loss adjustment expenses and other operating expenses (1) 0.6 0.5 Tax benefit (2.3 ) (2.0 ) Continued operations; net of tax Total reclassifications for the period $ 1.3 $ (0.1 ) Benefit (expense) reflected in income, 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, 2019 and 2018.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2019
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 inland marine, specialty program business, management and professional liability, surety and specialty property. 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 pools business. On December 28, 2018, the Company completed the sale of Chaucer, the major portion of its Lloyd’s international specialty business, to China Re. The sales of the Chaucer-related Irish and Australian entities were subsequently completed on February 14, 2019 and April 10, 2019, respectively. Accordingly, as of December 31, 2018, and for all prior periods, Chaucer’s results of operations have been classified as Discontinued Operations in the Consolidated Statements of Income and assets and liabilities related to the Chaucer business have been classified as held-for-sale in the Consolidated Balance Sheets The Company reports interest expense related to debt separately from the earnings of its operating segments. This consists 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 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) 2019 2018 Operating revenues: Commercial Lines $ 698.7 $ 676.6 Personal Lines 465.2 434.9 Other 7.4 2.9 Total 1,171.3 1,114.4 Net realized and unrealized investment gains (losses) 48.2 (22.9 ) Total revenues $ 1,219.5 $ 1,091.5 Operating income (loss) before interest expense and income taxes: Commercial Lines: Underwriting income $ 36.7 $ 16.3 Net investment income 44.3 45.3 Other expense (0.8 ) (0.2 ) Commercial Lines operating income 80.2 61.4 Personal Lines: Underwriting income 5.7 14.6 Net investment income 19.7 18.4 Other income 1.4 1.3 Personal Lines operating income 26.8 34.3 Other: Underwriting loss (0.3 ) (1.0 ) Net investment income 6.2 2.3 Other expense (3.1 ) (3.7 ) Other operating income (loss) 2.8 (2.4 ) Operating income before interest expense and income taxes 109.8 93.3 Interest on debt (9.4 ) (11.3 ) Operating income before income taxes 100.4 82.0 Non-operating income items: Net realized and unrealized investment gains (losses) 48.2 (22.9 ) Income from continuing operations before income taxes $ 148.6 $ 59.1 The following table provides identifiable assets for the Company’s business segments and discontinued operations: March 31, 2019 December 31, 2018 (in millions) Identifiable Assets U.S. Companies $ 11,856.2 $ 12,238.4 Assets held-for-sale (1) 23.6 57.4 Assets of discontinued operations 103.6 103.9 Total $ 11,983.4 $ 12,399.7 (1) See also Note 3 – “Discontinued Operations – Chaucer Business”. The Company reviews the assets of its U.S. 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, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	10. Stock-based Compensation As of March 31, 2019, there were 3,506,780 shares and 2,369,081 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) 2019 2018 Stock-based compensation expense $ 4.2 $ 2.5 Tax benefit (0.9 ) (0.5 ) Stock-based compensation expense, net of taxes $ 3.3 $ 2.0 Stock-based compensation expense for Chaucer, net of taxes, of $0.4 million for the three months ended March 31, 2018 is reported in discontinued operations and is excluded from the amounts disclosed above. Stock Options Information on the Company’s stock option activity for the three months ended March 31, 2019 and 2018 is summarized below. Three Months Ended March 31, 2019 2018 (in whole shares and dollars) Shares Weighted Average Exercise Price Shares Weighted Average Exercise Price Outstanding, beginning of period 1,099,076 $ 85.75 1,062,177 $ 75.53 Granted 232,568 95.05 291,390 110.58 Exercised (64,017 ) 75.98 (84,353 ) 70.31 Forfeited or cancelled (3,141 ) 95.39 (50,491 ) 88.48 Outstanding, end of period 1,264,486 87.93 1,218,723 83.73 Restricted Stock Units The following tables summarize activity information about employee restricted stock units: Three Months Ended March 31, 2019 2018 (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 332,481 $ 97.28 298,528 $ 83.45 Granted 144,072 117.51 131,290 110.60 Vested (99,855 ) 83.25 (50,810 ) 70.24 Forfeited (8,687 ) 97.14 (10,585 ) 87.47 Outstanding, end of period 368,011 109.01 368,423 94.83 Performance-based and market-based restricted stock units: Outstanding, beginning of period 69,838 $ 95.58 102,586 $ 81.21 Granted 42,119 117.68 29,715 116.82 Vested (10,089 ) 82.74 (14,032 ) 70.24 Forfeited — — (7,625 ) 81.91 Outstanding, end of period 101,868 105.99 110,644 92.12 In the first three months of 2019 and 2018, the Company granted market-based awards totaling 23,924 and 29,715, 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 period as compared to a pre-selected group of property and casualty companies. The fair value of market-based awards was estimated at the date of grant using a valuation model. These units have the potential to range from 0% to 150% of the shares disclosed. Included in the amount granted above in 2019 and 2018 are 5,820 shares and 3,115 shares, respectively, related to market-based awards that achieved a payout in excess of 100%. These awards vested in the first quarters of 2019 and 2018, respectively. The Company also granted performance-based restricted stock units in 2019 which are based upon the achievement of the performance metric at 100%. 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 2019 or 2018.

Earnings Per Share and Sharehol

Earnings Per Share and Shareholders' Equity Transactions	3 Months Ended
	Mar. 31, 2019
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) 2019 2018 Basic shares used in the calculation of earnings per share 40.6 42.5 Dilutive effect of securities: Employee stock options 0.3 0.3 Non-vested stock grants 0.3 0.3 Diluted shares used in the calculation of earnings per share 41.2 43.1 Per share effect of dilutive securities on income from continuing operations and net income $ (0.04 ) $ (0.02 ) Diluted earnings per share for the three months ended March 31, 2019 and 2018 excludes 0.2 million and 0.3 million, respectively, of common shares issuable under the Company’s stock compensation plans because their effect would be antidilutive. On December 30, 2018, the Board of Directors authorized a new stock repurchase program which provides for aggregate repurchases of up to $600 million. Under the repurchase authorization, the Company may repurchase, from time to time, common shares 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.

Liabilities For Outstanding Cla

Liabilities For Outstanding Claims, Losses And Loss Adjustment Expenses	3 Months Ended
	Mar. 31, 2019
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) 2019 2018 Gross loss and LAE reserves, beginning of period $ 5,304.1 $ 5,058.5 Reinsurance recoverable on unpaid losses 1,472.6 1,455.0 Net loss and LAE reserves, beginning of period 3,831.5 3,603.5 Net incurred losses and LAE in respect of losses occurring in: Current year 712.8 677.4 Prior years (13.2 ) (6.5 ) Total incurred losses and LAE 699.6 670.9 Net payments of losses and LAE in respect of losses occurring in: Current year 175.3 181.0 Prior years 459.1 425.5 Total payments 634.4 606.5 Net reserve for losses and LAE, end of period 3,896.7 3,667.9 Reinsurance recoverable on unpaid losses 1,484.9 1,420.0 Gross reserve for losses and LAE, end of period $ 5,381.6 $ 5,087.9 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 $13.2 million in 2019 in comparison to a decrease of $6.5 million in 2018. 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 anticipated subrogation recoveries on the 2017 and 2018 California wildfires. Our current estimate of these subrogation recoveries was informed by the recent sale of our subrogation rights for certain of these events to a large financial institution. In addition, higher than expected losses in our personal and commercial automobile lines were substantially offset by lower than expected losses in our workers’ compensation and commercial multiple peril lines. 2018 For the three months ended March 31, 2018, net favorable loss and LAE development was $6.5 million, primarily as a result of favorable catastrophe development related to the 2017 hurricanes and California wildfires.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Legal Proceedings Durand Litigation On March 12, 2007, a putative class action suit captioned Jennifer A. Durand v. The Hanover Insurance Group, Inc., and The Allmerica Financial Cash Balance Pension Plan The plaintiff filed an Amended Complaint adding two new named plaintiffs and additional claims on December 11, 2009. Two of the three new claims set forth in the Amended Complaint were dismissed by the District Court, which action was upheld in November 2015 by the U.S. Court of Appeals, Sixth Circuit. The District Court, however, did allow to stand the new claim in the Amended Complaint for breach of fiduciary duty and failure to meet notice requirements arising under the Employee Retirement Income Security Act of 1974 (“ERISA”) from the various interest crediting and lump sum distribution matters of which plaintiffs complain, but only as to plaintiffs’ “whipsaw” claim that remained in the case. On December 17, 2013, the Court entered an order certifying a class to bring “whipsaw” and related breach of fiduciary duty claims consisting of all persons who received a lump sum distribution between March 1, 1997 and December 31, 2003. On February 16, 2018, the Court entered an order limiting the claims of those participants who received lump sum distributions prior to March 13, 2002 to alleged violations of ERISA’s disclosure requirements and breaches of fiduciary duty. Subsequently, the parties entered into settlement discussions and reached a settlement. The Court approved the settlement and dismissed the case with prejudice on March 22, 2019. Effective April 24, 2019, such dismissal is no longer subject to appeal. The resulting settlement amount to be paid by the Company is not material to the Company’s financial position and will not have a material effect on its results of operations. Other Matters The Company has been named a defendant in various other legal proceedings arising in the normal course of business. In addition, the Company is involved, from time to time, in examinations, investigations and proceedings by governmental and self-regulatory agencies. The potential outcome of any such action or regulatory proceedings in which the Company has been named a defendant or the subject of an inquiry or investigation, and its ultimate liability, if any, from such action or regulatory proceedings, is difficult to predict at this time. The ultimate resolutions of such proceedings are not expected to have a material effect on its financial position, although they could have a material effect on the results of operations for a particular quarter or annual period. Residual Markets The Company is required to participate in residual markets in various states, which generally pertain to high risk insureds, disrupted markets or lines of business or geographic areas where rates are regarded as excessive. The results of the residual markets are not subject to the predictability associated with the Company’s own managed business, and are significant to both the personal and commercial automobile lines of business .

Other Items

Other Items	3 Months Ended
	Mar. 31, 2019
Federal Home Loan Banks [Abstract]
Other Items	14. Other Items On January 2, 2019, the Company repaid $125 million of its FHLB advances that were due 2029 and had an interest rate of 5.5%, along with related prepayment fees of $26 million; such fees were recognized in 2018.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events On April 10, 2019, the Company completed the sale of its Chaucer-related Australian entities for proceeds of $13 million.

New Accounting Pronouncements (

New Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Changes And Error Corrections [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements Recently Implemented Standards In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Codification (“ASC”) Update No. 2016-02, (Topic 842) Leases Leases Targeted Improvements In March 2019, the FASB issued ASC Update No. 2019-01, Leases (Topic 842) – Codification Improvements Accounting Changes and Error Corrections In March 2017, the FASB issued ASC Update No. 2017-08, (Subtopic 310-20) Receivables – Nonrefundable Fees and Other Costs: Premium Amortization on Purchased Callable Debt Securities Recently Issued Standards 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 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. 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 In June 2016, the FASB issued ASC Update No. 2016-13, (Topic 326) Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments Codification Improvements to Topic 326, Financial Instruments – Credit Losses

Discontinued Operations Chauc_2

Discontinued Operations Chaucer Business (Tables) - Chaucer [Member]	3 Months Ended
	Mar. 31, 2019
Summary of Discontinued Chaucer Business	The following table summarizes the results of Chaucer’s operations for the three months ended March 31, 2018: Three Months Ended March 31, (in millions) 2018 Revenues Net premiums earned $ 221.1 Net investment income 16.4 Other income 1.9 239.4 Losses and operating expenses Losses and LAE 115.0 Amortization of deferred acquisition costs 69.3 Other expenses 32.2 216.5 Income from Chaucer business before income taxes and other items (previously presented as Chaucer's operating income) 22.9 Other items: Interest expense (1.1 ) Net realized and unrealized investment losses (0.5 ) Other income 0.2 Income from Chaucer business before income taxes 21.5 Income tax expense (4.2 ) Income from Chaucer business, net of income taxes $ 17.3
Summary of Cash Flows Associated with the Discontinued Chaucer Business	The following table details the cash flows associated with the Chaucer business for the three months ended March 31, 2018: Three Months Ended March 31, (in millions) 2018 Net cash used in operating activities $ (5.9 ) Net cash provided by investing activities $ 47.7

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2019
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, 2019 Gross Gross OTTI Amortized Unrealized Unrealized Unrealized (in millions) Cost Gains Losses Fair Value Losses U.S. Treasury and government agencies $ 404.5 $ 4.7 $ 2.5 $ 406.7 $ — Foreign government 7.3 0.1 — 7.4 — Municipal 848.1 20.8 3.4 865.5 — Corporate 3,635.7 66.3 27.4 3,674.6 4.8 Residential mortgage-backed 819.2 6.8 6.1 819.9 — Commercial mortgage-backed 684.9 9.4 2.4 691.9 — Asset-backed 93.0 0.6 0.2 93.4 — Total fixed maturities $ 6,492.7 $ 108.7 $ 42.0 $ 6,559.4 $ 4.8 December 31, 2018 Gross Gross OTTI Amortized Unrealized Unrealized Unrealized (in millions) Cost Gains Losses Fair Value Losses U.S. Treasury and government agencies $ 414.7 $ 2.4 $ 7.2 $ 409.9 $ — Foreign government 7.3 0.1 — 7.4 — Municipal 879.0 16.6 9.8 885.8 — Corporate 3,476.6 26.1 92.0 3,410.7 6.6 Residential mortgage-backed 728.4 2.7 14.7 716.4 — Commercial mortgage-backed 648.4 1.7 9.8 640.3 — Asset-backed 91.5 0.2 0.7 91.0 — Fixed maturities, excluding held-for-sale (Chaucer) 6,245.9 49.8 134.2 6,161.5 6.6 Fixed maturities, held-for-sale 24.9 — 0.4 24.5 — Total fixed maturities $ 6,270.8 $ 49.8 $ 134.6 $ 6,186.0 $ 6.6
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, 2019 Amortized Fair (in millions) Cost Value Due in one year or less $ 249.2 $ 250.9 Due after one year through five years 1,969.6 2,001.6 Due after five years through ten years 2,407.4 2,423.2 Due after ten years 269.4 278.5 4,895.6 4,954.2 Mortgage-backed and asset-backed securities 1,597.1 1,605.2 Total fixed maturities $ 6,492.7 $ 6,559.4
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, 2019 and December 31, 2018 including the length of time the securities have been in an unrealized loss position: March 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 $ — $ — $ 2.5 $ 158.4 $ 2.5 $ 158.4 Foreign governments — — — 0.8 — 0.8 Municipal — 9.7 3.4 192.3 3.4 202.0 Corporate 0.9 15.3 19.7 993.2 20.6 1,008.5 Residential mortgage-backed — 2.1 6.1 352.6 6.1 354.7 Commercial mortgage-backed — 0.3 2.4 226.7 2.4 227.0 Asset-backed — — 0.2 31.9 0.2 31.9 Total investment grade 0.9 27.4 34.3 1,955.9 35.2 1,983.3 Below investment grade: Corporate 0.3 17.1 6.5 75.7 6.8 92.8 Total fixed maturities $ 1.2 $ 44.5 $ 40.8 $ 2,031.6 $ 42.0 $ 2,076.1 December 31, 2018 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 $ 1.1 $ 66.0 $ 6.1 $ 210.9 $ 7.2 $ 276.9 Foreign governments — 2.0 — 0.8 — 2.8 Municipal 0.8 110.0 9.0 248.0 9.8 358.0 Corporate 30.0 1,277.9 43.9 781.6 73.9 2,059.5 Residential mortgage-backed 2.6 201.2 12.1 323.7 14.7 524.9 Commercial mortgage-backed 3.4 293.0 6.4 175.5 9.8 468.5 Asset-backed 0.4 42.3 0.3 18.0 0.7 60.3 Total investment grade 38.3 1,992.4 77.8 1,758.5 116.1 3,750.9 Below investment grade: Municipal — — — 0.9 — 0.9 Corporate 8.1 185.6 10.0 54.0 18.1 239.6 Total below investment grade 8.1 185.6 10.0 54.9 18.1 240.5 Fixed maturities, excluding held-for-sale (Chaucer) 46.4 2,178.0 87.8 1,813.4 134.2 3,991.4 Fixed maturities, held-for-sale 0.1 4.0 0.3 18.0 0.4 22.0 Total fixed maturities $ 46.5 $ 2,182.0 $ 88.1 $ 1,831.4 $ 134.6 $ 4,013.4
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, 2019 2018 Proceeds from Gross Gross Proceeds from Gross Gross (in millions) Sales Gains Losses Sales Gains Losses Fixed maturities, excluding held-for-sale (Chaucer) $ 60.1 $ 1.0 $ 1.5 $ 57.1 $ 0.2 $ 1.7 Fixed maturities, held-for-sale 0.3 — — 70.7 0.4 0.6 Total fixed maturities $ 60.4 $ 1.0 $ 1.5 $ 127.8 $ 0.6 $ 2.3
Rollforward of Cumulative Amounts Related to Credit Loss Portion of OTTI Losses	The following table provides rollforwards of the cumulative amounts related to the Company’s credit loss portion of the OTTI losses on fixed maturity securities from continuing operations for which the non-credit portion of the loss is included in other comprehensive income. Three Months Ended March 31, (in millions) 2019 2018 Credit losses as of the beginning of the period $ 3.8 $ 3.6 Credit losses on securities for which an OTTI was not previously recognized — 0.2 Reductions for securities sold, matured or called (0.5 ) (0.7 ) Credit losses as of the end of the period $ 3.3 $ 3.1
Schedule of Pre-tax Realized and Unrealized Gains and Losses on Equity Securities From Continuing Operations	Three Months Ended March 31, (in millions) 2019 2018 Net gains (losses) recognized during the period $ 48.6 $ (22.9 ) Less: net gains recognized on equity securities sold during the period 1.1 0.5 Net unrealized gains (losses) recognized during the period on equity securities still held $ 47.5 $ (23.4 )

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	The estimated fair value of the financial instruments were as follows: March 31, 2019 December 31, 2018 Carrying Fair Carrying Fair (in millions) Value Value Value Value Financial Assets carried at: Fair Value through AOCI: Fixed maturities $ 6,559.4 $ 6,559.4 $ 6,161.5 $ 6,161.5 Fair Value through Net Income: Equity securities 504.7 504.7 464.4 464.4 Other investments 180.3 180.3 175.0 175.0 Amortized Cost/Cost: Other investments 421.5 425.7 414.4 418.9 Cash and cash equivalents 168.5 168.5 1,020.7 1,020.7 Total financial instruments, excluding held-for-sale 7,834.4 7,838.6 8,236.0 8,240.5 Financial instruments, held-for-sale (Chaucer) 2.8 2.8 27.8 27.8 Total financial instruments $ 7,837.2 $ 7,841.4 $ 8,263.8 $ 8,268.3 Financial Liabilities carried at: Amortized Cost: Debt $ 653.0 $ 694.2 $ 777.9 $ 825.0
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, 2019 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 406.7 $ 159.3 $ 247.4 $ — Foreign government 7.4 — 7.4 — Municipal 865.5 — 845.0 20.5 Corporate 3,674.6 — 3,673.9 0.7 Residential mortgage-backed, U.S. agency backed 817.2 — 817.2 — Residential mortgage-backed, non-agency 2.7 — 2.7 — Commercial mortgage-backed 691.9 — 679.1 12.8 Asset-backed 93.4 — 93.4 — Total fixed maturities 6,559.4 159.3 6,366.1 34.0 Equity securities 504.7 503.6 — 1.1 Other investments 3.5 — — 3.5 Total investment assets at fair value $ 7,067.6 $ 662.9 $ 6,366.1 $ 38.6 December 31, 2018 (in millions) Total Level 1 Level 2 Level 3 Fixed maturities: U.S. Treasury and government agencies $ 409.9 $ 154.9 $ 255.0 $ — Foreign government 7.4 — 7.4 — Municipal 885.8 — 864.7 21.1 Corporate 3,410.7 — 3,409.9 0.8 Residential mortgage-backed, U.S. agency backed 713.7 — 713.7 — Residential mortgage-backed, non-agency 2.7 — 2.7 — Commercial mortgage-backed 640.3 — 627.2 13.1 Asset-backed 91.0 — 91.0 — Total fixed maturities 6,161.5 154.9 5,971.6 35.0 Equity securities 464.4 463.3 — 1.1 Other investments 3.5 — — 3.5 Total investment assets at fair value, excluding held-for-sale (Chaucer) 6,629.4 618.2 5,971.6 39.6 Investment assets, held-for-sale 24.5 5.7 18.8 — Total investment assets at fair value $ 6,653.9 $ 623.9 $ 5,990.4 $ 39.6
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, 2019 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 168.5 $ 168.5 $ — $ — Other investments 425.7 — 1.8 423.9 Total financial instruments, excluding held-for-sale 594.2 168.5 1.8 423.9 Financial instruments, held-for-sale (Chaucer) 2.8 2.8 — — Total financial instruments $ 597.0 $ 171.3 $ 1.8 $ 423.9 Liabilities: Debt $ 694.2 $ — $ 694.2 $ — December 31, 2018 (in millions) Total Level 1 Level 2 Level 3 Assets: Cash and cash equivalents $ 1,020.7 $ 1,020.7 $ — $ — Other investments 418.9 — 8.7 410.2 Total financial instruments, excluding held-for-sale 1,439.6 1,020.7 8.7 410.2 Financial instruments, held-for-sale (Chaucer) 3.3 3.3 — — Total financial instruments $ 1,442.9 $ 1,024.0 $ 8.7 $ 410.2 Liabilities: Debt $ 825.0 $ — $ 825.0 $ —
Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3)	The table below provide a 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, 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 appreciation 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 Three Months Ended March 31, 2018 Balance January 1, 2018, excluding held-for-sale (Chaucer) $ 24.6 $ 0.9 $ 14.2 $ 39.7 $ 4.7 $ 44.4 Total gains (losses): 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 (0.5 ) — (0.2 ) (0.7 ) — (0.7 ) Sales (1.1 ) (0.1 ) (0.5 ) (1.7 ) — (1.7 ) Balance March 31, 2018, excluding held-for-sale (Chaucer) $ 23.1 $ 0.8 $ 13.5 $ 37.4 $ 4.7 $ 42.1
Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3 Assets	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, 2019 December 31, 2018 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 $ 20.5 0.7 - 6.8% (3.3%) 1.3% (1.3%) 0.3 - 0.5% (0.5%) $ 21.1 0.7 - 6.8% (3.4%) 1.3% (1.3%) 0.3 - 0.5% (0.5%) Corporate Discounted cash flow Discount for: Small issue size Above-market coupon 0.7 2.5% (2.5%) 0.3% (0.3%) 0.8 2.5% (2.5%) 0.3% (0.3%) Commercial mortgage-backed Discounted cash flow Discount for: Small issue size Above-market coupon Lease structure 12.8 1.9 - 3.1% (2.7%) 0.5% (0.5%) 0.3% (0.3%) 13.1 1.9 - 3.1% (2.7%) 0.5% (0.5%) 0.3% (0.3%) Equity securities Market comparables Net tangible asset market multiples 1.1 1.0X (1.0X) 1.1 1.0X (1.0X) Other Discounted cash flow Discount rate 3.5 18.0% (18.0%) 3.5 18.0% (18.0%)

Pension and Other Postretirem_2

Pension and Other Postretirement Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Components of Net Periodic Pension Cost	The components of net periodic pension cost for defined benefit pension and other postretirement benefit plans included in the Company’s results of operations are as follows: Three Months Ended March 31, 2019 2018 2019 2018 (in millions) Pension Plans Postretirement Plans Service cost - benefits earned during the period $ — $ — $ — $ — Interest cost 5.3 4.9 0.1 0.1 Expected return on plan assets (5.8 ) (5.2 ) — — Recognized net actuarial loss 2.8 2.5 — 0.1 Amortization of prior service cost — — — (0.1 ) Net periodic pension cost $ 2.3 $ 2.2 $ 0.1 $ 0.1

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Changes in Other Comprehensive Income (Loss)	The following tables provide changes in other comprehensive income (loss). Three Months Ended March 31, 2019 2018 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 $ 152.0 $ (32.0 ) $ 120.0 $ (153.7 ) $ 32.1 $ (121.6 ) Amount of realized gains (losses) from sales and other 0.3 (3.9 ) (3.6 ) 0.2 (2.5 ) (2.3 ) Portion of other-than-temporary impairment losses recognized in earnings — — — 0.5 (0.1 ) 0.4 Net unrealized gains (losses) 152.3 (35.9 ) 116.4 (153.0 ) 29.5 (123.5 ) Pension and postretirement benefits: Net change in net actuarial loss and prior service cost 2.9 (0.6 ) 2.3 (2.9 ) 0.6 (2.3 ) Cumulative foreign currency translation adjustment: Foreign currency translation recognized during the period 0.1 — 0.1 (0.6 ) 0.1 (0.5 ) Other comprehensive income (loss) $ 155.3 $ (36.5 ) $ 118.8 $ (156.5 ) $ 30.2 $ (126.3 )
Reclassifications Out of Accumulated Other Comprehensive Income	Reclassifications out of accumulated other comprehensive income were as follows: Three Months Ended March 31, (in millions) 2019 2018 Amount Reclassified from Details about Accumulated Other Accumulated Other Affected Line Item in the Statement Comprehensive Income Components Comprehensive Income Where Net Income is Presented Unrealized gains on available-for-sale securities $ (0.3 ) $ — Net realized losses from sales and other — (0.6 ) Net other-than-temporary impairment losses on investments recognized in earnings (0.3 ) (0.6 ) Total before tax 3.9 2.7 Tax benefit 3.6 2.1 Continued operations; net of tax — (0.2 ) Discontinued operations - Chaucer business 3.6 1.9 Net of tax Amortization of defined benefit pension and postretirement plans (2.9 ) (2.5 ) Loss adjustment expenses and other operating expenses (1) 0.6 0.5 Tax benefit (2.3 ) (2.0 ) Continued operations; net of tax Total reclassifications for the period $ 1.3 $ (0.1 ) Benefit (expense) reflected in income, 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, 2019 and 2018.

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2019
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) 2019 2018 Operating revenues: Commercial Lines $ 698.7 $ 676.6 Personal Lines 465.2 434.9 Other 7.4 2.9 Total 1,171.3 1,114.4 Net realized and unrealized investment gains (losses) 48.2 (22.9 ) Total revenues $ 1,219.5 $ 1,091.5 Operating income (loss) before interest expense and income taxes: Commercial Lines: Underwriting income $ 36.7 $ 16.3 Net investment income 44.3 45.3 Other expense (0.8 ) (0.2 ) Commercial Lines operating income 80.2 61.4 Personal Lines: Underwriting income 5.7 14.6 Net investment income 19.7 18.4 Other income 1.4 1.3 Personal Lines operating income 26.8 34.3 Other: Underwriting loss (0.3 ) (1.0 ) Net investment income 6.2 2.3 Other expense (3.1 ) (3.7 ) Other operating income (loss) 2.8 (2.4 ) Operating income before interest expense and income taxes 109.8 93.3 Interest on debt (9.4 ) (11.3 ) Operating income before income taxes 100.4 82.0 Non-operating income items: Net realized and unrealized investment gains (losses) 48.2 (22.9 ) Income from continuing operations before income taxes $ 148.6 $ 59.1
Identifiable Assets by Business Segment	The following table provides identifiable assets for the Company’s business segments and discontinued operations: March 31, 2019 December 31, 2018 (in millions) Identifiable Assets U.S. Companies $ 11,856.2 $ 12,238.4 Assets held-for-sale (1) 23.6 57.4 Assets of discontinued operations 103.6 103.9 Total $ 11,983.4 $ 12,399.7 (1) See also Note 3 – “Discontinued Operations – Chaucer Business”.

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
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) 2019 2018 Stock-based compensation expense $ 4.2 $ 2.5 Tax benefit (0.9 ) (0.5 ) Stock-based compensation expense, net of taxes $ 3.3 $ 2.0
Summary of Stock Option Plan Activity	Information on the Company’s stock option activity for the three months ended March 31, 2019 and 2018 is summarized below. Three Months Ended March 31, 2019 2018 (in whole shares and dollars) Shares Weighted Average Exercise Price Shares Weighted Average Exercise Price Outstanding, beginning of period 1,099,076 $ 85.75 1,062,177 $ 75.53 Granted 232,568 95.05 291,390 110.58 Exercised (64,017 ) 75.98 (84,353 ) 70.31 Forfeited or cancelled (3,141 ) 95.39 (50,491 ) 88.48 Outstanding, end of period 1,264,486 87.93 1,218,723 83.73
Summary of Restricted Stock Activity	The following tables summarize activity information about employee restricted stock units: Three Months Ended March 31, 2019 2018 (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 332,481 $ 97.28 298,528 $ 83.45 Granted 144,072 117.51 131,290 110.60 Vested (99,855 ) 83.25 (50,810 ) 70.24 Forfeited (8,687 ) 97.14 (10,585 ) 87.47 Outstanding, end of period 368,011 109.01 368,423 94.83 Performance-based and market-based restricted stock units: Outstanding, beginning of period 69,838 $ 95.58 102,586 $ 81.21 Granted 42,119 117.68 29,715 116.82 Vested (10,089 ) 82.74 (14,032 ) 70.24 Forfeited — — (7,625 ) 81.91 Outstanding, end of period 101,868 105.99 110,644 92.12

Earnings Per Share and Shareh_2

Earnings Per Share and Shareholders' Equity Transactions (Tables)	3 Months Ended
	Mar. 31, 2019
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) 2019 2018 Basic shares used in the calculation of earnings per share 40.6 42.5 Dilutive effect of securities: Employee stock options 0.3 0.3 Non-vested stock grants 0.3 0.3 Diluted shares used in the calculation of earnings per share 41.2 43.1 Per share effect of dilutive securities on income from continuing operations and net income $ (0.04 ) $ (0.02 )

Liabilities For Outstanding C_2

Liabilities For Outstanding Claims, Losses And Loss Adjustment Expenses (Tables)	3 Months Ended
	Mar. 31, 2019
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) 2019 2018 Gross loss and LAE reserves, beginning of period $ 5,304.1 $ 5,058.5 Reinsurance recoverable on unpaid losses 1,472.6 1,455.0 Net loss and LAE reserves, beginning of period 3,831.5 3,603.5 Net incurred losses and LAE in respect of losses occurring in: Current year 712.8 677.4 Prior years (13.2 ) (6.5 ) Total incurred losses and LAE 699.6 670.9 Net payments of losses and LAE in respect of losses occurring in: Current year 175.3 181.0 Prior years 459.1 425.5 Total payments 634.4 606.5 Net reserve for losses and LAE, end of period 3,896.7 3,667.9 Reinsurance recoverable on unpaid losses 1,484.9 1,420.0 Gross reserve for losses and LAE, end of period $ 5,381.6 $ 5,087.9

New Accounting Pronouncements_2

New Accounting Pronouncements (Narrative) (Details) $ in Millions	Jan. 01, 2019USD ($)
Accounting Standards Update No. 2018-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect to increase assets and liabilities	$ 35
Accounting Standards Update 2017-08 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	$ 1.5

Discontinued Operations Chauc_3

Discontinued Operations Chaucer Business (Narrative) (Details) - USD ($) $ in Millions	Apr. 10, 2019	Feb. 14, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenues from the Chaucer business			$ 1,219.5	$ 1,091.5
Operating losses			109.8	93.3
Assets held-for-sale			103.6		$ 103.9
Liabilities held-for-sale			118.3		115.9
Assets Held-for-Sale [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Assets held-for-sale			23.6		57.4
Liabilities held-for-sale			12		$ 22.2
Chaucer Irish Entity[Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from sale of businesses segment		$ 28
Australian Entities [Member] | Subsequent Event [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash proceeds to be received	$ 13
Chaucer [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Revenues from the Chaucer business			2.9	$ 239.4
Operating losses			$ 0.3

Discontinued Operations Chauc_4

Discontinued Operations Chaucer Business (Summary of Discontinued Chaucer Business) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues
Premiums	$ 1,095.1	$ 1,042.5
Net investment income	70.2	66
Total revenues	1,219.5	1,091.5
Losses and operating expenses
Losses and loss adjustment expenses	699.6	670.9
Amortization of deferred acquisition costs	229.5	218.7
Other operating expenses	132.4	131.5
Total losses and expenses	1,070.9	1,032.4
Other items:
Interest expense	(9.4)	(11.3)
Net realized and unrealized investment losses	48.4	(23.4)
Chaucer [Member]
Revenues
Premiums		221.1
Net investment income		16.4
Other income		1.9
Total revenues	2.9	239.4
Losses and operating expenses
Losses and loss adjustment expenses		115
Amortization of deferred acquisition costs		69.3
Other operating expenses		32.2
Total losses and expenses		216.5
Income from Chaucer business before income taxes and other items (previously presented as Chaucer's operating income)		22.9
Other items:
Interest expense		(1.1)
Net realized and unrealized investment losses		(0.5)
Other income		0.2
Income from Chaucer business before income taxes		21.5
Income tax expense		(4.2)
Income from Chaucer business, net of income taxes	$ (0.3)	$ 17.3

Discontinued Operations Chauc_5

Discontinued Operations Chaucer Business (Summary of Cash Flows Associated with the Discontinued Chaucer Business) (Details) - Chaucer [Member] $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net cash used in operating activities	$ (5.9)
Net cash provided by investing activities	$ 47.7

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Taxes [Line Items]
Federal income tax expense	$ 26	$ 8.6
Chaucer [Member]
Income Taxes [Line Items]
Income tax expense (benefit), discontinued operations		4.2
Chaucer [Member] | Federal [Member]
Income Taxes [Line Items]
Income tax expense (benefit), discontinued operations		5.9
Chaucer [Member] | Foreign [Member]
Income Taxes [Line Items]
Income tax expense (benefit), discontinued operations		$ (1.7)

Investments (Schedule of Availa

Investments (Schedule of Available-for-sale Fixed Maturities Reconciliation) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,492.7	$ 6,245.9
Fair Value	6,559.4	6,161.5
Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	848.1	879
Gross Unrealized Gains	20.8	16.6
Gross Unrealized Loss	3.4	9.8
Fair Value	865.5	885.8
Fixed Maturities Excluding Held-For-Sale Chaucer [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		6,245.9
Gross Unrealized Gains		49.8
Gross Unrealized Loss		134.2
Fair Value		6,161.5
OTTI Unrealized Losses		6.6
Fixed Maturities Held-For-Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		24.9
Gross Unrealized Loss		0.4
Fair Value		24.5
Fixed Maturities Including Held For Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,492.7	6,270.8
Gross Unrealized Gains	108.7	49.8
Gross Unrealized Loss	42	134.6
Fair Value	6,559.4	6,186
OTTI Unrealized Losses	4.8	6.6
US Treasury and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	404.5	414.7
Gross Unrealized Gains	4.7	2.4
Gross Unrealized Loss	2.5	7.2
Fair Value	406.7	409.9
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7.3	7.3
Gross Unrealized Gains	0.1	0.1
Fair Value	7.4	7.4
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,635.7	3,476.6
Gross Unrealized Gains	66.3	26.1
Gross Unrealized Loss	27.4	92
Fair Value	3,674.6	3,410.7
OTTI Unrealized Losses	4.8	6.6
Residential Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	819.2	728.4
Gross Unrealized Gains	6.8	2.7
Gross Unrealized Loss	6.1	14.7
Fair Value	819.9	716.4
Commercial Mortgage Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	684.9	648.4
Gross Unrealized Gains	9.4	1.7
Gross Unrealized Loss	2.4	9.8
Fair Value	691.9	640.3
Asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	93	91.5
Gross Unrealized Gains	0.6	0.2
Gross Unrealized Loss	0.2	0.7
Fair Value	$ 93.4	$ 91

Investments (Narrative) (Detail

Investments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Net unrealized gains on impaired securities	$ 7,400,000		$ 7,400,000
Other-than-temporary impairments on fixed maturities	$ 0	$ 900,000
Other-than-temporary impairments on fixed maturities recorded as unrealized losses in AOCI		300,000
Other-than-temporary impairments on fixed maturities recognized in earnings		$ 600,000

Investments (Investments Classi

Investments (Investments Classified by Contractual Maturity Date) (Details) $ in Millions	Mar. 31, 2019USD ($)
Available-for-sale Securities, Debt Maturities [Abstract]
Due in one year or less, Amortized Cost	$ 249.2
Due after one year through five years, Amortized Cost	1,969.6
Due after five years through ten years, Amortized Cost	2,407.4
Due after ten years, Amortized Cost	269.4
Gross fixed maturities, Amortized Cost	4,895.6
Mortgage-backed and asset-backed securities, Amortized Cost	1,597.1
Total fixed maturities, Amortized Cost	6,492.7
Due in one year or less, Fair Value	250.9
Due after one year through five years, Fair Value	2,001.6
Due after five years through ten years, Fair Value	2,423.2
Due after ten years, Fair Value	278.5
Gross fixed maturities, Fair Value	4,954.2
Mortgage-backed and asset-backed securities, Fair Value	1,605.2
Total fixed maturities, Fair Value	$ 6,559.4

Investments (Schedule of Unreal

Investments (Schedule of Unrealized Loss on Investments) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	$ 1.2
12 months or less, Fair Value	44.5
Greater than 12 months, Gross Unrealized Losses	40.8
Greater than 12 months, Fair Value	2,031.6
Total, Gross Unrealized Losses	42
Total, Fair Value	2,076.1
Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.9	$ 38.3
12 months or less, Fair Value	27.4	1,992.4
Greater than 12 months, Gross Unrealized Losses	34.3	77.8
Greater than 12 months, Fair Value	1,955.9	1,758.5
Total, Gross Unrealized Losses	35.2	116.1
Total, Fair Value	1,983.3	3,750.9
Below Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		8.1
12 months or less, Fair Value		185.6
Greater than 12 months, Gross Unrealized Losses		10
Greater than 12 months, Fair Value		54.9
Total, Gross Unrealized Losses		18.1
Total, Fair Value		240.5
Fixed Maturities Excluding Held-For-Sale Chaucer [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		46.4
12 months or less, Fair Value		2,178
Greater than 12 months, Gross Unrealized Losses		87.8
Greater than 12 months, Fair Value		1,813.4
Total, Gross Unrealized Losses		134.2
Total, Fair Value		3,991.4
Fixed Maturities Held-For-Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		0.1
12 months or less, Fair Value		4
Greater than 12 months, Gross Unrealized Losses		0.3
Greater than 12 months, Fair Value		18
Total, Gross Unrealized Losses		0.4
Total, Fair Value		22
Fixed Maturities Including Held For Sale [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		46.5
12 months or less, Fair Value		2,182
Greater than 12 months, Gross Unrealized Losses		88.1
Greater than 12 months, Fair Value		1,831.4
Total, Gross Unrealized Losses		134.6
Total, Fair Value		4,013.4
US Treasury and Government Agencies [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		1.1
12 months or less, Fair Value		66
Greater than 12 months, Gross Unrealized Losses	2.5	6.1
Greater than 12 months, Fair Value	158.4	210.9
Total, Gross Unrealized Losses	2.5	7.2
Total, Fair Value	158.4	276.9
Foreign Government [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Fair Value		2
Greater than 12 months, Fair Value	0.8	0.8
Total, Fair Value	0.8	2.8
Municipal [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		0.8
12 months or less, Fair Value	9.7	110
Greater than 12 months, Gross Unrealized Losses	3.4	9
Greater than 12 months, Fair Value	192.3	248
Total, Gross Unrealized Losses	3.4	9.8
Total, Fair Value	202	358
Municipal [Member] | Below Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Greater than 12 months, Fair Value		0.9
Total, Fair Value		0.9
Corporate [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.9	30
12 months or less, Fair Value	15.3	1,277.9
Greater than 12 months, Gross Unrealized Losses	19.7	43.9
Greater than 12 months, Fair Value	993.2	781.6
Total, Gross Unrealized Losses	20.6	73.9
Total, Fair Value	1,008.5	2,059.5
Corporate [Member] | Below Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses	0.3	8.1
12 months or less, Fair Value	17.1	185.6
Greater than 12 months, Gross Unrealized Losses	6.5	10
Greater than 12 months, Fair Value	75.7	54
Total, Gross Unrealized Losses	6.8	18.1
Total, Fair Value	92.8	239.6
Residential Mortgage Backed [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		2.6
12 months or less, Fair Value	2.1	201.2
Greater than 12 months, Gross Unrealized Losses	6.1	12.1
Greater than 12 months, Fair Value	352.6	323.7
Total, Gross Unrealized Losses	6.1	14.7
Total, Fair Value	354.7	524.9
Commercial Mortgage Backed [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		3.4
12 months or less, Fair Value	0.3	293
Greater than 12 months, Gross Unrealized Losses	2.4	6.4
Greater than 12 months, Fair Value	226.7	175.5
Total, Gross Unrealized Losses	2.4	9.8
Total, Fair Value	227	468.5
Asset-backed [Member] | Investment grade [Member]
Schedule of Available-for-sale Securities [Line Items]
12 months or less, Gross Unrealized Losses		0.4
12 months or less, Fair Value		42.3
Greater than 12 months, Gross Unrealized Losses	0.2	0.3
Greater than 12 months, Fair Value	31.9	18
Total, Gross Unrealized Losses	0.2	0.7
Total, Fair Value	$ 31.9	$ 60.3

Investments (Schedule of Realiz

Investments (Schedule of Realized Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fixed Maturities Excluding Held-For-Sale Chaucer [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	$ 60.1	$ 57.1
Gross Gains	1	0.2
Gross Losses	1.5	1.7
Fixed Maturities Held-For-Sale [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	0.3	70.7
Gross Gains		0.4
Gross Losses		0.6
Fixed Maturities Including Held For Sale [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	60.4	127.8
Gross Gains	1	0.6
Gross Losses	$ 1.5	$ 2.3

Investments (Rollforward of Cum

Investments (Rollforward of Cumulative Amounts Related to Credit Loss Portion of OTTI Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Credit losses as of the beginning of the period	$ 3.8	$ 3.6
Credit losses on securities for which an OTTI was not previously recognized		0.2
Reductions for securities sold, matured or called	(0.5)	(0.7)
Credit losses as of the end of the period	$ 3.3	$ 3.1

Investments (Schedule of Pre-ta

Investments (Schedule of Pre-tax Realized and Unrealized Gains and Losses on Equity Securities From Continuing Operations) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Investments Debt And Equity Securities [Abstract]
Net gains (losses) recognized during the period	$ 48.6	$ (22.9)
Less: net gains recognized on equity securities sold during the period	1.1	0.5
Net unrealized gains (losses) recognized during the period on equity securities still held	$ 47.5	$ (23.4)

Fair Value (Fair Value of Finan

Fair Value (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 168.5	$ 1,020.7
Total financial instruments, excluding held-for-sale	7,834.4	8,236
Total financial instruments	7,837.2	8,263.8
Carrying Value [Member] | Chaucer [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, held-for-sale (Chaucer)	2.8	27.8
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	168.5	1,020.7
Total financial instruments, excluding held-for-sale	7,838.6	8,240.5
Total financial instruments	7,841.4	8,268.3
Debt	694.2	825
Estimated Fair Value [Member] | Chaucer [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, held-for-sale (Chaucer)	2.8	27.8
Income Approach Valuation Technique [Member] | Carrying Value [Member] | Fair Value Through AOCI [Member] | Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	6,559.4	6,161.5
Income Approach Valuation Technique [Member] | Carrying Value [Member] | Fair Value Through Net Income [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	180.3	175
Income Approach Valuation Technique [Member] | Carrying Value [Member] | Fair Value Through Net Income [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	504.7	464.4
Income Approach Valuation Technique [Member] | Estimated Fair Value [Member] | Fair Value Through AOCI [Member] | Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	6,559.4	6,161.5
Income Approach Valuation Technique [Member] | Estimated Fair Value [Member] | Fair Value Through Net Income [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	180.3	175
Income Approach Valuation Technique [Member] | Estimated Fair Value [Member] | Fair Value Through Net Income [Member] | Equity Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	504.7	464.4
Cost Approach Valuation Technique [Member] | Carrying Value [Member] | Amortized Cost/Cost [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	168.5	1,020.7
Debt	653	777.9
Cost Approach Valuation Technique [Member] | Carrying Value [Member] | Amortized Cost/Cost [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	421.5	414.4
Cost Approach Valuation Technique [Member] | Estimated Fair Value [Member] | Amortized Cost/Cost [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	168.5	1,020.7
Debt	694.2	825
Cost Approach Valuation Technique [Member] | Estimated Fair Value [Member] | Amortized Cost/Cost [Member] | Other Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of investments	$ 425.7	$ 418.9

Fair Value (Fair Value,Investme

Fair Value (Fair Value,Investment Assets Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	$ 6,559.4	$ 6,161.5
Equity securities	504.7	464.4
Other investments	680.4	661.5
Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	865.5	885.8
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	1.1	1.1
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	6,559.4	6,161.5
Equity securities	504.7	464.4
Other investments	3.5	3.5
Total investment assets at fair value, excluding held-for-sale	7,067.6	6,653.9
Investment assets, held-for-sale		24.5
Fair Value, Measurements, Recurring [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment assets at fair value, excluding held-for-sale (Chaucer)		6,629.4
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	406.7	409.9
Fair Value, Measurements, Recurring [Member] | Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	7.4	7.4
Fair Value, Measurements, Recurring [Member] | Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	865.5	885.8
Fair Value, Measurements, Recurring [Member] | Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	3,674.6	3,410.7
Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed Securities U S Agency Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	817.2	713.7
Fair Value, Measurements, Recurring [Member] | Residential Mortgage Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	2.7	2.7
Fair Value, Measurements, Recurring [Member] | Commercial Mortgage Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	691.9	640.3
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	93.4	91
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	159.3	154.9
Equity securities	503.6	463.3
Total investment assets at fair value, excluding held-for-sale	662.9	623.9
Investment assets, held-for-sale		5.7
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment assets at fair value, excluding held-for-sale (Chaucer)		618.2
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	159.3	154.9
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	6,366.1	5,971.6
Total investment assets at fair value, excluding held-for-sale	6,366.1	5,990.4
Investment assets, held-for-sale		18.8
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment assets at fair value, excluding held-for-sale (Chaucer)		5,971.6
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	247.4	255
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	7.4	7.4
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	845	864.7
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	3,673.9	3,409.9
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Residential Mortgage Backed Securities U S Agency Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	817.2	713.7
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	2.7	2.7
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	679.1	627.2
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	93.4	91
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturities	34	35
Equity securities	1.1	1.1
Other investments	3.5	3.5
Total investment assets at fair value, excluding held-for-sale	38.6	39.6
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total investment assets at fair value, excluding held-for-sale (Chaucer)		39.6
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	20.5	21.1
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	0.7	0.8
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	$ 12.8	$ 13.1

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
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	176,800,000		$ 171,500,000
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, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	$ 504.7	$ 464.4
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	1.1	1.1
Other investments	3.5	3.5
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	168.5	1,020.7
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	168.5	1,020.7
Total financial instruments, excluding held-for-sale	594.2	1,439.6
Total financial instruments	597	1,442.9
Other investments	425.7	418.9
Debt	694.2	825
Estimated Fair Value [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	168.5	1,020.7
Total financial instruments, excluding held-for-sale	168.5	1,020.7
Total financial instruments	171.3	1,024
Estimated Fair Value [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments, excluding held-for-sale	1.8	8.7
Total financial instruments	1.8	8.7
Other investments	1.8	8.7
Debt	694.2	825
Estimated Fair Value [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial instruments, excluding held-for-sale	423.9	410.2
Total financial instruments	423.9	410.2
Other investments	423.9	410.2
Estimated Fair Value [Member] | Chaucer [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, held-for-sale (Chaucer)	2.8	3.3
Estimated Fair Value [Member] | Chaucer [Member] | Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial instruments, held-for-sale (Chaucer)	$ 2.8	$ 3.3

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, 2019	Mar. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 39.6
Included in total net realized and unrealized investment gains	0.1	$ 0.1
Included in other comprehensive income-net appreciation on available-for-sale securities	0.4	(0.7)
Sales	(1.5)	(1.7)
Ending Balance	38.6	42.1
Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		44.4
Municipal [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	21.1
Included in total net realized and unrealized investment gains	0.1	0.1
Included in other comprehensive income-net appreciation on available-for-sale securities	0.2	(0.5)
Sales	(0.9)	(1.1)
Ending Balance	20.5	23.1
Municipal [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		24.6
Corporate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	0.8
Sales	(0.1)	(0.1)
Ending Balance	0.7	0.8
Corporate [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		0.9
Commercial Mortgage Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	13.1
Included in other comprehensive income-net appreciation on available-for-sale securities	0.2	(0.2)
Sales	(0.5)	(0.5)
Ending Balance	12.8	13.5
Commercial Mortgage Backed [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		14.2
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	35
Included in total net realized and unrealized investment gains	0.1	0.1
Included in other comprehensive income-net appreciation on available-for-sale securities	0.4	(0.7)
Sales	(1.5)	(1.7)
Ending Balance	34	37.4
Fixed Maturities [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		39.7
Equity Securities and Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	4.6
Ending Balance	$ 4.6	4.7
Equity Securities and Other Investments [Member] | Chaucer [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance		$ 4.7

Fair Value (Schedule of Additio

Fair Value (Schedule of Additional Information About Significant Unobservable Inputs Used in Fair Valuations of Level 3 Assets) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value [Line Items]
Fair Value	$ 6,559.4	$ 6,161.5
Equity securities, at fair value	504.7	464.4
Level 3 [Member]
Fair Value [Line Items]
Equity securities, at fair value	$ 1.1	$ 1.1
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
Other investments	$ 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
Range	0.180	0.180
Level 3 [Member] | Weighted Average [Member]
Fair Value [Line Items]
Fair value measurement market multiples	1	1
Range	0.180	0.180
Municipal [Member]
Fair Value [Line Items]
Fair Value	$ 865.5	$ 885.8
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Fair Value	$ 20.5	$ 21.1
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Small issue size	1.30%	1.30%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Minimum [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Small issue size	0.70%	0.70%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Minimum [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Small issue size	0.30%	0.30%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Maximum [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Small issue size	6.80%	6.80%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Maximum [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Small issue size	0.50%	0.50%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount for Small Issue Size [Member]
Fair Value [Line Items]
Small issue size	3.30%	3.40%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input Discount For Credit Stress [Member]
Fair Value [Line Items]
Small issue size	1.30%	1.30%
Municipal [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Small issue size	0.50%	0.50%
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Fair Value	$ 0.7	$ 0.8
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount Rate [Member]
Fair Value [Line Items]
Small issue size	2.50%	2.50%
Above-market coupon	0.30%	0.30%
Corporate [Member] | Discounted cash flow [Member] | Level 3 [Member] | Weighted Average [Member] | Measurement Input, Discount Rate [Member]
Fair Value [Line Items]
Small issue size	2.50%	2.50%
Above-market coupon	0.30%	0.30%
Commercial Mortgage Backed [Member] | Discounted cash flow [Member] | Level 3 [Member]
Fair Value [Line Items]
Fair Value	$ 12.8	$ 13.1
Commercial Mortgage Backed [Member] | Discounted cash flow [Member] | Level 3 [Member] | Measurement Input, Discount For Above-market coupon [Member]
Fair Value [Line Items]
Small issue size	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]
Small issue size	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]
Small issue size	1.90%	1.90%
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]
Small issue size	3.10%	3.10%
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]
Small issue size	2.70%	2.70%
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]
Small issue size	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]
Small issue size	0.30%	0.30%

Pension and Other Postretirem_3

Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	$ 5.3	$ 4.9
Expected return on plan assets	(5.8)	(5.2)
Recognized net actuarial loss	2.8	2.5
Net periodic pension cost	2.3	2.2
Postretirement Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	0.1	0.1
Recognized net actuarial loss		0.1
Amortization of prior service cost		(0.1)
Net periodic pension cost	$ 0.1	$ 0.1

Other Comprehensive Income (Cha

Other Comprehensive Income (Changes in Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Equity [Abstract]
Unrealized gains (losses) arising during period, Pre-Tax	$ 152	$ (153.7)
Amount of realized gains (losses) from sales and other, Pre-Tax	0.3	0.2
Portion of other-than-temporary impairment losses recognized in earnings, Pre-Tax		0.5
Net unrealized gains (losses), Pre-Tax	152.3	(153)
Net change in net actuarial loss and prior service cost, Pre-Tax	2.9	(2.9)
Foreign currency translation recognized during the period, Pre-Tax	0.1	(0.6)
Other comprehensive (loss) income, Pre-Tax	155.3	(156.5)
Unrealized gains (losses) arising during period, Tax Benefit (Expense)	(32)	32.1
Amount of realized gains (losses) from sales and other, Tax Benefit (Expense)	(3.9)	(2.5)
Portion of other-than-temporary impairment losses recognized in earnings, Tax Benefit (Expense)		(0.1)
Net unrealized gains, Tax Benefit (Expense)	(35.9)	29.5
Net change in net actuarial loss and prior service cost, Tax Benefit (Expense)	(0.6)	0.6
Foreign currency translation recognized during the period, Tax Benefit (Expense)		0.1
Other comprehensive (loss) income, Tax Benefit (Expense)	(36.5)	30.2
Unrealized gains (losses) arising during period, Net of Tax	120	(121.6)
Amount of realized gains (losses) from sales and other, Net of Tax	(3.6)	(2.3)
Portion of other-than-temporary impairment losses recognized in earnings, Net of Tax		0.4
Total available-for-sale securities	116.4	(123.5)
Net change in net actuarial loss and prior service cost, Net of Tax	2.3	(2.3)
Foreign currency translation recognized during the period, Net of Tax	0.1	(0.5)
Total other comprehensive income (loss), net of tax	$ 118.8	$ (126.3)

Other Comprehensive Income (Rec

Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	$ (0.4)	$ 0.6
Net other–than–temporary impairment losses on investments recognized in earnings		(0.6)
Income from continuing operations before income taxes	148.6	59.1
Loss adjustment expenses and other operating expenses	(1,070.9)	(1,032.4)
Tax benefit	(26)	(8.6)
Continued operations; net of tax	122.6	50.5
Net of tax	122.4	67.7
Chaucer [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss adjustment expenses and other operating expenses		(216.5)
Discontinued operations - Chaucer business	(0.3)	17.3
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	1.3	(0.1)
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	(0.3)
Net other–than–temporary impairment losses on investments recognized in earnings		(0.6)
Income from continuing operations before income taxes	(0.3)	(0.6)
Tax benefit	3.9	2.7
Continued operations; net of tax	3.6	2.1
Net of tax	3.6	1.9
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member] | Chaucer [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - Chaucer business		(0.2)
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	(2.9)	(2.5)
Tax benefit	0.6	0.5
Continued operations; net of tax	$ (2.3)	$ (2)

Other Comprehensive Income (R_2

Other Comprehensive Income (Reclassifications out of Accumulated Other Comprehensive Income) (Parenthetical) (Details) - Defined Benefit Pension and Postretirement Plans [Member]	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Comprehensive Income (Loss) [Line Items]
Loss Adjustment Expense	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, 2019segment
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, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Operating revenues	$ 1,171.3	$ 1,114.4
Net realized and unrealized investment gains (losses)	48.2	(22.9)
Total revenues	1,219.5	1,091.5
Net investment income	70.2	66
Operating income (loss) before interest expense and income taxes	109.8	93.3
Interest on debt	(9.4)	(11.3)
Operating income before income taxes	100.4	82
Income from continuing operations before income taxes	148.6	59.1
Commercial Lines [Member]
Segment Reporting Information [Line Items]
Operating revenues	698.7	676.6
Underwriting income (loss)	36.7	16.3
Net investment income	44.3	45.3
Other income (expense)	(0.8)	(0.2)
Operating income (loss) before interest expense and income taxes	80.2	61.4
Personal Lines [Member]
Segment Reporting Information [Line Items]
Operating revenues	465.2	434.9
Underwriting income (loss)	5.7	14.6
Net investment income	19.7	18.4
Other income (expense)	1.4	1.3
Operating income (loss) before interest expense and income taxes	26.8	34.3
Other (including eliminations) [Member]
Segment Reporting Information [Line Items]
Operating revenues	7.4	2.9
Underwriting income (loss)	(0.3)	(1)
Net investment income	6.2	2.3
Other expense	(3.1)	(3.7)
Operating income (loss) before interest expense and income taxes	$ 2.8	$ (2.4)

Segment Information (Identifiab

Segment Information (Identifiable Assets by Business Segment) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Identifiable assets	$ 11,983.4	$ 12,399.7
Identifiable assets	103.6	103.9
Assets Held-for-Sale [Member]
Segment Reporting Information [Line Items]
Identifiable assets	23.6	57.4
Assets of Discontinued Operations [Member]
Segment Reporting Information [Line Items]
Identifiable assets	103.6	103.9
U.S. Companies [Member]
Segment Reporting Information [Line Items]
Identifiable assets	$ 11,856.2	$ 12,238.4

Stock-based Compensation (Narra

Stock-based Compensation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense, net of taxes	$ 3.3	$ 2
Market-based awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	23,924	29,715
Vesting period	3 years
Performance 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 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%
Market-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	5,820	3,115
Increase as grant in period, percentage	100.00%
Performance-based restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	0	0
Performance metric achieved	100.00%
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%
Chaucer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense, net of taxes		$ 0.4
2014 Stock Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant	3,506,780
ESPP Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant	2,369,081

Stock-based Compensation (Compe

Stock-based Compensation (Compensation Cost and Related Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based compensation expense	$ 4.2	$ 2.5
Tax benefit	(0.9)	(0.5)
Stock-based compensation expense, net of taxes	$ 3.3	$ 2

Stock-based Compensation (Summa

Stock-based Compensation (Summary of Stock Option Activity) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Shares
Outstanding, beginning of period, Shares	1,099,076	1,062,177
Granted, Shares	232,568	291,390
Exercised, Shares	(64,017)	(84,353)
Forfeited or cancelled, Shares	(3,141)	(50,491)
Outstanding, end of period, Shares	1,264,486	1,218,723
Weighted Average Exercise Price
Outstanding, beginning of period, Weighted Average Exercise Price	$ 85.75	$ 75.53
Granted, Weighted Average Exercise Price	95.05	110.58
Exercised, Weighted Average Exercise Price	75.98	70.31
Forfeited or cancelled, Weighted Average Exercise Price	95.39	88.48
Outstanding, end of period, Weighted Average Exercise Price	$ 87.93	$ 83.73

Stock-based Compensation (Sum_2

Stock-based Compensation (Summary of Restricted Stock Activity) (Details) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Time-Based Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning of period, Shares	332,481	298,528
Granted, Shares	144,072	131,290
Vested, Shares	(99,855)	(50,810)
Forfeited, Shares	(8,687)	(10,585)
Outstanding, end of period, Shares	368,011	368,423
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 97.28	$ 83.45
Granted, Weighted Average Grant Date Fair Value	117.51	110.60
Vested, Weighted Average Grant Date Fair Value	83.25	70.24
Forfeited, Weighted Average Grant Date Fair Value	97.14	87.47
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 109.01	$ 94.83
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	69,838	102,586
Granted, Shares	42,119	29,715
Vested, Shares	(10,089)	(14,032)
Forfeited, Shares		(7,625)
Outstanding, end of period, Shares	101,868	110,644
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 95.58	$ 81.21
Granted, Weighted Average Grant Date Fair Value	117.68	116.82
Vested, Weighted Average Grant Date Fair Value	82.74	70.24
Forfeited, Weighted Average Grant Date Fair Value		81.91
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 105.99	$ 92.12

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, 2019	Mar. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic shares used in the calculation of earnings per share	40.6	42.5
Diluted shares used in the calculation of earnings per share	41.2	43.1
Per share effect of dilutive securities on income from continuing operations and net income	$ (0.04)	$ (0.02)
Employee Stock Option [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of securities	0.3	0.3
Non-Vested Stock Grants [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of securities	0.3	0.3

Earnings Per Share and Shareh_4

Earnings Per Share and Shareholders' Equity Transactions (Narrative) (Details) - USD ($) shares in Millions	Jan. 02, 2019	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 30, 2018
Class Of Stock [Line Items]
Antidilutive securities excluded from calculation of earnings per share			0.2	0.3
Amount paid by company	$ 250,000,000
Initial delivery of shares of common stock received	1.8
Accelerated Share Repurchase Agreement [Member]
Class Of Stock [Line Items]
Shares repurchased under repurchase agreement, percentage	80.00%
Accelerated Share Repurchase Agreement [Member] | Scenario Forecast[Member]
Class Of Stock [Line Items]
Shares repurchased under repurchase agreement, percentage		20.00%
Maximum [Member] | Accelerated Share Repurchase Agreement [Member]
Class Of Stock [Line Items]
Repurchases common stock, authorized					$ 600,000,000

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, 2019	Mar. 31, 2018
Insurance [Abstract]
Gross loss and LAE reserves, beginning of period	$ 5,304.1	$ 5,058.5
Reinsurance recoverable on unpaid losses, beginning of period	1,472.6	1,455
Net loss and LAE reserves, beginning of period	3,831.5	3,603.5
Net incurred losses and LAE in respect of losses occurring in current year	712.8	677.4
Net incurred losses and LAE in respect of losses occurring in prior years	(13.2)	(6.5)
Total incurred losses and LAE	699.6	670.9
Net payments of losses and LAE in respect of losses occurring in Current year	175.3	181
Net payments of losses and LAE in respect of losses occurring in Prior years	459.1	425.5
Total payments	634.4	606.5
Net reserve for losses and LAE, end of period	3,896.7	3,667.9
Reinsurance recoverable on unpaid losses, end of Period	1,484.9	1,420
Gross reserve for losses and LAE, end of period	$ 5,381.6	$ 5,087.9

Liabilities For Outstanding C_4

Liabilities For Outstanding Claims, Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Insurance [Abstract]
(Favorable) unfavorable loss and LAE development	$ (13.2)	$ (6.5)

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details)	Dec. 11, 2009plaintiffclaim	Nov. 30, 2015claim	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Participant's retirement age			65 years
Number of plaintiffs | plaintiff	2
New claims	2	3
Claims Dismissed		2

Other Items - Additional Inform

Other Items - Additional Information (Details) $ in Millions	Jan. 02, 2019USD ($)
Federal Home Loan Banks [Abstract]
Prepayment fees	$ 26
FHLB Interest rate	5.50%
Repayment of FHLB advance	$ 125
FHLB due date	2029

Subsequent Events (Narrative) (

Subsequent Events (Narrative) (Details) $ in Millions	Apr. 10, 2019USD ($)
Australian Entities [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Cash proceeds to be received	$ 13