State Auto Financial (STFC) 10-Q 6 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 30, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
Document Transition Report	false
Entity File Number	000-19289
Entity Registrant Name	STATE AUTO FINANCIAL CORPORATION
Entity Central Index Key	0000874977
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	31-1324304
Entity Address, Address Line One	518 East Broad Street
Entity Address, State or Province	OH
Entity Address, City or Town	Columbus
Entity Address, Postal Zip Code	43215-3976
City Area Code	614
Local Phone Number	464-5000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding (shares)		44,223,498
NASDAQ/NGS (GLOBAL SELECT MARKET) [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common shares, without par value
Trading Symbol	STFC
Security Exchange Name	NASDAQ

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of State Auto Financial Corporation and Subsidiaries (“State Auto Financial” or the “Company”) have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by U.S. generally accepted accounting principles (“GAAP”) for complete financial statements. In the opinion of the Company, all adjustments (consisting of normal, recurring accruals) considered necessary for a fair statement have been included. Operating results for the three and six months ended June 30, 2021, are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. The balance sheet at December 31, 2020, has been derived from the audited financial statements at that date, but does not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 (the “2020 Form 10-K”). Capitalized terms used herein and not otherwise defined shall have the meaning ascribed to them in the 2020 Form 10-K. Adoption of Recent Accounting Pronouncements Income Taxes - Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12 which updated guidance for the accounting for income taxes. The updated guidance is intended to simplify the accounting for income taxes by removing several exceptions contained in existing guidance and amending other existing guidance to simplify several other income tax accounting matters. The guidance became effective for annual and interim reporting periods after December 15, 2020. On January 1, 2021, the Company adopted this guidance and it did not have a material impact on the Company's results of operations, consolidated financial position or cash flows. Pending Adoption of Recent Accounting Pronouncements For information regarding other accounting pronouncements that the Company has not yet adopted, see the “Pending Adoption of Recent Accounting Pronouncements” section of Note 1 of the Notes to Consolidated Financial Statements in the 2020 Form 10-K.

Contingencies and Litigation

Contingencies and Litigation	6 Months Ended
	Jun. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Litigation	Contingencies and LitigationIn accordance with the Contingencies Topic of the FASB's Accounting Standards Codification, the Company accrues for a litigation-related liability when it is probable that such a liability has been incurred and the amount can be reasonably estimated. The Company reviews all litigation on an ongoing basis when making accrual and disclosure decisions. For certain legal proceedings, the Company cannot reasonably estimate a loss or a range of loss, if any, particularly for proceedings that are in their early stages of development or where the plaintiffs seek indeterminate damages. Various factors, including, but not limited to, the outcome of potentially lengthy discovery and the resolution of important factual questions, may need to be determined before probability can be established or before a loss or range of loss can be reasonably estimated. If the loss contingency in question is not both probable and reasonably estimable, the Company does not establish an accrual and the matter will continue to be monitored for any developments that would make the loss contingency both probable and reasonably estimable. Based on currently available information known to the Company, it believes that its reserves for litigation-related liabilities are reasonable. However, in the event that a legal proceeding results in a substantial judgment against, or settlement by, the Company, there can be no assurance that any resulting liability or financial commitment would not have a material adverse effect on the financial condition, results of operations or cash flows of the consolidated financial statements of the Company. The Company is involved in lawsuits in the ordinary course of its business arising out of or otherwise related to its insurance policies. Additionally, from time to time the Company may be involved in lawsuits, including class actions, in the ordinary course of business but not arising out of or otherwise related to its insurance policies. Recently, these proceedings have included claims and lawsuits seeking coverage under commercial property policies for pure economic losses related to COVID-19. These lawsuits are in various stages of development, in various jurisdictions, and the Company intends to vigorously contest these matters. Based on currently available information, the Company does not believe that any such lawsuits will have a material adverse effect on its consolidated financial position, results of operations, or cash flows. However, the Company cannot provide assurance that it will not be negatively impacted by adverse legislation or adverse judicial rulings in some of these matters. Future court decisions and interpretations, as well as future changes, if any, in legislation could create uncertainties and additional liabilities may arise which could have a material adverse effect on the Company’s consolidated financial position, results of operations, or cash flows. Additionally, the Company may be impacted by adverse regulatory actions and adverse court decisions where insurance coverages are expanded beyond the scope originally contemplated in its insurance policies. The Company believes that the effects, if any, of such regulatory actions and published court decisions are not likely to have a material adverse effect on its consolidated financial position, results of operations or cash flows.

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost $2,134.9 and $2,117.0, respectively)	$ 2,214.9	$ 2,237.2
Equity securities	375.5	389.7
Other invested assets	79.6	71.1
Other invested assets, at cost	11.1	12.1
Notes receivable from affiliate	70	70
Total investments	2,751.1	2,780.1
Cash and cash equivalents	108.7	90.7
Accrued investment income and other assets	26.4	29.7
Premiums receivable	17.6	14
Deferred policy acquisition costs (affiliated net assumed $37.0 and $30.1, respectively)	127.2	122.2
Reinsurance recoverable on losses and loss expenses payable	19.7	24.3
Prepaid reinsurance premiums	8.8	8.3
Current federal income taxes	1.7	1.7
Net deferred federal income taxes	29	27.3
Property and equipment, at cost (net of accumulated depreciation of $3.5 and $3.5, respectively)	3.8	4.2
Total assets	3,094	3,102.5
Liabilities and Stockholders’ Equity
Losses and loss expenses payable (affiliated net assumed $441.9 and $438.8, respectively)	1,060.9	1,050.4
Unearned premiums (affiliated net assumed $494.7 and $452.4, respectively)	769.1	723.4
Notes payable (affiliates $15.3 and $15.3, respectively)	122.1	122.1
Pension and postretirement benefits	52.2	66.2
Due to affiliate	16.2	11.2
Other liabilities (affiliated net assumed $19.4 and $22.4, respectively)	95.2	119.2
Total liabilities	2,115.7	2,092.5
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 51.0 and 50.7 shares issued, respectively, at stated value of $2.50 per share	127.5	126.8
Treasury stock, 6.9 and 6.9 shares, respectively, at cost	(118.8)	(118.4)
Additional paid-in capital	213.1	213.3
Accumulated other comprehensive (loss) income	(13.3)	13.9
Retained earnings	769.8	774.4
Total stockholders’ equity	978.3	1,010
Total liabilities and stockholders’ equity	$ 3,094	$ 3,102.5

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fixed maturities, available-for-sale, amortized cost	$ 2,134.9	$ 2,117
Deferred policy acquisitions costs from affiliates	37	30.1
Losses and loss expenses payable, affiliates	441.9	438.8
Unearned premiums, affiliates	494.7	452.4
Notes payable, affiliates	15.3	15.3
Net Other Liabilities from Affiliates	$ 19.4	$ 22.4
Common stock, shares authorized (shares)	100	100
Common stock, shares issued (shares)	51	50.7
Common stock, stated value per share (usd per share)	$ 2.50	$ 2.50
Treasury stock (shares)	6.9	6.9
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ 3.5	$ 3.5
Class A Preferred Stock [Member]
Preferred stock, shares authorized (shares)	2.5	2.5
Class B Preferred Stock [Member]
Preferred stock, shares authorized (shares)	2.5	2.5

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Earned premiums (affiliated net assumed $71.9 and $115.3, respectively, and $251.1 and $349.0, respectively)	$ 369.9	$ 340.7	$ 725.8	$ 671.2
Net investment income (affiliate $1.3 and $1.3, respectively, and $3.7 and $3.7, respectively)	17.7	17.7	35.3	36.6
Net realized gains on investments:
Total net realized gains on investments	26.7	75.9	64.9	(59.3)
Other income from affiliates	0.4	0.5	0.9	1.1
Total revenues	414.7	434.8	826.9	649.6
Losses and loss expenses (affiliated net assumed $34.7 and $128.9, respectively, and $105.4 and $298.8, respectively)	299.8	271.2	580.6	510.6
Acquisition and operating expenses (affiliated net ceded $26.8 and affiliated net assumed $78.9, respectively, and $52.3 and $231.0, respectively)	107.2	119.5	228.2	234.4
Interest expense (affiliates $0.2 and $0.2, respectively, and $0.7 and $0.6, respectively)	1.1	1.3	2.2	2.5
Other Expenses	2.4	1.2	6.1	4.5
Costs and Expenses	410.5	393.2	817.1	752
Income before federal income taxes	4.2	41.6	9.8	(102.4)
Current Income Tax Expense (Benefit)	0	(0.4)	0	(0.4)
Deferred Income Tax Expense (Benefit)	3.6	7.7	5.6	(21.7)
Federal income tax expense	3.6	7.3	5.6	(22.1)
Net income	$ 0.6	$ 34.3	$ 4.2	$ (80.3)
Earnings (loss) per common share:
Basic (usd per share)	$ 0.01	$ 0.78	$ 0.10	$ (1.83)
Diluted (usd per share)	$ 0.01	$ 0.74	$ 0.09	$ (1.83)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Earned premiums, from affiliates	$ 92.2	$ 61.6	$ 170.2	$ 119.9
Net investment income, from affiliate	0.7	0.7	1.4	1.4
Losses and loss expenses, from affiliates	107.8	73.2	221.5	84.1
Net Acquisition and Operating Expenses, from affiliates	27	21	64.1	41.9
Interest Expense Debt To Affiliates	$ 0.1	$ 0.3	$ 0.3	$ 0.5

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 0.6	$ 34.3	$ 4.2	$ (80.3)
Net unrealized holding gains on fixed available-for-sale investments:
Unrealized holding (losses) gains	17.7	38.9	(39.5)	69.9
Reclassification adjustments for gains realized in net income	0.8	(1)	(0.7)	(3.4)
Income tax benefit (expense)	(3.9)	(7.9)	8.5	(13.9)
Total net unrealized holding (loss) gains on available-for-sale investments	14.6	30	(31.7)	52.6
Reclassification adjustments for amortization to statements of income:
Negative prior service cost	(1.6)	(1.6)	(3.2)	(3.2)
Net actuarial loss	4.4	3.6	8.9	7.3
Income tax expense	(0.6)	(0.4)	(1.2)	(0.9)
Total net unrecognized benefit plan obligations	2.2	1.6	4.5	3.2
Other comprehensive (loss) income	16.8	31.6	(27.2)	55.8
Comprehensive loss	$ 17.4	$ 65.9	$ (23)	$ (24.5)

Condensed Consolidated Statem_3

Condensed Consolidated Statement of Stockholders' Equity Statement - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Retained Earnings [Member]Cumulative Effect, Period of Adoption, Adjustment
Balance at beginning of year (shares) at Dec. 31, 2019		(50.4)	(6.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.3
Balance at end of year (shares) at Jun. 30, 2020		(50.7)	(6.9)
Balance at beginning of year at Dec. 31, 2019		$ (125.9)	$ (117.5)	$ (206.7)	$ 37.9	$ (782.7)
Balance at end of year at Jun. 30, 2020	$ (930.5)	(126.7)	(118.4)	(211.1)	(17.9)	(693.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.8		2.2
Shares acquired on stock award exercises and vested restricted shares			$ (0.9)
Stock awards granted				2.2
Change in net unrealized holding (losses) gains, net of tax	52.6				52.6
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	3.2				3.2
Net income (loss)	(80.3)					(80.3)
Cash dividends paid		$ (8.7)
Cumulative effect of change in accounting to establish an allowance for expected credit losses | Accounting Standards Update 2016-13							$ (0.5)
Balance at beginning of year (shares) at Mar. 31, 2020		(50.6)	(6.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.1
Balance at end of year (shares) at Jun. 30, 2020		(50.7)	(6.9)
Balance at beginning of year at Mar. 31, 2020		$ (126.5)	$ (118.4)	(209.1)	13.7	(663.2)
Balance at end of year at Jun. 30, 2020	(930.5)	(126.7)	(118.4)	(211.1)	(17.9)	(693.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.2		0.9
Shares acquired on stock award exercises and vested restricted shares			$ 0
Stock awards granted				1.1
Change in net unrealized holding (losses) gains, net of tax	30				30
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	1.6				1.6
Net income (loss)	$ 34.3					34.3
Cash dividends paid		$ (4.3)
Document Fiscal Year Focus	2021
Balance at beginning of year (shares) at Dec. 31, 2020		(50.7)	(6.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.3
Balance at end of year (shares) at Jun. 30, 2021		(51)	(6.9)
Balance at beginning of year at Dec. 31, 2020	$ (1,010)	$ (126.8)	$ (118.4)	(213.3)	(13.9)	(774.4)
Balance at end of year at Jun. 30, 2021	(978.3)	(127.5)	(118.8)	(213.1)	13.3	(769.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.7		1.4
Shares acquired on stock award exercises and vested restricted shares			$ (0.4)
Stock awards granted				(1.6)
Change in net unrealized holding (losses) gains, net of tax	(31.7)				(31.7)
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	4.5				4.5
Net income (loss)	4.2					4.2
Cash dividends paid		$ (8.8)
Cumulative effect of change in accounting to establish an allowance for expected credit losses | Accounting Standards Update 2016-13							$ 0
Balance at beginning of year (shares) at Mar. 31, 2021		(50.9)	(6.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.1
Balance at end of year (shares) at Jun. 30, 2021		(51)	(6.9)
Balance at beginning of year at Mar. 31, 2021		$ (127.4)	$ (118.9)	(220.1)	30.1	(773.5)
Balance at end of year at Jun. 30, 2021	(978.3)	(127.5)	(118.8)	(213.1)	13.3	(769.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.1		0.8
Shares acquired on stock award exercises and vested restricted shares			$ 0.1
Stock awards granted				$ (7.8)
Change in net unrealized holding (losses) gains, net of tax	14.6				14.6
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	2.2				$ 2.2
Net income (loss)	$ 0.6					$ 0.6
Cash dividends paid		$ (4.3)

Statement of Shareholders' Equi

Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Dividends paid per common share (usd per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20
Retained Earnings [Member]
Cash Dividends Paid to Affiliates	$ 2.6	$ 5.2	$ 5.2	$ 5.2

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net income (loss)	$ 4.2	$ (80.3)
Adjustments to reconcile net income (loss) to net cash used in operating activities
Depreciation and amortization, net	3.8	5.7
Share-based compensation	(1.5)	(0.5)
Net investment (gain) loss	(65.3)	59.3
Changes in operating assets and liabilities:
Deferred policy acquisition costs	(5)	(8.9)
Accrued investment income and other assets	3.3	0.6
Premiums receivables	(3.6)	(4.5)
Postretirement and pension benefits	(11.7)	(10.5)
Other liabilities and due to/from affiliates, net	(15.8)	(42)
Reinsurance recoverable on losses and loss expenses payable and prepaid reinsurance premiums	4.1	(23.8)
Losses and loss expenses payable	10.5	38.2
Unearned premiums	45.7	56.6
Excess Tax Benefit from Share-based Compensation, Operating Activities	(0.4)	(0.2)
Federal income taxes	6	(21.9)
Net cash used in operating activities	(25.7)	(32.2)
Cash flows from investing activities:
Purchases of fixed maturities available-for-sale	(359.4)	(280.8)
Purchases of equity securities	(12.9)	(42.7)
Purchases of other invested assets	(0.5)	(6.9)
Maturities, calls and pay downs of fixed maturities available-for-sale	203.3	186.7
Sales of fixed maturities available-for-sale	135.5	188.3
Sales of equity securities	83.5	30
Sales of other invested assets	1.3	0.6
Proceeds from Sale of Property, Plant, and Equipment	0	0.2
Net cash provided by investing activities	50.8	75.4
Cash flows from financing activities:
Proceeds from issuance of common stock	2.1	3
Payments to acquire treasury stock	(0.4)	(0.9)
Payment of dividends	(8.8)	(8.7)
Proceeds from short-term debt	0	60
Net cash (used in) provided by financing activities	(7.1)	53.4
Net increase in cash and cash equivalents	18	96.6
Cash and cash equivalents at beginning of period	90.7	78
Cash and cash equivalents at end of period	108.7	174.6
Supplemental disclosures:
Interest Paid, Excluding Capitalized Interest, Operating Activities	$ 2.2	$ 2.3

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Cash Flows [Abstract]
Interest Expense Debt To Affiliates	$ 0.1	$ 0.3	$ 0.3	$ 0.5

Investments

Investments	6 Months Ended
	Jun. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	Investments The following tables set forth the amortized cost and fair value of investments by investment category at June 30, 2021 and December 31, 2020: ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value June 30, 2021 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 461.6 $ 26.9 $ (0.1) $ 488.4 Obligations of states and political subdivisions 473.1 25.6 (0.1) 498.6 Corporate securities 457.7 18.3 (0.3) 475.7 U.S. government agencies mortgage-backed securities 742.5 16.6 (6.9) 752.2 Total available-for-sale fixed maturities $ 2,134.9 $ 87.4 $ (7.4) $ 2,214.9 ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 506.5 $ 45.2 $ — $ 551.7 Obligations of states and political subdivisions 511.3 30.4 (0.2) 541.5 Corporate securities 459.9 23.4 — 483.3 U.S. government agencies mortgage-backed securities 639.3 22.9 (1.5) 660.7 Total available-for-sale fixed maturities $ 2,117.0 $ 121.9 $ (1.7) $ 2,237.2 The following tables set forth the Company’s gross unrealized losses and fair value on its investments by lot, aggregated by investment category and length of time for individual securities that have been in a continuous unrealized loss position for which an allowance for credit losses has not been recorded at June 30, 2021 and December 31, 2020: ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions June 30, 2021 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 71.1 $ (0.1) 12 $ — $ — — $ 71.1 $ (0.1) 12 Obligations of states and political subdivisions 3.8 (0.1) 1 — — — 3.8 (0.1) 1 Corporate securities 42.5 (0.3) 9 — — — 42.5 (0.3) 9 U.S. government agencies mortgage-backed securities 320.5 (6.9) 72 8.4 — 5 328.9 (6.9) 77 Total temporarily impaired securities $ 437.9 $ (7.4) 94 $ 8.4 $ — 5 $ 446.3 $ (7.4) 99 ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions December 31, 2020 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 9.6 $ — 4 $ — $ — — $ 9.6 $ — 4 Obligations of states and political subdivisions 19.5 (0.2) 5 — — — 19.5 (0.2) 5 Corporate securities 1.5 — 2 — — — 1.5 — 2 U.S. government agencies mortgage-backed securities 136.1 (1.4) 35 7.0 (0.1) 3 143.1 (1.5) 38 Total temporarily impaired securities $ 166.7 $ (1.6) 46 $ 7.0 $ (0.1) 3 $ 173.7 $ (1.7) 49 The Company reviewed its available-for-sale fixed maturities at June 30, 2021, and determined that no credit impairment existed in the gross unrealized holding losses, due to the reasons discussed below: • U.S. treasury securities and obligations of U.S. government agencies: These securities were issued by the U.S. Treasury Department or Federal government-sponsored entities. The decline in fair values was attributable to changes in interest rates and not credit quality. The Company does not intend to sell these securities and it is likely that it will not do so before their anticipated recovery. Therefore, the Company does not consider these impaired securities. • Corporate securities: Corporations in various industries issued these securities. The decline in fair values was attributable to changes in interest rates and not credit quality. The Company reviewed the issuers of these securities to identify any significant adverse change in financial condition, a change in the quality of credit enhancement (if any), a ratings decrease, or negative outlook assignment from a major credit rating agency, and any failure to make interest or principal payments. After these reviews, the Company determined that the decline in fair values was attributable to changes in interest rates and not credit quality. The Company does not intend to sell these securities and it is likely that it will not do so before their anticipated recovery. Therefore, the Company does not consider these impaired securities. • U.S. government agencies mortgage-backed securities: Federal government-sponsored entities issued these securities. The decline in fair values was attributable to changes in interest rates and not credit quality. The Company does not intend to sell these securities and it is likely that it will not do so before their anticipated recovery. Therefore, the Company does not consider these impaired securities. The Company regularly monitors its available-for-sale fixed maturities that have fair values less than cost or amortized cost for signs of impairment, an assessment that requires significant management judgment regarding the evidence known. Such judgments could change in the future as more information becomes known, which could negatively impact the amounts reported. Among the factors that management considers for fixed maturity securities are the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. When a fixed maturity has been determined to have an impairment, the impairment charge representing the credit loss is recognized in earnings as a realized loss and on the balance sheet as an allowance for credit losses netted with the amortized cost of fixed maturities. Future increases in fair value, if related to credit factors, are recognized through earnings limited to the amount previously recognized as an allowance for credit losses. The amount related to non-credit factors is recognized in accumulated other comprehensive income and future increases or decreases in fair value, if not credit losses, are included in accumulated other comprehensive income. The following table sets forth the amortized cost and fair value of available-for-sale fixed maturities by contractual maturity at June 30, 2021: ($ millions) Amortized cost Fair Due in 1 year or less $ 135.7 $ 136.8 Due after 1 year through 5 years 571.0 596.8 Due after 5 years through 10 years 154.8 162.2 Due after 10 years 530.9 566.9 U.S. government agencies mortgage-backed securities 742.5 752.2 Total $ 2,134.9 $ 2,214.9 Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay the obligations with or without call or prepayment penalties. At June 30, 2021, State Auto P&C had U.S. government agencies mortgage-backed fixed maturity securities, with a carrying value of approximately $106.5 million pledged as collateral for loans from the Federal Home Loan Bank of Cincinnati ("FHLB"). In accordance with the terms of the FHLB Loans, State Auto P&C retains all rights regarding these pledged securities. At June 30, 2021, State Auto P&C had fixed maturities with fair values of approximately $32.9 million pledged as collateral for the performance obligations under its reinsurance agreement with Home State County Mutual Insurance Company. In accordance with the terms of the trust agreement, State Auto P&C retains all rights regarding these securities, which are included in the “U.S. treasury securities and obligations of U.S. government agencies” classification of the Company’s fixed maturity securities portfolio. Fixed maturities with fair values of $9.6 million and $9.7 million were on deposit with insurance regulators as required by law at June 30, 2021, and December 31, 2020, respectively. The Company retains all rights regarding these securities. The following table sets forth the components of net investment income for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Fixed maturities $ 15.4 $ 14.5 $ 30.8 $ 29.6 Equity securities 1.2 2.6 2.8 5.7 Cash and cash equivalents, and other 1.1 0.8 2.0 1.8 Investment income 17.7 17.9 35.6 37.1 Investment expenses — 0.2 0.3 0.5 Net investment income $ 17.7 $ 17.7 $ 35.3 $ 36.6 The Company’s current investment strategy does not rely on the use of derivative financial instruments. Proceeds on sales of investments were $220.3 million and $218.9 million for the six months ended June 30, 2021, and 2020, respectively. The following table sets forth the realized and unrealized holding gains (losses) on the Company’s investment portfolio for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Investment gain (loss), net: Fixed maturities: Realized gains on sales of securities $ 0.9 $ 1.9 $ 3.9 $ 5.5 Realized losses on sales of securities (1.7) (0.9) (3.2) (2.1) Net (loss) gain on fixed securities (0.8) 1.0 0.7 3.4 Net gain (loss) on equity securities 24.9 69.1 56.4 (53.3) Net gain (loss) on other invested assets 3.0 5.8 8.2 (9.6) Other net realized (loss)/gain (0.4) — (0.4) 0.2 Net gain (loss) on investments $ 26.7 $ 75.9 $ 64.9 $ (59.3) Change in net unrealized holding gains (losses), net of tax Fixed maturities $ 18.5 $ 37.9 $ (40.2) $ 66.5 Deferred federal income tax (liability) benefit (3.9) (7.9) 8.5 (13.9) Change in net unrealized holding gains (losses), net of tax $ 14.6 $ 30.0 $ (31.7) $ 52.6 The unrealized holding gains recognized for the three and six months ended June 30, 2021 on equity securities still held were $19.8 million and $46.1 million, respectively. The unrealized holding gains/(losses) recognized for the three and six months ended June 30, 2020 on equity securities still held were $78.6 million and $(44.7) million, respectively. The unrealized holding gains recognized for the three and six months ended June 30, 2021 on other invested assets still held were $3.0 million and $8.2 million, respectively. The unrealized holding gains/(losses) recognized for the three and six months ended June 30, 2020 on other invested assets still held were $5.8 million and $(9.6) million, respectively.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments Below is the fair value hierarchy that categorizes into three levels the inputs to valuation techniques that are used to measure fair value: • Level 1 includes observable inputs which reflect quoted prices for identical assets or liabilities in active markets at the measurement date. • Level 2 includes observable inputs for assets or liabilities other than quoted prices included in Level 1, and it includes valuation techniques which use prices for similar assets and liabilities. • Level 3 includes unobservable inputs which reflect the reporting entity’s estimates of the assumptions that market participants would use in pricing the asset or liability (including assumptions about risk). The Company utilizes a nationally recognized third party pricing service to estimate the majority of its investment portfolio’s fair value. The Company obtains one price per security and the processes and control procedures employed by the Company are designed to ensure the value is accurately recorded on an unadjusted basis. Through discussions with the pricing service, the Company gains an understanding of the methodologies used to price the different types of securities, that the data and the valuation methods utilized are appropriate and consistently applied, and that the assumptions are reasonable and representative of fair value. To validate the reasonableness of the valuations obtained from the pricing service, the Company compares to fair value pricing information gathered from other independent pricing sources. At June 30, 2021, and December 31, 2020, the Company did not adjust any of the prices received from the pricing service. Fixed Maturities The Company utilizes a nationally recognized third party pricing service to estimate fair value measurements for the majority of its fixed maturities. The fair value estimate of the Company’s fixed maturity investments are determined by evaluations that are based on observable market information rather than market quotes. Inputs to the evaluations include, but are not limited to, market prices from recently completed transactions and transactions of comparable securities, interest rate yield curves, credit spreads, and other market-observable information. The fixed maturity portfolio pricing obtained from the pricing service is reviewed for reasonableness. The Company regularly selects a sample of security prices which are compared to one or more alternative pricing sources for reasonableness. Any significant discrepancies with the pricing are returned to the pricing service for further explanation and, if necessary, adjustments are made. To date, the Company has not identified any significant discrepancies in the pricing provided by its third party pricing service. Investments valued using these inputs include U.S. treasury securities and obligations of U.S. government agencies, obligations of states and political subdivisions, corporate securities (except for a security discussed below), and U.S. government agencies' mortgage-backed securities. All unadjusted estimates of fair value for fixed maturities priced by the pricing service are included in the amounts disclosed in Level 2 of the hierarchy. If market inputs are unavailable, then no fair value is provided by the pricing service. For these securities, fair value is determined either by requesting brokers who are knowledgeable about these securities to provide a quote; or the Company internally determines the fair values by employing widely accepted pricing valuation models, and depending on the level of observable market inputs, renders the fair value estimate as Level 2 or Level 3. Equities The fair value of each equity security is based on an observable market price for an identical asset in an active market and is priced by the same pricing service discussed above. All equity securities are recorded using unadjusted market prices and have been disclosed in Level 1. Other Invested Assets Included in other invested assets is one international fund (“the fund”) that invests in equity securities of foreign issuers and is managed by a third party investment manager. The fund had a fair value of $63.0 million and $55.8 million at June 30, 2021, and December 31, 2020, respectively, which was determined using the fund’s net asset value. The Company employs procedures to assess the reasonableness of the fair value of the fund, including obtaining and reviewing the fund’s audited financial statements. There are no unfunded commitments related to the fund. The Company may not sell its investment in the fund; however, the Company may redeem all or a portion of its investment in the fund at net asset value per share with the appropriate prior written notice. In accordance with ASC 820-10, this investment is measured at fair value using the net asset value per share practical expedient and has not been classified in the fair value hierarchy. Fair values presented here are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated balance sheets. The remainder of the Company’s other invested assets consist primarily of holdings in publicly-traded mutual funds. The Company believes that its prices for these publicly-traded mutual funds, which are each based on an observable market price for an identical asset in an active market reflect their fair values and consequently these securities have been disclosed in Level 1. The following tables set forth the Company’s investments within the fair value hierarchy at June 30, 2021 and December 31, 2020: ($ millions) Total Level 1 Level 2 June 30, 2021 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 488.4 $ — $ 488.4 Obligations of states and political subdivisions 498.6 — 498.6 Corporate securities 475.7 — 475.7 U.S. government agencies mortgage-backed securities 752.2 — 752.2 Total available-for-sale fixed maturities 2,214.9 — 2,214.9 Equity securities: Large-cap securities 158.6 158.6 — Mutual and exchange traded funds 216.9 216.9 — Total equity securities 375.5 375.5 — Other invested assets 16.6 16.6 — Total investments $ 2,607.0 $ 392.1 $ 2,214.9 ($ millions) Total Level 1 Level 2 December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 551.7 $ — $ 551.7 Obligations of states and political subdivisions 541.5 — 541.5 Corporate securities 483.3 — 483.3 U.S. government agencies mortgage-backed securities 660.7 — 660.7 Total available-for-sale fixed maturities 2,237.2 — 2,237.2 Equity securities: Large-cap securities 134.2 134.2 — Mutual and exchange traded funds 255.5 255.5 — Total equity securities 389.7 389.7 — Other invested assets 15.3 15.3 — Total investments $ 2,642.2 $ 405.0 $ 2,237.2 The following sections describe the valuation methods used by the Company for each type of financial instrument it holds that is not measured at fair value but for which fair value is disclosed: Financial Instruments Disclosed, But Not Carried, At Fair Value Other Invested Assets, at Cost Included in other invested assets, at cost are common stock of the FHLB and the Trust Securities. The Trust Securities and FHLB common stock are carried at cost, which approximates fair value. The fair value of the FHLB common stock at June 30, 2021, was $10.6 million and the fair value of the Trust Securities was $0.5 million. The investments have been placed in Level 3 of the fair value hierarchy. Notes Receivable from Affiliate The Company has two separate credit agreements with State Automobile Mutual Insurance Company (“State Auto Mutual") pursuant to which it loaned State Auto Mutual a total of $70.0 million at an interest rate of 4.05%, with principal payable in May 2029. The Company estimates the fair value of the notes receivable from affiliate using market quotations for U.S. treasury securities with similar maturity dates and applies an appropriate credit spread. Consequently this has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) June 30, 2021 December 31, 2020 Carrying value Fair value Interest rate Carrying value Fair Interest rate Notes receivable from affiliate, issued May 2019 $ 70.0 $ 76.9 4.05 % $ 70.0 $ 80.4 4.05 % Notes Payable Included in notes payable are the FHLB Loans and Subordinated Debentures. The Company estimates the fair value of the FHLB Loans by discounting cash flows using a borrowing rate currently available to the Company for loans with similar terms. The FHLB Loans have been placed in Level 3 of the fair value hierarchy. The carrying amount of the Subordinated Debentures approximates its fair value as the interest rate adjusts quarterly and has been disclosed in Level 3. ($ millions, except interest rates) June 30, 2021 December 31, 2020 Carrying value Fair Value Interest rate Carrying value Fair value Interest rate FHLB Loan due 2030: issued $21.5, September 2020 with fixed interest $ 21.5 $ 20.8 1.37 % $ 21.5 $ 21.6 1.37 % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 103.7 3.96 % 85.3 107.1 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.3 15.3 4.33 % 15.3 15.3 4.43 % Total notes payable $ 122.1 $ 139.8 $ 122.1 $ 144.0

Deferred Acquisition Costs Defe

Deferred Acquisition Costs Deferred Acquisition Costs	6 Months Ended
	Jun. 30, 2021
Deferred Policy Acquisition Costs Disclosures [Abstract]
Deferred Policy Acquisition Costs [Text Block]	Deferred Acquisition Costs The following table sets forth net deferred acquisition costs for the three and six months ended June 30, 2021 and 2020: ($ millions) 2021 2020 Beginning balance at April 1 $ 121.2 $ 113.3 Acquisition costs deferred 68.4 100.3 Acquisition costs amortized to expense (62.4) (93.6) Ending balance at June 30 $ 127.2 $ 120.0 Beginning balance at January 1 $ 122.2 $ 111.1 Acquisition costs deferred 129.0 191.4 Acquisition costs amortized to expense (124.0) (182.5) Ending balance at June 30 $ 127.2 $ 120.0

Losses and Loss Expenses Payabl

Losses and Loss Expenses Payable Losses and Loss Expenses Payable	6 Months Ended
	Jun. 30, 2021
Losses and Loss Expenses Payable [Abstract]
Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block]	. Losses and Loss Expenses Payable The following table sets forth the activity in the liability for losses and loss expenses for the six months ended June 30, 2021 and 2020: ($ millions) 2021 2020 Losses and loss expenses payable, at beginning of period $ 1,050.4 $ 1,066.5 Less: reinsurance recoverable on losses and loss expenses payable 24.3 13.6 Net balance at beginning of period 1,026.1 1,052.9 Incurred related to: Current year 624.1 518.2 Prior years (43.5) (7.6) Total incurred 580.6 510.6 Paid related to: Current year 303.1 228.9 Prior years 262.4 265.7 Total paid 565.5 494.6 Net balance at end of period 1,041.2 1,068.9 Plus: reinsurance recoverable on losses and loss expenses payable 19.7 36.4 Losses and loss expenses payable, at end of period $ 1,060.9 $ 1,105.3 The Company recorded more favorable development related to prior years’ loss and loss expense reserves for the six months ended June 30, 2021, of $43.5 million compared to $7.6 million for the same 2020 period. Favorable development of prior accident years' non-catastrophe loss and ALAE reserves for the six months ended June 30, 2021 was $40.5 million, driven by favorable development of $38.5 million in the commercial insurance segment. In the commercial insurance segment, all products developed favorably, with workers' compensation and middle market commercial contributing $15.4 million and $13.5 million, respectively. For the six months ended June 30, 2020, favorable development of prior accident year's non-catastrophe loss and ALAE reserves was $12.5 million, due to favorable development in the commercial insurance segment. In the commercial insurance segment, all lines contributed favorable development, with small commercial package, workers' compensation and middle market commercial contributing $9.0 million, $8.8 million and $8.0 million respectively. Partially offsetting the favorable development was adverse development in the personal insurance segment and specialty run-off, which contributed $12.1 million and $6.1 million, respectively. The adverse development in the personal insurance segment was primarily driven by personal auto, which contributed $11.1 million of adverse development. The personal auto adverse development was driven by higher than expected severity of bodily injury claims and higher than expected frequency of property damage claims, primarily from the 2019 accident year. The specialty run-off adverse development primarily relates to an adverse court decision relating to an E&S casualty claim from 2016.

Reinsurance

Reinsurance	6 Months Ended
	Jun. 30, 2021
Insurance [Abstract]
Reinsurance	ReinsuranceThe insurance subsidiaries of State Auto Financial, referred to as the STFC Pooled Companies, participate in a quota share reinsurance pooling arrangement (“the Pooling Arrangement”) with the Mutual Pooled Companies. The following table sets forth a summary of the Company’s external reinsurance transactions, as well as reinsurance transactions with State Auto Mutual under the Pooling Arrangement, for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Premiums earned: Assumed from external insurers and reinsurers $ 20.2 $ 20.7 $ 42.0 $ 41.3 Assumed under Pooling Arrangement 369.9 340.7 725.8 671.2 Ceded to external insurers and reinsurers (8.5) (7.1) (17.5) (17.7) Ceded under Pooling Arrangement (277.7) (279.1) (555.6) (551.3) Net assumed premiums earned $ 103.9 $ 75.2 $ 194.7 $ 143.5 Losses and loss expenses incurred: Assumed from external insurers and reinsurers $ 21.6 $ 15.5 $ 36.1 $ 27.2 Assumed under Pooling Arrangement 299.8 271.2 580.6 510.6 Ceded to external insurers and reinsurers (3.0) (12.5) (6.3) (46.0) Ceded under Pooling Arrangement (192.0) (198.0) (359.1) (426.5) Net assumed losses and loss expenses incurred $ 126.4 $ 76.2 $ 251.3 $ 65.3

Notes Payable and Open Line of

Notes Payable and Open Line of Credit Notes Payable and Open Line of Credit	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Notes Payable and Open Line of Credit	7. Notes Payable and Open Line of Credit FHLB Loans State Auto P&C has an Open Line of Credit Commitment (the "OLC") with the FHLB that provides State Auto P&C with a $100.0 million one State Auto P&C also has a fifteen-year term loan and a ten-year term loan with the FHLB that are more fully disclosed in Note 10 of the Notes to Condensed Consolidated Financial Statements in the 2020 Form 10-K. The foregoing OLC and term loans from the FHLB are collectively referred to as the "FHLB Loans".

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table sets forth the reconciliation between actual federal income tax expense and the amount computed at the indicated statutory rate for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Amount at statutory rate $ 0.9 21.0 % $ 8.7 21.0 % $ 2.1 21.0 % $ (21.5) 21.0 % Tax-exempt interest and dividends received deduction (0.6) (14.2) (0.4) (0.9) (1.2) (12.6) (1.1) 1.1 Other, net 3.3 78.0 (1.0) (2.5) 4.7 48.6 0.5 (0.5) Federal income tax expense (benefit) $ 3.6 84.8 % $ 7.3 17.6 % $ 5.6 57.0 % $ (22.1) 21.6 %

Pension and Postretirement Bene

Pension and Postretirement Benefit Plans	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Pension and Postretirement Benefit Plans	Pension and Postretirement Benefit Plans The following table sets forth information regarding the Company’s share of pension and postretirement benefit plans’ components of net periodic cost for the three and six months ended June 30, 2021 and 2020: ($ millions) Pension Postretirement Pension Postretirement Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $ 1.2 $ 1.2 $ — $ — $ 2.5 $ 2.4 $ — $ — Interest cost 2.1 2.4 0.1 0.1 4.2 4.8 0.1 0.2 Expected return on plan assets (4.2) (4.3) — — (8.5) (8.7) — — Amortization of: Negative prior service cost — — (1.4) (1.3) — — (2.8) (2.7) Net actuarial loss/(gain) 3.5 2.3 (0.1) — 7.0 4.6 (0.1) 0.1 Net periodic cost (benefit) $ 2.6 $ 1.6 $ (1.4) $ (1.2) $ 5.2 $ 3.1 $ (2.8) $ (2.4) The Company contributed $10.0 million to its pension plan for the six months ended June 30, 2021 and expects to contribute an additional $5.0 million to its pension plan during 2021.

Other Comprehensive Income and

Other Comprehensive Income and Accumulated Other Comprehensive Income	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Other Comprehensive Income and Accumulated Other Comprehensive Income	Other Comprehensive Income (Loss) and Accumulated Other Comprehensive (Loss) Income The following tables set forth the changes in the Company’s accumulated other comprehensive (loss) income ("AOC(L)I"), net of tax, for the three and six months ended June 30, 2021 and 2020: ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at April 1, 2021 $ 51.2 $ (81.3) $ (30.1) Other comprehensive loss before reclassifications 14.0 — 14.0 Amounts reclassified from AOCI (a) 0.6 2.2 2.8 Net current period other comprehensive (loss) income 14.6 2.2 16.8 Ending balance at June 30, 2021 $ 65.8 $ (79.1) $ (13.3) Beginning balance at April 1, 2020 $ 63.0 $ (76.7) $ (13.7) Other comprehensive income before reclassifications 30.8 — 30.8 Amounts reclassified from AOCI (a) (0.8) 1.6 0.8 Net current period other comprehensive income 30.0 1.6 31.6 Ending balance at June 30, 2020 $ 93.0 $ (75.1) $ 17.9 (a) See separate table below for details about these reclassifications ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at January 1, 2021 $ 97.5 $ (83.6) $ 13.9 Other comprehensive income before reclassifications (31.1) — (31.1) Amounts reclassified from AOCI (a) (0.6) 4.5 3.9 Net current period other comprehensive income (31.7) 4.5 (27.2) Ending balance at June 30, 2021 $ 65.8 $ (79.1) $ (13.3) Beginning balance at January 1, 2020 $ 40.4 $ (78.3) $ (37.9) Other comprehensive loss before reclassifications 55.3 — 55.3 Amounts reclassified from AOCI (a) (2.7) 3.2 0.5 Net current period other comprehensive income 52.6 3.2 55.8 Ending balance at June 30, 2020 $ 93.0 $ (75.1) $ 17.9 (a) See separate table below for details about these reclassifications The following tables set forth the reclassifications out of accumulated other comprehensive (loss) income, by component, to the Company’s condensed consolidated statement of income for the three and six months ended June 30, 2021 and 2020: ($ millions) Details about Accumulated Other Three months ended June 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2021 2020 Unrealized gains on available-for-sale fixed maturity investments $ (0.8) $ 1.0 Realized gain on sale of securities (0.8) 1.0 Total before tax 0.2 (0.2) Tax expense (0.6) 0.8 Net of tax Amortization of benefit plan items Negative prior service cost 1.6 1.6 (b) Net actuarial loss (4.4) (3.6) (b) (2.8) (2.0) Total before tax 0.6 0.4 Tax benefit (2.2) (1.6) Net of tax Total reclassifications for the period $ (2.8) $ (0.8) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details). ($ millions) Details about Accumulated Other Six months ended June 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2021 2020 Unrealized gains on available-for-sale fixed maturity investments $ 0.7 $ 3.4 Realized gains on sale of securities 0.7 3.4 Total before tax (0.1) (0.7) Tax expense 0.6 2.7 Net of tax Amortization of benefit plan items Negative prior service cost 3.2 3.2 (b) Net actuarial loss (8.9) (7.3) (b) (5.7) (4.1) Total before tax 1.2 0.9 Tax benefit (4.5) (3.2) Net of tax Total reclassifications for the period $ (3.9) $ (0.5) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details).

Earnings per Common Share

Earnings per Common Share	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Earnings (Loss) per Common Share	Net Earnings (Loss) per Common Share The following table sets forth the compilation of basic and diluted earnings (loss) per common share for the three and six months ended June 30, 2021 and 2020: ($ and shares in millions, except per share amounts) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Numerator: Net income (loss) for basic earnings (loss) per common share $ 0.6 $ 34.3 $ 4.2 $ (80.3) Effect of dilutive share-based awards — (1.6) — — Adjusted net income (loss) for diluted earnings (loss) per common share $ 0.6 $ 32.7 $ 4.2 $ (80.3) Denominator: Weighted average shares for basic earnings (loss) per common share 44.0 43.8 44.0 43.7 Effect of dilutive share-based awards 0.8 0.3 0.6 — Adjusted weighted average shares for diluted earnings (loss) per common share 44.8 44.1 44.6 43.7 Basic net earnings (loss) per common share $ 0.01 $ 0.78 $ 0.10 $ (1.83) Diluted net earnings (loss) per common share $ 0.01 $ 0.74 $ 0.09 $ (1.83) The following table sets forth stock awards and restricted share units ("RSU award") of the Company that were not included in the computation of diluted earnings (loss) per common share because the exercise price of the awards was greater than the average market price or their inclusion would have been antidilutive for the six months ended June 30, 2021 and 2020: (shares in millions) Six months ended June 30 2021 2020 Total number of antidilutive awards — 0.4

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Segment Information	Segment Information The Company's reportable segments are: personal insurance, commercial insurance, and investment operations. The reportable insurance segments are business units managed separately because of the differences in the type of customers they serve, the products they provide or services they offer. The insurance segments market a broad line of property and casualty insurance products throughout the United States through independent insurance agencies, which include retail agents and wholesale brokers. The investment operations segment, managed by Stateco, provides investment services. The Company evaluates the performance of its insurance segments using industry financial measurements based on Statutory Accounting Practices (“SAP”), which include loss and loss adjustment expense ratios, underwriting expense ratios, combined ratios, statutory underwriting gain (loss), net premiums earned and net written premiums. One of the most significant differences between SAP and GAAP is that SAP requires all underwriting expenses to be expensed immediately and not deferred and amortized over the same period the premium is earned. The investment operations segment is evaluated based on investment returns of assets managed by Stateco. Asset information by segment is not reported for the insurance segments because the Company does not produce such information internally. The following table sets forth financial information regarding the Company’s reportable segments and specialty run-off (for the previously exited specialty insurance business) for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Revenue from external sources: Insurance operations Personal insurance $ 213.1 $ 202.8 $ 420.9 $ 400.9 Commercial insurance 157.6 137.9 306.3 270.3 Specialty run-off (0.8) — (1.4) — Total insurance operations 369.9 340.7 725.8 671.2 Investment operations Net investment income 17.7 17.7 35.3 36.6 Net investment gain (loss) 26.7 75.9 64.9 (59.3) Total investment operations 44.4 93.6 100.2 (22.7) All other 0.4 0.5 0.9 1.1 Total revenue from external sources 414.7 434.8 826.9 649.6 Intersegment revenue 1.6 1.5 3.2 3.1 Total revenue 416.3 436.3 830.1 652.7 Reconciling items: Eliminate intersegment revenue (1.6) (1.5) (3.2) (3.1) Total consolidated revenues $ 414.7 $ 434.8 $ 826.9 $ 649.6 Segment income (loss) before federal income tax: Insurance operations SAP underwriting (loss) gain Personal insurance $ (44.2) $ (40.4) $ (93.6) $ (40.1) Commercial insurance 2.8 (12.4) 5.8 (42.4) Specialty run-off (1.4) (6.3) 0.2 (6.7) Total insurance operations (42.8) (59.1) (87.6) (89.2) Investment operations Net investment income 17.7 17.7 35.3 36.6 Net investment gain (loss) 26.7 75.9 64.9 (59.3) Total investment operations 44.4 93.6 100.2 (22.7) All other — — — 0.1 Total segment income (loss) before reconciling items 1.6 34.5 12.6 (111.8) Reconciling items: GAAP expense adjustments 5.7 8.7 4.4 14.6 Interest expense on corporate debt (1.1) (1.3) (2.2) (2.5) Corporate expenses (2.0) (0.3) (5.0) (2.7) Total reconciling items 2.6 7.1 (2.8) 9.4 Total consolidated income (loss) before federal income tax $ 4.2 $ 41.6 $ 9.8 $ (102.4) Investable assets attributable to the Company’s investment operations segment totaled $2,859.8 million and $2,870.8 million at June 30, 2021, and December 31, 2020, respectively.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events The Company has evaluated all events occurring after June 30, 2021 through August 6, 2021, the date the interim unaudited financial statements for the period ending June 30, 2021 were available to be issued, to determine whether any event required either recognition or disclosure in the financial statements. Merger Agreement On July 12, 2021, the Company and State Automobile Mutual Insurance Company, an Ohio mutual insurance company and the owner of approximately 58.8% of the Company’s issued and outstanding common stock as of the date thereof (“SAM” or “State Auto Mutual”), entered into an Agreement and Plan of Merger and Combination (the “Merger Agreement”) with Liberty Mutual Holding Company Inc., a Massachusetts mutual holding company (“LMHC”), Pymatuning, Inc., an Ohio corporation and wholly-owned indirect subsidiary of LMHC (“Merger Sub I”), and Andover, Inc., an Ohio corporation and wholly-owned direct subsidiary of LMHC (“Merger Sub II”). The Merger Agreement provides for SAM to reorganize (in accordance with all applicable provisions of Sections 3913.25 to 3913.38 of the Ohio Revised Code) pursuant to a Plan of Reorganization (the “Plan of Reorganization”) adopted by the board of directors of SAM (the “SAM Board”), which reorganization shall be effectuated through a merger (pursuant to Section 3913.32(A) and Section 1702.411 of the Ohio Revised Code and Section 19T(b)(ii) of Chapter 175 of the Massachusetts General Laws) of Merger Sub II with and into SAM, with SAM surviving such merger as an Ohio domiciled reorganized stock insurance subsidiary of LMHC (SAM, as so reorganized, “Reorganized SAM”) and LMHC granting equity rights in LMHC to each SAM member upon the extinguishment of such SAM member’s equity rights in SAM at the effective time of such merger (the foregoing components of one simultaneous transaction, collectively, the “SAM Transaction”). Simultaneously with the SAM Transaction, the Merger Agreement provides for LMHC to effect the acquisition of the Company through the merger of Merger Sub I with and into the Company (the “Merger”) with the Company surviving the Merger as the surviving corporation (the Merger, together with the SAM Transaction, the “Transactions”). The completion of the Transactions is subject to the satisfaction or waiver of certain customary conditions, including, among others: (i) the adoption of the Merger Agreement by the Company’s shareholders (the “Company Shareholder Approval”); (ii) approval by the members of SAM of the Plan of Reorganization and the proposed articles of incorporation and code of regulations for Reorganized SAM (the “SAM Member Approval”); and (iii) the parties obtaining certain specified governmental and regulatory approvals. The Transactions are expected to close in 2022. Subject to the terms and conditions set forth in the Merger Agreement, if the Transactions are consummated, at the effective time of the Merger (the “Effective Time”): (i) the members of SAM will become members of LMHC; and (ii) each share of the Company’s common stock issued and outstanding immediately prior to the Effective Time (other than (1) shares owned by the Company as treasury shares and shares owned by LMHC and its subsidiaries, (2) shares owned by SAM or any of the Company’s subsidiaries, and (3) shares for which appraisal rights have been properly exercised under Ohio law) will be converted into the right to receive $52.00 in cash, without interest and less any applicable withholding taxes (the “Merger Consideration”). The Merger Agreement contains certain provisions giving LMHC, SAM and the Company the right to terminate the Merger Agreement under certain circumstances. Subject to certain limitations, pursuant to the Merger Agreement: • LMHC, SAM and the Company may terminate the Merger Agreement by mutual written consent, which consent shall have been approved by the action of their respective boards of directors; • LMHC, SAM or the Company may terminate the Merger Agreement if (a) any governmental authority shall have enacted any laws permanently preventing or otherwise permanently prohibiting the Transactions and such law shall have become final and non-appealable, (b) the SAM Member Approval shall not have been obtained following a vote thereon having been taken at a meeting of the members of SAM (the “SAM Member Meeting”), (c) the Company Shareholder Approval shall not have been obtained following a vote thereon having been taken at a meeting of the shareholders of the Company (the “Company Shareholder Meeting”) or (d) the Transactions shall not have been consummated prior to May 12, 2022 (as such date may be extended by a period of three months up to two times under certain circumstances); • The Company may terminate the Merger Agreement, prior to the receipt of the Company Shareholder Approval, to enter into a definitive agreement to implement a Superior Proposal (as such term is defined in the Merger Agreement); • The Company or SAM may terminate the Merger Agreement if there has been a breach by LMHC, Merger Sub I or Merger Sub II of any representation, warranty, covenant or agreement contained in the Merger Agreement to the extent such breach would result in the failure of a closing condition (subject to cure periods); and • LMHC may terminate the Merger Agreement if (i) prior to the receipt of the Company Shareholder Approval, the special committee of the board of directors of the Company makes an Adverse Recommendation Change (as such term is defined in the Merger Agreement), (ii) the Company or SAM willfully and materially breach certain covenants in the Merger Agreement relating to the SAM Member Meeting, the Company Shareholder Meeting or the no-solicitation provisions set forth in the Merger Agreement or (iii) the Company or SAM breaches any representation, warranty, covenant or agreement in the Merger Agreement to the extent such breach would result in the failure of a closing condition (subject to cure periods). Upon termination of the Merger Agreement, under specified circumstances, the Company (or, as applicable, SAM) may be required to pay a termination fee to LMHC in an aggregate amount of $70,793,307.

Basis of Presentation Significa

Basis of Presentation Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
New Accounting Pronouncements	Adoption of Recent Accounting Pronouncements Income Taxes - Simplifying the Accounting for Income Taxes In December 2019, the FASB issued ASU 2019-12 which updated guidance for the accounting for income taxes. The updated guidance is intended to simplify the accounting for income taxes by removing several exceptions contained in existing guidance and amending other existing guidance to simplify several other income tax accounting matters. The guidance became effective for annual and interim reporting periods after December 15, 2020. On January 1, 2021, the Company adopted this guidance and it did not have a material impact on the Company's results of operations, consolidated financial position or cash flows.

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Cost or Amortized Cost and Fair Value of Available-for-Sale Securities	The following tables set forth the amortized cost and fair value of investments by investment category at June 30, 2021 and December 31, 2020: ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value June 30, 2021 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 461.6 $ 26.9 $ (0.1) $ 488.4 Obligations of states and political subdivisions 473.1 25.6 (0.1) 498.6 Corporate securities 457.7 18.3 (0.3) 475.7 U.S. government agencies mortgage-backed securities 742.5 16.6 (6.9) 752.2 Total available-for-sale fixed maturities $ 2,134.9 $ 87.4 $ (7.4) $ 2,214.9 ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 506.5 $ 45.2 $ — $ 551.7 Obligations of states and political subdivisions 511.3 30.4 (0.2) 541.5 Corporate securities 459.9 23.4 — 483.3 U.S. government agencies mortgage-backed securities 639.3 22.9 (1.5) 660.7 Total available-for-sale fixed maturities $ 2,117.0 $ 121.9 $ (1.7) $ 2,237.2
Gross Unrealized Losses and Fair Value on its Investments	The following tables set forth the Company’s gross unrealized losses and fair value on its investments by lot, aggregated by investment category and length of time for individual securities that have been in a continuous unrealized loss position for which an allowance for credit losses has not been recorded at June 30, 2021 and December 31, 2020: ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions June 30, 2021 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 71.1 $ (0.1) 12 $ — $ — — $ 71.1 $ (0.1) 12 Obligations of states and political subdivisions 3.8 (0.1) 1 — — — 3.8 (0.1) 1 Corporate securities 42.5 (0.3) 9 — — — 42.5 (0.3) 9 U.S. government agencies mortgage-backed securities 320.5 (6.9) 72 8.4 — 5 328.9 (6.9) 77 Total temporarily impaired securities $ 437.9 $ (7.4) 94 $ 8.4 $ — 5 $ 446.3 $ (7.4) 99 ($ millions, except # of positions) Less than 12 months 12 months or more Total Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions December 31, 2020 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 9.6 $ — 4 $ — $ — — $ 9.6 $ — 4 Obligations of states and political subdivisions 19.5 (0.2) 5 — — — 19.5 (0.2) 5 Corporate securities 1.5 — 2 — — — 1.5 — 2 U.S. government agencies mortgage-backed securities 136.1 (1.4) 35 7.0 (0.1) 3 143.1 (1.5) 38 Total temporarily impaired securities $ 166.7 $ (1.6) 46 $ 7.0 $ (0.1) 3 $ 173.7 $ (1.7) 49
Amortized Cost and Fair Value of Available-for-Sale Fixed Maturities by Contractual Maturity	The following table sets forth the amortized cost and fair value of available-for-sale fixed maturities by contractual maturity at June 30, 2021: ($ millions) Amortized cost Fair Due in 1 year or less $ 135.7 $ 136.8 Due after 1 year through 5 years 571.0 596.8 Due after 5 years through 10 years 154.8 162.2 Due after 10 years 530.9 566.9 U.S. government agencies mortgage-backed securities 742.5 752.2 Total $ 2,134.9 $ 2,214.9
Components of Net Investment Income	The following table sets forth the components of net investment income for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Fixed maturities $ 15.4 $ 14.5 $ 30.8 $ 29.6 Equity securities 1.2 2.6 2.8 5.7 Cash and cash equivalents, and other 1.1 0.8 2.0 1.8 Investment income 17.7 17.9 35.6 37.1 Investment expenses — 0.2 0.3 0.5 Net investment income $ 17.7 $ 17.7 $ 35.3 $ 36.6

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
Company's Investments within Fair Value Hierarchy	The following tables set forth the Company’s investments within the fair value hierarchy at June 30, 2021 and December 31, 2020: ($ millions) Total Level 1 Level 2 June 30, 2021 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 488.4 $ — $ 488.4 Obligations of states and political subdivisions 498.6 — 498.6 Corporate securities 475.7 — 475.7 U.S. government agencies mortgage-backed securities 752.2 — 752.2 Total available-for-sale fixed maturities 2,214.9 — 2,214.9 Equity securities: Large-cap securities 158.6 158.6 — Mutual and exchange traded funds 216.9 216.9 — Total equity securities 375.5 375.5 — Other invested assets 16.6 16.6 — Total investments $ 2,607.0 $ 392.1 $ 2,214.9 ($ millions) Total Level 1 Level 2 December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 551.7 $ — $ 551.7 Obligations of states and political subdivisions 541.5 — 541.5 Corporate securities 483.3 — 483.3 U.S. government agencies mortgage-backed securities 660.7 — 660.7 Total available-for-sale fixed maturities 2,237.2 — 2,237.2 Equity securities: Large-cap securities 134.2 134.2 — Mutual and exchange traded funds 255.5 255.5 — Total equity securities 389.7 389.7 — Other invested assets 15.3 15.3 — Total investments $ 2,642.2 $ 405.0 $ 2,237.2
Company Estimates Receivable from Affiliate using Market Quotations for U.S. Treasury Securities	Consequently this has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) June 30, 2021 December 31, 2020 Carrying value Fair value Interest rate Carrying value Fair Interest rate Notes receivable from affiliate, issued May 2019 $ 70.0 $ 76.9 4.05 % $ 70.0 $ 80.4 4.05 %
Included in Notes Payable are Senior Notes and Subordinated Debentures	The carrying amount of the Subordinated Debentures approximates its fair value as the interest rate adjusts quarterly and has been disclosed in Level 3. ($ millions, except interest rates) June 30, 2021 December 31, 2020 Carrying value Fair Value Interest rate Carrying value Fair value Interest rate FHLB Loan due 2030: issued $21.5, September 2020 with fixed interest $ 21.5 $ 20.8 1.37 % $ 21.5 $ 21.6 1.37 % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 103.7 3.96 % 85.3 107.1 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.3 15.3 4.33 % 15.3 15.3 4.43 % Total notes payable $ 122.1 $ 139.8 $ 122.1 $ 144.0

Deferred Acquisition Costs De_2

Deferred Acquisition Costs Deferred Acquisition Costs (Tables)	6 Months Ended
	Jun. 30, 2021
Deferred Policy Acquisition Costs Disclosures [Abstract]
Deferred Policy Acquisition Costs [Table Text Block]	The following table sets forth net deferred acquisition costs for the three and six months ended June 30, 2021 and 2020: ($ millions) 2021 2020 Beginning balance at April 1 $ 121.2 $ 113.3 Acquisition costs deferred 68.4 100.3 Acquisition costs amortized to expense (62.4) (93.6) Ending balance at June 30 $ 127.2 $ 120.0 Beginning balance at January 1 $ 122.2 $ 111.1 Acquisition costs deferred 129.0 191.4 Acquisition costs amortized to expense (124.0) (182.5) Ending balance at June 30 $ 127.2 $ 120.0

Losses and Loss Expenses Paya_2

Losses and Loss Expenses Payable Losses and Loss Expenses Payable (Tables)	6 Months Ended
	Jun. 30, 2021
Losses and Loss Expenses Payable [Abstract]
Schedule Of Activity In Liability For Unpaid Losses And Loss Adjustment Expenses Table [Table Text Block]	The following table sets forth the activity in the liability for losses and loss expenses for the six months ended June 30, 2021 and 2020: ($ millions) 2021 2020 Losses and loss expenses payable, at beginning of period $ 1,050.4 $ 1,066.5 Less: reinsurance recoverable on losses and loss expenses payable 24.3 13.6 Net balance at beginning of period 1,026.1 1,052.9 Incurred related to: Current year 624.1 518.2 Prior years (43.5) (7.6) Total incurred 580.6 510.6 Paid related to: Current year 303.1 228.9 Prior years 262.4 265.7 Total paid 565.5 494.6 Net balance at end of period 1,041.2 1,068.9 Plus: reinsurance recoverable on losses and loss expenses payable 19.7 36.4 Losses and loss expenses payable, at end of period $ 1,060.9 $ 1,105.3

Reinsurance (Tables)

Reinsurance (Tables)	6 Months Ended
	Jun. 30, 2021
Insurance [Abstract]
Summary of External Reinsurance Transactions with State Auto Mutual Under Pooling Arrangement	The following table sets forth a summary of the Company’s external reinsurance transactions, as well as reinsurance transactions with State Auto Mutual under the Pooling Arrangement, for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Premiums earned: Assumed from external insurers and reinsurers $ 20.2 $ 20.7 $ 42.0 $ 41.3 Assumed under Pooling Arrangement 369.9 340.7 725.8 671.2 Ceded to external insurers and reinsurers (8.5) (7.1) (17.5) (17.7) Ceded under Pooling Arrangement (277.7) (279.1) (555.6) (551.3) Net assumed premiums earned $ 103.9 $ 75.2 $ 194.7 $ 143.5 Losses and loss expenses incurred: Assumed from external insurers and reinsurers $ 21.6 $ 15.5 $ 36.1 $ 27.2 Assumed under Pooling Arrangement 299.8 271.2 580.6 510.6 Ceded to external insurers and reinsurers (3.0) (12.5) (6.3) (46.0) Ceded under Pooling Arrangement (192.0) (198.0) (359.1) (426.5) Net assumed losses and loss expenses incurred $ 126.4 $ 76.2 $ 251.3 $ 65.3

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Reconciliation Between Actual Federal Income Tax Benefit and Amount Computed at Indicated Statutory Rate	The following table sets forth the reconciliation between actual federal income tax expense and the amount computed at the indicated statutory rate for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Amount at statutory rate $ 0.9 21.0 % $ 8.7 21.0 % $ 2.1 21.0 % $ (21.5) 21.0 % Tax-exempt interest and dividends received deduction (0.6) (14.2) (0.4) (0.9) (1.2) (12.6) (1.1) 1.1 Other, net 3.3 78.0 (1.0) (2.5) 4.7 48.6 0.5 (0.5) Federal income tax expense (benefit) $ 3.6 84.8 % $ 7.3 17.6 % $ 5.6 57.0 % $ (22.1) 21.6 %

Pension and Postretirement Be_2

Pension and Postretirement Benefit Plans (Tables)	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Company's Share of Net Periodic Cost Components	for the three and six months ended June 30, 2021 and 2020: ($ millions) Pension Postretirement Pension Postretirement Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 2021 2020 2021 2020 Service cost $ 1.2 $ 1.2 $ — $ — $ 2.5 $ 2.4 $ — $ — Interest cost 2.1 2.4 0.1 0.1 4.2 4.8 0.1 0.2 Expected return on plan assets (4.2) (4.3) — — (8.5) (8.7) — — Amortization of: Negative prior service cost — — (1.4) (1.3) — — (2.8) (2.7) Net actuarial loss/(gain) 3.5 2.3 (0.1) — 7.0 4.6 (0.1) 0.1 Net periodic cost (benefit) $ 2.6 $ 1.6 $ (1.4) $ (1.2) $ 5.2 $ 3.1 $ (2.8) $ (2.4)

Other Comprehensive Income an_2

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Changes in Accumulated Other Comprehensive Income by Component, Net of Tax	The following tables set forth the changes in the Company’s accumulated other comprehensive (loss) income ("AOC(L)I"), net of tax, for the three and six months ended June 30, 2021 and 2020: ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at April 1, 2021 $ 51.2 $ (81.3) $ (30.1) Other comprehensive loss before reclassifications 14.0 — 14.0 Amounts reclassified from AOCI (a) 0.6 2.2 2.8 Net current period other comprehensive (loss) income 14.6 2.2 16.8 Ending balance at June 30, 2021 $ 65.8 $ (79.1) $ (13.3) Beginning balance at April 1, 2020 $ 63.0 $ (76.7) $ (13.7) Other comprehensive income before reclassifications 30.8 — 30.8 Amounts reclassified from AOCI (a) (0.8) 1.6 0.8 Net current period other comprehensive income 30.0 1.6 31.6 Ending balance at June 30, 2020 $ 93.0 $ (75.1) $ 17.9 (a) See separate table below for details about these reclassifications ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at January 1, 2021 $ 97.5 $ (83.6) $ 13.9 Other comprehensive income before reclassifications (31.1) — (31.1) Amounts reclassified from AOCI (a) (0.6) 4.5 3.9 Net current period other comprehensive income (31.7) 4.5 (27.2) Ending balance at June 30, 2021 $ 65.8 $ (79.1) $ (13.3) Beginning balance at January 1, 2020 $ 40.4 $ (78.3) $ (37.9) Other comprehensive loss before reclassifications 55.3 — 55.3 Amounts reclassified from AOCI (a) (2.7) 3.2 0.5 Net current period other comprehensive income 52.6 3.2 55.8 Ending balance at June 30, 2020 $ 93.0 $ (75.1) $ 17.9 (a) See separate table below for details about these reclassifications
Schedule of Reclassifications Out of Accumulated Other Comprehensive Income by Component	The following tables set forth the reclassifications out of accumulated other comprehensive (loss) income, by component, to the Company’s condensed consolidated statement of income for the three and six months ended June 30, 2021 and 2020: ($ millions) Details about Accumulated Other Three months ended June 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2021 2020 Unrealized gains on available-for-sale fixed maturity investments $ (0.8) $ 1.0 Realized gain on sale of securities (0.8) 1.0 Total before tax 0.2 (0.2) Tax expense (0.6) 0.8 Net of tax Amortization of benefit plan items Negative prior service cost 1.6 1.6 (b) Net actuarial loss (4.4) (3.6) (b) (2.8) (2.0) Total before tax 0.6 0.4 Tax benefit (2.2) (1.6) Net of tax Total reclassifications for the period $ (2.8) $ (0.8) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details). ($ millions) Details about Accumulated Other Six months ended June 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2021 2020 Unrealized gains on available-for-sale fixed maturity investments $ 0.7 $ 3.4 Realized gains on sale of securities 0.7 3.4 Total before tax (0.1) (0.7) Tax expense 0.6 2.7 Net of tax Amortization of benefit plan items Negative prior service cost 3.2 3.2 (b) Net actuarial loss (8.9) (7.3) (b) (5.7) (4.1) Total before tax 1.2 0.9 Tax benefit (4.5) (3.2) Net of tax Total reclassifications for the period $ (3.9) $ (0.5) (b) These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see pension and postretirement benefit plans footnote for additional details).

Earnings per Common Share (Tabl

Earnings per Common Share (Tables)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Compilation of Basic and Diluted Earnings Per Common Share	The following table sets forth the compilation of basic and diluted earnings (loss) per common share for the three and six months ended June 30, 2021 and 2020: ($ and shares in millions, except per share amounts) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Numerator: Net income (loss) for basic earnings (loss) per common share $ 0.6 $ 34.3 $ 4.2 $ (80.3) Effect of dilutive share-based awards — (1.6) — — Adjusted net income (loss) for diluted earnings (loss) per common share $ 0.6 $ 32.7 $ 4.2 $ (80.3) Denominator: Weighted average shares for basic earnings (loss) per common share 44.0 43.8 44.0 43.7 Effect of dilutive share-based awards 0.8 0.3 0.6 — Adjusted weighted average shares for diluted earnings (loss) per common share 44.8 44.1 44.6 43.7 Basic net earnings (loss) per common share $ 0.01 $ 0.78 $ 0.10 $ (1.83) Diluted net earnings (loss) per common share $ 0.01 $ 0.74 $ 0.09 $ (1.83)
Options to Purchase Shares of Common Stock	The following table sets forth stock awards and restricted share units ("RSU award") of the Company that were not included in the computation of diluted earnings (loss) per common share because the exercise price of the awards was greater than the average market price or their inclusion would have been antidilutive for the six months ended June 30, 2021 and 2020: (shares in millions) Six months ended June 30 2021 2020 Total number of antidilutive awards — 0.4

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Financial Information Regarding Company's Reportable Segments	The following table sets forth financial information regarding the Company’s reportable segments and specialty run-off (for the previously exited specialty insurance business) for the three and six months ended June 30, 2021 and 2020: ($ millions) Three months ended June 30 Six months ended June 30 2021 2020 2021 2020 Revenue from external sources: Insurance operations Personal insurance $ 213.1 $ 202.8 $ 420.9 $ 400.9 Commercial insurance 157.6 137.9 306.3 270.3 Specialty run-off (0.8) — (1.4) — Total insurance operations 369.9 340.7 725.8 671.2 Investment operations Net investment income 17.7 17.7 35.3 36.6 Net investment gain (loss) 26.7 75.9 64.9 (59.3) Total investment operations 44.4 93.6 100.2 (22.7) All other 0.4 0.5 0.9 1.1 Total revenue from external sources 414.7 434.8 826.9 649.6 Intersegment revenue 1.6 1.5 3.2 3.1 Total revenue 416.3 436.3 830.1 652.7 Reconciling items: Eliminate intersegment revenue (1.6) (1.5) (3.2) (3.1) Total consolidated revenues $ 414.7 $ 434.8 $ 826.9 $ 649.6 Segment income (loss) before federal income tax: Insurance operations SAP underwriting (loss) gain Personal insurance $ (44.2) $ (40.4) $ (93.6) $ (40.1) Commercial insurance 2.8 (12.4) 5.8 (42.4) Specialty run-off (1.4) (6.3) 0.2 (6.7) Total insurance operations (42.8) (59.1) (87.6) (89.2) Investment operations Net investment income 17.7 17.7 35.3 36.6 Net investment gain (loss) 26.7 75.9 64.9 (59.3) Total investment operations 44.4 93.6 100.2 (22.7) All other — — — 0.1 Total segment income (loss) before reconciling items 1.6 34.5 12.6 (111.8) Reconciling items: GAAP expense adjustments 5.7 8.7 4.4 14.6 Interest expense on corporate debt (1.1) (1.3) (2.2) (2.5) Corporate expenses (2.0) (0.3) (5.0) (2.7) Total reconciling items 2.6 7.1 (2.8) 9.4 Total consolidated income (loss) before federal income tax $ 4.2 $ 41.6 $ 9.8 $ (102.4)

Investments - Cost or Amortized

Investments - Cost or Amortized Cost and Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 2,134.9	$ 2,117
Gross unrealized holding gains	87.4	121.9
Gross unrealized holding losses	(7.4)	(1.7)
Fair value	2,214.9	2,237.2
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	461.6	506.5
Gross unrealized holding gains	26.9	45.2
Gross unrealized holding losses	(0.1)	0
Fair value	488.4	551.7
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	473.1	511.3
Gross unrealized holding gains	25.6	30.4
Gross unrealized holding losses	(0.1)	(0.2)
Fair value	498.6	541.5
Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	457.7	459.9
Gross unrealized holding gains	18.3	23.4
Gross unrealized holding losses	(0.3)	0
Fair value	475.7	483.3
U.S. Government Agencies Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	742.5	639.3
Gross unrealized holding gains	16.6	22.9
Gross unrealized holding losses	(6.9)	(1.5)
Fair value	$ 752.2	$ 660.7

Investments - Available for Sal

Investments - Available for Sale Securities Continuous Unrealized Loss Position Fair Value and Aggregate Losses (Detail) $ in Millions	Jun. 30, 2021USD ($)position	Dec. 31, 2020USD ($)position
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 437.9	$ 166.7
Less than 12 months, Unrealized losses	$ (7.4)	$ (1.6)
Less than 12 months, Number of positions | position	94	46
12 months or more, Fair value	$ 8.4	$ 7
12 months or more, Unrealized losses	$ 0	$ (0.1)
12 months or more, Number of positions | position	5	3
Total, Fair value	$ 446.3	$ 173.7
Total, Unrealized losses	$ (7.4)	$ (1.7)
Total, Number of positions | position	99	49
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 71.1	$ 9.6
Less than 12 months, Unrealized losses	$ (0.1)	$ 0
Less than 12 months, Number of positions | position	12	4
12 months or more, Fair value	$ 0	$ 0
12 months or more, Unrealized losses	$ 0	$ 0
12 months or more, Number of positions | position	0	0
Total, Fair value	$ 71.1	$ 9.6
Total, Unrealized losses	$ (0.1)	$ 0
Total, Number of positions | position	12	4
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 3.8	$ 19.5
Less than 12 months, Unrealized losses	$ (0.1)	$ (0.2)
Less than 12 months, Number of positions | position	1	5
12 months or more, Fair value	$ 0	$ 0
12 months or more, Unrealized losses	$ 0	$ 0
12 months or more, Number of positions | position	0	0
Total, Fair value	$ 3.8	$ 19.5
Total, Unrealized losses	$ (0.1)	$ (0.2)
Total, Number of positions | position	1	5
Corporate Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 42.5	$ 1.5
Less than 12 months, Unrealized losses	$ (0.3)	$ 0
Less than 12 months, Number of positions | position	9	2
12 months or more, Fair value	$ 0	$ 0
12 months or more, Unrealized losses	$ 0	$ 0
12 months or more, Number of positions | position	0	0
Total, Fair value	$ 42.5	$ 1.5
Total, Unrealized losses	$ (0.3)	$ 0
Total, Number of positions | position	9	2
U.S. Government Agencies Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 320.5	$ 136.1
Less than 12 months, Unrealized losses	$ (6.9)	$ (1.4)
Less than 12 months, Number of positions | position	72	35
12 months or more, Fair value	$ 8.4	$ 7
12 months or more, Unrealized losses	$ 0	$ (0.1)
12 months or more, Number of positions | position	5	3
Total, Fair value	$ 328.9	$ 143.1
Total, Unrealized losses	$ (6.9)	$ (1.5)
Total, Number of positions | position	77	38

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Value of Available-for-Sale Fixed Maturities by Contractual Maturity (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Amortized cost
Due in 1 year or less, Amortized cost	$ 135.7
Due after 1 year through 5 years, Amortized cost	571
Due after 5 years through 10 years, Amortized cost	154.8
Due after 10 years, Amortized cost	530.9
U.S. government agencies mortgage-backed securities, Amortized cost	742.5
Total, Amortized cost	2,134.9	$ 2,117
Fair value
Due in 1 year or less, Fair value	136.8
Due after 1 year through 5 years, Fair value	596.8
Due after 5 years through 10 years, Fair value	162.2
Due after 10 years, Fair value	566.9
U.S. government agencies mortgage-backed securities, Fair value	752.2
Total, Fair value	$ 2,214.9	$ 2,237.2

Investments - Components of Net

Investments - Components of Net Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net Investment Income [Line Items]
Investment income	$ 17.7	$ 17.9	$ 35.6	$ 37.1
Investment expenses	0	0.2	0.3	0.5
Net investment income	17.7	17.7	35.3	36.6
Equity Securities [Member]
Net Investment Income [Line Items]
Investment income	1.2	2.6	2.8	5.7
Cash and Cash Equivalents, and Other [Member]
Net Investment Income [Line Items]
Investment income	1.1	0.8	2	1.8
Fixed Maturities [Member]
Net Investment Income [Line Items]
Investment income	$ 15.4	$ 14.5	$ 30.8	$ 29.6

Investments - Realized and Unre

Investments - Realized and Unrealized Holding Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt Securities, Realized Gain (Loss):
Debt Securities, Available-for-sale, Realized Gain	$ 0.9	$ 1.9	$ 3.9	$ 5.5
Debt Securities, Available-for-sale, Realized Loss	(1.7)	(0.9)	(3.2)	(2.1)
Debt Securities, Available-for-sale, Net Realized Gain (Loss)	(0.8)	1	0.7	3.4
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Unrealized Gain (Loss)	19.8	78.6	46.1	(44.7)
Other net realized loss	0.4	0	0.4	(0.2)
Gain (Loss) on Investments	26.7	75.9	64.9	(59.3)
Change in unrealized holding gains (losses), net of tax:
Change in net unrealized holding (losses) gains, net of tax	18.5	37.9	(40.2)	66.5
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(3.9)	(7.9)	8.5	(13.9)
Total net unrealized holding (loss) gains on available-for-sale investments	14.6	30	(31.7)	52.6
Equity Securities [Member]
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Net Gain (Loss)	24.9	69.1	56.4	(53.3)
Other Invested Assets [Member]
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Unrealized Gain (Loss)	3	5.8	8.2	(9.6)
Equity Securities, FV-NI, Net Gain (Loss)	$ 3	$ 5.8	$ 8.2	$ (9.6)

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	$ 32.9		$ 32.9
Fixed maturities fair value of deposit with insurance regulators	9.6		9.6		$ 9.7
Proceeds on sale of available-for-sale securities			220.3	$ 218.9
Equity Securities, FV-NI, Unrealized Gain (Loss)	19.8	$ 78.6	46.1	$ (44.7)
Federal Home Loan Bank of Cincinnati [Member]
Debt Securities, Available-for-sale [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 106.5		$ 106.5

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Company's Available-for-Sale Investments within Fair Value Hierarchy (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	$ 2,214.9	$ 2,237.2
Investments, Fair Value Disclosure	2,607	2,642.2
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	488.4	551.7
Investments, Fair Value Disclosure	488.4	551.7
Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	498.6	541.5
Investments, Fair Value Disclosure	498.6	541.5
Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	475.7	483.3
Investments, Fair Value Disclosure	475.7	483.3
U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	752.2	660.7
Investments, Fair Value Disclosure	752.2	660.7
Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	2,214.9	2,237.2
Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	158.6	134.2
Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	216.9	255.5
Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	375.5	389.7
Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	16.6	15.3
Level 1 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	392.1	405
Level 1 [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 1 [Member] | Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	158.6	134.2
Level 1 [Member] | Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	216.9	255.5
Level 1 [Member] | Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	375.5	389.7
Level 1 [Member] | Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	16.6	15.3
Level 2 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	2,214.9	2,237.2
Level 2 [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	488.4	551.7
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	498.6	541.5
Level 2 [Member] | Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	475.7	483.3
Level 2 [Member] | U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	752.2	660.7
Level 2 [Member] | Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	2,214.9	2,237.2
Level 2 [Member] | Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 2 [Member] | Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 2 [Member] | Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	0	0
Level 2 [Member] | Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	$ 0	$ 0

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Company Estimates Receivable from Affiliate using Market Quotations for U.S. Treasury Securities (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Document Period End Date	Jun. 30, 2021
Note Receivable from Affiliate, 2019 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate (percent)	4.05%	4.05%
Reported Value Measurement [Member] | Note Receivable from Affiliate, 2019 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	$ 70	$ 70
Estimate of Fair Value Measurement [Member] | Note Receivable from Affiliate, 2019 [Member] | Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	$ 76.9	$ 80.4

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Included in Notes Payable are the FHLB loan and Subordinated Debentures (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Document Period End Date	Jun. 30, 2021
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 21,500,000
Federal Home Loan Bank Advances due 2030 [Member]
Debt Instrument [Line Items]
Interest rate (percent)	1.37%	1.37%
Debt Instrument, Face Amount	$ 21,500,000
Federal Home Loan Bank of Cincinnati [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 85,000,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate (percent)	3.96%	3.96%
Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Interest rate (percent)	4.33%	4.43%
Debt Instrument, Face Amount	$ 15,500,000
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Total notes payable	122,100,000	$ 122,100,000
Reported Value Measurement [Member] | Federal Home Loan Bank Advances due 2030 [Member]
Debt Instrument [Line Items]
Total notes payable	21,500,000	21,500,000
Reported Value Measurement [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	85,300,000	85,300,000
Reported Value Measurement [Member] | Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Total notes payable	15,300,000	15,300,000
Estimate of Fair Value Measurement [Member]
Debt Instrument [Line Items]
Total notes payable	139,800,000	144,000,000
Estimate of Fair Value Measurement [Member] | Federal Home Loan Bank Advances due 2030 [Member]
Debt Instrument [Line Items]
Total notes payable	20,800,000	21,600,000
Estimate of Fair Value Measurement [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	103,700,000	107,100,000
Estimate of Fair Value Measurement [Member] | Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Total notes payable	$ 15,300,000	$ 15,300,000

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Additional Information (Detail) $ in Millions	1 Months Ended
	May 31, 2009Agreement	Jun. 30, 2021USD ($)	Dec. 31, 2020USD ($)
Fair Value Measurements Disclosure [Line Items]
Other invested assets		$ 79.6	$ 71.1
Other invested assets, at cost		11.1	12.1
Number of Credit Agreements | Agreement	2
Notes receivable from affiliate		70	70
Level 3 [Member]
Fair Value Measurements Disclosure [Line Items]
Federal home loan bank stock		10.6
Other invested assets, at cost		$ 0.5
International funds [Member]
Fair Value Measurements Disclosure [Line Items]
Number of available for sale securities		1
Other invested assets		$ 63	$ 55.8
Affiliated Entity [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable from affiliate		$ 70

Deferred Acquisition Costs De_3

Deferred Acquisition Costs Deferred Acquisition Costs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred Policy Acquisition Cost, Period Start	$ 121.2	$ 113.3	$ 122.2	$ 111.1
Deferred Policy Acquisition Cost, Capitalization	68.4	100.3	129	191.4
Deferred Policy Acquisition Costs, Disposition	(62.4)	(93.6)	(124)	(182.5)
Deferred Policy Acquisition Cost, Period End	$ 127.2	$ 120	$ 127.2	$ 120

Losses and Loss Expenses Paya_3

Losses and Loss Expenses Payable Losses and Loss Expenses Payable - Schedule of Activity in Liability for Unpaid Losses and Loss Expenses Payable (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Liability for Claims and Claims Adjustment Expense [Abstract]
Liability for Claims and Claims Adjustment Expense, Property Casualty Liability	$ 1,060.9	$ 1,105.3	$ 1,060.9	$ 1,105.3	$ 1,050.4	$ 1,066.5
Reinsurance Recoverables, Including Reinsurance Premium Paid	19.7	36.4	19.7	36.4	24.3	13.6
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,041.2	1,068.9	1,041.2	1,068.9	$ 1,026.1	$ 1,052.9
Current Year Claims and Claims Adjustment Expense			624.1	518.2
Prior Year Claims and Claims Adjustment Expense			(43.5)	(7.6)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	$ 299.8	$ 271.2	580.6	510.6
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			303.1	228.9
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			262.4	265.7
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid			$ 565.5	$ 494.6

Losses and Loss Expenses Paya_4

Losses and Loss Expenses Payable Losses and Loss Expenses Payable - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (43,500,000)	$ (7,600,000)
Specialty Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(6,100,000)
Personal Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(12,100,000)
Middle Market Commercial [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(13,500,000)	(8,000,000)
Personal Auto [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(11,100,000)
Workers' compensation [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(15,400,000)	(8,800,000)
Small commercial [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		(9,000,000)
Total Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(40,500,000)	$ (12,500,000)
Business Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ 38,500,000

Reinsurance - Summary of Extern

Reinsurance - Summary of External Reinsurance Transactions, as well as reinsurance transactions with State Auto Mutual Under the Pooling Arrangement (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Premiums earned:
Assumed from external insurers and reinsurers	$ 20.2	$ 20.7	$ 42	$ 41.3
Assumed under Pooling Arrangement	369.9	340.7	725.8	671.2
Ceded to external insurers and reinsurers	(8.5)	(7.1)	(17.5)	(17.7)
Ceded under Pooling Arrangement	(277.7)	(279.1)	(555.6)	(551.3)
Net assumed premiums earned	103.9	75.2	194.7	143.5
Losses and loss expenses incurred:
Assumed from external insurers and reinsurers	21.6	15.5	36.1	27.2
Assumed under Pooling Arrangement	299.8	271.2	580.6	510.6
Ceded to external insurers and reinsurers	(3)	(12.5)	(6.3)	(46)
Ceded under Pooling Arrangement	(192)	(198)	(359.1)	(426.5)
Net assumed losses and loss expenses incurred	$ 126.4	$ 76.2	$ 251.3	$ 65.3

Notes Payable and Open Line o_2

Notes Payable and Open Line of Credit Notes Payable and Open Line of Credit (Details) - Federal Home Loan Bank of Cincinnati [Member] $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 100
Line of Credit Facility, Expiration Period	1 year

Income Taxes - Reconciliation B

Income Taxes - Reconciliation Between Actual Federal Income Tax Expense (Benefit) and Amount Computed at Indicated Statutory Rate (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Amount at statutory rate	$ 0.9	$ 8.7	$ 2.1	$ (21.5)
Tax-exempt interest and dividends received deduction	(0.6)	(0.4)	(1.2)	(1.1)
Other, net	3.3	(1)	4.7	0.5
Federal income tax expense and effective rate	3.6	7.3	5.6	(22.1)
Income Tax Expense (Benefit)	$ 3.6	$ 7.3	$ 5.6	$ (22.1)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Amount at statutory rate (percent)	21.00%	21.00%	21.00%	21.00%
Tax-exempt interest and dividends received deduction (percent)	(14.20%)	(0.90%)	(12.60%)	1.10%
Other, net (percent)	78.00%	(2.50%)	48.60%	(0.50%)
Effective Income Tax Rate Reconciliation, Deduction, Percent	84.80%	17.60%	57.00%	21.60%

Pension and Postretirement Be_3

Pension and Postretirement Benefit Plans - Company's Share of Net Periodic Cost Components (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1.2	$ 1.2	$ 2.5	$ 2.4
Interest cost	2.1	2.4	4.2	4.8
Expected return on plan assets	(4.2)	(4.3)	(8.5)	(8.7)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	0	0	0
Amortization of:
Defined Benefit Plan, Amortization of Gain (Loss)	3.5	2.3	7	4.6
Net periodic cost (benefit)	2.6	1.6	5.2	3.1
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0	0
Interest cost	0.1	0.1	0.1	0.2
Expected return on plan assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(1.4)	(1.3)	(2.8)	(2.7)
Amortization of:
Defined Benefit Plan, Amortization of Gain (Loss)	(0.1)	0	(0.1)	0.1
Net periodic cost (benefit)	$ (1.4)	$ (1.2)	$ (2.8)	$ (2.4)

Pension and Postretirement Be_4

Pension and Postretirement Benefit Plans - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Retirement Benefits [Abstract]
Contributions by employer	$ 10
Defined Benefit Plan, Expected Future Benefit Payment, Remainder of Fiscal Year	$ 5

Other Comprehensive Income an_3

Other Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income by Component, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	$ (30.1)	$ (13.7)	$ 13.9	$ (37.9)
Other comprehensive income before reclassifications	14	30.8	(31.1)	55.3
Amounts reclassified from AOCI	2.8	0.8	3.9	0.5
Other comprehensive (loss) income	16.8	31.6	(27.2)	55.8
Ending balance	(13.3)	17.9	(13.3)	17.9
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Amounts reclassified from AOCI	2.8	0.8	3.9	0.5
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	51.2	63	97.5	40.4
Other comprehensive income before reclassifications	14	30.8	(31.1)	55.3
Amounts reclassified from AOCI	0.6	(0.8)	(0.6)	(2.7)
Other comprehensive (loss) income	14.6	30	(31.7)	52.6
Ending balance	65.8	93	65.8	93
Benefit Plan Items [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(81.3)	(76.7)	(83.6)	(78.3)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from AOCI	2.2	1.6	4.5	3.2
Other comprehensive (loss) income	2.2	1.6	4.5	3.2
Ending balance	$ (79.1)	$ (75.1)	$ (79.1)	$ (75.1)

Other Comprehensive Income an_4

Other Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income by Component (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain/(loss) on sale of securities	$ 26.7	$ 75.9	$ 64.9	$ (59.3)
Tax (expense) benefit	(3.6)	(7.3)	(5.6)	22.1
Total reclassifications for the period	(2.8)	(0.8)	(3.9)	(0.5)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(0.6)	0.8	0.6	2.7
Benefit Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(2.2)	(1.6)	(4.5)	(3.2)
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(2.8)	(0.8)	(3.9)	(0.5)
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain/(loss) on sale of securities	(0.8)	1	0.7	3.4
Total before tax	(0.8)	1	0.7	3.4
Tax (expense) benefit	0.2	(0.2)	(0.1)	(0.7)
Net of tax	(0.6)	0.8	0.6	2.7
Reclassification Out of Accumulated Other Comprehensive Income [Member] | Benefit Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Accumulated other comprehensive income components/Negative prior-service costs	1.6	1.6	3.2	3.2
Accumulated other comprehensive income components/Net actuarial loss	(4.4)	(3.6)	(8.9)	(7.3)
Total before tax	(2.8)	(2)	(5.7)	(4.1)
Tax (expense) benefit	0.6	0.4	1.2	0.9
Net of tax	$ (2.2)	$ (1.6)	$ (4.5)	$ (3.2)

Earnings Per Common Share - Com

Earnings Per Common Share - Compilation of Basic and Diluted Earnings (Loss) Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net income (loss)	$ 0.6	$ 34.3	$ 4.2	$ (80.3)
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units	0	(1.6)	0	0
Adjusted net income (loss) for diluted earnings (loss) per common share	$ 0.6	$ 32.7	$ 4.2	$ (80.3)
Denominator:
Weighted average shares for basic net earnings per common share (shares)	44	43.8	44	43.7
Effect of dilutive share-based awards (shares)	0.8	0.3	0.6	0
Adjusted weighted average shares for diluted net earnings per common share (shares)	44.8	44.1	44.6	43.7
Basic net (loss) earnings per common share (usd per share)	$ 0.01	$ 0.78	$ 0.10	$ (1.83)
Diluted net (loss) earnings per common share (usd per share)	$ 0.01	$ 0.74	$ 0.09	$ (1.83)

Earnings Per Common Share - Opt

Earnings Per Common Share - Options to Purchase Shares of Common Stock (Detail) - shares shares in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Number of antidilutive options and awards	0	0.4

Segment Information - Financial

Segment Information - Financial Information Regarding Company's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues from external sources:
Revenue	$ 414.7	$ 434.8	$ 826.9	$ 649.6
Other Income	0.4	0.5	0.9	1.1
Net Investment Income	17.7	17.7	35.3	36.6
Realized Investment Gains (Losses)	26.7	75.9	64.9	(59.3)
Segment income before federal income tax:
Interest expense on corporate debt	(1.1)	(1.3)	(2.2)	(2.5)
Income before federal income taxes	4.2	41.6	9.8	(102.4)
Operating Segments [Member]
Revenues from external sources:
Revenue	414.7	434.8	826.9	649.6
Segment income before federal income tax:
Income before federal income taxes	1.6	34.5	12.6	(111.8)
Operating Segments [Member] | Personal Insurance Segments [Member]
Revenues from external sources:
Revenue	213.1	202.8	420.9	400.9
Operating Segments [Member] | Business Insurance Segments [Member]
Revenues from external sources:
Revenue	157.6	137.9	306.3	270.3
Operating Segments [Member] | Specialty Insurance Segment [Member]
Revenues from external sources:
Revenue	(0.8)	0	(1.4)	0
Operating Segments [Member] | Total Insurance Segments [Member]
Revenues from external sources:
Revenue	369.9	340.7	725.8	671.2
Segment income before federal income tax:
Income before federal income taxes	(42.8)	(59.1)	(87.6)	(89.2)
Operating Segments [Member] | Net Investment Income [Member]
Revenues from external sources:
Net Investment Income	17.7	17.7	35.3	36.6
Operating Segments [Member] | Total Investment Operations [Member]
Revenues from external sources:
Revenue	44.4	93.6	100.2	(22.7)
Segment income before federal income tax:
Income before federal income taxes	44.4	93.6	100.2	(22.7)
Operating Segments [Member] | Total Investment Operations [Member] | Net Realized Capital Gains [Member]
Revenues from external sources:
Realized Investment Gains (Losses)		75.9		(59.3)
Segment income before federal income tax:
Income before federal income taxes	26.7	75.9	64.9	(59.3)
Operating Segments [Member] | All Other Segments [Member]
Revenues from external sources:
Revenue		0.5		1.1
Segment income before federal income tax:
Income before federal income taxes	0	0	0	0.1
Operating Segments [Member] | Personal Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	(44.2)	(40.4)	(93.6)	(40.1)
Operating Segments [Member] | Business Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	2.8	(12.4)	5.8	(42.4)
Operating Segments [Member] | Specialty Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	(1.4)	(6.3)	0.2	(6.7)
Eliminate Intersegment Revenues [Member]
Revenues from external sources:
Revenue	1.6	1.5	3.2	3.1
Segment Reconciling Items [Member]
Revenues from external sources:
Revenue	(1.6)	(1.5)	(3.2)	(3.1)
Segment income before federal income tax:
Gaap Expense Adjustments	5.7	8.7	4.4	14.6
Interest expense on corporate debt	1.1	1.3	2.2	2.5
Corporate Expenses	(2)	(0.3)	(5)	(2.7)
Income before federal income taxes	2.6	7.1	(2.8)	9.4
Corporate And Reconciling Items [Member]
Revenues from external sources:
Revenue	$ 416.3	$ 436.3	$ 830.1	$ 652.7

Segment Information - Additiona

Segment Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Acquisition And Operating Expenses	$ 107.2	$ 119.5	$ 228.2	$ 234.4
Investable assets	$ 2,859.8		$ 2,859.8		$ 2,870.8

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event [Member]	Jul. 17, 2021USD ($)$ / shares
Subsequent Event [Line Items]
Subsequent Event, Date	Jul. 12, 2021
Sale of Stock, Price Per Share | $ / shares	$ 52
Loss on Contract Termination | $	$ 70,793,307
State Automobile Mutual Insurance Company
Subsequent Event [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	58.80%