State Auto Financial (STFC) 10-Q 6 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
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	2020
Document Fiscal Period Focus	Q3
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)		43,837,768
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	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020, are not necessarily indicative of the results that may be expected for the year ending December 31, 2020. The balance sheet at December 31, 2019, 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, 2019 (the “2019 Form 10-K”). Capitalized terms used herein and not otherwise defined shall have the meaning ascribed to them in the 2019 Form 10-K. The COVID-19 pandemic has caused an economic downturn on a global scale, as well as significant market disruption and volatility. The scope, duration and magnitude of the effects of COVID-19 continue to evolve rapidly and in ways that are difficult or impossible to anticipate. The Company cannot, at this time, predict the impact the pandemic will have on its future consolidated financial position, cash flows or results of operations, however, the impact could be material. The Company's future financial results and operations depend in part on the duration and severity of the pandemic and what actions are taken to mitigate the outbreak. Adoption of Recent Accounting Pronouncements Measurement of Credit Losses on Financial Instruments On January 1, 2020, the Company adopted ASU 2016-13 Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments, which replaces the incurred loss methodology with an expected loss methodology that is referred to as the current expected credit loss (CECL) methodology. The measurement of expected credit losses under the CECL methodology is applicable to financial assets measured at amortized cost. This includes the Company's direct third party reinsurance recoverables, and the Company's share of the State Auto Group's third party reinsurance recoverables assumed via the Pooling Arrangement (as defined in Note 7). In addition, ASC 326 made changes to the accounting for available-for-sale fixed maturities. One such change is to require credit losses to be presented as an allowance rather than as a write-down on available-for-sale fixed maturities management does not intend to sell or believes that it is more likely than not they will not be required to sell. The adoption of this guidance reduced retained earnings by $0.5 million, net of tax, and established an allowance for estimated uncollectible reinsurance as of January 1, 2020. Adoption of ASC 326 for available-for-sale fixed maturities was prospective, and therefore there was no adjustment to retained earnings as of January 1, 2020. Changes to the Company's accounting policy resulting from the adoption of the guidance are discussed below. Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement In August 2018, the FASB issued ASU 2018-13 which changes the fair value measurement disclosure requirements of ASC 820 by adding, eliminating and modifying disclosures. The new guidance eliminates (i) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, (ii) the entity's policy for the timing of transfers between levels, and (iii) the entity's valuation process for Level 3 fair value measurements. Additionally, the guidance now requires the disclosure of (i) the changes in unrealized gains and losses in other comprehensive income for recurring Level 3 fair value measurements, and (ii) the range and weighted average used to develop significant unobservable inputs and how the weighted average was calculated for Level 3 fair value measurements. Finally, the guidance requires entities to provide information about the measurement uncertainty of Level 3 fair value measurements as of the reporting date rather than a point in the future. The guidance became effective for annual reporting periods after December 15, 2019 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 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 effective date of ASU 2019-12 is for interim and annual periods beginning after December 15, 2020. Early adoption is permitted. The ASU has not yet been adopted; however, it is not expected to have a material impact on the Company’s results of operations, consolidated financial position or cash flows. 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 2019 Form 10-K. Significant Accounting Policy Updates The following accounting policies have been updated to reflect the Company's adoption of ASU 2016-13 Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments as described above. Investments Investments in fixed maturities are classified as available-for-sale and are carried at fair value. For fixed maturities in an unrealized loss position, management considers 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. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security are compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded for the credit loss, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that has not been recorded through an allowance for credit losses is recognized in other comprehensive income. Changes in the allowance for credit losses are recorded in the "net investment gain (loss)" line item on the condensed consolidated statement of income. Losses are charged against the allowance when management believes the uncollectibility of a fixed maturity is confirmed or when either of the criteria regarding intent or requirement to sell is met. Description and disclosure of credit losses on fixed maturities are disclosed in Note 3 of the Notes to Condensed Consolidated Financial Statements. The Company excludes accrued interest receivable from both the estimated fair value and the amortized cost basis of available-for-sale fixed maturities and includes such amounts within "accrued investment income and other assets" on the Company's condensed consolidated balance sheets. Any uncollectible accrued interest receivable is written off in the period it is deemed uncollectible. Reinsurance Recoverables Management assesses expected credit losses on third party reinsurance recoverables for the entire State Auto Pool and, pursuant to the Pooling Arrangement (as defined in Note 7), the Company is responsible for its share of the estimated uncollectible reinsurance for the entire pool. Management uses A.M. Best’s Financial Strength ratings or equivalent such as S&P, Moody’s, or Fitch when an A.M. Best Financial Strength rating is not available to assess the credit risk of the reinsurance recoverables. The estimate of expected credit losses considers historical credit loss information as well as current conditions and reasonable and supportable forecasts. Description and disclosure of credit losses on reinsurance recoverables are disclosed in Note 8 of the Notes to Condensed Consolidated Financial Statements. Premiums Premiums are recognized as earned pro rata over the policy period. Unearned premiums represent the portion of premiums written relative to the unexpired terms of coverage. Under the terms of the Pooling Arrangement, each period State Auto Mutual collects all premiums from policyholders and pays all losses and expenses associated with the insurance business produced by the STFC Pooled Companies and the other pool participants, and then it settles the intercompany balances generated by these transactions with the pool participants within 60 days following each quarter end. When settling the intercompany balances, State Auto Mutual provides the pool participants with full credit for their share of the Pooled Companies net premiums written during the quarter.

Contingencies and Litigation

Contingencies and Litigation	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Litigation	Contingencies and Litigation In 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, which our policies were not intended to cover. These lawsuits, which seek to extend coverage beyond the terms and conditions of those policies, 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	Sep. 30, 2020	Dec. 31, 2019
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost $2,047.1 and $2,080.0, respectively)	$ 2,166.3	$ 2,127.9
Equity securities	339.5	395.2
Other invested assets	62.5	69.7
Other invested assets, at cost	12.5	6.5
Notes receivable from affiliate	70	70
Total investments	2,650.8	2,669.3
Cash and cash equivalents	131.4	78
Accrued investment income and other assets	31.1	31.7
Premiums receivable	14.1	13.6
Deferred policy acquisition costs (affiliated net assumed $27.6 and $20.2, respectively)	123.7	111.1
Reinsurance recoverable on losses and loss expenses payable	35.2	13.6
Prepaid reinsurance premiums	8.4	7.5
Due from Affiliates	18.3	7.9
Current federal income taxes	6.7	6.3
Net deferred federal income taxes	44.6	42.2
Property and equipment, held for sale	4.2	4.2
Total assets	3,068.5	2,985.4
Liabilities and Stockholders’ Equity
Losses and loss expenses payable (affiliated net assumed $450.9 and $500.8, respectively)	1,091.3	1,066.5
Unearned premiums (affiliated net assumed $450.8 and $415.8, respectively)	731	649.2
Notes payable (affiliates $15.2 and $15.2, respectively)	122	122
Pension and postretirement benefits	54	72.9
Other liabilities (affiliated net assumed $18.5 and $19.5, respectively)	126.1	114.9
Total liabilities	2,124.4	2,025.5
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 50.7 and 50.4 shares issued, respectively, at stated value of $2.50 per share	126.7	125.9
Treasury stock, 6.9 and 6.9 shares, respectively, at cost	(118.4)	(117.5)
Additional paid-in capital	212.1	206.7
Accumulated other comprehensive income (loss)	23.3	(37.9)
Retained earnings	700.4	782.7
Total stockholders’ equity	944.1	959.9
Total liabilities and stockholders’ equity	3,068.5	2,985.4
Class A Preferred Stock [Member]
Stockholders’ equity:
Preferred stock value	0	0
Class B Preferred Stock [Member]
Stockholders’ equity:
Preferred stock value	$ 0	$ 0

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fixed maturities, available-for-sale, amortized cost	$ 2,047.1	$ 2,080
Deferred policy acquisitions costs from affiliates	27.6	20.2
Losses and loss expenses payable, affiliates	450.9	500.8
Unearned premiums, affiliates	450.8	415.8
Notes payable, affiliates	15.2	15.2
Net Other Liabilities from Affiliates	$ 18.5	$ 19.5
Common stock, shares authorized (shares)	100	100
Common stock, shares issued (shares)	50.7	50.4
Common stock, stated value per share (usd per share)	$ 2.50	$ 2.50
Treasury stock (shares)	6.9	6.9
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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Earned premiums (affiliated net assumed $71.9 and $115.3, respectively, and $251.1 and $349.0, respectively)	$ 353.2	$ 319.6	$ 1,024.4	$ 930
Net investment income (affiliate $1.3 and $1.3, respectively, and $3.7 and $3.7, respectively)	17.9	19.3	54.5	60.4
Net realized gains on investments:
Total net realized gains on investments	20	(5)	(39.3)	50.2
Other income from affiliates	0.5	0.6	1.6	1.6
Total revenues	391.6	334.5	1,041.2	1,042.2
Losses and loss expenses (affiliated net assumed $34.7 and $128.9, respectively, and $105.4 and $298.8, respectively)	251.6	208.4	762.2	637.6
Acquisition and operating expenses (affiliated net ceded $26.8 and affiliated net assumed $78.9, respectively, and $52.3 and $231.0, respectively)	123	109.7	357.4	325.2
Interest expense (affiliates $0.2 and $0.2, respectively, and $0.7 and $0.6, respectively)	1.1	1.2	3.6	3.7
Other Expenses	1.1	2.5	5.6	9
Costs and Expenses	376.8	321.8	1,128.8	975.5
Income before federal income taxes	14.8	12.7	(87.6)	66.7
Current Income Tax Expense (Benefit)			(0.4)	(0.4)
Deferred Income Tax Expense (Benefit)	3.2	1.2	(18.5)	12.4
Federal income tax expense	3.2	1.2	(18.9)	12
Net income	$ 11.6	$ 11.5	$ (68.7)	$ 54.7
(Loss) earnings per common share:
Basic (usd per share)	$ 0.26	$ 0.26	$ (1.57)	$ 1.26
Diluted (usd per share)	$ 0.26	$ 0.25	$ (1.57)	$ 1.25

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Earned premiums, from affiliates	$ 69.3	$ 55.7	$ 189.2	$ 168.5
Net investment income, from affiliate	0.7	0.7	2.1	2.3
Losses and loss expenses, from affiliates	48.7	24.2	132.8	125.1
Net Acquisition and Operating Expenses, from affiliates	24.2	17.6	65.9	54.5
Interest Expense Debt To Affiliates	$ 0.1	$ 0.2	$ 0.6	$ 0.7

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ 11.6	$ 11.5	$ (68.7)	$ 54.7
Net unrealized holding gains on fixed available-for-sale investments:
Unrealized holding gains	4.6	22.6	74.5	91.8
Reclassification adjustments for gains realized in net income	0.2	(1.2)	(3.2)	(2.8)
Income tax expense	(1.1)	(4.5)	(15)	(18.7)
Total net unrealized holding gains on available-for-sale investments	3.7	16.9	56.3	70.3
Reclassification adjustments for amortization to statements of income:
Negative prior service cost	(1.6)	(1.6)	(4.8)	(4.8)
Net actuarial loss	3.7	2.4	11	7.2
Income tax expense	(0.4)	(0.2)	(1.3)	(0.5)
Total net unrecognized benefit plan obligations	1.7	0.6	4.9	1.9
Other comprehensive income	5.4	17.5	61.2	72.2
Comprehensive (loss) income	$ 17	$ 29	$ (7.5)	$ 126.9

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, 2018		(50)	(6.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		0.3
Balance at end of year (shares) at Sep. 30, 2019		(50.3)	(6.8)
Balance at beginning of year at Dec. 31, 2018		$ (125)	$ (117)	$ (194.2)	$ 96.4	$ (712.7)
Balance at end of year at Sep. 30, 2019	$ (943.7)	(125.8)	(117.5)	(205.2)	24.2	(754.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.8		4
Shares acquired on stock award exercises and vested restricted shares			$ (0.5)
Stock awards granted				7
Change in net unrealized holding (losses) gains, net of tax	70.3				70.3
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	1.9				1.9
Net income (loss)	54.7					54.7
Cash dividends paid		$ (13)
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 Jun. 30, 2019		(50.3)	(6.8)
Balance at end of year (shares) at Sep. 30, 2019		(50.3)	(6.8)
Balance at beginning of year at Jun. 30, 2019		$ (125.7)	$ (117.5)	(202.5)	41.7	(747.2)
Balance at end of year at Sep. 30, 2019	(943.7)	(125.8)	$ (117.5)	(205.2)	24.2	(754.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.1		0.7
Stock awards granted				2
Change in net unrealized holding (losses) gains, net of tax	16.9				16.9
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	0.6				0.6
Net income (loss)	$ 11.5					11.5
Cash dividends paid		$ (4.3)
Document Fiscal Year Focus	2020
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 Sep. 30, 2020		(50.7)	(6.9)
Balance at beginning of year at Dec. 31, 2019	$ (959.9)	$ (125.9)	$ (117.5)	(206.7)	37.9	(782.7)
Balance at end of year at Sep. 30, 2020	(944.1)	(126.7)	(118.4)	(212.1)	(23.3)	(700.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0.8		2
Shares acquired on stock award exercises and vested restricted shares			$ (0.9)
Stock awards granted				3.4
Change in net unrealized holding (losses) gains, net of tax	56.3				56.3
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	4.9				4.9
Net income (loss)	(68.7)					(68.7)
Cash dividends paid		$ (13.1)
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 Jun. 30, 2020		(50.7)	(6.9)
Balance at end of year (shares) at Sep. 30, 2020		(50.7)	(6.9)
Balance at beginning of year at Jun. 30, 2020		$ (126.7)	$ (118.4)	(211.1)	(17.9)	(693.2)
Balance at end of year at Sep. 30, 2020	(944.1)	(126.7)	$ (118.4)	(212.1)	(23.3)	(700.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		0		(0.2)
Stock awards granted				$ 1.2
Change in net unrealized holding (losses) gains, net of tax	3.7				3.7
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	1.7				$ 1.7
Net income (loss)	$ 11.6					$ 11.6
Cash dividends paid		$ (4.4)

Statement of Shareholders' Equi

Statement of Shareholders' Equity (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Dividends paid per common share (usd per share)	$ 0.10	$ 0.10	$ 0.30	$ 0.30
Retained Earnings [Member]
Cash Dividends Paid to Affiliates	$ 2.6	$ 2.6	$ 7.8	$ 7.8

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net (loss) income	$ (68.7)	$ 54.7
Adjustments to reconcile net (loss) income to net cash provided by (used in) operating activities
Depreciation and amortization, net	7.6	6.2
Share-based compensation	0	7
Net investment loss (gain)	39.3	(50.2)
Changes in operating assets and liabilities:
Deferred policy acquisition costs	(12.6)	(12.4)
Accrued investment income and other assets	0.6	(2.3)
Premiums receivables	(0.5)	(3.2)
Postretirement and pension benefits	(17)	(12.2)
Other liabilities and due to/from affiliates, net	8.5	(51.8)
Reinsurance recoverable on losses and loss expenses payable and prepaid reinsurance premiums	(22.5)	(2.6)
Losses and loss expenses payable	24.2	(54.1)
Unearned premiums	81.8	65
Excess Tax Benefit from Share-based Compensation, Operating Activities	(0.1)	(0.7)
Federal income taxes	(18.8)	12.7
Net cash provided by (used in) operating activities	21.8	(43.9)
Cash flows from investing activities:
Purchases of fixed maturities available-for-sale	(462.6)	(459.9)
Purchases of equity securities	(65.6)	(48.9)
Purchases of other invested assets	(7.3)	(12.9)
Maturities, calls and pay downs of fixed maturities available-for-sale	274.9	267.1
Sales of fixed maturities available-for-sale	216.1	248.7
Sales of equity securities	86.2	34.4
Sales of other invested assets	0.9	1
Proceeds from Sale of Property, Plant, and Equipment	0.2	1.6
Net cash provided by investing activities	42.8	31.1
Cash flows from financing activities:
Proceeds from issuance of common stock	2.8	4.8
Payments to acquire treasury stock	(0.9)	(0.5)
Payment of dividends	(13.1)	(13)
Proceeds from short-term debt	60	0
Repayment of short-term debt	(60)	0
Proceeds from long-term debt	21.5	0
Repayment of long-term debt	(21.5)	0
Net cash used in financing activities	(11.2)	(8.7)
Net increase (decrease) in cash and cash equivalents	53.4	(21.5)
Cash and cash equivalents at beginning of period	78	59.8
Cash and cash equivalents at end of period	131.4	38.3
Supplemental disclosures:
Interest Paid, Excluding Capitalized Interest, Operating Activities	$ 3.5	$ 3.5

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Cash Flows [Abstract]
Interest Expense Debt To Affiliates	$ 0.1	$ 0.2	$ 0.6	$ 0.7

Accounting Changes and Error Co

Accounting Changes and Error Corrections	9 Months Ended
	Sep. 30, 2020
Accounting Changes and Error Corrections [Abstract]
Accounting Standards Update and Change in Accounting Principle	Correction of Misstatement in Prior Period Financial Statements The Company has corrected the presentation of premiums receivable on its condensed consolidated balance sheet for the period ended December 31, 2019 to appropriately reflect outstanding balances for premiums billed and due on premiums written directly by the STFC Pooled Companies. Based on the Pooling Arrangement (as defined in Note 7), this has no impact on the underwriting operations of the STFC Pooled Companies given the role of State Auto Mutual as agent for the State Auto Group. The Company's balance sheet has been revised to include "premiums receivable", which represents the billed and due premium from its policyholders, with an offsetting adjustment to "due to/from affiliates". This adjustment was not material to the Company’s previously issued financial statements. The effect of the revisions on the Company's previously issued financial statements are provided in the tables below. Amounts throughout the consolidated financial statements and notes thereto have been adjusted to incorporate the revised amounts, where applicable. The following tables reconcile selected lines from the Company’s year-end 2019 consolidated balance sheet and the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 from the previously reported amounts to the revised amounts. There were no changes to the condensed consolidated statements of income, condensed consolidated statements of comprehensive income, and condensed consolidated statements of stockholders' equity. Revised Consolidated Balance Sheets ($ in millions) Year Ended December 31, 2019 As Reported Adjustment As Revised Assets Premiums receivable $ — $ 13.6 $ 13.6 Due from affiliate 21.5 (13.6) 7.9 Total Assets $ 2,985.4 $ — $ 2,985.4 Revised Consolidated Statement of Cash Flows ($ in millions) Nine months ended September 30, 2019 As Reported Adjustment As Revised Cash flows from operating activities: Changes in operating assets and liabilities: Premiums receivable $ — $ (3.2) $ (3.2) Other liabilities and due to/from affiliates, net (55.0) 3.2 (51.8) Net cash used in operating activities $ (43.9) $ — $ (43.9)

Investments

Investments	9 Months Ended
	Sep. 30, 2020
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 September 30, 2020 and December 31, 2019: ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value September 30, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 510.9 $ 48.1 $ — $ 559.0 Obligations of states and political subdivisions 527.5 26.7 (1.5) 552.7 Corporate securities 451.7 21.9 — 473.6 U.S. government agencies mortgage-backed securities 557.0 25.3 (1.3) 581.0 Total available-for-sale fixed maturities $ 2,047.1 $ 122.0 $ (2.8) $ 2,166.3 ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 569.2 $ 12.3 $ (3.3) $ 578.2 Obligations of states and political subdivisions 404.3 21.1 — 425.4 Corporate securities 460.5 11.7 (0.4) 471.8 U.S. government agencies mortgage-backed securities 646.0 11.1 (4.6) 652.5 Total available-for-sale fixed maturities $ 2,080.0 $ 56.2 $ (8.3) $ 2,127.9 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 September 30, 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 September 30, 2020 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 0.7 $ — 1 $ — $ — — $ 0.7 $ — 1 Obligations of states and political subdivisions 94.3 (1.5) 18 — — — 94.3 (1.5) 18 Corporate securities 15.1 — 4 — — — 15.1 — 4 U.S. government agencies mortgage-backed securities 76.1 (1.1) 22 9.4 (0.2) 4 85.5 (1.3) 26 Total temporarily impaired securities $ 186.2 $ (2.6) 45 $ 9.4 $ (0.2) 4 $ 195.6 $ (2.8) 49 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 at December 31, 2019: ($ 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, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 136.0 $ (2.5) 17 $ 157.6 $ (0.8) 11 $ 293.6 $ (3.3) 28 Corporate securities — — — 40.8 (0.4) 7 40.8 (0.4) 7 U.S. government agencies mortgage-backed securities 126.6 (1.5) 15 137.9 (3.1) 32 264.5 (4.6) 47 Total temporarily impaired securities $ 262.6 $ (4.0) 32 $ 336.3 $ (4.3) 50 $ 598.9 $ (8.3) 82 The Company reviewed its available-for-sale fixed maturities at September 30, 2020, and determined that no credit impairment existed in the gross unrealized holding losses, due to the reasons discussed below: • 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. • 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 September 30, 2020: ($ millions) Amortized cost Fair Due in 1 year or less $ 119.8 $ 120.9 Due after 1 year through 5 years 519.9 548.0 Due after 5 years through 10 years 168.0 178.9 Due after 10 years 682.4 737.5 U.S. government agencies mortgage-backed securities 557.0 581.0 Total $ 2,047.1 $ 2,166.3 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 September 30, 2020, 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"), which loans are further described in Note 9. In accordance with the terms of the FHLB Loans, State Auto P&C retains all rights regarding these pledged securities. At September 30, 2020, State Auto P&C had fixed maturities with fair values of approximately $31.7 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 $9.3 million were on deposit with insurance regulators as required by law at September 30, 2020, and December 31, 2019, respectively. The Company retains all rights regarding these securities. The following table sets forth the components of net investment income for the three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine Months Ended September 30 2020 2019 2020 2019 Fixed maturities $ 15.0 $ 15.3 $ 44.6 $ 47.7 Equity securities 2.1 3.0 7.8 8.9 Cash and cash equivalents, and other 0.9 1.1 2.7 4.2 Investment income 18.0 19.4 55.1 60.8 Investment expenses 0.1 0.1 0.6 0.4 Net investment income $ 17.9 $ 19.3 $ 54.5 $ 60.4 The Company’s current investment strategy does not rely on the use of derivative financial instruments. Proceeds on sales of investments were $303.2 million and $284.1 million for the nine months ended September 30, 2020, and 2019, respectively. The following table sets forth the realized and unrealized holding gains (losses) on the Company’s investment portfolio for the three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine Months Ended September 30 2020 2019 2020 2019 Investment gain (loss), net: Fixed maturities: Realized gains on sales of securities $ 1.3 $ 1.2 $ 6.8 $ 2.8 Realized losses on sales of securities (1.5) — (3.6) — Net (loss) gain on fixed securities (0.2) 1.2 3.2 2.8 Equity securities: Realized losses on sales of securities, net (42.3) (1.8) (50.9) (2.5) Unrealized gain (loss) on securities still held, net 60.5 (4.1) 15.8 46.4 Net gain (loss) on equity securities 18.2 (5.9) (35.1) 43.9 Other invested assets: Unrealized gain (loss) on securities still held, net 2.0 (0.3) (7.6) 4.8 Net gain (loss) on other invested assets 2.0 (0.3) (7.6) 4.8 Other net realized gain (loss) — — 0.2 (1.3) Net gain (loss) on investments $ 20.0 $ (5.0) $ (39.3) $ 50.2 Change in net unrealized holding gains, net of tax Fixed maturities $ 4.8 $ 21.4 $ 71.3 $ 89.0 Deferred federal income tax liability (1.1) (4.5) (15.0) (18.7) Change in net unrealized holding gains, net of tax $ 3.7 $ 16.9 $ 56.3 $ 70.3

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2020
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 September 30, 2020, and December 31, 2019, 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 $48.5 million and $56.4 million at September 30, 2020, and December 31, 2019, respectively, which was determined using the fund’s net asset value. The Company employs procedures to assess the reasonableness of the fair value of the fund, including obtaining and reviewing the fund’s audited financial statements. There are no unfunded commitments related to the fund. The Company may not sell its investment in the fund; however, the Company may redeem all or a portion of its investment in the fund at net asset value per share with the appropriate prior written notice. In accordance with ASC 820-10, this investment is measured at fair value using the net asset value per share practical expedient and has not been classified in the fair value hierarchy. Fair values presented here are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the condensed consolidated balance sheets. The remainder of the Company’s other invested assets consist primarily of holdings in publicly-traded mutual funds. The Company believes that its prices for these publicly-traded mutual funds based on an observable market price for an identical asset in an active market reflect their fair values and consequently these securities have been disclosed in Level 1. The following tables set forth the Company’s investments within the fair value hierarchy at September 30, 2020 and December 31, 2019: ($ millions) Total Level 1 Level 2 September 30, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 559.0 $ — $ 559.0 Obligations of states and political subdivisions 552.7 — 552.7 Corporate securities 473.6 — 473.6 U.S. government agencies mortgage-backed securities 581.0 — 581.0 Total available-for-sale fixed maturities 2,166.3 — 2,166.3 Equity securities: Large-cap securities 120.0 120.0 — Mutual and exchange traded funds 219.5 219.5 — Total equity securities 339.5 339.5 — Other invested assets 14.0 14.0 — Total investments $ 2,519.8 $ 353.5 $ 2,166.3 ($ millions) Total Level 1 Level 2 December 31, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 578.2 $ — $ 578.2 Obligations of states and political subdivisions 425.4 — 425.4 Corporate securities 471.8 — 471.8 U.S. government agencies mortgage-backed securities 652.5 — 652.5 Total available-for-sale fixed maturities 2,127.9 — 2,127.9 Equity securities: Large-cap securities 104.4 104.4 — Mutual and exchange traded funds 290.8 290.8 — Total equity securities 395.2 395.2 — Other invested assets 13.3 13.3 — Total investments $ 2,536.4 $ 408.5 $ 2,127.9 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 September 30, 2020, was $12.0 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 In May 2009, the Company entered into two separate credit agreements with State Automobile Mutual Insurance Company (“State Auto Mutual") pursuant to which it loaned State Auto Mutual a total of $70.0 million at an interest rate of 7.00%. In May 2019, the Company refinanced the two credit agreements with State Auto Mutual at an interest rate of 4.05%, with principal payable in May 2029. The Company estimates the fair value of the notes receivable from affiliate using market quotations for U.S. treasury securities with similar maturity dates and applies an appropriate credit spread. Consequently this has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) September 30, 2020 December 31, 2019 Carrying value Fair value Interest rate Carrying value Fair Interest rate Notes receivable from affiliate, issued May 2019 $ 70.0 $ 82.4 4.05 % $ 70.0 $ 74.6 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) September 30, 2020 December 31, 2019 Carrying value Fair Value Interest rate Carrying value Fair value Interest rate FHLB Loan due 2021: issued $21.5, September 2016 with fixed interest $ — $ — — % $ 21.5 $ 21.5 1.73 % FHLB Loan due 2030: issued $21.5, September 2020 with fixed interest 21.5 21.8 1.37 % — — — % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 108.6 3.96 % 85.3 97.8 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.2 15.2 4.44 % 15.2 15.2 6.11 % Total notes payable $ 122.0 $ 145.6 $ 122.0 $ 134.5

Deferred Acquisition Costs Defe

Deferred Acquisition Costs Deferred Acquisition Costs	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) 2020 2019 Beginning balance at July 1 $ 120.0 $ 109.1 Acquisition costs deferred 98.4 94.6 Acquisition costs amortized to expense (94.7) (89.4) Ending balance at September 30 $ 123.7 $ 114.3 Beginning balance at January 1 $ 111.1 $ 101.9 Acquisition costs deferred 289.8 270.6 Acquisition costs amortized to expense (277.2) (258.2) Ending balance at September 30 $ 123.7 $ 114.3

Losses and Loss Expenses Payabl

Losses and Loss Expenses Payable Losses and Loss Expenses Payable	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) 2020 2019 Losses and loss expenses payable, at beginning of period $ 1,066.5 $ 1,146.8 Less: reinsurance recoverable on losses and loss expenses payable 13.6 5.5 Net balance at beginning of period 1,052.9 1,141.3 Incurred related to: Current year 779.8 692.7 Prior years (17.6) (55.1) Total incurred 762.2 637.6 Paid related to: Current year 420.8 366.4 Prior years 338.2 327.0 Total paid 759.0 693.4 Net balance at end of period 1,056.1 1,085.5 Plus: reinsurance recoverable on losses and loss expenses payable 35.2 7.2 Losses and loss expenses payable, at end of period $ 1,091.3 $ 1,092.7 The Company recorded less favorable development related to prior years’ loss and loss expense reserves for the nine months ended September 30, 2020, of $17.6 million compared to $55.1 million for the same 2019 period. Favorable development of prior accident years' non-catastrophe loss and ALAE reserves for the nine months ended September 30, 2020 was $31.8 million, due to favorable development in the commercial insurance segment. In the commercial insurance segment, all products developed favorably, with small commercial package, workers' compensation, and middle market commercial contributing $16.5 million, $16.1 million, and $14.3 million, respectively. Partially offsetting the favorable development was adverse development in the personal insurance segment and specialty run-off, which contributed $20.2 million and $5.2 million, respectively. The adverse development in the personal insurance segment was primarily driven by personal auto, which contributed $19.1 million of adverse development. The personal auto adverse development was driven by higher than expected severity of bodily injury claims from multiple accident years. The specialty run-off adverse development primarily related to an adverse court decision relating to an E&S casualty claim from 2016. Partially offsetting the favorable development of prior years' non-catastrophe loss and ALAE reserves was adverse development in catastrophe loss and ALAE reserves driven by $12.4 million of adverse development in E&S property related to Hurricane Irma. For the nine months ended September 30, 2019, favorable development of prior accident year's non-catastrophe loss and ALAE reserves was $54.1 million. In the personal insurance segment, personal auto contributed $11.0 million of favorable development. In the commercial insurance segment, all lines contributed favorable development, with workers' compensation, small commercial package, and middle market commercial contributing $13.4 million, $11.8 million, and $7.2 million, respectively.

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Premiums earned: Assumed from external insurers and reinsurers $ 21.7 $ 21.0 $ 63.0 $ 59.3 Assumed under Pooling Arrangement 353.2 319.6 1,024.4 930.0 Ceded to external insurers and reinsurers (7.7) (6.6) (25.4) (18.8) Ceded under Pooling Arrangement (283.9) (263.9) (835.2) (761.5) Net assumed premiums earned $ 83.3 $ 70.1 $ 226.8 $ 209.0 Losses and loss expenses incurred: Assumed from external insurers and reinsurers $ 14.1 $ 14.6 $ 41.3 $ 45.6 Assumed under Pooling Arrangement 251.6 209.3 762.2 639.4 Ceded to external insurers and reinsurers (9.9) (0.6) (55.9) (6.2) Ceded under Pooling Arrangement (202.9) (185.1) (629.4) (514.3) Net assumed losses and loss expenses incurred $ 52.9 $ 38.2 $ 118.2 $ 164.5

Current Expected Credit Losses

Current Expected Credit Losses Current Expected Credit Losses	9 Months Ended
	Sep. 30, 2020
Credit Loss [Abstract]
Credit Loss, Financial Instrument [Text Block]	. Current Expected Credit Losses The Company is exposed to third-party credit risk both directly through its cessions to reinsurers and indirectly through its participation in the Pooling Arrangement. In addition to exposure to credit risk on reinsurance recoverables, the Company is also exposed to credit risk on amounts due from insureds and agents through the Pooling Arrangement. When settling the intercompany balances, State Auto Mutual provides the STFC Pooled Companies with full credit for the net premiums written and net losses paid during the quarter and retains all receivable amounts from insureds and agents and reinsurance recoverable on paid losses from unaffiliated reinsurers. At September 30, 2020, the determination of the allowance for credit losses for premiums receivable and reinsurance recoverables included considerations for the potential impacts of the COVID-19 pandemic on the Company's ability to collect balances due from its insureds, agents, and reinsurers. Reinsurance recoverables The State Auto Group monitors the credit quality of its reinsurance recoverables through the use of A.M. Best’s Financial Strength rating ("FSR"), or in the absence of an FSR consideration of credit ratings issued by approved rating agencies such as S&P, Moody’s, or Fitch. At September 30, 2020, the determination of the allowance for credit losses on reinsurance recoverables included analysis of (i) reinsurance recoverable balances by reinsurer FSR, (ii) estimated payment patterns associated with the claims underlying the reinsurance balances and (iii) historical default rates by reinsurer FSR as published by A.M. Best. In addition to the quantitative analysis, qualitative factors considered include but are not limited to (i) global reinsurer capital level, (ii) reinsurance market trends, (iii) the low interest rate environment and (iv) the stressed global economy, including the impact of COVID-19. The allowance for credit losses is included in the "reinsurance recoverables on losses and loss expenses payable" and "losses and loss expenses payable" line items in the Company's condensed consolidated balance sheets. The Company’s allowance for credit losses for reinsurance recoverables at September 30, 2020 is $0.8 million. The following table sets forth the amortized cost of the Company's direct third-party reinsurance recoverables by FSR, net of the allowance for credit losses, at September 30, 2020: ($ millions) Amortized Cost Financial strength rating: A++ $ 1.2 A+ 15.3 A 18.7 Reinsurance recoverable on losses and loss expenses payable, net of allowance for credit losses $ 35.2 Premiums Receivables Management utilizes an aging schedule to estimate an allowance for uncollectible amounts relating to the State Auto Pool premiums receivable balance including the Company's billed and due premium from its policyholders. In addition to reliance upon recent and historical collection trends, determination of the allowance for uncollectible premiums receivable at September 30, 2020 included consideration of other factors, including macro-economic conditions and trends, in particular the estimated impact of COVID-19. Credit risk is partially mitigated by the State Auto Group's ability to cancel a policy if the policyholder does not pay the premium due. Pursuant to the Pooling Arrangement, bad debt expense for uncollectible premiums receivable is allocated to pool members on the basis of pool participation and is included in the quarterly settlement of intercompany balances. Bad debt expense is included in "other expenses" on the condensed consolidated statements of income and reflected in “due to/from affiliates” on the Company's condensed consolidated balance sheets. The following table sets forth the changes in the Company's share of the allowance for uncollectible premiums receivable for the three and nine months ended September 30, 2020: ($ millions) Allowance for credit losses Beginning balance at July 1, 2020 $ 7.0 Current period provision 1.1 Writeoffs (1.1) Ending balance at September 30, 2020 $ 7.0 Beginning balance at January 1, 2020 $ 4.3 Current period provision 6.7 Writeoffs (4.0) Ending balance at September 30, 2020 $ 7.0

Notes Payable and Open Line of

Notes Payable and Open Line of Credit Notes Payable and Open Line of Credit	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Notes Payable and Open Line of Credit	Notes Payable and Open Line of Credit FHLB Loans On September 2, 2020 State Auto P&C retired its five ten 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 On March 19, 2020, State Auto P&C entered into a short-term loan arrangement with the FHLB in the principal amount of $60.0 million. This loan arrangement, known as REPO based advances, was for general corporate purposes and was intended to provide additional liquidity to State Auto P&C. The REPO based advances were repaid in full on September 22, 2020, and this loan arrangement was terminated. State Auto P&C also has a fifteen-year term loan with the FHLB that is more fully disclosed in Note 8 of the Notes to Consolidated Financial Statements in the 2019 Form 10-K. The foregoing OLC and term loans from the FHLB are collectively referred to as the "FHLB Loans."

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Interim Period Tax Expense Due to an increase in the frequency and severity of catastrophic events in 2020 and the uncertainty regarding the total impact of COVID-19 on the Company's future results of operations and financial condition, the Company's normal approach of using an estimated full-year effective income tax rate to determine interim period tax expense (benefit) produces an income tax benefit for the current year to date period that would have exceeded the tax benefit the Company expects to realize for the full year. Accordingly, the Company calculated a year to date tax benefit based on the year to date loss before federal income taxes using the U.S. Federal statutory tax rate and adjusted for the estimated impact of permanent differences and discrete items. The tax expense for the three months ended September 30, 2020 is the tax benefit for the nine months September 30, 2020 less the tax benefit recognized at June 30, 2020. The Company has foreign tax credit carryforwards of $0.5 million which will expire in 2021 and 2022. The Company believes it is more likely than not that the benefit from these foreign tax credit carryforwards will not be realized. In recognition of this risk, the Company has provided a valuation allowance of $0.5 million on the deferred tax assets related to these foreign tax credit carryforwards. The valuation allowance is included in the "other, net" line item in the table below. The following table sets forth the reconciliation between actual federal income tax expense and the amount computed at the indicated statutory rate for the three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Amount at statutory rate $ 3.1 21.0 % $ 2.7 21.0 % $ (18.4) 21.0 % $ 14.0 21.0 % Tax-exempt interest and dividends received deduction (0.6) (4.1) (0.7) (5.3) (1.7) 1.9 (2.1) (3.1) Other, net 0.7 4.5 (0.8) (6.3) 1.2 (1.4) 0.1 — Federal income tax expense (benefit) 3.2 21.4 % 1.2 9.4 % (18.9) 21.5 % $ 12.0 17.9 %

Pension and Postretirement Bene

Pension and Postretirement Benefit Plans	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) Pension Postretirement Pension Postretirement Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $ 1.2 $ 0.8 $ — $ — $ 3.6 $ 2.8 $ — $ — Interest cost 2.4 2.9 0.2 0.2 7.2 8.6 0.4 0.5 Expected return on plan assets (4.4) (4.2) — — (13.1) (12.5) — — Amortization of: Negative prior service cost — — (1.4) (1.4) — — (4.1) (4.1) Net actuarial loss 2.3 1.5 0.1 0.1 6.9 4.5 0.2 0.2 Net periodic cost (benefit) $ 1.5 $ 1.0 $ (1.1) $ (1.1) $ 4.6 $ 3.4 $ (3.5) $ (3.4) The Company contributed $15.0 million to its pension plan for the nine months ended September 30, 2020.

Other Comprehensive Income and

Other Comprehensive Income and Accumulated Other Comprehensive Income	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Other Comprehensive Income and Accumulated Other Comprehensive Income	Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Income (Loss) The following tables set forth the changes in the Company’s accumulated other comprehensive income (loss) ("AOCI(L)"), net of tax, for the three and nine months ended September 30, 2020 and 2019: ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at July 1, 2020 $ 93.0 $ (75.1) $ 17.9 Other comprehensive income before reclassifications 3.5 — 3.5 Amounts reclassified from AOCI (a) 0.2 1.7 1.9 Net current period other comprehensive income 3.7 1.7 5.4 Ending balance at September 30, 2020 $ 96.7 $ (73.4) $ 23.3 Beginning balance at July 1, 2019 $ 33.2 $ (74.9) $ (41.7) Other comprehensive income before reclassifications 17.8 — 17.8 Amounts reclassified from AOCI (a) (0.9) 0.6 (0.3) Net current period other comprehensive income 16.9 0.6 17.5 Ending balance at September 30, 2019 $ 50.1 $ (74.3) $ (24.2) (a) See separate table below for details about these reclassifications ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at January 1, 2020 $ 40.4 $ (78.3) $ (37.9) Other comprehensive income before reclassifications 58.8 — 58.8 Amounts reclassified from AOCI (a) (2.5) 4.9 2.4 Net current period other comprehensive income 56.3 4.9 61.2 Ending balance at September 30, 2020 $ 96.7 $ (73.4) $ 23.3 Beginning balance at January 1, 2019 $ (20.2) $ (76.2) $ (96.4) Other comprehensive loss before reclassifications 72.5 — 72.5 Amounts reclassified from AOCI (a) (2.2) 1.9 (0.3) Net current period other comprehensive income 70.3 1.9 72.2 Ending balance at September 30, 2019 $ 50.1 $ (74.3) $ (24.2) (a) See separate table below for details about these reclassifications The following tables set forth the reclassifications out of accumulated other comprehensive income, by component, to the Company’s condensed consolidated statement of income for the three and nine months ended September 30, 2020 and 2019: ($ millions) Details about Accumulated Other Three months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2020 2019 Unrealized gains on available-for-sale fixed maturity investments $ (0.2) $ 1.2 Realized gain on sale of securities (0.2) 1.2 Total before tax — (0.3) Tax expense (0.2) 0.9 Net of tax Amortization of benefit plan items Negative prior service cost 1.6 1.6 (b) Net actuarial loss (3.7) (2.4) (b) (2.1) (0.8) Total before tax 0.4 0.2 Tax benefit (1.7) (0.6) Net of tax Total reclassifications for the period $ (1.9) $ 0.3 (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 Nine months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2020 2019 Unrealized gains on available-for-sale fixed maturity investments $ 3.2 $ 2.8 Realized gains on sale of securities 3.2 2.8 Total before tax (0.7) (0.6) Tax expense 2.5 2.2 Net of tax Amortization of benefit plan items Negative prior service cost 4.8 4.8 (b) Net actuarial loss (11.0) (7.2) (b) (6.2) (2.4) Total before tax 1.3 0.5 Tax benefit (4.9) (1.9) Net of tax Total reclassifications for the period $ (2.4) $ 0.3 (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	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ and shares in millions, except per share amounts) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Numerator: Net income (loss) for basic earnings (loss) per common share $ 11.6 $ 11.5 $ (68.7) $ 54.7 Denominator: Weighted average shares for basic earnings (loss) per common share 43.8 43.5 43.7 43.4 Effect of dilutive share-based awards 0.5 0.5 — 0.6 Adjusted weighted average shares for diluted earnings (loss) per common share 44.3 44.0 43.7 44.0 Basic net earnings (loss) per common share $ 0.26 $ 0.26 $ (1.57) $ 1.26 Diluted net earnings (loss) per common share $ 0.26 $ 0.25 $ (1.57) $ 1.25 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 nine months ended September 30, 2020: (shares in millions) Nine months ended September 30 2020 Total number of antidilutive awards 0.6

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2020
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 three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Revenue from external sources: Insurance operations Personal insurance $ 208.8 $ 192.7 $ 609.7 $ 562.5 Commercial insurance 144.4 127.0 414.7 361.4 Specialty run-off — (0.1) — 6.1 Total insurance operations 353.2 319.6 1,024.4 930.0 Investment operations Net investment income 17.9 19.3 54.5 60.4 Net investment gain (loss) 20.0 (5.0) (39.3) 50.2 Total investment operations 37.9 14.3 15.2 110.6 All other 0.5 0.6 1.6 1.6 Total revenue from external sources 391.6 334.5 1,041.2 1,042.2 Intersegment revenue 1.5 1.7 4.6 4.9 Total revenue 393.1 336.2 1,045.8 1,047.1 Reconciling items: Eliminate intersegment revenue (1.5) (1.7) (4.6) (4.9) Total consolidated revenues $ 391.6 $ 334.5 $ 1,041.2 $ 1,042.2 Segment income (loss) before federal income tax: Insurance operations SAP underwriting (loss) gain Personal insurance $ (30.7) $ (6.3) $ (70.8) $ (32.0) Commercial insurance 14.4 1.2 (28.0) (17.1) Specialty run-off (10.4) (0.6) (17.1) (1.3) Total insurance operations (26.7) (5.7) (115.9) (50.4) Investment operations Net investment income 17.9 19.3 54.5 60.4 Net investment gain (loss) 20.0 (5.0) (39.3) 50.2 Total investment operations 37.9 14.3 15.2 110.6 All other — — 0.1 0.2 Total segment income (loss) before reconciling items 11.2 8.6 (100.6) 60.4 Reconciling items: GAAP expense adjustments 5.6 7.2 20.2 17.3 Interest expense on corporate debt (1.1) (1.2) (3.6) (3.7) Corporate expenses (0.9) (1.9) (3.6) (7.3) Total reconciling items 3.6 4.1 13.0 6.3 Total consolidated income (loss) before federal income tax $ 14.8 $ 12.7 $ (87.6) $ 66.7 Investable assets attributable to the Company’s investment operations segment totaled $2,782.2 million and $2,747.3 million at September 30, 2020, and December 31, 2019, respectively.

Basis of Presentation Significa

Basis of Presentation Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Investments	Investments Investments in fixed maturities are classified as available-for-sale and are carried at fair value. For fixed maturities in an unrealized loss position, management considers 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. If this assessment indicates that a credit loss exists, the present value of cash flows expected to be collected from the security are compared to the amortized cost basis of the security. If the present value of cash flows expected to be collected is less than the amortized cost basis, a credit loss exists and an allowance for credit losses is recorded for the credit loss, limited by the amount that the fair value is less than the amortized cost basis. Any impairment that has not been recorded through an allowance for credit losses is recognized in other comprehensive income. Changes in the allowance for credit losses are recorded in the "net investment gain (loss)" line item on the condensed consolidated statement of income. Losses are charged against the allowance when management believes the uncollectibility of a fixed maturity is confirmed or when either of the criteria regarding intent or requirement to sell is met. Description and disclosure of credit losses on fixed maturities are disclosed in Note 3 of the Notes to Condensed Consolidated Financial Statements.
Premiums	Premiums Premiums are recognized as earned pro rata over the policy period. Unearned premiums represent the portion of premiums written relative to the unexpired terms of coverage. Under the terms of the Pooling Arrangement, each period State Auto Mutual collects all premiums from policyholders and pays all losses and expenses associated with the insurance business produced by the STFC Pooled Companies and the other pool participants, and then it settles the intercompany balances generated by these transactions with the pool participants within 60 days following each quarter end. When settling the intercompany balances, State Auto Mutual provides the pool participants with full credit for their share of the Pooled Companies net premiums written during the quarter.
New Accounting Pronouncements	Adoption of Recent Accounting Pronouncements Measurement of Credit Losses on Financial Instruments On January 1, 2020, the Company adopted ASU 2016-13 Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments, which replaces the incurred loss methodology with an expected loss methodology that is referred to as the current expected credit loss (CECL) methodology. The measurement of expected credit losses under the CECL methodology is applicable to financial assets measured at amortized cost. This includes the Company's direct third party reinsurance recoverables, and the Company's share of the State Auto Group's third party reinsurance recoverables assumed via the Pooling Arrangement (as defined in Note 7). In addition, ASC 326 made changes to the accounting for available-for-sale fixed maturities. One such change is to require credit losses to be presented as an allowance rather than as a write-down on available-for-sale fixed maturities management does not intend to sell or believes that it is more likely than not they will not be required to sell. The adoption of this guidance reduced retained earnings by $0.5 million, net of tax, and established an allowance for estimated uncollectible reinsurance as of January 1, 2020. Adoption of ASC 326 for available-for-sale fixed maturities was prospective, and therefore there was no adjustment to retained earnings as of January 1, 2020. Changes to the Company's accounting policy resulting from the adoption of the guidance are discussed below. Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement
Reinsurance Recoverables	Reinsurance RecoverablesManagement assesses expected credit losses on third party reinsurance recoverables for the entire State Auto Pool and, pursuant to the Pooling Arrangement (as defined in Note 7), the Company is responsible for its share of the estimated uncollectible reinsurance for the entire pool. Management uses A.M. Best’s Financial Strength ratings or equivalent such as S&P, Moody’s, or Fitch when an A.M. Best Financial Strength rating is not available to assess the credit risk of the reinsurance recoverables. The estimate of expected credit losses considers historical credit loss information as well as current conditions and reasonable and supportable forecasts. Description and disclosure of credit losses on reinsurance recoverables are disclosed in Note 8 of the Notes to Condensed Consolidated Financial Statements.

Accounting Changes and Error _2

Accounting Changes and Error Corrections (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Changes and Error Corrections [Abstract]
Schedule of Error Corrections and Prior Period Adjustments	The following tables reconcile selected lines from the Company’s year-end 2019 consolidated balance sheet and the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 from the previously reported amounts to the revised amounts. There were no changes to the condensed consolidated statements of income, condensed consolidated statements of comprehensive income, and condensed consolidated statements of stockholders' equity. Revised Consolidated Balance Sheets ($ in millions) Year Ended December 31, 2019 As Reported Adjustment As Revised Assets Premiums receivable $ — $ 13.6 $ 13.6 Due from affiliate 21.5 (13.6) 7.9 Total Assets $ 2,985.4 $ — $ 2,985.4 Revised Consolidated Statement of Cash Flows ($ in millions) Nine months ended September 30, 2019 As Reported Adjustment As Revised Cash flows from operating activities: Changes in operating assets and liabilities: Premiums receivable $ — $ (3.2) $ (3.2) Other liabilities and due to/from affiliates, net (55.0) 3.2 (51.8) Net cash used in operating activities $ (43.9) $ — $ (43.9)

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2020
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 September 30, 2020 and December 31, 2019: ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value September 30, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 510.9 $ 48.1 $ — $ 559.0 Obligations of states and political subdivisions 527.5 26.7 (1.5) 552.7 Corporate securities 451.7 21.9 — 473.6 U.S. government agencies mortgage-backed securities 557.0 25.3 (1.3) 581.0 Total available-for-sale fixed maturities $ 2,047.1 $ 122.0 $ (2.8) $ 2,166.3 ($ millions) Amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 569.2 $ 12.3 $ (3.3) $ 578.2 Obligations of states and political subdivisions 404.3 21.1 — 425.4 Corporate securities 460.5 11.7 (0.4) 471.8 U.S. government agencies mortgage-backed securities 646.0 11.1 (4.6) 652.5 Total available-for-sale fixed maturities $ 2,080.0 $ 56.2 $ (8.3) $ 2,127.9
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 September 30, 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 September 30, 2020 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 0.7 $ — 1 $ — $ — — $ 0.7 $ — 1 Obligations of states and political subdivisions 94.3 (1.5) 18 — — — 94.3 (1.5) 18 Corporate securities 15.1 — 4 — — — 15.1 — 4 U.S. government agencies mortgage-backed securities 76.1 (1.1) 22 9.4 (0.2) 4 85.5 (1.3) 26 Total temporarily impaired securities $ 186.2 $ (2.6) 45 $ 9.4 $ (0.2) 4 $ 195.6 $ (2.8) 49 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 at December 31, 2019: ($ 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, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 136.0 $ (2.5) 17 $ 157.6 $ (0.8) 11 $ 293.6 $ (3.3) 28 Corporate securities — — — 40.8 (0.4) 7 40.8 (0.4) 7 U.S. government agencies mortgage-backed securities 126.6 (1.5) 15 137.9 (3.1) 32 264.5 (4.6) 47 Total temporarily impaired securities $ 262.6 $ (4.0) 32 $ 336.3 $ (4.3) 50 $ 598.9 $ (8.3) 82
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 September 30, 2020: ($ millions) Amortized cost Fair Due in 1 year or less $ 119.8 $ 120.9 Due after 1 year through 5 years 519.9 548.0 Due after 5 years through 10 years 168.0 178.9 Due after 10 years 682.4 737.5 U.S. government agencies mortgage-backed securities 557.0 581.0 Total $ 2,047.1 $ 2,166.3
Components of Net Investment Income	The following table sets forth the components of net investment income for the three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine Months Ended September 30 2020 2019 2020 2019 Fixed maturities $ 15.0 $ 15.3 $ 44.6 $ 47.7 Equity securities 2.1 3.0 7.8 8.9 Cash and cash equivalents, and other 0.9 1.1 2.7 4.2 Investment income 18.0 19.4 55.1 60.8 Investment expenses 0.1 0.1 0.6 0.4 Net investment income $ 17.9 $ 19.3 $ 54.5 $ 60.4
Realized and Unrealized Holding Gains (Losses)	The following table sets forth the realized and unrealized holding gains (losses) on the Company’s investment portfolio for the three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine Months Ended September 30 2020 2019 2020 2019 Investment gain (loss), net: Fixed maturities: Realized gains on sales of securities $ 1.3 $ 1.2 $ 6.8 $ 2.8 Realized losses on sales of securities (1.5) — (3.6) — Net (loss) gain on fixed securities (0.2) 1.2 3.2 2.8 Equity securities: Realized losses on sales of securities, net (42.3) (1.8) (50.9) (2.5) Unrealized gain (loss) on securities still held, net 60.5 (4.1) 15.8 46.4 Net gain (loss) on equity securities 18.2 (5.9) (35.1) 43.9 Other invested assets: Unrealized gain (loss) on securities still held, net 2.0 (0.3) (7.6) 4.8 Net gain (loss) on other invested assets 2.0 (0.3) (7.6) 4.8 Other net realized gain (loss) — — 0.2 (1.3) Net gain (loss) on investments $ 20.0 $ (5.0) $ (39.3) $ 50.2 Change in net unrealized holding gains, net of tax Fixed maturities $ 4.8 $ 21.4 $ 71.3 $ 89.0 Deferred federal income tax liability (1.1) (4.5) (15.0) (18.7) Change in net unrealized holding gains, net of tax $ 3.7 $ 16.9 $ 56.3 $ 70.3

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2020
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 September 30, 2020 and December 31, 2019: ($ millions) Total Level 1 Level 2 September 30, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 559.0 $ — $ 559.0 Obligations of states and political subdivisions 552.7 — 552.7 Corporate securities 473.6 — 473.6 U.S. government agencies mortgage-backed securities 581.0 — 581.0 Total available-for-sale fixed maturities 2,166.3 — 2,166.3 Equity securities: Large-cap securities 120.0 120.0 — Mutual and exchange traded funds 219.5 219.5 — Total equity securities 339.5 339.5 — Other invested assets 14.0 14.0 — Total investments $ 2,519.8 $ 353.5 $ 2,166.3 ($ millions) Total Level 1 Level 2 December 31, 2019 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 578.2 $ — $ 578.2 Obligations of states and political subdivisions 425.4 — 425.4 Corporate securities 471.8 — 471.8 U.S. government agencies mortgage-backed securities 652.5 — 652.5 Total available-for-sale fixed maturities 2,127.9 — 2,127.9 Equity securities: Large-cap securities 104.4 104.4 — Mutual and exchange traded funds 290.8 290.8 — Total equity securities 395.2 395.2 — Other invested assets 13.3 13.3 — Total investments $ 2,536.4 $ 408.5 $ 2,127.9
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) September 30, 2020 December 31, 2019 Carrying value Fair value Interest rate Carrying value Fair Interest rate Notes receivable from affiliate, issued May 2019 $ 70.0 $ 82.4 4.05 % $ 70.0 $ 74.6 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) September 30, 2020 December 31, 2019 Carrying value Fair Value Interest rate Carrying value Fair value Interest rate FHLB Loan due 2021: issued $21.5, September 2016 with fixed interest $ — $ — — % $ 21.5 $ 21.5 1.73 % FHLB Loan due 2030: issued $21.5, September 2020 with fixed interest 21.5 21.8 1.37 % — — — % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 108.6 3.96 % 85.3 97.8 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.2 15.2 4.44 % 15.2 15.2 6.11 % Total notes payable $ 122.0 $ 145.6 $ 122.0 $ 134.5

Deferred Acquisition Costs De_2

Deferred Acquisition Costs Deferred Acquisition Costs (Tables)	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) 2020 2019 Beginning balance at July 1 $ 120.0 $ 109.1 Acquisition costs deferred 98.4 94.6 Acquisition costs amortized to expense (94.7) (89.4) Ending balance at September 30 $ 123.7 $ 114.3 Beginning balance at January 1 $ 111.1 $ 101.9 Acquisition costs deferred 289.8 270.6 Acquisition costs amortized to expense (277.2) (258.2) Ending balance at September 30 $ 123.7 $ 114.3

Losses and Loss Expenses Paya_2

Losses and Loss Expenses Payable Losses and Loss Expenses Payable (Tables)	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) 2020 2019 Losses and loss expenses payable, at beginning of period $ 1,066.5 $ 1,146.8 Less: reinsurance recoverable on losses and loss expenses payable 13.6 5.5 Net balance at beginning of period 1,052.9 1,141.3 Incurred related to: Current year 779.8 692.7 Prior years (17.6) (55.1) Total incurred 762.2 637.6 Paid related to: Current year 420.8 366.4 Prior years 338.2 327.0 Total paid 759.0 693.4 Net balance at end of period 1,056.1 1,085.5 Plus: reinsurance recoverable on losses and loss expenses payable 35.2 7.2 Losses and loss expenses payable, at end of period $ 1,091.3 $ 1,092.7

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Premiums earned: Assumed from external insurers and reinsurers $ 21.7 $ 21.0 $ 63.0 $ 59.3 Assumed under Pooling Arrangement 353.2 319.6 1,024.4 930.0 Ceded to external insurers and reinsurers (7.7) (6.6) (25.4) (18.8) Ceded under Pooling Arrangement (283.9) (263.9) (835.2) (761.5) Net assumed premiums earned $ 83.3 $ 70.1 $ 226.8 $ 209.0 Losses and loss expenses incurred: Assumed from external insurers and reinsurers $ 14.1 $ 14.6 $ 41.3 $ 45.6 Assumed under Pooling Arrangement 251.6 209.3 762.2 639.4 Ceded to external insurers and reinsurers (9.9) (0.6) (55.9) (6.2) Ceded under Pooling Arrangement (202.9) (185.1) (629.4) (514.3) Net assumed losses and loss expenses incurred $ 52.9 $ 38.2 $ 118.2 $ 164.5

Current Expected Credit Losse_2

Current Expected Credit Losses Current Expected Credit Losses (Tables)	9 Months Ended
	Sep. 30, 2020
Credit Loss [Abstract]
Reinsurance Recoverable, Credit Quality Indicator [Table Text Block]	The following table sets forth the amortized cost of the Company's direct third-party reinsurance recoverables by FSR, net of the allowance for credit losses, at September 30, 2020: ($ millions) Amortized Cost Financial strength rating: A++ $ 1.2 A+ 15.3 A 18.7 Reinsurance recoverable on losses and loss expenses payable, net of allowance for credit losses $ 35.2
Premium Receivable, Allowance for Credit Loss [Table Text Block]	The following table sets forth the changes in the Company's share of the allowance for uncollectible premiums receivable for the three and nine months ended September 30, 2020: ($ millions) Allowance for credit losses Beginning balance at July 1, 2020 $ 7.0 Current period provision 1.1 Writeoffs (1.1) Ending balance at September 30, 2020 $ 7.0 Beginning balance at January 1, 2020 $ 4.3 Current period provision 6.7 Writeoffs (4.0) Ending balance at September 30, 2020 $ 7.0

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Amount at statutory rate $ 3.1 21.0 % $ 2.7 21.0 % $ (18.4) 21.0 % $ 14.0 21.0 % Tax-exempt interest and dividends received deduction (0.6) (4.1) (0.7) (5.3) (1.7) 1.9 (2.1) (3.1) Other, net 0.7 4.5 (0.8) (6.3) 1.2 (1.4) 0.1 — Federal income tax expense (benefit) 3.2 21.4 % 1.2 9.4 % (18.9) 21.5 % $ 12.0 17.9 %

Pension and Postretirement Be_2

Pension and Postretirement Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2020
Retirement Benefits [Abstract]
Company's Share of Net Periodic Cost Components	for the three and nine months ended September 30, 2020 and 2019: ($ millions) Pension Postretirement Pension Postretirement Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 2020 2019 2020 2019 Service cost $ 1.2 $ 0.8 $ — $ — $ 3.6 $ 2.8 $ — $ — Interest cost 2.4 2.9 0.2 0.2 7.2 8.6 0.4 0.5 Expected return on plan assets (4.4) (4.2) — — (13.1) (12.5) — — Amortization of: Negative prior service cost — — (1.4) (1.4) — — (4.1) (4.1) Net actuarial loss 2.3 1.5 0.1 0.1 6.9 4.5 0.2 0.2 Net periodic cost (benefit) $ 1.5 $ 1.0 $ (1.1) $ (1.1) $ 4.6 $ 3.4 $ (3.5) $ (3.4)

Other Comprehensive Income an_2

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Sep. 30, 2020
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 income (loss) ("AOCI(L)"), net of tax, for the three and nine months ended September 30, 2020 and 2019: ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at July 1, 2020 $ 93.0 $ (75.1) $ 17.9 Other comprehensive income before reclassifications 3.5 — 3.5 Amounts reclassified from AOCI (a) 0.2 1.7 1.9 Net current period other comprehensive income 3.7 1.7 5.4 Ending balance at September 30, 2020 $ 96.7 $ (73.4) $ 23.3 Beginning balance at July 1, 2019 $ 33.2 $ (74.9) $ (41.7) Other comprehensive income before reclassifications 17.8 — 17.8 Amounts reclassified from AOCI (a) (0.9) 0.6 (0.3) Net current period other comprehensive income 16.9 0.6 17.5 Ending balance at September 30, 2019 $ 50.1 $ (74.3) $ (24.2) (a) See separate table below for details about these reclassifications ($ millions) Unrealized Gains Benefit Plan Items Total Beginning balance at January 1, 2020 $ 40.4 $ (78.3) $ (37.9) Other comprehensive income before reclassifications 58.8 — 58.8 Amounts reclassified from AOCI (a) (2.5) 4.9 2.4 Net current period other comprehensive income 56.3 4.9 61.2 Ending balance at September 30, 2020 $ 96.7 $ (73.4) $ 23.3 Beginning balance at January 1, 2019 $ (20.2) $ (76.2) $ (96.4) Other comprehensive loss before reclassifications 72.5 — 72.5 Amounts reclassified from AOCI (a) (2.2) 1.9 (0.3) Net current period other comprehensive income 70.3 1.9 72.2 Ending balance at September 30, 2019 $ 50.1 $ (74.3) $ (24.2) (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 income, by component, to the Company’s condensed consolidated statement of income for the three and nine months ended September 30, 2020 and 2019: ($ millions) Details about Accumulated Other Three months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2020 2019 Unrealized gains on available-for-sale fixed maturity investments $ (0.2) $ 1.2 Realized gain on sale of securities (0.2) 1.2 Total before tax — (0.3) Tax expense (0.2) 0.9 Net of tax Amortization of benefit plan items Negative prior service cost 1.6 1.6 (b) Net actuarial loss (3.7) (2.4) (b) (2.1) (0.8) Total before tax 0.4 0.2 Tax benefit (1.7) (0.6) Net of tax Total reclassifications for the period $ (1.9) $ 0.3 (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 Nine months ended September 30 Affected line item in the Condensed Comprehensive Income Components Consolidated Statements of Income 2020 2019 Unrealized gains on available-for-sale fixed maturity investments $ 3.2 $ 2.8 Realized gains on sale of securities 3.2 2.8 Total before tax (0.7) (0.6) Tax expense 2.5 2.2 Net of tax Amortization of benefit plan items Negative prior service cost 4.8 4.8 (b) Net actuarial loss (11.0) (7.2) (b) (6.2) (2.4) Total before tax 1.3 0.5 Tax benefit (4.9) (1.9) Net of tax Total reclassifications for the period $ (2.4) $ 0.3 (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)	9 Months Ended
	Sep. 30, 2020
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 nine months ended September 30, 2020 and 2019: ($ and shares in millions, except per share amounts) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Numerator: Net income (loss) for basic earnings (loss) per common share $ 11.6 $ 11.5 $ (68.7) $ 54.7 Denominator: Weighted average shares for basic earnings (loss) per common share 43.8 43.5 43.7 43.4 Effect of dilutive share-based awards 0.5 0.5 — 0.6 Adjusted weighted average shares for diluted earnings (loss) per common share 44.3 44.0 43.7 44.0 Basic net earnings (loss) per common share $ 0.26 $ 0.26 $ (1.57) $ 1.26 Diluted net earnings (loss) per common share $ 0.26 $ 0.25 $ (1.57) $ 1.25
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 nine months ended September 30, 2020: (shares in millions) Nine months ended September 30 2020 Total number of antidilutive awards 0.6

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2020
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 three and nine months ended September 30, 2020 and 2019: ($ millions) Three months ended September 30 Nine months ended September 30 2020 2019 2020 2019 Revenue from external sources: Insurance operations Personal insurance $ 208.8 $ 192.7 $ 609.7 $ 562.5 Commercial insurance 144.4 127.0 414.7 361.4 Specialty run-off — (0.1) — 6.1 Total insurance operations 353.2 319.6 1,024.4 930.0 Investment operations Net investment income 17.9 19.3 54.5 60.4 Net investment gain (loss) 20.0 (5.0) (39.3) 50.2 Total investment operations 37.9 14.3 15.2 110.6 All other 0.5 0.6 1.6 1.6 Total revenue from external sources 391.6 334.5 1,041.2 1,042.2 Intersegment revenue 1.5 1.7 4.6 4.9 Total revenue 393.1 336.2 1,045.8 1,047.1 Reconciling items: Eliminate intersegment revenue (1.5) (1.7) (4.6) (4.9) Total consolidated revenues $ 391.6 $ 334.5 $ 1,041.2 $ 1,042.2 Segment income (loss) before federal income tax: Insurance operations SAP underwriting (loss) gain Personal insurance $ (30.7) $ (6.3) $ (70.8) $ (32.0) Commercial insurance 14.4 1.2 (28.0) (17.1) Specialty run-off (10.4) (0.6) (17.1) (1.3) Total insurance operations (26.7) (5.7) (115.9) (50.4) Investment operations Net investment income 17.9 19.3 54.5 60.4 Net investment gain (loss) 20.0 (5.0) (39.3) 50.2 Total investment operations 37.9 14.3 15.2 110.6 All other — — 0.1 0.2 Total segment income (loss) before reconciling items 11.2 8.6 (100.6) 60.4 Reconciling items: GAAP expense adjustments 5.6 7.2 20.2 17.3 Interest expense on corporate debt (1.1) (1.2) (3.6) (3.7) Corporate expenses (0.9) (1.9) (3.6) (7.3) Total reconciling items 3.6 4.1 13.0 6.3 Total consolidated income (loss) before federal income tax $ 14.8 $ 12.7 $ (87.6) $ 66.7

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Due from Affiliate, Current	$ 404.8		$ 371
Premium Receivable, Allowance for Credit Loss	$ 7	$ 7	$ 4.3

Accounting Changes and Error _3

Accounting Changes and Error Corrections (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Premiums receivable	$ 14.1		$ 13.6
Due from Affiliates	18.3		7.9
Assets	3,068.5		2,985.4
Premiums receivables	(0.5)	$ (3.2)
Increase (Decrease) in Other Operating Assets and Liabilities, Net	8.5	(51.8)
Net cash provided by (used in) operating activities	$ 21.8	(43.9)
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Premiums receivable			0
Due from Affiliates			21.5
Assets			2,985.4
Premiums receivables		0
Increase (Decrease) in Other Operating Assets and Liabilities, Net		55
Net cash provided by (used in) operating activities		(43.9)
Revision of Prior Period, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Premiums receivable			13.6
Due from Affiliates			(13.6)
Assets			$ 0
Premiums receivables		(3.2)
Increase (Decrease) in Other Operating Assets and Liabilities, Net		(3.2)
Net cash provided by (used in) operating activities		$ 0

Investments - Cost or Amortized

Investments - Cost or Amortized Cost and Fair Value of Available-for-Sale Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost	$ 2,047.1	$ 2,080
Gross unrealized holding gains	122	56.2
Gross unrealized holding losses	(2.8)	(8.3)
Fair value	2,166.3	2,127.9
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	510.9	569.2
Gross unrealized holding gains	48.1	12.3
Gross unrealized holding losses	0	(3.3)
Fair value	559	578.2
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	527.5	404.3
Gross unrealized holding gains	26.7	21.1
Gross unrealized holding losses	(1.5)	0
Fair value	552.7	425.4
Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	451.7	460.5
Gross unrealized holding gains	21.9	11.7
Gross unrealized holding losses	0	(0.4)
Fair value	473.6	471.8
U.S. Government Agencies Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized cost	557	646
Gross unrealized holding gains	25.3	11.1
Gross unrealized holding losses	(1.3)	(4.6)
Fair value	$ 581	$ 652.5

Investments - Available for Sal

Investments - Available for Sale Securities Continuous Unrealized Loss Position Fair Value and Aggregate Losses (Detail) $ in Millions	Sep. 30, 2020USD ($)position	Dec. 31, 2019USD ($)position
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 186.2	$ 262.6
Less than 12 months, Unrealized losses	$ (2.6)	$ (4)
Less than 12 months, Number of positions | position	45	32
12 months or more, Fair value	$ 9.4	$ 336.3
12 months or more, Unrealized losses	$ (0.2)	$ (4.3)
12 months or more, Number of positions | position	4	50
Total, Fair value	$ 195.6	$ 598.9
Total, Unrealized losses	$ (2.8)	$ (8.3)
Total, Number of positions | position	49	82
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	$ 0.7	$ 136
Less than 12 months, Unrealized losses	$ 0	$ (2.5)
Less than 12 months, Number of positions | position	1	17
12 months or more, Fair value	$ 0	$ 157.6
12 months or more, Unrealized losses	$ 0	$ (0.8)
12 months or more, Number of positions | position	0	11
Total, Fair value	$ 0.7	$ 293.6
Total, Unrealized losses	$ 0	$ (3.3)
Total, Number of positions | position	1	28
Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 94.3
Less than 12 months, Unrealized losses	$ (1.5)
Less than 12 months, Number of positions | position	18
12 months or more, Fair value	$ 0
12 months or more, Unrealized losses	$ 0
12 months or more, Number of positions | position	0
Total, Fair value	$ 94.3
Total, Unrealized losses	$ (1.5)
Total, Number of positions | position	18
Corporate Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 15.1	$ 0
Less than 12 months, Unrealized losses	$ 0	$ 0
Less than 12 months, Number of positions | position	4	0
12 months or more, Fair value	$ 0	$ 40.8
12 months or more, Unrealized losses	$ 0	$ (0.4)
12 months or more, Number of positions | position	0	7
Total, Fair value	$ 15.1	$ 40.8
Total, Unrealized losses	$ 0	$ (0.4)
Total, Number of positions | position	4	7
U.S. Government Agencies Mortgage-Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 76.1	$ 126.6
Less than 12 months, Unrealized losses	$ (1.1)	$ (1.5)
Less than 12 months, Number of positions | position	22	15
12 months or more, Fair value	$ 9.4	$ 137.9
12 months or more, Unrealized losses	$ (0.2)	$ (3.1)
12 months or more, Number of positions | position	4	32
Total, Fair value	$ 85.5	$ 264.5
Total, Unrealized losses	$ (1.3)	$ (4.6)
Total, Number of positions | position	26	47

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Value of Available-for-Sale Fixed Maturities by Contractual Maturity (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Amortized cost
Due in 1 year or less, Amortized cost	$ 119.8
Due after 1 year through 5 years, Amortized cost	519.9
Due after 5 years through 10 years, Amortized cost	168
Due after 10 years, Amortized cost	682.4
U.S. government agencies mortgage-backed securities, Amortized cost	557
Total, Amortized cost	2,047.1	$ 2,080
Fair value
Due in 1 year or less, Fair value	120.9
Due after 1 year through 5 years, Fair value	548
Due after 5 years through 10 years, Fair value	178.9
Due after 10 years, Fair value	737.5
U.S. government agencies mortgage-backed securities, Fair value	581
Total, Fair value	$ 2,166.3	$ 2,127.9

Investments - Components of Net

Investments - Components of Net Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Investment Income [Line Items]
Investment income	$ 18	$ 19.4	$ 55.1	$ 60.8
Investment expenses	0.1	0.1	0.6	0.4
Net investment income	17.9	19.3	54.5	60.4
Equity Securities [Member]
Net Investment Income [Line Items]
Investment income	2.1	3	7.8	8.9
Cash and Cash Equivalents, and Other [Member]
Net Investment Income [Line Items]
Investment income	0.9	1.1	2.7	4.2
Fixed Maturities [Member]
Net Investment Income [Line Items]
Investment income	$ 15	$ 15.3	$ 44.6	$ 47.7

Investments - Realized and Unre

Investments - Realized and Unrealized Holding Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Securities, Realized Gain (Loss):
Debt Securities, Available-for-sale, Realized Gain	$ 1.3	$ 1.2	$ 6.8	$ 2.8
Debt Securities, Available-for-sale, Realized Loss	(1.5)	0	(3.6)	0
Debt Securities, Available-for-sale, Net Realized Gain (Loss)	(0.2)	1.2	3.2	2.8
Equity Securities, FV-NI, Gain (Loss)
Other net realized loss	0	0	(0.2)	1.3
Gain (Loss) on Investments	20	(5)	(39.3)	50.2
Change in unrealized holding gains (losses), net of tax:
Change in net unrealized holding (losses) gains, net of tax	4.8	21.4	71.3	89
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(1.1)	(4.5)	(15)	(18.7)
Total net unrealized holding gains on available-for-sale investments	3.7	16.9	56.3	70.3
Equity Securities [Member]
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Realized Gain (Loss)	(42.3)	(1.8)	(50.9)	(2.5)
Equity Securities, FV-NI, Unrealized Gain (Loss)	60.5	(4.1)	15.8	46.4
Equity Securities, FV-NI, Net Gain (Loss)	18.2	(5.9)	(35.1)	43.9
Other Invested Assets [Member]
Equity Securities, FV-NI, Gain (Loss)
Equity Securities, FV-NI, Unrealized Gain (Loss)	2	(0.3)	(7.6)	4.8
Equity Securities, FV-NI, Net Gain (Loss)	$ 2	$ (0.3)	$ (7.6)	$ 4.8

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	$ 31.7
Fixed maturities fair value of deposit with insurance regulators	9.6		$ 9.3
Proceeds on sale of available-for-sale securities	303.2	$ 284.1
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

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	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	$ 2,166.3	$ 2,127.9
Investments, Fair Value Disclosure	2,519.8	2,536.4
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	559	578.2
Investments, Fair Value Disclosure	559	578.2
Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	552.7	425.4
Investments, Fair Value Disclosure	552.7	425.4
Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	473.6	471.8
Investments, Fair Value Disclosure	473.6	471.8
U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	581	652.5
Investments, Fair Value Disclosure	581	652.5
Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	2,166.3	2,127.9
Large-Cap Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	120	104.4
Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	219.5	290.8
Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	339.5	395.2
Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Investments, Fair Value Disclosure	14	13.3
Level 1 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	353.5	408.5
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	120	104.4
Level 1 [Member] | Mutual and exchange traded funds [Domain] [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	219.5	290.8
Level 1 [Member] | Equity Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	339.5	395.2
Level 1 [Member] | Other Invested Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	14	13.3
Level 2 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	2,166.3	2,127.9
Level 2 [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	559	578.2
Level 2 [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	552.7	425.4
Level 2 [Member] | Corporate Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	473.6	471.8
Level 2 [Member] | U.S. Government Agencies Mortgage-Backed Securities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	581	652.5
Level 2 [Member] | Fixed Maturities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value	2,166.3	2,127.9
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	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Document Period End Date		Sep. 30, 2020
Affiliated Entity [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable interest rate (percent)			7.00%
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		$ 82.4		$ 74.6

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Included in Notes Payable are the FHLB loan and Subordinated Debentures (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Document Period End Date	Sep. 30, 2020
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Interest rate (percent)	0.00%	1.73%
Debt Instrument, Face Amount	$ 21,500,000
Federal Home Loan Bank Advances due 2030 [Member]
Debt Instrument [Line Items]
Interest rate (percent)	1.37%	0.00%
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)	4.44%	6.11%
Debt Instrument, Face Amount	$ 15,500,000
Reported Value Measurement [Member]
Debt Instrument [Line Items]
Total notes payable	122,000,000	$ 122,000,000
Reported Value Measurement [Member] | Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Total notes payable	0	21,500,000
Reported Value Measurement [Member] | Federal Home Loan Bank Advances due 2030 [Member]
Debt Instrument [Line Items]
Total notes payable	21,500,000	0
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	15,200,000	15,200,000
Estimate of Fair Value Measurement [Member]
Debt Instrument [Line Items]
Total notes payable	145,600,000	134,500,000
Estimate of Fair Value Measurement [Member] | Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Total notes payable	0	21,500,000
Estimate of Fair Value Measurement [Member] | Federal Home Loan Bank Advances due 2030 [Member]
Debt Instrument [Line Items]
Total notes payable	21,800,000	0
Estimate of Fair Value Measurement [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	108,600,000	97,800,000
Estimate of Fair Value Measurement [Member] | Affiliate Subordinated Debentures Due 2033 [Member]
Debt Instrument [Line Items]
Total notes payable	$ 15,200,000	$ 15,200,000

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Additional Information (Detail) $ in Millions	1 Months Ended		9 Months Ended
	May 31, 2019Agreement	May 31, 2009Agreement	Sep. 30, 2019	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)
Fair Value Measurements Disclosure [Line Items]
Other invested assets				$ 62.5	$ 69.7
Other invested assets, at cost				12.5	6.5
Number of Credit Agreements | Agreement	2	2
Notes receivable from affiliate				70	70
Level 3 [Member]
Fair Value Measurements Disclosure [Line Items]
Federal home loan bank stock				12
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				$ 48.5	$ 56.4
Affiliated Entity [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable from affiliate				$ 70
Affiliated Entity [Member] | Level 2 [Member]
Fair Value Measurements Disclosure [Line Items]
Notes receivable interest rate (percent)			7.00%

Deferred Acquisition Costs De_3

Deferred Acquisition Costs Deferred Acquisition Costs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Deferred Policy Acquisition Cost, Period Start	$ 120	$ 109.1	$ 111.1	$ 101.9
Deferred Policy Acquisition Cost, Capitalization	98.4	94.6	289.8	270.6
Deferred Policy Acquisition Costs, Disposition	(94.7)	(89.4)	(277.2)	(258.2)
Deferred Policy Acquisition Cost, Period End	$ 123.7	$ 114.3	$ 123.7	$ 114.3

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Abstract]
Liability for Claims and Claims Adjustment Expense, Property Casualty Liability	$ 1,091.3	$ 1,092.7	$ 1,091.3	$ 1,092.7	$ 1,066.5	$ 1,146.8
Reinsurance Recoverables, Including Reinsurance Premium Paid	35.2	7.2	35.2	7.2	13.6	5.5
Liability for Unpaid Claims and Claims Adjustment Expense, Net	1,056.1	1,085.5	1,056.1	1,085.5	$ 1,052.9	$ 1,141.3
Current Year Claims and Claims Adjustment Expense			779.8	692.7
Prior Year Claims and Claims Adjustment Expense			(17.6)	(55.1)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	$ 251.6	$ 208.4	762.2	637.6
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			420.8	366.4
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			338.2	327
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid			$ 759	$ 693.4

Losses and Loss Expenses Paya_4

Losses and Loss Expenses Payable Losses and Loss Expenses Payable - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (17.6)	$ (55.1)
Specialty Insurance [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(5.2)
Personal Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(20.2)
Middle Market Commercial [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(14.3)	(7.2)
Personal Auto [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(19.1)	(11)
Workers' compensation [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(16.1)	(13.4)
Small commercial [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(16.5)	(11.8)
Total Insurance Segments [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(31.8)	$ (54.1)
E&S Property [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (12.4)

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Premiums earned:
Assumed from external insurers and reinsurers	$ 21.7	$ 21	$ 63	$ 59.3
Assumed under Pooling Arrangement	353.2	319.6	1,024.4	930
Ceded to external insurers and reinsurers	(7.7)	(6.6)	(25.4)	(18.8)
Ceded under Pooling Arrangement	(283.9)	(263.9)	(835.2)	(761.5)
Net assumed premiums earned	83.3	70.1	226.8	209
Losses and loss expenses incurred:
Assumed from external insurers and reinsurers	14.1	14.6	41.3	45.6
Assumed under Pooling Arrangement	251.6	209.3	762.2	639.4
Ceded to external insurers and reinsurers	(9.9)	(0.6)	(55.9)	(6.2)
Ceded under Pooling Arrangement	(202.9)	(185.1)	(629.4)	(514.3)
Net assumed losses and loss expenses incurred	$ 52.9	$ 38.2	$ 118.2	$ 164.5

Current Expected Credit Losse_3

Current Expected Credit Losses Reinsurance Recoverable, Credit Quality Indicator (Details) $ in Millions	Sep. 30, 2020USD ($)
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 35.2
AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	1.2
AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	15.3
AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 18.7

Current Expected Credit Losse_4

Current Expected Credit Losses Premiums Receivables, Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premium Receivable, Allowance for Credit Loss	$ 7	$ 7	$ 7	$ 4.3
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	1.1	6.7
Premium Receivable, Allowance for Credit Loss, Writeoff	$ (1.1)	$ (4)

Current Expected Credit Losse_5

Current Expected Credit Losses Current Expected Credit Losses - Additional Information (Details) $ in Millions	Sep. 30, 2020USD ($)
Credit Loss [Abstract]
Reinsurance Recoverable, Allowance for Credit Loss	$ 0.8

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	9 Months Ended
	Sep. 30, 2020USD ($)
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
Federal Home Loan Bank, Advances, Maturity Period, Fixed Rate	5 years
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Repayment and Penalties	$ 60
2016 [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank, Advances, Maturity Period, Fixed Rate	5 years
Long-term Federal Home Loan Bank Advances	$ 21.5
2020 [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank, Advances, Maturity Period, Fixed Rate	10 years
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Interest Rate	1.37%
Long-term Federal Home Loan Bank Advances	$ 21.5

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Amount at statutory rate	$ 3.1	$ 2.7	$ (18.4)	$ 14
Tax-exempt interest and dividends received deduction	(0.6)	(0.7)	(1.7)	(2.1)
Other, net	0.7	(0.8)	1.2	0.1
Federal income tax expense and effective rate	3.2	1.2	(18.9)	12
Income Tax Expense (Benefit)	$ 3.2	$ 1.2	$ (18.9)	$ 12
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)	(4.10%)	(5.30%)	1.90%	(3.10%)
Other, net (percent)	4.50%	(6.30%)	(1.40%)	0.00%
Effective Income Tax Rate Reconciliation, Deduction, Percent	21.40%	9.40%	21.50%	17.90%

Income Taxes Income Taxes (Addi

Income Taxes Income Taxes (Additional Information) (Details) $ in Millions	Sep. 30, 2020USD ($)
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	$ 0.5
Deferred Tax Assets, Valuation Allowance	$ 0.5

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1.2	$ 0.8	$ 3.6	$ 2.8
Interest cost	2.4	2.9	7.2	8.6
Expected return on plan assets	(4.4)	(4.2)	(13.1)	(12.5)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	0	0	0
Amortization of:
Defined Benefit Plan, Amortization of Gain (Loss)	2.3	1.5	6.9	4.5
Net periodic cost (benefit)	1.5	1	4.6	3.4
Postretirement [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0	0
Interest cost	0.2	0.2	0.4	0.5
Expected return on plan assets	0	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(1.4)	(1.4)	(4.1)	(4.1)
Amortization of:
Defined Benefit Plan, Amortization of Gain (Loss)	0.1	0.1	0.2	0.2
Net periodic cost (benefit)	$ (1.1)	$ (1.1)	$ (3.5)	$ (3.4)

Pension and Postretirement Be_4

Pension and Postretirement Benefit Plans - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Retirement Benefits [Abstract]
Contributions by employer	$ 15

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	$ 17.9	$ (41.7)	$ (37.9)	$ (96.4)
Other comprehensive income before reclassifications	3.5	17.8	58.8	72.5
Amounts reclassified from AOCI	1.9	(0.3)	2.4	(0.3)
Other comprehensive income	5.4	17.5	61.2	72.2
Ending balance	23.3	(24.2)	23.3	(24.2)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Amounts reclassified from AOCI	1.9	(0.3)	2.4	(0.3)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	93	33.2	40.4	(20.2)
Other comprehensive income before reclassifications	3.5	17.8	58.8	72.5
Amounts reclassified from AOCI	0.2	(0.9)	(2.5)	(2.2)
Other comprehensive income	3.7	16.9	56.3	70.3
Ending balance	96.7	50.1	96.7	50.1
Benefit Plan Items [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(75.1)	(74.9)	(78.3)	(76.2)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from AOCI	1.7	0.6	4.9	1.9
Other comprehensive income	1.7	0.6	4.9	1.9
Ending balance	$ (73.4)	$ (74.3)	$ (73.4)	$ (74.3)

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain/(loss) on sale of securities	$ 20	$ (5)	$ (39.3)	$ 50.2
Tax (expense) benefit	(3.2)	(1.2)	18.9	(12)
Total reclassifications for the period	(1.9)	0.3	(2.4)	0.3
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	(0.2)	0.9	2.5	2.2
Benefit Plan Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(1.7)	(0.6)	(4.9)	(1.9)
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(1.9)	0.3	(2.4)	0.3
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	(0.2)	1.2	3.2	2.8
Total before tax	(0.2)	1.2	3.2	2.8
Tax (expense) benefit	0	(0.3)	(0.7)	(0.6)
Net of tax	(0.2)	0.9	2.5	2.2
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	4.8	4.8
Accumulated other comprehensive income components/Net actuarial loss	(3.7)	(2.4)	(11)	(7.2)
Total before tax	(2.1)	(0.8)	(6.2)	(2.4)
Tax (expense) benefit	0.4	0.2	1.3	0.5
Net of tax	$ (1.7)	$ (0.6)	$ (4.9)	$ (1.9)

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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net (loss) income	$ 11.6	$ 11.5	$ (68.7)	$ 54.7
Denominator:
Weighted average shares for basic net earnings per common share (shares)	43.8	43.5	43.7	43.4
Effect of dilutive share-based awards (shares)	0.5	0.5	0	0.6
Adjusted weighted average shares for diluted net earnings per common share (shares)	44.3	44	43.7	44
Basic net (loss) earnings per common share (usd per share)	$ 0.26	$ 0.26	$ (1.57)	$ 1.26
Diluted net (loss) earnings per common share (usd per share)	$ 0.26	$ 0.25	$ (1.57)	$ 1.25

Earnings Per Common Share - Opt

Earnings Per Common Share - Options to Purchase Shares of Common Stock (Detail) shares in Millions	9 Months Ended
	Sep. 30, 2020shares
Earnings Per Share [Abstract]
Number of antidilutive options and awards	0.6

Segment Information - Financial

Segment Information - Financial Information Regarding Company's Reportable Segments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues from external sources:
Revenue	$ 391.6	$ 334.5	$ 1,041.2	$ 1,042.2
Other Income	0.5	0.6	1.6	1.6
Net Investment Income	17.9	19.3	54.5	60.4
Realized Investment Gains (Losses)	20	(5)	(39.3)	50.2
Segment income before federal income tax:
Interest expense on corporate debt	(1.1)	(1.2)	(3.6)	(3.7)
Income before federal income taxes	14.8	12.7	(87.6)	66.7
Operating Segments [Member]
Revenues from external sources:
Revenue	391.6	334.5	1,041.2	1,042.2
Segment income before federal income tax:
Income before federal income taxes	11.2	8.6	(100.6)	60.4
Operating Segments [Member] | Personal Insurance Segments [Member]
Revenues from external sources:
Revenue	208.8	192.7	609.7	562.5
Operating Segments [Member] | Business Insurance Segments [Member]
Revenues from external sources:
Revenue	144.4	127	414.7	361.4
Operating Segments [Member] | Specialty Insurance Segment [Member]
Revenues from external sources:
Revenue	0	(0.1)	0	6.1
Operating Segments [Member] | Total Insurance Segments [Member]
Revenues from external sources:
Revenue	353.2	319.6	1,024.4	930
Segment income before federal income tax:
Income before federal income taxes	(26.7)	(5.7)	(115.9)	(50.4)
Operating Segments [Member] | Net Investment Income [Member]
Revenues from external sources:
Net Investment Income	17.9	19.3	54.5	60.4
Operating Segments [Member] | Total Investment Operations [Member]
Revenues from external sources:
Revenue	37.9	14.3	15.2	110.6
Segment income before federal income tax:
Income before federal income taxes	37.9	14.3	15.2	110.6
Operating Segments [Member] | Total Investment Operations [Member] | Net Realized Capital Gains [Member]
Revenues from external sources:
Realized Investment Gains (Losses)		(5)		50.2
Segment income before federal income tax:
Income before federal income taxes	20	(5)	(39.3)	50.2
Operating Segments [Member] | All Other Segments [Member]
Revenues from external sources:
Revenue		0.6		1.6
Segment income before federal income tax:
Income before federal income taxes	0	0	0.1	0.2
Operating Segments [Member] | Personal Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	(30.7)	(6.3)	(70.8)	(32)
Operating Segments [Member] | Business Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	14.4	1.2	(28)	(17.1)
Operating Segments [Member] | Specialty Insurance [Member]
Segment income before federal income tax:
Income before federal income taxes	(10.4)	(0.6)	(17.1)	(1.3)
Eliminate Intersegment Revenues [Member]
Revenues from external sources:
Revenue	1.5	1.7	4.6	4.9
Segment Reconciling Items [Member]
Revenues from external sources:
Revenue	(1.5)	(1.7)	(4.6)	(4.9)
Segment income before federal income tax:
Corporate Expenses	(0.9)	(1.9)	(3.6)	(7.3)
Income before federal income taxes	3.6	4.1	13	6.3
Segment Reconciling Items [Member] | Segment Reconciling Items [Member]
Segment income before federal income tax:
Gaap Expense Adjustments	5.6	7.2	20.2	17.3
Interest expense on corporate debt	1.1	1.2	3.6	3.7
Corporate And Reconciling Items [Member]
Revenues from external sources:
Revenue	$ 393.1	$ 336.2	$ 1,045.8	$ 1,047.1

Segment Information - Additiona

Segment Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Acquisition And Operating Expenses	$ 123	$ 109.7	$ 357.4	$ 325.2
Investable assets	$ 2,782.2		$ 2,782.2		$ 2,747.3