State Auto Financial (STFC) 10-K 10 Mar 21 2020 FY Annual report Financial data

Document

Document - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 05, 2021	Jun. 30, 2020
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	000-19289
Entity Registrant Name	STATE AUTO FINANCIAL CORPORATION
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	31-1324304
Entity Address, Address Line One	518 East Broad Street
Entity Address, City or Town	Columbus
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	43215-3976
City Area Code	614
Local Phone Number	464-5000
Entity Well-known Seasoned Filer	No
Entity Voluntary Filer	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		44,041,707
Documents Incorporated by Reference	Portions of the Registrant’s Proxy Statement relating to the annual meeting of shareholders to be held May 14, 2021 (the “2021 Proxy Statement”), which will be filed within 120 days of December 31, 2020, are incorporated by reference into Part III of this Form 10-K.
Entity Public Float			$ 319,312,789
Entity Central Index Key	0000874977
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
ICFR Auditor Attestation Flag	true
Amendment Flag	false
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

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost $2,080.0 and $2,188.2, respectively)	$ 2,237.2	$ 2,128.4
Equity securities	389.7	395.2
Other invested assets	71.1	69.7
Other invested assets	12.1	6.5
Notes receivable from affiliate	70	70
Total Investments	2,780.1	2,669.8
Cash and cash equivalents	90.7	78
Premiums Receivable, Gross	14	13.6
Accrued investment income and other assets	29.7	31.7
Deferred policy acquisition costs (affiliated net assumed $20.2 and $19.9, respectively)	122.2	111.1
Reinsurance recoverable on losses and loss expenses payable	24.3	13.6
Prepaid reinsurance premiums	8.3	7.5
Due from affiliates	0	4.1
Current federal income taxes	1.7	6.3
Net deferred federal income taxes	27.3	39.7
Property and equipment, at cost (net of accumulated depreciation of $5.9 and $7.5, respectively)	4.2	4.2
Total assets	3,102.5	2,979.6
Liabilities and Stockholders’ Equity
Losses and loss expenses payable (affiliated net assumed $500.8 and $593.6, respectively)	1,050.4	1,066.5
Unearned Premiums (affiliated net assumed $116.7 and $112.4, respectively)	723.4	649.2
Notes payable (affiliates $15.2 and $15.2, respectively)	122.1	122
Postretirement and pension benefits	66.2	59.5
Due to affiliate	11.2	0
Other liabilities (affiliated net assumed $19.5 and $17.7, respectively)	119.2	114.9
Total liabilities	2,092.5	2,012.1
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 49.2 and 48.6 shares issued, respectively, at stated value of $2.50 per share	126.8	125.9
Treasury stock, 6.9 and 6.8 shares, respectively, at cost	(118.4)	(117.5)
Additional paid-in capital	213.3	206.7
Accumulated other comprehensive income	13.9	(26.9)
Retained earnings	774.4	779.3
Total stockholders’ equity	1,010	967.5
Total liabilities and stockholders’ equity	3,102.5	2,979.6
Class A Preferred stock
Stockholders’ equity:
Preferred stock value	0	0
Class B Preferred stock
Stockholders’ equity:
Preferred stock value	$ 0	$ 0

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fixed maturities, available-for-sale, amortized cost	$ 2,117	$ 2,080
Deferred Policy Acquisitions Costs from Affiliates	30.1	20.2
Property and equipment, accumulated depreciation	3.5	5.9
Losses And Loss Expenses Payable From Affiliates	438.8	500.8
Unearned premiums, affiliates	452.4	415.8
Net Other Liabilities from Affiliates	22.4	16.1
Notes payable, affiliates	$ 15.3	$ 15.2
Common stock, no par value (usd per share)	$ 0	$ 0
Common stock, shares authorized (shares)	100,000,000	100,000,000
Common stock, shares issued (shares)	50,700,000	50,400,000
Common Stock, Par or Stated Value Per Share	$ 2.50	$ 2.50
Treasury Stock, Shares	6,900,000	6,900,000
Class A Preferred stock
Preferred stock, no par value (usd per share)	$ 0	$ 0
Preferred stock, shares authorized (shares)	2,500,000	2,500,000
Preferred stock, shares issued (shares)	0	0
Class B Preferred stock
Notes payable, affiliates	$ 0	$ 0
Preferred stock, no par value (usd per share)	$ 2,500,000	$ 2,500,000
Preferred stock, shares authorized (shares)	0	0

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earned premiums (affiliated net assumed $220.3, $318.3 and $459.0, respectively)	$ 1,380.9	$ 1,250.2	$ 1,237.6
Net investment income (affiliates $3.6, $4.9 and $4.9, respectively)	72.1	80.4	84.9
Net realized gain on investments	27.3	74.2	(49.7)
Other income (affiliates $2.4, $2.6, and $2.3, respectively)	2.1	2.4	2.6
Total revenues	1,482.4	1,407.2	1,275.4
Losses and loss expenses (affiliated net assumed $169.3, $180.5 and $379.4, respectively)	972.6	844.8	796.4
Acquisition and operating expenses (affiliated net assumed $69.1, $108.7 and $160.7, respectively)	481.4	440.7	450.2
Interest expense (affiliates $1.1, $1.0, and $0.8, respectively)	4.7	4.9	5.7
Other Expenses	9.3	11.3	11
Total expenses	1,468	1,301.7	1,263.3
Income before federal income taxes	14.4	105.5	12.1
Current	(0.3)	(0.4)	(1.1)
Deferred Income Tax Expense (Benefit)	1.6	20.1	1
Total federal income tax expense (benefit)	1.3	19.7	(0.1)
Net (loss) income	$ 13.1	$ 85.8	$ 12.2
(Loss) earnings per common share:
Basic (usd per share)	$ 0.30	$ 1.98	$ 0.29
Diluted (usd per share)	$ 0.30	$ 1.93	$ 0.28

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums Earned, Net	$ 1,380.9	$ 1,250.2	$ 1,237.6
Net investment income, affiliates	2.8	3.6	4.9
Other income, affiliates	2.1	2.4	2.6
Losses and loss expenses, net affiliates	184.2	169.3	180.5
Net Acquisition and Operating Expenses	102.6	69.1	108.7
Interest Expense Debt To Affiliates	0.8	1.1	1
Affiliated entity
Premiums Earned, Net	267.5	222.5	318.6
Losses and loss expenses, net affiliates	184.2	169.3	180.5
Net Acquisition and Operating Expenses	$ 102.6	$ 69.1	$ 108.7

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ 13.1	$ 85.8	$ 12.2
Net change in unrealized holding gains (losses) on investments:
Unrealized holding gains (losses) arising during year	71.5	80.7	(46.4)
Reclassification adjustments for gains realized in net income	0.3	(3.5)	(2)
Income tax (expense) benefit	(15.1)	(16.2)	10.1
Total change in net unrealized holding gains (losses) on investments	56.7	61	(38.3)
Net unrecognized benefit plan obligations:
Net actuarial (loss) gain arising during period	(27.4)	7.5	(4.3)
Reclassification adjustments for amortization to statements of income:
Negative prior service cost	(6.3)	(6.3)	(6.3)
Net actuarial gain	13.7	9.6	13.2
Income tax expense	4.1	(2.3)	(0.6)
Total net unrecognized benefit plan obligations	(15.9)	8.5	2
Other comprehensive income (loss)	40.8	69.5	(36.3)
Comprehensive (loss) income	$ 53.9	$ 155.3	$ (24.1)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common shares:	Treasury shares:	Additional paid-in capital:	Accumulated other comprehensive income:	Accumulated other comprehensive income:Cumulative Effect, Period of Adoption, Adjustment	Retained earnings:	Retained earnings:Cumulative Effect, Period of Adoption, Adjustment
Balance at beginning of year (shares) at Dec. 31, 2017		49,200,000	6,800,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		(800,000)	0
Balance at end of year (shares) at Dec. 31, 2018		50,000,000	6,800,000
Balance at beginning of year at Dec. 31, 2017		$ 123	$ 116.8	$ 171.8	$ 3.8		$ 652
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		2		13.3
Shares acquired on stock award exercises and vested restricted shares			(0.2)
Stock awards granted				9.1
Change in unrealized holding gains (losses) on investments, net of tax	$ (38.3)				(38.3)
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	2				2
Stockholders' Equity, Period Increase (Decrease) | Accounting Standards Update 2016-01						$ (63.9)		$ 63.9
Stockholders' Equity, Period Increase (Decrease) | Accounting Standards Update 2016-13								0
Net (loss) income	12.2						12.2
Cash dividends paid (affiliates $10.4, $10.4 and $10.4, respectively)		(17.2)
Balance at end of year at Dec. 31, 2018	816.7	$ 125	$ 117	194.2	(96.4)		710.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		(400,000)	(100,000)
Balance at end of year (shares) at Dec. 31, 2019		50,400,000	6,900,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		$ 0.9		5.1
Shares acquired on stock award exercises and vested restricted shares			$ (0.5)
Stock awards granted				7.4
Change in unrealized holding gains (losses) on investments, net of tax	61				61
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	8.5				8.5
Stockholders' Equity, Period Increase (Decrease) | Accounting Standards Update 2016-01						0		0
Stockholders' Equity, Period Increase (Decrease) | Accounting Standards Update 2016-13								0
Net (loss) income	85.8						85.8
Cash dividends paid (affiliates $10.4, $10.4 and $10.4, respectively)		(17.4)
Balance at end of year at Dec. 31, 2019	967.5	$ 125.9	$ 117.5	206.7	(26.9)		779.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares (shares)		(300,000)	0
Balance at end of year (shares) at Dec. 31, 2020		50,700,000	6,900,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares		$ 0.9		3
Shares acquired on stock award exercises and vested restricted shares			$ (0.9)
Stock awards granted				3.6
Change in unrealized holding gains (losses) on investments, net of tax	56.7				56.7
Change in unrecognized benefit plan obligations, net of tax and reclassification adjustments	(15.9)				(15.9)
Stockholders' Equity, Period Increase (Decrease) | Accounting Standards Update 2016-01						$ 0		0
Stockholders' Equity, Period Increase (Decrease) | Accounting Standards Update 2016-13								$ (0.5)
Net (loss) income	13.1						13.1
Cash dividends paid (affiliates $10.4, $10.4 and $10.4, respectively)		(17.5)
Balance at end of year at Dec. 31, 2020	$ 1,010	$ 126.8	$ 118.4	$ 213.3	$ 13.9		$ 774.4

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retained earnings
Cash dividends paid affiliates	$ 10.4	$ 10.4	$ 10.4

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net (loss) income	$ 13,100	$ 85,800	$ 12,200
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation and amortization, net	10,600	9,400	8,900
Share-based compensation	900	6,100	11,100
Net realized gain on investments	(27,300)	(74,200)	49,700
Changes in operating assets and liabilities:
Deferred policy acquisition benefits	(11,100)	(9,200)	8,400
Accrued investment income and other assets	2,000	700	3,900
Increase (Decrease) in Premiums Receivable	(400)	(900)	(2,700)
Postretirement and pension benefits	(16,900)	(14,500)	(16,900)
Reinsurance recoverable on losses and loss expenses payable and prepaid reinsurance premiums	(11,500)	(9,000)	(2,600)
Other liabilities and due to/from affiliates, net	25,800	(42,500)	51,100
Losses and loss expenses payable	(16,600)	(80,300)	(108,800)
Unearned premiums	74,200	65,000	(27,600)
Excess tax expense on share-based awards	0	(900)	900
Federal income taxes	6,200	20,600	(1,000)
Net cash provided by operating activities	49,000	(43,900)	(13,400)
Cash flows from investing activities:
Purchases of fixed maturities available-for-sale	(661,000)	(592,600)	(349,600)
Purchases of equity securities available-for-sale	(88,900)	(63,400)	(91,400)
Purchases of other invested assets	(7,600)	(13,300)	(1,800)
Maturities, calls and pay downs of fixed maturities available-for-sale	384,100	386,300	229,800
Sales of fixed maturities available-for-sale	229,000	308,800	98,000
Sales of equity securities available-for-sale	121,100	45,400	97,800
Sales of other invested assets available-for-sale	1,300	1,300	1,200
Proceeds from Sale of Property, Plant, and Equipment	200	1,600	0
Net cash used in investing activities	(21,800)	74,100	(16,000)
Cash flows from financing activities:
Proceeds from issuance of common stock	3,900	5,900	15,400
Payments to acquire treasury stock	(900)	(500)	(200)
Payments of dividends (affiliates $10.4, $10.4 and $10.4, respectively)	(17,500)	(17,400)	(17,100)
Payment for Debt Extinguishment or Debt Prepayment Cost	0	0	400
Proceeds from Short-term Debt	(60,000)	0	0
Repayments of Short-term Debt	(60,000)	0	0
Repayments of Long-term Debt	(21,500)	0	0
Proceeds from long-term debt	21,500	0	0
Net cash (used in) provided by financing activities	(14,500)	(12,000)	(2,300)
Net increase (decrease) in cash and cash equivalents	12,700	18,200	(31,700)
Cash and cash equivalents at end of year	90,700	78,000	59,800
Supplemental disclosures:
Proceeds from Income Tax Refunds	4,900	0	0
Interest paid (affiliates $1.1, $1.0, and $0.8, respectively)	$ 4,700	$ 4,800	$ 5,700

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Cash Flows [Abstract]
Payments of dividends, affiliates	$ 10.4	$ 10.4	$ 10.4
Interest paid, affiliates	$ 0.8	$ 1.1	$ 1

SCHEDULE I - SUMMARY OF INVESTM

SCHEDULE I - SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES - Summary (Details) $ in Millions	Dec. 31, 2020USD ($)
Fixed maturities:
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown in the balance sheet	$ 2,237.2
U.S. treasury securities and obligations of U.S. government agencies
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown in the balance sheet	551.7
Obligations of states and political subdivisions
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown in the balance sheet	541.5
Corporate securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown in the balance sheet	483.3
U.S. government agencies mortgage-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Amount at which shown in the balance sheet	$ 660.7

SCHEDULE II - CONDENSED FINANCI

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Fixed maturities, available-for-sale, at fair value	$ 2,237.2	$ 2,128.4
Other invested assets	12.1	6.5
Cash and cash equivalents	90.7	78
Due from affiliates	0	4.1
Deferred Income Tax Assets, Net	27.3	39.7
Total consolidated assets	3,102.5	2,979.6
Liabilities and Stockholders’ Equity
Notes payable (affiliates $116.5 and $116.5, respectively)	122.1	122
Due to affiliate	11.2	0
Other liabilities	119.2	114.9
Liabilities	2,092.5	2,012.1
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 49.2 and 48.6 issued, respectively, at stated value of $2.50 per share	126.8	125.9
Treasury stock, 6.9 and 6.8 shares, respectively, at cost	(118.4)	(117.5)
Additional paid-in capital	213.3	206.7
Accumulated other comprehensive income	13.9	(26.9)
Retained earnings	774.4	779.3
Stockholders’ equity per accompanying consolidated financial statements	1,010	967.5
Total liabilities and stockholders' equity	3,102.5	2,979.6
Class A Preferred stock
Stockholders’ equity:
Preferred stock, value	0	0
Class B Preferred stock
Stockholders’ equity:
Preferred stock, value	0	0
State Auto Financial
Assets
Investments in common stock of subsidiaries (equity method)	1,108.6	1,067.5
Other invested assets	5.6	5
Cash and cash equivalents	7.3	8.8
Other assets	0	0.1
Due from affiliates	0.8	0
Deferred Income Tax Assets, Net	14	15.2
Total consolidated assets	1,136.3	1,096.6
Liabilities and Stockholders’ Equity
Notes payable (affiliates $116.5 and $116.5, respectively)	116.6	116.6
Due to affiliate	0	0.7
Other liabilities	9.7	11.8
Liabilities	126.3	129.1
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 49.2 and 48.6 issued, respectively, at stated value of $2.50 per share	126.8	125.9
Treasury stock, 6.9 and 6.8 shares, respectively, at cost	(118.4)	(117.5)
Additional paid-in capital	213.3	206.7
Accumulated other comprehensive income	13.9	(26.9)
Retained earnings	774.4	779.3
Stockholders’ equity per accompanying consolidated financial statements	1,010	967.5
Total liabilities and stockholders' equity	$ 1,136.3	$ 1,096.6

SCHEDULE II - CONDENSED FINAN_2

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Balance Sheets (Parenthetical) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Notes payable, affiliates	$ 15.3	$ 15.2
Common Stock, No Par Value	$ 0	$ 0
Common stock, shares authorized (shares)	100,000,000	100,000,000
Common stock, shares issued (shares)	50,700,000	50,400,000
Common stock, stated value per share (usd per share)	$ 2.50	$ 2.50
Treasury Stock, Shares	6,900,000	6,900,000
Class A Preferred stock
Condensed Financial Statements, Captions [Line Items]
Preferred stock, shares authorized (shares)	2,500,000	2,500,000
Preferred stock, shares issued (shares)	0	0
Class B Preferred stock
Condensed Financial Statements, Captions [Line Items]
Notes payable, affiliates	$ 0	$ 0
Preferred stock, shares authorized (shares)	0	0
State Auto Financial
Condensed Financial Statements, Captions [Line Items]
Notes payable, affiliates	$ 116.5	$ 116.5

SCHEDULE II - CONDENSED FINAN_3

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Financial Statements, Captions [Line Items]
Net investment income	$ 72.1	$ 80.4	$ 84.9
Net realized gain on investments	27.3	74.2	(49.7)
Total revenues	1,482.4	1,407.2	1,275.4
Interest expense (affiliates $6.1, $6.1 and $6.0, respectively)	4.7	4.9	5.7
Total expenses	1,468	1,301.7	1,263.3
Income before federal income taxes	14.4	105.5	12.1
Federal income tax expense (benefit)	(1.3)	(19.7)	0.1
State Auto Financial
Condensed Financial Statements, Captions [Line Items]
Net investment income	0.4	0.5	0.5
Net realized gain on investments	0.2	0.8	(0.6)
Total revenues	0.6	1.3	(0.1)
Interest expense (affiliates $6.1, $6.1 and $6.0, respectively)	6.1	6.3	6.3
Other operating expenses	1	5.2	7.1
Total expenses	7.1	11.5	13.4
Income before federal income taxes	(6.5)	(10.2)	(13.5)
Federal income tax expense (benefit)	(1.5)	(2.8)	(3.4)
Net (loss) income before equity in net income of subsidiaries	(5)	(7.4)	(10.1)
Equity in net income of subsidiaries	18.1	93.2	22.3
Net Income (Loss) Attributable to Parent	$ 13.1	$ 85.8	$ 12.2

SCHEDULE II - CONDENSED FINAN_4

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Income (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
State Auto Financial
Condensed Income Statements, Captions [Line Items]
Interest Expense Debt To Affiliates, Parent Company	$ 6.3	$ 6.1	$ 6.1

SCHEDULE II - CONDENSED FINAN_5

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net unrealized holding gains on investments:
Unrealized holding gain arising during the year	$ 71.5	$ 80.7	$ (46.4)
Reclassification adjustments for gains realized in net income	0.3	(3.5)	(2)
Income tax expense	(15.1)	(16.2)	10.1
Total change in net unrealized holding gains (losses) on investments	56.7	61	(38.3)
Other comprehensive income (loss)	40.8	69.5	(36.3)
Comprehensive Income (loss)	53.9	155.3	(24.1)
State Auto Financial
Condensed Financial Statements, Captions [Line Items]
Net Income (Loss) Attributable to Parent	13.1	85.8	12.2
Net unrealized holding gains on investments:
Unrealized equity in subsidiaries	40.8	69.5	(36.3)
Other comprehensive income (loss)	40.8	69.5	(36.3)
Comprehensive Income (loss)	$ 53.9	$ 155.3	$ (24.1)

SCHEDULE II - CONDENSED FINAN_6

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Depreciation and amortization, net	$ 10,600	$ 9,400	$ 8,900
Share-based compensation	900	6,100	11,100
Gain (Loss) on Sale of Investments	27,300	74,200	(49,700)
Changes in operating assets and liabilities:
Other liabilities and due from affiliates	25,800	(42,500)	51,100
Excess tax expense on share-based awards	0	(900)	900
Federal income taxes, net	6,200	20,600	(1,000)
Net cash provided by operating activities	49,000	(43,900)	(13,400)
Cash flows from investing activities:
Purchases of equity securities - available-for-sale	(88,900)	(63,400)	(91,400)
Purchases of other invested assets	(7,600)	(13,300)	(1,800)
Maturities, calls and pay downs of fixed maturities - available-for-sale	384,100	386,300	229,800
Sales of fixed maturities - available-for-sale	229,000	308,800	98,000
Sales of equity securities - available-for-sale	121,100	45,400	97,800
Net cash used in investing activities	(21,800)	74,100	(16,000)
Cash flows from financing activities:
Proceeds from issuance of common stock	3,900	5,900	15,400
Payments to acquire treasury stock	(900)	(500)	(200)
Payment of dividends	(17,500)	(17,400)	(17,100)
Proceeds from long-term debt	21,500	0	0
Net cash (used in) provided by financing activities	(14,500)	(12,000)	(2,300)
Cash and cash equivalents at beginning of year	78,000	59,800	91,500
Cash and cash equivalents at end of year	90,700	78,000	59,800
State Auto Financial
Condensed Financial Statements, Captions [Line Items]
Net Income (Loss) Attributable to Parent	13,100	85,800	12,200
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Share-based compensation	(2,700)	(1,400)	2,000
Gain (Loss) on Sale of Investments	(200)	(800)	500
Equity in net income from consolidated subsidiaries	(18,100)	(93,200)	(22,300)
Changes in operating assets and liabilities:
Other liabilities and due from affiliates	(800)	1,100	(100)
Excess tax expense on share-based awards	0	(900)	900
Federal income taxes, net	1,200	900	(300)
Net cash provided by operating activities	(7,500)	(8,500)	(7,100)
Cash flows from investing activities:
Dividends received from consolidated subsidiaries	21,000	14,800	15,400
Purchases of other invested assets	(500)	(300)	(400)
Net cash used in investing activities	20,500	14,500	15,000
Cash flows from financing activities:
Proceeds from issuance of common stock	3,900	5,900	15,400
Payments to acquire treasury stock	(900)	(500)	(200)
Payment of dividends	(17,500)	(17,400)	(17,100)
Net cash (used in) provided by financing activities	(14,500)	(12,000)	(1,900)
Net increase (decrease) in cash and cash equivalents	(1,500)	(6,000)	6,000
Cash and cash equivalents at beginning of year	8,800	14,800	8,800
Cash and cash equivalents at end of year	7,300	8,800	14,800
Supplemental disclosures:
Federal income tax received	2,700	2,800	4,000
Interest paid (affiliates $6.1, $6.1 and $6.0, respectively)	$ (6,100)	$ (6,300)	$ (6,300)

SCHEDULE II - CONDENSED FINAN_7

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Condensed Statements of Cash Flows (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Interest paid, affiliates	$ 1
State Auto Financial
Condensed Financial Statements, Captions [Line Items]
Interest paid, affiliates	$ 6.3	$ 6.1	$ 6.1

SCHEDULE II - CONDENSED FINAN_8

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Narrative (Details)	Jul. 11, 2013USD ($)internationalFund	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Condensed Financial Statements, Captions [Line Items]
Number of subsidiaries with shared credit agreements (subsidiaries) | internationalFund	2
Interest rate (percent)		5.28%
Retained earnings		$ 779,300,000
Deferred Income Tax Assets, Net		39,700,000
Tax expense		(19,700,000)	$ 100,000
Previously Reported [Member]
Condensed Financial Statements, Captions [Line Items]
Retained earnings		782,700,000
Deferred Income Tax Assets, Net		42,200,000
Tax expense		(19,600,000)	(100,000)
State Auto Financial
Condensed Financial Statements, Captions [Line Items]
Investments in common stock of subsidiaries (equity method)		1,067,500,000
Retained earnings		779,300,000
Deferred Income Tax Assets, Net		15,200,000
Tax expense		(2,800,000)	(3,400,000)
Equity in net income of subsidiaries		93,200,000	22,300,000
State Auto Financial | Previously Reported [Member]
Condensed Financial Statements, Captions [Line Items]
Investments in common stock of subsidiaries (equity method)		1,059,800,000
Retained earnings		782,700,000
Deferred Income Tax Assets, Net		15,300,000
Tax expense		(2,900,000)
Equity in net income of subsidiaries		94,700,000	22,900,000
Notes Payable
Condensed Financial Statements, Captions [Line Items]
Number of credit agreements (agreements) | internationalFund	2
Debt instrument, issued		100,000,000
Fair Value		122,800,000
Interest rate (percent)	5.28%
Notes Payable | State Auto P&C
Condensed Financial Statements, Captions [Line Items]
Debt instrument, issued	$ 85,000,000	85,000,000	85,000,000
Fair Value		104,400,000
Notes Payable | Milbank
Condensed Financial Statements, Captions [Line Items]
Debt instrument, issued	$ 15,000,000	15,000,000	$ 15,000,000
Fair Value		$ 18,400,000

SCHEDULE III - SUPPLEMENTARY IN

SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION - Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	$ 122.2	$ 111.1	$ 101.9
Future benefits, claims and losses	1,026.1	1,052.9	1,141.3
Unearned premiums	715.1	641.7	577.6
Other policy claims and benefits payable	0	0	0
Premium revenue	1,380.9	1,250.2	1,237.6
Net investment income	72.1	80.4	84.9
Benefits, losses and settlement expenses	973.9	846.5	798.1
Amortization of deferred policy acquisition costs	236.6	216.5	220
Other operating expenses	244.8	225.5	229.8
Premiums written	1,456.3	1,315.3	1,209.9
Personal insurance
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	68.7	62.6	59
Future benefits, claims and losses	280.6	247.2	240.5
Unearned premiums	418.1	373.9	340.9
Other policy claims and benefits payable	0	0	0
Premium revenue	819	755.9	673.4
Net investment income	0	0	0
Benefits, losses and settlement expenses	617.2	553.4	442.3
Amortization of deferred policy acquisition costs	135.1	127.5	114.7
Other operating expenses	125	110	116.3
Premiums written	863.2	789.1	726
Commercial insurance segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	53.4	48.3	41.6
Future benefits, claims and losses	572.2	572	581.9
Unearned premiums	296.9	267.5	230.7
Other policy claims and benefits payable	0	0	0
Premium revenue	561.8	488.6	464.4
Net investment income	0	0	0
Benefits, losses and settlement expenses	339.9	280.4	275.2
Amortization of deferred policy acquisition costs	101.3	88.2	84.1
Other operating expenses	119.1	113.3	115.7
Premiums written	593.3	526.3	469.8
Specialty insurance segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition cost	0	0.2	1.3
Future benefits, claims and losses	173.3	233.7	318.9
Unearned premiums	0.1	0.3	6
Other policy claims and benefits payable	0	0	0
Premium revenue	0.1	5.7	99.8
Net investment income	0	0	0
Benefits, losses and settlement expenses	16.8	12.7	80.6
Amortization of deferred policy acquisition costs	0.2	0.8	21.2
Other operating expenses	0.7	2.2	(2.2)
Premiums written	(0.2)	(0.1)	14
Investment operations segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net investment income	72.1	80.4	84.9
Benefits, losses and settlement expenses	0	0	0
Amortization of deferred policy acquisition costs	0	0	0
Other operating expenses	0	0	0
Premiums written	$ 0	$ 0	$ 0

SCHEDULE IV - REINSURANCE - Sum

SCHEDULE IV - REINSURANCE - Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	$ 1,067.6	$ 976.8	$ 881.3
Premiums Earned, Net Assumed (Ceded)	$ 1,380.9	$ 1,250.2	$ 1,237.6
Percentage of amount assumed to net (percent)	6.10%	6.50%	4.90%
Affiliated entity
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded to	$ 1,113.4	$ 1,027.1	$ 919.3
Assumed from	1,380.9	1,250.2	1,237.6
Premiums Earned, Net Assumed (Ceded)	1,380.9	1,250.2	1,237.6
Unaffiliated Companies
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded to	39	31	23
Assumed from	$ 84.8	$ 81.3	$ 61

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies a. Principles of Consolidation The consolidated financial statements include State Auto Financial Corporation (“State Auto Financial”), an Ohio corporation, and the following wholly owned subsidiaries of State Auto Financial: • State Auto Property and Casualty Insurance Company (“State Auto P&C”), an Iowa corporation • Milbank Insurance Company (“Milbank”), an Iowa corporation • State Auto Insurance Company of Ohio (“SA Ohio”), an Ohio corporation • Stateco Financial Services, Inc. (“Stateco”), an Ohio corporation The consolidated financial statements also include the operations and financial position of 518 Property Management and Leasing, LLC (“518 PML”), an Ohio limited liability company whose only members are State Auto P&C and Stateco. State Auto Financial is a majority-owned subsidiary of State Automobile Mutual Insurance Company (“State Auto Mutual”), an Ohio corporation. State Auto Financial and its subsidiaries are referred to herein as the “Company.” All intercompany balances and transactions have been eliminated in consolidation. b. Description of Business The Company markets its insurance products throughout the United States primarily through independent agencies, which include retail agencies and wholesale brokers. The Company’s principal lines of insurance include personal and commercial automobile, homeowners, commercial multi-peril, workers’ compensation, general liability and fire insurance. State Auto P&C, Milbank and SA Ohio are chartered and licensed property and casualty insurers. As such, they are subject to the regulations of the applicable Departments of Insurance of their respective states of domicile (the “Departments”) and the regulations of each state in which they operate. These property and casualty insurance companies undergo periodic financial examination by the Departments and insurance regulatory agencies of the states that choose to participate. A large portion of the Company’s revenues are derived from a reinsurance pooling agreement with State Auto Mutual and its affiliates. The underwriting activity and geographic distribution of State Auto Mutual and its affiliates is generally the same as the underwriting activity and geographic distribution of the Company. Through the employees of State Auto P&C, the Company provides management and operation services under management agreements for all of its insurance and non-insurance affiliates. Through Stateco, the Company provides investment management services to affiliated companies. c. Basis of Presentation The consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”), which vary in certain respects from statutory accounting practices (“SAP”) followed by State Auto P&C, Milbank and SA Ohio that are prescribed or permitted by the Departments. The Company’s insurance subsidiaries, domiciled in Ohio and Iowa, are required to prepare statutory basis financial statements in accordance with the accounting practices prescribed or permitted by the insurance departments of the states of domicile. Prescribed statutory accounting practices are those practices that are incorporated directly or by reference in state laws, regulations, and general administrative rules applicable to all insurance enterprises domiciled in a particular state. The Ohio and Iowa Departments of Insurance require insurers domiciled in their respective states to prepare statutory financial statements in accordance with National Association of Insurance Commissioners’ (“NAIC”) statutory accounting practices. Permitted statutory accounting practices are those practices that differ either from state-prescribed statutory accounting practices or NAIC statutory accounting practices. The Company’s insurance subsidiaries do not apply any statutory accounting practices that would be considered a prescribed statutory accounting practice that differs from NAIC statutory accounting practices. In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet, revenues and expenses for the periods then ended, and the accompanying notes to the financial statements. Such estimates and assumptions could change in the future as more information becomes known which could impact the amounts reported and disclosed herein. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of losses and loss expenses payable. In connection with the determination of losses and loss expenses payable, management uses historical data, current business conditions and assumptions about future conditions to formulate estimates of the ultimate cost to settle claims. These estimates by their nature are subject to uncertainties for various reasons. d. Investments Investments in fixed maturities are classified as available-for-sale and are carried at fair value. On January 1, 2020, the Company adopted ASU 2016-13 Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments on a prospective basis for its fixed maturities. The updated and prior policy for the available-for-sale fixed maturities are outlined below. December 31, 2020 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 4 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. December 31, 2019 and 2018 The unrealized holding gains and losses, net of applicable deferred income taxes, are shown as a separate component of stockholders’ equity as a part of accumulated other comprehensive income and, as such, are not included in the determination of net income. Realized gains and losses on the sales of investments are computed using the first-in, first-out method. The Company views gross unrealized losses on fixed maturities as being temporary since it is its assessment that these securities will recover in the near term, allowing the Company to realize the anticipated long-term economic value. The Company regularly monitors its investments that have fair values less than cost or amortized cost for signs of other-than-temporary 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 financial condition of the issuer, including receipt of scheduled principal and interest cash flows, and intent to sell, including if it is more likely than not that the Company will be required to sell the investments before recovery. When a fixed maturity security has been determined to have an other-than-temporary impairment, the impairment charge is separated into an amount representing the credit loss, which is recognized in earnings as a realized loss and the amount related to non-credit factors, which is recognized in other comprehensive income. Future increases or decreases in fair value, if not other-than-temporary, are included in other comprehensive income. e. Cash Equivalents The Company considers all liquid debt instruments with a maturity of three months or less at the time of acquisition to be cash equivalents. The carrying amounts reported approximate their fair value. f. Deferred Acquisition Costs Acquisition costs, consisting of net commissions (including ceding commissions), premium taxes and certain underwriting expenses related to the successful acquisition or renewal of property and casualty business, are deferred and amortized over the same period in which the related premiums are earned. Ceding commissions relating to reinsurance agreements reimburse us for both deferrable and non-deferrable acquisition costs. Excess ceding commissions are amortized in proportion to net revenue recognized on the underlying policies resulting in excess ceding commissions being recognized as a reduction of acquisition and operating expenses. The method followed for computing the acquisition costs limits the amount of such deferred costs to their estimated realizable value. In determining estimated realizable value, the computation gives effect to the premium to be earned, losses and loss expenses expected to be incurred, and certain other costs expected to be incurred as premium is earned. Future changes in estimates, the most significant of which is expected losses and loss adjustment expenses, that indicate a reduction in expected future profitability may result in unrecoverable deferred acquisition costs. Anticipated investment income is considered in determining whether a premium deficiency exists. The following table sets forth net deferred acquisition costs for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Balance, beginning of year $ 111.1 $ 101.9 $ 110.3 Acquisition costs deferred 247.7 225.7 211.6 Acquisition costs amortized to expense (236.6) (216.5) (220.0) Balance, end of year $ 122.2 $ 111.1 $ 101.9 g. Federal Income Taxes The Company files a consolidated federal income tax return. Pursuant to a written tax sharing agreement, each entity within the consolidated group pays or receives its share of federal income taxes based on separate return calculations. The Company recognizes deferred income tax assets and liabilities for the expected future tax effects attributable to temporary differences between the financial statement and tax return bases of assets and liabilities, based on enacted tax rates and other provisions of the tax law. The effect of a change in tax laws or rates on deferred tax assets and liabilities is recognized in income in the period in which such change is enacted. Deferred tax assets and liabilities include provisions for unrealized investment gains and losses as well as the net funded status of pension and other postretirement benefit obligations with the changes for each period included in the respective components of other comprehensive income. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that all or some portion of the deferred tax assets will not be realized. Interest and penalties related to uncertain tax positions are recorded in the balance sheet as other liabilities, and recognized in the income statement as other expenses. h. Losses and Loss Expenses Payable Losses and loss expenses payable reflect the estimated ultimate unpaid liability for losses and loss expenses with respect to reported and unreported claims incurred as of the end of each accounting period. Loss reserves are estimated using various standard actuarial projection methods and assumptions based on historical reporting and settlement patterns, expected loss ratios, trends in claims severity and frequency and other factors. There can be no assurance that the ultimate liability will not vary materially from such estimates. Estimates are refined as part of a regular, ongoing process as historical loss experience develops and additional claims are reported and settled, and such adjustments are included in current operations (see Note 5). Anticipated salvage and subrogation is estimated using historical experience. The liability for unpaid losses and loss expenses, net of estimated salvage and subrogation recoverable of $28.7 million and $28.2 million at December 31, 2020 and 2019, respectively, represents management’s best estimate of the ultimate liability related to reported and unreported claims. i. 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 9), 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. j. 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. Premiums receivable represents the billed and due premium written directly by the STFC Pooled Companies. 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. Description and disclosure of the allowance for uncollectible premiums receivable balance is disclosed in Note 9. l. New Accounting Standards 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 9). 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. 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. Compensation—Retirement Benefits—Defined Benefit Plans—General On August 28, 2018, the FASB issued ASU 2018-14, which amends ASC 715 to add, remove, and clarify disclosure requirements related to defined benefit pension and other postretirement plans. The ASU is effective for fiscal years beginning after December 15, 2020 and will be effective January 1, 2021. The Company has early-adopted these disclosure updates in this Form 10-K. 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. Reference Rate Reform: Facilitation of the Effects of Reference Rate Reform on Financial Reporting In March 2020, the FASB issued ASU 2020-04 to address constituents’ concerns about certain accounting consequences that could result from the global markets’ anticipated transition away from the use of the London Interbank Offered Rate (LIBOR) and other interbank offered rates to alternative reference rates. ASU 2020-04 was effective upon issuance through December 31, 2022. 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.

Accounting Changes and Error Co

Accounting Changes and Error Corrections	12 Months Ended
	Dec. 31, 2020
Accounting Changes and Error Corrections [Abstract]
Accounting Standards Update and Change in Accounting Principle	Revision of Misstatement in Prior Year Financial Statements Management identified a number of errors in the Company’s historical financial statements as further described below. In accordance with the guidance set forth in SEC Staff Accounting Bulletin No. 99, Materiality, and SEC Staff Accounting Bulletin No. 108, Considering the Effects of Prior Year Misstatements when Quantifying Misstatements in Current Year Financial Statements, management concluded that the errors were not material to the consolidated financial statements as presented in the Company’s quarterly and annual financial statements that had been previously filed in the Company’s Quarterly Reports on Form 10-Q and Annual Reports on Form 10-K. As a result, amendment of such reports is not required. The Company revised the previously issued annual consolidated financial statements for 2019 and 2018 in this Form 10-K to correct these errors as well as other immaterial out of period adjustments previously identified. As periods prior to 2018 were impacted, retained earnings as of January 1, 2018 was decreased by $1.2 million to recognize the cumulative net of tax impact of the correction of the errors as of that date. The Company corrected a balance sheet classification error at December 31, 2019 to separately present premiums receivable on its consolidated balance sheet. This had no impact on the underwriting results or cash flows of the Company. The Company changed the funding of its postretirement benefit plan effective January 1, 2020. As a result, the reported pension and postretirement benefits liability was reduced and reported stockholders' equity increased by recording additional pre-tax actuarial gain within accumulated other comprehensive income (loss) for the period ended December 31, 2019. There was no income statement impact for this change. The effect of the revisions on the Company's previously issued financial statements are provided in the tables below. Amounts throughout the consolidated financial statements and notes thereto have been adjusted to incorporate the revised amounts, where applicable. The following tables reconcile selected lines from the Company’s year-end 2019 consolidated balance sheet and year-end 2019 and 2018 consolidated statements of income, consolidated statements of comprehensive income and consolidated statements of cash flow from the previously reported amounts to the revised amounts. Revised Consolidated Balance Sheet ($ in millions) Year Ended December 31, 2019 As Reported Adjustment As Revised Assets Fixed maturities, available-for-sale, at fair value $ 2,127.9 $ 0.5 $ 2,128.4 Premiums receivable — 13.6 13.6 Due from affiliate 21.5 (17.4) 4.1 Net deferred federal income taxes 42.2 (2.5) 39.7 Total Assets 2,985.4 (5.8) 2,979.6 Liabilities and Stockholders’ Equity Pension and postretirement benefits 72.9 (13.4) 59.5 Total liabilities 2,025.5 (13.4) 2,012.1 Stockholders’ equity: Accumulated other comprehensive income (loss) (37.9) 11.0 (26.9) Retained earnings 782.7 (3.4) 779.3 Total stockholders’ equity 959.9 7.6 967.5 Total liabilities and stockholders’ equity 2,985.4 (5.8) 2,979.6 Revised Consolidated Statement of Income ($ in millions, except per share amounts) Year Ended December 31, 2019 Year Ended December 31, 2018 As Reported Adjustment As Revised As Reported Adjustment As Revised Earned premiums $ 1,253.0 $ (2.8) $ 1,250.2 $ 1,238.0 $ (0.4) $ 1,237.6 Total revenues 1,410.0 (2.8) 1,407.2 1,275.8 (0.4) 1,275.4 Acquisition and operating expenses 442.0 (1.3) 440.7 449.8 0.4 450.2 Total expenses 1,303.0 (1.3) 1,301.7 1,262.9 0.4 1,263.3 Income before federal income taxes 107.0 (1.5) 105.5 12.9 (0.8) 12.1 Deferred income tax expense (benefit) 20.0 0.1 20.1 1.2 (0.2) 1.0 Total federal income tax expense (benefit) 19.6 0.1 19.7 0.1 (0.2) (0.1) Net income 87.4 (1.6) 85.8 12.8 (0.6) 12.2 Earnings per common share: Basic $ 2.01 $ (0.03) $ 1.98 $ 0.30 $ (0.01) $ 0.29 Diluted $ 1.96 $ (0.03) $ 1.93 $ 0.29 $ (0.01) $ 0.28 Revised Consolidated Statement of Comprehensive Income ($ millions) Year Ended December 31, 2019 As Reported Adjustment As Revised Net income $ 87.4 $ (1.6) $ 85.8 Other comprehensive income, net of tax: Net change in unrealized holding gain on available-for-sale investments: Unrealized holding gains arising during year 80.2 0.5 80.7 Income tax expense (16.1) (0.1) (16.2) Total change in net unrealized holding gain on available-for-sale investments 60.6 0.4 61.0 Net unrecognized benefit plan obligations: Net actuarial gain (loss) arising during period (5.9) 13.4 7.5 Income tax benefit (expense) 0.5 (2.8) (2.3) Total net unrecognized benefit plan obligations (2.1) 10.6 8.5 Other comprehensive income 58.5 11.0 69.5 Comprehensive income 145.9 9.4 155.3 Revised Consolidated Statement of Cash Flows ($ in millions) Year ended December 31, 2019 Year ended December 31, 2018 As Reported Adjustment As Revised As Reported Adjustment As Revised Cash flows from operating activities: Net income $ 87.4 $ (1.6) $ 85.8 $ 12.8 $ (0.6) $ 12.2 Adjustments to reconcile net income to net cash (used in) provided by operating activities: Changes in operating assets and liabilities: Premiums receivable — (0.9) (0.9) — (2.7) (2.7) Other liabilities and due to/from affiliates, net (44.9) 2.4 (42.5) 47.6 3.5 51.1 Federal income taxes 20.5 0.1 20.6 (0.8) (0.2) (1.0) Net cash used in operating activities (43.9) — (43.9) (13.4) — (13.4)

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments [Abstract]
Investments	Investments The following tables set forth the cost or amortized cost and fair value of investments by lot at December 31, 2020 and 2019: ($ millions) Cost or amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 506.5 $ 45.2 $ — $ 551.7 Obligations of states and political subdivisions 511.3 30.4 (0.2) 541.5 Corporate securities 459.9 23.4 — 483.3 U.S. government agencies mortgage-backed securities 639.3 22.9 (1.5) 660.7 Total available-for-sale fixed maturities $ 2,117.0 $ 121.9 $ (1.7) $ 2,237.2 ($ millions) Cost or 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 $ 12.6 $ (3.3) $ 578.5 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 11.3 (4.6) 652.7 Total available-for-sale fixed maturities $ 2,080.0 $ 56.7 $ (8.3) $ 2,128.4 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 was not recorded at December 31, 2020 and 2019: ($ millions, except # of positions) Less than 12 months 12 months or more Total December 31, 2020 Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 9.6 $ — 4 $ — $ — — $ 9.6 $ — 4 Obligations of states and political subdivisions 19.5 (0.2) 5 — — — 19.5 (0.2) 5 Corporate securities 1.5 — 2 — — — 1.5 — 2 U.S. government agencies mortgage-backed securities 136.1 (1.4) 35 7.0 (0.1) 3 143.1 (1.5) 38 Total fixed maturities $ 166.7 $ (1.6) 46 $ 7.0 $ (0.1) 3 $ 173.7 $ (1.7) 49 ($ millions, except # of positions) Less than 12 months 12 months or more Total December 31, 2019 Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions 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 fixed maturities $ 262.6 $ (4.0) 32 $ 336.3 $ (4.3) 50 $ 598.9 $ (8.3) 82 The Company reviewed its investments at December 31, 2020 and determined that no credit impairment existed in the gross unrealized holding losses, due to the reasons discussed below: • U.S. treasury securities and obligations of U.S. government agencies: These securities were issued by the U.S. Treasury Department or Federal government-sponsored entities. The decline in fair values was attributable to changes in interest rates and not credit quality. The Company does not intend to sell these securities and it is likely that it will not do so before their anticipated recovery. Therefore, the Company does not consider these impaired securities. • Corporate securities: Corporations in various industries issued these securities. The decline in fair values was attributable to changes in interest rates and not credit quality. The Company reviewed the issuers of these securities to identify any significant adverse change in financial condition, a change in the quality of credit enhancement (if any), a ratings decrease, or negative outlook assignment from a major credit rating agency, and any failure to make interest or principal payments. After these reviews, the Company determined that the decline in fair values was attributable to changes in interest rates and not credit quality. The Company does not intend to sell these securities and it is likely that it will not do so before their anticipated recovery. Therefore, the Company does not consider these impaired securities. • U.S. government agencies mortgage-backed securities: Federal government-sponsored entities issued these securities. The decline in fair values was attributable to changes in interest rates and not credit quality. The Company does not intend to sell these securities and it is likely that it will not do so before their anticipated recovery. Therefore, the Company does not consider these impaired securities. The following table sets forth the amortized cost and fair value of available-for-sale fixed maturities by contractual maturity at December 31, 2020: ($ millions) Amortized cost Fair value Due in 1 year or less $ 140.5 $ 141.6 Due after 1 year through 5 years 510.3 540.4 Due after 5 years through 10 years 161.6 172.6 Due after 10 years 665.3 721.9 U.S. government agencies mortgage-backed securities 639.3 660.7 Total $ 2,117.0 $ 2,237.2 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 December 31, 2020, State Auto P&C had fixed maturity securities, with a carrying value of approximately $106.5 million, that were pledged as collateral for the FHLB Loan (as defined in Note 10). In accordance with the terms of the FHLB Loan, State Auto P&C retains all rights regarding these securities, which are included in the “U.S. government agencies mortgage-backed securities” classification of the Company’s fixed maturity securities portfolio. At December 31, 2020, State Auto P&C had fixed maturities with fair values of approximately $32.2 million pledged as collateral for the performance obligations under its reinsurance agreement with Home State County Mutual Insurance Company ("Home State") as defined in Note 7. 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 approximately $9.7 million and $9.3 million were on deposit with insurance regulators as required by law at December 31, 2020 and 2019, respectively. The following table sets forth the components of net investment income for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Fixed maturities $ 59.6 $ 62.3 $ 65.3 Equity securities 9.3 13.2 13.4 Cash and cash equivalents, and other 4.0 5.5 7.2 Investment income 72.9 81.0 85.9 Investment expenses 0.8 0.6 1.0 Net investment income $ 72.1 $ 80.4 $ 84.9 The Company’s current investment strategy does not rely on the use of derivative financial instruments. Proceeds on sales of investments in 2020, 2019 and 2018 were $351.4 million, $355.5 million, and $197.0 million, respectively. The following table sets forth the gains (losses) on investments on the Company’s investment portfolio for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Investment gain (loss), net: Fixed maturities: Realized gains on securities sold $ 5.2 $ 3.5 $ 2.0 Realized losses on securities sold (5.5) — — Net (loss) gain on fixed maturities (0.3) 3.5 2.0 Net gain (loss) on equity securities 26.7 62.1 (44.0) Net gain (loss) on other invested assets 0.7 9.9 (7.7) Other net realized gain (loss) 0.2 (1.3) — Net gain (loss) on investments $ 27.3 $ 74.2 $ (49.7) Change in net unrealized holding gains (losses), net of tax Fixed maturities $ 71.8 $ 77.2 $ (48.4) Deferred federal income tax (liability) benefit (15.1) (16.2) 10.1 Change in net unrealized holding gains (losses), net of tax $ 56.7 $ 61.0 $ (38.3) The unrealized holding gains (losses) recognized during the reporting period on equity securities still held at December 31, 2020, 2019 and 2018 were $58.5 million, $63.9 million, and $(49.7) million, respectively. The unrealized holding gains (losses) recognized during the reporting period on other invested assets still held at December 31, 2020, 2019 and 2018 were $0.8 million, $9.9 million, and $(7.7) million, respectively.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 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 pricing service to estimate the majority of its investment portfolio’s fair value. The Company obtains one price per security. The Company’s processes and control procedures are designed to ensure the price is accurately recorded on an unadjusted basis. Through discussions with the pricing service, the Company obtains 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 the valuations received to other fair value pricing from other independent pricing sources. At December 31, 2020 and 2019, the Company did not adjust any of the prices received from the pricing service. The following sections describe the valuation methods used by the Company for each type of financial instrument carried at fair value. 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 third party investment managers. The fund had a fair value of $55.8 million and $56.4 million at December 31, 2020 and 2019, respectively, which was determined using the fund’s net asset value. The Company employs procedures to assess the reasonableness of the fair value of the fund including obtaining and reviewing the fund’s audited financial statements. There is no unfunded commitment related to the fund. The Company may not sell its investment in the fund; however, the Company may redeem all or a portion of its investment in the fund at net asset value per share with the appropriate prior written notice. In accordance with Accounting Standard Codification 820-10, this investment is measured at fair value using the net asset value per share practical expedient and has not been classified in the fair value hierarchy. Fair values presented here are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the consolidated balance sheets. The remainder of the Company’s other invested assets consist of holdings in publicly-traded mutual funds. The Company believes that its prices for these publicly-traded mutual funds, based on an observable market price for an identical asset in an active market, reflect their fair values and consequently these securities have been disclosed in Level 1. The following tables set forth the Company’s investments within the fair value hierarchy at December 31, 2020 and 2019: ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 551.7 $ — $ 551.7 Obligations of states and political subdivisions 541.5 — 541.5 Corporate securities 483.3 — 483.3 U.S. government agencies mortgage-backed securities 660.7 — 660.7 Total available-for-sale fixed maturities 2,237.2 — 2,237.2 Equity securities: Large-cap securities 134.2 134.2 — Mutual and exchange traded funds 255.5 255.5 — Total equity securities 389.7 389.7 — Other invested assets 15.3 15.3 — Total investments $ 2,642.2 $ 405.0 $ 2,237.2 ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 578.5 $ — $ 578.5 Obligations of states and political subdivisions 425.4 — 425.4 Corporate securities 471.8 — 471.8 U.S. government agencies mortgage-backed securities 652.7 — 652.7 Total fixed maturities 2,128.4 — 2,128.4 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 $ 2,536.9 $ 408.5 $ 2,128.4 Financial Instruments Disclosed, But Not Carried, At Fair Value Other Invested Assets Included in other invested assets are common stock of the Federal Home Loan Bank of Cincinnati (the “FHLB”), and the Trust Securities (as defined in Note 9b). The Trust Securities and FHLB common stock are carried at cost, which approximates fair value. The fair value of the FHLB common stock at December 31, 2020 was $11.6 million and the fair value of the Trust Securities were $0.5 million. Both investments have been placed in Level 3 of the fair value hierarchy. Notes Receivable from Affiliates In May 2019, the Company refinanced its two prior credit agreements with State Auto Mutual at an interest rate of 4.05%, with principal payable in May 2029. The Company estimates the fair value of the notes receivable from affiliates using market quotations for U.S. treasury securities with similar maturity dates and applies an appropriate credit spread. This has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) December 31, 2020 December 31, 2019 Carrying value Fair value Interest rate Carrying value Fair value Interest rate Notes receivable from affiliate, issued May 2019 $ 70.0 $ 80.4 4.05 % $ 70.0 $ 74.6 4.05 % Notes Payable Included in notes payable are the FHLB Loans (as defined in Note 10) 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 a loan 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) December 31, 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 21.6 1.37 % — — — % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 107.1 3.96 % 85.3 97.8 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.3 15.3 4.43 % 15.2 15.2 6.11 % Total notes payable $ 122.1 $ 144.0 $ 122.0 $ 134.5

Losses and Loss Expenses Payabl

Losses and Loss Expenses Payable	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Losses and Loss Expenses Payable	. Losses and Loss Expenses Payable The following table sets forth the activity in the liability for losses and loss expenses for the years ended December 31: ($ millions) 2020 2019 2018 Losses and loss expenses payable, at beginning of year $ 1,066.5 $ 1,146.8 $ 1,255.6 Less: reinsurance recoverable on losses and loss expenses payable 13.6 5.5 3.1 Net balance at beginning of year 1,052.9 1,141.3 1,252.5 Incurred related to: Current year 1,008.2 913.5 876.6 Prior years (35.6) (68.7) (80.2) Total incurred 972.6 844.8 796.4 Paid related to: Current year 599.5 530.4 456.5 Prior years 399.9 402.8 451.1 Total paid 999.4 933.2 907.6 Net balance at end of year 1,026.1 1,052.9 1,141.3 Plus: reinsurance recoverable on losses and loss expenses payable 24.3 13.6 5.5 Losses and loss expenses payable $ 1,050.4 $ 1,066.5 $ 1,146.8 The Company recorded favorable development related to prior years’ loss and loss expense reserves in 2020 of $35.6 million. Favorable development of prior accident years' non-catastrophe loss and ALAE reserves was due to $78.4 million of favorable development in the commercial insurance segment. In the commercial insurance segment, all products developed favorably, with workers' compensation, small commercial package and middle market commercial contributing $24.9 million, $23.0 million and $16.7 million, respectively. Partially offsetting the favorable development was adverse development in the personal insurance segment and specialty run-off, which contributed $21.7 million and $5.2 million, respectively. The adverse development in the personal insurance segment was primarily driven by personal auto, which contributed $20.3 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 for 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 of $13.4 million driven by $12.4 million of adverse development in E&S property related to Hurricane Irma. The Company recorded favorable development related to prior years’ loss and loss expense reserves in 2019 of $68.7 million. Favorable development of prior accident years' non-catastrophe loss and ALAE reserves was due to $71.3 million of favorable development in the personal and commercial insurance segments. In the personal insurance segment, personal auto contributed $10.7 million of favorable development, primarily from the 2018 and 2017 accident years. In the commercial insurance segment, workers' compensation, small commercial package, and middle market commercial contributed $20.9 million, $15.2 million, and $11.8 million, respectively, of favorable development from multiple accident years. The favorable development from prior years' non-catastrophe loss and ALAE reserves was partially offset by $5.7 million of adverse development in catastrophe reserves driven by $10.7 million of adverse development from specialty run-off, primarily from the 2017 accident year.

Short-Duration Insurance Contra

Short-Duration Insurance Contracts	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Short-Duration Insurance and Deposit Contracts [Text Block]	. Short-Duration Insurance Contracts The following tables set forth: • undiscounted, incurred and paid claims and allocated claim adjustment expenses by accident year, on a net basis after reinsurance; • the sum of IBNR claims liabilities + expected development on reported claims ("IBNR+") included within the incurred claims development tables, for each accident year, for the most recent reporting period; • cumulative claim frequency information for each accident year; and • average annual percentage payout of incurred claims by age, net of reinsurance. The above information is provided for each of the Company’s reportable insurance segments and specialty run-off and then is further disaggregated between short and long-tail where "tail" refers to the time period between the occurrence of a loss and the ultimate settlement of the claims. See Note 18 for discussion of the Company’s reportable segments. The personal insurance segment generally consists of only short-tail business, whereas the commercial insurance segment and specialty run-off have both short and long-tail business. The Company determined that these disaggregated groupings have more homogeneous risk characteristics with similar development patterns and are generally subject to similar trends. Short-Tail Business: For short-tail business, claims are typically settled within five years, and the most common actuarial estimates are based on methods using link ratio projections of incurred losses (paid plus outstanding amounts) and paid losses, and methods projecting claim counts and claim severities. Separate projections are made for catastrophes based on specific information known through the reporting date. Long-Tail Business: For long-tail business, a material portion of claims may not be settled within five years. Reserve estimates for long-tail business use the same methods listed above along with several other methods as determined by the actuary. For example, premium-based methods may be used in developing ultimate loss estimates, including the Expected Loss Ratio and Bornhuetter-Ferguson methods. Cumulative Claim Frequency: Cumulative claim frequency is defined as the cumulative number of reported claims ("reported claims"). Reported claims include claims that do not result in a liability (e.g. those below a deductible). Reported claims disclosed in the tables below are for the State Auto Group and have not been pooled (see Note 9a for additional information regarding the Pooling Arrangement). Personal Insurance Segment - Short-Tail The change in incurred losses and loss adjustment expenses for prior accident years was due to higher than expected emergence of all personal insurance products. The emergence was primarily attributable to higher severity for bodily injury claims from the 2017, 2018 and 2019 accident years. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2016 $ 368.5 $ 370.0 $ 361.4 $ 360.8 $ 361.4 $ 0.9 151,620 2017 372.4 355.0 351.9 356.0 1.3 151,727 2018 418.5 411.4 418.2 4.4 154,705 2019 497.5 508.2 21.0 163,378 2020 509.3 87.4 123,234 Total $ 2,153.1 * Supplementary information and unaudited (1) Personal insurance segment - short-tail is an aggregation of the homeowners and personal auto product lines. Homeowners reported claims are counted by claimant and personal auto claims are counted by coverage. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 2016 $ 231.9 $ 316.2 $ 342.6 $ 352.1 $ 356.5 2017 236.8 315.8 335.7 347.9 2018 276.4 375.1 400.2 2019 343.7 457.7 2020 344.4 Total $ 1,906.7 All outstanding liabilities before 2016, net of reinsurance $ 3.8 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 250.2 * Supplementary information and unaudited Commercial Insurance Segment - Short-Tail The change in incurred losses and loss adjustment expenses for prior accident years was primarily driven by lower than expected emergence for the small commercial package and middle market commercial products. The emergence in these products was driven by lower than expected bodily injury claim severity from multiple accident years. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2016 $ 237.0 $ 227.6 $ 225.2 $ 220.6 $ 217.2 $ 6.0 34,872 2017 236.8 225.5 215.9 209.1 9.0 32,101 2018 228.4 216.4 207.3 17.7 31,055 2019 248.2 236.1 44.1 32,362 2020 328.2 75.0 29,540 Total $ 1,197.9 * Supplementary information and unaudited (1) Commercial insurance segment - short-tail is an aggregation of the commercial auto, small commercial package, middle market commercial and farm & ranch product lines. Commercial auto reported claims are counted by coverage and small commercial package, middle market commercial and farm & ranch reported claims are counted by claimant. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 2016 $ 99.2 $ 147.3 $ 176.7 $ 196.1 $ 204.2 2017 104.9 153.9 175.5 188.0 2018 98.7 144.6 161.0 2019 108.4 159.7 2020 170.6 Total $ 883.5 All outstanding liabilities before 2016, net of reinsurance $ 34.9 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 349.3 * Supplementary information and unaudited Commercial Insurance Segment - Long-Tail The change in incurred losses and loss adjustment expenses for prior accident years was due to lower than expected emergence in the workers’ compensation product, primarily driven by lower than expected severity from multiple accident years. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2011 $ 44.6 $ 47.4 $ 45.5 $ 44.8 $ 44.8 $ 44.9 $ 43.9 $ 42.9 $ 42.3 $ 41.7 $ 1.9 12,228 2012 49.7 45.8 43.7 44.1 43.9 42.9 41.7 40.5 39.8 2.1 12,762 2013 48.7 45.4 44.1 43.4 42.9 41.5 40.5 39.2 3.5 11,319 2014 51.6 50.0 47.1 45.7 45.3 43.4 41.0 4.8 11,570 2015 59.7 59.4 56.5 53.7 51.3 48.7 6.7 11,161 2016 62.6 60.6 57.2 53.9 49.5 9.2 12,453 2017 59.0 56.4 53.7 49.1 8.7 12,574 2018 56.4 53.6 49.3 11.6 12,541 2019 54.4 52.9 13.3 12,045 2020 55.5 26.0 10,851 Total $ 466.7 * Supplementary information and unaudited (1) Commercial insurance segment-long-tail consists of the workers' compensation product. Workers' compensation reported claims are counted by a combination of claimant and coverage. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 2011 $ 12.4 $ 25.4 $ 31.9 $ 35.0 $ 36.9 $ 37.7 $ 38.1 $ 38.6 $ 38.9 $ 39.0 2012 12.6 23.5 29.8 32.7 34.7 35.8 36.4 36.6 36.8 2013 12.3 23.3 29.0 32.3 33.7 34.2 34.4 34.6 2014 12.4 24.4 30.0 32.8 34.1 34.6 35.0 2015 13.9 28.2 35.7 38.3 39.5 40.2 2016 12.6 26.8 32.3 35.6 37.0 2017 13.2 27.0 32.8 36.8 2018 13.2 26.4 32.5 2019 14.7 29.2 2020 13.3 $ 334.4 All outstanding liabilities before 2011, net of reinsurance $ 30.6 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 162.9 * Supplementary information and unaudited Specialty run-off - Short-Tail The change in incurred losses and loss adjustment expenses for prior accident years was due to increases in estimates for claims related to Hurricane Irma. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2016 $ 99.3 $ 99.5 $ 102.7 $ 105.7 $ 105.3 $ 5.3 9,413 2017 134.2 129.7 138.3 150.6 16.3 11,340 2018 18.5 20.5 19.8 2.4 2,410 2019 1.0 1.1 — 61 2020 0.3 0.1 13 Total $ 277.1 * Supplementary information and unaudited (1) Specialty run-off-short-tail is an aggregation of the E&S Property and programs product lines. E&S Property and programs reported claims are counted by claimant. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 2016 $ 25.2 $ 50.2 $ 69.9 $ 87.4 $ 96.0 2017 39.0 77.5 101.2 121.3 2018 6.3 10.7 13.3 2019 0.5 0.9 2020 0.1 Total $ 231.6 All outstanding liabilities before 2016, net of reinsurance $ 13.7 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 59.2 * Supplementary information and unaudited Specialty run-off - Long-Tail The change in incurred losses and loss adjustment expenses for prior accident years was primarily related to an adverse court decision relating to an E&S casualty claim from accident year 2016. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2011 $ 11.9 $ 10.7 $ 10.7 $ 10.2 $ 10.1 $ 10.9 $ 10.5 $ 9.7 $ 9.5 $ 9.5 $ 0.8 1,250 2012 16.7 16.7 15.4 17.6 17.4 16.5 16.0 16.1 16.2 $ 0.6 1,199 2013 20.1 18.9 17.9 16.5 15.9 15.3 15.0 15.4 $ 1.0 1,562 2014 23.3 25.2 27.1 28.3 29.5 30.0 31.0 2.6 2,030 2015 38.6 44.9 44.8 45.7 45.0 48.6 6.3 3,167 2016 60.8 62.9 64.8 64.3 70.2 10.6 9,505 2017 71.6 73.1 70.5 66.3 20.6 9,245 2018 53.0 53.3 51.5 21.5 6,203 2019 4.1 4.6 4.2 2,352 2020 0.2 0.2 19 Total $ 313.5 * Supplementary information and unaudited (1) Specialty run-off-long-tail consists of the E&S Casualty product line. E&S Casualty reported claims are counted by claimant. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 2011 $ 0.9 $ 3.0 $ 5.2 $ 6.6 $ 7.1 $ 7.9 $ 8.1 $ 8.4 $ 8.6 $ 8.7 2012 0.9 4.0 7.3 10.3 12.5 14.0 14.1 14.7 14.9 2013 1.1 3.7 6.7 9.0 10.5 12.0 13.3 13.6 2014 1.2 7.2 12.5 16.7 21.5 24.2 25.7 2015 2.7 10.9 20.6 29.1 34.7 36.9 2016 6.0 15.7 31.5 39.7 53.5 2017 5.5 16.4 25.2 35.7 2018 2.7 12.8 20.6 2019 0.1 0.5 2020 — Total $ 210.1 All outstanding liabilities before 2011, net of reinsurance $ 3.8 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 107.3 * Supplementary information and unaudited The following table sets forth the reconciliation of the claims development tables to the balance sheet losses and loss expenses payable, with separate disclosure of unallocated loss adjustment expenses, net of reinsurance ("ULAE") and reinsurance recoverable on losses and loss expenses payable, for the years ended December 31: ($ in millions) 2020 2019 2018 Net losses and allocated loss adjustment expenses payable: Personal Insurance Segment Short-tail $ 250.2 $ 220.6 $ 216.0 Other personal 14.9 14.4 13.5 Commercial Insurance Segment Short-tail 349.3 330.8 336.4 Long-tail 162.9 174.2 182.1 Other commercial 25.5 30.9 27.4 Specialty run-off Short-tail 59.2 84.9 128.5 Long-tail 107.3 139.1 177.6 Net losses and loss expenses payable 969.3 994.9 1,081.5 ULAE 56.8 58.0 59.8 Reinsurance recoverable on losses and loss expenses payable 24.3 13.6 5.5 Total losses and loss expenses payable $ 1,050.4 $ 1,066.5 $ 1,146.8 The following table sets forth the historical average annual payout of incurred losses and allocated loss adjustment expenses (claims duration) for short-duration contracts, based on the disaggregated information in the paid loss development tables, net of reinsurance: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years Segment 1* 2* 3* 4* 5* 6* 7* 8* 9* 10* Personal Insurance: Short-tail 66.4 % 22.9 % 6.3 % 3.0 % 1.2 % N/A N/A N/A N/A N/A Commercial Insurance: Short-tail 48.3 % 22.4 % 10.6 % 7.5 % 3.7 % N/A N/A N/A N/A N/A Long-tail 28.2 % 28.5 % 13.8 % 7.2 % 3.6 % 1.7 % 1.0 % 0.8 % 0.5 % 0.3 % Specialty run-off: Short-tail 32.5 % 27.5 % 15.7 % 15.0 % 8.2 % N/A N/A N/A N/A N/A Long-tail 5.6 % 16.9 % 19.0 % 15.2 % 12.5 % 8.1 % 3.8 % 3.0 % 2.2 % 0.4 % * Supplementary information and unaudited

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2018
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance In the ordinary course of business, the Company assumes and cedes reinsurance with other insurers and reinsurers and is a member in various pools and associations. See Note 9a for discussion of reinsurance with affiliates. The voluntary arrangements provide greater diversification of business and limit the maximum net loss potential arising from large risks and catastrophes. Most of the ceded reinsurance is effected under reinsurance contracts known as treaties; the remainder is by negotiation on individual risks. Although the ceding of reinsurance does not discharge the original insurer from its primary liability to its policyholder, the insurance company that assumes the coverage assumes the related liability. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business. The recoverability of these assets depends on the reinsurers’ ability to perform under the reinsurance agreements. The Company evaluates and monitors the financial condition and concentrations of credit risk associated with its reinsurers under voluntary reinsurance arrangements to minimize its exposure to significant losses from reinsurer insolvencies. The Company has reported ceded losses and loss expenses payable and prepaid reinsurance premiums with other insurers and reinsurers as assets. All reinsurance contracts provide for indemnification against loss or liability relating to insurance risk and have been accounted for as reinsurance. Effective June 1, 2017, State Auto P&C entered into a quota share agreement with Home State to assume 100% of the business issued under this agreement, defined as Texas Private Passenger Automobile. Home State receives a variable fee (capped at 2%) in consideration for this arrangement. The following table sets forth the effect of the Company’s external reinsurance on its balance sheets at December 31, 2020 and 2019, prior to the reinsurance transaction with State Auto Mutual under the Pooling Arrangement, as discussed in Note 9a: ($ millions) 2020 2019 Losses and loss expenses payable: Direct $ 581.3 $ 540.1 Assumed 30.3 25.6 Ceded (24.3) (13.6) Net losses and loss expenses payable $ 587.3 $ 552.1 Unearned premiums: Direct $ 507.7 $ 495.8 Assumed 39.5 36.7 Ceded (8.3) (7.5) Net unearned premiums $ 538.9 $ 525.0 The following table sets forth the effect of the Company’s external reinsurance on its income statements for the years ended December 31, 2020, 2019 and 2018, prior to the reinsurance transaction with State Auto Mutual under the Pooling Arrangement, as discussed in Note 9a: ($ millions) 2020 2019 2018 Written premiums: Direct $ 1,080.5 $ 1,036.9 $ 915.1 Assumed 87.6 82.5 75.1 Ceded (39.8) (31.9) (23.1) Net written premiums $ 1,128.3 $ 1,087.5 $ 967.1 Earned premiums: Direct $ 1,067.6 $ 976.8 $ 881.3 Assumed 84.8 81.3 61.0 Ceded (39.0) (31.0) (23.0) Net earned premiums $ 1,113.4 $ 1,027.1 $ 919.3 Losses and loss expenses incurred: Direct $ 789.0 $ 631.4 $ 572.5 Assumed 56.8 59.6 48.4 Ceded (57.6) (15.6) (4.9) Net losses and loss expenses incurred $ 788.2 $ 675.4 $ 616.0

Current Expected Credit Losses

Current Expected Credit Losses Current Expected Credit Losses	12 Months Ended
	Dec. 31, 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 December 31, 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 December 31, 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 December 31, 2020 was $0.9 million. The following table sets forth the amortized cost of the Company's direct third-party reinsurance recoverables by FSR, net of the allowance for credit losses, at December 31, 2020: ($ millions) Amortized Cost Financial strength rating: A++ $ 1.1 A+ 9.5 A 13.7 Reinsurance recoverable on losses and loss expenses payable, net of allowance for credit losses $ 24.3 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 December 31, 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 twelve months ended December 31, 2020: ($ millions) Allowance for credit losses Beginning balance at January 1, 2020 $ 4.3 Current period provision 8.2 Writeoffs (5.4) Ending balance at December 31, 2020 $ 7.1

Transactions with Affiliates

Transactions with Affiliates	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Transactions with Affiliates	. Transactions with Affiliates a. Reinsurance The insurance subsidiaries of State Auto Financial, including State Auto P&C, Milbank and SA Ohio (collectively referred to as the “STFC Pooled Companies”) participate in a quota share reinsurance pooling arrangement (“the Pooling Arrangement”) with State Auto Mutual and its subsidiaries and affiliates, State Auto Insurance Company of Wisconsin, Meridian Security Insurance Company, Patrons Mutual Insurance Company of Connecticut, Rockhill Insurance Company, Plaza Insurance Company, American Compensation Insurance Company and Bloomington Compensation Insurance Company, (collectively referred to as the “Mutual Pooled Companies”). RIC, Plaza, American Compensation and Bloomington Compensation are referred to as the “Rockhill Insurers.” The STFC Pooled Companies, the Mutual Pooled Companies and the Rockhill Insurers are collectively referred to as the “State Auto Group.” In general, under the Pooling Arrangement, the STFC Pooled Companies and the Mutual Pooled Companies other than State Auto Mutual cede to State Auto Mutual all of their insurance business and assume from State Auto Mutual an amount equal to their respective participation percentages in the Pooling Arrangement. All premiums, losses and loss expenses and underwriting expenses are allocated among the participants on the basis of each Company’s participation percentage in the Pooling Arrangement. The Pooling Arrangement provides indemnification against loss or liability relating to insurance risk and has been accounted for as reinsurance. The Pooling Arrangement does not relieve each individual pooled subsidiary of its primary liability as the originating insurer; consequently, there is a concentration of credit risk arising from business ceded to State Auto Mutual. As the Pooling Arrangement provides for the right of offset, the Company has reported losses and loss expenses payable and prepaid reinsurance premiums to State Auto Mutual as assets only in situations when net amounts ceded to State Auto Mutual exceed net amounts assumed. All parties that participate in the Pooling Arrangement have an A.M. Best rating of A- (Excellent). The following table sets forth the reinsurance transactions on the Company’s balance sheets for the Pooling Arrangement between the STFC Pooled Companies and State Auto Mutual at December 31, 2020 and 2019: ($ millions) 2020 2019 Assets Deferred policy acquisition costs: Ceded $ (92.1) $ (90.9) Assumed 122.2 111.1 Net assumed $ 30.1 $ 20.2 Liabilities Losses and loss expenses payable: Ceded $ (587.3) $ (552.1) Assumed 1,026.1 1,052.9 Net assumed $ 438.8 $ 500.8 Unearned premiums: Ceded $ (262.7) $ (225.9) Assumed 715.1 641.7 Net assumed $ 452.4 $ 415.8 Other liabilities: Ceded $ (77.1) $ (77.8) Assumed 99.5 94.0 Net assumed $ 22.4 $ 16.1 The following table sets forth the reinsurance transactions on the Company’s income statements for the Pooling Arrangement between the STFC Pooled Companies and State Auto Mutual for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Written premiums: Ceded $ (1,128.3) $ (1,088.1) $ (966.8) Assumed 1,456.3 1,315.3 1,209.9 Net assumed $ 328.0 $ 227.2 $ 243.1 Earned premiums: Ceded $ (1,113.4) $ (1,027.7) $ (919.0) Assumed 1,380.9 1,250.2 1,237.6 Net assumed $ 267.5 $ 222.5 $ 318.6 Losses and loss expenses incurred: Ceded $ (789.7) $ (677.2) $ (617.6) Assumed 973.9 846.5 798.1 Net assumed $ 184.2 $ 169.3 $ 180.5 Acquisition and operating expenses: Ceded (374.8) (370.0) (341.1) Assumed 477.4 439.1 449.8 Net assumed $ 102.6 $ 69.1 $ 108.7 Intercompany Balances 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. Management utilizes an aging schedule to estimate an allowance for uncollectible amounts relating to the State Auto Group’s premiums receivable balance. Current and historical collection experience along with reasonable and supportable forecasts are used to estimate the percentage of the premiums receivable balance that will be uncollectible. Credit risk is partially mitigated by the State Auto Group's ability to cancel the policy if the policyholder does not pay the premium. 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. This 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 Company’s share of the premium balances due to State Auto Mutual from agents and insureds at December 31, 2020 and 2019 is approximately $389.4 million and $371.0 million, respectively, net of the allowance for uncollectible premiums receivable of $7.1 million and $4.3 million, respectively. b. Notes Payable In May 2003, State Auto Financial formed a Delaware business trust (the “Capital Trust”) to issue $15.0 million of mandatorily redeemable preferred capital securities to a third party and $0.5 million of common securities to State Auto Financial (the capital and common securities are collectively referred to as the “Trust Securities”). The Capital Trust loaned $15.5 million, the proceeds from the issuance of its Trust Securities, to State Auto Financial in the form of Floating Rate Junior Subordinated Debt Securities due in 2033 (the “Subordinated Debentures”). The Subordinated Debentures and interest accrued thereon are the Capital Trust’s only assets. Interest on the Trust Securities is payable quarterly at a rate equal to the three-month LIBOR rate plus 4.20% adjusted quarterly (total 4.43% at December 31, 2020). Because the interest rate and interest payment dates on the Subordinated Debentures are the same as the interest rate and interest payment dates on the Trust Securities, payments from the Subordinated Debentures finance the distributions paid on the Trust Securities. State Auto Financial has the right to redeem the Subordinated Debentures, in whole or in part, on or after May 2008. State Auto Financial has unconditionally and irrevocably guaranteed payment of any required distributions on the capital securities, the redemption price when the capital securities are to be redeemed, and any amounts due if the Capital Trust is liquidated or terminated. State Auto Financial’s equity interest in the Capital Trust is included in other invested assets. In accordance with the Consolidation Topic of the FASB ASC 810, State Auto Financial determined that the business trust is a variable interest entity for which it is not the primary beneficiary and therefore, does not consolidate the Capital Trust with the Company. c. Notes Receivable In May 2009, the Company entered into two separate credit agreements with State Automobile Mutual Insurance Company pursuant to which it loaned State Auto Mutual $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. There is no prepayment penalty, and no collateral was given as security for the payment for these loans. Pursuant to these agreements, the Company earned interest of $2.8 million for the year ended December 31, 2020 and $3.6 million and $4.9 million for the years ended December 31, 2019 and 2018, respectively. See Note 4 for the notes receivable fair value discussion. d. Management Services Stateco provides State Auto Mutual and its affiliates investment management services. Investment management income is recognized quarterly based on a percentage of the average fair value of investable assets and the equity portfolio performance of each company managed. Revenue related to these services amounted to $2.0 million, $2.1 million and $2.0 million in 2020, 2019 and 2018, respectively, and is included in other income (affiliates) on the consolidated statements of income.

Notes Payable and Credit Facili

Notes Payable and Credit Facility	12 Months Ended
	Dec. 31, 2020
Notes Payable [Abstract]
Notes Payable and Open Line of Credit	10. Notes Payable and Open Line of Credit FHLB Loans State Auto Financial’s subsidiary, State Auto P&C, is a member of the Federal Home Loan Bank of Cincinnati (the “FHLB”). On September 2, 2020 State Auto P&C retired its five ten fifteen The 2018 and 2020 FHLB Loans are fully secured by a pledge of specific investment securities of State Auto P&C. 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. FHLB Line of Credit 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

Federal Income Taxes

Federal Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal Income Taxes	. Federal Income Taxes The Company has foreign tax credit carryforwards of $0.3 million which will expire in 2021. 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 $0.3 million on the deferred tax assets related to these foreign tax credit carryforwards. The valuation allowance is included in the "other, net" line item in the table below. The following table sets forth the reconciliation between actual federal income tax expense and the amount computed at the indicated statutory rate for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Amount at statutory rate $ 3.0 21.0 % $ 22.2 21.0 % $ 2.6 21.0 % Tax-exempt interest and dividends received deduction (2.3) (16.4) (2.3) (2.1) (2.3) (18.7) Other, net 0.6 4.2 (0.2) (0.2) (0.4) (3.0) Federal income tax expense (benefit) $ 1.3 8.8 % $ 19.7 18.7 % $ (0.1) (0.7) % In computing taxable income, property and casualty insurers are required to discount their unpaid loss reserves. During 2018, the Internal Revenue Service (IRS) released proposed regulations addressing the mechanics of the reserve discounting. Under those regulations and a related Revenue Procedure 2019-06 ("Rev. Proc. 2019-06"), the interest rate term was not to exceed seventeen and one-half years. The provisional amount was based on twenty years. After discounting the January 1, 2018 reserves using the Rev. Proc. 2019-06 published factors, the impact was $47.5 million on a pretax basis down from the initial estimate of $50.9 million for a tax-effected change of $0.7 million in the impact of the transitional amount. During 2019, the IRS released Rev. Proc. 2019-31 with final discount factors, which were used in the 2018 tax return filed in 2019. After discounting the January 1, 2018 reserves using these final factors, the impact was $42.7 million on a pretax basis down from the revised estimate of $47.5 million for a tax-effected change of $1.0 million in the impact of the transitional amount. The following table sets forth the tax effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities at December 31, 2020 and 2019: ($ millions) 2020 2019 Deferred tax assets: Unearned premiums not currently deductible $ 30.1 $ 27.0 Losses and loss expenses payable discounting 10.5 10.6 Postretirement and pension benefits 19.3 17.1 Other liabilities 12.2 13.4 Net operating loss carryforward 19.8 12.6 Capital loss carryforward 6.1 — Tax credit carryforward 1.9 2.5 Other 1.1 1.1 Total deferred tax assets 101.0 84.3 Deferred tax liabilities: Deferral of policy acquisition costs 25.7 23.3 Investments 48.0 21.3 Total deferred tax liabilities 73.7 44.6 Net deferred federal income taxes $ 27.3 $ 39.7 Deferred income tax assets and liabilities represent the tax effect of the differences between the financial statement carrying value of existing assets and liabilities and their respective tax bases. The Company periodically evaluates its deferred tax assets, which requires significant judgment, to determine if they are realizable based upon weighing all available evidence, both positive and negative, including loss carryback potential, past operating results, existence of cumulative losses in the most recent years, projected performance of the business, future taxable income, including the ability to generate capital gains, and prudent and feasible tax planning strategies. In making such judgments, significant weight is given to evidence that can be objectively verified. At December 31, 2020, the tax benefit of the net operating loss (“NOL”) carryforward was $19.8 million. The NOL carryforwards do not begin to expire until 2032 and will not fully expire until 2040. At December 31, 2020, the Company carried no balance for uncertain tax positions. The Company had no accrual for the payment of interest and penalties at December 31, 2020 or 2019.

Pension and Postretirement Bene

Pension and Postretirement Benefit Plans	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Pension and Postretirement Benefit Plans	12. Pension and Postretirement Benefit Plans The Company, through the employees of State Auto P&C, provides management and operation services under management agreements for all insurance and non-insurance affiliates. The Company provides eligible employees and retirees pension and postretirement benefits and records the funded status of these plans on its balance sheet while the annual net periodic costs are allocated to affiliated companies based on allocations pursuant to intercompany management agreements including the Pooling Arrangement for insurance subsidiaries and affiliates party to this agreement. The Company provides a defined benefit pension plan for eligible employees hired prior to January 1, 2010 at which time the plan was closed to new participants. All Company employees participating in the plan are vested. The Company’s policy is to fund pension costs in accordance with the requirements of the Employee Retirement Income Security Act of 1974. Benefits are determined by applying factors specified in the plan to a participant’s defined average annual compensation. The defined benefit pension and postretirement benefit plans are referred to herein as “the benefit plans.” The following table sets forth information regarding the pension and postretirement benefit plans’ change in benefit obligation, plan assets and funded status at December 31, 2020 and 2019: ($ millions) Pension Postretirement 2020 2019 2020 2019 Change in benefit obligation: Benefit obligation at beginning of year $ 478.4 $ 428.1 $ 11.4 $ 25.5 Service cost 7.3 5.8 — — Interest cost 14.5 17.2 0.3 1.0 Actuarial loss (gain) 72.3 60.6 (0.9) (12.6) Benefits paid (22.9) (33.3) (0.6) (2.5) Benefit obligation at end of year 549.6 478.4 10.2 11.4 Change in plan assets available for plan benefits: Fair value of plan assets available for plan benefits at beginning of year 442.1 381.6 — — Employer contribution 15.0 10.0 — — Actual return on plan assets 72.5 83.8 — — Benefits paid (22.9) (33.3) — — Fair value of plan assets at end of year $ 506.7 $ 442.1 $ — $ — Supplemental executive retirement plan (13.1) (11.8) — — Funded status at end of year $ (56.0) $ (48.1) $ (10.2) $ (11.4) Accumulated benefit obligation end of year $ 522.8 $ 453.8 The 2020 pension plan actuarial loss was primarily due to (i) a 78-basis-point reduction in the discount rate assumption at December 31, 2020, and (ii) revisions to mortality rate assumptions. Effective January 1, 2020, the Company changed the funding of its postretirement benefit plan from self-insured to a fully-insured group Medicare advantage program. The group Medicare advantage program is less than half the cost of the self-insured plan. As a result of this funding change, the postretirement benefit plan's liability decreased, and accumulated other comprehensive income (loss) increased by $13.9 million, respectively, for the year ended December 31, 2019. The following table sets forth the amounts included in accumulated other comprehensive income (loss) that has not been recognized in net periodic cost at December 31, 2020 and 2019: ($ millions) 2020 2019 Prior service benefit $ (37.0) $ (43.4) Net actuarial loss 157.4 143.7 Total $ 120.4 $ 100.3 The following table sets forth information regarding the Company’s share of pension and postretirement benefit plans’ components of net periodic cost for the years ended December 31, 2020, 2019 and 2018: ($ millions) Pension Postretirement 2020 2019 2018 2020 2019 2018 Components of net periodic cost: Service cost $ 4.8 $ 3.8 $ 5.1 $ — $ — $ — Interest cost 9.7 11.5 10.7 0.2 0.7 0.8 Expected return on plan assets (17.5) (17.8) (18.0) — — — Amortization of: Prior service benefit — — — (5.5) (5.5) (5.5) Net actuarial loss 9.2 6.0 8.2 (0.2) 0.2 0.2 Net periodic cost (benefit) $ 6.2 $ 3.5 $ 6.0 $ (5.5) $ (4.6) $ (4.5) The following table sets forth the benefit payments, which reflect expected future service, expected to be paid: ($ millions) Pension Postretirement 2021 $ 18.3 $ 0.7 2022 18.9 0.6 2023 19.6 0.6 2024 20.6 0.6 2025 21.6 0.6 2026-2030 123.0 3.1 The postretirement plan’s gross benefit payments for 2020 were $0.6 million, including the prescription drug benefits. The postretirement plan’s subsidy related to Medicare Prescription Drug Improvement and Modernization Act of 2003 estimates future annual subsidies to be approximately $0.3 million. The following table sets forth the weighted average assumptions used to determine the benefit plans’ obligations at December 31, 2020 and 2019: Pension Postretirement 2020 2019 2020 2019 Benefit obligations weighted-average assumptions: Discount rate 2.32 % 3.10 % 1.95 % 3.00 % Rates of increase in compensation levels 3.00 3.25 — — The following table sets forth the weighted average assumptions used to determine the benefit plans’ net periodic cost for the years ended December 31, 2020, 2019 and 2018: Pension Postretirement 2020 2019 2018 2020 2019 2018 Weighted-average assumptions: Discount rate 3.10 % 4.12 % 3.50 % 3.10 % 4.12 % 3.50 % Expected long-term rate of return on assets 6.50 6.75 7.00 — — — Rates of increase in compensation levels 3.25 3.25 3.25 — — — The benefit plans’ obligations are long-term in nature and consequently the investment strategies have a long-term time horizon. In establishing the long-term rate of return assumption on plan assets, management, along with its pension consulting actuary, reviews the historical performance of the plan assets and the stability in the mix of the investment portfolio. The expected inflation rate and expected real rates of return of applicable asset classes are then determined to assist in setting appropriate assumptions. The following table sets forth the assumed health care cost trend rates used for the years ended December 31, 2020, 2019 and 2018: Postretirement 2020 2019 2018 Assumed health care cost trend rates: Health care cost trend rate assumed for the next year 5.50 % 5.50 % 5.50 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.00 % 4.00 % 3.80 % Year that the rate reaches the ultimate trend rate 2075 2075 2075 The pension plan’s investment policy objective is to preserve the investment principal while generating income and appreciation in fair value to meet the pension plan’s obligations. The pension plan’s investment strategy and risk tolerance is balanced between meeting cash obligation requirements and a long-term relatively high risk tolerance takes into account the predictable cash requirements, nature of the plan’s liabilities and the plan’s long term time horizon. Since the nature and timing of the benefit plans’ liabilities and cash requirements are predictable, the liquidity requirements are somewhat moderate. One of the goals of diversifying the benefit plans’ portfolio among different asset classes is the elimination of concentration of risk in one asset class. Management also has investment policy guidelines with respect to limiting the ownership in any single debt or equity issuer. The international fund investments are also composed of numerous securities to reduce our exposure to a single issuer. The following table sets forth the asset allocation targets, as a percentage of total fair value, which are used as a guide by management when allocating funds as they become available. Asset allocation target (0 to 100%) Asset Category: Fixed maturity 61.0 % U.S. large-cap equity 19.8 U.S. small-cap equity 8.3 International equity 7.6 Emerging market equity 3.3 Total 100.0 % Effective January 1, 2014, the Investment Committee approved a change to a liability driven investment (LDI) for the pension plan assets. The primary goal of the LDI strategy is to shift the asset allocation to more closely align with the plan liability, thereby reducing the volatility of the funded status. The implementation of the LDI strategy occurred over time and the actual asset allocation at any point in time is dependent upon the funded status and the level of interest rates. This glide path helps to balance interest rate risk, curve steepness risk, and credit spread risk, as incremental changes are made to the allocation over time. This allocation strategy reduces exposure to equity holdings and increases exposure to long duration fixed maturity holdings. This change resulted in lower volatility for the plan assets. By moving more of the plan’s assets to long duration fixed income, the duration of the assets increased to more closely match the duration of the plan’s liabilities. See Note 4 for the valuation methods used by the Company for each type of financial instrument the plans hold that are carried at fair value. There were no transfers between level categorizations during the years ended December 31, 2020 and 2019. Included in the pension plan’s investments are two international funds (“the funds”) that invests in equity securities of foreign issuers and are managed by third party investment managers. The funds had a fair value of $47.3 million and $38.2 million at December 31, 2020 and 2019, respectively, which was determined using the funds' net asset value. In accordance with ASC 820-10, since these investments are measured at fair value using the net asset value per share practical expedient they have not been classified in the table below. The following tables set forth the plan’s investments within the fair value hierarchy at December 31, 2020 and 2019: ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2020 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 90.5 $ — $ 90.5 Corporate securities 183.9 — 183.9 U.S. government agencies mortgage-backed securities 3.9 — 3.9 Total fixed maturities 278.3 — 278.3 Equity securities: Large-cap securities 116.2 116.2 — Mutual and exchange traded funds 56.1 56.1 — Total equity securities 172.3 172.3 — Total pension plan investments $ 450.6 $ 172.3 $ 278.3 ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 98.6 $ — $ 98.6 Corporate securities 153.1 — 153.1 U.S. government agencies mortgage-backed securities 4.0 — 4.0 Total fixed maturities 255.7 — 255.7 Equity securities: Large-cap securities 91.9 91.9 — Mutual and exchange traded funds 49.7 49.7 — Total equity securities 141.6 141.6 — Total pension plan investments $ 397.3 $ 141.6 $ 255.7 The actuarially prepared funding amount to the pension plan ranges from the minimum amount the Company would be required to contribute to the maximum amount that would be deductible for tax purposes. Contributed amounts in excess of the minimum amounts are deemed voluntary. Amounts in excess of the maximum amount would be subject to an excise tax and may not be deductible for tax purposes. The Company expects to contribute up to $15.0 million to the pension plan during 2021. The Company maintains a defined contribution plan that covers substantially all employees of the Company. The Company matches the first 1% of contributions of participants’ salary at the rate of one dollar for each dollar contributed. Participant contributions of 2% to 6% are matched at a rate of 50 cents for each dollar contributed. In addition, the Company contributes a percentage of the employee’s annual income for those employees hired on or after January 1, 2010, and for those employees hired prior to January 1, 2010 who chose to freeze their existing accrued pension benefit effective June 30, 2010. The Company’s share of the expense under the plan totaled $7.3 million, $6.4 million and $5.6 million for 2020, 2019 and 2018, respectively.

Other Comprehensive Income and

Other Comprehensive Income and Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Other Comprehensive Income and Accumulated Other Comprehensive Income	13. 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) component ("AOCI(L)"), net of tax, for the years ended December 31, 2020, 2019 and 2018: ($ millions) Unrealized Gains and Losses on Available-for-Sale Securities Benefit Plan Items Total Beginning balance at January 1, 2020 $ 40.8 $ (67.7) $ (26.9) Other comprehensive income (loss) before reclassifications 56.4 (27.4) 29.0 Amounts reclassified from AOCI (a) $ 0.3 11.5 11.8 Net current period other comprehensive income (loss) 56.7 (15.9) 40.8 Ending balance at December 31, 2020 $ 97.5 $ (83.6) $ 13.9 Beginning balance at January 1, 2019 $ (20.2) $ (76.2) $ (96.4) Other comprehensive income before reclassifications 63.8 7.5 71.3 Amounts reclassified from AOCI (a) (2.8) 1.0 (1.8) Net current period other comprehensive income 61.0 8.5 69.5 Ending balance at December 31, 2019 $ 40.8 $ (67.7) $ (26.9) Beginning balance at January 1, 2018 $ 66.0 $ (62.2) $ 3.8 Cumulative effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018 (47.9) (16.0) (63.9) Other comprehensive loss before reclassifications (36.7) (4.3) (41.0) Amounts reclassified from AOCI (a) (1.6) 6.3 4.7 Net current period other comprehensive (loss) income (38.3) 2.0 (36.3) Ending balance at December 31, 2018 $ (20.2) $ (76.2) $ (96.4) (a) See separate table below for details about these reclassifications The following tables set forth the reclassifications out of accumulated other comprehensive income (loss), by component, to the Company’s consolidated statement of income for the years ended December 31, 2020, 2019 and 2018: ($ millions) Details about Accumulated Other December 31 Affected line item in the Condensed Comprehensive (Loss) Income Components 2020 2019 2018 Consolidated Statements of Income Unrealized (losses) gains on available for sale securities $ (0.3) $ 3.5 $ 2.0 Realized (loss) gain on sale of securities (0.3) 3.5 2.0 Total before tax — (0.7) (0.4) Tax expense (0.3) 2.8 1.6 Net of tax Amortization of benefit plan items: Negative prior service costs 6.3 6.3 6.3 (b) Net loss (13.7) (9.6) (13.2) (b) (7.4) (3.3) (6.9) Total before tax (4.1) 2.3 0.6 Tax benefit (11.5) (1.0) (6.3) Net of tax Total reclassifications for the period $ (11.8) $ 1.8 $ (4.7) (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).

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity Note [Abstract]
Stockholders' Equity	14. Stockholders’ Equity a. Dividend Restrictions and Statutory Financial Information State Auto P&C, Milbank and SA Ohio are subject to regulations and restrictions under which payment of dividends from statutory surplus can be made to State Auto Financial during the year without prior approval of regulatory authorities. Under the insurance regulations of Iowa and Ohio (the states of domicile), the maximum amount of dividends that the Company may pay out of earned surplus to shareholders within a twelve month period without prior approval of the Department is limited to the greater of 10% of the most recent year-end policyholders’ surplus or net income for the twelve month period ending the 31st day of December of the previous year-end. Pursuant to these rules, approximately $91.0 million is available for payment to State Auto Financial from its insurance subsidiaries in 2021 without prior approval. State Auto Financial received dividends from its insurance subsidiaries in the amount of $15.0 million, $10.0 million and $10.0 million in 2020, 2019 and 2018, respectively. The Company’s insurance subsidiaries are subject to risk-based capital (“RBC”) requirements that have been adopted by individual states. These requirements subject insurers having statutory capital less than that required by the RBC calculation to varying degrees of regulatory action, depending on the level of capital inadequacy. The RBC formulas specify various weighting factors to be applied to financial balances or various levels of activity based on the perceived degree of risk. Regulatory compliance is determined by a ratio of total adjusted capital to authorized control level RBC. Generally, no remedial action is required by an insurance company if its adjusted statutory surplus exceeds 200% of the authorized level RBC. As of December 31, 2020, each of the Company’s insurance subsidiaries maintained adjusted statutory surplus in excess of 400% of the authorized control level RBC. The Company's statutory capital and surplus was $910.3 million and $913.3 million at December 31, 2020 and 2019, respectively. The Company's net (loss) income, as determined using SAP, was $(39.1) million, $31.1 million, and $65.1 million for the years ended December 31, 2020, 2019, and 2018, respectively.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2020
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Preferred Stock	15. Preferred Stock State Auto Financial has two authorized classes of preferred stock. For both classes, upon issuance, the Board of Directors has authority to fix and determine the significant features of the shares issued, including, among other things, the dividend rate, redemption price, redemption rights, conversion features and liquidation price payable in the event of any liquidation, dissolution, or winding up of the affairs of State Auto Financial. The Class A preferred stock is not entitled to voting rights until, for any period, dividends are in arrears in the amount of six or more quarterly dividends.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement, Noncash Expense [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	16. Share-Based Compensation The Company maintains share-based compensation plans for key employees and outside, or non-employee, directors. Since May 5, 2017, the share-based compensation plan for key employees has been the State Auto Financial Corporation 2017 Long-Term Incentive Plan (the “2017 LTIP”). The 2017 LTIP replaced the State Auto Financial Corporation 2009 Equity Compensation Plan (the “2009 Equity Plan”). The stock-based compensation plan for outside directors is the Outside Directors Restricted Share Unit Plan (the “RSU Plan”). The Company’s share-based compensation plans authorize the granting of various equity-based incentives including performance-based stock awards, performance-based unit awards, restricted stock, and other stock based awards to employees and non-employee directors. The expense for these equity-based incentives is based on their fair value at the date of grant and amortized over their vesting period. As of December 31, 2020, 0.8 million common shares had been issued and 1.6 million common shares were available for issuance under the 2017 LTIP. The 2017 LTIP provides that (i) the maximum value of performance stock awards or performance unit awards settled in cash that may be granted in any calendar year is equal to the excess of the number of awards multiplied by the fair market value of the company’s common shares on the applicable payment or settlement date of the award multiplied by 5 and (ii) the maximum number of common shares subject to awards of performance stock and performance units that may be granted in any calendar year to any one individual is 250,000 shares. The 2017 LTIP remains in effect until terminated by the Board of Directors. Restricted Stock and Performance Unit Awards Service-based restricted stock awards granted to employees are subject to a vesting schedule based on the employee’s continued employment (“Restriction Period”), for which vesting is generally on the third anniversary after the date of grant. The Company recognizes compensation expense based on the number of restricted shares granted at the then grant date fair value over the Restriction Period. The Company recognizes forfeitures as they occur. Awards with both service and performance conditions granted to employees are subject to (i) the Restriction Period, and (ii) the achievement of predetermined performance goals within specified time periods. All performance-based awards include a specified number of units that will vest. The number of performance-based awards that are ultimately earned for each grant is dependent upon meeting specified target and performance goals that range from 0% to 500% of the target number of performance units awarded based on the extent to which the Company achieves the performance goals for the performance measures as set forth in a performance matrix established by the Compensation Committee. Generally, service-based and performance-based equity awards are expensed pro-rata over their respective vesting periods based on the market value of the awards at the time of grant. Performance-based equity awards that contain variable vesting criteria are expensed based on management’s expectation of the percentage of the award that will ultimately be earned. These estimates can change periodically throughout the measurement period. The following table sets forth the Company’s total activity and related information for performance unit award activity for the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 Shares Weighted Shares Weighted Shares Weighted Outstanding, beginning of year 460,189 $ 29.37 356,400 $ 27.47 147,869 $ 27.20 Granted 153,574 24.40 130,680 33.67 224,449 27.65 Vested (103,345) 27.24 (12,500) 27.65 — — Forfeited (5,915) 28.64 (14,391) 29.59 (15,918) 27.37 Outstanding, end of year 504,503 $ 28.06 460,189 $ 29.37 356,400 $ 27.47 As of December 31, 2020, there was $4.4 million of total unrecognized compensation cost related to performance unit awards. The remaining cost is expected to be recognized over a period of 1.05 years. The following table sets forth the Company’s total activity and related information for service-based restricted stock award activity for the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 Shares Weighted Shares Weighted Shares Weighted Outstanding, beginning of year 67,934 $ 27.65 126,946 $ 26.21 71,578 $ 22.44 Granted 30,618 16.33 — — 97,049 27.65 Vested (27,716) 27.65 (58,801) 24.57 (37,644) 22.88 Forfeited — — (211) 21.54 (4,037) 24.82 Outstanding, end of year 70,836 $ 22.76 67,934 $ 27.65 126,946 $ 26.21 As of December 31, 2020, there was $0.5 million of total unrecognized compensation cost related to service-based restricted stock awards. The remaining cost is expected to be recognized over a period of 0.84 years. Stock Options In accordance with the terms of the 2009 Equity Plan, options previously granted were all vested as of December 31, 2019 and must be exercised no later than ten years from the date of grant. If not exercised, outstanding options will expire in 2026. The fair value of each stock option was estimated on the date of grant using the Black-Scholes closed-form pricing model. The pricing model requires assumptions such as the expected life of the option and expected volatility of the Company’s stock over the expected life of the option, which significantly impacts the assumed fair value. The Company used historical data to determine these assumptions The expected life of the options for employees represented the period of time the options are expected to be outstanding and is based on historical trends. For non-employees the expected life of the option approximates the remaining contractual term of the option. The expected stock price volatility is based on the historical volatility of the Company’s stock for a period approximating the expected life and the expected dividend yield is based on the Company’s most recent period’s dividend payout. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant and has a term approximating the expected life of the option. The following table sets forth the Company’s stock option activity and related information for the years ended December 31, 2020, 2019 and 2018: (millions, except per share amounts) 2020 2019 2018 Options Weighted- Average Exercise Price Options Weighted- Average Exercise Price Options Weighted- Average Exercise Price Outstanding, beginning of year 0.8 $ 19.18 1.0 $ 18.50 1.7 $ 19.22 Exercised (0.1) 18.55 (0.2) 16.45 (0.7) 20.08 Outstanding, end of year 0.7 $ 19.28 0.8 $ 19.18 1.0 $ 18.50 Intrinsic value for stock options is defined as the difference between the current market value and the grant price. For the years ended December 31, 2020, 2019 and 2018, the total intrinsic value of stock options exercised was $1.0 million, $4.5 million and $7.2 million, respectively. The following table sets forth information pertaining to the total options outstanding and exercisable at December 31, 2020: (Options in millions) Options Outstanding Options Exercisable Number Weighted- Average Remaining Contractual Life Weighted- Average Exercise Price Number Weighted- Average Exercise Price Range of Exercise Prices: $10.01 – $20.00 0.3 1.5 $ 16.33 0.3 $ 16.33 $20.01 – $30.00 0.4 4.0 21.97 0.4 21.97 Total 0.7 2.8 $ 19.28 0.7 $ 19.28 Aggregate intrinsic value for total options outstanding and exercisable at December 31, 2020 was $0.4 million, respectively. Employee Stock Purchase Plan The Company also has a broad-based employee stock purchase plan under which employees of the Company may choose, at two different specified time intervals each year, to have up to 6% of their annual base earnings withheld to purchase the Company’s common shares. The purchase price of the common shares is 85% of the lower of its beginning-of-interval or end-of-interval market price. As of December 31, 2020, 3.8 million common shares had been purchased under this plan and 0.3 million common shares were available for purchase. This plan remains in effect until terminated by the Board of Directors. Outside Directors Plan The RSU Plan is an unfunded deferred compensation plan which currently provides each outside director with an award of 1,400 restricted share units (the “RSU award”) following each annual meeting of shareholders. The amount of the award may change from year to year, based on the provision described below. The RSU awards are fully vested six months after the date of grant. RSU awards are not common shares of the Company and, as such, no participant has any rights as a holder of common shares under the RSU Plan. RSU awards represent the right to receive an amount, payable in cash or common shares of the Company, as previously elected by the outside director, equal to the value of a specified number of common shares of the Company at the end of the restricted period. Such election may be changed within the constraints set forth in the RSU Plan. The restricted period for the RSU awards begins on the date of grant and expires on the date the outside director retires from or otherwise terminates service as a director of the Company. During the restricted period, outside directors are credited with dividends, equivalent in value to those declared and paid on the Company’s common shares, on all RSU awards granted to them. At the end of the restricted period, outside directors receive cash or common share distributions of their RSU awards either (i) in a single lump sum payment, or (ii) in annual installment payments over a 5- or 10-year period, as previously elected by the outside director. The administrative committee for the RSU Plan (currently the Company’s Compensation Committee) retains the right to increase the annual number of RSU awards granted to each outside director to as many as 10,000 or to decrease such annual number to not less than 500, without seeking shareholder approval, if such increase or decrease is deemed appropriate by the administrative committee to maintain director compensation at appropriate levels. No awards may be made under the RSU Plan after May 31, 2026. The Company accounts for the RSU Plan as a liability plan. There were 17,416 RSUs, 18,837 RSUs, and 23,080 RSUs granted in 2020, 2019 and 2018, respectively. During 2020 and 2019, common shares valued at approximately $0.1 million and $1.2 million, respectively, were distributed by the Company under the RSU Plan. Share-based compensation expense recognized during 2020, 2019 and 2018 was $0.9 million, $6.1 million and $11.1 million, respectively. Share-based compensation is recognized as a component of loss and loss adjustment expense and acquisition and operating expense in a manner consistent with other employee compensation. As of December 31, 2020, there was $4.9 million of total unrecognized compensation cost related to compensation arrangements granted under the plans. The remaining cost is expected to be recognized over a period of 1.03 years.

Net (Loss) Earnings Per Common

Net (Loss) Earnings Per Common Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Earnings (Loss) Per Common Share	17. Net Earnings Per Common Share The following table sets forth the compilation of basic and diluted net earnings per common share for the years ended December 31, 2020, 2019 and 2018: (millions, except per share amounts) 2020 2019 2018 Numerator: Net earnings for basic net earnings per common share $ 13.1 $ 85.8 $ 12.2 Effect of dilutive share-based awards — (1.1) — Adjusted net earnings for dilutive net earnings per common share $ 13.1 $ 84.7 $ 12.2 Denominator: Weighted average shares for basic net earnings per common share 43.7 43.4 42.8 Effect of dilutive share-based awards 0.6 0.6 0.6 Adjusted weighted average shares for diluted net earnings per common share 44.3 44.0 43.4 Basic net earnings per common share $ 0.30 $ 1.98 $ 0.29 Diluted net earnings per common share $ 0.30 $ 1.93 $ 0.28 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 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 year ended December 31, 2018: (millions) 2018 Total number of antidilutive options and awards 0.1

Reportable Segments

Reportable Segments	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Reportable Segments	Reportable Segments 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 personal insurance segment primarily provides personal automobile and homeowners to the personal insurance market. The commercial insurance segment primarily provides commercial automobile, commercial multi-peril, fire & allied, general liability, workers’ compensation insurance covering small-to-medium sized commercial exposures in the commercial insurance market. In addition, the commercial insurance segment provides farm & ranch insurance. The Company evaluates the performance of its insurance segments using industry financial measurements based on 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, managed by Stateco, provides investment services and is evaluated based on investment returns of assets. Asset information by segment is not reported for the insurance segments because the Company does not produce such information internally. The Company’s reportable insurance segments, and the products within each, are as follows: • Personal Insurance Segment - personal auto, homeowners, and other personal • Commercial Insurance Segment - commercial auto, small commercial package, middle market commercial, workers’ compensation, farm & ranch, and other commercial The following table sets forth financial information regarding the Company’s reportable segments for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Revenues from external sources: Insurance operations Personal insurance $ 819.0 $ 755.9 $ 673.4 Commercial insurance 561.8 488.6 464.4 Specialty run-off 0.1 5.7 99.8 Total insurance operations 1,380.9 1,250.2 1,237.6 Investment operations segment Net investment income 72.1 80.4 84.9 Net investment gain (loss) 27.3 74.2 (49.7) Total investment operations 99.4 154.6 35.2 All other 2.1 2.4 2.6 Total revenues from external sources 1,482.4 1,407.2 1,275.4 Intersegment revenues 6.2 6.5 6.5 Total revenues 1,488.6 1,413.7 1,281.9 Reconciling items: Eliminate intersegment revenues (6.2) (6.5) (6.5) Total consolidated revenue $ 1,482.4 $ 1,407.2 $ 1,275.4 Segment (loss) income before federal income taxes: Insurance operations SAP underwriting (loss) gain Personal insurance $ (68.8) $ (42.2) $ 2.8 Commercial insurance (7.4) (0.2) (8.7) Specialty run-off (17.6) (9.7) 0.4 Total insurance operations (93.8) (52.1) (5.5) Investment operations segment: Net investment income 72.1 80.4 84.9 Net investment gain (loss) 27.3 74.2 (49.7) Total investment operations 99.4 154.6 35.2 All other (0.1) 0.3 0.4 Reconciling items: GAAP adjustments 19.8 14.7 (3.7) Interest expense on corporate debt (4.7) (4.9) (5.7) Corporate expenses (6.2) (7.1) (8.6) Total reconciling items $ 8.9 $ 2.7 $ (18.0) Total consolidated income before federal income taxes $ 14.4 $ 105.5 $ 12.1 The following table sets forth financial information regarding the Company’s reportable segments at December 31, 2020 and 2019: ($ millions) 2020 2019 Segment assets: Investment operations segment $ 2,870.8 $ 2,747.8 Total segment assets 2,870.8 2,747.8 Reconciling items: Corporate assets 231.7 231.8 Total consolidated assets $ 3,102.5 $ 2,979.6 Assets attributed to the investment operations segment include the total investments and cash and cash equivalent categories from the balance sheet. All other assets are corporate assets and are not assigned to a segment.

Contingencies

Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies In accordance with the Contingencies Topic of the Financial Accounting Standards Board’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 losses 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. These lawsuits are in various stages of development. The Company generally will contest these matters vigorously but may pursue settlement if appropriate. Based on currently available information, the Company does not believe it is reasonably possible that any such lawsuit or related lawsuits will be material to its results of operations or have a material adverse effect on its consolidated financial position 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 results of operations or have a material adverse effect on its consolidated financial position or cash flows.

SCHEDULE I - SUMMARY OF INVES_2

SCHEDULE I - SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract]
SCHEDULE I - SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES	SCHEDULE I – SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES December 31, 2020 ($ millions) December 31, 2020 Cost or amortized cost (1) Fair value Amount at which shown in the balance sheet Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 506.5 $ 551.7 $ 551.7 Obligations of states and political subdivisions 511.3 541.5 541.5 Corporate securities 459.9 483.3 483.3 U.S. government agencies residential mortgage-backed securities 639.3 660.7 660.7 Total available-for-sale fixed maturities 2,117.0 2,237.2 2,237.2 (1) Original cost of fixed maturities, original cost reduced by repayments and adjusted for amortization of premiums or accrual of discounts.

SCHEDULE II - CONDENSED FINAN_9

SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT	12 Months Ended
	Dec. 31, 2020
Schedule II Condensed Financial Information of Registrant [Abstract]
SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT	Condensed Balance Sheets ($ and shares in millions, except per share amounts) December 31 2020 2019 Assets Investments in common stock of subsidiaries (equity method) $ 1,108.6 $ 1,067.5 Other invested assets 5.6 5.0 Cash and cash equivalents 7.3 8.8 Other assets — 0.1 Due from affiliates 0.8 — Federal income tax, net 14.0 15.2 Total assets $ 1,136.3 $ 1,096.6 Liabilities and Stockholders’ Equity Notes payable (affiliates $116.6 and $116.6, respectively) $ 116.6 $ 116.6 Due to affiliates — 0.7 Other liabilities 9.7 11.8 Total liabilities 126.3 129.1 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 126.8 125.9 Treasury stock, 6.9 and 6.9 shares, respectively, at cost (118.4) (117.5) Additional paid-in capital 213.3 206.7 Accumulated other comprehensive income 13.9 (26.9) Retained earnings 774.4 779.3 Total stockholders’ equity 1,010.0 967.5 Total liabilities and stockholders’ equity $ 1,136.3 $ 1,096.6 See accompanying notes to condensed financial statements. STATE AUTO FINANCIAL CORPORATION SCHEDULE II – CONDENSED FINANCIAL INFORMATION OF REGISTRANT CONTINUED Condensed Statements of Income ($ millions) Year ended December 31 2020 2019 2018 Net investment income $ 0.4 $ 0.5 $ 0.5 Net investment gain (loss) 0.2 0.8 (0.6) Total revenues 0.6 1.3 (0.1) Interest expense (affiliates $6.1, $6.3 and $6.3, respectively) 6.1 6.3 6.3 Other operating expenses 1.0 5.2 7.1 Total expenses 7.1 11.5 13.4 Loss before federal income taxes (6.5) (10.2) (13.5) Federal income tax benefit (1.5) (2.8) (3.4) Net loss before equity in net income of subsidiaries (5.0) (7.4) (10.1) Equity in net income of subsidiaries 18.1 93.2 22.3 Net income $ 13.1 $ 85.8 $ 12.2 See accompanying notes to condensed financial statements. STATE AUTO FINANCIAL CORPORATION SCHEDULE II – CONDENSED FINANCIAL INFORMATION OF REGISTRANT CONTINUED Condensed Statements of Comprehensive Income ($ millions, except per share amounts) Year ended December 31 2020 2019 2018 Net income $ 13.1 $ 85.8 $ 12.2 Other comprehensive income (loss), net of tax: Unrealized equity in subsidiaries 40.8 69.5 (36.3) Other comprehensive income (loss) 40.8 69.5 (36.3) Comprehensive income (loss) $ 53.9 $ 155.3 $ (24.1) See accompanying notes to condensed financial statements. STATE AUTO FINANCIAL CORPORATION SCHEDULE II – CONDENSED FINANCIAL INFORMATION OF REGISTRANT CONTINUED Condensed Statements of Cash Flows ($ millions) Year ended December 31 2020 2019 2018 Cash flows used in operating activities: Net income $ 13.1 $ 85.8 $ 12.2 Adjustments to reconcile net income to net cash used in operating activities: Share-based compensation (2.7) (1.4) 2.0 Net investment (gain) loss (0.2) (0.8) 0.5 Equity in net gain from consolidated subsidiaries (18.1) (93.2) (22.3) Changes in operating assets and liabilities: Other liabilities and due from affiliates (0.8) 1.1 (0.1) Excess tax (benefit) expense on share-based awards — (0.9) 0.9 Federal income taxes, net 1.2 0.9 (0.3) Net cash used in operating activities (7.5) (8.5) (7.1) Cash flows provided by investing activities: Dividends received from consolidated subsidiaries 21.0 14.8 15.4 Purchases of other invested assets (0.5) (0.3) (0.4) Net cash provided by investing activities 20.5 14.5 15.0 Cash flows used in financing activities: Proceeds from issuance of common stock 3.9 5.9 15.4 Payments to acquire treasury stock (0.9) (0.5) (0.2) Payment of dividends (17.5) (17.4) (17.1) Net cash used in financing activities (14.5) (12.0) (1.9) Net (decrease) increase in cash and cash equivalents (1.5) (6.0) 6.0 Cash and cash equivalents at beginning of year 8.8 14.8 8.8 Cash and cash equivalents at end of year $ 7.3 $ 8.8 $ 14.8 Supplemental Disclosures: Federal income tax received 2.7 2.8 4.0 Interest paid (affiliates $6.1, $6.3 and $6.3, respectively) $ (6.1) $ (6.3) $ (6.3) See accompanying notes to condensed financial statements. STATE AUTO FINANCIAL CORPORATION SCHEDULE II – CONDENSED FINANCIAL INFORMATION OF REGISTRANT CONTINUED Notes to Condensed Financial Statements STFC’s investment in subsidiaries is stated at cost plus equity in net income from consolidated subsidiaries since the date of acquisition. STFC’s share of net income of its unconsolidated subsidiaries is included in consolidated income using the equity method. These financial statements should be read in conjunction with the consolidated financial statements of State Auto Financial Corporation. In preparing the Company's consolidated financial information for the year ended December 31, 2020, the Company made certain immaterial revisions to its financial statements for historical periods. Such changes are reflected in the financial results as of and for the years ended December 31, 2019 and 2018, and included in the condensed financial information on Schedule II, and will also be reflected in the historical financial results included in the Company's subsequent condensed financial information. See Note 2 Revision of Misstatement in Prior Year Financial Statements to these Consolidated Financial Statements for additional information as to the nature of the immaterial errors. As a result of the revision, investments in subsidiaries was adjusted from $1,059.8 million to $1,067.5 million, the net federal income tax asset was adjusted from $15.3 million to $15.2 million, and retained earnings was adjusted from $782.7 million to $779.3 million within the condensed balance sheets on Schedule II for 2019. Income tax benefit was adjusted from $2.9 million to $2.8 million, and equity in earnings of subsidiaries, net of tax was adjusted from $94.7 million to $93.2 million within the condensed statements of income on Schedule II for 2019. Additionally, equity in earnings of subsidiaries, net of tax was adjusted from $22.9 million to $22.3 million million within the condensed statements of income on Schedule II for 2018. Certain line items in the Statements of Comprehensive Income and Cash Flows, were immaterially affected by the revision of previously issued financial statements as of and for the years ended December 31, 2019 and 2018. On July 11, 2013, STFC entered into two separate credit agreements with two of its subsidiaries, State Auto P&C and Milbank. Under the terms of the credit agreements, STFC borrowed $85.0 million and $15.0 million, from State Auto P&C and Milbank, respectively. Under the terms of each credit agreement, interest is payable semi-annually at a fixed annual interest rate of 5.28%, with the principal due at the maturity date. There are no prepayment penalties and no collateral was given as security for the payment of either of these loans. Financial Instruments Disclosed, But Not Carried, At Fair Value Notes Payable Included in notes payable are the credit agreements described above with State Auto P&C and Milbank. STFC estimates the fair value of each note payable by obtaining market quotations for U.S. treasury securities with similar maturity dates and applies an appropriate credit spread. These have been placed in Level 3 of the fair value hierarchy. ($ millions, except interest rates) December 31, 2020 December 31, 2019 Carrying Fair Interest Carrying Fair Interest Affiliate note payable with Milbank, issued $15.0, July 2013 with fixed interest $ 15.0 $ 20.3 5.28 % $ 15.0 $ 18.4 5.28 % Affiliate note payable with State Auto P&C, issued $85.0, July 2013 with fixed interest 85.0 114.9 5.28 % 85.0 104.4 5.28 % Total notes payable to affiliates $ 100.0 $ 135.2 $ 100.0 $ 122.8

SCHEDULE III - SUPPLEMENTARY _2

SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
SCHEDULE III - SUPPLEMENTARY INSURANCE INFORMATION	STATE AUTO FINANCIAL CORPORATION AND SUBSIDIARIES SCHEDULE III – SUPPLEMENTARY INSURANCE INFORMATION Years Ended December 31, 2020, 2019 and 2018 ($ millions) Segment Deferred policy acquisition cost Future benefits, claims and losses (1) Unearned premiums Other policy claims and benefits payable Premium revenue Year ended December 31, 2020: Personal insurance segment $ 68.7 $ 280.6 $ 418.1 $ — $ 819.0 Commercial insurance segment 53.4 572.2 296.9 — 561.8 Specialty run-off — 173.3 0.1 — 0.1 Total $ 122.2 $ 1,026.1 $ 715.1 $ — $ 1,380.9 Year ended December 31, 2019: Personal insurance segment $ 62.6 $ 247.2 $ 373.9 $ — $ 755.9 Commercial insurance segment 48.3 572.0 267.5 — 488.6 Specialty run-off 0.2 233.7 0.3 — 5.7 Total $ 111.1 $ 1,052.9 $ 641.7 $ — $ 1,250.2 Year ended December 31, 2018: Personal insurance segment $ 59.0 $ 240.5 $ 340.9 $ — $ 673.4 Commercial insurance segment 41.6 581.9 230.7 — 464.4 Specialty run-off 1.3 318.9 6.0 — 99.8 Total $ 101.9 $ 1,141.3 $ 577.6 $ — $ 1,237.6 Segment Net investment income Benefits, losses and settlement expenses (2) Amort. of deferred policy acquisition costs Other operating expenses Premiums written Year ended December 31, 2020: Personal insurance segment $ — $ 617.2 $ 135.1 $ 125.0 $ 863.2 Commercial insurance segment — 339.9 101.3 119.1 593.3 Specialty run-off — 16.8 0.2 0.7 (0.2) Investment operations segment 72.1 — — — — Total $ 72.1 $ 973.9 $ 236.6 $ 244.8 $ 1,456.3 Year ended December 31, 2019: Personal insurance segment $ — $ 553.4 $ 127.5 $ 110.0 $ 789.1 Commercial insurance segment — 280.4 88.2 113.3 526.3 Specialty run-off — 12.7 0.8 2.2 (0.1) Investment operations segment 80.4 — — — — Total $ 80.4 $ 846.5 $ 216.5 $ 225.5 $ 1,315.3 Year ended December 31, 2018: Personal insurance segment $ — $ 442.3 $ 114.7 $ 116.3 $ 726.0 Commercial insurance segment — 275.2 84.1 115.7 469.8 Specialty run-off — 80.6 21.2 (2.2) 14.0 Investment operations segment 84.9 — — — — Total $ 84.9 $ 798.1 $ 220.0 $ 229.8 $ 1,209.9 (1) Segmented balances are net of reinsurance recoverable on losses and loss expenses payable. (2) Benefits, losses and settlement expenses are monitored on a statutory basis.

SCHEDULE IV - REINSURANCE

SCHEDULE IV - REINSURANCE	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]
SCHEDULE IV - REINSURANCE	STATE AUTO FINANCIAL CORPORATION AND SUBSIDIARIES SCHEDULE IV – REINSURANCE Years Ended December 31, 2020, 2019 and 2018 ($ million, except percentages) Ceded to Assumed from Gross Unaffiliated Affiliated Companies (1) Unaffiliated Affiliated Companies (1) Net Percentage of amount assumed to net (2) Property-casualty 2020 $ 1,067.6 $ 39.0 $ 1,113.4 $ 84.8 $ 1,380.9 $ 1,380.9 6.1 % 2019 976.8 31.0 1,027.1 81.3 1,250.2 1,250.2 6.5 % 2018 881.3 23.0 919.3 61.0 1,237.6 1,237.6 4.9 % (1) These columns include the effect of intercompany pooling. (2) Calculated as earned premiums assumed from outside companies to net amount.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include State Auto Financial Corporation (“State Auto Financial”), an Ohio corporation, and the following wholly owned subsidiaries of State Auto Financial: • State Auto Property and Casualty Insurance Company (“State Auto P&C”), an Iowa corporation • Milbank Insurance Company (“Milbank”), an Iowa corporation • State Auto Insurance Company of Ohio (“SA Ohio”), an Ohio corporation • Stateco Financial Services, Inc. (“Stateco”), an Ohio corporation The consolidated financial statements also include the operations and financial position of 518 Property Management and Leasing, LLC (“518 PML”), an Ohio limited liability company whose only members are State Auto P&C and Stateco. State Auto Financial is a majority-owned subsidiary of State Automobile Mutual Insurance Company (“State Auto Mutual”), an Ohio corporation. State Auto Financial and its subsidiaries are referred to herein as the “Company.” All intercompany balances and transactions have been eliminated in consolidation.
Description of Business	Description of Business The Company markets its insurance products throughout the United States primarily through independent agencies, which include retail agencies and wholesale brokers. The Company’s principal lines of insurance include personal and commercial automobile, homeowners, commercial multi-peril, workers’ compensation, general liability and fire insurance. State Auto P&C, Milbank and SA Ohio are chartered and licensed property and casualty insurers. As such, they are subject to the regulations of the applicable Departments of Insurance of their respective states of domicile (the “Departments”) and the regulations of each state in which they operate. These property and casualty insurance companies undergo periodic financial examination by the Departments and insurance regulatory agencies of the states that choose to participate. A large portion of the Company’s revenues are derived from a reinsurance pooling agreement with State Auto Mutual and its affiliates. The underwriting activity and geographic distribution of State Auto Mutual and its affiliates is generally the same as the underwriting activity and geographic distribution of the Company. Through the employees of State Auto P&C, the Company provides management and operation services under management agreements for all of its insurance and non-insurance affiliates. Through Stateco, the Company provides investment management services to affiliated companies.
Basis of Presentation	Basis of Presentation The consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”), which vary in certain respects from statutory accounting practices (“SAP”) followed by State Auto P&C, Milbank and SA Ohio that are prescribed or permitted by the Departments. The Company’s insurance subsidiaries, domiciled in Ohio and Iowa, are required to prepare statutory basis financial statements in accordance with the accounting practices prescribed or permitted by the insurance departments of the states of domicile. Prescribed statutory accounting practices are those practices that are incorporated directly or by reference in state laws, regulations, and general administrative rules applicable to all insurance enterprises domiciled in a particular state. The Ohio and Iowa Departments of Insurance require insurers domiciled in their respective states to prepare statutory financial statements in accordance with National Association of Insurance Commissioners’ (“NAIC”) statutory accounting practices. Permitted statutory accounting practices are those practices that differ either from state-prescribed statutory accounting practices or NAIC statutory accounting practices. The Company’s insurance subsidiaries do not apply any statutory accounting practices that would be considered a prescribed statutory accounting practice that differs from NAIC statutory accounting practices. In preparing the consolidated financial statements, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet, revenues and expenses for the periods then ended, and the accompanying notes to the financial statements. Such estimates and assumptions could change in the future as more information becomes known which could impact the amounts reported and disclosed herein. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of losses and loss expenses payable. In connection with the determination of losses and loss expenses payable, management uses historical data, current business conditions and assumptions about future conditions to formulate estimates of the ultimate cost to settle claims. These estimates by their nature are subject to uncertainties for various reasons.
Investments	Investments Investments in fixed maturities are classified as available-for-sale and are carried at fair value. On January 1, 2020, the Company adopted ASU 2016-13 Financial Instruments - Credit Losses (ASC 326): Measurement of Credit Losses on Financial Instruments on a prospective basis for its fixed maturities. The updated and prior policy for the available-for-sale fixed maturities are outlined below. December 31, 2020 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 4 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. December 31, 2019 and 2018 The unrealized holding gains and losses, net of applicable deferred income taxes, are shown as a separate component of stockholders’ equity as a part of accumulated other comprehensive income and, as such, are not included in the determination of net income. Realized gains and losses on the sales of investments are computed using the first-in, first-out method. The Company views gross unrealized losses on fixed maturities as being temporary since it is its assessment that these securities will recover in the near term, allowing the Company to realize the anticipated long-term economic value. The Company regularly monitors its investments that have fair values less than cost or amortized cost for signs of other-than-temporary 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 financial condition of the issuer, including receipt of scheduled principal and interest cash flows, and intent to sell, including if it is more likely than not that the Company will be required to sell the investments before recovery. When a fixed maturity security has been determined to have an other-than-temporary impairment, the impairment charge is separated into an amount representing the credit loss, which is recognized in earnings as a realized loss and the amount related to non-credit factors, which is recognized in other comprehensive income. Future increases or decreases in fair value, if not other-than-temporary, are included in other comprehensive income.
Cash Equivalents	Cash EquivalentsThe Company considers all liquid debt instruments with a maturity of three months or less at the time of acquisition to be cash equivalents. The carrying amounts reported approximate their fair value.
Deferred Acquisition Costs	Deferred Acquisition Costs Acquisition costs, consisting of net commissions (including ceding commissions), premium taxes and certain underwriting expenses related to the successful acquisition or renewal of property and casualty business, are deferred and amortized over the same period in which the related premiums are earned. Ceding commissions relating to reinsurance agreements reimburse us for both deferrable and non-deferrable acquisition costs. Excess ceding commissions are amortized in proportion to net revenue recognized on the underlying policies resulting in excess ceding commissions being recognized as a reduction of acquisition and operating expenses. The method followed for computing the acquisition costs limits the amount of such deferred costs to their estimated realizable value. In determining estimated realizable value, the computation gives effect to the premium to be earned, losses and loss expenses expected to be incurred, and certain other costs expected to be incurred as premium is earned. Future changes in estimates, the most significant of which is expected losses and loss adjustment expenses, that indicate a reduction in expected future profitability may result in unrecoverable deferred acquisition costs. Anticipated investment income is considered in determining whether a premium deficiency exists. The following table sets forth net deferred acquisition costs for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Balance, beginning of year $ 111.1 $ 101.9 $ 110.3 Acquisition costs deferred 247.7 225.7 211.6 Acquisition costs amortized to expense (236.6) (216.5) (220.0) Balance, end of year $ 122.2 $ 111.1 $ 101.9
Federal Income Taxes	Federal Income Taxes The Company files a consolidated federal income tax return. Pursuant to a written tax sharing agreement, each entity within the consolidated group pays or receives its share of federal income taxes based on separate return calculations. The Company recognizes deferred income tax assets and liabilities for the expected future tax effects attributable to temporary differences between the financial statement and tax return bases of assets and liabilities, based on enacted tax rates and other provisions of the tax law. The effect of a change in tax laws or rates on deferred tax assets and liabilities is recognized in income in the period in which such change is enacted. Deferred tax assets and liabilities include provisions for unrealized investment gains and losses as well as the net funded status of pension and other postretirement benefit obligations with the changes for each period included in the respective components of other comprehensive income. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that all or some portion of the deferred tax assets will not be realized. Interest and penalties related to uncertain tax positions are recorded in the balance sheet as other liabilities, and recognized in the income statement as other expenses.
Losses and Loss Expenses Payable	. Losses and Loss Expenses PayableLosses and loss expenses payable reflect the estimated ultimate unpaid liability for losses and loss expenses with respect to reported and unreported claims incurred as of the end of each accounting period. Loss reserves are estimated using various standard actuarial projection methods and assumptions based on historical reporting and settlement patterns, expected loss ratios, trends in claims severity and frequency and other factors. There can be no assurance that the ultimate liability will not vary materially from such estimates. Estimates are refined as part of a regular, ongoing process as historical loss experience develops and additional claims are reported and settled, and such adjustments are included in current operations (see Note 5). Anticipated salvage and subrogation is estimated using historical experience. The liability for unpaid losses and loss expenses, net of estimated salvage and subrogation recoverable of $28.7 million and $28.2 million at December 31, 2020 and 2019, respectively, represents management’s best estimate of the ultimate liability related to reported and unreported claims.
Reinsurance Recoverable	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 9), 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 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. Premiums receivable represents the billed and due premium written directly by the STFC Pooled Companies. 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. Description and disclosure of the allowance for uncollectible premiums receivable balance is disclosed in Note 9.
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 9). 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. 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. Compensation—Retirement Benefits—Defined Benefit Plans—General On August 28, 2018, the FASB issued ASU 2018-14, which amends ASC 715 to add, remove, and clarify disclosure requirements related to defined benefit pension and other postretirement plans. The ASU is effective for fiscal years beginning after December 15, 2020 and will be effective January 1, 2021. The Company has early-adopted these disclosure updates in this Form 10-K.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of Net Deferred Acquisition Costs	The following table sets forth net deferred acquisition costs for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Balance, beginning of year $ 111.1 $ 101.9 $ 110.3 Acquisition costs deferred 247.7 225.7 211.6 Acquisition costs amortized to expense (236.6) (216.5) (220.0) Balance, end of year $ 122.2 $ 111.1 $ 101.9

Accounting Changes and Error _2

Accounting Changes and Error Corrections (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Changes and Error Corrections [Abstract]
Schedule of Error Corrections and Prior Period Adjustments [Table Text Block]	Revised Consolidated Balance Sheet ($ in millions) Year Ended December 31, 2019 As Reported Adjustment As Revised Assets Fixed maturities, available-for-sale, at fair value $ 2,127.9 $ 0.5 $ 2,128.4 Premiums receivable — 13.6 13.6 Due from affiliate 21.5 (17.4) 4.1 Net deferred federal income taxes 42.2 (2.5) 39.7 Total Assets 2,985.4 (5.8) 2,979.6 Liabilities and Stockholders’ Equity Pension and postretirement benefits 72.9 (13.4) 59.5 Total liabilities 2,025.5 (13.4) 2,012.1 Stockholders’ equity: Accumulated other comprehensive income (loss) (37.9) 11.0 (26.9) Retained earnings 782.7 (3.4) 779.3 Total stockholders’ equity 959.9 7.6 967.5 Total liabilities and stockholders’ equity 2,985.4 (5.8) 2,979.6 Revised Consolidated Statement of Income ($ in millions, except per share amounts) Year Ended December 31, 2019 Year Ended December 31, 2018 As Reported Adjustment As Revised As Reported Adjustment As Revised Earned premiums $ 1,253.0 $ (2.8) $ 1,250.2 $ 1,238.0 $ (0.4) $ 1,237.6 Total revenues 1,410.0 (2.8) 1,407.2 1,275.8 (0.4) 1,275.4 Acquisition and operating expenses 442.0 (1.3) 440.7 449.8 0.4 450.2 Total expenses 1,303.0 (1.3) 1,301.7 1,262.9 0.4 1,263.3 Income before federal income taxes 107.0 (1.5) 105.5 12.9 (0.8) 12.1 Deferred income tax expense (benefit) 20.0 0.1 20.1 1.2 (0.2) 1.0 Total federal income tax expense (benefit) 19.6 0.1 19.7 0.1 (0.2) (0.1) Net income 87.4 (1.6) 85.8 12.8 (0.6) 12.2 Earnings per common share: Basic $ 2.01 $ (0.03) $ 1.98 $ 0.30 $ (0.01) $ 0.29 Diluted $ 1.96 $ (0.03) $ 1.93 $ 0.29 $ (0.01) $ 0.28 Revised Consolidated Statement of Comprehensive Income ($ millions) Year Ended December 31, 2019 As Reported Adjustment As Revised Net income $ 87.4 $ (1.6) $ 85.8 Other comprehensive income, net of tax: Net change in unrealized holding gain on available-for-sale investments: Unrealized holding gains arising during year 80.2 0.5 80.7 Income tax expense (16.1) (0.1) (16.2) Total change in net unrealized holding gain on available-for-sale investments 60.6 0.4 61.0 Net unrecognized benefit plan obligations: Net actuarial gain (loss) arising during period (5.9) 13.4 7.5 Income tax benefit (expense) 0.5 (2.8) (2.3) Total net unrecognized benefit plan obligations (2.1) 10.6 8.5 Other comprehensive income 58.5 11.0 69.5 Comprehensive income 145.9 9.4 155.3 Revised Consolidated Statement of Cash Flows ($ in millions) Year ended December 31, 2019 Year ended December 31, 2018 As Reported Adjustment As Revised As Reported Adjustment As Revised Cash flows from operating activities: Net income $ 87.4 $ (1.6) $ 85.8 $ 12.8 $ (0.6) $ 12.2 Adjustments to reconcile net income to net cash (used in) provided by operating activities: Changes in operating assets and liabilities: Premiums receivable — (0.9) (0.9) — (2.7) (2.7) Other liabilities and due to/from affiliates, net (44.9) 2.4 (42.5) 47.6 3.5 51.1 Federal income taxes 20.5 0.1 20.6 (0.8) (0.2) (1.0) Net cash used in operating activities (43.9) — (43.9) (13.4) — (13.4)

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Investments [Abstract]
Schedule of Available-for-sale Securities Reconciliation	The following tables set forth the cost or amortized cost and fair value of investments by lot at December 31, 2020 and 2019: ($ millions) Cost or amortized cost Gross unrealized holding gains Gross unrealized holding losses Fair value December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 506.5 $ 45.2 $ — $ 551.7 Obligations of states and political subdivisions 511.3 30.4 (0.2) 541.5 Corporate securities 459.9 23.4 — 483.3 U.S. government agencies mortgage-backed securities 639.3 22.9 (1.5) 660.7 Total available-for-sale fixed maturities $ 2,117.0 $ 121.9 $ (1.7) $ 2,237.2 ($ millions) Cost or 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 $ 12.6 $ (3.3) $ 578.5 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 11.3 (4.6) 652.7 Total available-for-sale fixed maturities $ 2,080.0 $ 56.7 $ (8.3) $ 2,128.4
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 was not recorded at December 31, 2020 and 2019: ($ millions, except # of positions) Less than 12 months 12 months or more Total December 31, 2020 Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 9.6 $ — 4 $ — $ — — $ 9.6 $ — 4 Obligations of states and political subdivisions 19.5 (0.2) 5 — — — 19.5 (0.2) 5 Corporate securities 1.5 — 2 — — — 1.5 — 2 U.S. government agencies mortgage-backed securities 136.1 (1.4) 35 7.0 (0.1) 3 143.1 (1.5) 38 Total fixed maturities $ 166.7 $ (1.6) 46 $ 7.0 $ (0.1) 3 $ 173.7 $ (1.7) 49 ($ millions, except # of positions) Less than 12 months 12 months or more Total December 31, 2019 Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions Fair value Unrealized losses Number of positions 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 fixed maturities $ 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 December 31, 2020: ($ millions) Amortized cost Fair value Due in 1 year or less $ 140.5 $ 141.6 Due after 1 year through 5 years 510.3 540.4 Due after 5 years through 10 years 161.6 172.6 Due after 10 years 665.3 721.9 U.S. government agencies mortgage-backed securities 639.3 660.7 Total $ 2,117.0 $ 2,237.2
Components of Net Investment Income	The following table sets forth the components of net investment income for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Fixed maturities $ 59.6 $ 62.3 $ 65.3 Equity securities 9.3 13.2 13.4 Cash and cash equivalents, and other 4.0 5.5 7.2 Investment income 72.9 81.0 85.9 Investment expenses 0.8 0.6 1.0 Net investment income $ 72.1 $ 80.4 $ 84.9
Realized and Unrealized Holding Gains (Losses)	The following table sets forth the gains (losses) on investments on the Company’s investment portfolio for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Investment gain (loss), net: Fixed maturities: Realized gains on securities sold $ 5.2 $ 3.5 $ 2.0 Realized losses on securities sold (5.5) — — Net (loss) gain on fixed maturities (0.3) 3.5 2.0 Net gain (loss) on equity securities 26.7 62.1 (44.0) Net gain (loss) on other invested assets 0.7 9.9 (7.7) Other net realized gain (loss) 0.2 (1.3) — Net gain (loss) on investments $ 27.3 $ 74.2 $ (49.7) Change in net unrealized holding gains (losses), net of tax Fixed maturities $ 71.8 $ 77.2 $ (48.4) Deferred federal income tax (liability) benefit (15.1) (16.2) 10.1 Change in net unrealized holding gains (losses), net of tax $ 56.7 $ 61.0 $ (38.3)

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Company's Available-for-Sale Investments within Fair Value Hierarchy	The following tables set forth the Company’s investments within the fair value hierarchy at December 31, 2020 and 2019: ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2020 Available-for-sale fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 551.7 $ — $ 551.7 Obligations of states and political subdivisions 541.5 — 541.5 Corporate securities 483.3 — 483.3 U.S. government agencies mortgage-backed securities 660.7 — 660.7 Total available-for-sale fixed maturities 2,237.2 — 2,237.2 Equity securities: Large-cap securities 134.2 134.2 — Mutual and exchange traded funds 255.5 255.5 — Total equity securities 389.7 389.7 — Other invested assets 15.3 15.3 — Total investments $ 2,642.2 $ 405.0 $ 2,237.2 ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 578.5 $ — $ 578.5 Obligations of states and political subdivisions 425.4 — 425.4 Corporate securities 471.8 — 471.8 U.S. government agencies mortgage-backed securities 652.7 — 652.7 Total fixed maturities 2,128.4 — 2,128.4 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 $ 2,536.9 $ 408.5 $ 2,128.4
Company Estimates Receivable from Affiliate using Market Quotations for U.S. Treasury Securities	The Company estimates the fair value of the notes receivable from affiliates using market quotations for U.S. treasury securities with similar maturity dates and applies an appropriate credit spread. This has been placed in Level 2 of the fair value hierarchy. ($ millions, except interest rates) December 31, 2020 December 31, 2019 Carrying value Fair value Interest rate Carrying value Fair value Interest rate Notes receivable from affiliate, issued May 2019 $ 70.0 $ 80.4 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) December 31, 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 21.6 1.37 % — — — % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 107.1 3.96 % 85.3 97.8 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.3 15.3 4.43 % 15.2 15.2 6.11 % Total notes payable $ 122.1 $ 144.0 $ 122.0 $ 134.5
Company's Assets and Liabilities within 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) December 31, 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 21.6 1.37 % — — — % FHLB Loan due 2033: issued $85.0, May 2018 with fixed interest 85.3 107.1 3.96 % 85.3 97.8 3.96 % Affiliate Subordinated Debentures due 2033: issued $15.5, May 2003 with variable interest 15.3 15.3 4.43 % 15.2 15.2 6.11 % Total notes payable $ 122.1 $ 144.0 $ 122.0 $ 134.5

Losses and Loss Expenses Paya_2

Losses and Loss Expenses Payable (Tables)	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Schedule of Activity in Liability for Losses and Loss Expenses	The following table sets forth the activity in the liability for losses and loss expenses for the years ended December 31: ($ millions) 2020 2019 2018 Losses and loss expenses payable, at beginning of year $ 1,066.5 $ 1,146.8 $ 1,255.6 Less: reinsurance recoverable on losses and loss expenses payable 13.6 5.5 3.1 Net balance at beginning of year 1,052.9 1,141.3 1,252.5 Incurred related to: Current year 1,008.2 913.5 876.6 Prior years (35.6) (68.7) (80.2) Total incurred 972.6 844.8 796.4 Paid related to: Current year 599.5 530.4 456.5 Prior years 399.9 402.8 451.1 Total paid 999.4 933.2 907.6 Net balance at end of year 1,026.1 1,052.9 1,141.3 Plus: reinsurance recoverable on losses and loss expenses payable 24.3 13.6 5.5 Losses and loss expenses payable $ 1,050.4 $ 1,066.5 $ 1,146.8

Short-Duration Insurance Cont_2

Short-Duration Insurance Contracts (Tables)	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Short-duration Insurance Contracts, Claims Development [Table Text Block]	Personal Insurance Segment - Short-Tail The change in incurred losses and loss adjustment expenses for prior accident years was due to higher than expected emergence of all personal insurance products. The emergence was primarily attributable to higher severity for bodily injury claims from the 2017, 2018 and 2019 accident years. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2016 $ 368.5 $ 370.0 $ 361.4 $ 360.8 $ 361.4 $ 0.9 151,620 2017 372.4 355.0 351.9 356.0 1.3 151,727 2018 418.5 411.4 418.2 4.4 154,705 2019 497.5 508.2 21.0 163,378 2020 509.3 87.4 123,234 Total $ 2,153.1 * Supplementary information and unaudited (1) Personal insurance segment - short-tail is an aggregation of the homeowners and personal auto product lines. Homeowners reported claims are counted by claimant and personal auto claims are counted by coverage. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 2016 $ 231.9 $ 316.2 $ 342.6 $ 352.1 $ 356.5 2017 236.8 315.8 335.7 347.9 2018 276.4 375.1 400.2 2019 343.7 457.7 2020 344.4 Total $ 1,906.7 All outstanding liabilities before 2016, net of reinsurance $ 3.8 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 250.2 * Supplementary information and unaudited Commercial Insurance Segment - Short-Tail The change in incurred losses and loss adjustment expenses for prior accident years was primarily driven by lower than expected emergence for the small commercial package and middle market commercial products. The emergence in these products was driven by lower than expected bodily injury claim severity from multiple accident years. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2016 $ 237.0 $ 227.6 $ 225.2 $ 220.6 $ 217.2 $ 6.0 34,872 2017 236.8 225.5 215.9 209.1 9.0 32,101 2018 228.4 216.4 207.3 17.7 31,055 2019 248.2 236.1 44.1 32,362 2020 328.2 75.0 29,540 Total $ 1,197.9 * Supplementary information and unaudited (1) Commercial insurance segment - short-tail is an aggregation of the commercial auto, small commercial package, middle market commercial and farm & ranch product lines. Commercial auto reported claims are counted by coverage and small commercial package, middle market commercial and farm & ranch reported claims are counted by claimant. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 2016 $ 99.2 $ 147.3 $ 176.7 $ 196.1 $ 204.2 2017 104.9 153.9 175.5 188.0 2018 98.7 144.6 161.0 2019 108.4 159.7 2020 170.6 Total $ 883.5 All outstanding liabilities before 2016, net of reinsurance $ 34.9 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 349.3 * Supplementary information and unaudited Commercial Insurance Segment - Long-Tail The change in incurred losses and loss adjustment expenses for prior accident years was due to lower than expected emergence in the workers’ compensation product, primarily driven by lower than expected severity from multiple accident years. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2011 $ 44.6 $ 47.4 $ 45.5 $ 44.8 $ 44.8 $ 44.9 $ 43.9 $ 42.9 $ 42.3 $ 41.7 $ 1.9 12,228 2012 49.7 45.8 43.7 44.1 43.9 42.9 41.7 40.5 39.8 2.1 12,762 2013 48.7 45.4 44.1 43.4 42.9 41.5 40.5 39.2 3.5 11,319 2014 51.6 50.0 47.1 45.7 45.3 43.4 41.0 4.8 11,570 2015 59.7 59.4 56.5 53.7 51.3 48.7 6.7 11,161 2016 62.6 60.6 57.2 53.9 49.5 9.2 12,453 2017 59.0 56.4 53.7 49.1 8.7 12,574 2018 56.4 53.6 49.3 11.6 12,541 2019 54.4 52.9 13.3 12,045 2020 55.5 26.0 10,851 Total $ 466.7 * Supplementary information and unaudited (1) Commercial insurance segment-long-tail consists of the workers' compensation product. Workers' compensation reported claims are counted by a combination of claimant and coverage. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 2011 $ 12.4 $ 25.4 $ 31.9 $ 35.0 $ 36.9 $ 37.7 $ 38.1 $ 38.6 $ 38.9 $ 39.0 2012 12.6 23.5 29.8 32.7 34.7 35.8 36.4 36.6 36.8 2013 12.3 23.3 29.0 32.3 33.7 34.2 34.4 34.6 2014 12.4 24.4 30.0 32.8 34.1 34.6 35.0 2015 13.9 28.2 35.7 38.3 39.5 40.2 2016 12.6 26.8 32.3 35.6 37.0 2017 13.2 27.0 32.8 36.8 2018 13.2 26.4 32.5 2019 14.7 29.2 2020 13.3 $ 334.4 All outstanding liabilities before 2011, net of reinsurance $ 30.6 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 162.9 * Supplementary information and unaudited Specialty run-off - Short-Tail The change in incurred losses and loss adjustment expenses for prior accident years was due to increases in estimates for claims related to Hurricane Irma. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2016 $ 99.3 $ 99.5 $ 102.7 $ 105.7 $ 105.3 $ 5.3 9,413 2017 134.2 129.7 138.3 150.6 16.3 11,340 2018 18.5 20.5 19.8 2.4 2,410 2019 1.0 1.1 — 61 2020 0.3 0.1 13 Total $ 277.1 * Supplementary information and unaudited (1) Specialty run-off-short-tail is an aggregation of the E&S Property and programs product lines. E&S Property and programs reported claims are counted by claimant. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident Year 2016* 2017* 2018* 2019* 2020 2016 $ 25.2 $ 50.2 $ 69.9 $ 87.4 $ 96.0 2017 39.0 77.5 101.2 121.3 2018 6.3 10.7 13.3 2019 0.5 0.9 2020 0.1 Total $ 231.6 All outstanding liabilities before 2016, net of reinsurance $ 13.7 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 59.2 * Supplementary information and unaudited Specialty run-off - Long-Tail The change in incurred losses and loss adjustment expenses for prior accident years was primarily related to an adverse court decision relating to an E&S casualty claim from accident year 2016. ($ in millions except number of claims) Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance As of December 31, 2020 For the Years Ended December 31, Accident Year 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 IBNR+ Reported Claims (1) 2011 $ 11.9 $ 10.7 $ 10.7 $ 10.2 $ 10.1 $ 10.9 $ 10.5 $ 9.7 $ 9.5 $ 9.5 $ 0.8 1,250 2012 16.7 16.7 15.4 17.6 17.4 16.5 16.0 16.1 16.2 $ 0.6 1,199 2013 20.1 18.9 17.9 16.5 15.9 15.3 15.0 15.4 $ 1.0 1,562 2014 23.3 25.2 27.1 28.3 29.5 30.0 31.0 2.6 2,030 2015 38.6 44.9 44.8 45.7 45.0 48.6 6.3 3,167 2016 60.8 62.9 64.8 64.3 70.2 10.6 9,505 2017 71.6 73.1 70.5 66.3 20.6 9,245 2018 53.0 53.3 51.5 21.5 6,203 2019 4.1 4.6 4.2 2,352 2020 0.2 0.2 19 Total $ 313.5 * Supplementary information and unaudited (1) Specialty run-off-long-tail consists of the E&S Casualty product line. E&S Casualty reported claims are counted by claimant. ($ in millions) Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance For the Years Ended December 31, Accident 2011* 2012* 2013* 2014* 2015* 2016* 2017* 2018* 2019* 2020 2011 $ 0.9 $ 3.0 $ 5.2 $ 6.6 $ 7.1 $ 7.9 $ 8.1 $ 8.4 $ 8.6 $ 8.7 2012 0.9 4.0 7.3 10.3 12.5 14.0 14.1 14.7 14.9 2013 1.1 3.7 6.7 9.0 10.5 12.0 13.3 13.6 2014 1.2 7.2 12.5 16.7 21.5 24.2 25.7 2015 2.7 10.9 20.6 29.1 34.7 36.9 2016 6.0 15.7 31.5 39.7 53.5 2017 5.5 16.4 25.2 35.7 2018 2.7 12.8 20.6 2019 0.1 0.5 2020 — Total $ 210.1 All outstanding liabilities before 2011, net of reinsurance $ 3.8 Losses and allocated loss adjustment expenses payable, net of reinsurance $ 107.3 * Supplementary information and unaudited
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Table Text Block]	The following table sets forth the reconciliation of the claims development tables to the balance sheet losses and loss expenses payable, with separate disclosure of unallocated loss adjustment expenses, net of reinsurance ("ULAE") and reinsurance recoverable on losses and loss expenses payable, for the years ended December 31: ($ in millions) 2020 2019 2018 Net losses and allocated loss adjustment expenses payable: Personal Insurance Segment Short-tail $ 250.2 $ 220.6 $ 216.0 Other personal 14.9 14.4 13.5 Commercial Insurance Segment Short-tail 349.3 330.8 336.4 Long-tail 162.9 174.2 182.1 Other commercial 25.5 30.9 27.4 Specialty run-off Short-tail 59.2 84.9 128.5 Long-tail 107.3 139.1 177.6 Net losses and loss expenses payable 969.3 994.9 1,081.5 ULAE 56.8 58.0 59.8 Reinsurance recoverable on losses and loss expenses payable 24.3 13.6 5.5 Total losses and loss expenses payable $ 1,050.4 $ 1,066.5 $ 1,146.8
Short-duration Insurance Contracts, Schedule of Historical Claims Duration [Table Text Block]	The following table sets forth the historical average annual payout of incurred losses and allocated loss adjustment expenses (claims duration) for short-duration contracts, based on the disaggregated information in the paid loss development tables, net of reinsurance: Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years Segment 1* 2* 3* 4* 5* 6* 7* 8* 9* 10* Personal Insurance: Short-tail 66.4 % 22.9 % 6.3 % 3.0 % 1.2 % N/A N/A N/A N/A N/A Commercial Insurance: Short-tail 48.3 % 22.4 % 10.6 % 7.5 % 3.7 % N/A N/A N/A N/A N/A Long-tail 28.2 % 28.5 % 13.8 % 7.2 % 3.6 % 1.7 % 1.0 % 0.8 % 0.5 % 0.3 % Specialty run-off: Short-tail 32.5 % 27.5 % 15.7 % 15.0 % 8.2 % N/A N/A N/A N/A N/A Long-tail 5.6 % 16.9 % 19.0 % 15.2 % 12.5 % 8.1 % 3.8 % 3.0 % 2.2 % 0.4 % * Supplementary information and unaudited

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2020
Reinsurance Disclosures [Abstract]
External Reinsurance on Balance Sheets	The following table sets forth the effect of the Company’s external reinsurance on its balance sheets at December 31, 2020 and 2019, prior to the reinsurance transaction with State Auto Mutual under the Pooling Arrangement, as discussed in Note 9a: ($ millions) 2020 2019 Losses and loss expenses payable: Direct $ 581.3 $ 540.1 Assumed 30.3 25.6 Ceded (24.3) (13.6) Net losses and loss expenses payable $ 587.3 $ 552.1 Unearned premiums: Direct $ 507.7 $ 495.8 Assumed 39.5 36.7 Ceded (8.3) (7.5) Net unearned premiums $ 538.9 $ 525.0
External Reinsurance on Income Statements	The following table sets forth the effect of the Company’s external reinsurance on its income statements for the years ended December 31, 2020, 2019 and 2018, prior to the reinsurance transaction with State Auto Mutual under the Pooling Arrangement, as discussed in Note 9a: ($ millions) 2020 2019 2018 Written premiums: Direct $ 1,080.5 $ 1,036.9 $ 915.1 Assumed 87.6 82.5 75.1 Ceded (39.8) (31.9) (23.1) Net written premiums $ 1,128.3 $ 1,087.5 $ 967.1 Earned premiums: Direct $ 1,067.6 $ 976.8 $ 881.3 Assumed 84.8 81.3 61.0 Ceded (39.0) (31.0) (23.0) Net earned premiums $ 1,113.4 $ 1,027.1 $ 919.3 Losses and loss expenses incurred: Direct $ 789.0 $ 631.4 $ 572.5 Assumed 56.8 59.6 48.4 Ceded (57.6) (15.6) (4.9) Net losses and loss expenses incurred $ 788.2 $ 675.4 $ 616.0

Current Expected Credit Losse_2

Current Expected Credit Losses Current Expected Credit Losses (Tables)	12 Months Ended
	Dec. 31, 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 December 31, 2020: ($ millions) Amortized Cost Financial strength rating: A++ $ 1.1 A+ 9.5 A 13.7 Reinsurance recoverable on losses and loss expenses payable, net of allowance for credit losses $ 24.3
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 twelve months ended December 31, 2020: ($ millions) Allowance for credit losses Beginning balance at January 1, 2020 $ 4.3 Current period provision 8.2 Writeoffs (5.4) Ending balance at December 31, 2020 $ 7.1

Transactions with Affiliates (T

Transactions with Affiliates (Tables)	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Schedule of Reinsurance Transactions on Balance Sheets for Pooling Arrangement	The following table sets forth the reinsurance transactions on the Company’s balance sheets for the Pooling Arrangement between the STFC Pooled Companies and State Auto Mutual at December 31, 2020 and 2019: ($ millions) 2020 2019 Assets Deferred policy acquisition costs: Ceded $ (92.1) $ (90.9) Assumed 122.2 111.1 Net assumed $ 30.1 $ 20.2 Liabilities Losses and loss expenses payable: Ceded $ (587.3) $ (552.1) Assumed 1,026.1 1,052.9 Net assumed $ 438.8 $ 500.8 Unearned premiums: Ceded $ (262.7) $ (225.9) Assumed 715.1 641.7 Net assumed $ 452.4 $ 415.8 Other liabilities: Ceded $ (77.1) $ (77.8) Assumed 99.5 94.0 Net assumed $ 22.4 $ 16.1
Schedule of Reinsurance Transactions on Income Statements for Pooling Arrangement	The following table sets forth the reinsurance transactions on the Company’s income statements for the Pooling Arrangement between the STFC Pooled Companies and State Auto Mutual for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Written premiums: Ceded $ (1,128.3) $ (1,088.1) $ (966.8) Assumed 1,456.3 1,315.3 1,209.9 Net assumed $ 328.0 $ 227.2 $ 243.1 Earned premiums: Ceded $ (1,113.4) $ (1,027.7) $ (919.0) Assumed 1,380.9 1,250.2 1,237.6 Net assumed $ 267.5 $ 222.5 $ 318.6 Losses and loss expenses incurred: Ceded $ (789.7) $ (677.2) $ (617.6) Assumed 973.9 846.5 798.1 Net assumed $ 184.2 $ 169.3 $ 180.5 Acquisition and operating expenses: Ceded (374.8) (370.0) (341.1) Assumed 477.4 439.1 449.8 Net assumed $ 102.6 $ 69.1 $ 108.7

Federal Income Taxes (Tables)

Federal Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Reconciliation Between Actual Federal Income Tax Expense (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 years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Amount at statutory rate $ 3.0 21.0 % $ 22.2 21.0 % $ 2.6 21.0 % Tax-exempt interest and dividends received deduction (2.3) (16.4) (2.3) (2.1) (2.3) (18.7) Other, net 0.6 4.2 (0.2) (0.2) (0.4) (3.0) Federal income tax expense (benefit) $ 1.3 8.8 % $ 19.7 18.7 % $ (0.1) (0.7) %
Tax Effects of Temporary Differences of Deferred Tax Assets and Deferred Tax Liabilities	The following table sets forth the tax effects of temporary differences that give rise to significant portions of deferred tax assets and deferred tax liabilities at December 31, 2020 and 2019: ($ millions) 2020 2019 Deferred tax assets: Unearned premiums not currently deductible $ 30.1 $ 27.0 Losses and loss expenses payable discounting 10.5 10.6 Postretirement and pension benefits 19.3 17.1 Other liabilities 12.2 13.4 Net operating loss carryforward 19.8 12.6 Capital loss carryforward 6.1 — Tax credit carryforward 1.9 2.5 Other 1.1 1.1 Total deferred tax assets 101.0 84.3 Deferred tax liabilities: Deferral of policy acquisition costs 25.7 23.3 Investments 48.0 21.3 Total deferred tax liabilities 73.7 44.6 Net deferred federal income taxes $ 27.3 $ 39.7

Pension and Postretirement Be_2

Pension and Postretirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Summary of Pension and Postretirement Benefit Plans' Change in Benefit Obligation, Plan Assets and Funded Status	The following table sets forth information regarding the pension and postretirement benefit plans’ change in benefit obligation, plan assets and funded status at December 31, 2020 and 2019: ($ millions) Pension Postretirement 2020 2019 2020 2019 Change in benefit obligation: Benefit obligation at beginning of year $ 478.4 $ 428.1 $ 11.4 $ 25.5 Service cost 7.3 5.8 — — Interest cost 14.5 17.2 0.3 1.0 Actuarial loss (gain) 72.3 60.6 (0.9) (12.6) Benefits paid (22.9) (33.3) (0.6) (2.5) Benefit obligation at end of year 549.6 478.4 10.2 11.4 Change in plan assets available for plan benefits: Fair value of plan assets available for plan benefits at beginning of year 442.1 381.6 — — Employer contribution 15.0 10.0 — — Actual return on plan assets 72.5 83.8 — — Benefits paid (22.9) (33.3) — — Fair value of plan assets at end of year $ 506.7 $ 442.1 $ — $ — Supplemental executive retirement plan (13.1) (11.8) — — Funded status at end of year $ (56.0) $ (48.1) $ (10.2) $ (11.4) Accumulated benefit obligation end of year $ 522.8 $ 453.8
Company's Share of Amounts Included in Accumulated Other Comprehensive Income (Loss)	The following table sets forth the amounts included in accumulated other comprehensive income (loss) that has not been recognized in net periodic cost at December 31, 2020 and 2019: ($ millions) 2020 2019 Prior service benefit $ (37.0) $ (43.4) Net actuarial loss 157.4 143.7 Total $ 120.4 $ 100.3
Company's Share of Net Periodic Cost Components	The following table sets forth information regarding the Company’s share of pension and postretirement benefit plans’ components of net periodic cost for the years ended December 31, 2020, 2019 and 2018: ($ millions) Pension Postretirement 2020 2019 2018 2020 2019 2018 Components of net periodic cost: Service cost $ 4.8 $ 3.8 $ 5.1 $ — $ — $ — Interest cost 9.7 11.5 10.7 0.2 0.7 0.8 Expected return on plan assets (17.5) (17.8) (18.0) — — — Amortization of: Prior service benefit — — — (5.5) (5.5) (5.5) Net actuarial loss 9.2 6.0 8.2 (0.2) 0.2 0.2 Net periodic cost (benefit) $ 6.2 $ 3.5 $ 6.0 $ (5.5) $ (4.6) $ (4.5)
Company's Share of Expected Future Benefits Payments Schedule	The following table sets forth the benefit payments, which reflect expected future service, expected to be paid: ($ millions) Pension Postretirement 2021 $ 18.3 $ 0.7 2022 18.9 0.6 2023 19.6 0.6 2024 20.6 0.6 2025 21.6 0.6 2026-2030 123.0 3.1
Weighted Average Assumptions Used to Determine Benefit Plans' Obligations	The following table sets forth the weighted average assumptions used to determine the benefit plans’ obligations at December 31, 2020 and 2019: Pension Postretirement 2020 2019 2020 2019 Benefit obligations weighted-average assumptions: Discount rate 2.32 % 3.10 % 1.95 % 3.00 % Rates of increase in compensation levels 3.00 3.25 — —
Weighted Average Assumptions Used to Determine Benefit Plans' Net Periodic Cost [Table Text Block]	The following table sets forth the weighted average assumptions used to determine the benefit plans’ net periodic cost for the years ended December 31, 2020, 2019 and 2018: Pension Postretirement 2020 2019 2018 2020 2019 2018 Weighted-average assumptions: Discount rate 3.10 % 4.12 % 3.50 % 3.10 % 4.12 % 3.50 % Expected long-term rate of return on assets 6.50 6.75 7.00 — — — Rates of increase in compensation levels 3.25 3.25 3.25 — — —
Schedule of Assumed Health Care Cost Trend Rates Used	The following table sets forth the assumed health care cost trend rates used for the years ended December 31, 2020, 2019 and 2018: Postretirement 2020 2019 2018 Assumed health care cost trend rates: Health care cost trend rate assumed for the next year 5.50 % 5.50 % 5.50 % Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) 4.00 % 4.00 % 3.80 % Year that the rate reaches the ultimate trend rate 2075 2075 2075
Summary of Asset Allocation Targets	The following table sets forth the asset allocation targets, as a percentage of total fair value, which are used as a guide by management when allocating funds as they become available. Asset allocation target (0 to 100%) Asset Category: Fixed maturity 61.0 % U.S. large-cap equity 19.8 U.S. small-cap equity 8.3 International equity 7.6 Emerging market equity 3.3 Total 100.0 %
Defined Benefit Plan, Plan Assets, Allocation	The following tables set forth the plan’s investments within the fair value hierarchy at December 31, 2020 and 2019: ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2020 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 90.5 $ — $ 90.5 Corporate securities 183.9 — 183.9 U.S. government agencies mortgage-backed securities 3.9 — 3.9 Total fixed maturities 278.3 — 278.3 Equity securities: Large-cap securities 116.2 116.2 — Mutual and exchange traded funds 56.1 56.1 — Total equity securities 172.3 172.3 — Total pension plan investments $ 450.6 $ 172.3 $ 278.3 ($ millions) Total Quoted prices in active markets for identical assets (Level 1) Significant other observable inputs (Level 2) December 31, 2019 Fixed maturities: U.S. treasury securities and obligations of U.S. government agencies $ 98.6 $ — $ 98.6 Corporate securities 153.1 — 153.1 U.S. government agencies mortgage-backed securities 4.0 — 4.0 Total fixed maturities 255.7 — 255.7 Equity securities: Large-cap securities 91.9 91.9 — Mutual and exchange traded funds 49.7 49.7 — Total equity securities 141.6 141.6 — Total pension plan investments $ 397.3 $ 141.6 $ 255.7

Other Comprehensive Income an_2

Other Comprehensive Income and Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following tables set forth the changes in the Company’s accumulated other comprehensive income (loss) component ("AOCI(L)"), net of tax, for the years ended December 31, 2020, 2019 and 2018: ($ millions) Unrealized Gains and Losses on Available-for-Sale Securities Benefit Plan Items Total Beginning balance at January 1, 2020 $ 40.8 $ (67.7) $ (26.9) Other comprehensive income (loss) before reclassifications 56.4 (27.4) 29.0 Amounts reclassified from AOCI (a) $ 0.3 11.5 11.8 Net current period other comprehensive income (loss) 56.7 (15.9) 40.8 Ending balance at December 31, 2020 $ 97.5 $ (83.6) $ 13.9 Beginning balance at January 1, 2019 $ (20.2) $ (76.2) $ (96.4) Other comprehensive income before reclassifications 63.8 7.5 71.3 Amounts reclassified from AOCI (a) (2.8) 1.0 (1.8) Net current period other comprehensive income 61.0 8.5 69.5 Ending balance at December 31, 2019 $ 40.8 $ (67.7) $ (26.9) Beginning balance at January 1, 2018 $ 66.0 $ (62.2) $ 3.8 Cumulative effect of change in accounting for equity securities and other invested assets and reclassification of stranded tax effects as of January 1, 2018 (47.9) (16.0) (63.9) Other comprehensive loss before reclassifications (36.7) (4.3) (41.0) Amounts reclassified from AOCI (a) (1.6) 6.3 4.7 Net current period other comprehensive (loss) income (38.3) 2.0 (36.3) Ending balance at December 31, 2018 $ (20.2) $ (76.2) $ (96.4) (a) See separate table below for details about these reclassifications
Reclassification out of Accumulated Other Comprehensive Income	The following tables set forth the reclassifications out of accumulated other comprehensive income (loss), by component, to the Company’s consolidated statement of income for the years ended December 31, 2020, 2019 and 2018: ($ millions) Details about Accumulated Other December 31 Affected line item in the Condensed Comprehensive (Loss) Income Components 2020 2019 2018 Consolidated Statements of Income Unrealized (losses) gains on available for sale securities $ (0.3) $ 3.5 $ 2.0 Realized (loss) gain on sale of securities (0.3) 3.5 2.0 Total before tax — (0.7) (0.4) Tax expense (0.3) 2.8 1.6 Net of tax Amortization of benefit plan items: Negative prior service costs 6.3 6.3 6.3 (b) Net loss (13.7) (9.6) (13.2) (b) (7.4) (3.3) (6.9) Total before tax (4.1) 2.3 0.6 Tax benefit (11.5) (1.0) (6.3) Net of tax Total reclassifications for the period $ (11.8) $ 1.8 $ (4.7) (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).

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Share-based Payment Arrangement, Noncash Expense [Abstract]
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity - Performance Based [Table Text Block]	The following table sets forth the Company’s total activity and related information for performance unit award activity for the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 Shares Weighted Shares Weighted Shares Weighted Outstanding, beginning of year 460,189 $ 29.37 356,400 $ 27.47 147,869 $ 27.20 Granted 153,574 24.40 130,680 33.67 224,449 27.65 Vested (103,345) 27.24 (12,500) 27.65 — — Forfeited (5,915) 28.64 (14,391) 29.59 (15,918) 27.37 Outstanding, end of year 504,503 $ 28.06 460,189 $ 29.37 356,400 $ 27.47
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity - Service Based [Table Text Block]	The following table sets forth the Company’s total activity and related information for service-based restricted stock award activity for the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 Shares Weighted Shares Weighted Shares Weighted Outstanding, beginning of year 67,934 $ 27.65 126,946 $ 26.21 71,578 $ 22.44 Granted 30,618 16.33 — — 97,049 27.65 Vested (27,716) 27.65 (58,801) 24.57 (37,644) 22.88 Forfeited — — (211) 21.54 (4,037) 24.82 Outstanding, end of year 70,836 $ 22.76 67,934 $ 27.65 126,946 $ 26.21
Share-based Compensation, Stock Options, Activity [Table Text Block]	The following table sets forth the Company’s stock option activity and related information for the years ended December 31, 2020, 2019 and 2018: (millions, except per share amounts) 2020 2019 2018 Options Weighted- Average Exercise Price Options Weighted- Average Exercise Price Options Weighted- Average Exercise Price Outstanding, beginning of year 0.8 $ 19.18 1.0 $ 18.50 1.7 $ 19.22 Exercised (0.1) 18.55 (0.2) 16.45 (0.7) 20.08 Outstanding, end of year 0.7 $ 19.28 0.8 $ 19.18 1.0 $ 18.50
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]	The following table sets forth information pertaining to the total options outstanding and exercisable at December 31, 2020: (Options in millions) Options Outstanding Options Exercisable Number Weighted- Average Remaining Contractual Life Weighted- Average Exercise Price Number Weighted- Average Exercise Price Range of Exercise Prices: $10.01 – $20.00 0.3 1.5 $ 16.33 0.3 $ 16.33 $20.01 – $30.00 0.4 4.0 21.97 0.4 21.97 Total 0.7 2.8 $ 19.28 0.7 $ 19.28

Net (Loss) Earnings Per Commo_2

Net (Loss) Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Compilation of Basic and Diluted Net (Loss) Per Common Share	The following table sets forth the compilation of basic and diluted net earnings per common share for the years ended December 31, 2020, 2019 and 2018: (millions, except per share amounts) 2020 2019 2018 Numerator: Net earnings for basic net earnings per common share $ 13.1 $ 85.8 $ 12.2 Effect of dilutive share-based awards — (1.1) — Adjusted net earnings for dilutive net earnings per common share $ 13.1 $ 84.7 $ 12.2 Denominator: Weighted average shares for basic net earnings per common share 43.7 43.4 42.8 Effect of dilutive share-based awards 0.6 0.6 0.6 Adjusted weighted average shares for diluted net earnings per common share 44.3 44.0 43.4 Basic net earnings per common share $ 0.30 $ 1.98 $ 0.29 Diluted net earnings per common share $ 0.30 $ 1.93 $ 0.28
Options to Purchase Shares of Common Stock	year ended December 31, 2018: (millions) 2018 Total number of antidilutive options and awards 0.1

Reportable Segments (Tables)

Reportable Segments (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Financial Information Regarding Company's Reportable Segments	The following table sets forth financial information regarding the Company’s reportable segments for the years ended December 31, 2020, 2019 and 2018: ($ millions) 2020 2019 2018 Revenues from external sources: Insurance operations Personal insurance $ 819.0 $ 755.9 $ 673.4 Commercial insurance 561.8 488.6 464.4 Specialty run-off 0.1 5.7 99.8 Total insurance operations 1,380.9 1,250.2 1,237.6 Investment operations segment Net investment income 72.1 80.4 84.9 Net investment gain (loss) 27.3 74.2 (49.7) Total investment operations 99.4 154.6 35.2 All other 2.1 2.4 2.6 Total revenues from external sources 1,482.4 1,407.2 1,275.4 Intersegment revenues 6.2 6.5 6.5 Total revenues 1,488.6 1,413.7 1,281.9 Reconciling items: Eliminate intersegment revenues (6.2) (6.5) (6.5) Total consolidated revenue $ 1,482.4 $ 1,407.2 $ 1,275.4 Segment (loss) income before federal income taxes: Insurance operations SAP underwriting (loss) gain Personal insurance $ (68.8) $ (42.2) $ 2.8 Commercial insurance (7.4) (0.2) (8.7) Specialty run-off (17.6) (9.7) 0.4 Total insurance operations (93.8) (52.1) (5.5) Investment operations segment: Net investment income 72.1 80.4 84.9 Net investment gain (loss) 27.3 74.2 (49.7) Total investment operations 99.4 154.6 35.2 All other (0.1) 0.3 0.4 Reconciling items: GAAP adjustments 19.8 14.7 (3.7) Interest expense on corporate debt (4.7) (4.9) (5.7) Corporate expenses (6.2) (7.1) (8.6) Total reconciling items $ 8.9 $ 2.7 $ (18.0) Total consolidated income before federal income taxes $ 14.4 $ 105.5 $ 12.1
Financial Information Regarding Company's Reportable Segments	The following table sets forth financial information regarding the Company’s reportable segments at December 31, 2020 and 2019: ($ millions) 2020 2019 Segment assets: Investment operations segment $ 2,870.8 $ 2,747.8 Total segment assets 2,870.8 2,747.8 Reconciling items: Corporate assets 231.7 231.8 Total consolidated assets $ 3,102.5 $ 2,979.6

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Net Deferred Acquisition Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of year	$ 111.1	$ 101.9	$ 110.3
Acquisition costs deferred	247.7	225.7	211.6
Acquisition costs amortized to expense	(236.6)	(216.5)	(220)
Balance, end of year	$ 122.2	$ 111.1	$ 101.9

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salvage and Subrogation Recoveries, Value	$ 28.7	$ 28.2

Accounting Changes and Error _3

Accounting Changes and Error Corrections (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement
Premiums Receivable, Gross	$ 14	$ 13.6
Fixed maturities, available-for-sale, at fair value	2,237.2	2,128.4
Due from affiliates	0	4.1
Deferred Income Tax Assets, Net	27.3	39.7
Total consolidated assets	3,102.5	2,979.6
Postretirement and pension benefits	66.2	59.5
Liabilities	2,092.5	2,012.1
Accumulated other comprehensive income	13.9	(26.9)	$ (96.4)	$ 3.8
Retained earnings	774.4	779.3
Stockholders’ equity per accompanying consolidated financial statements	1,010	967.5	816.7
Total liabilities and stockholders' equity	3,102.5	2,979.6
Premiums Earned, Net	1,380.9	1,250.2	1,237.6
Intersegment revenues	1,482.4	1,407.2	1,275.4
Acquisition and operating expenses (affiliated net assumed $69.1, $108.7 and $160.7, respectively)	481.4	440.7	450.2
Income (loss) before federal income tax	14.4	105.5	12.1
Total expenses	1,468	1,301.7	1,263.3
Deferred Income Tax Expense (Benefit)	1.6	20.1	1
Income Tax Expense (Benefit)	1.3	19.7	(0.1)
Net (loss) income	$ 13.1	$ 85.8	$ 12.2
Basic (usd per share)	$ 0.30	$ 1.98	$ 0.29
Diluted (usd per share)	$ 0.30	$ 1.93	$ 0.28
Unrealized holding gains (losses) arising during year	$ 71.5	$ 80.7	$ (46.4)
Income tax expense	(15.1)	(16.2)	10.1
Change in unrealized holding gains (losses) on investments, net of tax	56.7	61	(38.3)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(27.4)	7.5	(4.3)
Income tax expense	4.1	(2.3)	(0.6)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(15.9)	8.5	2
Net current period other comprehensive income	40.8	69.5	(36.3)
Comprehensive Income (loss)	53.9	155.3	(24.1)
Increase (Decrease) in Premiums Receivable	(0.4)	(0.9)	(2.7)
Other liabilities and due from affiliates	25.8	(42.5)	51.1
Federal income taxes	6.2	20.6	(1)
Net Cash Provided by (Used in) Operating Activities	$ 49	(43.9)	(13.4)
Previously Reported [Member]
Error Corrections and Prior Period Adjustments Restatement
Premiums Receivable, Gross		0
Fixed maturities, available-for-sale, at fair value		2,127.9
Due from affiliates		21.5
Deferred Income Tax Assets, Net		42.2
Total consolidated assets		2,985.4
Postretirement and pension benefits		72.9
Liabilities		2,025.5
Accumulated other comprehensive income		(37.9)
Retained earnings		782.7
Stockholders’ equity per accompanying consolidated financial statements		959.9
Total liabilities and stockholders' equity		2,985.4
Premiums Earned, Net		1,253	1,238
Intersegment revenues		1,410	1,275.8
Acquisition and operating expenses (affiliated net assumed $69.1, $108.7 and $160.7, respectively)		442	449.8
Income (loss) before federal income tax		107	12.9
Total expenses		1,303	1,262.9
Deferred Income Tax Expense (Benefit)		20	1.2
Income Tax Expense (Benefit)		19.6	0.1
Net (loss) income		$ 87.4	$ 12.8
Basic (usd per share)		$ 2.01	$ 0.30
Diluted (usd per share)		$ 1.96	$ 0.29
Unrealized holding gains (losses) arising during year		$ 80.2
Income tax expense		(16.1)
Change in unrealized holding gains (losses) on investments, net of tax		60.6
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		(5.9)
Income tax expense		0.5
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		(2.1)
Net current period other comprehensive income		58.5
Comprehensive Income (loss)		145.9
Increase (Decrease) in Premiums Receivable		0	$ 0
Other liabilities and due from affiliates		(44.9)	47.6
Federal income taxes		20.5	(0.8)
Net Cash Provided by (Used in) Operating Activities		(43.9)	(13.4)
Restatement Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement
Premiums Receivable, Gross		13.6
Fixed maturities, available-for-sale, at fair value		0.5
Due from affiliates		(17.4)
Deferred Income Tax Assets, Net		(2.5)
Total consolidated assets		(5.8)
Postretirement and pension benefits		(13.4)
Liabilities		(13.4)
Accumulated other comprehensive income		11
Retained earnings		(3.4)		$ 1.2
Stockholders’ equity per accompanying consolidated financial statements		7.6
Total liabilities and stockholders' equity		(5.8)
Premiums Earned, Net		(2.8)	(0.4)
Intersegment revenues		(2.8)	(0.4)
Acquisition and operating expenses (affiliated net assumed $69.1, $108.7 and $160.7, respectively)		(1.3)	0.4
Income (loss) before federal income tax		(1.5)	(0.8)
Total expenses		(1.3)	0.4
Deferred Income Tax Expense (Benefit)		0.1	(0.2)
Income Tax Expense (Benefit)		0.1	(0.2)
Net (loss) income		$ (1.6)	$ (0.6)
Basic (usd per share)		$ (0.03)	$ (0.01)
Diluted (usd per share)		$ (0.03)	$ (0.01)
Unrealized holding gains (losses) arising during year		$ 0.5
Income tax expense		(0.1)
Change in unrealized holding gains (losses) on investments, net of tax		0.4
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		13.4
Income tax expense		(2.8)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		10.6
Net current period other comprehensive income		11
Comprehensive Income (loss)		9.4
Increase (Decrease) in Premiums Receivable		(0.9)	$ (2.7)
Other liabilities and due from affiliates		2.4	3.5
Federal income taxes		0.1	(0.2)
Net Cash Provided by (Used in) Operating Activities		$ 0	$ 0

Investments - Cost or Amortized

Investments - Cost or Amortized Cost and Fair Value of Available-for-Sale Securities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, amortized cost	$ 2,117	$ 2,080
Gross unrealized holding gains	121.9	56.7
Gross unrealized holding losses	(1.7)	(8.3)
Fixed maturities, available-for-sale, at fair value	2,237.2	2,128.4
U.S. treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, amortized cost	506.5	569.2
Gross unrealized holding gains	45.2	12.6
Gross unrealized holding losses	0	(3.3)
Fixed maturities, available-for-sale, at fair value	551.7	578.5
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, amortized cost	511.3	404.3
Gross unrealized holding gains	30.4	21.1
Gross unrealized holding losses	(0.2)	0
Fixed maturities, available-for-sale, at fair value	541.5	425.4
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, amortized cost	459.9	460.5
Gross unrealized holding gains	23.4	11.7
Gross unrealized holding losses	0	(0.4)
Fixed maturities, available-for-sale, at fair value	483.3	471.8
U.S. government agencies mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, amortized cost	639.3	646
Gross unrealized holding gains	22.9	11.3
Gross unrealized holding losses	(1.5)	(4.6)
Fixed maturities, available-for-sale, at fair value	$ 660.7	$ 652.7

Investments - Gross Unrealized

Investments - Gross Unrealized Losses and Fair Value on its Investments (Details) $ in Millions	Dec. 31, 2020USD ($)position	Dec. 31, 2019USD ($)position
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 166.7	$ 262.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (1.6)	$ (4)
Less than 12 months, Number of positions (positions) | position	46	32
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 7	$ 336.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (0.1)	$ (4.3)
12 months or more, Number of positions (positions) | position	3	50
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 173.7	$ 598.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1.7)	$ (8.3)
Total, Number of positions (positions) | position	49	82
U.S. treasury securities and obligations of U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 9.6	$ 136
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ (2.5)
Less than 12 months, Number of positions (positions) | position	4	17
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 0	$ 157.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ (0.8)
12 months or more, Number of positions (positions) | position	0	11
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 9.6	$ 293.6
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 0	$ (3.3)
Total, Number of positions (positions) | position	4	28
Obligations of states and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 19.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (0.2)
Less than 12 months, Number of positions (positions) | position	5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0
12 months or more, Number of positions (positions) | position	0
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 19.5
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (0.2)
Total, Number of positions (positions) | position	5
Corporate securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 1.5	$ 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ 0	$ 0
Less than 12 months, Number of positions (positions) | position	2	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 0	$ 40.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0	$ (0.4)
12 months or more, Number of positions (positions) | position	0	7
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 1.5	$ 40.8
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 0	$ (0.4)
Total, Number of positions (positions) | position	2	7
U.S. government agencies mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 136.1	$ 126.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	$ (1.4)	$ (1.5)
Less than 12 months, Number of positions (positions) | position	35	15
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	$ 7	$ 137.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ (0.1)	$ (3.1)
12 months or more, Number of positions (positions) | position	3	32
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 143.1	$ 264.5
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ (1.5)	$ (4.6)
Total, Number of positions (positions) | position	38	47

Investments - Amortized Cost an

Investments - Amortized Cost and Fair Value of Available-for-Sale Fixed Maturities by Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amortized cost
Due in 1 year or less	$ 140.5
Due after 1 year through 5 years	510.3
Due after 5 years through 10 years	161.6
Due after 10 years	665.3
U.S. government agencies mortgage-backed securities	639.3
Total	2,117	$ 2,080
Fair value
Due in 1 year or less	141.6
Due after 1 year through 5 years	540.4
Due after 5 years through 10 years	172.6
Due after 10 years	721.9
U.S. government agencies mortgage-backed securities	660.7
Total	$ 2,237.2	$ 2,128.4

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 58.5	$ 63.9	$ (49.7)
Financial Instruments, Owned and Pledged as Collateral, at Fair Value	32.2
Proceeds on sales of available-for-sale securities	351.4	355.5	197
Carrying value of securities pledged as collateral for the FHLB Loan	106.5
Fixed maturities fair value of deposit with insurance regulators	9.7	9.3
Other Invested Assets [Member]
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 0.8	$ 9.9	$ (7.7)

Investments - Components of Net

Investments - Components of Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 72.9	$ 81	$ 85.9
Investment expenses	0.8	0.6	1
Net investment income	72.1	80.4	84.9
Fixed maturities:
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	59.6	62.3	65.3
Equity securities:
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	9.3	13.2	13.4
Cash and cash equivalents, and other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 4	$ 5.5	$ 7.2

Investments - Realized and Unre

Investments - Realized and Unrealized Holding Gains (Losses) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Realized Gain (Loss) [Abstract]
Debt Securities, Available-for-sale, Realized Gain	$ 5,200,000	$ 3,500,000	$ 2,000,000
Debt Securities, Available-for-sale, Realized Loss	(5,500,000)	0	0
Debt Securities, Available-for-sale, Realized Gain (Loss), Total	(300,000)	3,500,000	2,000,000
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Equity Securities, FV-NI, Gain (Loss)	26,700,000	62,100,000	(44,000,000)
Gain (Loss) on Disposition of Property Plant Equipment	200,000	(1,300,000)
Gain (Loss) on Investments	27,300,000	74,200,000	(49,700,000)
Change in unrealized holding gains (losses), net of tax:
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(15,100,000)	(16,200,000)	10,100,000
Total change in net unrealized holding gains (losses) on investments	56,700,000	61,000,000	(38,300,000)
Fixed maturities:
Change in unrealized holding gains (losses), net of tax:
Change in net unrealized holding gains, before tax	71,800,000	77,200,000	(48,400,000)
Other Invested Assets [Member]
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Equity Securities, FV-NI, Gain (Loss)	$ 700,000	$ 9,900,000	$ (7,700,000)

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Narrative (Details) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2009USD ($)internationalFund	Dec. 31, 2020USD ($)positioninternationalFund	Dec. 31, 2019USD ($)
Fair Value Measurements Disclosure [Line Items]
Other investments and securities, at cost		$ 12.1	$ 6.5
Number of credit agreements (agreements)	2	2
Notes receivable from affiliate	$ 70	$ 70	70
Other invested assets		71.1	69.7
International funds
Fair Value Measurements Disclosure [Line Items]
Other invested assets		$ 55.8	$ 56.4
International funds | Fair Value, Inputs, Level 3
Fair Value Measurements Disclosure [Line Items]
Number of available for sale securities (securities) | internationalFund		1

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Available-for-Sale Investments within Fair Value Hierarchy (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Investments, Fair Value Disclosure [Abstract]
Investments, Fair Value Disclosure	$ 2,642.2	$ 2,536.9
Equity Securities, FV-NI	389.7	395.2
Fixed maturities, available-for-sale, at fair value	2,237.2	2,128.4
U.S. treasury securities and obligations of U.S. government agencies
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	551.7	578.5
Obligations of states and political subdivisions
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	541.5	425.4
Corporate securities
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	483.3	471.8
U.S. government agencies mortgage-backed securities
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	660.7	652.7
Large-cap securities
Investments, Fair Value Disclosure [Abstract]
Equity Securities, FV-NI	134.2	104.4
Mutual and exchange traded funds [Domain] [Member]
Investments, Fair Value Disclosure [Abstract]
Equity Securities, FV-NI	255.5	290.8
Other Invested Assets [Member]
Investments, Fair Value Disclosure [Abstract]
Other invested assets	15.3	13.3
Quoted prices in active markets for identical assets (Level 1)
Investments, Fair Value Disclosure [Abstract]
Investments, Fair Value Disclosure	405	408.5
Equity Securities, FV-NI	389.7	395.2
Fixed maturities, available-for-sale, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | U.S. treasury securities and obligations of U.S. government agencies
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | Obligations of states and political subdivisions
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | Corporate securities
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | U.S. government agencies mortgage-backed securities
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	0	0
Quoted prices in active markets for identical assets (Level 1) | Large-cap securities
Investments, Fair Value Disclosure [Abstract]
Equity Securities, FV-NI	134.2	104.4
Quoted prices in active markets for identical assets (Level 1) | Mutual and exchange traded funds [Domain] [Member]
Investments, Fair Value Disclosure [Abstract]
Equity Securities, FV-NI	255.5	290.8
Quoted prices in active markets for identical assets (Level 1) | Other Invested Assets [Member]
Investments, Fair Value Disclosure [Abstract]
Other invested assets	15.3	13.3
Significant other observable inputs (Level 2)
Investments, Fair Value Disclosure [Abstract]
Investments, Fair Value Disclosure	2,237.2	2,128.4
Equity Securities, FV-NI	0	0
Fixed maturities, available-for-sale, at fair value	2,237.2	2,128.4
Other invested assets	0	0
Significant other observable inputs (Level 2) | U.S. treasury securities and obligations of U.S. government agencies
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	551.7	578.5
Significant other observable inputs (Level 2) | Obligations of states and political subdivisions
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	541.5	425.4
Significant other observable inputs (Level 2) | Corporate securities
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	483.3	471.8
Significant other observable inputs (Level 2) | U.S. government agencies mortgage-backed securities
Investments, Fair Value Disclosure [Abstract]
Fixed maturities, available-for-sale, at fair value	660.7	652.7
Significant other observable inputs (Level 2) | Large-cap securities
Investments, Fair Value Disclosure [Abstract]
Equity Securities, FV-NI	0	0
Significant other observable inputs (Level 2) | Mutual and exchange traded funds [Domain] [Member]
Investments, Fair Value Disclosure [Abstract]
Equity Securities, FV-NI	$ 0	$ 0

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Company Estimates Receivable from Affiliate using Market Quotations for U.S. Treasury Securities (Details) - Note Receivable from Affiliate, 2019 [Member] - Affiliated entity - Significant other observable inputs (Level 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate (percent)	4.05%	4.05%
Carrying value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	$ 70	$ 70
Fair value
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes receivable from affiliate	$ 80.4	$ 74.6

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Included in Notes Payable are Senior Notes and Subordinated Debentures (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Interest rate (percent)	5.28%	5.28%
Notes Payable, Total	$ 122,100,000	$ 122,000,000
Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest rate (percent)	3.96%	3.96%
Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Interest rate (percent)	0.00%	1.73%
Debt instrument, issued			$ 21,500,000
Federal Home Loan Bank of Cincinnati [Member]
Debt Instrument [Line Items]
Debt instrument, issued			85,000,000
Affiliate Subordinated Debentures due 2033
Debt Instrument [Line Items]
Interest rate (percent)	4.43%	6.11%
Debt instrument, issued			$ 15,500,000
Federal Home Loan Bank Advances due 2030
Debt Instrument [Line Items]
Interest rate (percent)	1.37%	0.00%
Carrying value
Debt Instrument [Line Items]
Total notes payable	$ 122,100,000	$ 122,000,000
Carrying value | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	85,300,000	85,300,000
Carrying value | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Total notes payable	0	21,500,000
Carrying value | Affiliate Subordinated Debentures due 2033
Debt Instrument [Line Items]
Total notes payable	15,300,000	15,200,000
Carrying value | Federal Home Loan Bank Advances due 2030
Debt Instrument [Line Items]
Total notes payable	21,500,000	0
Fair value
Debt Instrument [Line Items]
Total notes payable	144,000,000	134,500,000
Fair value | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Total notes payable	107,100,000	97,800,000
Fair value | Federal Home Loan Bank Advances
Debt Instrument [Line Items]
Total notes payable	0	21,500,000
Fair value | Affiliate Subordinated Debentures due 2033
Debt Instrument [Line Items]
Total notes payable	15,300,000	15,200,000
Fair value | Federal Home Loan Bank Advances due 2030
Debt Instrument [Line Items]
Total notes payable	$ 21,600,000	$ 0

Losses and Loss Expenses Paya_3

Losses and Loss Expenses Payable - Activity in Liability for Losses and Loss Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Losses and loss expenses payable, at beginning of year	$ 1,066.5	$ 1,146.8	$ 1,255.6
Less: reinsurance recoverable on losses and loss expenses payable	13.6	5.5	3.1
Net balance at beginning of year	1,052.9	1,141.3	1,252.5
Incurred related to:
Current year	1,008.2	913.5	876.6
Prior years	(35.6)	(68.7)	(80.2)
Total incurred	972.6	844.8	796.4
Paid related to:
Current year	599.5	530.4	456.5
Prior years	399.9	402.8	451.1
Total paid	999.4	933.2	907.6
Net balance at end of year	1,026.1	1,052.9	1,141.3
Plus: reinsurance recoverable on losses and loss expenses payable	24.3	13.6	5.5
Losses and loss expenses payable, at end of year (affiliates $711.4, $630.9, and $532.4, respectively)	$ 1,050.4	$ 1,066.5	$ 1,146.8

Losses and Loss Expenses Paya_4

Losses and Loss Expenses Payable - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	$ 35.6	$ 68.7	$ 80.2
Personal and Commercial Insurance Segments [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years		(71.3)	(79.7)
Small Commercial Package [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	23	(15.2)	(9.6)
Unallocated loss adjustment expense [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years			(7.1)
Personal Insurance Segments [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	(21.7)
Personal Auto [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	(20.3)	(10.7)	(24.4)
Homeowners [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years			(7.3)
Commercial insurance segment
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	(78.4)
Commercial Auto [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years			(8.4)
Workers' compensation [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	24.9	(20.9)	(13.3)
Specialty Insurance Segment [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	(5.2)		3.1
Programs [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years			1.2
Excess & Surplus Casualty [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years			2.7
Middle Market Commercial [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	16.7	(11.8)	$ (8)
Catastrophe [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	(13.4)	5.7
Specialty Insurance Segment [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years		$ 10.7
Excess & Surplus Property [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Prior years	$ (12.4)

Short-Duration Insurance Cont_3

Short-Duration Insurance Contracts - Claims Development (Details) $ in Millions	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Dec. 31, 2011USD ($)
Claims Development [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 969.3	$ 994.9	$ 1,081.5
Short-tail | Personal Insurance Segments [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	2,153.1
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	1,906.7
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	3.8
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	250.2	220.6	216
Short-tail | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	1,197.9
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	883.5
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	34.9
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	349.3	330.8	336.4
Short-tail | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	277.1
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	231.6
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	13.7
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	59.2	84.9	128.5
Short-tail | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal Insurance Segments [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	361.4	360.8	361.4	$ 370	$ 368.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims	151,620
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 356.5	352.1	342.6	316.2	231.9
Short-tail | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	217.2	220.6	225.2	227.6	237
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6
Short-duration Insurance Contract, Cumulative Number of Reported Claims	34,872
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 204.2	196.1	176.7	147.3	99.2
Short-tail | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	105.3	105.7	102.7	99.5	99.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 5.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,413
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 96	87.4	69.9	50.2	25.2
Short-tail | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Personal Insurance Segments [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	356	351.9	355	372.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims	151,727
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 347.9	335.7	315.8	236.8
Short-tail | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	209.1	215.9	225.5	236.8
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 9
Short-duration Insurance Contract, Cumulative Number of Reported Claims	32,101
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 188	175.5	153.9	104.9
Short-tail | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	150.6	138.3	129.7	134.2
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 16.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,340
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 121.3	101.2	77.5	39
Short-tail | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Personal Insurance Segments [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	418.2	411.4	418.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims	154,705
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 400.2	375.1	276.4
Short-tail | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	207.3	216.4	228.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 17.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims	31,055
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 161	144.6	98.7
Short-tail | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	19.8	20.5	18.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,410
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 13.3	10.7	6.3
Short-tail | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Personal Insurance Segments [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	508.2	497.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 21
Short-duration Insurance Contract, Cumulative Number of Reported Claims	163,378
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 457.7	343.7
Short-tail | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	236.1	248.2
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 44.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims	32,362
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 159.7	108.4
Short-tail | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	1.1	1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims	61
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 0.9	0.5
Short-tail | Short-Duration Insurance Contract, Accident Year 2020 [Member] | Personal Insurance Segments [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	509.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 87.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims	123,234
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 344.4
Short-tail | Short-Duration Insurance Contract, Accident Year 2020 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	328.2
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 75
Short-duration Insurance Contract, Cumulative Number of Reported Claims	29,540
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 170.6
Short-tail | Short-Duration Insurance Contract, Accident Year 2020 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	0.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims	13
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 0.1
Long-tail | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	466.7
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	334.4
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	30.6
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	162.9	174.2	182.1
Long-tail | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	313.5
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	210.1
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	3.8
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	107.3	139.1	177.6
Long-tail | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	41.7	42.3	42.9	43.9	44.9	$ 44.8	$ 44.8	$ 45.5	$ 47.4	$ 44.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims	12,228
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 39	38.9	38.6	38.1	37.7	36.9	35	31.9	25.4	12.4
Long-tail | Short-duration Insurance Contracts, Accident Year 2011 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	9.5	9.5	9.7	10.5	10.9	10.1	10.2	10.7	10.7	11.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.8
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,250
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 8.7	8.6	8.4	8.1	7.9	7.1	6.6	5.2	3	$ 0.9
Long-tail | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	39.8	40.5	41.7	42.9	43.9	44.1	43.7	45.8	49.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims	12,762
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 36.8	36.6	36.4	35.8	34.7	32.7	29.8	23.5	12.6
Long-tail | Short-duration Insurance Contracts, Accident Year 2012 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	16.2	16.1	16	16.5	17.4	17.6	15.4	16.7	16.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,199
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 14.9	14.7	14.1	14	12.5	10.3	7.3	4	$ 0.9
Long-tail | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	39.2	40.5	41.5	42.9	43.4	44.1	45.4	48.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,319
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 34.6	34.4	34.2	33.7	32.3	29	23.3	12.3
Long-tail | Short-duration Insurance Contracts, Accident Year 2013 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	15.4	15	15.3	15.9	16.5	17.9	18.9	20.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1
Short-duration Insurance Contract, Cumulative Number of Reported Claims	1,562
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 13.6	13.3	12	10.5	9	6.7	3.7	$ 1.1
Long-tail | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	41	43.4	45.3	45.7	47.1	50	51.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4.8
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,570
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 35	34.6	34.1	32.8	30	24.4	12.4
Long-tail | Short-duration Insurance Contracts, Accident Year 2014 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	31	30	29.5	28.3	27.1	25.2	23.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,030
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 25.7	24.2	21.5	16.7	12.5	7.2	$ 1.2
Long-tail | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	48.7	51.3	53.7	56.5	59.4	59.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims	11,161
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 40.2	39.5	38.3	35.7	28.2	13.9
Long-tail | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	48.6	45	45.7	44.8	44.9	38.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims	3,167
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 36.9	34.7	29.1	20.6	10.9	$ 2.7
Long-tail | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	49.5	53.9	57.2	60.6	62.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 9.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims	12,453
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 37	35.6	32.3	26.8	12.6
Long-tail | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	70.2	64.3	64.8	62.9	60.8
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 10.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,505
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 53.5	39.7	31.5	15.7	$ 6
Long-tail | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	49.1	53.7	56.4	59
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 8.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims	12,574
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 36.8	32.8	27	13.2
Long-tail | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	66.3	70.5	73.1	71.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 20.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims	9,245
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 35.7	25.2	16.4	$ 5.5
Long-tail | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	49.3	53.6	56.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 11.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims	12,541
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 32.5	26.4	13.2
Long-tail | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	51.5	53.3	53
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 21.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims	6,203
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 20.6	12.8	$ 2.7
Long-tail | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	52.9	54.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 13.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims	12,045
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 29.2	14.7
Long-tail | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	4.6	4.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 4.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims	2,352
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 0.5	$ 0.1
Long-tail | Short-Duration Insurance Contract, Accident Year 2020 [Member] | Commercial insurance
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	55.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 26
Short-duration Insurance Contract, Cumulative Number of Reported Claims	10,851
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 13.3
Long-tail | Short-Duration Insurance Contract, Accident Year 2020 [Member] | Specialty Insurance Segment [Member]
Claims Development [Line Items]
Short-duration Insurance Contracts, Incurred Claims and Allocated Claim Adjustment Expense, Net	0.2
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims	19
Short-duration Insurance Contracts, Cumulative Paid Claims and Allocated Claim Adjustment Expense, Net	$ 0

Short-Duration Insurance Cont_4

Short-Duration Insurance Contracts - Reconciliation of Claims Development to Liability (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 969.3	$ 994.9	$ 1,081.5
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claims Adjustment Expense, Accumulated Unallocated Claim Adjustment Expense	56.8	58	59.8
Reinsurance recoverable on losses and loss expenses payable	24.3	13.6	5.5	$ 3.1
Liability for Claims and Claims Adjustment Expense, Property Casualty Liability	1,050.4	1,066.5	1,146.8	$ 1,255.6
Personal Insurance Segments [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item	14.9	14.4	13.5
Commercial insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item	25.5	30.9	27.4
Short-tail | Personal Insurance Segments [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	250.2	220.6	216
Short-tail | Commercial insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	349.3	330.8	336.4
Short-tail | Specialty Insurance Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	59.2	84.9	128.5
Long-tail | Commercial insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	162.9	174.2	182.1
Long-tail | Specialty Insurance Segment [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Short-duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	$ 107.3	$ 139.1	$ 177.6

Short-Duration Insurance Cont_5

Short-Duration Insurance Contracts - Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance (Details)	Dec. 31, 2020
Short-tail | Personal Insurance Segments [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	66.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	22.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	6.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	3.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	1.20%
Short-tail | Commercial insurance
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	48.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	22.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	10.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	7.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	3.70%
Short-tail | Specialty Insurance Segment [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	32.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	27.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	15.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	15.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	8.20%
Long-tail | Commercial insurance
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	28.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	28.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	13.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	7.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	3.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	1.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	1.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	0.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	0.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.30%
Long-tail | Specialty Insurance Segment [Member]
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	5.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	16.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	19.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	15.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	12.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	8.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	3.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	3.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	2.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.40%

Reinsurance - Narrative (Detail

Reinsurance - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reinsurance [Line Items]
Document Period End Date	Dec. 31, 2020
Unearned premium	$ 723.4	$ 649.2

Reinsurance - External Reinsura

Reinsurance - External Reinsurance on Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Unearned premiums:
Unearned Premiums From Affiliates	$ 452.4	$ 415.8
Prior to reinsurance transaction with State Auto Mutual
Losses and loss expenses payable:
Direct	581.3	540.1
Assumed	30.3	25.6
Ceded	24.3	13.6
Net losses and loss expenses payable	587.3	552.1
Unearned premiums:
Direct	507.7	495.8
Assumed	39.5	36.7
Ceded	(8.3)	(7.5)
Unearned Premiums From Affiliates	$ 538.9	$ 525

Reinsurance - External Reinsu_2

Reinsurance - External Reinsurance on Income Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earned premiums:
Direct	$ 1,067.6	$ 976.8	$ 881.3
Premiums Earned, Net	1,380.9	1,250.2	1,237.6
Losses and loss expenses incurred:
Net losses and loss expenses incurred	184.2	169.3	180.5
Prior to reinsurance transaction with State Auto Mutual
Written premiums:
Direct	1,080.5	1,036.9	915.1
Assumed	87.6	82.5	75.1
Ceded	(39.8)	(31.9)	(23.1)
Net written premiums	1,128.3	1,087.5	967.1
Earned premiums:
Direct	1,067.6	976.8	881.3
Assumed	84.8	81.3	61
Ceded	(39)	(31)	(23)
Premiums Earned, Net	1,113.4	1,027.1	919.3
Losses and loss expenses incurred:
Direct	789	631.4	572.5
Assumed	56.8	59.6	48.4
Ceded	(57.6)	(15.6)	(4.9)
Net losses and loss expenses incurred	$ 788.2	$ 675.4	$ 616

Current Expected Credit Losse_3

Current Expected Credit Losses Reinsurance Recoverable, Credit Quality Indicator (Details) $ in Millions	Dec. 31, 2020USD ($)
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 24.3
AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	1.1
AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	9.5
AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 13.7

Current Expected Credit Losse_4

Current Expected Credit Losses Premiums Receivables, Allowance for Credit Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Premium Receivable, Allowance for Credit Loss [Roll Forward]
Premium Receivable, Allowance for Credit Loss	$ 7.1	$ 4.3
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	8.2
Premium Receivable, Allowance for Credit Loss, Writeoff	$ (5.4)

Current Expected Credit Losse_5

Current Expected Credit Losses Current Expected Credit Losses - Additional Information (Details) $ in Millions	Dec. 31, 2020USD ($)
Credit Loss [Abstract]
Reinsurance Recoverable, Allowance for Credit Loss	$ 0.9

Transactions with Affiliates -

Transactions with Affiliates - Narrative (Details) $ in Millions	1 Months Ended			12 Months Ended
	May 31, 2019	May 31, 2009USD ($)internationalFund	May 31, 2003USD ($)	Dec. 31, 2020USD ($)position	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Impact Of Pooling Arrangement Amendment On Balance Sheet [Line Items]
Document Period End Date				Dec. 31, 2020
Number of days intercompany balances settled after quarter end				60 days
Company's premium share balances due				$ 389.4	$ 371
Mandatorily redeemable preferred capital securities issued to third party			$ 15
Common securities issued to state auto financial			0.5	$ 3.9	$ 5.9	$ 15.4
Proceeds from the issuance of Trust Securities			$ 15.5
Description of variable rate basis			three-month LIBOR rate plus 4.20%
Subordinated Borrowing, Due Date			Dec. 31, 2033
Interest rate (percent)				5.28%	5.28%
Number of credit agreements (agreements)		2		2
Credit agreement loan amount		$ 70		$ 70	$ 70
Interest income earned				2.8	3.6	4.9	$ 4.9	$ 4.9
Revenue from Contract with Customer, Excluding Assessed Tax				2	2.1	$ 2
Premium Receivable, Allowance for Credit Loss				$ 7.1	$ 4.3
Affiliate Subordinated Debentures due 2033
Impact Of Pooling Arrangement Amendment On Balance Sheet [Line Items]
Interest rate (percent)				4.43%	6.11%
3 month LIBOR | Affiliate Subordinated Debentures due 2033
Impact Of Pooling Arrangement Amendment On Balance Sheet [Line Items]
Interest rate of Trust Securities payable quarterly (percent)			4.20%
Note Receivable from Affiliate, 2009 [Member]
Impact Of Pooling Arrangement Amendment On Balance Sheet [Line Items]
Fixed annual interest rate (percent)		7.00%
Note Receivable from Affiliate, 2019 [Member]
Impact Of Pooling Arrangement Amendment On Balance Sheet [Line Items]
Fixed annual interest rate (percent)	4.05%

Transactions with Affiliates _2

Transactions with Affiliates - Reinsurance Transactions on Balance Sheets for Pooling Arrangement (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Policy Acquisition Costs:
Deferred Policy Acquisitions Costs from Affiliates	$ 30.1	$ 20.2
Losses and loss expenses payable:
Losses And Loss Expenses Payable From Affiliates	438.8	500.8
Unearned premium	723.4	649.2
Unearned Premiums From Affiliates	452.4	415.8
Other Liabilities	22.4	16.1
Affiliated entity
Deferred Policy Acquisition Costs:
Deferred Policy Acquisition Costs Ceded	(92.1)	(90.9)
Deferred Policy Acquisition Costs Assumed	122.2	111.1
Deferred Policy Acquisitions Costs from Affiliates	30.1	20.2
Losses and loss expenses payable:
Ceded	(587.3)	(552.1)
Assumed	1,026.1	1,052.9
Losses And Loss Expenses Payable From Affiliates	438.8	500.8
Ceded	(262.7)	(225.9)
Assumed	715.1	641.7
Unearned Premiums From Affiliates	452.4	415.8
Other Liabilities Ceded	(77.1)	(77.8)
Other Liabilities Assumed	99.5	94
Other Liabilities	$ 22.4	$ 16.1

Transactions with Affiliates _3

Transactions with Affiliates - Reinsurance Transactions on Income Statements for Pooling Arrangement (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earned premiums:
Premiums Earned, Net Assumed (Ceded)	$ 1,380.9	$ 1,250.2	$ 1,237.6
Losses and loss expenses incurred:
Losses and loss expenses incurred, Net	184.2	169.3	180.5
Acquisition and Operating Expenses [Abstract]
Acquisition and Operating Expenses, Net	102.6	69.1	108.7
Affiliated entity
Earned premiums:
Ceded	(1,113.4)	(1,027.7)	(919)
Assumed	1,380.9	1,250.2	1,237.6
Premiums Earned, Net Assumed (Ceded)	267.5	222.5	318.6
Written premiums:
Ceded	(1,128.3)	(1,088.1)	(966.8)
Assumed	1,456.3	1,315.3	1,209.9
Premiums Written, Net	328	227.2	243.1
Losses and loss expenses incurred:
Ceded	(789.7)	(677.2)	(617.6)
Assumed	973.9	846.5	798.1
Losses and loss expenses incurred, Net	184.2	169.3	180.5
Acquisition and Operating Expenses [Abstract]
Ceded	(374.8)	(370)	(341.1)
Assumed	477.4	439.1	449.8
Acquisition and Operating Expenses, Net	$ 102.6	$ 69.1	$ 108.7

Notes Payable and Credit Faci_2

Notes Payable and Credit Facility - Narrative (Details) - USD ($) $ in Millions	May 17, 2018	Sep. 03, 2016	Dec. 31, 2020	Apr. 03, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 02, 2016	Jul. 11, 2013
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost			$ 0		$ 0	$ 0.4
Expiration period				1 year
Document Period End Date			Dec. 31, 2020
Interest income earned			$ 2.8		$ 3.6	$ 4.9	$ 4.9	$ 4.9
Federal Home Loan Bank of Cincinnati
Debt Instrument [Line Items]
Federal home loan Bank, advances, general debt obligations, disclosures, repayment and penalties			60
Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds			100
2016 [Member] | Federal Home Loan Bank of Cincinnati
Debt Instrument [Line Items]
Long-term Federal Home Loan Bank Advances									$ 21.5
Federal Home Loan Bank, Advances, Maturity Period, Fixed Rate		5 years
2018 [Member] | Federal Home Loan Bank of Cincinnati
Debt Instrument [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances										$ 85
Federal home loan bank, advances, branch of FHLB Bank, interest rate (percent)	3.96%
Federal Home Loan Bank, Advances, Maturity Period, Fixed Rate	15 years
2020 [Member] | Federal Home Loan Bank of Cincinnati
Debt Instrument [Line Items]
Long-term Federal Home Loan Bank Advances			$ 21.5
Federal home loan bank, advances, branch of FHLB Bank, interest rate (percent)			1.37%
Federal Home Loan Bank, Advances, Maturity Period, Fixed Rate			10 years

Federal Income Taxes - Reconcil

Federal Income Taxes - Reconciliation Between Actual Federal Income Tax Expense (Benefit) and Amount Computed at Indicated Statutory Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Amount at statutory rate	$ 3	$ 22.2	$ 2.6
Tax-exempt interest and dividends received deduction	(2.3)	(2.3)	(2.3)
Other, net	0.6	(0.2)	(0.4)
Total federal income tax expense (benefit)	$ 1.3	$ 19.7	$ (0.1)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	21.00%
Tax-exempt interest and dividends received deduction (percent)	(16.40%)	(2.10%)	(18.70%)
Other, net (percent)	4.20%	(0.20%)	(3.00%)
Federal income tax expense (benefit) and effective rate (percent)	8.80%	18.70%	(0.70%)

Federal Income Taxes - Tax Effe

Federal Income Taxes - Tax Effects of Temporary Differences of Deferred Tax Assets and Deferred Tax Liabilities (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Unearned premiums not currently deductible	$ 30,100,000	$ 27,000,000
Losses and loss expenses payable discounting	10,500,000	10,600,000
Postretirement and pension benefits	19,300,000	17,100,000
Other liabilities	12,200,000	13,400,000
Net operating loss carryforward	19,800,000	12,600,000
Deferred Tax Assets, Capital Loss Carryforwards	6,100,000	0
Tax credit carryforward	1,900,000	2,500,000
Other	1,100,000	1,100,000
Total deferred tax assets	101,000,000	84,300,000
Deferred tax liabilities:
Deferral of policy acquisition costs	25,700,000	23,300,000
Investments	48,000,000	21,300,000
Total deferred tax liabilities	73,700,000	44,600,000
Net deferred federal income taxes	$ 27,300,000	$ 39,700,000

Federal Income Taxes - Narrativ

Federal Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Tax-effected change to the Provisional Change in Discounted Loss Reserves attributable to TCJA changes to loss reserve discounting		$ 1,000,000	$ 700,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	21.00%
Pre-tax provisional change in discounted loss reserves attributable to TCJA		$ 42,700,000	$ 50,900,000	$ 47,500,000
Deferred tax asset related to net operating loss carryforwards	$ 19,800,000	$ 12,600,000
Balance for uncertain tax positions	0
Interest and penalties payable			$ 0		$ 0
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	300,000
Deferred Tax Assets, Valuation Allowance	$ 300,000

Pension and Postretirement Be_3

Pension and Postretirement Benefit Plans - Narrative (Details)	12 Months Ended
	Dec. 31, 2020USD ($)internationalFund	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Document Period End Date	Dec. 31, 2020
Postretirement plan's gross benefit payments	$ 600,000
Postretirement plan's estimated future subsidies	300,000
Employer contribution	$ 15,000,000
Contributions of participant salary (percent)	1.00%
Matching contribution on participant's salary	$ 1
Participant's contribution (percent)	2.00%
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	6.00%
Matching contribution by the employer	$ 0.50
Company's share of expense under the plan	7,300,000	$ 6,400,000	$ 5,600,000
Postretirement Benefit Costs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contribution	0	0
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	13,900,000
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Postretirement plan's gross benefit payments	$ 18,300,000
Pension | Private Equity Funds, Non-US [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Invested Assets Fair Value Disclosure		$ 38,200,000
Causeway Capital Fund [Member] | Private Equity Funds, Non-US [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Invested Assets Fair Value Disclosure | internationalFund	1
Silchester International [Member] | Private Equity Funds, Non-US [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Invested Assets Fair Value Disclosure | internationalFund	2
Silchester International [Member] | Pension | Private Equity Funds, Non-US [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Other Invested Assets Fair Value Disclosure	$ 47,300,000

Pension and Postretirement Be_4

Pension and Postretirement Benefit Plans - Change in Benefit Obligation, Plan Assets and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Actuarial loss (gain)	$ 27.4	$ (7.5)	$ 4.3
Change in plan assets available for plan benefits:
Employer contribution	15
Pension Costs
Change in benefit obligation:
Benefit obligation at beginning of year	478.4	428.1
Service cost	7.3	5.8
Interest cost	14.5	17.2
Actuarial loss (gain)	72.3	60.6
Benefits paid	(22.9)	(33.3)
The Company’s portion of benefit obligation at end of year	549.6	478.4	428.1
Change in plan assets available for plan benefits:
Fair value of plan assets available for plan benefits at beginning of year	442.1	381.6
Employer contribution	15	10
Actual return on plan assets	72.5	83.8
Benefits paid	(22.9)	(33.3)
The Company’s portion of fair value of plan assets at end of year	506.7	442.1	381.6
Supplemental executive retirement plan	(13.1)	(11.8)
Funded status at end of year	(56)	(48.1)
Accumulated benefit obligation end of year	522.8	453.8
Postretirement Benefit Costs
Change in benefit obligation:
Benefit obligation at beginning of year	11.4	25.5
Service cost	0	0
Interest cost	0.3	1
Actuarial loss (gain)	(0.9)	(12.6)
Benefits paid	(0.6)	(2.5)
The Company’s portion of benefit obligation at end of year	10.2	11.4	25.5
Change in plan assets available for plan benefits:
Fair value of plan assets available for plan benefits at beginning of year	0	0
Employer contribution	0	0
Actual return on plan assets	0	0
Benefits paid	0	0
The Company’s portion of fair value of plan assets at end of year	0	0	$ 0
Supplemental executive retirement plan	0	0
Funded status at end of year	$ (10.2)	$ (11.4)

Pension and Postretirement Be_5

Pension and Postretirement Benefit Plans - Share of Amounts Included in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Prior service benefit	$ (37)	$ (43.4)
Net actuarial loss	157.4	143.7
Total	$ 120.4	$ 100.3

Pension and Postretirement Be_6

Pension and Postretirement Benefit Plans - Share of Net Periodic Cost Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension
Components of net periodic cost:
Service cost	$ 4.8	$ 3.8	$ 5.1
Interest cost	9.7	11.5	10.7
Expected return on plan assets	(17.5)	(17.8)	(18)
Amortization of:
Prior service benefit	0	0	0
Net actuarial loss	9.2	6	8.2
Net periodic cost (benefit)	6.2	3.5	6
Postretirement
Components of net periodic cost:
Service cost	0	0	0
Interest cost	0.2	0.7	0.8
Expected return on plan assets	0	0	0
Amortization of:
Prior service benefit	(5.5)	(5.5)	(5.5)
Net actuarial loss	(0.2)	0.2	0.2
Net periodic cost (benefit)	$ (5.5)	$ (4.6)	$ (4.5)

Pension and Postretirement Be_7

Pension and Postretirement Benefit Plans - Share of Expected Future Benefits Payments Schedule (Details) $ in Millions	Dec. 31, 2020USD ($)
Schedule of Expected Future Pension Benefit Payment [Line Items]
2018	$ 0.6
Pension
Schedule of Expected Future Pension Benefit Payment [Line Items]
2018	18.3
2019	18.9
2020	19.6
2021	20.6
2022	21.6
2023 - 2027	123
Postretirement
Schedule of Expected Future Pension Benefit Payment [Line Items]
2018	0.7
2019	0.6
2020	0.6
2021	0.6
2022	0.6
2023 - 2027	$ 3.1

Pension and Postretirement Be_8

Pension and Postretirement Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Plans' Obligations (Details)	Dec. 31, 2020	Dec. 31, 2019
Pension
Benefit obligations weighted-average assumptions:
Discount rate (percent)	2.32%	3.10%
Rates of increase in compensation levels (percent)	3.00%	3.25%
Postretirement
Benefit obligations weighted-average assumptions:
Discount rate (percent)	1.95%	3.00%
Rates of increase in compensation levels (percent)	0.00%	0.00%

Pension and Postretirement Be_9

Pension and Postretirement Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Plan's Net Periodic Cost (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate (percent)	3.10%	4.12%	3.50%
Expected long-term rate of return on assets (percent)	6.50%	6.75%	7.00%
Rates of increase in compensation levels (percent)	3.25%	3.25%	3.25%
Postretirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate (percent)	3.10%	4.12%	3.50%
Expected long-term rate of return on assets (percent)	0.00%	0.00%	0.00%
Rates of increase in compensation levels (percent)	0.00%	0.00%	0.00%

Pension and Postretirement B_10

Pension and Postretirement Benefit Plans - Assumed Health Care Cost Trend Rates Used (Details) - Postretirement	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assumed health care cost trend rates:
Health care cost trend rate assumed for the next year (percent)	5.50%	5.50%	5.50%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate) (percent)	4.00%	4.00%	3.80%
Year that the rate reaches the ultimate trend rate	2075	2075	2075

Pension and Postretirement B_11

Pension and Postretirement Benefit Plans - Asset Allocation Targets (Details)	Dec. 31, 2020
Asset Category:
Asset allocation target (percent)	100.00%
Fixed maturity
Asset Category:
Asset allocation target (percent)	61.00%
Large-cap securities
Asset Category:
Asset allocation target (percent)	19.80%
Small-cap securities
Asset Category:
Asset allocation target (percent)	8.30%
International equity
Asset Category:
Asset allocation target (percent)	7.60%
Emerging market equity
Asset Category:
Asset allocation target (percent)	3.30%

Pension and Postretirement B_12

Pension and Postretirement Benefit Plans - Company's Share of Postretirement Plans' Investments (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 450.6	$ 397.3
Defined Benefit Plan, Debt Security [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	278.3	255.7
U.S. treasury securities and obligations of U.S. government agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	90.5	98.6
Corporate securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	183.9	153.1
U.S. government agencies mortgage-backed securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3.9	4
Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	172.3	141.6
Large-cap securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	116.2	91.9
Mutual and exchange traded funds [Domain] [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	56.1	49.7
Quoted prices in active markets for identical assets (Level 1)
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	172.3	141.6
Quoted prices in active markets for identical assets (Level 1) | Defined Benefit Plan, Debt Security [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Quoted prices in active markets for identical assets (Level 1) | U.S. treasury securities and obligations of U.S. government agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Quoted prices in active markets for identical assets (Level 1) | Corporate securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Quoted prices in active markets for identical assets (Level 1) | U.S. government agencies mortgage-backed securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Quoted prices in active markets for identical assets (Level 1) | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	172.3	141.6
Quoted prices in active markets for identical assets (Level 1) | Large-cap securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	116.2	91.9
Quoted prices in active markets for identical assets (Level 1) | Mutual and exchange traded funds [Domain] [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	56.1	49.7
Significant other observable inputs (Level 2)
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	278.3	255.7
Significant other observable inputs (Level 2) | Defined Benefit Plan, Debt Security [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	278.3	255.7
Significant other observable inputs (Level 2) | U.S. treasury securities and obligations of U.S. government agencies
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	90.5	98.6
Significant other observable inputs (Level 2) | Corporate securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	183.9	153.1
Significant other observable inputs (Level 2) | U.S. government agencies mortgage-backed securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	3.9	4
Significant other observable inputs (Level 2) | Defined Benefit Plan, Equity Securities [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Significant other observable inputs (Level 2) | Large-cap securities
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	0	0
Significant other observable inputs (Level 2) | Mutual and exchange traded funds [Domain] [Member]
Defined Benefit Plan, Plan Assets, Category [Line Items]
Defined Benefit Plan, Plan Assets, Amount	$ 0	$ 0

Other Comprehensive Income an_3

Other Comprehensive Income and Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component, Net of Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (26.9)	$ (96.4)	$ 3.8
Other comprehensive income before reclassifications	29	71.3	(41)
Amounts reclassified from AOCI	(11.8)	1.8	(4.7)
Net current period other comprehensive income	40.8	69.5	(36.3)
Ending balance	13.9	(26.9)	(96.4)
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	40.8	(20.2)	66
Other comprehensive income before reclassifications	56.4	63.8	(36.7)
Amounts reclassified from AOCI	(0.3)	2.8	1.6
Net current period other comprehensive income	56.7	61	(38.3)
Ending balance	97.5	40.8	(20.2)
Unrealized Gains and Losses on Available-for-Sale Securities | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Stockholders' Equity, Period Increase (Decrease)			(47.9)
Benefit Plan Items
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(67.7)	(76.2)	(62.2)
Other comprehensive income before reclassifications	(27.4)	7.5	(4.3)
Amounts reclassified from AOCI	(11.5)	(1)	(6.3)
Net current period other comprehensive income	(15.9)	8.5	2
Ending balance	(83.6)	(67.7)	(76.2)
Benefit Plan Items | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Stockholders' Equity, Period Increase (Decrease)			(16)
Accumulated other comprehensive income: | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Stockholders' Equity, Period Increase (Decrease)	$ 0	$ 0	$ (63.9)

Other Comprehensive Income an_4

Other Comprehensive Income and Accumulated Other Comprehensive Income - Reclassifications Out of Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain on sale of securities	$ 27.3	$ 74.2	$ (49.7)
Tax expense	(1.3)	(19.7)	0.1
Total reclassifications for the period	(11.8)	1.8	(4.7)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(11.8)	1.8	(4.7)
Unrealized Gains and Losses on Available-for-Sale Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(0.3)	2.8	1.6
Unrealized Gains and Losses on Available-for-Sale Securities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain on sale of securities	(0.3)	3.5	2
Total before tax	(0.3)	3.5	2
Tax expense	0	(0.7)	(0.4)
Total reclassifications for the period	0.3	(2.8)	(1.6)
Benefit Plan Items
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	(11.5)	(1)	(6.3)
Benefit Plan Items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(7.4)	(3.3)	(6.9)
Tax expense	(4.1)	2.3	0.6
Negative prior service costs	6.3	6.3	6.3
Net loss	(13.7)	(9.6)	(13.2)
Total reclassifications for the period	$ 11.5	$ 1	$ 6.3

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity, Class of Treasury Stock [Line Items]
Statutory Accounting Policies, Statutory Percent Available for Dividend Payments without Regulatory Approval	10.00%
Amount of dividends available for distributions without prior approval	$ 91
Statutory surplus in excess of authorized level, no remedial action required (percent)	2
Statutory surplus in excess of authorized level, level maintained by company and subsidiaries (percent)	4
Statutory Accounting Practices, Statutory Capital and Surplus, Balance	$ 910.3	$ 913.3
Statutory net (loss) income of insurance subsidiaries	$ (39.1)	31.1	$ 65.1
Document Period End Date	Dec. 31, 2020
State Auto Financial
Equity, Class of Treasury Stock [Line Items]
Dividends received from insurance subsidiaries	$ 15	$ 10	$ 10

Preferred Stock - Summary (Deta

Preferred Stock - Summary (Details)	12 Months Ended
	Dec. 31, 2020class_of_stockquarter
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Number of authorized classes of preferred stock (class of stock) | class_of_stock	2
Minimum number of quarters dividends are paid in arrears (minimum of 6 quarters) | quarter	6

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details)	12 Months Ended
	Dec. 31, 2020USD ($)internationalFundshares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | $	$ 400,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value | $	1,000,000	$ 4,500,000	$ 7,200,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $	$ 4,900,000
Document Period End Date	Dec. 31, 2020
Common shares valued (shares) | $	$ 126,800,000	125,900,000
Share-based compensation | $	$ 900,000	6,100,000	$ 11,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Number of Shares Per Employee	250,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	300,000
Share-based compensation performance unit award minimum award earned	0.00%
Share-based compensation performance unit award maximum award earned	500.00%
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 10 days
Percentage Of Annual Base Earnings	6.00%
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent	85.00%
Share-based Compensation Arrangement by Share-based Payment Award, Shares Purchased for Award	3,800,000
Stock Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number Of Securities Available For Issuance Under Equity Compensation Plans	1,600,000
Maximum value of awards that may be granted in any calendar year	5		5
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	800,000
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Annual Vesting Percentage			33.33%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Vesting Percentage Three Years After Grant Date			100.00%
Restricted Stock Units (RSUs) Performance Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $	$ 4,400,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 18 days
Restricted Stock Units (RSUs) Service Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized | $	$ 500,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	10 months 2 days
Outside Directors Award Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares valued (shares) | $	$ 100,000	$ 1,200,000
Share Based Compensation Arrangement, Restricted Stock Units Awarded to Directors, Award Vesting Period	6 months
Number Of Shares Of Restricted Stock Issued To Each Non Employee Director	1,400
Restricted Stock Plan Termination Date	May 31, 2026
Stock Issued During Period, Shares, Restricted Stock Award, Gross	17,416	18,837	23,080
Outside Directors Award Plan [Member] | Restricted Stock Units (RSUs) [Member] | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement, Restricted Stock Units, Annual Installment Payments	10 years
Share Based Compensation Restricted Stock Units Awarded To Directors	10,000
Outside Directors Award Plan [Member] | Restricted Stock Units (RSUs) [Member] | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement, Restricted Stock Units, Annual Installment Payments	5 years
Share Based Compensation Restricted Stock Units Awarded To Directors	500
Exercise Prices Range One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit | $ / shares			$ 10.01
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit | $ / shares			20
Exercise Prices Range Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit | $ / shares			20.01
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit | $ / shares			$ 30

Share-Based Compensation - Non-

Share-Based Compensation - Non-Vested and Vested Restricted Shares and Changes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock Units (RSUs) Service Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	0	211	4,037
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	70,836	67,934	126,946	71,578
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 22.76	$ 27.65	$ 26.21	$ 22.44
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	30,618	0	97,049
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Intrinsic Value, Amount Per Share	$ 16.33	$ 0	$ 27.65
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	27,716	58,801	37,644
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Intrinsic Value, Amount Per Share	$ 27.65	$ 24.57	$ 22.88
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 0	$ 21.54	$ 24.82
Restricted Stock Units (RSUs) Performance Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	5,915	14,391	15,918
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	504,503	460,189	356,400	147,869
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 28.06	$ 29.37	$ 27.47	$ 27.20
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	153,574	130,680	224,449
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Intrinsic Value, Amount Per Share	$ 24.40	$ 33.67	$ 27.65
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	103,345	12,500	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Intrinsic Value, Amount Per Share	$ 27.24	$ 27.65	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 28.64	$ 29.59	$ 27.37

Share-Based Compensation - Stoc

Share-Based Compensation - Stock Option Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Payment Arrangement, Noncash Expense [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	700,000	800,000	1,000,000	1,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(100,000)	(200,000)	(700,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 19.28	$ 19.18	$ 18.50	$ 19.22
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 18.55	$ 16.45	$ 20.08
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	700,000

Share-Based Compensation - St_2

Share-Based Compensation - Stock Options Outstanding and Exercisable (Details) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Share Based Compensation Arrangement [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	0.7
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 19.28	$ 19.18	$ 18.50	$ 19.22
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	0.7
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 19.28
Exercise Prices Range One [Member]
Schedule Of Share Based Compensation Arrangement [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	0.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 6 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 16.33
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	0.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 16.33
Exercise Prices Range Two [Member]
Schedule Of Share Based Compensation Arrangement [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	0.4
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 21.97
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	0.4
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 21.97

Net (Loss) Earnings Per Commo_3

Net (Loss) Earnings Per Common Share - Compilation of Basic and Diluted Net (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net (loss) earnings for basic net earnings per common share	$ 13.1	$ 85.8	$ 12.2
Adjusted net (loss) earnings for dilutive net (loss) earnings per common share	$ 13.1	$ 84.7	$ 12.2
Denominator:
Weighted average shares for basic net earnings (loss) per common share (shares)	43.7	43.4	42.8
Effect of dilutive share-based awards (shares)	0.6	0.6	0.6
Adjusted weighted average shares for diluted net earnings (loss) per common share (shares)	44.3	44	43.4
Basic net earnings (loss) per common share (usd per share)	$ 0.30	$ 1.98	$ 0.29
Diluted net earnings (loss) per common share (usd per share)	$ 0.30	$ 1.93	$ 0.28
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units	$ 0	$ (1.1)	$ 0

Net (Loss) Earnings Per Commo_4

Net (Loss) Earnings Per Common Share - Options to Purchase Shares of Common Stock (Details) shares in Millions	12 Months Ended
	Dec. 31, 2018shares
Earnings Per Share [Abstract]
Number of options and awards (shares)	0.1

Reportable Segments - Financial

Reportable Segments - Financial Information Regarding Company's Reportable Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from external sources:
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue	$ 1,380.9	$ 1,250.2	$ 1,237.6
Intersegment revenues	1,482.4	1,407.2	1,275.4
Segment loss before federal income tax:
Income (loss) before federal income tax	14.4	105.5	12.1
Net Investment Income	72.1	80.4	84.9
Income (loss) before federal income tax	14.4	105.5	12.1
Segment assets:
Total segment assets	2,870.8	2,747.8
Reconciling items:
Total consolidated assets	3,102.5	2,979.6
Interest expense (affiliates $1.1, $1.0, and $0.8, respectively)	4.7	4.9	5.7
Personal Insurance Segments [Member]
Revenues from external sources:
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue	819	755.9	673.4
Commercial insurance
Revenues from external sources:
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue	561.8	488.6	464.4
Specialty insurance
Revenues from external sources:
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information, Premium Revenue	0.1	5.7	99.8
Total investment operations segment
Segment assets:
Total segment assets	2,870.8	2,747.8
Total internal and external revenue [Member]
Revenues from external sources:
Intersegment revenues	1,488.6	1,413.7	1,281.9
Segment Reconciling Items [Member]
Revenues from external sources:
Intersegment revenues	6.2	6.5	6.5
Segment loss before federal income tax:
Income (loss) before federal income tax	8.9	2.7	(18)
Income (loss) before federal income tax	8.9	2.7	(18)
Reconciling items:
Gaap Expense Adjustments	19.8	14.7	(3.7)
Interest expense (affiliates $1.1, $1.0, and $0.8, respectively)	(4.7)	(4.9)	(5.7)
Corporate Expenses	(6.2)	(7.1)	(8.6)
Corporate, Non-Segment [Member]
Reconciling items:
Total consolidated assets	231.7	231.8
Intersegment Eliminations [Member]
Revenues from external sources:
Intersegment revenues	(6.2)	(6.5)	(6.5)
Reportable segments | Personal Insurance Segments [Member]
Segment loss before federal income tax:
Income (loss) before federal income tax	(68.8)	(42.2)	2.8
Income (loss) before federal income tax	(68.8)	(42.2)	2.8
Reportable segments | Commercial insurance
Segment loss before federal income tax:
Income (loss) before federal income tax	(7.4)	(0.2)	(8.7)
Income (loss) before federal income tax	(7.4)	(0.2)	(8.7)
Reportable segments | Specialty insurance
Segment loss before federal income tax:
Income (loss) before federal income tax	(17.6)	(9.7)	0.4
Income (loss) before federal income tax	(17.6)	(9.7)	0.4
Reportable segments | Total insurance segments
Segment loss before federal income tax:
Income (loss) before federal income tax	(93.8)	(52.1)	(5.5)
Income (loss) before federal income tax	(93.8)	(52.1)	(5.5)
Reportable segments | Net investment income
Segment loss before federal income tax:
Net Investment Income	72.1	80.4	84.9
Reportable segments | Net realized capital gains
Segment loss before federal income tax:
Income (loss) before federal income tax	27.3	74.2	(49.7)
Income (loss) before federal income tax	27.3	74.2	(49.7)
Reportable segments | Total investment operations segment
Segment loss before federal income tax:
Investment income	99.4	154.6	35.2
Reportable segments | All other
Revenues from external sources:
Intersegment revenues	2.1	2.4	2.6
Segment loss before federal income tax:
Income (loss) before federal income tax	(0.1)	0.3	0.4
Income (loss) before federal income tax	$ (0.1)	$ 0.3	$ 0.4