The Progressive Corporation (PGR) 10-Q 1 Nov 22 2022 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2022 shares
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2022
Document Transition Report	false
Entity File Number	001-09518
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	34-0963169
Entity Address, Address Line One	6300 Wilson Mills Road,
Entity Address, City or Town	Mayfield Village,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	44143
City Area Code	440
Local Phone Number	461-5000
Entity Information, Former Legal or Registered Name	Not Applicable
Title of 12(b) Security	Common Shares, $1.00 Par Value
Trading Symbol	PGR
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	585,069,712
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	0000080661
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Revenues
Net premiums earned		$ 12,398.9	$ 11,364.8	$ 36,349.7	$ 32,767.3
Investment income		333.6	208.9	868.2	639.8
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales		(62.1)	53.9	430	607.8
Net holding period gains (losses) on securities		(152.1)	(15.9)	(2,262.9)	479.8
Net impairment losses recognized in earnings		(2.2)	(1.2)	(6.5)	(3.7)
Total net realized gains (losses) on securities		(216.4)	36.8	(1,839.4)	1,083.9
Fees and other revenues		181.4	174.9	531.9	516.8
Service revenues		82.7	73.8	230.5	202.1
Total revenues		12,780.2	11,859.2	36,140.9	35,209.9
Expenses
Losses and loss adjustment expenses		10,018.7	9,250.7	28,298.2	24,767.6
Policy acquisition costs		970.9	951.5	2,867.9	2,754.7
Other underwriting expenses		1,496.4	1,384.4	4,433.9	4,306
Investment expenses		5.8	6.6	17.4	18.5
Service expenses		82.8	72.8	221.5	190
Interest expense		63.1	54.2	180.4	167
Goodwill impairment	[1]	0	0	224.8	0
Total expenses		12,637.7	11,720.2	36,244.1	32,203.8
Net Income (Loss)
Income (loss) before income taxes		142.5	139	(103.2)	3,006.1
Provision for income taxes		18.4	20.5	1.7	617.5
Net income (loss)		124.1	118.5	(104.9)	2,388.6
Other Comprehensive Income (Loss)
Total net unrealized gains (losses) on fixed-maturity securities		(920.3)	(129.8)	(3,170)	(578.3)
Net unrealized losses on forecasted transactions		0.1	0.1	0.3	0.6
Foreign currency translation adjustment		(0.7)	(0.2)	(0.9)	(0.7)
Other comprehensive income (loss)		(920.9)	(129.9)	(3,170.6)	(578.4)
Comprehensive income (loss)		(796.8)	(11.4)	(3,275.5)	1,810.2
Computation of Earnings Per Common Share
Net income (loss)		124.1	118.5	(104.9)	2,388.6
Less: Preferred share dividends		6.7	6.7	20.1	20.1
Net income (loss) available to common shareholders		$ 117.4	$ 111.8	$ (125)	$ 2,368.5
Average common shares outstanding - Basic		584.5	584.7	584.4	584.7
Net effect of dilutive stock-based compensation		2.6	2.4	2.7	2.6
Total average equivalent common shares - Diluted		587.1	587.1	587.1	587.3
Basic: Earnings per common share		$ 0.20	$ 0.19	$ (0.21)	$ 4.05
Diluted: Earnings per common share		$ 0.20	$ 0.19	$ (0.21)	$ 4.03
[1] See Note 12 – Goodwill and Intangible Assets

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Assets
Fixed maturities (amortized cost: $48,205.7, $44,556.0, and $43,794.2)		$ 44,173.1	$ 43,873.1	$ 45,045.7
Short-term investments (amortized cost: $4,237.6, $1,088.7, and $942.6)		4,237.6	942.6	1,088.7
Total available-for-sale securities		48,410.7	44,815.7	46,134.4
Nonredeemable preferred stocks (cost: $1,417.6, $1,479.9, and $1,571.8)		1,254.4	1,639.9	1,572.8
Common equities (cost: $803.7, $1,238.4, and $1,264.1)		2,665.3	5,058.5	4,580.2
Total equity securities		3,919.7	6,698.4	6,153
Total investments		52,330.4	51,514.1	52,287.4
Cash and cash equivalents		350.9	187.1	270.6
Restricted cash and cash equivalents		14.4	15	14.9
Total cash, cash equivalents, restricted cash, and restricted cash equivalents		365.3	202.1	285.5
Accrued investment income		217.4	181.7	168.6
Premiums receivable, net of allowance for credit losses of $295.0, $257.3, and $280.4		10,867.7	9,399.5	10,246.7
Reinsurance recoverables		6,306.8	4,980.5	5,044.9
Prepaid reinsurance premiums		367.5	457.6	661.1
Deferred acquisition costs		1,585.2	1,355.6	1,430.7
Property and equipment, net of accumulated depreciation of $1,499.0, $1,422.2, and $1,407.4		1,067.1	1,137.3	1,161
Goodwill		227.9	452.7	452.7
Intangible assets, net of accumulated amortization of $153.1, $369.2, and $383.8		91.8	117.3	131.9
Net federal deferred income taxes		1,269.5	0	0
Other assets		827.6	1,333.9	747.6
Total assets		75,524.2	71,132.3	72,618.1
Liabilities
Unearned premiums		17,796.9	15,615.8	16,671.4
Loss and loss adjustment expense reserves		30,631.8	26,164.1	25,926.3
Net federal deferred income taxes		0	152.9	110.7
Accounts payable, accrued expenses, and other liabilities		5,931.9	6,069.1	6,453.4
Debt	[1]	6,387.4	4,898.8	4,898.2
Total liabilities		60,748	52,900.7	54,060
Shareholders' Equity
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5)		493.9	493.9	493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 212.5, 212.6, and 213.2)		585.1	584.4	585
Paid-in capital		1,839.6	1,772.9	1,735.9
Retained earnings		14,987.5	15,339.7	15,390
Accumulated other comprehensive income (loss):
Net unrealized gains (losses) on fixed-maturity securities		(3,113.8)	56.2	369
Net unrealized losses on forecasted transactions		(14.6)	(14.9)	(15)
Foreign currency translation adjustment		(1.5)	(0.6)	(0.7)
Total accumulated other comprehensive income (loss)		(3,129.9)	40.7	353.3
Total shareholders’ equity		14,776.2	18,231.6	18,558.1
Total liabilities and shareholders’ equity		$ 75,524.2	$ 71,132.3	$ 72,618.1
[1] Consists of long-term debt. See Note 4 – Debt for further discussion.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Fixed maturities, amortized cost	$ 48,205.7	$ 43,794.2	$ 44,556
Short-term investments, amortized cost	4,237.6	942.6	1,088.7
Nonredeemable preferred stocks, cost	1,417.6	1,571.8	1,479.9
Common equities, cost	803.7	1,264.1	1,238.4
Premium Receivable, Allowance for Credit Loss	295	280.4	257.3
Property and equipment, accumulated depreciation	1,499	1,407.4	1,422.2
Intangible Assets, Accumulated Amortization	$ 153.1	$ 383.8	$ 369.2
Common Shares, par value (USD per share)	$ 1	$ 1	$ 1
Common Shares, authorized (shares)	900,000,000	900,000,000	900,000,000
Common Shares, issued (shares)	797,600,000	797,600,000	797,600,000
Common Shares, treasury shares (shares)	212,500,000	213,200,000	212,600,000
Serial Preferred Stock
Preferred Stock, Shares Authorized (shares)	20,000,000	20,000,000	20,000,000
Series B Preferred Stock | Serial Preferred Stock
Preferred Stock, No Par Value	$ 0	$ 0	$ 0
Preferred Stock, Liquidation Preference Per Share (USD per share)	$ 1,000	$ 1,000	$ 1,000
Preferred Stock, Shares Authorized (shares)	500,000	500,000	500,000
Preferred Stock, Shares Issued (shares)	500,000	500,000	500,000
Preferred Stock, Shares Outstanding (shares)	500,000	500,000	500,000

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Serial Preferred Stock	Preferred Shares, No Par Value	Common Shares, $1.00 Par Value	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Series B Preferred Stock Serial Preferred Stock	Voting Preference Shares
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 26.875
Balance, Beginning of period at Dec. 31, 2020			$ 493.9	$ 585.2	$ 1,672.9	$ 13,354.9	$ 931.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 2,388.6					2,388.6
Treasury shares purchased				(1.8)	(5.3)	(160.1)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(175.2)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $26.875 per share)						(13.4)
Reinvested dividends on restricted stock units					1.2	(1.2)
Net restricted equity awards issued/vested				1.6	(1.6)
Amortization of equity-based compensation					68.7
Other comprehensive income (loss)	(578.4)						(578.4)
Other, net						(3.6)
Balance, End of period at Sep. 30, 2021	$ 18,558.1		493.9	585	1,735.9	15,390	353.3
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2021			493.9	585.2	1,712.3	15,401	483.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 118.5					118.5
Treasury shares purchased				(0.7)	(2.3)	(68.8)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $26.875 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Net restricted equity awards issued/vested				0.5	(0.5)
Amortization of equity-based compensation					26
Other comprehensive income (loss)	(129.9)						(129.9)
Other, net						11.5
Balance, End of period at Sep. 30, 2021	$ 18,558.1		493.9	585	1,735.9	15,390	353.3
Preferred Stock, No Par Value								$ 0
Common Shares, par value (USD per share)	$ 1
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000	5,000,000
Preferred Stock, Shares Issued (shares)								500,000	0
Preferred Stock, No Par Value								$ 0
Common Shares, par value (USD per share)	1
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000
Preferred Stock, Shares Issued (shares)								500,000
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 26.875
Balance, Beginning of period at Dec. 31, 2021	$ 18,231.6		493.9	584.4	1,772.9	15,339.7	40.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(104.9)					(104.9)
Treasury shares purchased				(0.7)	(2.2)	(75.7)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(175.2)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $26.875 per share)						(13.4)
Reinvested dividends on restricted stock units					0.6	(0.6)
Net restricted equity awards issued/vested				1.4	(1.4)
Amortization of equity-based compensation					69.7
Other comprehensive income (loss)	(3,170.6)						(3,170.6)
Other, net						17.6
Balance, End of period at Sep. 30, 2022	$ 14,776.2		493.9	585.1	1,839.6	14,987.5	(3,129.9)
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2022			493.9	584.9	1,815.2	14,967.7	(2,209)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 124.1					124.1
Treasury shares purchased				(0.4)	(1.3)	(47.4)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $26.875, and $26.875 per share)						(13.4)
Reinvested dividends on restricted stock units					0.3	(0.3)
Net restricted equity awards issued/vested				0.6	(0.6)
Amortization of equity-based compensation					26
Other comprehensive income (loss)	(920.9)						(920.9)
Other, net						15.2
Balance, End of period at Sep. 30, 2022	$ 14,776.2		$ 493.9	$ 585.1	$ 1,839.6	$ 14,987.5	$ (3,129.9)
Preferred Stock, No Par Value								$ 0
Common Shares, par value (USD per share)	$ 1
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000	5,000,000
Preferred Stock, Shares Issued (shares)								500,000	0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021
Cash Flows From Operating Activities
Net income (loss)		$ (104.9)	$ 2,388.6
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation		227.5	203.9
Amortization of intangible assets		25.5	43.1
Net amortization of fixed-income securities		1.6	97.2
Amortization of equity-based compensation		69.7	68.7
Net realized (gains) losses on securities		1,839.4	(1,083.9)
Net (gains) losses on disposition of property and equipment		5.3	(4)
Goodwill impairment	[1]	224.8	0
Changes in:
Premiums receivable		(1,468.2)	(1,994)
Reinsurance recoverables		(1,326.3)	(573.1)
Prepaid reinsurance premiums		90.1	(278.4)
Deferred acquisition costs		(229.6)	(193.5)
Income taxes		(591.6)	(156.2)
Unearned premiums		2,181.1	3,167
Loss and loss adjustment expense reserves		4,467.7	4,511.7
Accounts payable, accrued expenses, and other liabilities		546.5	1,033
Other, net		(39.4)	79.5
Net cash provided by operating activities		5,919.2	7,309.6
Purchases:
Fixed maturities		(18,672.7)	(25,222.2)
Equity securities		(126.5)	(464.9)
Sales:
Fixed maturities		9,737.6	11,747.1
Equity securities		1,467	625.2
Maturities, paydowns, calls, and other:
Fixed maturities		4,158.5	5,545.5
Equity securities		39.3	119.1
Net (purchases) sales of short-term investments		(3,266.6)	4,209.3
Net unsettled security transactions		(68.7)	304.2
Acquisition of Protective Insurance Corporation, net of cash, cash equivalents, and restricted cash equivalents acquired		0	(313.2)
Purchases of property and equipment		(245)	(188.3)
Sales of property and equipment		16	63.1
Net cash used in investing activities		(6,961.1)	(3,575.1)
Cash Flows From Financing Activities
Dividends paid to common shareholders		(175.5)	(2,811.5)
Dividends paid to preferred shareholders		(26.8)	(26.8)
Acquisition of treasury shares for restricted stock tax liabilities		(76.2)	(66.9)
Acquisition of treasury shares acquired in open market		(2.4)	(100.3)
Net proceeds from debt issuances		1,486	0
Payment of acquired company debt		0	(20)
Payments of debt		0	(500)
Net cash provided by (used in) financing activities		1,205.1	(3,525.5)
Increase in cash, cash equivalents, restricted cash, and restricted cash equivalents		163.2	209
Cash, cash equivalents, restricted cash, and restricted cash equivalents – January 1		202.1	76.5
Cash, cash equivalents, restricted cash, and restricted cash equivalents – September 30		$ 365.3	$ 285.5
[1] See Note 12 – Goodwill and Intangible Assets

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying consolidated financial statements include the accounts of The Progressive Corporation, our wholly owned insurance and non-insurance subsidiaries, and affiliates in which we have a controlling financial interest (Progressive). The consolidated financial statements reflect all normal recurring adjustments that, in the opinion of management, were necessary for a fair statement of the results for the interim periods presented. The results of operations for the period ended September 30, 2022, are not necessarily indicative of the results expected for the full year. These consolidated financial statements and the notes thereto should be read in conjunction with Progressive’s audited financial statements and accompanying notes included in Exhibit 13 to our Annual Report on Form 10-K for the year ended December 31, 2021 (2021 Annual Report to Shareholders). Insurance Premiums and Receivables We perform analyses to evaluate our premiums receivable for expected credit losses. See the 2021 Annual Report to Shareholders for a discussion on our premiums receivable allowance for credit loss policy. The following table summarizes changes in our allowance for credit loss exposure on our premiums receivable: Three Months Ended September 30, Nine Months Ended September 30, (millions) 2022 2021 2022 2021 Allowance for credit losses, beginning of period $ 265.8 $ 245.2 $ 280.4 $ 356.2 Allowance acquired during period 1 0 0 0 3.5 Increase in allowance 2 130.9 107.2 320.6 255.5 Write-offs 3 (101.7) (95.1) (306.0) (357.9) Allowance for credit losses, end of period $ 295.0 $ 257.3 $ 295.0 $ 257.3 1 Represents the amount of the allowance acquired in the Protective Insurance Corporation and subsidiaries (Protective Insurance) acquisition. 2 Represents the incremental increase in other underwriting expenses. 3 Represents portion of allowance that is reversed when premiums receivable are written off. Premiums receivable balances are written off once we have exhausted our collection efforts. Property and Equipment Other assets on the consolidated balance sheets include certain long-lived assets that are considered “ held for sale. ” The carrying value of these held-for-sale assets was $47.4 million at September 30, 2022, $12.6 million at September 30, 2021, and $10.8 million at December 31, 2021. Goodwill and Intangible Assets We evaluate goodwill for impairment using a qualitative or quantitative approach annually and when changes in circumstances indicate the carrying value of certain portions of goodwill may not be recoverable. See Note 12 – Goodwill and Intangible Assets for further discussion. Earnings per Common Share When a net loss is reported, earnings per common share are calculated using basic average equivalent shares since diluted earnings per share would be antidilutive given the net loss reported for the period. Amounts are reported on a diluted basis for all other periods presented.

Investments

Investments	9 Months Ended
	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Investments	Investments — The following tables present the composition of our investment portfolio by major security type. Our securities are reported in our consolidated balance sheets at fair value. The changes in fair value for our fixed-maturity securities (other than hybrid securities) are reported as a component of accumulated other comprehensive income (loss), net of deferred income taxes, in our consolidated balance sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value of the securities. The changes in the net holding period gains (losses) between periods for the hybrid securities and equity securities are recorded as a component of net realized gains (losses) on securities in our consolidated statements of comprehensive income. ($ in millions) Cost Gross Gross Net Fair % of September 30, 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 24,260.9 $ 0 $ (1,855.4) $ 0 $ 22,405.5 42.8 % State and local government obligations 2,140.9 0 (215.4) 0 1,925.5 3.7 Foreign government obligations 16.7 0 (1.4) 0 15.3 0.1 Corporate debt securities 10,119.8 0 (832.5) (58.9) 9,228.4 17.6 Residential mortgage-backed securities 754.2 0.4 (16.5) (15.1) 723.0 1.4 Commercial mortgage-backed securities 5,833.9 1.4 (747.4) 0 5,087.9 9.7 Other asset-backed securities 4,876.7 0 (268.9) (1.9) 4,605.9 8.8 Redeemable preferred stocks 202.6 0 (5.6) (15.4) 181.6 0.3 Total fixed maturities 48,205.7 1.8 (3,943.1) (91.3) 44,173.1 84.4 Short-term investments 4,237.6 0 0 0 4,237.6 8.1 Total available-for-sale securities 52,443.3 1.8 (3,943.1) (91.3) 48,410.7 92.5 Equity securities: Nonredeemable preferred stocks 1,417.6 0 0 (163.2) 1,254.4 2.4 Common equities 803.7 0 0 1,861.6 2,665.3 5.1 Total equity securities 2,221.3 0 0 1,698.4 3,919.7 7.5 Total portfolio 1 $ 54,664.6 $ 1.8 $ (3,943.1) $ 1,607.1 $ 52,330.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of September 30, 2021 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 21,093.1 $ 144.9 $ (95.9) $ 0 $ 21,142.1 40.3 % State and local government obligations 2,123.8 48.8 (6.7) 0 2,165.9 4.1 Foreign government obligations 12.3 0 0 0 12.3 0.1 Corporate debt securities 10,556.4 314.6 (10.5) 1.2 10,861.7 20.7 Residential mortgage-backed securities 624.4 3.4 (0.9) 1.0 627.9 1.2 Commercial mortgage-backed securities 5,739.4 70.2 (20.6) 0 5,789.0 11.1 Other asset-backed securities 4,235.6 29.4 (2.8) 0 4,262.2 8.2 Redeemable preferred stocks 171.0 1.3 (0.7) 13.0 184.6 0.4 Total fixed maturities 44,556.0 612.6 (138.1) 15.2 45,045.7 86.1 Short-term investments 1,088.7 0 0 0 1,088.7 2.1 Total available-for-sale securities 45,644.7 612.6 (138.1) 15.2 46,134.4 88.2 Equity securities: Nonredeemable preferred stocks 1,479.9 0 0 92.9 1,572.8 3.0 Common equities 1,238.4 0 0 3,341.8 4,580.2 8.8 Total equity securities 2,718.3 0 0 3,434.7 6,153.0 11.8 Total portfolio 1 $ 48,363.0 $ 612.6 $ (138.1) $ 3,449.9 $ 52,287.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of December 31, 2021 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 18,586.1 $ 92.9 $ (190.8) $ 0 $ 18,488.2 35.9 % State and local government obligations 2,162.6 36.7 (14.0) 0 2,185.3 4.2 Foreign government obligations 17.9 0 0 0 17.9 0.1 Corporate debt securities 10,526.2 202.6 (33.4) (3.3) 10,692.1 20.7 Residential mortgage-backed securities 787.7 2.3 (0.6) 0.6 790.0 1.5 Commercial mortgage-backed securities 6,561.0 38.9 (64.3) 0 6,535.6 12.7 Other asset-backed securities 4,981.8 13.3 (12.4) (0.4) 4,982.3 9.7 Redeemable preferred stocks 170.9 0.7 (0.5) 10.6 181.7 0.4 Total fixed maturities 43,794.2 387.4 (316.0) 7.5 43,873.1 85.2 Short-term investments 942.6 0 0 0 942.6 1.8 Total available-for-sale securities 44,736.8 387.4 (316.0) 7.5 44,815.7 87.0 Equity securities: Nonredeemable preferred stocks 1,571.8 0 0 68.1 1,639.9 3.2 Common equities 1,264.1 0 0 3,794.4 5,058.5 9.8 Total equity securities 2,835.9 0 0 3,862.5 6,698.4 13.0 Total portfolio 1 $ 47,572.7 $ 387.4 $ (316.0) $ 3,870.0 $ 51,514.1 100.0 % 1 Includes $74.7 million, $399.7 million, and $143.4 million of net unsettled security purchase transactions at September 30, 2022 and 2021, and December 31, 2021, respectively, with the offsetting payable included in other liabilities. The total fair value of the portfolio at September 30, 2022 and 2021, and December 31, 2021, included $4.2 billion, $2.9 billion, and $4.2 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of unsettled security transactions. At September 30, 2022, bonds and certificates of deposit in the principal amount of $468.7 million were on deposit to meet state insurance regulatory requirements. We did not hold any securities of any one issuer, excluding U.S. government obligations, with an aggregate cost or fair value exceeding 10% of total shareholders’ equity at September 30, 2022 or 2021, or December 31, 2021. At September 30, 2022, we did not hold any debt securities that were non-income producing during the preceding 12 months. Short-Term Investments Our short-term investments may include commercial paper and other investments that are expected to mature or are redeemable within one year. We invested in repurchase and reverse repurchase transactions during 2022 and 2021, but did not have any open positions at September 30, 2022 and 2021, or December 31, 2021. To the extent we enter into repurchase or reverse repurchase transactions, consistent with past practice, we would elect not to offset these transactions and would report them on a gross basis in our consolidated balance sheets, despite the option to elect to offset these transactions as long as they were with the same counterparty and subject to an enforceable master netting arrangement. Hybrid Securities Certain securities in our fixed-maturity portfolio are accounted for as hybrid securities because they contain embedded derivatives that are not deemed to be clearly and closely related to the host investments. These securities are reported at fair value: September 30, (millions) 2022 2021 December 31, 2021 Fixed Maturities: Corporate debt securities $ 500.4 $ 363.3 $ 479.1 Residential mortgage-backed securities 550.8 217.0 536.2 Other asset-backed securities 51.4 104.5 89.2 Redeemable preferred stocks 133.0 133.2 130.8 Total hybrid securities $ 1,235.6 $ 818.0 $ 1,235.3 Since the embedded derivatives (e.g., change-in-control put option, debt-to-equity conversion, or any other feature unrelated to the credit quality or risk of default of the issuer that could impact the amount or timing of our expected future cash flows) do not have observable intrinsic values, we have elected to record the changes in fair value of these securities through income as a component of net realized gains or losses. Fixed Maturities The composition of fixed maturities by maturity at September 30, 2022, was: (millions) Cost Fair Value Less than one year $ 5,461.3 $ 5,321.6 One to five years 29,752.3 27,694.2 Five to ten years 12,946.4 11,119.1 Ten years or greater 45.7 38.2 Total $ 48,205.7 $ 44,173.1 Asset-backed securities are classified in the maturity distribution table based upon their projected cash flows. All other securities that do not have a single maturity date are reported based upon expected average maturity. Contractual maturities may differ from expected maturities because the issuers of the securities may have the right to call or prepay obligations. Gross Unrealized Losses The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized September 30, 2022 U.S. government obligations 157 $ 22,385.4 $ (1,855.4) 103 $ 16,085.8 $ (1,095.6) 54 $ 6,299.6 $ (759.8) State and local government obligations 353 1,911.0 (215.4) 292 1,363.1 (129.8) 61 547.9 (85.6) Foreign government obligations 1 15.3 (1.4) 1 15.3 (1.4) 0 0 0 Corporate debt securities 452 8,885.6 (832.5) 391 7,875.5 (699.0) 61 1,010.1 (133.5) Residential mortgage-backed securities 44 165.1 (16.5) 34 126.0 (11.8) 10 39.1 (4.7) Commercial mortgage-backed securities 234 5,074.3 (747.4) 182 3,856.0 (425.4) 52 1,218.3 (322.0) Other asset-backed securities 277 4,544.8 (268.9) 217 3,597.1 (183.4) 60 947.7 (85.5) Redeemable preferred stocks 4 48.6 (5.6) 3 37.7 (4.0) 1 10.9 (1.6) Total fixed maturities 1,522 $ 43,030.1 $ (3,943.1) 1,223 $ 32,956.5 $ (2,550.4) 299 $ 10,073.6 $ (1,392.7) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized September 30, 2021 U.S. government obligations 73 $ 13,352.8 $ (95.9) 65 $ 12,152.6 $ (70.1) 8 $ 1,200.2 $ (25.8) State and local government obligations 96 710.3 (6.7) 81 635.9 (4.9) 15 74.4 (1.8) Corporate debt securities 227 1,581.3 (10.5) 225 1,551.5 (10.0) 2 29.8 (0.5) Residential mortgage-backed securities 63 149.3 (0.9) 53 135.1 (0.6) 10 14.2 (0.3) Commercial mortgage-backed securities 70 1,758.8 (20.6) 65 1,543.6 (19.9) 5 215.2 (0.7) Other asset-backed securities 114 1,625.9 (2.8) 109 1,614.2 (2.7) 5 11.7 (0.1) Redeemable preferred stocks 1 11.8 (0.7) 0 0 0 1 11.8 (0.7) Total fixed maturities 644 $ 19,190.2 $ (138.1) 598 $ 17,632.9 $ (108.2) 46 $ 1,557.3 $ (29.9) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized December 31, 2021 U.S. government obligations 92 $ 14,745.8 $ (190.8) 85 $ 13,790.8 $ (158.5) 7 $ 955.0 $ (32.3) State and local government obligations 127 954.2 (14.0) 122 927.3 (13.1) 5 26.9 (0.9) Corporate debt securities 220 3,496.6 (33.4) 219 3,491.7 (33.3) 1 4.9 (0.1) Residential mortgage-backed securities 20 138.6 (0.6) 14 135.4 (0.5) 6 3.2 (0.1) Commercial mortgage-backed securities 168 4,315.4 (64.3) 165 4,295.0 (63.9) 3 20.4 (0.4) Other asset-backed securities 178 3,204.7 (12.4) 176 3,200.6 (12.3) 2 4.1 (0.1) Redeemable preferred stocks 1 12.0 (0.5) 0 0 0 1 12.0 (0.5) Total fixed maturities 806 $ 26,867.3 $ (316.0) 781 $ 25,840.8 $ (281.6) 25 $ 1,026.5 $ (34.4) The increase in the number of securities in an unrealized loss position since both September 30, 2021 and December 31, 2021, was primarily the result of an increase in interest rates. As of September 30, 2022, we had five corporate debt securities that had their credit ratings downgraded during the quarter, with a combined fair value of $99.3 million and an unrealized loss of $23.7 million. A review of the securities in an unrealized loss position indicated that the issuers were current with respect to their interest obligations and that there was no evidence of deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. Allowance For Credit and Uncollectible Losses We are required to measure the amount of potential credit losses for all fixed-maturity securities in an unrealized loss position. We did not record any allowances for credit losses or any write-offs for amounts deemed to be uncollectible during the first nine months of 2022 or 2021, and did not have a material credit loss allowance balance as of September 30, 2022 and 2021, or December 31, 2021. We considered several factors and inputs related to the individual securities as part of our analysis. The methodology and significant inputs used to measure the amount of credit losses in our portfolio included: • current performance indicators on the business model or underlying assets (e.g., delinquency rates, foreclosure rates, and default rates); • credit support (via current levels of subordination); • historical credit ratings; and • updated cash flow expectations based upon these performance indicators. In order to determine the amount of credit loss, if any, we initially reviewed securities in a loss position to determine whether it was likely that we would be required, or intended, to sell any of the securities prior to the recovery of their respective cost bases (which could be maturity). If we were likely to, or intended to, sell prior to a potential recovery, we would write off the unrealized loss. For those securities that we determined we were not likely to, or did not intend to, sell prior to a potential recovery, we calculated the net present value (NPV) of the cash flows expected (i.e., expected recovery value) using the current book yield for each security. The NPV was then compared to the security’s current amortized value to determine if a credit loss existed. In the event that the NPV was below the amortized value, and the amount was determined to be material individually, or in aggregate, a credit loss would be deemed to exist, and either an allowance for credit losses would be created, or if an allowance currently existed, either a recovery of the previous allowance, or an incremental loss, would be recorded to net realized gains (losses) on securities. As of September 30, 2022 and 2021, and December 31, 2021, we believe none of the unrealized losses relate to material credit losses on any specific securities, or in the aggregate. We continue to expect all the securities in our portfolio to pay their principal and interest obligations. In addition, we reviewed our accrued investment income outstanding on those securities in an unrealized loss position at September 30, 2022 and 2021, and December 31, 2021, to determine if the accrued interest amounts were determined to be uncollectible. Based on our analysis, we believe the issuers have sufficient liquidity and capital reserves to meet their current interest, and future principal, obligations and, therefore, did not write off any accrued income as uncollectible at September 30, 2022 and 2021, or December 31, 2021. Realized Gains (Losses) The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2022 2021 2022 2021 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 0 $ 19.6 $ 4.6 $ 97.5 State and local government obligations 0 6.0 0 50.3 Corporate and other debt securities 0.3 23.6 6.8 84.4 Residential mortgage-backed securities 0 0 0.7 0.3 Commercial mortgage-backed securities 0 1.4 0 40.7 Other asset-backed securities 0 0.3 0.1 1.0 Redeemable preferred stocks 0 0 0 1.5 Total available-for-sale securities 0.3 50.9 12.2 275.7 Equity securities: Nonredeemable preferred stocks 0.1 2.3 17.6 26.0 Common equities 1.4 6.2 832.5 352.3 Total equity securities 1.5 8.5 850.1 378.3 Subtotal gross realized gains on security sales 1.8 59.4 862.3 654.0 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations 0 (2.0) (233.5) (28.5) State and local government obligations 0 0 (1.0) (3.0) Corporate and other debt securities (14.0) (0.7) (51.8) (6.1) Residential mortgage-backed securities 0 (0.3) 0 (0.3) Commercial mortgage-backed securities (44.8) (0.5) (58.6) (1.6) Other asset-backed securities 0 0 (2.1) (0.4) Short-term investments 0 0 (0.3) 0 Total available-for-sale securities (58.8) (3.5) (347.3) (39.9) Equity securities: Nonredeemable preferred stocks (5.1) (0.3) (7.0) (0.7) Common equities 0 (1.7) (78.0) (5.6) Total equity securities (5.1) (2.0) (85.0) (6.3) Subtotal gross realized losses on security sales (63.9) (5.5) (432.3) (46.2) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 0 17.6 (228.9) 69.0 State and local government obligations 0 6.0 (1.0) 47.3 Corporate and other debt securities (13.7) 22.9 (45.0) 78.3 Residential mortgage-backed securities 0 (0.3) 0.7 0 Commercial mortgage-backed securities (44.8) 0.9 (58.6) 39.1 Other asset-backed securities 0 0.3 (2.0) 0.6 Redeemable preferred stocks 0 0 0 1.5 Short-term investments 0 0 (0.3) 0 Total available-for-sale securities (58.5) 47.4 (335.1) 235.8 Equity securities: Nonredeemable preferred stocks (5.0) 2.0 10.6 25.3 Common equities 1.4 4.5 754.5 346.7 Total equity securities (3.6) 6.5 765.1 372.0 Subtotal net realized gains (losses) on security sales (62.1) 53.9 430.0 607.8 Net holding period gains (losses) Hybrid securities (11.4) 1.0 (98.8) 0 Equity securities (140.7) (16.9) (2,164.1) 479.8 Subtotal net holding period gains (losses) (152.1) (15.9) (2,262.9) 479.8 Other asset impairment (2.2) (1.2) (6.5) (3.7) Total net realized gains (losses) on securities $ (216.4) $ 36.8 $ (1,839.4) $ 1,083.9 Realized gains (losses) on securities sold are computed using the first-in-first-out method. The loss from the fixed-maturity sales reflected the continued rise in interest rates throughout 2022, which resulted in valuation declines for most of our available-for-sale securities. The majority of the sales in the fixed-maturity portfolio during the first nine months of 2022 were from U.S. Treasuries, which were sold to shorten duration. During the third quarter 2022, we selectively sold securities, which were primarily commercial mortgage-backed securities. During the first nine months of 2022, we sold common equity securities, which were in a realized gain position, as part of our plan to incrementally reduce risk in the portfolio in response to the likelihood of a more difficult economic environment over the near term. The other asset impairment loss was recorded as a result of our investment in a federal new markets tax credit fund, which was entered into during the second quarter 2021, and reported in other assets in the consolidated balance sheets. The following table reflects our holding period realized gains (losses) recognized on equity securities held at the respective quarter ends: Three Months Nine Months (millions) 2022 2021 2022 2021 Total net gains (losses) recognized during the period on equity securities $ (144.3) $ (10.4) $ (1,399.0) $ 851.8 Less: Net gains (losses) recognized on equity securities sold during the period (3.6) 6.5 765.1 372.0 Net holding period gains (losses) recognized during the period on equity securities held at period end $ (140.7) $ (16.9) $ (2,164.1) $ 479.8 Net Investment Income The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2022 2021 2022 2021 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 86.1 $ 39.0 $ 205.4 $ 106.8 State and local government obligations 9.8 9.7 29.3 34.6 Foreign government obligations 0.1 0 0.2 0 Corporate debt securities 71.8 70.2 215.4 228.6 Residential mortgage-backed securities 8.8 3.2 23.2 9.4 Commercial mortgage-backed securities 48.3 35.0 138.1 105.2 Other asset-backed securities 52.1 16.1 116.5 47.1 Redeemable preferred stocks 3.0 2.3 8.5 7.1 Total fixed maturities 280.0 175.5 736.6 538.8 Short-term investments 24.8 0.4 29.6 2.6 Total available-for-sale securities 304.8 175.9 766.2 541.4 Equity securities: Nonredeemable preferred stocks 17.3 17.3 53.6 52.5 Common equities 11.5 15.7 48.4 45.9 Total equity securities 28.8 33.0 102.0 98.4 Investment income 333.6 208.9 868.2 639.8 Investment expenses (5.8) (6.6) (17.4) (18.5) Net investment income $ 327.8 $ 202.3 $ 850.8 $ 621.3 On a year-over-year basis for the three and nine months ended September 30, 2022, investment income (interest and dividends) increased 60% and 36%, respectively, compared to the same periods last year, primarily due to an increase in interest rates on floating-rate securities in our portfolio and purchases of new investments with higher coupon rates. The recurring investment book yield increased 39% for the third quarter 2022 and 16% for the first nine months of 2022, compared to the same periods in 2021, reflecting investing new cash and cash from maturities in higher interest rate securities given the rising interest rate environment.

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2022
Fair Value Disclosures [Abstract]
Fair Value	Fair Value — We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows: • Level 1 : Inputs are unadjusted, quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, which are continually priced on a daily basis, active exchange-traded equity securities, and certain short-term securities). • Level 2 : Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 : Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments). Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations. The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2022 Fixed maturities: U.S. government obligations $ 22,405.5 $ 0 $ 0 $ 22,405.5 $ 24,260.9 State and local government obligations 0 1,925.5 0 1,925.5 2,140.9 Foreign government obligations 0 15.3 0 15.3 16.7 Corporate debt securities 0 9,228.4 0 9,228.4 10,119.8 Subtotal 22,405.5 11,169.2 0 33,574.7 36,538.3 Asset-backed securities: Residential mortgage-backed 0 723.0 0 723.0 754.2 Commercial mortgage-backed 0 5,087.9 0 5,087.9 5,833.9 Other asset-backed 0 4,605.9 0 4,605.9 4,876.7 Subtotal asset-backed securities 0 10,416.8 0 10,416.8 11,464.8 Redeemable preferred stocks: Financials 0 39.8 0 39.8 43.6 Utilities 0 8.8 0 8.8 10.5 Industrials 8.9 124.1 0 133.0 148.5 Subtotal redeemable preferred stocks 8.9 172.7 0 181.6 202.6 Total fixed maturities 22,414.4 21,758.7 0 44,173.1 48,205.7 Short-term investments 4,219.6 18.0 0 4,237.6 4,237.6 Total available-for-sale securities 26,634.0 21,776.7 0 48,410.7 52,443.3 Equity securities: Nonredeemable preferred stocks: Financials 60.9 1,015.6 64.9 1,141.4 1,297.6 Utilities 0 71.3 0 71.3 79.9 Industrials 0 24.7 17.0 41.7 40.1 Subtotal nonredeemable preferred stocks 60.9 1,111.6 81.9 1,254.4 1,417.6 Common equities: Common stocks 2,597.3 49.3 0 2,646.6 785.0 Other risk investments 0 0 18.7 18.7 18.7 Subtotal common equities 2,597.3 49.3 18.7 2,665.3 803.7 Total equity securities 2,658.2 1,160.9 100.6 3,919.7 2,221.3 Total portfolio $ 29,292.2 $ 22,937.6 $ 100.6 $ 52,330.4 $ 54,664.6 Debt $ 0 $ 5,634.7 $ 0 $ 5,634.7 $ 6,387.4 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2021 Fixed maturities: U.S. government obligations $ 21,142.1 $ 0 $ 0 $ 21,142.1 $ 21,093.1 State and local government obligations 0 2,165.9 0 2,165.9 2,123.8 Foreign government obligations 0 12.3 0 12.3 12.3 Corporate debt securities 0 10,861.7 0 10,861.7 10,556.4 Subtotal 21,142.1 13,039.9 0 34,182.0 33,785.6 Asset-backed securities: Residential mortgage-backed 0 627.9 0 627.9 624.4 Commercial mortgage-backed 0 5,789.0 0 5,789.0 5,739.4 Other asset-backed 0 4,262.2 0 4,262.2 4,235.6 Subtotal asset-backed securities 0 10,679.1 0 10,679.1 10,599.4 Redeemable preferred stocks: Financials 0 51.4 0 51.4 50.8 Utilities 0 0 0 0 0 Industrials 10.6 122.6 0 133.2 120.2 Subtotal redeemable preferred stocks 10.6 174.0 0 184.6 171.0 Total fixed maturities 21,152.7 23,893.0 0 45,045.7 44,556.0 Short-term investments 1,078.5 10.2 0 1,088.7 1,088.7 Total available-for-sale securities 22,231.2 23,903.2 0 46,134.4 45,644.7 Equity securities: Nonredeemable preferred stocks: Financials 89.8 1,304.6 76.4 1,470.8 1,399.8 Utilities 0 42.1 0 42.1 40.0 Industrials 0 25.5 34.4 59.9 40.1 Subtotal nonredeemable preferred stocks 89.8 1,372.2 110.8 1,572.8 1,479.9 Common equities: Common stocks 4,513.1 0 54.5 4,567.6 1,225.8 Other risk investments 0 0 12.6 12.6 12.6 Subtotal common equities 4,513.1 0 67.1 4,580.2 1,238.4 Total equity securities 4,602.9 1,372.2 177.9 6,153.0 2,718.3 Total portfolio $ 26,834.1 $ 25,275.4 $ 177.9 $ 52,287.4 $ 48,363.0 Debt $ 0 $ 5,881.7 $ 0 $ 5,881.7 $ 4,898.2 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2021 Fixed maturities: U.S. government obligations $ 18,488.2 $ 0 $ 0 $ 18,488.2 $ 18,586.1 State and local government obligations 0 2,185.3 0 2,185.3 2,162.6 Foreign government obligations 0 17.9 0 17.9 17.9 Corporate debt securities 0 10,692.1 0 10,692.1 10,526.2 Subtotal 18,488.2 12,895.3 0 31,383.5 31,292.8 Asset-backed securities: Residential mortgage-backed 0 790.0 0 790.0 787.7 Commercial mortgage-backed 0 6,535.6 0 6,535.6 6,561.0 Other asset-backed 0 4,982.3 0 4,982.3 4,981.8 Subtotal asset-backed securities 0 12,307.9 0 12,307.9 12,330.5 Redeemable preferred stocks: Financials 0 50.9 0 50.9 50.7 Utilities 0 0 0 0 0 Industrials 10.7 120.1 0 130.8 120.2 Subtotal redeemable preferred stocks 10.7 171.0 0 181.7 170.9 Total fixed maturities 18,498.9 25,374.2 0 43,873.1 43,794.2 Short-term investments 942.4 0.2 0 942.6 942.6 Total available-for-sale securities 19,441.3 25,374.4 0 44,815.7 44,736.8 Equity securities: Nonredeemable preferred stocks: Financials 115.3 1,305.7 76.4 1,497.4 1,451.7 Utilities 0 82.9 0 82.9 80.0 Industrials 0 25.2 34.4 59.6 40.1 Subtotal nonredeemable preferred stocks 115.3 1,413.8 110.8 1,639.9 1,571.8 Common equities: Common stocks 4,991.6 50.0 0 5,041.6 1,247.2 Other risk investments 0 0 16.9 16.9 16.9 Subtotal common equities 4,991.6 50.0 16.9 5,058.5 1,264.1 Total equity securities 5,106.9 1,463.8 127.7 6,698.4 2,835.9 Total portfolio $ 24,548.2 $ 26,838.2 $ 127.7 $ 51,514.1 $ 47,572.7 Debt $ 0 $ 5,857.4 $ 0 $ 5,857.4 $ 4,898.8 Our portfolio valuations, excluding short-term investments, classified as either Level 1 or Level 2 in the above tables are priced exclusively by external sources, including pricing vendors, dealers/market makers, and exchange-quoted prices. Our short-term investments classified as Level 1 are highly liquid, actively marketed, and have a very short duration, primarily 90 days or less to redemption. These securities are held at their original cost, adjusted for any accretion of discount, since that value very closely approximates what an active market participant would be willing to pay for such securities. The remainder of our short-term investments are classified as Level 2 and are not priced externally since these securities continually trade at par value. These securities are classified as Level 2 since they are primarily longer-dated securities issued by municipalities that contain either liquidity facilities or mandatory put features within one year. At September 30, 2022, vendor-quoted prices represented 90% of our Level 1 classifications (excluding short-term investments), compared to 82% and 79% at September 30, 2021 and December 31, 2021, respectively. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded, and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. At both September 30, 2022 and December 31, 2021, vendor-quoted prices comprised 98% of our Level 2 classifications (excluding short-term investments and common stock), while dealer-quoted prices represented the remaining 2%, compared to 97% and 3% at September 30, 2021. In our process for selecting a source (e.g., dealer or pricing service) to provide pricing for securities in our portfolio, we reviewed documentation from the sources that detailed the pricing techniques and methodologies used by these sources and determined if their policies adequately considered market activity, either based on specific transactions for the particular security type or based on modeling of securities with similar credit quality, duration, yield, and structure that were recently transacted. Once a source is chosen, we continue to monitor any changes or modifications to their processes by reviewing their documentation on internal controls for pricing and market reviews. We review quality control measures of our sources as they become available to determine if any significant changes have occurred from period to period that might indicate issues or concerns regarding their evaluation or market coverage. As part of our pricing procedures, we obtain quotes from more than one source to help us fully evaluate the market price of securities. However, our internal pricing policy is to use a consistent source for individual securities in order to maintain the integrity of our valuation process. Quotes obtained from the sources are not considered binding offers to transact. Under our policy, when a review of the valuation received from our selected source appears to be outside of what is considered market level activity (which is defined as trading at spreads or yields significantly different than those of comparable securities or outside the general sector level movement without a reasonable explanation), we may use an alternate source’s price. To the extent we determine that it may be prudent to substitute one source’s price for another, we will contact the initial source to obtain an understanding of the factors that may be contributing to the significant price variance. To allow us to determine if our initial source is providing a price that is outside of a reasonable range, we review our portfolio pricing on a weekly basis. When necessary, we challenge prices from our sources when a price provided does not match our expectations based on our evaluation of market trends and activity. Initially, we perform a review of our portfolio by sector to identify securities whose prices appear outside of a reasonable range. We then perform a more detailed review of fair values for securities disclosed as Level 2. We review dealer bids and quotes for these and/or similar securities to determine the market level context for our valuations. We then evaluate inputs relevant for each class of securities disclosed in the preceding hierarchy tables. For structured debt securities, including commercial, residential, and other asset-backed securities, we evaluate available market-related data for these and similar securities related to collateral, delinquencies, and defaults for historical trends and reasonably estimable projections, as well as historical prepayment rates and current prepayment assumptions and cash flow estimates. We further stratify each class of our structured debt securities into more finite sectors (e.g., planned amortization class, first pay, second pay, senior, subordinated, etc.) and use duration, credit quality, and coupon to determine if the fair value is appropriate. For corporate debt and preferred stock (redeemable and nonredeemable) portfolios, as well as the notes issued by The Progressive Corporation (see Note 4 – Debt ), we review securities by duration, coupon, and credit quality, as well as changes in interest rate and credit spread movements within that stratification. The review also includes recent trades, including: volume traded at various levels that establish a market; issuer specific fundamentals; and industry specific economic news as it comes to light. For municipal securities (e.g., general obligations, revenue, and housing), we stratify the portfolio to evaluate securities by type, coupon, credit quality, and duration to review price changes relative to credit spread and interest rate changes. Additionally, we look to economic data as it relates to geographic location as an indication of price-to-call or maturity predictors. For municipal housing securities, we look to changes in cash flow projections, both historical and reasonably estimable projections, to understand yield changes and their effect on valuation. For short-term securities, we look at acquisition price relative to the coupon or yield. Since our short-term securities are typically 90 days or less to maturity, with the majority listed in Level 2 being 30 days or less to redemption, we believe that acquisition price is the best estimate of fair value. We also review data assumptions as supplied by our sources to determine if that data is relevant to current market conditions. In addition, we independently review each sector for transaction volumes, new issuances, and changes in spreads, as well as the overall movement of interest rates along the yield curve to determine if sufficient activity and liquidity exists to provide a credible source for our market valuations. During each valuation period, we create internal estimations of portfolio valuation (performance returns), based on current market-related activity (i.e., interest rate and credit spread movements and other credit-related factors) within each major sector of our portfolio. We compare our internally generated portfolio results with those generated based on quotes we receive externally and research material valuation differences. We compare our results to index returns for each major sector adjusting for duration and credit quality differences to better understand our portfolio’s results. Additionally, we review on a monthly basis our external sales transactions and compare the actual final market sales prices to previous market valuation prices. This review provides us further validation that our pricing sources are providing market level prices, since we are able to explain significant price changes (i.e., greater than 2%) as known events occur in the marketplace and affect a particular security’s price at sale. This analysis provides us with additional comfort regarding the source’s process, the quality of its review, and its willingness to improve its analysis based on feedback from clients. We believe this effort helps ensure that we are reporting the most representative fair values for our securities. After all the valuations are received and our review of Level 2 securities is complete, if the inputs used by vendors are determined to not contain sufficient observable market information, we will reclassify the affected securities to Level 3. Except as described below, our Level 3 securities are priced externally; however, due to several factors (e.g., nature of the securities, level of activity, and lack of similar securities trading to obtain observable market level inputs), these valuations are more subjective in nature. To the extent we receive prices from external sources (e.g., broker, valuation firm) for the Level 3 securities, we review those prices for reasonableness using internally developed assumptions and then compare our derived prices to the prices received from the external sources. Based on our review, all prices received from external sources remained unadjusted. If we do not receive prices from an external source, we perform an internal fair value comparison, which includes a review and analysis of market-comparable securities, to determine if fair value changes are needed. Based on this analysis, certain private equity investments included in the Level 3 category remain valued at cost or were priced using a recent transaction as the basis for fair value. At least annually, these private equity investments are priced by an external source. Our Level 3 other risk investments include securities accounted for under the equity method of accounting and, therefore, are not subject to fair value reporting. Since these securities represent less than 0.1% of our total portfolio, we will continue to include them in our Level 3 disclosures and report the activity from these investments as “other” changes in the summary of changes in fair value table and categorize these securities as “pricing exemption securities” in the quantitative information table. The Level 3 common stock held at September 30, 2021 was transferred to Level 2 at December 31, 2021. At September 30, 2022 and 2021, and December 31, 2021, we did not have any securities in our fixed-maturity portfolio listed as Level 3. Other than goodwill, during the third quarter and first nine months of 2022 and 2021, there were no material assets or liabilities measured at fair value on a nonrecurring basis. During the second quarter 2022, we determined that the fair value of the goodwill related to our ARX Holding Corp. ( ARX) reporting unit was less than the carrying value and we wrote down $224.8 million of our total goodwill asset. See Note 12 – Goodwill and Intangible Assets for further discussion. Due to the relative size of the Level 3 securities’ fair values compared to the total portfolio’s fair value, any changes in pricing methodology would not have a significant change in valuation that would materially impact net or comprehensive income. The following tables provide a summary of changes in fair value associated with Level 3 assets for the three and nine months ended September 30, 2022 and 2021: Level 3 Fair Value (millions) Fair Value at June 30, 2022 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2022 Equity securities: Nonredeemable preferred stocks: Financials $ 64.9 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 64.9 Industrials 17.0 0 0 0 0 0 0 17.0 Common equities: Other risk investments 18.5 0.2 0 0 0 0 0 18.7 Total Level 3 securities $ 100.4 $ 0.2 $ 0 $ 0 $ 0 $ 0 $ 0 $ 100.6 Level 3 Fair Value (millions) Fair Value at June 30, 2021 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2021 Equity securities: Nonredeemable preferred stocks: Financials $ 76.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 76.4 Industrials 34.4 0 0 0 0 0 0 34.4 Common equities: Common stocks 52.5 0 2.0 0 0 0 0 54.5 Other risk investments 11.6 1.0 0 0 0 0 0 12.6 Total Level 3 securities $ 174.9 $ 1.0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 177.9 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2021 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2022 Equity securities: Nonredeemable preferred stocks: Financials $ 76.4 $ 0 $ 0 $ (15.0) $ (17.2) $ 20.7 $ 0 $ 64.9 Industrials 34.4 (0.5) 0 0 0 (16.9) 0 17.0 Common equities: Other risk investments 16.9 1.8 0 0 0 0 0 18.7 Total Level 3 securities $ 127.7 $ 1.3 $ 0 $ (15.0) $ (17.2) $ 3.8 $ 0 $ 100.6 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2020 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2021 Equity securities: Nonredeemable preferred stocks: Financials $ 10.0 $ 0 $ 60.2 $ 0 $ 0 $ 6.2 $ 0 $ 76.4 Industrials 16.7 0 5.0 (5.0) (4.5) 22.2 0 34.4 Common equities: Common stocks 25.0 0 2.0 0 0 27.5 0 54.5 Other risk investments 3.1 9.5 0 0 0 0 0 12.6 Total Level 3 securities $ 54.8 $ 9.5 $ 67.2 $ (5.0) $ (4.5) $ 55.9 $ 0 $ 177.9 The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2022 and 2021, and December 31, 2021: Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2022 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 81.9 Market comparables Weighted average market capitalization price change % (20.7)% to (1.1)% (6.6) % Subtotal Level 3 securities 81.9 Pricing exemption securities 18.7 Total Level 3 securities $ 100.6 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2021 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 110.8 Market comparables Weighted average market capitalization price change % (8.5)% to 19.8% 6.5 % Common stocks 54.5 Market comparables Weighted average market capitalization price change % (1.6)% to 55.8% 0.9 % Subtotal Level 3 securities 165.3 Pricing exemption securities 12.6 Total Level 3 securities $ 177.9 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2021 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 110.8 Market comparables Weighted average market capitalization price change % (20.2)% to (2.3)% (7.7)% Subtotal Level 3 securities 110.8 Pricing exemption securities 16.9 Total Level 3 securities $ 127.7

Debt

Debt	9 Months Ended
	Sep. 30, 2022
Debt Disclosure [Abstract]
Debt	Debt — Debt at each of the balance sheet periods consisted of: September 30, 2022 September 30, 2021 December 31, 2021 (millions) Carrying Fair Carrying Fair Carrying Fair 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) $ 498.1 $ 459.7 $ 497.6 $ 530.6 $ 497.7 $ 517.9 2.50% Senior Notes due 2027 (issued: $500.0, March 2022) 497.4 451.6 0 0 0 0 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 297.4 322.1 297.1 390.9 297.2 388.2 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 546.3 519.5 545.8 627.9 545.9 621.0 3.20% Senior Notes due 2030 (issued: $500.0, March 2020) 496.8 439.3 496.4 543.2 496.5 536.3 3.00% Senior Notes due 2032 (issued: $500.0, March 2022) 495.8 418.8 0 0 0 0 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 396.4 426.0 396.1 545.5 396.2 547.9 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.9 298.5 346.8 433.6 346.8 428.4 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.7 305.7 395.6 456.2 395.6 447.1 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 842.0 710.3 841.9 1,018.5 841.9 1,029.3 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 590.3 505.9 590.2 736.3 590.2 741.3 3.95% Senior Notes due 2050 (issued: $500.0, March 2020) 490.9 396.6 490.7 599.0 490.8 600.0 3.70% Senior Notes due 2052 (issued: $500.0, March 2022) 493.4 380.7 0 0 0 0 Total $ 6,387.4 $ 5,634.7 $ 4,898.2 $ 5,881.7 $ 4,898.8 $ 5,857.4 The Progressive Corporation issued $500 million of 2.50% Senior Notes due 2027, $500 million of 3.00% Senior Notes due 2032, and $500 million of 3.70% Senior Notes due 2052 in March 2022, in an underwritten public offering. The net proceeds from the issuances, after deducting underwriters’ discounts, commissions, and other issuance costs, were approximately $1,486.0 million in aggregate. Consistent with the other senior notes issued by Progressive, interest on these notes is payable semiannually, principal is due at maturity, and the notes are redeemable, in whole or in part, at any time, subject to a treasury “make whole” provision. There was no short-term debt outstanding at September 30, 2022 and 2021, and December 31, 2021. The Progressive Corporation has a line of credit with PNC Bank, National Association (PNC), in the maximum principal amount of $250 million, which has the same terms as the line of credit with PNC that expired in April 2022. See the 2021 Annual Report to Shareholders for a discussion of the terms of this line of credit. We had no borrowings under the line of credit during the periods presented.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes — Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. We review our deferred tax assets regularly for recoverability. At September 30, 2022 and 2021, and December 31, 2021, we determined that we did not need a valuation allowance on our gross deferred tax assets. Although realization of the deferred tax assets is not assured, management believes that it is more likely than not the deferred tax assets will be realized based on our expectation that we will be able to fully utilize the deductions that are ultimately recognized for tax purposes. For the nine months ended September 30, 2022, there have been no material changes in our reserve for uncertain tax positions. The effective tax rate for the three and nine months ended September 30, 2022, was 12.9% and (1.6)%, respectively, compared to 14.7% and 20.5% for the same periods last year. The difference between our effective tax rate and the statutory rate, for the three months ended September 30, 2022 and 2021, and the nine months ended September 30, 2022, is primarily driven by the low amount of income (loss) before taxes during those periods. The provision for income taxes differed from the statutory rate as follows: Three Months Ended September 30, Nine Months Ended September 30, ($ in millions) 2022 2021 2022 2021 Income (loss) before income taxes $ 142.5 $ 139.0 $ (103.2) $ 3,006.1 Tax at statutory federal rate $ 29.9 21.0 % $ 29.2 21.0 % $ (21.7) 21.0 % $ 631.3 21.0 % Tax effect of: Goodwill impairment 0 0 0 0 47.2 (45.7) 0 0 Stock-based compensation (9.6) (6.7) (7.9) (5.7) (17.7) 17.2 (19.2) (0.6) State income taxes, net of federal taxes 4.5 3.2 5.5 4.0 9.7 (9.4) 17.7 0.6 Tax-preferenced investment income (2.8) (2.0) (3.3) (2.4) (9.5) 9.2 (10.0) (0.3) Tax credits (5.2) (3.6) (3.7) (2.7) (9.4) 9.1 (6.1) (0.2) Nondeductible compensation expense 1.8 1.3 1.9 1.4 5.4 (5.2) 5.6 0.2 Tax deductible dividends (0.4) (0.3) (0.5) (0.4) (1.4) 1.4 (1.6) (0.1) Other items, net 0.2 0 (0.7) (0.5) (0.9) 0.8 (0.2) (0.1) Total income tax provision $ 18.4 12.9 % $ 20.5 14.7 % $ 1.7 (1.6) % $ 617.5 20.5 %

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	9 Months Ended
	Sep. 30, 2022
Loss and Loss Adjustment Expenses Reserves [Abstract]
Loss and Loss Adjustment Expenses Reserves	Loss and Loss Adjustment Expense Reserves — Activity in the loss and loss adjustment expense reserves is summarized as follows: September 30, (millions) 2022 2021 Balance at January 1 $ 26,164.1 $ 20,265.8 Less reinsurance recoverables on unpaid losses 4,733.6 3,798.2 Net balance at January 1 21,430.5 16,467.6 Net loss and loss adjustment expense reserves acquired 1 0 732.5 Total beginning reserves 21,430.5 17,200.1 Incurred related to: Current year 28,245.4 24,610.8 Prior years 52.8 156.8 Total incurred 28,298.2 24,767.6 Paid related to: Current year 15,712.4 13,650.6 Prior years 9,418.5 7,213.3 Total paid 25,130.9 20,863.9 Net balance at September 30 24,597.8 21,103.8 Plus reinsurance recoverables on unpaid losses 6,034.0 4,822.5 Balance at September 30 $ 30,631.8 $ 25,926.3 1 Net reserves acquired in the Protective Insurance acquisition. We experienced unfavorable reserve development of $52.8 million and $156.8 million during the first nine months of 2022 and 2021, respectively, which is reflected as “incurred related to prior years ” in the table above. Year-to-date September 30, 2022 • The unfavorable prior year reserve development included approximately $45 million attributable to accident year 2021 and $29 million to 2019 and prior accident years, partially offset by $21 million favorable development attributable to accident year 2020. • Our personal auto products incurred about $28 million of favorable loss and loss adjustment expense (LAE) reserve development, with about $25 million attributable to the Direct business. The favorable development was primarily attributable to more subrogation and salvage recoveries and lower loss adjustment expenses than originally anticipated, partially offset by higher than anticipated severity and frequency of auto property damage payments on previously closed claims and late reported injury claims. • Our Commercial Lines business experienced about $77 million of unfavorable development, primarily due to higher than anticipated severity of injury case reserves and higher than anticipated severity and frequency of late reported claims in our transportation network company business. • Our Property business experienced minimal unfavorable prior accident year development, which was almost completely offset by minimal favorable development in our special lines products. Year-to-date September 30, 2021 • The unfavorable prior year reserve development included $109 million attributable to accident year 2019 and $113 million to 2018 and prior accident years, partially offset by favorable development attributable to accident year 2020. • Our personal auto products incurred $48 million of unfavorable loss and LAE reserve development, with about $44 million attributable to the Agency business. The unfavorable development was primarily attributable to a higher than anticipated frequency of reopened personal injury protection claims, primarily in Florida, and higher than anticipated bodily injury severity, partially offset by less late reported claims than anticipated for accident year 2020 and lower adjusting expenses than anticipated. • Our Commercial Lines business experienced $91 million of unfavorable development, primarily due to increased injury severity and the emergence of large injury claims, at rates higher than originally anticipated, primarily in Texas and Florida. • Our Property business experienced $31 million of unfavorable development, primarily due to higher than anticipated severity and reopened claims activity in Florida. • Our special lines products experienced about $12 million of favorable development.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2022
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information — Cash and cash equivalents include bank demand deposits and daily overnight reverse repurchase commitments of funds held in bank demand deposit accounts by certain subsidiaries. The amount of reverse repurchase commitments, which are not considered part of the investment portfolio, held by these subsidiaries at September 30, 2022 and 2021, and December 31, 2021, were $123.0 million, $134.6 million, and $137.1 million, respectively. Restricted cash and cash equivalents include collateral held against unpaid deductibles and cash that is restricted to pay flood claims under the National Flood Insurance Program’s “Write Your Own” program, for which certain subsidiaries are administrators. Non-cash activity included the following in the respective periods: Nine Months Ended September 30, (millions) 2022 2021 Common share dividends 1 $ 58.5 $ 58.5 Operating lease liabilities 2 29.7 79.5 1 Declared but unpaid. See Note 9 – Dividends for further discussion. 2 From obtaining right-of-use assets. We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2022 2021 Income taxes $ 595.9 $ 669.5 Interest 191.3 186.3 Operating lease liabilities 62.5 67.8

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2022
Segment Reporting [Abstract]
Segment Information	Segment Information — Our Personal Lines segment writes insurance for personal autos and recreational vehicles (our special lines products). Our Commercial Lines segment writes auto-related liability and physical damage insurance, workers’ compensation insurance primarily for the transportation industry, and business-related general liability and property insurance, predominately for small businesses. Our Property segment writes residential property insurance for homeowners, other property owners, and renters. Our service businesses provide insurance-related services, including processing Commercial Automobile Insurance Procedures/Plans (CAIP) business and serving as an agent for homeowners, general liability, and workers’ compensation insurance, among other products, through programs in our direct Personal Lines and Commercial Lines businesses. As previously discussed in our Annual Report on Form 10-K for the year ended December 31, 2021, during the third quarter 2022, our CAIP service contract expired and we did not renew the contract. This non-renewal will not materially affect our financial condition, results of operations, or cash flows. All segment revenues are generated from external customers; all intercompany transactions are eliminated in consolidation. Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 (millions) Revenues Pretax Revenues Pretax Revenues Pretax Revenues Pretax Personal Lines Agency $ 4,441.9 $ (41.3) $ 4,267.9 $ 41.0 $ 13,131.7 $ 507.6 $ 12,586.4 $ 796.0 Direct 5,077.4 40.6 4,690.2 (62.4) 14,776.9 389.4 13,755.8 480.6 Total Personal Lines 1 9,519.3 (0.7) 8,958.1 (21.4) 27,908.6 897.0 26,342.2 1,276.6 Commercial Lines 2,317.9 238.1 1,877.4 197.5 6,749.5 683.5 4,917.0 556.1 Property 2 561.0 (141.0) 526.5 (222.7) 1,689.6 (289.6) 1,501.3 (376.7) Other indemnity 3 0.7 (2.1) 2.8 (0.3) 2.0 (9.3) 6.8 (0.2) Total underwriting operations 12,398.9 94.3 11,364.8 (46.9) 36,349.7 1,281.6 32,767.3 1,455.8 Fees and other revenues 4 181.4 NA 174.9 NA 531.9 NA 516.8 NA Service businesses 82.7 (0.1) 73.8 1.0 230.5 9.0 202.1 12.1 Investments 5 117.2 111.4 245.7 239.1 (971.2) (988.6) 1,723.7 1,705.2 Interest expense NA (63.1) NA (54.2) NA (180.4) NA (167.0) Property - Goodwill impairment 2 NA 0 NA 0 NA (224.8) NA 0 Consolidated total $ 12,780.2 $ 142.5 $ 11,859.2 $ 139.0 $ 36,140.9 $ (103.2) $ 35,209.9 $ 3,006.1 NA = Not applicable 1 Personal auto products accounted for 94% of the total Personal Lines segment net premiums earned during the three and nine months ended September 30, 2022 and 2021; our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 The total pretax loss, including goodwill impairment, for the Property segment was $514.4 million for the nine months ended September 30, 2022. For the three and nine months ended September 30, 2022, pretax profit (loss) also included $5.0 million and $24.1 million, respectively, of amortization expense associated with acquisition-related intangible assets attributable to our Property segment, and $14.2 million and $42.5 million for the same periods in 2021. See Note 12 – Goodwill and Intangible Assets for further discussion. 3 Primarily includes run-off business operations. 4 Pretax profit (loss) for fees and other revenues is allocated to operating segments. 5 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit (loss) is net of investment expense. Our management uses underwriting margin and combined ratio as primary measures of underwriting profitability. The underwriting margin is the pretax underwriting profit (loss) expressed as a percentage of net premiums earned (i.e., revenues from underwriting operations). Pretax underwriting profit (loss) is calculated as net premiums earned plus fees and other revenues, less: (i) losses and loss adjustment expenses; (ii) policy acquisition costs; and (iii) other underwriting expenses. Combined ratio is the complement of the underwriting margin. Following are the underwriting margins and combined ratios for our underwriting operations for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 Under-writing Combined Under-writing Combined Under-writing Combined Under-writing Combined Personal Lines Agency (0.9) % 100.9 1.0 % 99.0 3.9 % 96.1 6.3 % 93.7 Direct 0.8 99.2 (1.3) 101.3 2.6 97.4 3.5 96.5 Total Personal Lines 0 100.0 (0.2) 100.2 3.2 96.8 4.9 95.1 Commercial Lines 10.3 89.7 10.5 89.5 10.1 89.9 11.3 88.7 Property 1 (25.1) 125.1 (42.3) 142.3 (17.1) 117.1 (25.1) 125.1 Total underwriting operations 0.8 99.2 (0.4) 100.4 3.5 96.5 4.4 95.6 1 Included in the three and nine months ended September 30, 2022, is 0.9 points and 1.4 points, respectively, of amortization expense associated with intangible assets and 2.7 points and 2.8 points, respectively, for the same periods in 2021.

Dividends

Dividends	9 Months Ended
	Sep. 30, 2022
Dividends [Abstract]
Dividends	Dividends — Following is a summary of our common and preferred share dividends that were declared and/or paid during the nine months ended September 30, 2022 and 2021: (millions, except per share amounts) Amount Declared Payable Per Share Accrued/Paid 1 Common - Quarterly Dividends: August 2022 October 2022 $ 0.10 $ 58.5 May 2022 July 2022 0.10 58.5 March 2022 April 2022 0.10 58.5 December 2021 January 2022 0.10 58.5 August 2021 October 2021 0.10 58.5 May 2021 July 2021 0.10 58.5 March 2021 April 2021 0.10 58.5 December 2020 January 2021 0.10 58.6 Common - Annual Variable Dividends: December 2020 January 2021 4.50 2,635.9 Preferred Dividends: August 2022 September 2022 26.875 13.4 December 2021 March 2022 26.875 13.4 August 2021 September 2021 26.875 13.4 December 2020 March 2021 26.875 13.4 1 The common share dividend accrual is based on an estimate of common shares outstanding as of the record date and all accruals are recorded as a part of accounts payable, accrued expenses, and other liabilities on the consolidated balance sheets until paid. See Note 14 – Dividends in our 2021 Annual Report to Shareholders for a discussion of our quarterly and annual common share dividends and our preferred share dividend policies, including a discussion of the $1.50 per common share, or $876.5 million in the aggregate, 2021 annual variable common share dividend that was declared and paid in the fourth quarter 2021.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2022
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) — The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net unrealized gains (losses) on securities Net unrealized losses on forecasted transactions Foreign Balance at June 30, 2022 $ (2,795.5) $ 586.5 $ (2,209.0) $ (2,193.5) $ (14.7) $ (0.8) Other comprehensive income (loss) before reclassifications: Investment securities (1,223.3) 256.9 (966.4) (966.4) 0 0 Foreign currency translation adjustment (0.9) 0.2 (0.7) 0 0 (0.7) Total other comprehensive income (loss) before reclassifications (1,224.2) 257.1 (967.1) (966.4) 0 (0.7) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (58.4) 12.3 (46.1) (46.1) 0 0 Interest expense (0.2) 0.1 (0.1) 0 (0.1) 0 Total reclassification adjustment for amounts realized in net income (58.6) 12.4 (46.2) (46.1) (0.1) 0 Total other comprehensive income (loss) (1,165.6) 244.7 (920.9) (920.3) 0.1 (0.7) Balance at September 30, 2022 $ (3,961.1) $ 831.2 $ (3,129.9) $ (3,113.8) $ (14.6) $ (1.5) Components of Changes in (millions) Pretax total Total tax After tax total Total net unrealized gains (losses) on securities Net unrealized losses on forecasted transactions Foreign Balance at June 30, 2021 $ 619.6 $ (136.4) $ 483.2 $ 498.8 $ (15.1) $ (0.5) Other comprehensive income (loss) before reclassifications: Investment securities (117.9) 24.8 (93.1) (93.1) 0 0 Foreign currency translation adjustment (0.3) 0.1 (0.2) 0 0 (0.2) Total other comprehensive income (loss) before reclassifications (118.2) 24.9 (93.3) (93.1) 0 (0.2) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 46.4 (9.7) 36.7 36.7 0 0 Interest expense (0.2) 0.1 (0.1) 0 (0.1) 0 Total reclassification adjustment for amounts realized in net income 46.2 (9.6) 36.6 36.7 (0.1) 0 Total other comprehensive income (loss) (164.4) 34.5 (129.9) (129.8) 0.1 (0.2) Balance at September 30, 2021 $ 455.2 $ (101.9) $ 353.3 $ 369.0 $ (15.0) $ (0.7) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized losses on forecasted transactions Foreign Balance at December 31, 2021 $ 52.3 $ (11.6) $ 40.7 $ 56.2 $ (14.9) $ (0.6) Other comprehensive income (loss) before reclassifications: Investment securities (4,321.7) 907.6 (3,414.1) (3,414.1) 0 0 Foreign currency translation adjustment (1.1) 0.2 (0.9) 0 0 (0.9) Total other comprehensive income (loss) before reclassifications (4,322.8) 907.8 (3,415.0) (3,414.1) 0 (0.9) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (309.0) 64.9 (244.1) (244.1) 0 0 Interest expense (0.4) 0.1 (0.3) 0 (0.3) 0 Total reclassification adjustment for amounts realized in net income (309.4) 65.0 (244.4) (244.1) (0.3) 0 Total other comprehensive income (loss) (4,013.4) 842.8 (3,170.6) (3,170.0) 0.3 (0.9) Balance at September 30, 2022 $ (3,961.1) $ 831.2 $ (3,129.9) $ (3,113.8) $ (14.6) $ (1.5) Components of Changes in (millions) Pretax total Total tax After tax total Total net unrealized gains (losses) on securities Net unrealized losses on forecasted transactions Foreign Balance at December 31, 2020 $ 1,187.4 $ (255.7) $ 931.7 $ 947.3 $ (15.6) $ 0 Other comprehensive income (loss) before reclassifications: Investment securities (494.6) 103.9 (390.7) (390.7) 0 0 Foreign currency translation adjustment (0.9) 0.2 (0.7) 0 0 (0.7) Total other comprehensive income (loss) before reclassifications (495.5) 104.1 (391.4) (390.7) 0 (0.7) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 237.5 (49.9) 187.6 187.6 0 0 Interest expense (0.8) 0.2 (0.6) 0 (0.6) 0 Total reclassification adjustment for amounts realized in net income 236.7 (49.7) 187.0 187.6 (0.6) 0 Total other comprehensive income (loss) (732.2) 153.8 (578.4) (578.3) 0.6 (0.7) Balance at September 30, 2021 $ 455.2 $ (101.9) $ 353.3 $ 369.0 $ (15.0) $ (0.7) In an effort to manage interest rate risk, we entered into forecasted transactions on certain of Progressive’s debt issuances. We expect to reclassify $0.5 million (pretax) into interest expense during the next 12 months, related to net unrealized losses on these forecasted transactions (see Note 4 – Debt in our 2021 Annual Report to Shareholders for further discussion).

Litigation

Litigation	9 Months Ended
	Sep. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Litigation	Litigation — The Progressive Corporation and/or its insurance subsidiaries are named as defendants in various lawsuits arising out of claims made under insurance policies written by our insurance subsidiaries in the ordinary course of business. We consider all legal actions relating to such claims in establishing our loss and loss adjustment expense reserves. In addition, The Progressive Corporation and/or its subsidiaries are named as defendants in a number of class action or individual lawsuits that challenge certain of the operations of the subsidiaries. These cases include and/or typically have included those alleging damages as a result of, among other things: our subsidiaries’ methods used for evaluating and paying medical or injury claims or benefits, including, but not limited to, certain bodily injury, personal injury protection, uninsured motorist/underinsured motorist (UM/UIM), and medical payment claims and for reimbursing medical costs incurred by Medicare/Medicaid beneficiaries; other claims handling procedures, including, but not limited to, challenges relating to our network of repair facilities, our methods used for estimating physical damage to vehicles for repair purposes and for evaluating the actual cash value of total loss vehicles, our payment of fees and taxes, our subrogation practices, our salvage practices, and our handling of diminution of value claims; homeowner claims handling practices and procedures; our assessment of fees related to insufficient funds or reversed payments; interpretations of the provisions of our insurance policies; our insurance product design; certain of our premium actions, including those in response to the COVID-19 pandemic; rating practices; certain marketing, sales, services, implementation and renewal practices and procedures, including with respect to accessibility; our usage-based insurance program; certain relationships with independent insurance agents; patent matters; alleged violation of the Telephone Consumer Protection Act; commercial disputes, including breach of contract; and certain employment practices, including claims relating to pay practices and fair employment practices, among other matters. Other insurance companies face many of these same issues. The nature and volume of litigation pending against The Progressive Corporation and/or its insurance subsidiaries is similar to that which was disclosed in Note 12 – Litigation in our 2021 Annual Report to Shareholders. We plan to contest the pending lawsuits vigorously, but may pursue settlement negotiations in some cases, as we deem appropriate. Although outcomes of pending cases are uncertain until final disposition, we establish accruals for these lawsuits when it is probable that a loss has been or will be incurred and we can reasonably estimate potential loss exposure, which may include a range of loss. As to lawsuits for which the loss is considered neither probable nor estimable, or is considered probable but not estimable, we do not establish an accrual. Nevertheless, we continue to evaluate pending litigation to determine if any losses not deemed probable and estimable become so, at which point we would establish an accrual at our best estimate of the loss or range of loss. With respect to our pending lawsuits that are not related to claims under insurance policies, the accruals that we have established, if any, were not material at September 30, 2022 and 2021, or December 31, 2021, and there were no material settlements during 2021 or the first nine months of 2022. For most of these lawsuits, we do not consider any losses to be both probable and estimable, and we are unable to estimate a meaningful range of loss, if any, at this time, due to the factors discussed in Note 12 – Litigation in our 2021 Annual Report to Shareholders. In the event that any one or more of these lawsuits results in a substantial judgment against us, or settlement by us, or if our accruals (if any) prove to be inadequate by a significant amount, the resulting liability could have a material adverse effect on our consolidated financial condition, cash flows, and/or results of operations. For a further discussion on our pending litigation and related reserving policies, see Note 12 – Litigation in our 2021 Annual Report to Shareholders.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill The majority of the goodwill recorded as of September 30, 2022 and 2021, and December 31, 2021, related to the April 1, 2015, acquisition of a controlling interest in ARX. In the second quarter 2022, we performed an interim impairment test of our goodwill allocated to the ARX reporting unit and recorded an impairment loss of $224.8 million, which is disclosed as a separate line item in our consolidated statements of comprehensive income. The impairment loss was fully allocated to our Property segment. There were no previously recorded goodwill impairment losses on any of the outstanding goodwill. The indicators of impairment primarily related to the magnitude of recent weather events relative to forecasted expectations, as well as other factors impacting our plans to restore our Property business to target profitability in a timely fashion and the subsequent reduced forecasted profitability of ARX. The quantitative goodwill impairment assessment consisted of comparing the fair value of the reporting unit to its carrying value. To determine the fair value of a reporting unit, we use a discounted cash flow model. The model uses assumptions including, but not limited to, discount rate, forecasted growth, profitability, investment return, and capital requirements. The assumptions and estimates were consistent with those we believe other non-related marketplace participants would use and were based on management’s best estimates at the time of the analysis. The calculated fair value of the ARX reporting unit was below its carrying value at June 30, 2022, which resulted in recording the goodwill impairment. There was no indication of impairment on the remaining $227.9 million goodwill, of which 98% was attributable to our Personal Lines Agency business and related to the ARX acquisition. Intangible Assets The following table is a summary of the net carrying amount of other intangible assets: (millions) September 30, 2022 September 30, 2021 December 31, 2021 Intangible assets subject to amortization $ 79.4 $ 119.5 $ 104.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 91.8 $ 131.9 $ 117.3 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for all periods presented. Intangible assets subject to amortization consisted of the following: (millions) September 30, 2022 September 30, 2021 December 31, 2021 Category Gross Accumulated Net Gross Accumulated Net Gross Accumulated Net Policies in force $ 0 $ 0 $ 0 $ 256.2 $ 237.9 $ 18.3 $ 256.2 $ 247.1 $ 9.1 Agency relationships 159.2 85.3 73.9 159.2 73.9 85.3 159.2 76.8 82.4 Software rights 69.1 64.8 4.3 69.1 56.2 12.9 69.1 58.3 10.8 Trade name 3.6 2.4 1.2 3.6 0.6 3.0 3.6 1.0 2.6 Total $ 231.9 $ 152.5 $ 79.4 $ 488.1 $ 368.6 $ 119.5 $ 488.1 $ 383.2 $ 104.9 Amortization expense was $5.4 million and $25.5 million for the three and nine months ended September 30, 2022, respectively, compared to $14.6 million and $43.1 million during the same periods last year. During the first quarter 2022, the policies in force intangible asset, with a gross carrying value of $256.2 million, was fully amortized.

New Accounting Standards

New Accounting Standards	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
New Accounting Standards	New Accounting Standards — We did not adopt any new accounting standards during the nine months ended September 30, 2022. We assessed the adoption impacts of recently issued accounting standards by the Financial Accounting Standards Board on our consolidated financial statements as well as material updates to previous assessments, if any, from our Annual Report on Form 10-K for the fiscal year ended December 31, 2021. There were no new material accounting standards issued in the nine months ended September 30, 2022, that are expected to impact The Progressive Corporation or its subsidiaries.

Basis of Presentation (Policies

Basis of Presentation (Policies)	9 Months Ended
	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible AssetsWe evaluate goodwill for impairment using a qualitative or quantitative approach annually and when changes in circumstances indicate the carrying value of certain portions of goodwill may not be recoverable.
Earnings Per Common Share	Earnings per Common Share When a net loss is reported, earnings per common share are calculated using basic average equivalent shares since diluted earnings per share would be antidilutive given the net loss reported for the period. Amounts are reported on a diluted basis for all other periods presented.

Basis of Presentation (Tables)

Basis of Presentation (Tables)	9 Months Ended
	Sep. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table summarizes changes in our allowance for credit loss exposure on our premiums receivable: Three Months Ended September 30, Nine Months Ended September 30, (millions) 2022 2021 2022 2021 Allowance for credit losses, beginning of period $ 265.8 $ 245.2 $ 280.4 $ 356.2 Allowance acquired during period 1 0 0 0 3.5 Increase in allowance 2 130.9 107.2 320.6 255.5 Write-offs 3 (101.7) (95.1) (306.0) (357.9) Allowance for credit losses, end of period $ 295.0 $ 257.3 $ 295.0 $ 257.3 1 Represents the amount of the allowance acquired in the Protective Insurance Corporation and subsidiaries (Protective Insurance) acquisition. 2 Represents the incremental increase in other underwriting expenses. 3 Represents portion of allowance that is reversed when premiums receivable are written off. Premiums receivable balances are written off once we have exhausted our collection efforts.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Schedule of Debt and Equity Securities Reconciliation	Investments — The following tables present the composition of our investment portfolio by major security type. Our securities are reported in our consolidated balance sheets at fair value. The changes in fair value for our fixed-maturity securities (other than hybrid securities) are reported as a component of accumulated other comprehensive income (loss), net of deferred income taxes, in our consolidated balance sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value of the securities. The changes in the net holding period gains (losses) between periods for the hybrid securities and equity securities are recorded as a component of net realized gains (losses) on securities in our consolidated statements of comprehensive income. ($ in millions) Cost Gross Gross Net Fair % of September 30, 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 24,260.9 $ 0 $ (1,855.4) $ 0 $ 22,405.5 42.8 % State and local government obligations 2,140.9 0 (215.4) 0 1,925.5 3.7 Foreign government obligations 16.7 0 (1.4) 0 15.3 0.1 Corporate debt securities 10,119.8 0 (832.5) (58.9) 9,228.4 17.6 Residential mortgage-backed securities 754.2 0.4 (16.5) (15.1) 723.0 1.4 Commercial mortgage-backed securities 5,833.9 1.4 (747.4) 0 5,087.9 9.7 Other asset-backed securities 4,876.7 0 (268.9) (1.9) 4,605.9 8.8 Redeemable preferred stocks 202.6 0 (5.6) (15.4) 181.6 0.3 Total fixed maturities 48,205.7 1.8 (3,943.1) (91.3) 44,173.1 84.4 Short-term investments 4,237.6 0 0 0 4,237.6 8.1 Total available-for-sale securities 52,443.3 1.8 (3,943.1) (91.3) 48,410.7 92.5 Equity securities: Nonredeemable preferred stocks 1,417.6 0 0 (163.2) 1,254.4 2.4 Common equities 803.7 0 0 1,861.6 2,665.3 5.1 Total equity securities 2,221.3 0 0 1,698.4 3,919.7 7.5 Total portfolio 1 $ 54,664.6 $ 1.8 $ (3,943.1) $ 1,607.1 $ 52,330.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of September 30, 2021 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 21,093.1 $ 144.9 $ (95.9) $ 0 $ 21,142.1 40.3 % State and local government obligations 2,123.8 48.8 (6.7) 0 2,165.9 4.1 Foreign government obligations 12.3 0 0 0 12.3 0.1 Corporate debt securities 10,556.4 314.6 (10.5) 1.2 10,861.7 20.7 Residential mortgage-backed securities 624.4 3.4 (0.9) 1.0 627.9 1.2 Commercial mortgage-backed securities 5,739.4 70.2 (20.6) 0 5,789.0 11.1 Other asset-backed securities 4,235.6 29.4 (2.8) 0 4,262.2 8.2 Redeemable preferred stocks 171.0 1.3 (0.7) 13.0 184.6 0.4 Total fixed maturities 44,556.0 612.6 (138.1) 15.2 45,045.7 86.1 Short-term investments 1,088.7 0 0 0 1,088.7 2.1 Total available-for-sale securities 45,644.7 612.6 (138.1) 15.2 46,134.4 88.2 Equity securities: Nonredeemable preferred stocks 1,479.9 0 0 92.9 1,572.8 3.0 Common equities 1,238.4 0 0 3,341.8 4,580.2 8.8 Total equity securities 2,718.3 0 0 3,434.7 6,153.0 11.8 Total portfolio 1 $ 48,363.0 $ 612.6 $ (138.1) $ 3,449.9 $ 52,287.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of December 31, 2021 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 18,586.1 $ 92.9 $ (190.8) $ 0 $ 18,488.2 35.9 % State and local government obligations 2,162.6 36.7 (14.0) 0 2,185.3 4.2 Foreign government obligations 17.9 0 0 0 17.9 0.1 Corporate debt securities 10,526.2 202.6 (33.4) (3.3) 10,692.1 20.7 Residential mortgage-backed securities 787.7 2.3 (0.6) 0.6 790.0 1.5 Commercial mortgage-backed securities 6,561.0 38.9 (64.3) 0 6,535.6 12.7 Other asset-backed securities 4,981.8 13.3 (12.4) (0.4) 4,982.3 9.7 Redeemable preferred stocks 170.9 0.7 (0.5) 10.6 181.7 0.4 Total fixed maturities 43,794.2 387.4 (316.0) 7.5 43,873.1 85.2 Short-term investments 942.6 0 0 0 942.6 1.8 Total available-for-sale securities 44,736.8 387.4 (316.0) 7.5 44,815.7 87.0 Equity securities: Nonredeemable preferred stocks 1,571.8 0 0 68.1 1,639.9 3.2 Common equities 1,264.1 0 0 3,794.4 5,058.5 9.8 Total equity securities 2,835.9 0 0 3,862.5 6,698.4 13.0 Total portfolio 1 $ 47,572.7 $ 387.4 $ (316.0) $ 3,870.0 $ 51,514.1 100.0 % 1 Includes $74.7 million, $399.7 million, and $143.4 million of net unsettled security purchase transactions at September 30, 2022 and 2021, and December 31, 2021, respectively, with the offsetting payable included in other liabilities. The total fair value of the portfolio at September 30, 2022 and 2021, and December 31, 2021, included $4.2 billion, $2.9 billion, and $4.2 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of unsettled security transactions.
Hybrid Instruments Table	Certain securities in our fixed-maturity portfolio are accounted for as hybrid securities because they contain embedded derivatives that are not deemed to be clearly and closely related to the host investments. These securities are reported at fair value: September 30, (millions) 2022 2021 December 31, 2021 Fixed Maturities: Corporate debt securities $ 500.4 $ 363.3 $ 479.1 Residential mortgage-backed securities 550.8 217.0 536.2 Other asset-backed securities 51.4 104.5 89.2 Redeemable preferred stocks 133.0 133.2 130.8 Total hybrid securities $ 1,235.6 $ 818.0 $ 1,235.3
Investments Classified by Contractual Maturity Date	The composition of fixed maturities by maturity at September 30, 2022, was: (millions) Cost Fair Value Less than one year $ 5,461.3 $ 5,321.6 One to five years 29,752.3 27,694.2 Five to ten years 12,946.4 11,119.1 Ten years or greater 45.7 38.2 Total $ 48,205.7 $ 44,173.1
Schedule of Unrealized Loss on Investments	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized September 30, 2022 U.S. government obligations 157 $ 22,385.4 $ (1,855.4) 103 $ 16,085.8 $ (1,095.6) 54 $ 6,299.6 $ (759.8) State and local government obligations 353 1,911.0 (215.4) 292 1,363.1 (129.8) 61 547.9 (85.6) Foreign government obligations 1 15.3 (1.4) 1 15.3 (1.4) 0 0 0 Corporate debt securities 452 8,885.6 (832.5) 391 7,875.5 (699.0) 61 1,010.1 (133.5) Residential mortgage-backed securities 44 165.1 (16.5) 34 126.0 (11.8) 10 39.1 (4.7) Commercial mortgage-backed securities 234 5,074.3 (747.4) 182 3,856.0 (425.4) 52 1,218.3 (322.0) Other asset-backed securities 277 4,544.8 (268.9) 217 3,597.1 (183.4) 60 947.7 (85.5) Redeemable preferred stocks 4 48.6 (5.6) 3 37.7 (4.0) 1 10.9 (1.6) Total fixed maturities 1,522 $ 43,030.1 $ (3,943.1) 1,223 $ 32,956.5 $ (2,550.4) 299 $ 10,073.6 $ (1,392.7) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized September 30, 2021 U.S. government obligations 73 $ 13,352.8 $ (95.9) 65 $ 12,152.6 $ (70.1) 8 $ 1,200.2 $ (25.8) State and local government obligations 96 710.3 (6.7) 81 635.9 (4.9) 15 74.4 (1.8) Corporate debt securities 227 1,581.3 (10.5) 225 1,551.5 (10.0) 2 29.8 (0.5) Residential mortgage-backed securities 63 149.3 (0.9) 53 135.1 (0.6) 10 14.2 (0.3) Commercial mortgage-backed securities 70 1,758.8 (20.6) 65 1,543.6 (19.9) 5 215.2 (0.7) Other asset-backed securities 114 1,625.9 (2.8) 109 1,614.2 (2.7) 5 11.7 (0.1) Redeemable preferred stocks 1 11.8 (0.7) 0 0 0 1 11.8 (0.7) Total fixed maturities 644 $ 19,190.2 $ (138.1) 598 $ 17,632.9 $ (108.2) 46 $ 1,557.3 $ (29.9) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized December 31, 2021 U.S. government obligations 92 $ 14,745.8 $ (190.8) 85 $ 13,790.8 $ (158.5) 7 $ 955.0 $ (32.3) State and local government obligations 127 954.2 (14.0) 122 927.3 (13.1) 5 26.9 (0.9) Corporate debt securities 220 3,496.6 (33.4) 219 3,491.7 (33.3) 1 4.9 (0.1) Residential mortgage-backed securities 20 138.6 (0.6) 14 135.4 (0.5) 6 3.2 (0.1) Commercial mortgage-backed securities 168 4,315.4 (64.3) 165 4,295.0 (63.9) 3 20.4 (0.4) Other asset-backed securities 178 3,204.7 (12.4) 176 3,200.6 (12.3) 2 4.1 (0.1) Redeemable preferred stocks 1 12.0 (0.5) 0 0 0 1 12.0 (0.5) Total fixed maturities 806 $ 26,867.3 $ (316.0) 781 $ 25,840.8 $ (281.6) 25 $ 1,026.5 $ (34.4)
Realized Gain (Loss) on Investments	The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2022 2021 2022 2021 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 0 $ 19.6 $ 4.6 $ 97.5 State and local government obligations 0 6.0 0 50.3 Corporate and other debt securities 0.3 23.6 6.8 84.4 Residential mortgage-backed securities 0 0 0.7 0.3 Commercial mortgage-backed securities 0 1.4 0 40.7 Other asset-backed securities 0 0.3 0.1 1.0 Redeemable preferred stocks 0 0 0 1.5 Total available-for-sale securities 0.3 50.9 12.2 275.7 Equity securities: Nonredeemable preferred stocks 0.1 2.3 17.6 26.0 Common equities 1.4 6.2 832.5 352.3 Total equity securities 1.5 8.5 850.1 378.3 Subtotal gross realized gains on security sales 1.8 59.4 862.3 654.0 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations 0 (2.0) (233.5) (28.5) State and local government obligations 0 0 (1.0) (3.0) Corporate and other debt securities (14.0) (0.7) (51.8) (6.1) Residential mortgage-backed securities 0 (0.3) 0 (0.3) Commercial mortgage-backed securities (44.8) (0.5) (58.6) (1.6) Other asset-backed securities 0 0 (2.1) (0.4) Short-term investments 0 0 (0.3) 0 Total available-for-sale securities (58.8) (3.5) (347.3) (39.9) Equity securities: Nonredeemable preferred stocks (5.1) (0.3) (7.0) (0.7) Common equities 0 (1.7) (78.0) (5.6) Total equity securities (5.1) (2.0) (85.0) (6.3) Subtotal gross realized losses on security sales (63.9) (5.5) (432.3) (46.2) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 0 17.6 (228.9) 69.0 State and local government obligations 0 6.0 (1.0) 47.3 Corporate and other debt securities (13.7) 22.9 (45.0) 78.3 Residential mortgage-backed securities 0 (0.3) 0.7 0 Commercial mortgage-backed securities (44.8) 0.9 (58.6) 39.1 Other asset-backed securities 0 0.3 (2.0) 0.6 Redeemable preferred stocks 0 0 0 1.5 Short-term investments 0 0 (0.3) 0 Total available-for-sale securities (58.5) 47.4 (335.1) 235.8 Equity securities: Nonredeemable preferred stocks (5.0) 2.0 10.6 25.3 Common equities 1.4 4.5 754.5 346.7 Total equity securities (3.6) 6.5 765.1 372.0 Subtotal net realized gains (losses) on security sales (62.1) 53.9 430.0 607.8 Net holding period gains (losses) Hybrid securities (11.4) 1.0 (98.8) 0 Equity securities (140.7) (16.9) (2,164.1) 479.8 Subtotal net holding period gains (losses) (152.1) (15.9) (2,262.9) 479.8 Other asset impairment (2.2) (1.2) (6.5) (3.7) Total net realized gains (losses) on securities $ (216.4) $ 36.8 $ (1,839.4) $ 1,083.9
Components of Equity Realized Gains (Losses)	The following table reflects our holding period realized gains (losses) recognized on equity securities held at the respective quarter ends: Three Months Nine Months (millions) 2022 2021 2022 2021 Total net gains (losses) recognized during the period on equity securities $ (144.3) $ (10.4) $ (1,399.0) $ 851.8 Less: Net gains (losses) recognized on equity securities sold during the period (3.6) 6.5 765.1 372.0 Net holding period gains (losses) recognized during the period on equity securities held at period end $ (140.7) $ (16.9) $ (2,164.1) $ 479.8
Components of Net Investment Income	The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2022 2021 2022 2021 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 86.1 $ 39.0 $ 205.4 $ 106.8 State and local government obligations 9.8 9.7 29.3 34.6 Foreign government obligations 0.1 0 0.2 0 Corporate debt securities 71.8 70.2 215.4 228.6 Residential mortgage-backed securities 8.8 3.2 23.2 9.4 Commercial mortgage-backed securities 48.3 35.0 138.1 105.2 Other asset-backed securities 52.1 16.1 116.5 47.1 Redeemable preferred stocks 3.0 2.3 8.5 7.1 Total fixed maturities 280.0 175.5 736.6 538.8 Short-term investments 24.8 0.4 29.6 2.6 Total available-for-sale securities 304.8 175.9 766.2 541.4 Equity securities: Nonredeemable preferred stocks 17.3 17.3 53.6 52.5 Common equities 11.5 15.7 48.4 45.9 Total equity securities 28.8 33.0 102.0 98.4 Investment income 333.6 208.9 868.2 639.8 Investment expenses (5.8) (6.6) (17.4) (18.5) Net investment income $ 327.8 $ 202.3 $ 850.8 $ 621.3

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2022
Fair Value Disclosures [Abstract]
Composition of Investment Portfolio by Major Security Type	The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2022 Fixed maturities: U.S. government obligations $ 22,405.5 $ 0 $ 0 $ 22,405.5 $ 24,260.9 State and local government obligations 0 1,925.5 0 1,925.5 2,140.9 Foreign government obligations 0 15.3 0 15.3 16.7 Corporate debt securities 0 9,228.4 0 9,228.4 10,119.8 Subtotal 22,405.5 11,169.2 0 33,574.7 36,538.3 Asset-backed securities: Residential mortgage-backed 0 723.0 0 723.0 754.2 Commercial mortgage-backed 0 5,087.9 0 5,087.9 5,833.9 Other asset-backed 0 4,605.9 0 4,605.9 4,876.7 Subtotal asset-backed securities 0 10,416.8 0 10,416.8 11,464.8 Redeemable preferred stocks: Financials 0 39.8 0 39.8 43.6 Utilities 0 8.8 0 8.8 10.5 Industrials 8.9 124.1 0 133.0 148.5 Subtotal redeemable preferred stocks 8.9 172.7 0 181.6 202.6 Total fixed maturities 22,414.4 21,758.7 0 44,173.1 48,205.7 Short-term investments 4,219.6 18.0 0 4,237.6 4,237.6 Total available-for-sale securities 26,634.0 21,776.7 0 48,410.7 52,443.3 Equity securities: Nonredeemable preferred stocks: Financials 60.9 1,015.6 64.9 1,141.4 1,297.6 Utilities 0 71.3 0 71.3 79.9 Industrials 0 24.7 17.0 41.7 40.1 Subtotal nonredeemable preferred stocks 60.9 1,111.6 81.9 1,254.4 1,417.6 Common equities: Common stocks 2,597.3 49.3 0 2,646.6 785.0 Other risk investments 0 0 18.7 18.7 18.7 Subtotal common equities 2,597.3 49.3 18.7 2,665.3 803.7 Total equity securities 2,658.2 1,160.9 100.6 3,919.7 2,221.3 Total portfolio $ 29,292.2 $ 22,937.6 $ 100.6 $ 52,330.4 $ 54,664.6 Debt $ 0 $ 5,634.7 $ 0 $ 5,634.7 $ 6,387.4 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2021 Fixed maturities: U.S. government obligations $ 21,142.1 $ 0 $ 0 $ 21,142.1 $ 21,093.1 State and local government obligations 0 2,165.9 0 2,165.9 2,123.8 Foreign government obligations 0 12.3 0 12.3 12.3 Corporate debt securities 0 10,861.7 0 10,861.7 10,556.4 Subtotal 21,142.1 13,039.9 0 34,182.0 33,785.6 Asset-backed securities: Residential mortgage-backed 0 627.9 0 627.9 624.4 Commercial mortgage-backed 0 5,789.0 0 5,789.0 5,739.4 Other asset-backed 0 4,262.2 0 4,262.2 4,235.6 Subtotal asset-backed securities 0 10,679.1 0 10,679.1 10,599.4 Redeemable preferred stocks: Financials 0 51.4 0 51.4 50.8 Utilities 0 0 0 0 0 Industrials 10.6 122.6 0 133.2 120.2 Subtotal redeemable preferred stocks 10.6 174.0 0 184.6 171.0 Total fixed maturities 21,152.7 23,893.0 0 45,045.7 44,556.0 Short-term investments 1,078.5 10.2 0 1,088.7 1,088.7 Total available-for-sale securities 22,231.2 23,903.2 0 46,134.4 45,644.7 Equity securities: Nonredeemable preferred stocks: Financials 89.8 1,304.6 76.4 1,470.8 1,399.8 Utilities 0 42.1 0 42.1 40.0 Industrials 0 25.5 34.4 59.9 40.1 Subtotal nonredeemable preferred stocks 89.8 1,372.2 110.8 1,572.8 1,479.9 Common equities: Common stocks 4,513.1 0 54.5 4,567.6 1,225.8 Other risk investments 0 0 12.6 12.6 12.6 Subtotal common equities 4,513.1 0 67.1 4,580.2 1,238.4 Total equity securities 4,602.9 1,372.2 177.9 6,153.0 2,718.3 Total portfolio $ 26,834.1 $ 25,275.4 $ 177.9 $ 52,287.4 $ 48,363.0 Debt $ 0 $ 5,881.7 $ 0 $ 5,881.7 $ 4,898.2 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2021 Fixed maturities: U.S. government obligations $ 18,488.2 $ 0 $ 0 $ 18,488.2 $ 18,586.1 State and local government obligations 0 2,185.3 0 2,185.3 2,162.6 Foreign government obligations 0 17.9 0 17.9 17.9 Corporate debt securities 0 10,692.1 0 10,692.1 10,526.2 Subtotal 18,488.2 12,895.3 0 31,383.5 31,292.8 Asset-backed securities: Residential mortgage-backed 0 790.0 0 790.0 787.7 Commercial mortgage-backed 0 6,535.6 0 6,535.6 6,561.0 Other asset-backed 0 4,982.3 0 4,982.3 4,981.8 Subtotal asset-backed securities 0 12,307.9 0 12,307.9 12,330.5 Redeemable preferred stocks: Financials 0 50.9 0 50.9 50.7 Utilities 0 0 0 0 0 Industrials 10.7 120.1 0 130.8 120.2 Subtotal redeemable preferred stocks 10.7 171.0 0 181.7 170.9 Total fixed maturities 18,498.9 25,374.2 0 43,873.1 43,794.2 Short-term investments 942.4 0.2 0 942.6 942.6 Total available-for-sale securities 19,441.3 25,374.4 0 44,815.7 44,736.8 Equity securities: Nonredeemable preferred stocks: Financials 115.3 1,305.7 76.4 1,497.4 1,451.7 Utilities 0 82.9 0 82.9 80.0 Industrials 0 25.2 34.4 59.6 40.1 Subtotal nonredeemable preferred stocks 115.3 1,413.8 110.8 1,639.9 1,571.8 Common equities: Common stocks 4,991.6 50.0 0 5,041.6 1,247.2 Other risk investments 0 0 16.9 16.9 16.9 Subtotal common equities 4,991.6 50.0 16.9 5,058.5 1,264.1 Total equity securities 5,106.9 1,463.8 127.7 6,698.4 2,835.9 Total portfolio $ 24,548.2 $ 26,838.2 $ 127.7 $ 51,514.1 $ 47,572.7 Debt $ 0 $ 5,857.4 $ 0 $ 5,857.4 $ 4,898.8
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	The following tables provide a summary of changes in fair value associated with Level 3 assets for the three and nine months ended September 30, 2022 and 2021: Level 3 Fair Value (millions) Fair Value at June 30, 2022 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2022 Equity securities: Nonredeemable preferred stocks: Financials $ 64.9 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 64.9 Industrials 17.0 0 0 0 0 0 0 17.0 Common equities: Other risk investments 18.5 0.2 0 0 0 0 0 18.7 Total Level 3 securities $ 100.4 $ 0.2 $ 0 $ 0 $ 0 $ 0 $ 0 $ 100.6 Level 3 Fair Value (millions) Fair Value at June 30, 2021 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2021 Equity securities: Nonredeemable preferred stocks: Financials $ 76.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 76.4 Industrials 34.4 0 0 0 0 0 0 34.4 Common equities: Common stocks 52.5 0 2.0 0 0 0 0 54.5 Other risk investments 11.6 1.0 0 0 0 0 0 12.6 Total Level 3 securities $ 174.9 $ 1.0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 177.9 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2021 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2022 Equity securities: Nonredeemable preferred stocks: Financials $ 76.4 $ 0 $ 0 $ (15.0) $ (17.2) $ 20.7 $ 0 $ 64.9 Industrials 34.4 (0.5) 0 0 0 (16.9) 0 17.0 Common equities: Other risk investments 16.9 1.8 0 0 0 0 0 18.7 Total Level 3 securities $ 127.7 $ 1.3 $ 0 $ (15.0) $ (17.2) $ 3.8 $ 0 $ 100.6 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2020 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2021 Equity securities: Nonredeemable preferred stocks: Financials $ 10.0 $ 0 $ 60.2 $ 0 $ 0 $ 6.2 $ 0 $ 76.4 Industrials 16.7 0 5.0 (5.0) (4.5) 22.2 0 34.4 Common equities: Common stocks 25.0 0 2.0 0 0 27.5 0 54.5 Other risk investments 3.1 9.5 0 0 0 0 0 12.6 Total Level 3 securities $ 54.8 $ 9.5 $ 67.2 $ (5.0) $ (4.5) $ 55.9 $ 0 $ 177.9
Fair Value Measurement Inputs and Valuation Techniques	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2022 and 2021, and December 31, 2021: Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2022 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 81.9 Market comparables Weighted average market capitalization price change % (20.7)% to (1.1)% (6.6) % Subtotal Level 3 securities 81.9 Pricing exemption securities 18.7 Total Level 3 securities $ 100.6 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2021 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 110.8 Market comparables Weighted average market capitalization price change % (8.5)% to 19.8% 6.5 % Common stocks 54.5 Market comparables Weighted average market capitalization price change % (1.6)% to 55.8% 0.9 % Subtotal Level 3 securities 165.3 Pricing exemption securities 12.6 Total Level 3 securities $ 177.9 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2021 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 110.8 Market comparables Weighted average market capitalization price change % (20.2)% to (2.3)% (7.7)% Subtotal Level 3 securities 110.8 Pricing exemption securities 16.9 Total Level 3 securities $ 127.7

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2022
Debt Disclosure [Abstract]
Debt Table	Debt at each of the balance sheet periods consisted of: September 30, 2022 September 30, 2021 December 31, 2021 (millions) Carrying Fair Carrying Fair Carrying Fair 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) $ 498.1 $ 459.7 $ 497.6 $ 530.6 $ 497.7 $ 517.9 2.50% Senior Notes due 2027 (issued: $500.0, March 2022) 497.4 451.6 0 0 0 0 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 297.4 322.1 297.1 390.9 297.2 388.2 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 546.3 519.5 545.8 627.9 545.9 621.0 3.20% Senior Notes due 2030 (issued: $500.0, March 2020) 496.8 439.3 496.4 543.2 496.5 536.3 3.00% Senior Notes due 2032 (issued: $500.0, March 2022) 495.8 418.8 0 0 0 0 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 396.4 426.0 396.1 545.5 396.2 547.9 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.9 298.5 346.8 433.6 346.8 428.4 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.7 305.7 395.6 456.2 395.6 447.1 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 842.0 710.3 841.9 1,018.5 841.9 1,029.3 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 590.3 505.9 590.2 736.3 590.2 741.3 3.95% Senior Notes due 2050 (issued: $500.0, March 2020) 490.9 396.6 490.7 599.0 490.8 600.0 3.70% Senior Notes due 2052 (issued: $500.0, March 2022) 493.4 380.7 0 0 0 0 Total $ 6,387.4 $ 5,634.7 $ 4,898.2 $ 5,881.7 $ 4,898.8 $ 5,857.4

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation	The provision for income taxes differed from the statutory rate as follows: Three Months Ended September 30, Nine Months Ended September 30, ($ in millions) 2022 2021 2022 2021 Income (loss) before income taxes $ 142.5 $ 139.0 $ (103.2) $ 3,006.1 Tax at statutory federal rate $ 29.9 21.0 % $ 29.2 21.0 % $ (21.7) 21.0 % $ 631.3 21.0 % Tax effect of: Goodwill impairment 0 0 0 0 47.2 (45.7) 0 0 Stock-based compensation (9.6) (6.7) (7.9) (5.7) (17.7) 17.2 (19.2) (0.6) State income taxes, net of federal taxes 4.5 3.2 5.5 4.0 9.7 (9.4) 17.7 0.6 Tax-preferenced investment income (2.8) (2.0) (3.3) (2.4) (9.5) 9.2 (10.0) (0.3) Tax credits (5.2) (3.6) (3.7) (2.7) (9.4) 9.1 (6.1) (0.2) Nondeductible compensation expense 1.8 1.3 1.9 1.4 5.4 (5.2) 5.6 0.2 Tax deductible dividends (0.4) (0.3) (0.5) (0.4) (1.4) 1.4 (1.6) (0.1) Other items, net 0.2 0 (0.7) (0.5) (0.9) 0.8 (0.2) (0.1) Total income tax provision $ 18.4 12.9 % $ 20.5 14.7 % $ 1.7 (1.6) % $ 617.5 20.5 %

Loss and Loss Adjustment Expe_2

Loss and Loss Adjustment Expense Reserves (Tables)	9 Months Ended
	Sep. 30, 2022
Loss and Loss Adjustment Expenses Reserves [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	Activity in the loss and loss adjustment expense reserves is summarized as follows: September 30, (millions) 2022 2021 Balance at January 1 $ 26,164.1 $ 20,265.8 Less reinsurance recoverables on unpaid losses 4,733.6 3,798.2 Net balance at January 1 21,430.5 16,467.6 Net loss and loss adjustment expense reserves acquired 1 0 732.5 Total beginning reserves 21,430.5 17,200.1 Incurred related to: Current year 28,245.4 24,610.8 Prior years 52.8 156.8 Total incurred 28,298.2 24,767.6 Paid related to: Current year 15,712.4 13,650.6 Prior years 9,418.5 7,213.3 Total paid 25,130.9 20,863.9 Net balance at September 30 24,597.8 21,103.8 Plus reinsurance recoverables on unpaid losses 6,034.0 4,822.5 Balance at September 30 $ 30,631.8 $ 25,926.3 1 Net reserves acquired in the Protective Insurance acquisition.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2022
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Cash Flow Information, Non Cash Activity	Non-cash activity included the following in the respective periods: Nine Months Ended September 30, (millions) 2022 2021 Common share dividends 1 $ 58.5 $ 58.5 Operating lease liabilities 2 29.7 79.5 1 Declared but unpaid. See Note 9 – Dividends for further discussion. 2 From obtaining right-of-use assets.
Supplemental Cash Flow Information Table	We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2022 2021 Income taxes $ 595.9 $ 669.5 Interest 191.3 186.3 Operating lease liabilities 62.5 67.8

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2022
Segment Reporting [Abstract]
Reconciliation of Revenue and operating Income from Segments to Consolidated	Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 (millions) Revenues Pretax Revenues Pretax Revenues Pretax Revenues Pretax Personal Lines Agency $ 4,441.9 $ (41.3) $ 4,267.9 $ 41.0 $ 13,131.7 $ 507.6 $ 12,586.4 $ 796.0 Direct 5,077.4 40.6 4,690.2 (62.4) 14,776.9 389.4 13,755.8 480.6 Total Personal Lines 1 9,519.3 (0.7) 8,958.1 (21.4) 27,908.6 897.0 26,342.2 1,276.6 Commercial Lines 2,317.9 238.1 1,877.4 197.5 6,749.5 683.5 4,917.0 556.1 Property 2 561.0 (141.0) 526.5 (222.7) 1,689.6 (289.6) 1,501.3 (376.7) Other indemnity 3 0.7 (2.1) 2.8 (0.3) 2.0 (9.3) 6.8 (0.2) Total underwriting operations 12,398.9 94.3 11,364.8 (46.9) 36,349.7 1,281.6 32,767.3 1,455.8 Fees and other revenues 4 181.4 NA 174.9 NA 531.9 NA 516.8 NA Service businesses 82.7 (0.1) 73.8 1.0 230.5 9.0 202.1 12.1 Investments 5 117.2 111.4 245.7 239.1 (971.2) (988.6) 1,723.7 1,705.2 Interest expense NA (63.1) NA (54.2) NA (180.4) NA (167.0) Property - Goodwill impairment 2 NA 0 NA 0 NA (224.8) NA 0 Consolidated total $ 12,780.2 $ 142.5 $ 11,859.2 $ 139.0 $ 36,140.9 $ (103.2) $ 35,209.9 $ 3,006.1 NA = Not applicable 1 Personal auto products accounted for 94% of the total Personal Lines segment net premiums earned during the three and nine months ended September 30, 2022 and 2021; our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 The total pretax loss, including goodwill impairment, for the Property segment was $514.4 million for the nine months ended September 30, 2022. For the three and nine months ended September 30, 2022, pretax profit (loss) also included $5.0 million and $24.1 million, respectively, of amortization expense associated with acquisition-related intangible assets attributable to our Property segment, and $14.2 million and $42.5 million for the same periods in 2021. See Note 12 – Goodwill and Intangible Assets for further discussion. 3 Primarily includes run-off business operations. 4 Pretax profit (loss) for fees and other revenues is allocated to operating segments. 5 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit (loss) is net of investment expense.
Underwriting Margins and Combined Ratios for our Underwriting Operations	Following are the underwriting margins and combined ratios for our underwriting operations for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 Under-writing Combined Under-writing Combined Under-writing Combined Under-writing Combined Personal Lines Agency (0.9) % 100.9 1.0 % 99.0 3.9 % 96.1 6.3 % 93.7 Direct 0.8 99.2 (1.3) 101.3 2.6 97.4 3.5 96.5 Total Personal Lines 0 100.0 (0.2) 100.2 3.2 96.8 4.9 95.1 Commercial Lines 10.3 89.7 10.5 89.5 10.1 89.9 11.3 88.7 Property 1 (25.1) 125.1 (42.3) 142.3 (17.1) 117.1 (25.1) 125.1 Total underwriting operations 0.8 99.2 (0.4) 100.4 3.5 96.5 4.4 95.6 1 Included in the three and nine months ended September 30, 2022, is 0.9 points and 1.4 points, respectively, of amortization expense associated with intangible assets and 2.7 points and 2.8 points, respectively, for the same periods in 2021.

Dividends (Tables)

Dividends (Tables)	9 Months Ended
	Sep. 30, 2022
Dividends [Abstract]
Dividends	Following is a summary of our common and preferred share dividends that were declared and/or paid during the nine months ended September 30, 2022 and 2021: (millions, except per share amounts) Amount Declared Payable Per Share Accrued/Paid 1 Common - Quarterly Dividends: August 2022 October 2022 $ 0.10 $ 58.5 May 2022 July 2022 0.10 58.5 March 2022 April 2022 0.10 58.5 December 2021 January 2022 0.10 58.5 August 2021 October 2021 0.10 58.5 May 2021 July 2021 0.10 58.5 March 2021 April 2021 0.10 58.5 December 2020 January 2021 0.10 58.6 Common - Annual Variable Dividends: December 2020 January 2021 4.50 2,635.9 Preferred Dividends: August 2022 September 2022 26.875 13.4 December 2021 March 2022 26.875 13.4 August 2021 September 2021 26.875 13.4 December 2020 March 2021 26.875 13.4 1 The common share dividend accrual is based on an estimate of common shares outstanding as of the record date and all accruals are recorded as a part of accounts payable, accrued expenses, and other liabilities on the consolidated balance sheets until paid.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2022
Equity [Abstract]
Components of Other Comprehensive Income (Loss)	The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net unrealized gains (losses) on securities Net unrealized losses on forecasted transactions Foreign Balance at June 30, 2022 $ (2,795.5) $ 586.5 $ (2,209.0) $ (2,193.5) $ (14.7) $ (0.8) Other comprehensive income (loss) before reclassifications: Investment securities (1,223.3) 256.9 (966.4) (966.4) 0 0 Foreign currency translation adjustment (0.9) 0.2 (0.7) 0 0 (0.7) Total other comprehensive income (loss) before reclassifications (1,224.2) 257.1 (967.1) (966.4) 0 (0.7) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (58.4) 12.3 (46.1) (46.1) 0 0 Interest expense (0.2) 0.1 (0.1) 0 (0.1) 0 Total reclassification adjustment for amounts realized in net income (58.6) 12.4 (46.2) (46.1) (0.1) 0 Total other comprehensive income (loss) (1,165.6) 244.7 (920.9) (920.3) 0.1 (0.7) Balance at September 30, 2022 $ (3,961.1) $ 831.2 $ (3,129.9) $ (3,113.8) $ (14.6) $ (1.5) Components of Changes in (millions) Pretax total Total tax After tax total Total net unrealized gains (losses) on securities Net unrealized losses on forecasted transactions Foreign Balance at June 30, 2021 $ 619.6 $ (136.4) $ 483.2 $ 498.8 $ (15.1) $ (0.5) Other comprehensive income (loss) before reclassifications: Investment securities (117.9) 24.8 (93.1) (93.1) 0 0 Foreign currency translation adjustment (0.3) 0.1 (0.2) 0 0 (0.2) Total other comprehensive income (loss) before reclassifications (118.2) 24.9 (93.3) (93.1) 0 (0.2) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 46.4 (9.7) 36.7 36.7 0 0 Interest expense (0.2) 0.1 (0.1) 0 (0.1) 0 Total reclassification adjustment for amounts realized in net income 46.2 (9.6) 36.6 36.7 (0.1) 0 Total other comprehensive income (loss) (164.4) 34.5 (129.9) (129.8) 0.1 (0.2) Balance at September 30, 2021 $ 455.2 $ (101.9) $ 353.3 $ 369.0 $ (15.0) $ (0.7) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized losses on forecasted transactions Foreign Balance at December 31, 2021 $ 52.3 $ (11.6) $ 40.7 $ 56.2 $ (14.9) $ (0.6) Other comprehensive income (loss) before reclassifications: Investment securities (4,321.7) 907.6 (3,414.1) (3,414.1) 0 0 Foreign currency translation adjustment (1.1) 0.2 (0.9) 0 0 (0.9) Total other comprehensive income (loss) before reclassifications (4,322.8) 907.8 (3,415.0) (3,414.1) 0 (0.9) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (309.0) 64.9 (244.1) (244.1) 0 0 Interest expense (0.4) 0.1 (0.3) 0 (0.3) 0 Total reclassification adjustment for amounts realized in net income (309.4) 65.0 (244.4) (244.1) (0.3) 0 Total other comprehensive income (loss) (4,013.4) 842.8 (3,170.6) (3,170.0) 0.3 (0.9) Balance at September 30, 2022 $ (3,961.1) $ 831.2 $ (3,129.9) $ (3,113.8) $ (14.6) $ (1.5) Components of Changes in (millions) Pretax total Total tax After tax total Total net unrealized gains (losses) on securities Net unrealized losses on forecasted transactions Foreign Balance at December 31, 2020 $ 1,187.4 $ (255.7) $ 931.7 $ 947.3 $ (15.6) $ 0 Other comprehensive income (loss) before reclassifications: Investment securities (494.6) 103.9 (390.7) (390.7) 0 0 Foreign currency translation adjustment (0.9) 0.2 (0.7) 0 0 (0.7) Total other comprehensive income (loss) before reclassifications (495.5) 104.1 (391.4) (390.7) 0 (0.7) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 237.5 (49.9) 187.6 187.6 0 0 Interest expense (0.8) 0.2 (0.6) 0 (0.6) 0 Total reclassification adjustment for amounts realized in net income 236.7 (49.7) 187.0 187.6 (0.6) 0 Total other comprehensive income (loss) (732.2) 153.8 (578.4) (578.3) 0.6 (0.7) Balance at September 30, 2021 $ 455.2 $ (101.9) $ 353.3 $ 369.0 $ (15.0) $ (0.7)

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Indefinite-Lived Intangible Assets	The following table is a summary of the net carrying amount of other intangible assets: (millions) September 30, 2022 September 30, 2021 December 31, 2021 Intangible assets subject to amortization $ 79.4 $ 119.5 $ 104.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 91.8 $ 131.9 $ 117.3
Intangible Assets Subject to Amortization	The following table is a summary of the net carrying amount of other intangible assets: (millions) September 30, 2022 September 30, 2021 December 31, 2021 Intangible assets subject to amortization $ 79.4 $ 119.5 $ 104.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 91.8 $ 131.9 $ 117.3 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for all periods presented. Intangible assets subject to amortization consisted of the following: (millions) September 30, 2022 September 30, 2021 December 31, 2021 Category Gross Accumulated Net Gross Accumulated Net Gross Accumulated Net Policies in force $ 0 $ 0 $ 0 $ 256.2 $ 237.9 $ 18.3 $ 256.2 $ 247.1 $ 9.1 Agency relationships 159.2 85.3 73.9 159.2 73.9 85.3 159.2 76.8 82.4 Software rights 69.1 64.8 4.3 69.1 56.2 12.9 69.1 58.3 10.8 Trade name 3.6 2.4 1.2 3.6 0.6 3.0 3.6 1.0 2.6 Total $ 231.9 $ 152.5 $ 79.4 $ 488.1 $ 368.6 $ 119.5 $ 488.1 $ 383.2 $ 104.9

Basis of Presentation - Reporti

Basis of Presentation - Reporting and Accounting Policies - Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Allowance for Credit Loss [Abstract]
Allowance for credit losses, beginning of period	$ 265.8	$ 245.2	$ 280.4	$ 356.2
Allowance acquired during period	0	0	0	3.5
Increase in allowance	130.9	107.2	320.6	255.5
Write-offs	(101.7)	(95.1)	(306)	(357.9)
Allowance for credit losses, end of period	$ 295	$ 257.3	$ 295	$ 257.3

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Assets held-for-sale	$ 47.4	$ 10.8	$ 12.6

Investments - Investment Portfo

Investments - Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 52,443.3	$ 44,736.8	$ 45,644.7
Gross Unrealized Gains	1.8	387.4	612.6
Gross Unrealized Losses	(3,943.1)	(316)	(138.1)
Net Holding Period Gains (Losses)	(91.3)	7.5	15.2
Total available-for-sale securities	$ 48,410.7	$ 44,815.7	$ 46,134.4
% of Total Fair Value	92.50%	87%	88.20%
Equity securities, at Fair Value
Cost	$ 2,221.3	$ 2,835.9	$ 2,718.3
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	1,698.4	3,862.5	3,434.7
Fair Value	$ 3,919.7	$ 6,698.4	$ 6,153
% of Total Fair Value	7.50%	13%	11.80%
Debt and Equity Securities, at Fair Value
Cost	$ 54,664.6	$ 47,572.7	$ 48,363
Gross Unrealized Gains	1.8	387.4	612.6
Gross Unrealized Losses	(3,943.1)	(316)	(138.1)
Net Holding Period Gains (Losses)	1,607.1	3,870	3,449.9
Fair Value	$ 52,330.4	$ 51,514.1	$ 52,287.4
% of Total Fair Value	100%	100%	100%
Unsettled security transactions, payable	$ 74.7	$ 143.4	$ 399.7
Total fair value of non-insurance subsidiary portfolio	4,200	4,200	2,900
Nonredeemable preferred stocks
Equity securities, at Fair Value
Cost	1,417.6	1,571.8	1,479.9
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	(163.2)	68.1	92.9
Fair Value	$ 1,254.4	$ 1,639.9	$ 1,572.8
% of Total Fair Value	2.40%	3.20%	3%
Common equities
Equity securities, at Fair Value
Cost	$ 803.7	$ 1,264.1	$ 1,238.4
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	1,861.6	3,794.4	3,341.8
Fair Value	$ 2,665.3	$ 5,058.5	$ 4,580.2
% of Total Fair Value	5.10%	9.80%	8.80%
Total fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 48,205.7	$ 43,794.2	$ 44,556
Gross Unrealized Gains	1.8	387.4	612.6
Gross Unrealized Losses	(3,943.1)	(316)	(138.1)
Net Holding Period Gains (Losses)	(91.3)	7.5	15.2
Total available-for-sale securities	$ 44,173.1	$ 43,873.1	$ 45,045.7
% of Total Fair Value	84.40%	85.20%	86.10%
Total fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 24,260.9	$ 18,586.1	$ 21,093.1
Gross Unrealized Gains	0	92.9	144.9
Gross Unrealized Losses	(1,855.4)	(190.8)	(95.9)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 22,405.5	$ 18,488.2	$ 21,142.1
% of Total Fair Value	42.80%	35.90%	40.30%
Total fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 2,140.9	$ 2,162.6	$ 2,123.8
Gross Unrealized Gains	0	36.7	48.8
Gross Unrealized Losses	(215.4)	(14)	(6.7)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 1,925.5	$ 2,185.3	$ 2,165.9
% of Total Fair Value	3.70%	4.20%	4.10%
Total fixed maturities | Foreign government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 16.7	$ 17.9	$ 12.3
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(1.4)	0	0
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 15.3	$ 17.9	$ 12.3
% of Total Fair Value	0.10%	0.10%	0.10%
Total fixed maturities | Corporate debt securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 10,119.8	$ 10,526.2	$ 10,556.4
Gross Unrealized Gains	0	202.6	314.6
Gross Unrealized Losses	(832.5)	(33.4)	(10.5)
Net Holding Period Gains (Losses)	(58.9)	(3.3)	1.2
Total available-for-sale securities	$ 9,228.4	$ 10,692.1	$ 10,861.7
% of Total Fair Value	17.60%	20.70%	20.70%
Total fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 754.2	$ 787.7	$ 624.4
Gross Unrealized Gains	0.4	2.3	3.4
Gross Unrealized Losses	(16.5)	(0.6)	(0.9)
Net Holding Period Gains (Losses)	(15.1)	0.6	1
Total available-for-sale securities	$ 723	$ 790	$ 627.9
% of Total Fair Value	1.40%	1.50%	1.20%
Total fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 5,833.9	$ 6,561	$ 5,739.4
Gross Unrealized Gains	1.4	38.9	70.2
Gross Unrealized Losses	(747.4)	(64.3)	(20.6)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 5,087.9	$ 6,535.6	$ 5,789
% of Total Fair Value	9.70%	12.70%	11.10%
Total fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,876.7	$ 4,981.8	$ 4,235.6
Gross Unrealized Gains	0	13.3	29.4
Gross Unrealized Losses	(268.9)	(12.4)	(2.8)
Net Holding Period Gains (Losses)	(1.9)	(0.4)	0
Total available-for-sale securities	$ 4,605.9	$ 4,982.3	$ 4,262.2
% of Total Fair Value	8.80%	9.70%	8.20%
Total fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 202.6	$ 170.9	$ 171
Gross Unrealized Gains	0	0.7	1.3
Gross Unrealized Losses	(5.6)	(0.5)	(0.7)
Net Holding Period Gains (Losses)	(15.4)	10.6	13
Total available-for-sale securities	$ 181.6	$ 181.7	$ 184.6
% of Total Fair Value	0.30%	0.40%	0.40%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,237.6	$ 942.6	$ 1,088.7
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 4,237.6	$ 942.6	$ 1,088.7
% of Total Fair Value	8.10%	1.80%	2.10%

Investments - Hybrid Securities

Investments - Hybrid Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Hybrid Instruments [Line Items]
Hybrid securities	$ 1,235.6	$ 1,235.3	$ 818
Corporate debt securities
Hybrid Instruments [Line Items]
Hybrid securities	500.4	479.1	363.3
Residential mortgage-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	550.8	536.2	217
Other asset-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	51.4	89.2	104.5
Redeemable preferred stocks
Hybrid Instruments [Line Items]
Hybrid securities	$ 133	$ 130.8	$ 133.2

Investments - Composition of Fi

Investments - Composition of Fixed Maturities by Maturity (Detail) - Total fixed maturities $ in Millions	Sep. 30, 2022 USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 5,461.3
One to five years	29,752.3
Five to ten years	12,946.4
Ten years or greater	45.7
Cost	48,205.7
Fair Value
Less than one year	5,321.6
One to five years	27,694.2
Five to ten years	11,119.1
Ten years or greater	38.2
Fair Value	$ 44,173.1

Investments - Gross Unrealized

Investments - Gross Unrealized losses by Major Security (Detail) $ in Millions	Sep. 30, 2022 USD ($) security	Dec. 31, 2021 USD ($) security	Sep. 30, 2021 USD ($) security
Number of Securities
Total | security	1,522	806	644
Less than 12 Months | security	1,223	781	598
12 Months or Greater | security	299	25	46
Fair Value
Total	$ 43,030.1	$ 26,867.3	$ 19,190.2
Less than 12 Months	32,956.5	25,840.8	17,632.9
12 Months or Greater	10,073.6	1,026.5	1,557.3
Unrealized Losses
Total	(3,943.1)	(316)	(138.1)
Less than 12 Months	(2,550.4)	(281.6)	(108.2)
12 Months or Greater	$ (1,392.7)	$ (34.4)	$ (29.9)
U.S. government obligations
Number of Securities
Total | security	157	92	73
Less than 12 Months | security	103	85	65
12 Months or Greater | security	54	7	8
Fair Value
Total	$ 22,385.4	$ 14,745.8	$ 13,352.8
Less than 12 Months	16,085.8	13,790.8	12,152.6
12 Months or Greater	6,299.6	955	1,200.2
Unrealized Losses
Total	(1,855.4)	(190.8)	(95.9)
Less than 12 Months	(1,095.6)	(158.5)	(70.1)
12 Months or Greater	$ (759.8)	$ (32.3)	$ (25.8)
State and local government obligations
Number of Securities
Total | security	353	127	96
Less than 12 Months | security	292	122	81
12 Months or Greater | security	61	5	15
Fair Value
Total	$ 1,911	$ 954.2	$ 710.3
Less than 12 Months	1,363.1	927.3	635.9
12 Months or Greater	547.9	26.9	74.4
Unrealized Losses
Total	(215.4)	(14)	(6.7)
Less than 12 Months	(129.8)	(13.1)	(4.9)
12 Months or Greater	$ (85.6)	$ (0.9)	$ (1.8)
Foreign government obligations
Number of Securities
Total | security	1
Less than 12 Months | security	1
12 Months or Greater | security	0
Fair Value
Total	$ 15.3
Less than 12 Months	15.3
12 Months or Greater	0
Unrealized Losses
Total	(1.4)
Less than 12 Months	(1.4)
12 Months or Greater	$ 0
Corporate debt securities
Number of Securities
Total | security	452	220	227
Less than 12 Months | security	391	219	225
12 Months or Greater | security	61	1	2
Fair Value
Total	$ 8,885.6	$ 3,496.6	$ 1,581.3
Less than 12 Months	7,875.5	3,491.7	1,551.5
12 Months or Greater	1,010.1	4.9	29.8
Unrealized Losses
Total	(832.5)	(33.4)	(10.5)
Less than 12 Months	(699)	(33.3)	(10)
12 Months or Greater	$ (133.5)	$ (0.1)	$ (0.5)
Residential mortgage-backed securities
Number of Securities
Total | security	44	20	63
Less than 12 Months | security	34	14	53
12 Months or Greater | security	10	6	10
Fair Value
Total	$ 165.1	$ 138.6	$ 149.3
Less than 12 Months	126	135.4	135.1
12 Months or Greater	39.1	3.2	14.2
Unrealized Losses
Total	(16.5)	(0.6)	(0.9)
Less than 12 Months	(11.8)	(0.5)	(0.6)
12 Months or Greater	$ (4.7)	$ (0.1)	$ (0.3)
Commercial mortgage-backed securities
Number of Securities
Total | security	234	168	70
Less than 12 Months | security	182	165	65
12 Months or Greater | security	52	3	5
Fair Value
Total	$ 5,074.3	$ 4,315.4	$ 1,758.8
Less than 12 Months	3,856	4,295	1,543.6
12 Months or Greater	1,218.3	20.4	215.2
Unrealized Losses
Total	(747.4)	(64.3)	(20.6)
Less than 12 Months	(425.4)	(63.9)	(19.9)
12 Months or Greater	$ (322)	$ (0.4)	$ (0.7)
Other asset-backed securities
Number of Securities
Total | security	277	178	114
Less than 12 Months | security	217	176	109
12 Months or Greater | security	60	2	5
Fair Value
Total	$ 4,544.8	$ 3,204.7	$ 1,625.9
Less than 12 Months	3,597.1	3,200.6	1,614.2
12 Months or Greater	947.7	4.1	11.7
Unrealized Losses
Total	(268.9)	(12.4)	(2.8)
Less than 12 Months	(183.4)	(12.3)	(2.7)
12 Months or Greater	$ (85.5)	$ (0.1)	$ (0.1)
Redeemable preferred stocks
Number of Securities
Total | security	4	1	1
Less than 12 Months | security	3	0	0
12 Months or Greater | security	1	1	1
Fair Value
Total	$ 48.6	$ 12	$ 11.8
Less than 12 Months	37.7	0	0
12 Months or Greater	10.9	12	11.8
Unrealized Losses
Total	(5.6)	(0.5)	(0.7)
Less than 12 Months	(4)	0	0
12 Months or Greater	$ (1.6)	$ (0.5)	$ (0.7)

Investments - Components of Net

Investments - Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	$ 0.3	$ 50.9	$ 12.2	$ 275.7
Equity Securities, FV-NI, Gross Realized Gains on Sales	1.5	8.5	850.1	378.3
Debt and Equity Securities, Gross Realized Gains on Sales	1.8	59.4	862.3	654
Debt Securities, Available-for-Sale, Realized Loss	(58.8)	(3.5)	(347.3)	(39.9)
Equity Securities, FV-NI, Gross Realized Losses on Sales	(5.1)	(2)	(85)	(6.3)
Debt and Equity Securities, Gross Realized Losses on Sales	(63.9)	(5.5)	(432.3)	(46.2)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(58.5)	47.4	(335.1)	235.8
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	(3.6)	6.5	765.1	372
Net realized gains (losses) on security sales	(62.1)	53.9	430	607.8
Unrealized Gain (Loss) on Hybrid Instrument, Net	(11.4)	1	(98.8)	0
Equity Securities, FV-NI, Unrealized Gain (Loss)	(140.7)	(16.9)	(2,164.1)	479.8
Net holding period gains (losses) on securities	(152.1)	(15.9)	(2,262.9)	479.8
Net impairment losses recognized in earnings	(2.2)	(1.2)	(6.5)	(3.7)
Total net realized gains (losses) on securities	(216.4)	36.8	(1,839.4)	1,083.9
Other Assets
Gain (Loss) on Securities [Line Items]
Net impairment losses recognized in earnings	(2.2)	(1.2)	(6.5)	(3.7)
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	19.6	4.6	97.5
Debt Securities, Available-for-Sale, Realized Loss	0	(2)	(233.5)	(28.5)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	17.6	(228.9)	69
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	6	0	50.3
Debt Securities, Available-for-Sale, Realized Loss	0	0	(1)	(3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	6	(1)	47.3
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0.3	23.6	6.8	84.4
Debt Securities, Available-for-Sale, Realized Loss	(14)	(0.7)	(51.8)	(6.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(13.7)	22.9	(45)	78.3
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0	0.7	0.3
Debt Securities, Available-for-Sale, Realized Loss	0	(0.3)	0	(0.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	(0.3)	0.7	0
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	1.4	0	40.7
Debt Securities, Available-for-Sale, Realized Loss	(44.8)	(0.5)	(58.6)	(1.6)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(44.8)	0.9	(58.6)	39.1
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0.3	0.1	1
Debt Securities, Available-for-Sale, Realized Loss	0	0	(2.1)	(0.4)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	0.3	(2)	0.6
Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0	0	1.5
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	0	0	1.5
Short-term investments
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Loss	0	0	(0.3)	0
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	0	(0.3)	0
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	0.1	2.3	17.6	26
Equity Securities, FV-NI, Gross Realized Losses on Sales	(5.1)	(0.3)	(7)	(0.7)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	(5)	2	10.6	25.3
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	1.4	6.2	832.5	352.3
Equity Securities, FV-NI, Gross Realized Losses on Sales	0	(1.7)	(78)	(5.6)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	$ 1.4	$ 4.5	$ 754.5	$ 346.7

Investments - Components of Equ

Investments - Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Realized Investment Gains (Losses)	$ (144.3)	$ (10.4)	$ (1,399)	$ 851.8
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	(3.6)	6.5	765.1	372
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ (140.7)	$ (16.9)	$ (2,164.1)	$ 479.8

Investments - Components of N_2

Investments - Components of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net Investment Income [Line Items]
Gross investment income	$ 333.6	$ 208.9	$ 868.2	$ 639.8
Investment expenses	(5.8)	(6.6)	(17.4)	(18.5)
Net Investment Income	327.8	202.3	850.8	621.3
Available-for-sale Securities
Net Investment Income [Line Items]
Gross investment income	304.8	175.9	766.2	541.4
Total equity securities
Net Investment Income [Line Items]
Gross investment income	28.8	33	102	98.4
Total equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	17.3	17.3	53.6	52.5
Total equity securities | Common equities
Net Investment Income [Line Items]
Gross investment income	11.5	15.7	48.4	45.9
Total fixed maturities
Net Investment Income [Line Items]
Gross investment income	280	175.5	736.6	538.8
Total fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Gross investment income	86.1	39	205.4	106.8
Total fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Gross investment income	9.8	9.7	29.3	34.6
Total fixed maturities | Foreign government obligations
Net Investment Income [Line Items]
Gross investment income	0.1	0	0.2	0
Total fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Gross investment income	71.8	70.2	215.4	228.6
Total fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	8.8	3.2	23.2	9.4
Total fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	48.3	35	138.1	105.2
Total fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Gross investment income	52.1	16.1	116.5	47.1
Total fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	3	2.3	8.5	7.1
Short-term investments
Net Investment Income [Line Items]
Gross investment income	$ 24.8	$ 0.4	$ 29.6	$ 2.6

Investments - Additional Inform

Investments - Additional Information (Detail)	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($) security	Sep. 30, 2022 USD ($) security	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Schedule of Debt and Equity Securities [Line Items]
Principal amount of bonds and certificates of deposit	$ 468,700,000	$ 468,700,000
Securities Exceeding 10% of Shareholders' Equity	0	0	$ 0	$ 0
Non-Income Producing Securities	0	0
Open reverse repurchase commitments	0	0	0	0
Securities Sold under Agreements to Repurchase	0	0	0	0
Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value, Downgraded in Period	99,300,000	99,300,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Downgraded in Period	23,700,000	23,700,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Not Previously Recorded		0	0
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0	0	0	0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff		$ 0	$ 0	$ 0
Percent Change in Investment Income	60%	36%
Percent Change in Book Yield	39%	16%
Corporate debt securities
Schedule of Debt and Equity Securities [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Downgraded | security	5	5

Fair Value - Composition of Inv

Fair Value - Composition of Investment Portfolio by Major Security Type (Detail) - USD ($)	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 52,330,400,000	$ 51,514,100,000	$ 52,287,400,000
Fair Value	5,634,700,000	5,857,400,000	5,881,700,000
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	48,410,700,000	44,815,700,000	46,134,400,000
Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	44,173,100,000	43,873,100,000	45,045,700,000
Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	33,574,700,000	31,383,500,000	34,182,000,000
Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,405,500,000	18,488,200,000	21,142,100,000
Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,925,500,000	2,185,300,000	2,165,900,000
Available-for-sale Securities | Total fixed maturities | Debt Securities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	15,300,000	17,900,000	12,300,000
Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,228,400,000	10,692,100,000	10,861,700,000
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,416,800,000	12,307,900,000	10,679,100,000
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	723,000,000	790,000,000	627,900,000
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	5,087,900,000	6,535,600,000	5,789,000,000
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,605,900,000	4,982,300,000	4,262,200,000
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	181,600,000	181,700,000	184,600,000
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	39,800,000	50,900,000	51,400,000
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	8,800,000	0	0
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	133,000,000	130,800,000	133,200,000
Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,237,600,000	942,600,000	1,088,700,000
Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,919,700,000	6,698,400,000	6,153,000,000
Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,254,400,000	1,639,900,000	1,572,800,000
Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,141,400,000	1,497,400,000	1,470,800,000
Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	71,300,000	82,900,000	42,100,000
Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	41,700,000	59,600,000	59,900,000
Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,665,300,000	5,058,500,000	4,580,200,000
Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,646,600,000	5,041,600,000	4,567,600,000
Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	18,700,000	16,900,000	12,600,000
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	29,292,200,000	24,548,200,000	26,834,100,000
Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	26,634,000,000	19,441,300,000	22,231,200,000
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,414,400,000	18,498,900,000	21,152,700,000
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,405,500,000	18,488,200,000	21,142,100,000
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,405,500,000	18,488,200,000	21,142,100,000
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	8,900,000	10,700,000	10,600,000
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	8,900,000	10,700,000	10,600,000
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,219,600,000	942,400,000	1,078,500,000
Fair Value, Inputs, Level 1 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,658,200,000	5,106,900,000	4,602,900,000
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	60,900,000	115,300,000	89,800,000
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	60,900,000	115,300,000	89,800,000
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,597,300,000	4,991,600,000	4,513,100,000
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,597,300,000	4,991,600,000	4,513,100,000
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,937,600,000	26,838,200,000	25,275,400,000
Fair Value	5,634,700,000	5,857,400,000	5,881,700,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	21,776,700,000	25,374,400,000	23,903,200,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	21,758,700,000	25,374,200,000	23,893,000,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	11,169,200,000	12,895,300,000	13,039,900,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,925,500,000	2,185,300,000	2,165,900,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	15,300,000	17,900,000	12,300,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,228,400,000	10,692,100,000	10,861,700,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,416,800,000	12,307,900,000	10,679,100,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	723,000,000	790,000,000	627,900,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	5,087,900,000	6,535,600,000	5,789,000,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,605,900,000	4,982,300,000	4,262,200,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	172,700,000	171,000,000	174,000,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	39,800,000	50,900,000	51,400,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	8,800,000	0	0
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	124,100,000	120,100,000	122,600,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	18,000,000	200,000	10,200,000
Fair Value, Inputs, Level 2 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,160,900,000	1,463,800,000	1,372,200,000
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,111,600,000	1,413,800,000	1,372,200,000
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,015,600,000	1,305,700,000	1,304,600,000
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	71,300,000	82,900,000	42,100,000
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	24,700,000	25,200,000	25,500,000
Fair Value, Inputs, Level 2 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	49,300,000	50,000,000	0
Fair Value, Inputs, Level 2 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	49,300,000	50,000,000	0
Fair Value, Inputs, Level 2 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	100,600,000	127,700,000	177,900,000
Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	100,600,000	127,700,000	177,900,000
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	81,900,000	110,800,000	110,800,000
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	64,900,000	76,400,000	76,400,000
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	17,000,000	34,400,000	34,400,000
Fair Value, Inputs, Level 3 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	18,700,000	16,900,000	67,100,000
Fair Value, Inputs, Level 3 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	54,500,000
Fair Value, Inputs, Level 3 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	18,700,000	16,900,000	12,600,000
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	54,664,600,000	47,572,700,000	48,363,000,000
Long-term Debt	6,387,400,000	4,898,800,000	4,898,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	52,443,300,000	44,736,800,000	45,644,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	48,205,700,000	43,794,200,000	44,556,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	36,538,300,000	31,292,800,000	33,785,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	24,260,900,000	18,586,100,000	21,093,100,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,140,900,000	2,162,600,000	2,123,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	16,700,000	17,900,000	12,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,119,800,000	10,526,200,000	10,556,400,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	11,464,800,000	12,330,500,000	10,599,400,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	754,200,000	787,700,000	624,400,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	5,833,900,000	6,561,000,000	5,739,400,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,876,700,000	4,981,800,000	4,235,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	202,600,000	170,900,000	171,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	43,600,000	50,700,000	50,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,500,000	0	0
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	148,500,000	120,200,000	120,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,237,600,000	942,600,000	1,088,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,221,300,000	2,835,900,000	2,718,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,417,600,000	1,571,800,000	1,479,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,297,600,000	1,451,700,000	1,399,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	79,900,000	80,000,000	40,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	40,100,000	40,100,000	40,100,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	803,700,000	1,264,100,000	1,238,400,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	785,000,000	1,247,200,000	1,225,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 18,700,000	$ 16,900,000	$ 12,600,000

Fair Value - Summary of Changes

Fair Value - Summary of Changes in Fair Value Associated with Level 3 Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 100.4	$ 174.9	$ 127.7	$ 54.8
Calls/ Maturities/ Paydowns	0.2	1	1.3	9.5
Purchases	0	2	0	67.2
Sales	0	0	(15)	(5)
Net Realized (Gain)/Loss on Sales	0	0	(17.2)	(4.5)
Change in Valuation	0	0	3.8	55.9
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	100.6	177.9	100.6	177.9
Total equity securities | Financials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	64.9	76.4	76.4	10
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	60.2
Sales	0	0	(15)	0
Net Realized (Gain)/Loss on Sales	0	0	(17.2)	0
Change in Valuation	0	0	20.7	6.2
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	64.9	76.4	64.9	76.4
Total equity securities | Industrials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	17	34.4	34.4	16.7
Calls/ Maturities/ Paydowns	0	0	(0.5)	0
Purchases	0	0	0	5
Sales	0	0	0	(5)
Net Realized (Gain)/Loss on Sales	0	0	0	(4.5)
Change in Valuation	0	0	(16.9)	22.2
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	17	34.4	17	34.4
Total equity securities | Common Stocks, excluding Other Risk | Common equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance		52.5		25
Calls/ Maturities/ Paydowns		0		0
Purchases		2		2
Sales		0		0
Net Realized (Gain)/Loss on Sales		0		0
Change in Valuation		0		27.5
Net Transfers In (Out)		0		0
Fair value, ending balance		54.5		54.5
Total equity securities | Other risk investments | Common equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	18.5	11.6	16.9	3.1
Calls/ Maturities/ Paydowns	0.2	1	1.8	9.5
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	$ 18.7	$ 12.6	$ 18.7	$ 12.6

Fair Value - Summary of Quantit

Fair Value - Summary of Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 52,330.4	$ 52,287.4	$ 51,514.1
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	100.6	177.9	127.7
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	81.9	165.3	110.8
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	18.7	12.6	16.9
Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 81.9	$ 110.8	$ 110.8
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum	(20.70%)	(8.50%)	(20.20%)
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum	(1.10%)	19.80%	(2.30%)
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average	(6.60%)	6.50%	(7.70%)
Fair Value, Inputs, Level 3 | Common equities | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value		$ 54.5
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum		(1.60%)
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum		55.80%
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average		0.90%

Fair Value - Additional Informa

Fair Value - Additional Information (Detail) - USD ($)	3 Months Ended					9 Months Ended
	Sep. 30, 2022		Jun. 30, 2022	Sep. 30, 2021		Sep. 30, 2022		Sep. 30, 2021		Dec. 31, 2021
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 52,330,400,000			$ 52,287,400,000		$ 52,330,400,000		$ 52,287,400,000		$ 51,514,100,000
Goodwill impairment	$ 0	[1]	$ 224,800,000	$ 0	[1]	$ 224,800,000	[1]	$ 0	[1]
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	90%			82%		90%		82%		79%
Investments, Fair Value	$ 29,292,200,000			$ 26,834,100,000		$ 29,292,200,000		$ 26,834,100,000		$ 24,548,200,000
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	98%			97%		98%		97%		98%
Dealer Quoted Prices, Percent of FV Hierarchy Level	2%			3%		2%		3%		2%
Investments, Fair Value	$ 22,937,600,000			$ 25,275,400,000		$ 22,937,600,000		$ 25,275,400,000		$ 26,838,200,000
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	100,600,000			177,900,000		100,600,000		177,900,000		127,700,000
Available-for-sale Securities
Fair Value Measurements [Line Items]
Investments, Fair Value	48,410,700,000			46,134,400,000		48,410,700,000		46,134,400,000		44,815,700,000
Available-for-sale Securities | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	44,173,100,000			45,045,700,000		44,173,100,000		45,045,700,000		43,873,100,000
Available-for-sale Securities | Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Investments, Fair Value	26,634,000,000			22,231,200,000		26,634,000,000		22,231,200,000		19,441,300,000
Available-for-sale Securities | Fair Value, Inputs, Level 1 | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	22,414,400,000			21,152,700,000		22,414,400,000		21,152,700,000		18,498,900,000
Available-for-sale Securities | Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Investments, Fair Value	21,776,700,000			23,903,200,000		21,776,700,000		23,903,200,000		25,374,400,000
Available-for-sale Securities | Fair Value, Inputs, Level 2 | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	21,758,700,000			23,893,000,000		21,758,700,000		23,893,000,000		25,374,200,000
Available-for-sale Securities | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	0			0		0		0		0
Available-for-sale Securities | Fair Value, Inputs, Level 3 | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 0			$ 0		$ 0		$ 0		$ 0
[1] See Note 12 – Goodwill and Intangible Assets

Debt - Summary of Debt (Detail)

Debt - Summary of Debt (Detail) - USD ($)		Sep. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Mar. 31, 2020	Oct. 31, 2018	Mar. 31, 2018	Apr. 30, 2017	Aug. 31, 2016	Jan. 31, 2015	Apr. 30, 2014	Nov. 30, 2002	Mar. 31, 1999
Debt Instrument [Line Items]
Fair Value		$ 5,634,700,000		$ 5,857,400,000	$ 5,881,700,000
Debt, Long-term and Short-term, Combined Amount	[1]	6,387,400,000		4,898,800,000	4,898,200,000
2.45% Senior Notes due 2027 (issued: $500.0, August 2016)
Debt Instrument [Line Items]
Long-term Debt		498,100,000		497,700,000	497,600,000
Fair Value		459,700,000		517,900,000	530,600,000
Debt, stated interest rate										2.45%
Debt, face amount										$ 500,000,000
2.50% Senior Notes due 2027 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Long-term Debt		497,400,000		0	0
Fair Value		451,600,000		0	0
Debt, stated interest rate			2.50%
Debt, face amount			$ 500,000,000
6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)
Debt Instrument [Line Items]
Long-term Debt		297,400,000		297,200,000	297,100,000
Fair Value		322,100,000		388,200,000	390,900,000
Debt, stated interest rate														6.625%
Debt, face amount														$ 300,000,000
4.00% Senior Notes due 2029 (issued: $550.0, October 2018)
Debt Instrument [Line Items]
Long-term Debt		546,300,000		545,900,000	545,800,000
Fair Value		519,500,000		621,000,000	627,900,000
Debt, stated interest rate							4%
Debt, face amount							$ 550,000,000
3.20% Senior Notes due 2030 (issued: $500.0, March 2020)
Debt Instrument [Line Items]
Long-term Debt		496,800,000		496,500,000	496,400,000
Fair Value		439,300,000		536,300,000	543,200,000
Debt, stated interest rate						3.20%
Debt, face amount						$ 500,000,000
3.00% Senior Notes due 2032 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Long-term Debt		495,800,000		0	0
Fair Value		418,800,000		0	0
Debt, stated interest rate			3%
Debt, face amount			$ 500,000,000
6.25% Senior Notes due 2032 (issued: $400.0, November 2002)
Debt Instrument [Line Items]
Long-term Debt		396,400,000		396,200,000	396,100,000
Fair Value		426,000,000		547,900,000	545,500,000
Debt, stated interest rate													6.25%
Debt, face amount													$ 400,000,000
4.35% Senior Notes due 2044 (issued: $350.0, April 2014)
Debt Instrument [Line Items]
Long-term Debt		346,900,000		346,800,000	346,800,000
Fair Value		298,500,000		428,400,000	433,600,000
Debt, stated interest rate												4.35%
Debt, face amount												$ 350,000,000
3.70% Senior Notes due 2045 (issued: $400.0, January 2015)
Debt Instrument [Line Items]
Long-term Debt		395,700,000		395,600,000	395,600,000
Fair Value		305,700,000		447,100,000	456,200,000
Debt, stated interest rate											3.70%
Debt, face amount											$ 400,000,000
4.125% Senior Notes due 2047 (issued: $850.0, April 2017)
Debt Instrument [Line Items]
Long-term Debt		842,000,000		841,900,000	841,900,000
Fair Value		710,300,000		1,029,300,000	1,018,500,000
Debt, stated interest rate									4.125%
Debt, face amount									$ 850,000,000
4.20% Senior Notes due 2048 (issued: $600.0, March 2018)
Debt Instrument [Line Items]
Long-term Debt		590,300,000		590,200,000	590,200,000
Fair Value		505,900,000		741,300,000	736,300,000
Debt, stated interest rate								4.20%
Debt, face amount								$ 600,000,000
3.95% Senior Notes due 2050 (issued: $500.0, March 2020)
Debt Instrument [Line Items]
Long-term Debt		490,900,000		490,800,000	490,700,000
Fair Value		396,600,000		600,000,000	599,000,000
Debt, stated interest rate						3.95%
Debt, face amount						$ 500,000,000
3.70% Senior Notes due 2052 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Long-term Debt		493,400,000		0	0
Fair Value		$ 380,700,000		$ 0	$ 0
Debt, stated interest rate			3.70%
Debt, face amount			$ 500,000,000
[1] Consists of long-term debt. See Note 4 – Debt for further discussion.

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2022	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Debt Instrument [Line Items]
Proceeds from Debt, Net of Issuance Costs	$ 1,486,000,000
Long-term Debt, Current Maturities		$ 0	$ 0	$ 0
2.50% Senior Notes due 2027 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Debt, face amount	$ 500,000,000
Debt, stated interest rate	2.50%
3.00% Senior Notes due 2032 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Debt, face amount	$ 500,000,000
Debt, stated interest rate	3%
3.70% Senior Notes due 2052 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Debt, face amount	$ 500,000,000
Debt, stated interest rate	3.70%
Discretionary Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		250,000,000
Borrowings outstanding		$ 0	$ 0	$ 0

Income Taxes Reconciliation of

Income Taxes Reconciliation of Provision (Benefit) for Income Taxes Reported in Consolidated Statements of Income with Tax at Statutory Rate (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income (loss) before income taxes	$ 142.5	$ 139	$ (103.2)	$ 3,006.1
Tax at statutory federal rate	29.9	29.2	(21.7)	631.3
Goodwill impairment	0	0	47.2	0
Stock-based compensation	(9.6)	(7.9)	(17.7)	(19.2)
State income taxes, net of federal taxes	4.5	5.5	9.7	17.7
Tax-preferenced investment income	(2.8)	(3.3)	(9.5)	(10)
Tax credits	(5.2)	(3.7)	(9.4)	(6.1)
Nondeductible compensation expense	1.8	1.9	5.4	5.6
Tax deductible dividends	(0.4)	(0.5)	(1.4)	(1.6)
Other items, net	0.2	(0.7)	(0.9)	(0.2)
Provision for income taxes	$ 18.4	$ 20.5	$ 1.7	$ 617.5
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Tax at statutory federal rate	21%	21%	21%	21%
Goodwill impairment	0%	0%	(45.70%)	0%
Stock-based compensation	(6.70%)	(5.70%)	17.20%	(0.60%)
State income taxes, net of federal taxes	3.20%	4%	(9.40%)	0.60%
Tax-preferenced investment income	(2.00%)	(2.40%)	9.20%	(0.30%)
Tax credits	(3.60%)	(2.70%)	9.10%	(0.20%)
Nondeductible compensation expense	1.30%	1.40%	(5.20%)	0.20%
Tax deductible dividends	(0.30%)	(0.40%)	1.40%	(0.10%)
Other items, net	0%	(0.50%)	0.80%	(0.10%)
Provision for income taxes	12.90%	14.70%	(1.60%)	20.50%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Valuation allowance	$ 0	$ 0	$ 0	$ 0	$ 0
Provision for income taxes	12.90%	14.70%	(1.60%)	20.50%

Loss and Loss Adjustment Expe_3

Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Millions			9 Months Ended
	Jan. 01, 2022	Jan. 01, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expense reserves			$ 30,631.8	$ 25,926.3	$ 26,164.1	$ 20,265.8
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments and Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item			6,034	4,822.5	4,733.6	3,798.2
Liability for Unpaid Claims and Claims Adjustment Expense, Net	$ 21,430.5	$ 17,200.1	24,597.8	21,103.8	$ 21,430.5	$ 16,467.6
Liability for Unpaid Claims and Claims Adjustment Expense, Business Acquisitions	$ 0	$ 732.5
Current Year Claims and Claims Adjustment Expense			28,245.4	24,610.8
Prior Year Claims and Claims Adjustment Expense			(52.8)	(156.8)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims			28,298.2	24,767.6
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year			15,712.4	13,650.6
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years			9,418.5	7,213.3
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid			25,130.9	20,863.9
Short-Duration Insurance Contract, Accident Year 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense			(45)
Short-Duration Insurance Contract, Accident Year 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense				(109)
Short-Duration Insurance Contract, Accident Years 2018 and Prior
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense				(113)
Short-Duration Insurance Contract, Accident Years 2019 and Prior
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense			(29)
Short-Duration Insurance Contract, Accident Year 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense			21
Personal Lines | Personal auto business
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense			28	(48)
Personal Lines | special lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense				12
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense			(77)	(91)
Property
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense				(31)
Agency | Personal Lines | Personal auto business
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense				$ (44)
Direct | Personal Lines | Personal auto business
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense			$ 25

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Open reverse repurchase commitments	$ 0	$ 0	$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	29,700,000	79,500,000
Income Taxes Paid	595,900,000	669,500,000
Interest Paid, Excluding Capitalized Interest, Operating Activities	191,300,000	186,300,000
Operating Lease, Payments	62,500,000	67,800,000
Cash and Cash Equivalents
Open reverse repurchase commitments	123,000,000	134,600,000	$ 137,100,000
Common equities | Quarterly dividend
Dividends Payable	$ 58,500,000	$ 58,500,000

Segment Information - Operating

Segment Information - Operating Results (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Revenues	$ 12,780.2	$ 11,859.2	$ 36,140.9	$ 35,209.9
Pretax Profit (Loss)	142.5	139	(103.2)	3,006.1
Amortization of intangible assets	5.4	14.6	25.5	43.1
Personal Lines | Agency | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	4,441.9	4,267.9	13,131.7	12,586.4
Pretax Profit (Loss)	(41.3)	41	507.6	796
Personal Lines | Direct | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	5,077.4	4,690.2	14,776.9	13,755.8
Pretax Profit (Loss)	40.6	(62.4)	389.4	480.6
Operating Segments | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	12,398.9	11,364.8	36,349.7	32,767.3
Pretax Profit (Loss)	94.3	(46.9)	1,281.6	1,455.8
Operating Segments | Personal Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	9,519.3	8,958.1	27,908.6	26,342.2
Pretax Profit (Loss)	$ (0.7)	$ (21.4)	$ 897	$ 1,276.6
Personal auto insurance percentage of the total personal lines segment net premiums earned	94%	94%	94%	94%
Operating Segments | Commercial Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	$ 2,317.9	$ 1,877.4	$ 6,749.5	$ 4,917
Pretax Profit (Loss)	238.1	197.5	683.5	556.1
Operating Segments | Property
Segment Reporting Information [Line Items]
Pretax Profit (Loss)			(514.4)
Operating Segments | Property | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	561	526.5	1,689.6	1,501.3
Pretax Profit (Loss)	(141)	(222.7)	(289.6)	(376.7)
Amortization of intangible assets	5	14.2	24.1	42.5
Operating Segments | Property | Property - Goodwill impairment
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	0	0	(224.8)	0
Operating Segments | Other Indemnity | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	0.7	2.8	2	6.8
Pretax Profit (Loss)	(2.1)	(0.3)	(9.3)	(0.2)
Segment Reconciling Items | Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	181.4	174.9	531.9	516.8
Segment Reconciling Items | Service businesses
Segment Reporting Information [Line Items]
Revenues	82.7	73.8	230.5	202.1
Pretax Profit (Loss)	(0.1)	1	9	12.1
Segment Reconciling Items | Investment income
Segment Reporting Information [Line Items]
Revenues	117.2	245.7	(971.2)	1,723.7
Pretax Profit (Loss)	111.4	239.1	(988.6)	1,705.2
Segment Reconciling Items | Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (63.1)	$ (54.2)	$ (180.4)	$ (167)

Segment Information - Underwrit

Segment Information - Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Underwriting operations	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Personal Lines | Agency
Segment Reporting Information [Line Items]
Underwriting Margin	(0.90%)	1%	3.90%	6.30%
Combined Ratio	100.90%	99%	96.10%	93.70%
Personal Lines | Direct
Segment Reporting Information [Line Items]
Underwriting Margin	0.80%	(1.30%)	2.60%	3.50%
Combined Ratio	99.20%	101.30%	97.40%	96.50%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	0.80%	(0.40%)	3.50%	4.40%
Combined Ratio	99.20%	100.40%	96.50%	95.60%
Operating Segments | Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	0%	(0.20%)	3.20%	4.90%
Combined Ratio	100%	100.20%	96.80%	95.10%
Operating Segments | Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	10.30%	10.50%	10.10%	11.30%
Combined Ratio	89.70%	89.50%	89.90%	88.70%
Operating Segments | Property
Segment Reporting Information [Line Items]
Underwriting Margin	(25.10%)	(42.30%)	(17.10%)	(25.10%)
Combined Ratio	125.10%	142.30%	117.10%	125.10%
Combined ratio amortization points	0.009	0.027	0.014	0.028

Dividends (Details)

Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended												3 Months Ended			9 Months Ended
	Sep. 30, 2022	Aug. 31, 2022	Jul. 31, 2022	Apr. 30, 2022	Mar. 31, 2022	Jan. 31, 2022	Oct. 31, 2021	Sep. 30, 2021	Jul. 31, 2021	Apr. 30, 2021	Mar. 31, 2021	Jan. 31, 2021	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Common Stock, Dividends, Per Share, Declared													$ 0.10		$ 0.10	$ 0.30	$ 0.30
Payments of Ordinary Dividends, Common Stock																$ 175.5	$ 2,811.5
Payments of Ordinary Dividends, Preferred Stock and Preference Stock																26.8	26.8
Quarterly dividend
Common Stock, Dividends, Per Share, Declared		$ 0.10
Common Stock, Dividends, Per Share, Cash Paid			$ 0.10	$ 0.10		$ 0.10	$ 0.10		$ 0.10	$ 0.10		$ 0.10
Payments of Ordinary Dividends, Common Stock			$ 58.5	$ 58.5		$ 58.5	$ 58.5		$ 58.5	$ 58.5		$ 58.6
Annual variable dividend
Common Stock, Dividends, Per Share, Cash Paid												$ 4.50		$ 1.50
Payments of Ordinary Dividends, Common Stock												$ 2,635.9		$ 876.5
Series B Preferred Stock
Preferred Stock, Dividends, Per Share, Cash Paid	$ 26.875				$ 26.875			$ 26.875			$ 26.875
Payments of Ordinary Dividends, Preferred Stock and Preference Stock	$ 13.4				$ 13.4			$ 13.4			$ 13.4
Common equities | Quarterly dividend
Dividends Payable	$ 58.5							$ 58.5					$ 58.5		$ 58.5	$ 58.5	$ 58.5

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ (2,795.5)	$ 619.6	$ 52.3	$ 1,187.4
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax	(1,223.3)	(117.9)	(4,321.7)	(494.6)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax	(0.9)	(0.3)	(1.1)	(0.9)
OCI, before Reclassifications, before Tax, Attributable to Parent	(1,224.2)	(118.2)	(4,322.8)	(495.5)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(58.4)	46.4	(309)	237.5
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(0.2)	(0.2)	(0.4)	(0.8)
Total reclassification adjustment for amounts realized in net income, pre tax	(58.6)	46.2	(309.4)	236.7
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	(1,165.6)	(164.4)	(4,013.4)	(732.2)
AOCI before Tax, Attributable to Parent, ending balance	(3,961.1)	455.2	(3,961.1)	455.2
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	586.5	(136.4)	(11.6)	(255.7)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax	256.9	24.8	907.6	103.9
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax, Portion Attributable to Parent	(0.2)	(0.1)	(0.2)	(0.2)
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax	257.1	24.9	907.8	104.1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	12.3	(9.7)	64.9	(49.9)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	(0.1)	(0.1)	(0.1)	(0.2)
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	12.4	(9.6)	65	(49.7)
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	244.7	34.5	842.8	153.8
AOCI Tax, Attributable to Parent, ending balance	831.2	(101.9)	831.2	(101.9)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(2,209)	483.2	40.7	931.7
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	(966.4)	(93.1)	(3,414.1)	(390.7)
Foreign currency translation adjustment	(0.7)	(0.2)	(0.9)	(0.7)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(967.1)	(93.3)	(3,415)	(391.4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(46.1)	36.7	(244.1)	187.6
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.1)	(0.1)	(0.3)	(0.6)
Total reclassification adjustment for amounts realized in net income, after tax	(46.2)	36.6	(244.4)	187
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(920.9)	(129.9)	(3,170.6)	(578.4)
After tax total accumulated other comprehensive income, ending balance	(3,129.9)	353.3	(3,129.9)	353.3
Total net unrealized gains (losses) on securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(2,193.5)	498.8	56.2	947.3
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	(966.4)	(93.1)	(3,414.1)	(390.7)
Foreign currency translation adjustment	0	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(966.4)	(93.1)	(3,414.1)	(390.7)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(46.1)	36.7	(244.1)	187.6
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0	0	0	0
Total reclassification adjustment for amounts realized in net income, after tax	(46.1)	36.7	(244.1)	187.6
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(920.3)	(129.8)	(3,170)	(578.3)
After tax total accumulated other comprehensive income, ending balance	(3,113.8)	369	(3,113.8)	369
Net unrealized gains (losses) on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(14.7)	(15.1)	(14.9)	(15.6)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	0	0	0	0
Foreign currency translation adjustment	0	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.1)	(0.1)	(0.3)	(0.6)
Total reclassification adjustment for amounts realized in net income, after tax	(0.1)	(0.1)	(0.3)	(0.6)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.1	0.1	0.3	0.6
After tax total accumulated other comprehensive income, ending balance	(14.6)	(15)	(14.6)	(15)
Accumulated Foreign Currency Adjustment Attributable to Parent
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(0.8)	(0.5)	(0.6)	0
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	0	0	0	0
Foreign currency translation adjustment	(0.7)	(0.2)	(0.9)	(0.7)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.7)	(0.2)	(0.9)	(0.7)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0	0	0	0
Total reclassification adjustment for amounts realized in net income, after tax	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(0.7)	(0.2)	(0.9)	(0.7)
After tax total accumulated other comprehensive income, ending balance	$ (1.5)	$ (0.7)	$ (1.5)	$ (0.7)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement, Additional Information (Detail) $ in Millions	Sep. 30, 2022 USD ($)
Statement of Comprehensive Income [Abstract]
Net unrealized losses on forecasted transactions, expected to reclassify into income within the next 12 months	$ 0.5

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Schedule of Other Intangible Assets [Line Items]
Indefinite lived intangible assets	$ 12.4	$ 12.4	$ 12.4
Total	91.8	117.3	131.9
Accumulated amortization	153.1	383.8	369.2
Licensing Agreements
Schedule of Other Intangible Assets [Line Items]
Accumulated amortization	0.6	0.6	0.6
Finite-Lived Intangible Assets
Schedule of Other Intangible Assets [Line Items]
Intangible assets subject to amortization	79.4	104.9	119.5
Accumulated amortization	$ 152.5	$ 383.2	$ 368.6

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 153.1	$ 383.8	$ 369.2
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	256.2	256.2
Accumulated Amortization	0	247.1	237.9
Net Carrying Amount	0	9.1	18.3
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2
Accumulated Amortization	85.3	76.8	73.9
Net Carrying Amount	73.9	82.4	85.3
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	69.1	69.1	69.1
Accumulated Amortization	64.8	58.3	56.2
Net Carrying Amount	4.3	10.8	12.9
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3.6	3.6	3.6
Accumulated Amortization	2.4	1	0.6
Net Carrying Amount	1.2	2.6	3
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	231.9	488.1	488.1
Accumulated Amortization	152.5	383.2	368.6
Net Carrying Amount	$ 79.4	$ 104.9	$ 119.5

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Goodwill (Details) - USD ($)	3 Months Ended					9 Months Ended
	Sep. 30, 2022		Jun. 30, 2022	Sep. 30, 2021		Sep. 30, 2022		Sep. 30, 2021		Mar. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	[1]	$ 224,800,000	$ 0	[1]	$ 224,800,000	[1]	$ 0	[1]
Goodwill, Impaired, Accumulated Impairment Loss	224,800,000					224,800,000				$ 0
Goodwill	227,900,000			452,700,000		227,900,000		452,700,000			$ 452,700,000
Amortization of intangible assets	$ 5,400,000			14,600,000		$ 25,500,000		43,100,000
Property
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment			$ 224,800,000
Personal Lines | Agency
Finite-Lived Intangible Assets [Line Items]
Goodwill Attributable to Reporting Unit, Percent	98%					98%
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 0			$ 256,200,000		$ 0		$ 256,200,000			$ 256,200,000
Policies in force | Fully Amortized
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount										$ 256,200,000
[1] See Note 12 – Goodwill and Intangible Assets