The Progressive Corporation (PGR) 10-Q 2 May 23 2023 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2023 shares
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2023
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	585,366,448
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	0000080661
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Amendment Flag	false

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Revenues
Net premiums earned		$ 13,533.1	$ 11,802.9
Investment income		419.6	242.2
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales		(30.3)	(54.5)
Net holding period gains (losses) on securities		104.4	(388.6)
Net impairment losses recognized in earnings		(2.3)	(2.2)
Total net realized gains (losses) on securities		71.8	(445.3)
Fees and other revenues		206.2	174
Service revenues		72.5	67.7
Total revenues		14,303.2	11,841.5
Expenses
Losses and loss adjustment expenses		10,624	8,858.4
Policy acquisition costs		1,115.8	963.4
Other underwriting expenses		1,857.9	1,506.3
Investment expenses		5.5	5.7
Service expenses		82.3	63.2
Interest expense		63.3	54.3
Total expenses		13,748.8	11,451.3
Net Income
Income before income taxes		554.4	390.2
Provision for income taxes		106.5	76.3
Net income		447.9	313.9
Other Comprehensive Income (Loss)
Total net unrealized gains (losses) on fixed-maturity securities		603.2	(1,426.9)
Net unrealized losses on forecasted transactions		0.1	0.2
Foreign currency translation adjustment		0	0.2
Other comprehensive income (loss)		603.3	(1,426.5)
Comprehensive income (loss)		1,051.2	(1,112.6)
Computation of Earnings Per Common Share
Net income		447.9	313.9
Less: Preferred share dividends1	[1]	7.3	6.7
Net income available to common shareholders		$ 440.6	$ 307.2
Average common shares outstanding - Basic		584.9	584.3
Net effect of dilutive stock-based compensation		2.1	2
Total average equivalent common shares - Diluted		587	586.3
Basic: Earnings per common share		$ 0.75	$ 0.53
Diluted: Earnings per common share		$ 0.75	$ 0.52
[1] Changed to a floating dividend rate. See Note 1 – Basis of Presentation for further discussion.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Assets
Fixed maturities (amortized cost: $53,123.9, $48,082.7, and $50,264.0)		$ 50,289.2	$ 46,651.9	$ 46,316.4
Short-term investments (amortized cost: $2,524.1, $529.9, and $2,861.7)		2,524.1	2,861.7	529.9
Total available-for-sale securities		52,813.3	49,513.6	46,846.3
Nonredeemable preferred stocks (cost: $1,197.7, $1,545.5, and $1,364.2)		1,078.8	1,213.2	1,527.5
Common equities (cost: $740.5, $1,281.7, and $826.1)		2,794.3	2,821.5	4,812.6
Total equity securities		3,873.1	4,034.7	6,340.1
Total investments		56,686.4	53,548.3	53,186.4
Cash and cash equivalents		273.7	203.5	272.7
Restricted cash and cash equivalents		14.9	17.4	14.6
Total cash, cash equivalents, restricted cash, and restricted cash equivalents		288.6	220.9	287.3
Accrued investment income		299.5	282.5	193.4
Premiums receivable, net of allowance for credit losses of $340.9, $276.2, and $343.3		12,411.4	10,416.9	10,519
Reinsurance recoverables		5,616.2	5,832.1	5,025
Prepaid reinsurance premiums		269.6	295.5	455.1
Deferred acquisition costs		1,626.8	1,544.4	1,407.7
Property and equipment, net of accumulated depreciation of $1,576.2, $1,455.7, and $1,551.1		949	1,034	1,104.4
Goodwill		227.9	227.9	452.7
Intangible assets, net of accumulated amortization of $164.0, $142.2, and $158.6		80.9	86.3	102.7
Net federal deferred income taxes		1,057	1,131.5	370.5
Other assets		893.8	844.7	825.4
Total assets		80,407.1	75,465	73,929.6
Liabilities
Unearned premiums		19,844.3	17,293.6	16,991.4
Loss and loss adjustment expense reserves		31,026.4	30,359.3	26,754.2
Accounts payable, accrued expenses, and other liabilities		6,278.7	5,532.8	6,747.2
Debt	[1]	6,389.3	6,388.3	6,385.6
Total liabilities		63,538.7	59,574	56,878.4
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 212.2, 212.7, and 212.7)		585.4	584.9	584.9
Paid-in capital		1,907.7	1,893	1,788.6
Retained earnings		16,080.1	15,721.2	15,569.6
Accumulated other comprehensive income (loss):
Net unrealized gains (losses) on fixed-maturity securities		(2,183.1)	(2,786.3)	(1,370.7)
Net unrealized losses on forecasted transactions		(14.4)	(14.5)	(14.7)
Foreign currency translation adjustment		(1.2)	(1.2)	(0.4)
Total accumulated other comprehensive income (loss)		(2,198.7)	(2,802)	(1,385.8)
Total shareholders’ equity		16,868.4	15,891	17,051.2
Total liabilities and shareholders’ equity		$ 80,407.1	$ 75,465	$ 73,929.6
[1] Consists of long-term debt. See Note 4 – Debt for further discussion.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Fixed maturities, amortized cost	$ 53,123.9	$ 50,264	$ 48,082.7
Short-term investments, amortized cost	2,524.1	2,861.7	529.9
Nonredeemable preferred stocks, cost	1,197.7	1,364.2	1,545.5
Common equities, cost	740.5	826.1	1,281.7
Premium Receivable, Allowance for Credit Loss	340.9	343.3	276.2
Property and equipment, accumulated depreciation	1,576.2	1,551.1	1,455.7
Intangible Assets, Accumulated Amortization	$ 164	$ 158.6	$ 142.2
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)	212,200,000	212,700,000	212,700,000
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	$ 0.10
Balance, Beginning of period at Dec. 31, 2021			$ 493.9	$ 584.4	$ 1,772.9	$ 15,339.7	$ 40.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 313.9					313.9
Treasury shares purchased				(0.3)	(0.8)	(27.6)
Net restricted equity awards issued/vested				0.8	(0.8)
Amortization of equity-based compensation					17.3
Reinvested dividends on restricted stock units					0	0
Cash dividends declared on common shares ($0.10 and $0.10 per share)						(58.4)
Other, net						2
Other comprehensive income (loss)	(1,426.5)						(1,426.5)
Balance, End of period at Mar. 31, 2022	$ 17,051.2		493.9	584.9	1,788.6	15,569.6	(1,385.8)
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	$ 0.10
Balance, Beginning of period at Dec. 31, 2022	$ 15,891		493.9	584.9	1,893	15,721.2	(2,802)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	447.9					447.9
Treasury shares purchased				(0.2)	(0.8)	(31.7)
Net restricted equity awards issued/vested				0.7	(0.7)
Amortization of equity-based compensation					15.9
Reinvested dividends on restricted stock units					0.3	(0.3)
Cash dividends declared on common shares ($0.10 and $0.10 per share)						(58.5)
Other, net						1.5
Other comprehensive income (loss)	603.3						603.3
Balance, End of period at Mar. 31, 2023	$ 16,868.4		$ 493.9	$ 585.4	$ 1,907.7	$ 16,080.1	$ (2,198.7)
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	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash Flows From Operating Activities
Net income	$ 447.9	$ 313.9
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	68	71.1
Amortization of intangible assets	5.4	14.6
Net amortization (accretion) of fixed-income securities	(5)	27
Amortization of equity-based compensation	15.9	17.3
Net realized (gains) losses on securities	(71.8)	445.3
Net (gains) losses on disposition of property and equipment	16.5	3.3
Changes in:
Premiums receivable	(1,994.5)	(1,119.5)
Reinsurance recoverables	215.9	(44.5)
Prepaid reinsurance premiums	25.9	2.5
Deferred acquisition costs	(82.4)	(52.1)
Income taxes	106.6	76.2
Unearned premiums	2,550.7	1,375.6
Loss and loss adjustment expense reserves	667.1	590.1
Accounts payable, accrued expenses, and other liabilities	565.5	545.1
Other, net	(82.2)	236.4
Net cash provided by operating activities	2,449.5	2,502.3
Purchases:
Fixed maturities	(6,119.5)	(11,453.4)
Equity securities	(17.8)	(74.3)
Sales:
Fixed maturities	2,202.6	5,889.9
Equity securities	277.3	59.2
Maturities, paydowns, calls, and other:
Fixed maturities	976	1,177.6
Equity securities	25.1	39.3
Net (purchases) sales of short-term investments	360.8	413.1
Net change in unsettled security transactions	57.2	212.6
Purchases of property and equipment	(43.2)	(73)
Sales of property and equipment	4.3	6.5
Net cash used in investing activities	(2,277.2)	(3,802.5)
Cash Flows From Financing Activities
Dividends paid to common shareholders	(58.5)	(58.5)
Dividends paid to preferred shareholders	(13.4)	(13.4)
Acquisition of treasury shares for restricted stock tax liabilities	(32.7)	(28.7)
Net proceeds from debt issuances	0	1,486
Net cash provided by (used in) financing activities	(104.6)	1,385.4
Increase in cash, cash equivalents, restricted cash, and restricted cash equivalents	67.7	85.2
Cash, cash equivalents, restricted cash, and restricted cash equivalents – January 1	220.9	202.1
Cash, cash equivalents, restricted cash, and restricted cash equivalents – March 31	$ 288.6	$ 287.3

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Reporting and Accounting	BASIS OF REPORTING AND ACCOUNTING 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 March 31, 2023, 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, 2022 (2022 Annual Report to Shareholders). Insurance Premiums and Receivables We perform analyses to evaluate our premiums receivable for expected credit losses. See the 2022 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 March 31, (millions) 2023 2022 Allowance for credit losses, beginning of period $ 343.3 $ 280.4 Increase in allowance 1 116.9 93.9 Write-offs 2 (119.3) (98.1) Allowance for credit losses, end of period $ 340.9 $ 276.2 1 Represents the incremental increase in other underwriting expenses. 2 Represents the 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 Included in other assets in the consolidated balance sheets are “held for sale” property. When property is transferred to held for sale, the property is written down to its fair value less estimated costs to sell the property. At March 31, 2023 and 2022, and December 31, 2022, we had held for sale property of $67.8 million, $20.2 million, and $48.7 million, respectively. Earnings Per Share Net income is reduced by preferred share dividends to determine net income available to common shareholders, and is used in our calculation of the per common share amounts. Beginning March 15, 2023, the annual dividend rate for our Series B Preferred Shares switched to a floating rate. The floating nature of the dividend rate will impact the amount of the adjustment required to calculate net income available to common shareholders. See Note 9 – Dividends for further discussion.

Investments

Investments	3 Months Ended
	Mar. 31, 2023
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 for the hybrid and equity securities. The changes in the net holding period gains (losses) between periods 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 March 31, 2023 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 28,490.9 $ 68.8 $ (1,209.6) $ 0 $ 27,350.1 48.3 % State and local government obligations 2,222.4 0.9 (161.7) 0 2,061.6 3.6 Foreign government obligations 16.9 0 (1.1) 0 15.8 0.1 Corporate debt securities 11,195.8 45.6 (525.4) (34.7) 10,681.3 18.8 Residential mortgage-backed securities 655.0 0.2 (16.3) (8.9) 630.0 1.1 Commercial mortgage-backed securities 5,252.6 1.6 (751.2) 0 4,503.0 7.9 Other asset-backed securities 5,087.8 1.8 (222.5) (1.3) 4,865.8 8.6 Redeemable preferred stocks 202.5 0 (5.2) (15.7) 181.6 0.3 Total fixed maturities 53,123.9 118.9 (2,893.0) (60.6) 50,289.2 88.7 Short-term investments 2,524.1 0 0 0 2,524.1 4.5 Total available-for-sale securities 55,648.0 118.9 (2,893.0) (60.6) 52,813.3 93.2 Equity securities: Nonredeemable preferred stocks 1,197.7 0 0 (118.9) 1,078.8 1.9 Common equities 740.5 0 0 2,053.8 2,794.3 4.9 Total equity securities 1,938.2 0 0 1,934.9 3,873.1 6.8 Total portfolio 1 $ 57,586.2 $ 118.9 $ (2,893.0) $ 1,874.3 $ 56,686.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of March 31, 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 20,399.6 $ 5.9 $ (876.7) $ 0 $ 19,528.8 36.7 % State and local government obligations 2,236.9 4.4 (97.1) 0 2,144.2 4.0 Foreign government obligations 18.3 0 (0.9) 0 17.4 0.1 Corporate debt securities 11,590.2 31.2 (315.5) (25.9) 11,280.0 21.2 Residential mortgage-backed securities 962.3 1.1 (5.1) (7.2) 951.1 1.8 Commercial mortgage-backed securities 7,296.4 2.2 (380.1) 0 6,918.5 13.0 Other asset-backed securities 5,359.9 1.1 (103.6) (1.5) 5,255.9 9.9 Redeemable preferred stocks 219.1 0.1 (1.8) 3.1 220.5 0.4 Total fixed maturities 48,082.7 46.0 (1,780.8) (31.5) 46,316.4 87.1 Short-term investments 529.9 0 0 0 529.9 1.0 Total available-for-sale securities 48,612.6 46.0 (1,780.8) (31.5) 46,846.3 88.1 Equity securities: Nonredeemable preferred stocks 1,545.5 0 0 (18.0) 1,527.5 2.9 Common equities 1,281.7 0 0 3,530.9 4,812.6 9.0 Total equity securities 2,827.2 0 0 3,512.9 6,340.1 11.9 Total portfolio 1 $ 51,439.8 $ 46.0 $ (1,780.8) $ 3,481.4 $ 53,186.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of December 31, 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 26,770.7 $ 1.4 $ (1,604.7) $ 0 $ 25,167.4 47.0 % State and local government obligations 2,180.0 0 (202.9) 0 1,977.1 3.7 Foreign government obligations 16.8 0 (1.3) 0 15.5 0.1 Corporate debt securities 10,125.8 9.8 (676.1) (46.8) 9,412.7 17.6 Residential mortgage-backed securities 696.1 0.3 (17.5) (12.1) 666.8 1.2 Commercial mortgage-backed securities 5,446.0 1.5 (784.0) 0 4,663.5 8.7 Other asset-backed securities 4,826.0 0.9 (260.5) (1.8) 4,564.6 8.5 Redeemable preferred stocks 202.6 0 (4.5) (13.8) 184.3 0.3 Total fixed maturities 50,264.0 13.9 (3,551.5) (74.5) 46,651.9 87.1 Short-term investments 2,861.7 0 0 0 2,861.7 5.4 Total available-for-sale securities 53,125.7 13.9 (3,551.5) (74.5) 49,513.6 92.5 Equity securities: Nonredeemable preferred stocks 1,364.2 0 0 (151.0) 1,213.2 2.3 Common equities 826.1 0 0 1,995.4 2,821.5 5.2 Total equity securities 2,190.3 0 0 1,844.4 4,034.7 7.5 Total portfolio 1 $ 55,316.0 $ 13.9 $ (3,551.5) $ 1,769.9 $ 53,548.3 100.0 % 1 At March 31, 2023 and 2022, we had $22.8 million and $356.0 million, respectively, of net unsettled security purchase transactions included in other liabilities, compared to $34.4 million included in other assets at December 31, 2022. The total fair value of the portfolio at March 31, 2023 and 2022, and December 31, 2022, included $4.1 billion, $5.1 billion, and $4.4 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of unsettled security transactions. At March 31, 2023, bonds and certificates of deposit in the principal amount of $604.4 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 March 31, 2023 or 2022, or December 31, 2022. At March 31, 2023, 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 did not enter into any repurchase or reverse repurchase transactions during the first quarter 2023, but did invest in repurchase transactions during 2022; however, we did not have any open positions at March 31, 2023 and 2022, or December 31, 2022. 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: March 31, (millions) 2023 2022 Dec. 31, 2022 Fixed Maturities: Corporate debt securities $ 548.6 $ 535.8 $ 535.4 Residential mortgage-backed securities 482.1 721.7 509.6 Other asset-backed securities 33.8 75.0 42.0 Redeemable preferred stocks 132.8 152.1 134.7 Total hybrid securities $ 1,197.3 $ 1,484.6 $ 1,221.7 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 use the fair value option 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 March 31, 2023, was: (millions) Cost Fair Value Less than one year $ 7,941.7 $ 7,706.0 One to five years 31,574.9 30,132.2 Five to ten years 13,505.5 12,353.0 Ten years or greater 101.8 98.0 Total $ 53,123.9 $ 50,289.2 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 March 31, 2023 U.S. government obligations 148 $ 19,446.8 $ (1,209.6) 40 $ 5,938.5 $ (127.5) 108 $ 13,508.3 $ (1,082.1) State and local government obligations 343 1,943.6 (161.7) 72 350.7 (7.4) 271 1,592.9 (154.3) Foreign government obligations 1 15.8 (1.1) 0 0 0 1 15.8 (1.1) Corporate debt securities 390 8,129.9 (525.4) 93 2,239.3 (75.5) 297 5,890.6 (449.9) Residential mortgage-backed securities 43 141.7 (16.3) 13 10.0 (0.4) 30 131.7 (15.9) Commercial mortgage-backed securities 220 4,484.5 (751.2) 11 53.4 (1.5) 209 4,431.1 (749.7) Other asset-backed securities 267 4,391.9 (222.5) 61 884.8 (6.2) 206 3,507.1 (216.3) Redeemable preferred stocks 4 48.8 (5.2) 1 10.6 (1.4) 3 38.2 (3.8) Total fixed maturities 1,416 $ 38,603.0 $ (2,893.0) 291 $ 9,487.3 $ (219.9) 1,125 $ 29,115.7 $ (2,673.1) 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 March 31, 2022 U.S. government obligations 116 $ 18,478.0 $ (876.7) 97 $ 15,467.4 $ (649.4) 19 $ 3,010.6 $ (227.3) State and local government obligations 290 1,767.7 (97.1) 279 1,627.3 (82.1) 11 140.4 (15.0) Foreign government obligations 1 17.4 (0.9) 1 17.4 (0.9) 0 0 0 Corporate debt securities 416 7,830.6 (315.5) 407 7,623.8 (294.2) 9 206.8 (21.3) Residential mortgage-backed securities 32 201.8 (5.1) 26 189.0 (4.1) 6 12.8 (1.0) Commercial mortgage-backed securities 264 6,584.4 (380.1) 245 6,133.0 (327.9) 19 451.4 (52.2) Other asset-backed securities 269 4,927.4 (103.6) 263 4,873.8 (102.7) 6 53.6 (0.9) Redeemable preferred stocks 3 37.4 (1.8) 2 26.4 (0.3) 1 11.0 (1.5) Total fixed maturities 1,391 $ 39,844.7 $ (1,780.8) 1,320 $ 35,958.1 $ (1,461.6) 71 $ 3,886.6 $ (319.2) 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, 2022 U.S. government obligations 160 $ 24,802.5 $ (1,604.7) 90 $ 17,327.2 $ (699.2) 70 $ 7,475.3 $ (905.5) State and local government obligations 348 1,948.8 (202.9) 239 1,124.2 (76.8) 109 824.6 (126.1) Foreign government obligations 1 15.5 (1.3) 0 0 0 1 15.5 (1.3) Corporate debt securities 422 8,449.6 (676.1) 285 5,717.6 (426.1) 137 2,732.0 (250.0) Residential mortgage-backed securities 45 151.0 (17.5) 27 65.1 (6.8) 18 85.9 (10.7) Commercial mortgage-backed securities 226 4,651.1 (784.0) 99 1,702.0 (192.1) 127 2,949.1 (591.9) Other asset-backed securities 262 4,247.8 (260.5) 130 2,144.8 (100.9) 132 2,103.0 (159.6) Redeemable preferred stocks 4 49.6 (4.5) 3 38.5 (3.1) 1 11.1 (1.4) Total fixed maturities 1,468 $ 44,315.9 $ (3,551.5) 873 $ 28,119.4 $ (1,505.0) 595 $ 16,196.5 $ (2,046.5) As of March 31, 2023, we had four securities that had their credit ratings downgraded during the quarter, with a combined fair value of $28.8 million and an unrealized loss of $1.7 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 three months of 2023 or 2022, and did not have a material credit loss allowance balance as of March 31, 2023 and 2022, or December 31, 2022. 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 performed additional analysis to determine if the loss was credit related. For securities subject to credit related loss, 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 March 31, 2023 and 2022, and December 31, 2022, we believe none of the unrealized losses were related 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 March 31, 2023 and 2022, and December 31, 2022, 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 March 31, 2023 and 2022, or December 31, 2022. Realized Gains (Losses) The components of net realized gains (losses) for the three months ended March 31, were: Three Months (millions) 2023 2022 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 3.8 $ 3.3 Corporate debt securities 0.1 4.5 Residential mortgage-backed securities 0 0.1 Other asset-backed securities 0 0.1 Total available-for-sale securities 3.9 8.0 Equity securities: Nonredeemable preferred stocks 0.1 17.3 Common equities 132.0 0.5 Total equity securities 132.1 17.8 Subtotal gross realized gains on security sales 136.0 25.8 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (11.5) (69.2) State and local government obligations 0 (1.0) Corporate debt securities (20.4) (7.7) Commercial mortgage-backed securities (34.5) 0 Other asset-backed securities (0.2) (0.1) Short-term investments (0.1) 0 Total available-for-sale securities (66.7) (78.0) Equity securities: Nonredeemable preferred stocks (101.0) (1.7) Common equities (11.8) (0.6) Total equity securities (112.8) (2.3) Subtotal gross realized losses on security sales (179.5) (80.3) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations (7.7) (65.9) State and local government obligations 0 (1.0) Corporate debt securities (20.3) (3.2) Residential mortgage-backed securities 0 0.1 Commercial mortgage-backed securities (34.5) 0 Other asset-backed securities (0.2) 0 Short-term investments (0.1) 0 Total available-for-sale securities (62.8) (70.0) Equity securities: Nonredeemable preferred stocks (100.9) 15.6 Common equities 120.2 (0.1) Total equity securities 19.3 15.5 Subtotal net realized gains (losses) on security sales (43.5) (54.5) Other assets Gain 13.2 0 Impairment (2.3) (2.2) Subtotal net realized gains (losses) on other assets 10.9 (2.2) Net holding period gains (losses) Hybrid securities 13.9 (39.0) Equity securities 90.5 (349.6) Subtotal net holding period gains (losses) 104.4 (388.6) Total net realized gains (losses) on securities $ 71.8 $ (445.3) Realized gains (losses) on securities sold are computed using the first-in-first-out method. For the first three months of 2023, the gross gains in common equities reflected sales of securities, as part of our plan to incrementally reduce risk in the portfolio in response to the potential of a more difficult economic environment over the near term. The gross 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. In addition, during the first quarter 2023, we selectively sold securities, which were primarily corporate debt securities and commercial mortgage-backed securities. The gross loss incurred in our nonredeemable preferred stocks is primarily related to the sale of certain of our holdings in U. S. bank preferred stocks. The other asset gain for 2023, related to proceeds received as the result of litigation in conjunction with three renewable energy investments we made from 2016 through 2018 (the original investments were previously written down in full). 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 is 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 (millions) 2023 2022 Total net gains (losses) recognized during the period on equity securities $ 109.8 $ (334.1) Less: Net gains (losses) recognized on equity securities sold during the period 19.3 15.5 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 90.5 $ (349.6) Net Investment Income The components of net investment income for the three months ended March 31, were: Three Months (millions) 2023 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 163.2 $ 51.4 State and local government obligations 10.6 9.2 Foreign government obligations 0.1 0.1 Corporate debt securities 83.6 68.1 Residential mortgage-backed securities 9.2 4.8 Commercial mortgage-backed securities 50.0 43.3 Other asset-backed securities 48.5 25.1 Redeemable preferred stocks 2.9 2.5 Total fixed maturities 368.1 204.5 Short-term investments 24.7 0.4 Total available-for-sale securities 392.8 204.9 Equity securities: Nonredeemable preferred stocks 15.1 18.2 Common equities 11.7 19.1 Total equity securities 26.8 37.3 Investment income 419.6 242.2 Investment expenses (5.5) (5.7) Net investment income $ 414.1 $ 236.5 On a year-over-year basis, investment income (interest and dividends) increased 73% and the recurring investment book yield increased 50%, compared to the same periods last year, primarily due to an increase in interest rates on floating-rate securities in our portfolio and investing new cash and cash from maturities in higher interest rate securities given the rising interest rate environment.

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2023
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 that 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 March 31, 2023 Fixed maturities: U.S. government obligations $ 27,350.1 $ 0 $ 0 $ 27,350.1 $ 28,490.9 State and local government obligations 0 2,061.6 0 2,061.6 2,222.4 Foreign government obligations 0 15.8 0 15.8 16.9 Corporate debt securities 0 10,681.3 0 10,681.3 11,195.8 Subtotal 27,350.1 12,758.7 0 40,108.8 41,926.0 Asset-backed securities: Residential mortgage-backed 0 630.0 0 630.0 655.0 Commercial mortgage-backed 0 4,503.0 0 4,503.0 5,252.6 Other asset-backed 0 4,865.8 0 4,865.8 5,087.8 Subtotal asset-backed securities 0 9,998.8 0 9,998.8 10,995.4 Redeemable preferred stocks: Financials 0 40.0 0 40.0 43.5 Utilities 0 8.8 0 8.8 10.5 Industrials 9.6 123.2 0 132.8 148.5 Subtotal redeemable preferred stocks 9.6 172.0 0 181.6 202.5 Total fixed maturities 27,359.7 22,929.5 0 50,289.2 53,123.9 Short-term investments 2,524.1 0 0 2,524.1 2,524.1 Total available-for-sale securities 29,883.8 22,929.5 0 52,813.3 55,648.0 Equity securities: Nonredeemable preferred stocks: Financials 40.0 884.5 67.4 991.9 1,102.7 Utilities 0 70.5 0 70.5 80.0 Industrials 0 0 16.4 16.4 15.0 Subtotal nonredeemable preferred stocks 40.0 955.0 83.8 1,078.8 1,197.7 Common equities: Common stocks 2,755.7 0 18.3 2,774.0 720.2 Other risk investments 0 0 20.3 20.3 20.3 Subtotal common equities 2,755.7 0 38.6 2,794.3 740.5 Total equity securities 2,795.7 955.0 122.4 3,873.1 1,938.2 Total portfolio $ 32,679.5 $ 23,884.5 $ 122.4 $ 56,686.4 $ 57,586.2 Debt $ 0 $ 5,881.0 $ 0 $ 5,881.0 $ 6,389.3 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost March 31, 2022 Fixed maturities: U.S. government obligations $ 19,528.8 $ 0 $ 0 $ 19,528.8 $ 20,399.6 State and local government obligations 0 2,144.2 0 2,144.2 2,236.9 Foreign government obligations 0 17.4 0 17.4 18.3 Corporate debt securities 0 11,280.0 0 11,280.0 11,590.2 Subtotal 19,528.8 13,441.6 0 32,970.4 34,245.0 Asset-backed securities: Residential mortgage-backed 0 951.1 0 951.1 962.3 Commercial mortgage-backed 0 6,918.5 0 6,918.5 7,296.4 Other asset-backed 0 5,255.9 0 5,255.9 5,359.9 Subtotal asset-backed securities 0 13,125.5 0 13,125.5 13,618.6 Redeemable preferred stocks: Financials 0 61.2 0 61.2 62.6 Utilities 0 7.2 0 7.2 7.5 Industrials 10.3 141.8 0 152.1 149.0 Subtotal redeemable preferred stocks 10.3 210.2 0 220.5 219.1 Total fixed maturities 19,539.1 26,777.3 0 46,316.4 48,082.7 Short-term investments 512.9 17.0 0 529.9 529.9 Total available-for-sale securities 20,052.0 26,794.3 0 46,846.3 48,612.6 Equity securities: Nonredeemable preferred stocks: Financials 92.2 1,237.3 61.4 1,390.9 1,425.4 Utilities 0 78.1 0 78.1 80.0 Industrials 0 24.6 33.9 58.5 40.1 Subtotal nonredeemable preferred stocks 92.2 1,340.0 95.3 1,527.5 1,545.5 Common equities: Common stocks 4,743.2 49.3 0 4,792.5 1,261.6 Other risk investments 0 0 20.1 20.1 20.1 Subtotal common equities 4,743.2 49.3 20.1 4,812.6 1,281.7 Total equity securities 4,835.4 1,389.3 115.4 6,340.1 2,827.2 Total portfolio $ 24,887.4 $ 28,183.6 $ 115.4 $ 53,186.4 $ 51,439.8 Debt $ 0 $ 6,692.6 $ 0 $ 6,692.6 $ 6,385.6 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2022 Fixed maturities: U.S. government obligations $ 25,167.4 $ 0 $ 0 $ 25,167.4 $ 26,770.7 State and local government obligations 0 1,977.1 0 1,977.1 2,180.0 Foreign government obligations 0 15.5 0 15.5 16.8 Corporate debt securities 0 9,412.7 0 9,412.7 10,125.8 Subtotal 25,167.4 11,405.3 0 36,572.7 39,093.3 Asset-backed securities: Residential mortgage-backed 0 666.8 0 666.8 696.1 Commercial mortgage-backed 0 4,663.5 0 4,663.5 5,446.0 Other asset-backed 0 4,564.6 0 4,564.6 4,826.0 Subtotal asset-backed securities 0 9,894.9 0 9,894.9 10,968.1 Redeemable preferred stocks: Financials 0 40.5 0 40.5 43.6 Utilities 0 9.1 0 9.1 10.5 Industrials 9.2 125.5 0 134.7 148.5 Subtotal redeemable preferred stocks 9.2 175.1 0 184.3 202.6 Total fixed maturities 25,176.6 21,475.3 0 46,651.9 50,264.0 Short-term investments 2,800.7 61.0 0 2,861.7 2,861.7 Total available-for-sale securities 27,977.3 21,536.3 0 49,513.6 53,125.7 Equity securities: Nonredeemable preferred stocks: Financials 39.0 994.4 67.4 1,100.8 1,244.2 Utilities 0 71.2 0 71.2 79.9 Industrials 0 24.8 16.4 41.2 40.1 Subtotal nonredeemable preferred stocks 39.0 1,090.4 83.8 1,213.2 1,364.2 Common equities: Common stocks 2,783.4 0 18.3 2,801.7 806.3 Other risk investments 0 0 19.8 19.8 19.8 Subtotal common equities 2,783.4 0 38.1 2,821.5 826.1 Total equity securities 2,822.4 1,090.4 121.9 4,034.7 2,190.3 Total portfolio $ 30,799.7 $ 22,626.7 $ 121.9 $ 53,548.3 $ 55,316.0 Debt $ 0 $ 5,717.9 $ 0 $ 5,717.9 $ 6,388.3 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 March 31, 2023, vendor-quoted prices represented 91% of our Level 1 classifications (excluding short-term investments), compared to 81% and 90% at March 31, 2022 and December 31, 2022, 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 March 31, 2023 and December 31, 2022, 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 March 31, 2022. 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 2 common stock held at March 31, 2022 was transferred to Level 3 at December 31, 2022. At March 31, 2023 and 2022, and December 31, 2022, we did not have any securities in our fixed-maturity portfolio listed as Level 3. During the first three months of 2023 and 2022, there were no material assets or liabilities measured at fair value on a nonrecurring basis. 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 months ended March 31, 2023 and 2022: Level 3 Fair Value (millions) Fair Value at Dec. 31, 2022 Calls/ Purchases Sales Net Realized Change in Net Fair Value at March 31, 2023 Equity securities: Nonredeemable preferred stocks: Financials $ 67.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 67.4 Industrials 16.4 0 0 0 0 0 0 16.4 Common equities: Common stocks 18.3 0 0 0 0 0 0 18.3 Other risk investments 19.8 0.5 0 0 0 0 0 20.3 Total Level 3 securities $ 121.9 $ 0.5 $ 0 $ 0 $ 0 $ 0 $ 0 $ 122.4 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2021 Calls/ Purchases Sales Net Realized Change in Net Fair Value at March 31, 2022 Equity securities: Nonredeemable preferred stocks: Financials $ 76.4 $ 0 $ 0 $ (15.0) $ (17.2) $ 17.2 $ 0 $ 61.4 Industrials 34.4 (0.5) 0 0 0 0 0 33.9 Common equities: Other risk investments 16.9 3.2 0 0 0 0 0 20.1 Total Level 3 securities $ 127.7 $ 2.7 $ 0 $ (15.0) $ (17.2) $ 17.2 $ 0 $ 115.4 The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at March 31, 2023 and 2022, and December 31, 2022: Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 2023 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 83.8 Market comparables Weighted average market capitalization price change % 2.7% to 23.3% 9.2 % Common stocks 18.3 Market comparables Weighted average market capitalization price change % (51.3)% to 48.3% 15.6 % Subtotal Level 3 securities 102.1 Pricing exemption securities 20.3 Total Level 3 securities $ 122.4 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 2022 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 95.3 Market comparables Weighted average market capitalization price change % (27.9)% to (12.7)% 20.1 % Subtotal Level 3 securities 95.3 Pricing exemption securities 20.1 Total Level 3 securities $ 115.4 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2022 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 83.8 Market comparables Weighted average market capitalization price change % (0.6)% to 19.9% 10.5% Common stocks 18.3 Market comparables Weighted average market capitalization price change % (42.5)% to 59.1% 0.3% Subtotal Level 3 securities 102.1 Pricing exemption securities 19.8 Total Level 3 securities $ 121.9

Debt

Debt	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
Debt	DEBT Debt at each of the balance sheet periods consisted of: March 31, 2023 March 31, 2022 December 31, 2022 (millions) Carrying Fair Carrying Fair Carrying Fair 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) $ 498.3 $ 464.2 $ 497.8 $ 487.9 $ 498.2 $ 457.7 2.50% Senior Notes due 2027 (issued: $500.0, March 2022) 497.7 463.8 497.1 489.4 497.5 460.3 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 297.6 329.6 297.3 358.8 297.5 326.8 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 546.5 538.5 546.1 573.5 546.4 527.8 3.20% Senior Notes due 2030 (issued: $500.0, March 2020) 497.0 460.0 496.6 496.2 496.9 448.6 3.00% Senior Notes due 2032 (issued: $500.0, March 2022) 496.0 446.9 495.6 487.0 495.9 438.1 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 396.5 448.1 396.2 494.8 396.4 435.4 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.9 312.3 346.8 368.7 346.9 298.4 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.8 324.0 395.7 386.0 395.7 310.2 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 842.1 743.8 841.9 894.5 842.1 716.2 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 590.4 530.0 590.3 637.4 590.4 507.0 3.95% Senior Notes due 2050 (issued: $500.0, March 2020) 491.0 420.3 490.8 514.9 490.9 404.9 3.70% Senior Notes due 2052 (issued: $500.0, March 2022) 493.5 399.5 493.4 503.5 493.5 386.5 Total $ 6,389.3 $ 5,881.0 $ 6,385.6 $ 6,692.6 $ 6,388.3 $ 5,717.9 There was no short-term debt outstanding at March 31, 2023 and 2022, and December 31, 2022. The Progressive Corporation has a line of credit with PNC Bank, National Association (PNC), in the maximum principal amount of $250 million. See the 2022 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	3 Months Ended
	Mar. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXESDeferred 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 March 31, 2023 and 2022, and December 31, 2022, 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. At March 31, 2023 and 2022, and December 31, 2022, the net deferred tax asset includes a gross deferred tax asset of $582.6 million, $364.3 million, and $742.9 million, respectively, related to unrealized losses on fixed-maturity securities. We believe this deferred tax asset will be realized based on the existence of prior year capital gains, current temporary differences related to unrealized gains in our equity portfolio, and other tax planning strategies. At March 31, 2023 and 2022, and December 31, 2022, we had no reserves for uncertain tax positions.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	3 Months Ended
	Mar. 31, 2023
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: March 31, (millions) 2023 2022 Balance at January 1 $ 30,359.3 $ 26,164.1 Less reinsurance recoverables on unpaid losses 5,559.2 4,733.6 Net balance at January 1 24,800.1 21,430.5 Incurred related to: Current year 10,002.8 8,667.6 Prior years 621.2 190.8 Total incurred 10,624.0 8,858.4 Paid related to: Current year 3,962.6 3,601.4 Prior years 5,736.2 4,691.7 Total paid 9,698.8 8,293.1 Net balance at March 31 25,725.3 21,995.8 Plus reinsurance recoverables on unpaid losses 5,301.1 4,758.4 Balance at March 31 $ 31,026.4 $ 26,754.2 We experienced unfavorable reserve development of $621.2 million and $190.8 million during the first three months of 2023 and 2022, respectively, which is reflected as “incurred related to prior years ” in the table above. First Quarter 2023 • The unfavorable prior year reserve development included approximately $498 million attributable to accident year 2022, $30 million to accident year 2021, and the remainder to accident years 2020 and prior. • Our personal auto products incurred about $428 million of unfavorable loss and loss adjustment expense (LAE) reserve development, with the Agency and Direct auto businesses each contributing about half. The unfavorable development was primarily attributable to higher than anticipated severity in auto property and physical damage coverages, higher than anticipated late reported injury claims, and, to a lessor extent, increased loss costs in Florida injury and medical coverages in small part due to the impact of the legislation enacted in March 2023 in Florida. • Our Commercial Lines business experienced about $144 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 injury claims. • Our Property business experience d $42 million of unfavorable development, primarily from higher than anticipated claims expenses and higher than anticipated severity in our homeowner liability peril and umbrella products. First Quarter 2022 • The unfavorable prior year reserve development included $146 million attributable to accident year 2021, $23 million to accident year 2020, and the remainder to accident years 2019 and prior. • Our personal auto products incurred about $106 million of unfavorable loss and LAE reserve development, with the Agency and Direct auto businesses each contributing about half. The unfavorable development was primarily attributable to higher than anticipated severity of auto property damage payments on previously closed claims. • Our Commercial Lines business experienced about $99 million of unfavorable development, primarily due to injury claims settling at costs higher than originally anticipated. • Our Property business experienced about $16 million of favorable development, primarily attributable to lower losses than anticipated on 2021 catastrophe events. • Our special lines products experienced about $2 million of unfavorable development.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2023
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 March 31, 2023 and 2022, and December 31, 2022, were $177.5 million, $152.2 million, and $125.9 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 participants. Non-cash activity included the following in the respective periods: Three Months Ended March 31, (millions) 2023 2022 Common share dividends 1 $ 58.5 $ 58.5 Operating lease liabilities 2 9.3 10.8 1 Declared but unpaid. See Note 9 – Dividends for further discussion. 2 From obtaining right-of-use assets. In the respective periods, we paid the following: Three Months Ended March 31, (millions) 2023 2022 Income taxes $ 0.1 $ 0 Interest 87.9 64.9 Operating lease liabilities 21.5 22.0

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2023
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, business-related general liability and property insurance predominately for small businesses, and workers’ compensation insurance primarily for the transportation industry. Our Property segment writes residential property insurance for homeowners, other property owners, and renters. Our service businesses provide insurance-related services, including 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 disclosed in our 2022 Annual Report to Shareholders, during 2022, our contract to act as a servicing agent for processing Commercial Automobile Insurance Procedures/Plans (CAIP) business expired in 2022 and we did not renew the contract. This non-renewal did 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 March 31, 2023 2022 (millions) Revenues Pretax Revenues Pretax Personal Lines Agency $ 4,860.2 $ 162.6 $ 4,323.3 $ 288.6 Direct 5,717.4 (22.1) 4,793.6 150.4 Total Personal Lines 1 10,577.6 140.5 9,116.9 439.0 Commercial Lines 2,356.1 37.2 2,127.2 202.4 Property 2 598.7 (32.7) 558.1 8.3 Other indemnity 3 0.7 (3.4) 0.7 (0.9) Total underwriting operations 13,533.1 141.6 11,802.9 648.8 Fees and other revenues 4 206.2 NA 174.0 NA Service businesses 72.5 (9.8) 67.7 4.5 Investments 5 491.4 485.9 (203.1) (208.8) Interest expense NA (63.3) NA (54.3) Consolidated total $ 14,303.2 $ 554.4 $ 11,841.5 $ 390.2 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three months ended March 31, 2023 and 2022; insurance for our special lines products (e.g., motorcycles, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 For the three months ended March 31, 2023 and 2022, pretax profit (loss) included $5.0 million and $14.1 million, respectively, of amortization expense associated with intangible assets attributable to our Property segment. See Note 12 – Goodwill and Intangible Assets for further discussion. 3 Includes other underwriting business and run-off operations. 4 Pretax profit (loss) for fees and other revenues is allocated to operating segments based on revenue. 5 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit (loss) is net of investment expenses. 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 March 31, 2023 2022 Under-writing Combined Under-writing Combined Personal Lines Agency 3.3 % 96.7 6.7 % 93.3 Direct (0.4) 100.4 3.1 96.9 Total Personal Lines 1.3 98.7 4.8 95.2 Commercial Lines 1.6 98.4 9.5 90.5 Property 1 (5.5) 105.5 1.5 98.5 Total underwriting operations 1.0 99.0 5.5 94.5 1 Included in the three months ended March 31, 2023 and 2022, is 0.8 points and 2.5 points, respectively, of amortization expense associated with intangible assets.

Dividends

Dividends	3 Months Ended
	Mar. 31, 2023
Dividends [Abstract]
Dividends	DIVIDENDS Following is a summary of our common and preferred share dividends that were declared and/or paid during the three months ended March 31, 2023 and 2022: (millions, except per share amounts) Amount Declared Payable Per Share Accrued/Paid 1 Common – Quarterly Dividends: March 2023 April 2023 $ 0.10 $ 58.5 December 2022 January 2023 0.10 58.5 March 2022 April 2022 0.10 58.5 December 2021 January 2022 0.10 58.5 Preferred Dividends: December 2022 March 2023 26.875 13.4 December 2021 March 2022 26.875 13.4 1 The accrual is based on an estimate of shares outstanding as of the record date and recorded as a component of accounts payable, accrued expenses, and other liabilities on the consolidated balance sheets until paid; the prior year common share dividend accrual was reclassified into this line item from dividends payable on common shares to conform to the current year presentation. Beginning March 15, 2023, the annual dividend rate for our Series B Preferred Shares switched to a floating rate equal to the three-month London Interbank Offered Rate (LIBOR), or a comparable successor base rate, plus a spread of 2.539% applied to the stated amount per share. During the floating rate period, dividends on the Series B Preferred Shares will be payable quarterly, if and when declared by the Board of Directors. See Note 14 – Dividends in our 2022 Annual Report to Shareholders for a discussion of our quarterly and annual common share dividends and our preferred share dividend policies.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2023
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 Net unrealized losses on forecasted transactions Foreign Balance at December 31, 2022 $ (3,556.9) $ 754.9 $ (2,802.0) $ (2,786.3) $ (14.5) $ (1.2) Other comprehensive income (loss) before reclassifications: Investment securities 705.6 (148.2) 557.4 557.4 0 0 Total other comprehensive income (loss) before reclassifications 705.6 (148.2) 557.4 557.4 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (57.9) 12.1 (45.8) (45.8) 0 0 Interest expense (0.1) 0 (0.1) 0 (0.1) 0 Total reclassification adjustment for amounts realized in net income (58.0) 12.1 (45.9) (45.8) (0.1) 0 Total other comprehensive income (loss) 763.6 (160.3) 603.3 603.2 0.1 0 Balance at March 31, 2023 $ (2,793.3) $ 594.6 $ (2,198.7) $ (2,183.1) $ (14.4) $ (1.2) 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, 2021 $ 52.3 $ (11.6) $ 40.7 $ 56.2 $ (14.9) $ (0.6) Other comprehensive income (loss) before reclassifications: Investment securities (1,851.7) 388.9 (1,462.8) (1,462.8) 0 0 Foreign currency translation adjustment 0.3 (0.1) 0.2 0 0 0.2 Total other comprehensive income (loss) before reclassifications (1,851.4) 388.8 (1,462.6) (1,462.8) 0 0.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (45.5) 9.6 (35.9) (35.9) 0 0 Interest expense (0.2) 0 (0.2) 0 (0.2) 0 Total reclassification adjustment for amounts realized in net income (45.7) 9.6 (36.1) (35.9) (0.2) 0 Total other comprehensive income (loss) (1,805.7) 379.2 (1,426.5) (1,426.9) 0.2 0.2 Balance at March 31, 2022 $ (1,753.4) $ 367.6 $ (1,385.8) $ (1,370.7) $ (14.7) $ (0.4) In an effort to manage interest rate risk, we entered into forecasted transactions on certain of Progressive’s debt issuances. We expect to reclassify $0.6 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 2022 Annual Report to Shareholders for further discussion).

Litigation

Litigation	3 Months Ended
	Mar. 31, 2023
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 (PIP), 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, the application of a negotiation adjustment in calculating total loss valuations, 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. As of March 31, 2023, lawsuits have been certified or conditionally certified as class/collective actions in cases alleging: we improperly value total loss claims in Florida, New York and Washington; we improperly fail to pay fees and taxes associated with total losses in Florida, Michigan and New York; we improperly adjust medical bills in Washington; we improperly calculate basic economic loss as it relates to wage loss coverage in New York; we improperly fail to timely process and pay PIP claims in Texas; and that certain of our compensation practices and overtime payment practices are improper, including our classification of certain employees as exempt from overtime pay requirements. 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 2022 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 March 31, 2023 and 2022, or December 31, 2022, and there were no material settlements during 2022 or the first three months of 2023. 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 2022 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 2022 Annual Report to Shareholders.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Mar. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	GOODWILL AND INTANGIBLE ASSETS Goodwill The majority of the goodwill recorded as of March 31, 2023 and 2022, and December 31, 2022, related to the April 1, 2015, acquisition of a controlling interest in ARX Holding Corp. (ARX). During the three months ended March 31, 2023, there were no changes to the carrying amount of goodwill. 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 . The impairment loss was fully allocated to our Property operating segment. There were no previously recorded goodwill impairment losses on any of the outstanding goodwill. See Note 15 – Goodwill and Intangible Assets in our 2022 Annual Report to Shareholders for a discussion of our goodwill impairment evaluation. Intangible Assets The following table is a summary of the net carrying amount of other intangible assets: (millions) March 31, 2023 March 31, 2022 December 31, 2022 Intangible assets subject to amortization $ 68.5 $ 90.3 $ 73.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 80.9 $ 102.7 $ 86.3 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) March 31, 2023 March 31, 2022 December 31, 2022 Category Gross Accumulated Net Gross Accumulated Net Gross Accumulated Net Agency relationships $ 159.2 $ 91.0 $ 68.2 $ 159.2 $ 79.6 $ 79.6 $ 159.2 $ 88.1 $ 71.1 Software rights 69.1 69.1 0 69.1 60.5 8.6 69.1 67.0 2.1 Trade name 3.6 3.3 0.3 3.6 1.5 2.1 3.6 2.9 0.7 Total $ 231.9 $ 163.4 $ 68.5 $ 231.9 $ 141.6 $ 90.3 $ 231.9 $ 158.0 $ 73.9 Amortization expense for the three months ended March 31, 2023 was $5.4 million, compared to $14.6 million for the same period last year.

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Earnings Per Share	Earnings Per ShareNet income is reduced by preferred share dividends to determine net income available to common shareholders, and is used in our calculation of the per common share amounts.
New Accounting Standards	New Accounting StandardsDuring the first quarter 2023, the Financial Accounting Standards Board issued an Accounting Standards Update (ASU), which permits an election to amortize the cost of tax equity investments to the provision for income taxes if certain conditions are met. Currently, these investments are accounted for under the equity method of accounting. This ASU will be effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2023 (2024 for calendar-year companies). If elected, this standard must be applied on either a modified retrospective or a retrospective basis. We are still evaluating whether we will elect this new standard, however, we do not expect this standard to have a material impact on our financial position or results of operations

Basis of Presentation (Tables)

Basis of Presentation (Tables)	3 Months Ended
	Mar. 31, 2023
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 March 31, (millions) 2023 2022 Allowance for credit losses, beginning of period $ 343.3 $ 280.4 Increase in allowance 1 116.9 93.9 Write-offs 2 (119.3) (98.1) Allowance for credit losses, end of period $ 340.9 $ 276.2 1 Represents the incremental increase in other underwriting expenses. 2 Represents the 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)	3 Months Ended
	Mar. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Schedule of Debt and Equity Securities Reconciliation	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 for the hybrid and equity securities. The changes in the net holding period gains (losses) between periods 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 March 31, 2023 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 28,490.9 $ 68.8 $ (1,209.6) $ 0 $ 27,350.1 48.3 % State and local government obligations 2,222.4 0.9 (161.7) 0 2,061.6 3.6 Foreign government obligations 16.9 0 (1.1) 0 15.8 0.1 Corporate debt securities 11,195.8 45.6 (525.4) (34.7) 10,681.3 18.8 Residential mortgage-backed securities 655.0 0.2 (16.3) (8.9) 630.0 1.1 Commercial mortgage-backed securities 5,252.6 1.6 (751.2) 0 4,503.0 7.9 Other asset-backed securities 5,087.8 1.8 (222.5) (1.3) 4,865.8 8.6 Redeemable preferred stocks 202.5 0 (5.2) (15.7) 181.6 0.3 Total fixed maturities 53,123.9 118.9 (2,893.0) (60.6) 50,289.2 88.7 Short-term investments 2,524.1 0 0 0 2,524.1 4.5 Total available-for-sale securities 55,648.0 118.9 (2,893.0) (60.6) 52,813.3 93.2 Equity securities: Nonredeemable preferred stocks 1,197.7 0 0 (118.9) 1,078.8 1.9 Common equities 740.5 0 0 2,053.8 2,794.3 4.9 Total equity securities 1,938.2 0 0 1,934.9 3,873.1 6.8 Total portfolio 1 $ 57,586.2 $ 118.9 $ (2,893.0) $ 1,874.3 $ 56,686.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of March 31, 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 20,399.6 $ 5.9 $ (876.7) $ 0 $ 19,528.8 36.7 % State and local government obligations 2,236.9 4.4 (97.1) 0 2,144.2 4.0 Foreign government obligations 18.3 0 (0.9) 0 17.4 0.1 Corporate debt securities 11,590.2 31.2 (315.5) (25.9) 11,280.0 21.2 Residential mortgage-backed securities 962.3 1.1 (5.1) (7.2) 951.1 1.8 Commercial mortgage-backed securities 7,296.4 2.2 (380.1) 0 6,918.5 13.0 Other asset-backed securities 5,359.9 1.1 (103.6) (1.5) 5,255.9 9.9 Redeemable preferred stocks 219.1 0.1 (1.8) 3.1 220.5 0.4 Total fixed maturities 48,082.7 46.0 (1,780.8) (31.5) 46,316.4 87.1 Short-term investments 529.9 0 0 0 529.9 1.0 Total available-for-sale securities 48,612.6 46.0 (1,780.8) (31.5) 46,846.3 88.1 Equity securities: Nonredeemable preferred stocks 1,545.5 0 0 (18.0) 1,527.5 2.9 Common equities 1,281.7 0 0 3,530.9 4,812.6 9.0 Total equity securities 2,827.2 0 0 3,512.9 6,340.1 11.9 Total portfolio 1 $ 51,439.8 $ 46.0 $ (1,780.8) $ 3,481.4 $ 53,186.4 100.0 % ($ in millions) Cost Gross Gross Net Fair % of December 31, 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 26,770.7 $ 1.4 $ (1,604.7) $ 0 $ 25,167.4 47.0 % State and local government obligations 2,180.0 0 (202.9) 0 1,977.1 3.7 Foreign government obligations 16.8 0 (1.3) 0 15.5 0.1 Corporate debt securities 10,125.8 9.8 (676.1) (46.8) 9,412.7 17.6 Residential mortgage-backed securities 696.1 0.3 (17.5) (12.1) 666.8 1.2 Commercial mortgage-backed securities 5,446.0 1.5 (784.0) 0 4,663.5 8.7 Other asset-backed securities 4,826.0 0.9 (260.5) (1.8) 4,564.6 8.5 Redeemable preferred stocks 202.6 0 (4.5) (13.8) 184.3 0.3 Total fixed maturities 50,264.0 13.9 (3,551.5) (74.5) 46,651.9 87.1 Short-term investments 2,861.7 0 0 0 2,861.7 5.4 Total available-for-sale securities 53,125.7 13.9 (3,551.5) (74.5) 49,513.6 92.5 Equity securities: Nonredeemable preferred stocks 1,364.2 0 0 (151.0) 1,213.2 2.3 Common equities 826.1 0 0 1,995.4 2,821.5 5.2 Total equity securities 2,190.3 0 0 1,844.4 4,034.7 7.5 Total portfolio 1 $ 55,316.0 $ 13.9 $ (3,551.5) $ 1,769.9 $ 53,548.3 100.0 % 1 At March 31, 2023 and 2022, we had $22.8 million and $356.0 million, respectively, of net unsettled security purchase transactions included in other liabilities, compared to $34.4 million included in other assets at December 31, 2022. The total fair value of the portfolio at March 31, 2023 and 2022, and December 31, 2022, included $4.1 billion, $5.1 billion, and $4.4 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: March 31, (millions) 2023 2022 Dec. 31, 2022 Fixed Maturities: Corporate debt securities $ 548.6 $ 535.8 $ 535.4 Residential mortgage-backed securities 482.1 721.7 509.6 Other asset-backed securities 33.8 75.0 42.0 Redeemable preferred stocks 132.8 152.1 134.7 Total hybrid securities $ 1,197.3 $ 1,484.6 $ 1,221.7
Investments Classified by Contractual Maturity Date	The composition of fixed maturities by maturity at March 31, 2023, was: (millions) Cost Fair Value Less than one year $ 7,941.7 $ 7,706.0 One to five years 31,574.9 30,132.2 Five to ten years 13,505.5 12,353.0 Ten years or greater 101.8 98.0 Total $ 53,123.9 $ 50,289.2
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 March 31, 2023 U.S. government obligations 148 $ 19,446.8 $ (1,209.6) 40 $ 5,938.5 $ (127.5) 108 $ 13,508.3 $ (1,082.1) State and local government obligations 343 1,943.6 (161.7) 72 350.7 (7.4) 271 1,592.9 (154.3) Foreign government obligations 1 15.8 (1.1) 0 0 0 1 15.8 (1.1) Corporate debt securities 390 8,129.9 (525.4) 93 2,239.3 (75.5) 297 5,890.6 (449.9) Residential mortgage-backed securities 43 141.7 (16.3) 13 10.0 (0.4) 30 131.7 (15.9) Commercial mortgage-backed securities 220 4,484.5 (751.2) 11 53.4 (1.5) 209 4,431.1 (749.7) Other asset-backed securities 267 4,391.9 (222.5) 61 884.8 (6.2) 206 3,507.1 (216.3) Redeemable preferred stocks 4 48.8 (5.2) 1 10.6 (1.4) 3 38.2 (3.8) Total fixed maturities 1,416 $ 38,603.0 $ (2,893.0) 291 $ 9,487.3 $ (219.9) 1,125 $ 29,115.7 $ (2,673.1) 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 March 31, 2022 U.S. government obligations 116 $ 18,478.0 $ (876.7) 97 $ 15,467.4 $ (649.4) 19 $ 3,010.6 $ (227.3) State and local government obligations 290 1,767.7 (97.1) 279 1,627.3 (82.1) 11 140.4 (15.0) Foreign government obligations 1 17.4 (0.9) 1 17.4 (0.9) 0 0 0 Corporate debt securities 416 7,830.6 (315.5) 407 7,623.8 (294.2) 9 206.8 (21.3) Residential mortgage-backed securities 32 201.8 (5.1) 26 189.0 (4.1) 6 12.8 (1.0) Commercial mortgage-backed securities 264 6,584.4 (380.1) 245 6,133.0 (327.9) 19 451.4 (52.2) Other asset-backed securities 269 4,927.4 (103.6) 263 4,873.8 (102.7) 6 53.6 (0.9) Redeemable preferred stocks 3 37.4 (1.8) 2 26.4 (0.3) 1 11.0 (1.5) Total fixed maturities 1,391 $ 39,844.7 $ (1,780.8) 1,320 $ 35,958.1 $ (1,461.6) 71 $ 3,886.6 $ (319.2) 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, 2022 U.S. government obligations 160 $ 24,802.5 $ (1,604.7) 90 $ 17,327.2 $ (699.2) 70 $ 7,475.3 $ (905.5) State and local government obligations 348 1,948.8 (202.9) 239 1,124.2 (76.8) 109 824.6 (126.1) Foreign government obligations 1 15.5 (1.3) 0 0 0 1 15.5 (1.3) Corporate debt securities 422 8,449.6 (676.1) 285 5,717.6 (426.1) 137 2,732.0 (250.0) Residential mortgage-backed securities 45 151.0 (17.5) 27 65.1 (6.8) 18 85.9 (10.7) Commercial mortgage-backed securities 226 4,651.1 (784.0) 99 1,702.0 (192.1) 127 2,949.1 (591.9) Other asset-backed securities 262 4,247.8 (260.5) 130 2,144.8 (100.9) 132 2,103.0 (159.6) Redeemable preferred stocks 4 49.6 (4.5) 3 38.5 (3.1) 1 11.1 (1.4) Total fixed maturities 1,468 $ 44,315.9 $ (3,551.5) 873 $ 28,119.4 $ (1,505.0) 595 $ 16,196.5 $ (2,046.5)
Realized Gain (Loss) on Investments	The components of net realized gains (losses) for the three months ended March 31, were: Three Months (millions) 2023 2022 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 3.8 $ 3.3 Corporate debt securities 0.1 4.5 Residential mortgage-backed securities 0 0.1 Other asset-backed securities 0 0.1 Total available-for-sale securities 3.9 8.0 Equity securities: Nonredeemable preferred stocks 0.1 17.3 Common equities 132.0 0.5 Total equity securities 132.1 17.8 Subtotal gross realized gains on security sales 136.0 25.8 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (11.5) (69.2) State and local government obligations 0 (1.0) Corporate debt securities (20.4) (7.7) Commercial mortgage-backed securities (34.5) 0 Other asset-backed securities (0.2) (0.1) Short-term investments (0.1) 0 Total available-for-sale securities (66.7) (78.0) Equity securities: Nonredeemable preferred stocks (101.0) (1.7) Common equities (11.8) (0.6) Total equity securities (112.8) (2.3) Subtotal gross realized losses on security sales (179.5) (80.3) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations (7.7) (65.9) State and local government obligations 0 (1.0) Corporate debt securities (20.3) (3.2) Residential mortgage-backed securities 0 0.1 Commercial mortgage-backed securities (34.5) 0 Other asset-backed securities (0.2) 0 Short-term investments (0.1) 0 Total available-for-sale securities (62.8) (70.0) Equity securities: Nonredeemable preferred stocks (100.9) 15.6 Common equities 120.2 (0.1) Total equity securities 19.3 15.5 Subtotal net realized gains (losses) on security sales (43.5) (54.5) Other assets Gain 13.2 0 Impairment (2.3) (2.2) Subtotal net realized gains (losses) on other assets 10.9 (2.2) Net holding period gains (losses) Hybrid securities 13.9 (39.0) Equity securities 90.5 (349.6) Subtotal net holding period gains (losses) 104.4 (388.6) Total net realized gains (losses) on securities $ 71.8 $ (445.3)
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 (millions) 2023 2022 Total net gains (losses) recognized during the period on equity securities $ 109.8 $ (334.1) Less: Net gains (losses) recognized on equity securities sold during the period 19.3 15.5 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 90.5 $ (349.6)
Components of Net Investment Income	The components of net investment income for the three months ended March 31, were: Three Months (millions) 2023 2022 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 163.2 $ 51.4 State and local government obligations 10.6 9.2 Foreign government obligations 0.1 0.1 Corporate debt securities 83.6 68.1 Residential mortgage-backed securities 9.2 4.8 Commercial mortgage-backed securities 50.0 43.3 Other asset-backed securities 48.5 25.1 Redeemable preferred stocks 2.9 2.5 Total fixed maturities 368.1 204.5 Short-term investments 24.7 0.4 Total available-for-sale securities 392.8 204.9 Equity securities: Nonredeemable preferred stocks 15.1 18.2 Common equities 11.7 19.1 Total equity securities 26.8 37.3 Investment income 419.6 242.2 Investment expenses (5.5) (5.7) Net investment income $ 414.1 $ 236.5

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2023
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 March 31, 2023 Fixed maturities: U.S. government obligations $ 27,350.1 $ 0 $ 0 $ 27,350.1 $ 28,490.9 State and local government obligations 0 2,061.6 0 2,061.6 2,222.4 Foreign government obligations 0 15.8 0 15.8 16.9 Corporate debt securities 0 10,681.3 0 10,681.3 11,195.8 Subtotal 27,350.1 12,758.7 0 40,108.8 41,926.0 Asset-backed securities: Residential mortgage-backed 0 630.0 0 630.0 655.0 Commercial mortgage-backed 0 4,503.0 0 4,503.0 5,252.6 Other asset-backed 0 4,865.8 0 4,865.8 5,087.8 Subtotal asset-backed securities 0 9,998.8 0 9,998.8 10,995.4 Redeemable preferred stocks: Financials 0 40.0 0 40.0 43.5 Utilities 0 8.8 0 8.8 10.5 Industrials 9.6 123.2 0 132.8 148.5 Subtotal redeemable preferred stocks 9.6 172.0 0 181.6 202.5 Total fixed maturities 27,359.7 22,929.5 0 50,289.2 53,123.9 Short-term investments 2,524.1 0 0 2,524.1 2,524.1 Total available-for-sale securities 29,883.8 22,929.5 0 52,813.3 55,648.0 Equity securities: Nonredeemable preferred stocks: Financials 40.0 884.5 67.4 991.9 1,102.7 Utilities 0 70.5 0 70.5 80.0 Industrials 0 0 16.4 16.4 15.0 Subtotal nonredeemable preferred stocks 40.0 955.0 83.8 1,078.8 1,197.7 Common equities: Common stocks 2,755.7 0 18.3 2,774.0 720.2 Other risk investments 0 0 20.3 20.3 20.3 Subtotal common equities 2,755.7 0 38.6 2,794.3 740.5 Total equity securities 2,795.7 955.0 122.4 3,873.1 1,938.2 Total portfolio $ 32,679.5 $ 23,884.5 $ 122.4 $ 56,686.4 $ 57,586.2 Debt $ 0 $ 5,881.0 $ 0 $ 5,881.0 $ 6,389.3 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost March 31, 2022 Fixed maturities: U.S. government obligations $ 19,528.8 $ 0 $ 0 $ 19,528.8 $ 20,399.6 State and local government obligations 0 2,144.2 0 2,144.2 2,236.9 Foreign government obligations 0 17.4 0 17.4 18.3 Corporate debt securities 0 11,280.0 0 11,280.0 11,590.2 Subtotal 19,528.8 13,441.6 0 32,970.4 34,245.0 Asset-backed securities: Residential mortgage-backed 0 951.1 0 951.1 962.3 Commercial mortgage-backed 0 6,918.5 0 6,918.5 7,296.4 Other asset-backed 0 5,255.9 0 5,255.9 5,359.9 Subtotal asset-backed securities 0 13,125.5 0 13,125.5 13,618.6 Redeemable preferred stocks: Financials 0 61.2 0 61.2 62.6 Utilities 0 7.2 0 7.2 7.5 Industrials 10.3 141.8 0 152.1 149.0 Subtotal redeemable preferred stocks 10.3 210.2 0 220.5 219.1 Total fixed maturities 19,539.1 26,777.3 0 46,316.4 48,082.7 Short-term investments 512.9 17.0 0 529.9 529.9 Total available-for-sale securities 20,052.0 26,794.3 0 46,846.3 48,612.6 Equity securities: Nonredeemable preferred stocks: Financials 92.2 1,237.3 61.4 1,390.9 1,425.4 Utilities 0 78.1 0 78.1 80.0 Industrials 0 24.6 33.9 58.5 40.1 Subtotal nonredeemable preferred stocks 92.2 1,340.0 95.3 1,527.5 1,545.5 Common equities: Common stocks 4,743.2 49.3 0 4,792.5 1,261.6 Other risk investments 0 0 20.1 20.1 20.1 Subtotal common equities 4,743.2 49.3 20.1 4,812.6 1,281.7 Total equity securities 4,835.4 1,389.3 115.4 6,340.1 2,827.2 Total portfolio $ 24,887.4 $ 28,183.6 $ 115.4 $ 53,186.4 $ 51,439.8 Debt $ 0 $ 6,692.6 $ 0 $ 6,692.6 $ 6,385.6 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2022 Fixed maturities: U.S. government obligations $ 25,167.4 $ 0 $ 0 $ 25,167.4 $ 26,770.7 State and local government obligations 0 1,977.1 0 1,977.1 2,180.0 Foreign government obligations 0 15.5 0 15.5 16.8 Corporate debt securities 0 9,412.7 0 9,412.7 10,125.8 Subtotal 25,167.4 11,405.3 0 36,572.7 39,093.3 Asset-backed securities: Residential mortgage-backed 0 666.8 0 666.8 696.1 Commercial mortgage-backed 0 4,663.5 0 4,663.5 5,446.0 Other asset-backed 0 4,564.6 0 4,564.6 4,826.0 Subtotal asset-backed securities 0 9,894.9 0 9,894.9 10,968.1 Redeemable preferred stocks: Financials 0 40.5 0 40.5 43.6 Utilities 0 9.1 0 9.1 10.5 Industrials 9.2 125.5 0 134.7 148.5 Subtotal redeemable preferred stocks 9.2 175.1 0 184.3 202.6 Total fixed maturities 25,176.6 21,475.3 0 46,651.9 50,264.0 Short-term investments 2,800.7 61.0 0 2,861.7 2,861.7 Total available-for-sale securities 27,977.3 21,536.3 0 49,513.6 53,125.7 Equity securities: Nonredeemable preferred stocks: Financials 39.0 994.4 67.4 1,100.8 1,244.2 Utilities 0 71.2 0 71.2 79.9 Industrials 0 24.8 16.4 41.2 40.1 Subtotal nonredeemable preferred stocks 39.0 1,090.4 83.8 1,213.2 1,364.2 Common equities: Common stocks 2,783.4 0 18.3 2,801.7 806.3 Other risk investments 0 0 19.8 19.8 19.8 Subtotal common equities 2,783.4 0 38.1 2,821.5 826.1 Total equity securities 2,822.4 1,090.4 121.9 4,034.7 2,190.3 Total portfolio $ 30,799.7 $ 22,626.7 $ 121.9 $ 53,548.3 $ 55,316.0 Debt $ 0 $ 5,717.9 $ 0 $ 5,717.9 $ 6,388.3
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 months ended March 31, 2023 and 2022: Level 3 Fair Value (millions) Fair Value at Dec. 31, 2022 Calls/ Purchases Sales Net Realized Change in Net Fair Value at March 31, 2023 Equity securities: Nonredeemable preferred stocks: Financials $ 67.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 67.4 Industrials 16.4 0 0 0 0 0 0 16.4 Common equities: Common stocks 18.3 0 0 0 0 0 0 18.3 Other risk investments 19.8 0.5 0 0 0 0 0 20.3 Total Level 3 securities $ 121.9 $ 0.5 $ 0 $ 0 $ 0 $ 0 $ 0 $ 122.4 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2021 Calls/ Purchases Sales Net Realized Change in Net Fair Value at March 31, 2022 Equity securities: Nonredeemable preferred stocks: Financials $ 76.4 $ 0 $ 0 $ (15.0) $ (17.2) $ 17.2 $ 0 $ 61.4 Industrials 34.4 (0.5) 0 0 0 0 0 33.9 Common equities: Other risk investments 16.9 3.2 0 0 0 0 0 20.1 Total Level 3 securities $ 127.7 $ 2.7 $ 0 $ (15.0) $ (17.2) $ 17.2 $ 0 $ 115.4
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 March 31, 2023 and 2022, and December 31, 2022: Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 2023 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 83.8 Market comparables Weighted average market capitalization price change % 2.7% to 23.3% 9.2 % Common stocks 18.3 Market comparables Weighted average market capitalization price change % (51.3)% to 48.3% 15.6 % Subtotal Level 3 securities 102.1 Pricing exemption securities 20.3 Total Level 3 securities $ 122.4 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 2022 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 95.3 Market comparables Weighted average market capitalization price change % (27.9)% to (12.7)% 20.1 % Subtotal Level 3 securities 95.3 Pricing exemption securities 20.1 Total Level 3 securities $ 115.4 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2022 Valuation Technique Unobservable Input Range of Input Values Increase (Decrease) Weighted Average Increase (Decrease) Equity securities: Nonredeemable preferred stocks $ 83.8 Market comparables Weighted average market capitalization price change % (0.6)% to 19.9% 10.5% Common stocks 18.3 Market comparables Weighted average market capitalization price change % (42.5)% to 59.1% 0.3% Subtotal Level 3 securities 102.1 Pricing exemption securities 19.8 Total Level 3 securities $ 121.9

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2023
Debt Disclosure [Abstract]
Debt Table	Debt at each of the balance sheet periods consisted of: March 31, 2023 March 31, 2022 December 31, 2022 (millions) Carrying Fair Carrying Fair Carrying Fair 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) $ 498.3 $ 464.2 $ 497.8 $ 487.9 $ 498.2 $ 457.7 2.50% Senior Notes due 2027 (issued: $500.0, March 2022) 497.7 463.8 497.1 489.4 497.5 460.3 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 297.6 329.6 297.3 358.8 297.5 326.8 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 546.5 538.5 546.1 573.5 546.4 527.8 3.20% Senior Notes due 2030 (issued: $500.0, March 2020) 497.0 460.0 496.6 496.2 496.9 448.6 3.00% Senior Notes due 2032 (issued: $500.0, March 2022) 496.0 446.9 495.6 487.0 495.9 438.1 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 396.5 448.1 396.2 494.8 396.4 435.4 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.9 312.3 346.8 368.7 346.9 298.4 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.8 324.0 395.7 386.0 395.7 310.2 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 842.1 743.8 841.9 894.5 842.1 716.2 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 590.4 530.0 590.3 637.4 590.4 507.0 3.95% Senior Notes due 2050 (issued: $500.0, March 2020) 491.0 420.3 490.8 514.9 490.9 404.9 3.70% Senior Notes due 2052 (issued: $500.0, March 2022) 493.5 399.5 493.4 503.5 493.5 386.5 Total $ 6,389.3 $ 5,881.0 $ 6,385.6 $ 6,692.6 $ 6,388.3 $ 5,717.9

Loss and Loss Adjustment Expe_2

Loss and Loss Adjustment Expense Reserves (Tables)	3 Months Ended
	Mar. 31, 2023
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: March 31, (millions) 2023 2022 Balance at January 1 $ 30,359.3 $ 26,164.1 Less reinsurance recoverables on unpaid losses 5,559.2 4,733.6 Net balance at January 1 24,800.1 21,430.5 Incurred related to: Current year 10,002.8 8,667.6 Prior years 621.2 190.8 Total incurred 10,624.0 8,858.4 Paid related to: Current year 3,962.6 3,601.4 Prior years 5,736.2 4,691.7 Total paid 9,698.8 8,293.1 Net balance at March 31 25,725.3 21,995.8 Plus reinsurance recoverables on unpaid losses 5,301.1 4,758.4 Balance at March 31 $ 31,026.4 $ 26,754.2

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2023
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Cash Flow Information, Non Cash Activity	Non-cash activity included the following in the respective periods: Three Months Ended March 31, (millions) 2023 2022 Common share dividends 1 $ 58.5 $ 58.5 Operating lease liabilities 2 9.3 10.8 1 Declared but unpaid. See Note 9 – Dividends for further discussion. 2 From obtaining right-of-use assets.
Supplemental Cash Flow Information Table	In the respective periods, we paid the following: Three Months Ended March 31, (millions) 2023 2022 Income taxes $ 0.1 $ 0 Interest 87.9 64.9 Operating lease liabilities 21.5 22.0

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2023
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 March 31, 2023 2022 (millions) Revenues Pretax Revenues Pretax Personal Lines Agency $ 4,860.2 $ 162.6 $ 4,323.3 $ 288.6 Direct 5,717.4 (22.1) 4,793.6 150.4 Total Personal Lines 1 10,577.6 140.5 9,116.9 439.0 Commercial Lines 2,356.1 37.2 2,127.2 202.4 Property 2 598.7 (32.7) 558.1 8.3 Other indemnity 3 0.7 (3.4) 0.7 (0.9) Total underwriting operations 13,533.1 141.6 11,802.9 648.8 Fees and other revenues 4 206.2 NA 174.0 NA Service businesses 72.5 (9.8) 67.7 4.5 Investments 5 491.4 485.9 (203.1) (208.8) Interest expense NA (63.3) NA (54.3) Consolidated total $ 14,303.2 $ 554.4 $ 11,841.5 $ 390.2 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three months ended March 31, 2023 and 2022; insurance for our special lines products (e.g., motorcycles, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 For the three months ended March 31, 2023 and 2022, pretax profit (loss) included $5.0 million and $14.1 million, respectively, of amortization expense associated with intangible assets attributable to our Property segment. See Note 12 – Goodwill and Intangible Assets for further discussion. 3 Includes other underwriting business and run-off operations. 4 Pretax profit (loss) for fees and other revenues is allocated to operating segments based on revenue. 5 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit (loss) is net of investment expenses.
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 March 31, 2023 2022 Under-writing Combined Under-writing Combined Personal Lines Agency 3.3 % 96.7 6.7 % 93.3 Direct (0.4) 100.4 3.1 96.9 Total Personal Lines 1.3 98.7 4.8 95.2 Commercial Lines 1.6 98.4 9.5 90.5 Property 1 (5.5) 105.5 1.5 98.5 Total underwriting operations 1.0 99.0 5.5 94.5 1 Included in the three months ended March 31, 2023 and 2022, is 0.8 points and 2.5 points, respectively, of amortization expense associated with intangible assets.

Dividends (Tables)

Dividends (Tables)	3 Months Ended
	Mar. 31, 2023
Dividends [Abstract]
Dividends	Following is a summary of our common and preferred share dividends that were declared and/or paid during the three months ended March 31, 2023 and 2022: (millions, except per share amounts) Amount Declared Payable Per Share Accrued/Paid 1 Common – Quarterly Dividends: March 2023 April 2023 $ 0.10 $ 58.5 December 2022 January 2023 0.10 58.5 March 2022 April 2022 0.10 58.5 December 2021 January 2022 0.10 58.5 Preferred Dividends: December 2022 March 2023 26.875 13.4 December 2021 March 2022 26.875 13.4 1 The accrual is based on an estimate of shares outstanding as of the record date and recorded as a component of accounts payable, accrued expenses, and other liabilities on the consolidated balance sheets until paid; the prior year common share dividend accrual was reclassified into this line item from dividends payable on common shares to conform to the current year presentation.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2023
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 Net unrealized losses on forecasted transactions Foreign Balance at December 31, 2022 $ (3,556.9) $ 754.9 $ (2,802.0) $ (2,786.3) $ (14.5) $ (1.2) Other comprehensive income (loss) before reclassifications: Investment securities 705.6 (148.2) 557.4 557.4 0 0 Total other comprehensive income (loss) before reclassifications 705.6 (148.2) 557.4 557.4 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (57.9) 12.1 (45.8) (45.8) 0 0 Interest expense (0.1) 0 (0.1) 0 (0.1) 0 Total reclassification adjustment for amounts realized in net income (58.0) 12.1 (45.9) (45.8) (0.1) 0 Total other comprehensive income (loss) 763.6 (160.3) 603.3 603.2 0.1 0 Balance at March 31, 2023 $ (2,793.3) $ 594.6 $ (2,198.7) $ (2,183.1) $ (14.4) $ (1.2) 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, 2021 $ 52.3 $ (11.6) $ 40.7 $ 56.2 $ (14.9) $ (0.6) Other comprehensive income (loss) before reclassifications: Investment securities (1,851.7) 388.9 (1,462.8) (1,462.8) 0 0 Foreign currency translation adjustment 0.3 (0.1) 0.2 0 0 0.2 Total other comprehensive income (loss) before reclassifications (1,851.4) 388.8 (1,462.6) (1,462.8) 0 0.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (45.5) 9.6 (35.9) (35.9) 0 0 Interest expense (0.2) 0 (0.2) 0 (0.2) 0 Total reclassification adjustment for amounts realized in net income (45.7) 9.6 (36.1) (35.9) (0.2) 0 Total other comprehensive income (loss) (1,805.7) 379.2 (1,426.5) (1,426.9) 0.2 0.2 Balance at March 31, 2022 $ (1,753.4) $ 367.6 $ (1,385.8) $ (1,370.7) $ (14.7) $ (0.4)

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2023
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) March 31, 2023 March 31, 2022 December 31, 2022 Intangible assets subject to amortization $ 68.5 $ 90.3 $ 73.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 80.9 $ 102.7 $ 86.3
Intangible Assets Subject to Amortization	The following table is a summary of the net carrying amount of other intangible assets: (millions) March 31, 2023 March 31, 2022 December 31, 2022 Intangible assets subject to amortization $ 68.5 $ 90.3 $ 73.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 80.9 $ 102.7 $ 86.3 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) March 31, 2023 March 31, 2022 December 31, 2022 Category Gross Accumulated Net Gross Accumulated Net Gross Accumulated Net Agency relationships $ 159.2 $ 91.0 $ 68.2 $ 159.2 $ 79.6 $ 79.6 $ 159.2 $ 88.1 $ 71.1 Software rights 69.1 69.1 0 69.1 60.5 8.6 69.1 67.0 2.1 Trade name 3.6 3.3 0.3 3.6 1.5 2.1 3.6 2.9 0.7 Total $ 231.9 $ 163.4 $ 68.5 $ 231.9 $ 141.6 $ 90.3 $ 231.9 $ 158.0 $ 73.9

Basis of Presentation - Reporti

Basis of Presentation - Reporting and Accounting Policies - Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Allowance for credit losses, beginning of period	$ 343.3	$ 280.4
Increase in allowance	116.9	93.9
Write-offs	(119.3)	(98.1)
Allowance for credit losses, end of period	$ 340.9	$ 276.2

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Assets held-for-sale	$ 67.8	$ 48.7	$ 20.2

Investments - Investment Portfo

Investments - Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 55,648	$ 53,125.7	$ 48,612.6
Gross Unrealized Gains	118.9	13.9	46
Gross Unrealized Losses	(2,893)	(3,551.5)	(1,780.8)
Net Holding Period Gains (Losses)	(60.6)	(74.5)	(31.5)
Total available-for-sale securities	$ 52,813.3	$ 49,513.6	$ 46,846.3
% of Total Fair Value	93.20%	92.50%	88.10%
Equity securities, at Fair Value
Cost	$ 1,938.2	$ 2,190.3	$ 2,827.2
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	1,934.9	1,844.4	3,512.9
Fair Value	$ 3,873.1	$ 4,034.7	$ 6,340.1
% of Total Fair Value	6.80%	7.50%	11.90%
Debt and Equity Securities, at Fair Value
Cost	$ 57,586.2	$ 55,316	$ 51,439.8
Gross Unrealized Gains	118.9	13.9	46
Gross Unrealized Losses	(2,893)	(3,551.5)	(1,780.8)
Net Holding Period Gains (Losses)	1,874.3	1,769.9	3,481.4
Fair Value	$ 56,686.4	$ 53,548.3	$ 53,186.4
% of Total Fair Value	100%	100%	100%
Unsettled security transactions, payable	$ 22.8		$ 356
Other Receivable from Broker-Dealer and Clearing Organization		$ 34.4
Total fair value of non-insurance subsidiary portfolio	4,100	4,400	5,100
Nonredeemable preferred stocks
Equity securities, at Fair Value
Cost	1,197.7	1,364.2	1,545.5
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	(118.9)	(151)	(18)
Fair Value	$ 1,078.8	$ 1,213.2	$ 1,527.5
% of Total Fair Value	1.90%	2.30%	2.90%
Common equities
Equity securities, at Fair Value
Cost	$ 740.5	$ 826.1	$ 1,281.7
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	2,053.8	1,995.4	3,530.9
Fair Value	$ 2,794.3	$ 2,821.5	$ 4,812.6
% of Total Fair Value	4.90%	5.20%	9%
Total fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 53,123.9	$ 50,264	$ 48,082.7
Gross Unrealized Gains	118.9	13.9	46
Gross Unrealized Losses	(2,893)	(3,551.5)	(1,780.8)
Net Holding Period Gains (Losses)	(60.6)	(74.5)	(31.5)
Total available-for-sale securities	$ 50,289.2	$ 46,651.9	$ 46,316.4
% of Total Fair Value	88.70%	87.10%	87.10%
Total fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 28,490.9	$ 26,770.7	$ 20,399.6
Gross Unrealized Gains	68.8	1.4	5.9
Gross Unrealized Losses	(1,209.6)	(1,604.7)	(876.7)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 27,350.1	$ 25,167.4	$ 19,528.8
% of Total Fair Value	48.30%	47%	36.70%
Total fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 2,222.4	$ 2,180	$ 2,236.9
Gross Unrealized Gains	0.9	0	4.4
Gross Unrealized Losses	(161.7)	(202.9)	(97.1)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 2,061.6	$ 1,977.1	$ 2,144.2
% of Total Fair Value	3.60%	3.70%	4%
Total fixed maturities | Foreign government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 16.9	$ 16.8	$ 18.3
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	(1.1)	(1.3)	(0.9)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 15.8	$ 15.5	$ 17.4
% 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	$ 11,195.8	$ 10,125.8	$ 11,590.2
Gross Unrealized Gains	45.6	9.8	31.2
Gross Unrealized Losses	(525.4)	(676.1)	(315.5)
Net Holding Period Gains (Losses)	(34.7)	(46.8)	(25.9)
Total available-for-sale securities	$ 10,681.3	$ 9,412.7	$ 11,280
% of Total Fair Value	18.80%	17.60%	21.20%
Total fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 655	$ 696.1	$ 962.3
Gross Unrealized Gains	0.2	0.3	1.1
Gross Unrealized Losses	(16.3)	(17.5)	(5.1)
Net Holding Period Gains (Losses)	(8.9)	(12.1)	(7.2)
Total available-for-sale securities	$ 630	$ 666.8	$ 951.1
% of Total Fair Value	1.10%	1.20%	1.80%
Total fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 5,252.6	$ 5,446	$ 7,296.4
Gross Unrealized Gains	1.6	1.5	2.2
Gross Unrealized Losses	(751.2)	(784)	(380.1)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 4,503	$ 4,663.5	$ 6,918.5
% of Total Fair Value	7.90%	8.70%	13%
Total fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 5,087.8	$ 4,826	$ 5,359.9
Gross Unrealized Gains	1.8	0.9	1.1
Gross Unrealized Losses	(222.5)	(260.5)	(103.6)
Net Holding Period Gains (Losses)	(1.3)	(1.8)	(1.5)
Total available-for-sale securities	$ 4,865.8	$ 4,564.6	$ 5,255.9
% of Total Fair Value	8.60%	8.50%	9.90%
Total fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 202.5	$ 202.6	$ 219.1
Gross Unrealized Gains	0	0	0.1
Gross Unrealized Losses	(5.2)	(4.5)	(1.8)
Net Holding Period Gains (Losses)	(15.7)	(13.8)	3.1
Total available-for-sale securities	$ 181.6	$ 184.3	$ 220.5
% of Total Fair Value	0.30%	0.30%	0.40%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 2,524.1	$ 2,861.7	$ 529.9
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	$ 2,524.1	$ 2,861.7	$ 529.9
% of Total Fair Value	4.50%	5.40%	1%

Investments - Hybrid Securities

Investments - Hybrid Securities (Detail) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Hybrid Instruments [Line Items]
Hybrid securities	$ 1,197.3	$ 1,221.7	$ 1,484.6
Corporate debt securities
Hybrid Instruments [Line Items]
Hybrid securities	548.6	535.4	535.8
Residential mortgage-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	482.1	509.6	721.7
Other asset-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	33.8	42	75
Redeemable preferred stocks
Hybrid Instruments [Line Items]
Hybrid securities	$ 132.8	$ 134.7	$ 152.1

Investments - Composition of Fi

Investments - Composition of Fixed Maturities by Maturity (Detail) - Total fixed maturities $ in Millions	Mar. 31, 2023 USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 7,941.7
One to five years	31,574.9
Five to ten years	13,505.5
Ten years or greater	101.8
Cost	53,123.9
Fair Value
Less than one year	7,706
One to five years	30,132.2
Five to ten years	12,353
Ten years or greater	98
Fair Value	$ 50,289.2

Investments - Gross Unrealized

Investments - Gross Unrealized losses by Major Security (Detail) $ in Millions	Mar. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security	Mar. 31, 2022 USD ($) security
Number of Securities
Total | security	1,416	1,468	1,391
Less than 12 Months | security	291	873	1,320
12 Months or Greater | security	1,125	595	71
Fair Value
Total	$ 38,603	$ 44,315.9	$ 39,844.7
Less than 12 Months	9,487.3	28,119.4	35,958.1
12 Months or Greater	29,115.7	16,196.5	3,886.6
Unrealized Losses
Total	(2,893)	(3,551.5)	(1,780.8)
Less than 12 Months	(219.9)	(1,505)	(1,461.6)
12 Months or Greater	$ (2,673.1)	$ (2,046.5)	$ (319.2)
U.S. government obligations
Number of Securities
Total | security	148	160	116
Less than 12 Months | security	40	90	97
12 Months or Greater | security	108	70	19
Fair Value
Total	$ 19,446.8	$ 24,802.5	$ 18,478
Less than 12 Months	5,938.5	17,327.2	15,467.4
12 Months or Greater	13,508.3	7,475.3	3,010.6
Unrealized Losses
Total	(1,209.6)	(1,604.7)	(876.7)
Less than 12 Months	(127.5)	(699.2)	(649.4)
12 Months or Greater	$ (1,082.1)	$ (905.5)	$ (227.3)
State and local government obligations
Number of Securities
Total | security	343	348	290
Less than 12 Months | security	72	239	279
12 Months or Greater | security	271	109	11
Fair Value
Total	$ 1,943.6	$ 1,948.8	$ 1,767.7
Less than 12 Months	350.7	1,124.2	1,627.3
12 Months or Greater	1,592.9	824.6	140.4
Unrealized Losses
Total	(161.7)	(202.9)	(97.1)
Less than 12 Months	(7.4)	(76.8)	(82.1)
12 Months or Greater	$ (154.3)	$ (126.1)	$ (15)
Foreign government obligations
Number of Securities
Total | security	1	1	1
Less than 12 Months | security	0	0	1
12 Months or Greater | security	1	1	0
Fair Value
Total	$ 15.8	$ 15.5	$ 17.4
Less than 12 Months	0	0	17.4
12 Months or Greater	15.8	15.5	0
Unrealized Losses
Total	(1.1)	(1.3)	(0.9)
Less than 12 Months	0	0	(0.9)
12 Months or Greater	$ (1.1)	$ (1.3)	$ 0
Corporate debt securities
Number of Securities
Total | security	390	422	416
Less than 12 Months | security	93	285	407
12 Months or Greater | security	297	137	9
Fair Value
Total	$ 8,129.9	$ 8,449.6	$ 7,830.6
Less than 12 Months	2,239.3	5,717.6	7,623.8
12 Months or Greater	5,890.6	2,732	206.8
Unrealized Losses
Total	(525.4)	(676.1)	(315.5)
Less than 12 Months	(75.5)	(426.1)	(294.2)
12 Months or Greater	$ (449.9)	$ (250)	$ (21.3)
Residential mortgage-backed securities
Number of Securities
Total | security	43	45	32
Less than 12 Months | security	13	27	26
12 Months or Greater | security	30	18	6
Fair Value
Total	$ 141.7	$ 151	$ 201.8
Less than 12 Months	10	65.1	189
12 Months or Greater	131.7	85.9	12.8
Unrealized Losses
Total	(16.3)	(17.5)	(5.1)
Less than 12 Months	(0.4)	(6.8)	(4.1)
12 Months or Greater	$ (15.9)	$ (10.7)	$ (1)
Commercial mortgage-backed securities
Number of Securities
Total | security	220	226	264
Less than 12 Months | security	11	99	245
12 Months or Greater | security	209	127	19
Fair Value
Total	$ 4,484.5	$ 4,651.1	$ 6,584.4
Less than 12 Months	53.4	1,702	6,133
12 Months or Greater	4,431.1	2,949.1	451.4
Unrealized Losses
Total	(751.2)	(784)	(380.1)
Less than 12 Months	(1.5)	(192.1)	(327.9)
12 Months or Greater	$ (749.7)	$ (591.9)	$ (52.2)
Other asset-backed securities
Number of Securities
Total | security	267	262	269
Less than 12 Months | security	61	130	263
12 Months or Greater | security	206	132	6
Fair Value
Total	$ 4,391.9	$ 4,247.8	$ 4,927.4
Less than 12 Months	884.8	2,144.8	4,873.8
12 Months or Greater	3,507.1	2,103	53.6
Unrealized Losses
Total	(222.5)	(260.5)	(103.6)
Less than 12 Months	(6.2)	(100.9)	(102.7)
12 Months or Greater	$ (216.3)	$ (159.6)	$ (0.9)
Redeemable preferred stocks
Number of Securities
Total | security	4	4	3
Less than 12 Months | security	1	3	2
12 Months or Greater | security	3	1	1
Fair Value
Total	$ 48.8	$ 49.6	$ 37.4
Less than 12 Months	10.6	38.5	26.4
12 Months or Greater	38.2	11.1	11
Unrealized Losses
Total	(5.2)	(4.5)	(1.8)
Less than 12 Months	(1.4)	(3.1)	(0.3)
12 Months or Greater	$ (3.8)	$ (1.4)	$ (1.5)

Investments - Components of Net

Investments - Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	$ 3.9	$ 8
Equity Securities, FV-NI, Gross Realized Gains on Sales	132.1	17.8
Debt and Equity Securities, Gross Realized Gains on Sales	136	25.8
Debt Securities, Available-for-Sale, Realized Loss	(66.7)	(78)
Equity Securities, FV-NI, Gross Realized Losses on Sales	(112.8)	(2.3)
Debt and Equity Securities, Gross Realized Losses on Sales	(179.5)	(80.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(62.8)	(70)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	19.3	15.5
Net realized gains (losses) on security sales	(43.5)	(54.5)
Realized Gain (Loss) on Security Sales, Other Assets	13.2	0
Net impairment losses recognized in earnings	(2.3)	(2.2)
Realized Gains (Losses), Other Assets	10.9	(2.2)
Unrealized Gain (Loss) on Hybrid Instrument, Net	13.9	(39)
Equity Securities, FV-NI, Unrealized Gain (Loss)	90.5	(349.6)
Net holding period gains (losses) on securities	104.4	(388.6)
Total net realized gains (losses) on securities	71.8	(445.3)
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	3.8	3.3
Debt Securities, Available-for-Sale, Realized Loss	(11.5)	(69.2)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(7.7)	(65.9)
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Loss	0	(1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	(1)
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0.1	4.5
Debt Securities, Available-for-Sale, Realized Loss	(20.4)	(7.7)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(20.3)	(3.2)
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0.1
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	0.1
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Loss	(34.5)	0
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(34.5)	0
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0.1
Debt Securities, Available-for-Sale, Realized Loss	(0.2)	(0.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(0.2)	0
Short-term investments
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Loss	(0.1)	0
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(0.1)	0
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	0.1	17.3
Equity Securities, FV-NI, Gross Realized Losses on Sales	(101)	(1.7)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	(100.9)	15.6
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	132	0.5
Equity Securities, FV-NI, Gross Realized Losses on Sales	(11.8)	(0.6)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	$ 120.2	$ (0.1)

Investments - Components of Equ

Investments - Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Realized Investment Gains (Losses)	$ 109.8	$ (334.1)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	19.3	15.5
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 90.5	$ (349.6)

Investments - Components of N_2

Investments - Components of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net Investment Income [Line Items]
Gross investment income	$ 419.6	$ 242.2
Investment expenses	(5.5)	(5.7)
Net Investment Income	414.1	236.5
Available-for-sale Securities
Net Investment Income [Line Items]
Gross investment income	392.8	204.9
Total equity securities
Net Investment Income [Line Items]
Gross investment income	26.8	37.3
Total equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	15.1	18.2
Total equity securities | Common equities
Net Investment Income [Line Items]
Gross investment income	11.7	19.1
Total fixed maturities
Net Investment Income [Line Items]
Gross investment income	368.1	204.5
Total fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Gross investment income	163.2	51.4
Total fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Gross investment income	10.6	9.2
Total fixed maturities | Foreign government obligations
Net Investment Income [Line Items]
Gross investment income	0.1	0.1
Total fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Gross investment income	83.6	68.1
Total fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	9.2	4.8
Total fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	50	43.3
Total fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Gross investment income	48.5	25.1
Total fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	2.9	2.5
Short-term investments
Net Investment Income [Line Items]
Gross investment income	$ 24.7	$ 0.4

Investments - Additional Inform

Investments - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2023 USD ($) security	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Debt and Equity Securities [Line Items]
Principal amount of bonds and certificates of deposit	$ 604,400,000
Securities Exceeding 10% of Shareholders' Equity	0	$ 0	$ 0
Non-Income Producing Securities	0
Open reverse repurchase commitments	0	0	0
Securities Sold under Agreements to Repurchase	$ 0	0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions Downgraded | security	4
Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value, Downgraded in Period	$ 28,800,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Downgraded in Period	1,700,000
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
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff	$ 0	$ 0	$ 0
Recovery of Impairment, Other Assets, Number of Positions | security	3
Percent Change in Investment Income	73%
Percent Change in Book Yield	50%

Fair Value - Composition of Inv

Fair Value - Composition of Investment Portfolio by Major Security Type (Detail) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 56,686,400,000	$ 53,548,300,000	$ 53,186,400,000
Fair Value	5,881,000,000	5,717,900,000	6,692,600,000
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	52,813,300,000	49,513,600,000	46,846,300,000
Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	50,289,200,000	46,651,900,000	46,316,400,000
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	40,108,800,000	36,572,700,000	32,970,400,000
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	27,350,100,000	25,167,400,000	19,528,800,000
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	2,061,600,000	1,977,100,000	2,144,200,000
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	15,800,000	15,500,000	17,400,000
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	10,681,300,000	9,412,700,000	11,280,000,000
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	9,998,800,000	9,894,900,000	13,125,500,000
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	630,000,000	666,800,000	951,100,000
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	4,503,000,000	4,663,500,000	6,918,500,000
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	4,865,800,000	4,564,600,000	5,255,900,000
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	184,300,000	220,500,000
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	40,000,000	40,500,000	61,200,000
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	9,100,000	7,200,000
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	132,800,000	134,700,000	152,100,000
Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,524,100,000	2,861,700,000	529,900,000
Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,873,100,000	4,034,700,000	6,340,100,000
Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,078,800,000	1,213,200,000	1,527,500,000
Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	991,900,000	1,100,800,000	1,390,900,000
Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	70,500,000	71,200,000	78,100,000
Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	16,400,000	41,200,000	58,500,000
Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,794,300,000	2,821,500,000	4,812,600,000
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	2,774,000,000	2,801,700,000	4,792,500,000
Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	20,300,000	19,800,000	20,100,000
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	32,679,500,000	30,799,700,000	24,887,400,000
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	29,883,800,000	27,977,300,000	20,052,000,000
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	27,359,700,000	25,176,600,000	19,539,100,000
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	27,350,100,000	25,167,400,000	19,528,800,000
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	27,350,100,000	25,167,400,000	19,528,800,000
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	9,600,000	9,200,000	10,300,000
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	9,600,000	9,200,000	10,300,000
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	2,524,100,000	2,800,700,000	512,900,000
Fair Value, Inputs, Level 1 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,795,700,000	2,822,400,000	4,835,400,000
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	40,000,000	39,000,000	92,200,000
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	40,000,000	39,000,000	92,200,000
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	2,755,700,000	2,783,400,000	4,743,200,000
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	2,755,700,000	2,783,400,000	4,743,200,000
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	23,884,500,000	22,626,700,000	28,183,600,000
Fair Value	5,881,000,000	5,717,900,000	6,692,600,000
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	22,929,500,000	21,536,300,000	26,794,300,000
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	22,929,500,000	21,475,300,000	26,777,300,000
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	12,758,700,000	11,405,300,000	13,441,600,000
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	2,061,600,000	1,977,100,000	2,144,200,000
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	15,800,000	15,500,000	17,400,000
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	10,681,300,000	9,412,700,000	11,280,000,000
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	9,998,800,000	9,894,900,000	13,125,500,000
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	630,000,000	666,800,000	951,100,000
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	4,503,000,000	4,663,500,000	6,918,500,000
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	4,865,800,000	4,564,600,000	5,255,900,000
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	172,000,000	175,100,000	210,200,000
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	40,000,000	40,500,000	61,200,000
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	9,100,000	7,200,000
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	123,200,000	125,500,000	141,800,000
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	0	61,000,000	17,000,000
Fair Value, Inputs, Level 2 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	955,000,000	1,090,400,000	1,389,300,000
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	955,000,000	1,090,400,000	1,340,000,000
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	884,500,000	994,400,000	1,237,300,000
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	70,500,000	71,200,000	78,100,000
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	0	24,800,000	24,600,000
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	0	0	49,300,000
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	0	0	49,300,000
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	122,400,000	121,900,000	115,400,000
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	122,400,000	121,900,000	115,400,000
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	83,800,000	83,800,000	95,300,000
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	67,400,000	67,400,000	61,400,000
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	16,400,000	16,400,000	33,900,000
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	38,600,000	38,100,000	20,100,000
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	18,300,000	18,300,000	0
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	20,300,000	19,800,000	20,100,000
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	57,586,200,000	55,316,000,000	51,439,800,000
Long-term Debt	6,389,300,000	6,388,300,000	6,385,600,000
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	55,648,000,000	53,125,700,000	48,612,600,000
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	53,123,900,000	50,264,000,000	48,082,700,000
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	41,926,000,000	39,093,300,000	34,245,000,000
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	28,490,900,000	26,770,700,000	20,399,600,000
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	2,222,400,000	2,180,000,000	2,236,900,000
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	16,900,000	16,800,000	18,300,000
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	11,195,800,000	10,125,800,000	11,590,200,000
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	10,995,400,000	10,968,100,000	13,618,600,000
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	655,000,000	696,100,000	962,300,000
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	5,252,600,000	5,446,000,000	7,296,400,000
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	5,087,800,000	4,826,000,000	5,359,900,000
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	202,500,000	202,600,000	219,100,000
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	43,500,000	43,600,000	62,600,000
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	10,500,000	7,500,000
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	148,500,000	149,000,000
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	2,524,100,000	2,861,700,000	529,900,000
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	1,938,200,000	2,190,300,000	2,827,200,000
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	1,197,700,000	1,364,200,000	1,545,500,000
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	1,102,700,000	1,244,200,000	1,425,400,000
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	80,000,000	79,900,000	80,000,000
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	15,000,000	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	740,500,000	826,100,000	1,281,700,000
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	720,200,000	806,300,000	1,261,600,000
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	$ 20,300,000	$ 19,800,000	$ 20,100,000

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
	Mar. 31, 2023	Mar. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 121.9	$ 127.7
Calls/ Maturities/ Paydowns	0.5	2.7
Purchases	0	0
Sales	0	(15)
Net Realized (Gain)/Loss on Sales	0	(17.2)
Change in Valuation	0	17.2
Net Transfers In (Out)	0	0
Fair value, ending balance	122.4	115.4
Total equity securities | Financials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	67.4	76.4
Calls/ Maturities/ Paydowns	0	0
Purchases	0	0
Sales	0	(15)
Net Realized (Gain)/Loss on Sales	0	(17.2)
Change in Valuation	0	17.2
Net Transfers In (Out)	0	0
Fair value, ending balance	67.4	61.4
Total equity securities | Industrials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	16.4	34.4
Calls/ Maturities/ Paydowns	0	(0.5)
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Fair value, ending balance	16.4	33.9
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	18.3
Calls/ Maturities/ Paydowns	0
Purchases	0
Sales	0
Net Realized (Gain)/Loss on Sales	0
Change in Valuation	0
Net Transfers In (Out)	0
Fair value, ending balance	18.3
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	19.8	16.9
Calls/ Maturities/ Paydowns	0.5	3.2
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Fair value, ending balance	$ 20.3	$ 20.1

Fair Value - Summary of Quantit

Fair Value - Summary of Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 56,686.4	$ 53,186.4	$ 53,548.3
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	122.4	115.4	121.9
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	102.1	95.3	102.1
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	20.3	20.1	19.8
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	$ 83.8	$ 95.3	$ 83.8
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum	2.70%	(27.90%)	(0.60%)
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum	23.30%	(12.70%)	19.90%
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average	9.20%	20.10%	10.50%
Fair Value, Inputs, Level 3 | Common equities | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 18.3		$ 18.3
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum	(51.30%)		(42.50%)
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum	48.30%		59.10%
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average	15.60%		30%

Fair Value - Additional Informa

Fair Value - Additional Information (Detail) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 56,686,400,000	$ 53,548,300,000	$ 53,186,400,000
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	91%	90%	81%
Investments, Fair Value	$ 32,679,500,000	$ 30,799,700,000	$ 24,887,400,000
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	98%	98%	97%
Dealer Quoted Prices, Percent of FV Hierarchy Level	2%	2%	3%
Investments, Fair Value	$ 23,884,500,000	$ 22,626,700,000	$ 28,183,600,000
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	122,400,000	121,900,000	115,400,000
Available-for-sale Securities
Fair Value Measurements [Line Items]
Investments, Fair Value	52,813,300,000	49,513,600,000	46,846,300,000
Available-for-sale Securities | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	50,289,200,000	46,651,900,000	46,316,400,000
Available-for-sale Securities | Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Investments, Fair Value	29,883,800,000	27,977,300,000	20,052,000,000
Available-for-sale Securities | Fair Value, Inputs, Level 1 | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	27,359,700,000	25,176,600,000	19,539,100,000
Available-for-sale Securities | Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Investments, Fair Value	22,929,500,000	21,536,300,000	26,794,300,000
Available-for-sale Securities | Fair Value, Inputs, Level 2 | Total fixed maturities
Fair Value Measurements [Line Items]
Investments, Fair Value	22,929,500,000	21,475,300,000	26,777,300,000
Available-for-sale Securities | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	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

Debt - Summary of Debt (Detail)

Debt - Summary of Debt (Detail) - USD ($)		Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	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]
Debt, Long-term and Short-term, Combined Amount	[1]	$ 6,389,300,000	$ 6,388,300,000	$ 6,385,600,000
Fair Value		5,881,000,000	5,717,900,000	6,692,600,000
2.45% Senior Notes due 2027 (issued: $500.0, August 2016)
Debt Instrument [Line Items]
Long-term Debt		498,300,000	498,200,000	497,800,000
Fair Value		464,200,000	457,700,000	487,900,000
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		497,700,000	497,500,000	497,100,000
Fair Value		463,800,000	460,300,000	$ 489,400,000
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		297,600,000	297,500,000	297,300,000
Fair Value		329,600,000	326,800,000	358,800,000
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		546,500,000	546,400,000	546,100,000
Fair Value		538,500,000	527,800,000	573,500,000
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		497,000,000	496,900,000	496,600,000
Fair Value		460,000,000	448,600,000	496,200,000
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		496,000,000	495,900,000	495,600,000
Fair Value		446,900,000	438,100,000	$ 487,000,000
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		396,500,000	396,400,000	396,200,000
Fair Value		448,100,000	435,400,000	494,800,000
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	346,900,000	346,800,000
Fair Value		312,300,000	298,400,000	368,700,000
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		395,800,000	395,700,000	395,700,000
Fair Value		324,000,000	310,200,000	386,000,000
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		842,100,000	842,100,000	841,900,000
Fair Value		743,800,000	716,200,000	894,500,000
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		590,400,000	590,400,000	590,300,000
Fair Value		530,000,000	507,000,000	637,400,000
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		491,000,000	490,900,000	490,800,000
Fair Value		420,300,000	404,900,000	514,900,000
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		493,500,000	493,500,000	493,400,000
Fair Value		$ 399,500,000	$ 386,500,000	$ 503,500,000
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 ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term Debt, Current Maturities	$ 0	$ 0	$ 0
Discretionary Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	250,000,000
Borrowings outstanding	$ 0	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Valuation allowance	$ 0	$ 0	$ 0
Provision for income taxes	19.20%	19.60%
Deferred Tax Asset, Debt Securities, Trading, Unrealized Loss	$ 582,600,000	$ 364,300,000	$ 742,900,000

Loss and Loss Adjustment Expe_3

Loss and Loss Adjustment Expense Reserves Activity in Loss and Loss Adjustment Expense Reserves (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Dec. 31, 2021
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at January 1	$ 30,359.3	$ 26,164.1
Less reinsurance recoverables on unpaid losses	5,301.1	4,758.4	$ 5,559.2	$ 4,733.6
Net balance at January 1	24,800.1	21,430.5
Incurred related to:
Current year	10,002.8	8,667.6
Prior years	621.2	190.8
Total incurred	10,624	8,858.4
Paid related to:
Current year	3,962.6	3,601.4
Prior years	5,736.2	4,691.7
Total paid	9,698.8	8,293.1
Net balance at March 31	25,725.3	21,995.8
Plus reinsurance recoverables on unpaid losses	5,301.1	4,758.4
Balance at March 31	$ 31,026.4	$ 26,754.2

Loss and Loss Adjustment Expe_4

Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years	$ 621.2	$ 190.8
Personal Lines | Personal auto business
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years	428	106
Personal Lines | special lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years		2
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years	144	99
Property
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years	42	(16)
Short-Duration Insurance Contract, Accident Year 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years	498
Short-Duration Insurance Contract, Accident Year 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years	$ 30	146
Short-Duration Insurance Contract, Accident Year 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior years		$ 23

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Open reverse repurchase commitments	$ 0	$ 0	$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	9,300,000	10,800,000
Income Taxes Paid	100,000	0
Interest Paid, Excluding Capitalized Interest, Operating Activities	87,900,000	64,900,000
Operating Lease, Payments	21,500,000	22,000,000
Cash and Cash Equivalents
Open reverse repurchase commitments	177,500,000	152,200,000	$ 125,900,000
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
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Revenues	$ 14,303.2	$ 11,841.5
Pretax Profit (Loss)	554.4	390.2
Amortization of intangible assets	5.4	14.6
Personal Lines | Agency | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	4,860.2	4,323.3
Pretax Profit (Loss)	162.6	288.6
Personal Lines | Direct | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	5,717.4	4,793.6
Pretax Profit (Loss)	(22.1)	150.4
Operating Segments | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	13,533.1	11,802.9
Pretax Profit (Loss)	141.6	648.8
Operating Segments | Personal Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	10,577.6	9,116.9
Pretax Profit (Loss)	$ 140.5	$ 439
Personal auto insurance percentage of the total personal lines segment net premiums earned	94%	94%
Operating Segments | Commercial Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	$ 2,356.1	$ 2,127.2
Pretax Profit (Loss)	37.2	202.4
Operating Segments | Property | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	598.7	558.1
Pretax Profit (Loss)	(32.7)	8.3
Amortization of intangible assets	5	14.1
Operating Segments | Other Indemnity | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	0.7	0.7
Pretax Profit (Loss)	(3.4)	(0.9)
Segment Reconciling Items | Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	206.2	174
Segment Reconciling Items | Service businesses
Segment Reporting Information [Line Items]
Revenues	72.5	67.7
Pretax Profit (Loss)	(9.8)	4.5
Segment Reconciling Items | Investment income
Segment Reporting Information [Line Items]
Revenues	491.4	(203.1)
Pretax Profit (Loss)	485.9	(208.8)
Segment Reconciling Items | Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (63.3)	$ (54.3)

Segment Information - Underwrit

Segment Information - Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Underwriting operations	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Personal Lines | Agency
Segment Reporting Information [Line Items]
Underwriting Margin	3.30%	6.70%
Combined Ratio	96.70%	93.30%
Personal Lines | Direct
Segment Reporting Information [Line Items]
Underwriting Margin	(0.40%)	3.10%
Combined Ratio	100.40%	96.90%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	1%	5.50%
Combined Ratio	99%	94.50%
Operating Segments | Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	1.30%	4.80%
Combined Ratio	98.70%	95.20%
Operating Segments | Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	1.60%	9.50%
Combined Ratio	98.40%	90.50%
Operating Segments | Property
Segment Reporting Information [Line Items]
Underwriting Margin	(5.50%)	1.50%
Combined Ratio	105.50%	98.50%
Combined ratio amortization points	0.008	0.025

Dividends (Details)

Dividends (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended					3 Months Ended
	Mar. 15, 2023	Mar. 31, 2023	Jan. 31, 2023	Apr. 30, 2022	Mar. 31, 2022	Jan. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Common Stock, Dividends, Per Share, Declared							$ 0.10	$ 0.10
Payments of Ordinary Dividends, Common Stock							$ 58.5	$ 58.5
Payments of Ordinary Dividends, Preferred Stock and Preference Stock							$ 13.4	13.4
Quarterly dividend
Common Stock, Dividends, Per Share, Declared							$ 0.10
Common Stock, Dividends, Per Share, Cash Paid			$ 0.10	$ 0.10		$ 0.10
Payments of Ordinary Dividends, Common Stock			$ 58.5	$ 58.5		$ 58.5
Series B Preferred Stock
Preferred Stock, Dividends, Per Share, Cash Paid		$ 26.875			$ 26.875
Payments of Ordinary Dividends, Preferred Stock and Preference Stock		$ 13.4			$ 13.4
Series B Preferred Stock | London Interbank Offered Rate (LIBOR)
Preferred Stock, Basis Spread on Variable Rate	2.539%
Common equities | Quarterly dividend
Dividends Payable		$ 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
	Mar. 31, 2023	Mar. 31, 2022
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ (3,556.9)	$ 52.3
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax	705.6	(1,851.7)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax		0.3
OCI, before Reclassifications, before Tax, Attributable to Parent	705.6	(1,851.4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(57.9)	(45.5)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(0.1)	(0.2)
Total reclassification adjustment for amounts realized in net income, pre tax	(58)	(45.7)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	763.6	(1,805.7)
AOCI before Tax, Attributable to Parent, ending balance	(2,793.3)	(1,753.4)
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	754.9	(11.6)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax	(148.2)	388.9
OCI, Foreign Currency Transaction and Translation Gain (Loss), Arising During Period, Tax		0.1
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax	(148.2)	388.8
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	12.1	9.6
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	0	0
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	12.1	9.6
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	(160.3)	379.2
AOCI Tax, Attributable to Parent, ending balance	594.6	367.6
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(2,802)	40.7
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	557.4	(1,462.8)
Foreign currency translation adjustment	0	0.2
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	557.4	(1,462.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(45.8)	(35.9)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.1)	(0.2)
Total reclassification adjustment for amounts realized in net income, after tax	(45.9)	(36.1)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	603.3	(1,426.5)
After tax total accumulated other comprehensive income, ending balance	(2,198.7)	(1,385.8)
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	(2,786.3)	56.2
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	557.4	(1,462.8)
Foreign currency translation adjustment		0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	557.4	(1,462.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(45.8)	(35.9)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0	0
Total reclassification adjustment for amounts realized in net income, after tax	(45.8)	(35.9)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	603.2	(1,426.9)
After tax total accumulated other comprehensive income, ending balance	(2,183.1)	(1,370.7)
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	(14.5)	(14.9)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	0	0
Foreign currency translation adjustment		0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.1)	(0.2)
Total reclassification adjustment for amounts realized in net income, after tax	(0.1)	(0.2)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.1	0.2
After tax total accumulated other comprehensive income, ending balance	(14.4)	(14.7)
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	(1.2)	(0.6)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	0	0
Foreign currency translation adjustment		0.2
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0.2
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0	0
Total reclassification adjustment for amounts realized in net income, after tax	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	0.2
After tax total accumulated other comprehensive income, ending balance	$ (1.2)	$ (0.4)

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	Mar. 31, 2023 USD ($)
Equity [Abstract]
Net unrealized losses on forecasted transactions, expected to reclassify into income within the next 12 months	$ 0.6

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Schedule of Other Intangible Assets [Line Items]
Indefinite lived intangible assets	$ 12.4	$ 12.4	$ 12.4
Total	80.9	86.3	102.7
Accumulated amortization	164	158.6	142.2
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	68.5	73.9	90.3
Accumulated amortization	$ 163.4	$ 158	$ 141.6

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 164	$ 158.6	$ 142.2
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2
Accumulated Amortization	91	88.1	79.6
Net Carrying Amount	68.2	71.1	79.6
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	69.1	69.1	69.1
Accumulated Amortization	69.1	67	60.5
Net Carrying Amount	0	2.1	8.6
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3.6	3.6	3.6
Accumulated Amortization	3.3	2.9	1.5
Net Carrying Amount	0.3	0.7	2.1
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	231.9	231.9	231.9
Accumulated Amortization	163.4	158	141.6
Net Carrying Amount	$ 68.5	$ 73.9	$ 90.3

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Goodwill (Details) - USD ($)	3 Months Ended
	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022
Finite-Lived Intangible Assets [Line Items]
Goodwill, Impaired, Accumulated Impairment Loss			$ 0
Amortization of intangible assets	$ 5,400,000		$ 14,600,000
Goodwill, Other Increase (Decrease)	$ 0
Property
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment		$ 224,800,000