3,902.4

721.5

3,350.9

Total net unrealized gains (losses) on fixed-maturity securities

1,185.5

(2,842.5)

(891.1)

Net unrealized losses on forecasted transactions

0.5

0.4

0.7

Foreign currency translation adjustment

0.3

(0.6)

Comprehensive income (loss)

1,186.3

(2,842.7)

(891.0)

5,088.7

(2,121.2)

2,459.9

Computation of Earnings Per Common Share

Less: Preferred share dividends

3,902.4

721.5

3,350.9

^[1]

37.6

26.9

Net income available to common shareholders

$ 3,864.8

$ 694.6

$ 3,324.0

Average common shares outstanding - Basic

584.9

584.4

584.5

Net effect of dilutive stock-based compensation

2.6

2.7

2.6

Total average equivalent common shares - Diluted

587.5

587.1

Basic: Earnings per share (usd per share)

$ 6.61

$ 1.19

$ 5.69

Diluted: Earnings per share (usd per share)

$ 6.58

$ 1.18

$ 5.66

[1]	Changed to a floating dividend rate in March 2023. See Note 14 – Dividends for further discussion.

Consolidated Balance Sheets - USD ($)
$ in Millions

Dec. 31, 2023

Dec. 31, 2022

Available-for-sale securities, at fair value:

Fixed maturities (amortized cost: $62,441.9 and $50,264.0)

$ 60,378.2

$ 46,651.9

Short-term investments (amortized cost: $1,789.9 and $2,861.7)

1,789.9

2,861.7

Total available-for-sale securities

62,168.1

49,513.6

Equity securities, at fair value:

Nonredeemable preferred stocks (cost: $977.1 and $1,364.2)

902.1

1,213.2

Common equities (cost: $706.0 and $826.1)

2,928.4

2,821.5

Total equity securities

3,830.5

4,034.7

Total investments

65,998.6

53,548.3

Cash and cash equivalents

84.9

203.5

Restricted cash and cash equivalents

14.7

17.4

Total cash, cash equivalents, restricted cash, and restricted cash equivalents

99.6

220.9

Accrued investment income

438.0

282.5

Premiums receivable, net of allowance for credit losses of $369.1 and $343.3

11,958.2

10,416.9

Reinsurance recoverables

5,093.9

5,832.1

Prepaid reinsurance premiums

249.8

295.5

Deferred acquisition costs

1,687.4

1,544.4

Property and equipment, net of accumulated depreciation of $1,655.1 and $1,551.1

880.8

1,034.0

Net federal deferred income taxes

936.0

1,131.5

Other assets

1,348.5

1,158.9

Total assets

88,690.8

75,465.0

Liabilities

Unearned premiums

20,133.7

17,293.6

Loss and loss adjustment expense reserves

34,389.2

30,359.3

Accounts payable, accrued expenses, and other liabilities

^[1]

7,002.2

5,532.8

Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)

^[2]

6,888.6

6,388.3

Total liabilities

68,413.7

59,574.0

Shareholders' Equity

493.9

Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 212.3 and 212.7)

585.3

584.9

Paid-in capital

2,013.1

1,893.0

Retained earnings

18,800.5

15,721.2

Accumulated other comprehensive income (loss):

Net unrealized gains (losses) on fixed-maturity securities

(1,600.8)

(2,786.3)

Net unrealized losses on forecasted transactions

(14.0)

(14.5)

Foreign currency translation adjustment

(0.9)

(1.2)

Total accumulated other comprehensive income (loss)

(1,615.7)

(2,802.0)

Total shareholders’ equity

20,277.1

15,891.0

Total liabilities and shareholders’ equity

$ 88,690.8

$ 75,465.0

[1]	See Note 1 – Reporting and Accounting Policies, Commitments and Contingencies and Note 12 – Litigation for further discussion.
[2]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fixed maturities, amortized cost	$ 62,441.9	$ 50,264.0
Short-term investments, amortized cost	1,789.9	2,861.7
Nonredeemable preferred stocks, cost	977.1	1,364.2
Equity Securities Common Equities Cost	706.0	826.1
Premium receivable, allowance for credit loss	369.1	343.3
Property and equipment, accumulated depreciation	$ 1,655.1	$ 1,551.1
Common Shares, par value (USD per share)	$ 1.00	$ 1.00
Common Shares, authorized (shares)	900,000,000.0	900,000,000.0
Common Shares, issued (shares)	797,600,000	797,600,000
Treasury Stock, Common, Shares	212,300,000	212,700,000
Serial Preferred Stock
Preferred shares, authorized (in shares)	20,000,000.0	20,000,000.0
Series B Preferred Stock \| Serial Preferred Stock
Preferred shares, authorized (in shares)	500,000	500,000
Preferred stock, par value	$ 0	$ 0
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000
Preferred shares, issued (in shares)	500,000	500,000
Preferred Stock, Shares Outstanding (in shares)	500,000	500,000

Consolidated Statements of Changes in Shareholders' Equity - USD ($)
$ in Millions

Total

Preferred Shares, No Par Value

Common Shares, $1.00 Par Value

Paid-In Capital

Retained Earnings

Accumulated Other Comprehensive Income (Loss)

Balance, beginning of year at Dec. 31, 2020

$ 493.9

$ 585.2

$ 1,672.9

$ 13,354.9

$ 931.7

Treasury shares purchased

(2.4)

(7.1)

(213.5)

Net restricted equity awards issued/vested

1.6

(1.6)

Reinvested dividends on restricted stock units

100.7

8.0

(8.0)

Cash dividends declared on common shares ($1.15, $0.40, and $1.90 per share)1

$ 3,350.9

3,350.9

^[1]

(1,109.0)

Cash dividends declared on Serial Preferred Shares, Series B ($60.354787, $53.75, and $53.75 per share)1

^[1]

(26.8)

(8.8)

Balance, end of year at Dec. 31, 2021

(891.0)

18,231.6

493.9

584.4

1,772.9

15,339.7

40.7

Treasury shares purchased

(0.9)

(2.6)

(95.5)

Net restricted equity awards issued/vested

1.4

(1.4)

Reinvested dividends on restricted stock units

122.7

1.4

(1.4)

Cash dividends declared on common shares ($1.15, $0.40, and $1.90 per share)1

721.5

^[1]

(233.7)

Cash dividends declared on Serial Preferred Shares, Series B ($60.354787, $53.75, and $53.75 per share)1

^[1]

(26.8)

17.4

Balance, end of year at Dec. 31, 2022

(2,842.7)

15,891.0

493.9

584.9

1,893.0

15,721.2

(2,802.0)

Treasury shares purchased

(1.0)

(3.3)

(136.4)

Net restricted equity awards issued/vested

1.4

(1.4)

Reinvested dividends on restricted stock units

121.3

3.5

(3.5)

Cash dividends declared on common shares ($1.15, $0.40, and $1.90 per share)1

3,902.4

^[1]

(672.7)

Cash dividends declared on Serial Preferred Shares, Series B ($60.354787, $53.75, and $53.75 per share)1

^[1]

(30.2)

19.7

Balance, end of year at Dec. 31, 2023

1,186.3

$ 20,277.1

$ 493.9

$ 585.3

$ 2,013.1

$ 18,800.5

$ (1,615.7)

[1]	See Note 14 – Dividends for further discussion.

Consolidated Statements of Cash Flows - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Cash Flows From Operating Activities

Adjustments to reconcile net income to net cash provided by operating activities:

$ 3,902.4

$ 721.5

$ 3,350.9

Depreciation

285.5

305.6

279.7

Amortization of intangible assets

14.2

31.0

57.7

Net amortization (accretion) of fixed-income securities

41.4

(25.2)

130.3

Net realized (gains) losses on securities

121.3

122.7

100.7

(353.1)

1,912.2

(1,509.2)

Net (gains) losses on disposition of property and equipment

36.2

(0.6)

(3.6)

Goodwill impairment

0.0

224.8

0.0

Prepaid reinsurance premiums

Premiums receivable

(1,541.3)

(1,017.4)

(1,146.8)

Reinsurance recoverables

738.2

(851.6)

(508.7)

45.7

162.1

(74.9)

Deferred acquisition costs

(143.0)

(188.8)

(118.4)

Income taxes

181.2

(515.3)

(86.0)

Unearned premiums

2,840.1

1,677.8

2,111.4

Loss and loss adjustment expense reserves

4,029.9

4,195.2

4,752.8

Accounts payable, accrued expenses, and other liabilities

699.6

199.5

399.7

Net cash provided by operating activities

(255.0)

(104.7)

26.1

10,643.3

6,848.8

7,761.7

Purchases:

Fixed maturities

(25,776.9)

(26,510.4)

(33,177.5)

Equity securities

(86.6)

(158.1)

(838.1)

Sales:

Fixed maturities

8,234.4

14,055.2

18,965.2

Equity securities

791.3

1,496.1

780.6

Maturities, paydowns, calls, and other:

Fixed maturities

4,990.3

5,380.3

7,013.8

Equity securities

65.2

83.6

223.1

Net (purchases) sales of short-term investments

1,155.7

(1,868.2)

4,355.7

Net change in unsettled security transactions

(11.2)

(177.8)

47.9

Acquisition of Protective Insurance Corporation, net of cash, cash equivalents, and restricted cash equivalents acquired

0.0

(313.2)

Purchases of property and equipment

(252.0)

(292.0)

(243.5)

Sales of property and equipment

47.2

35.1

66.2

Net cash used in investing activities

(10,842.6)

(7,956.2)

(3,119.8)

Cash Flows From Financing Activities

Dividends paid to common shareholders

^[1]

(234.0)

(3,746.5)

Dividends paid to preferred shareholders

^[1]

(43.6)

(26.8)

Acquisition of treasury shares for restricted stock tax liabilities

(95.0)

(76.7)

(67.2)

Acquisition of treasury shares acquired in open market

(45.7)

(22.3)

(155.8)

Net proceeds from debt issuance

496.3

1,486.0

0.0

Payment of acquired company debt

0.0

(20.0)

Payments of debt

0.0

(500.0)

Net cash provided by (used in) financing activities

78.0

1,126.2

(4,516.3)

Increase (decrease) in cash, cash equivalents, restricted cash, and restricted cash equivalents

(121.3)

18.8

125.6

Cash, cash equivalents, restricted cash, and restricted cash equivalents - beginning of year

220.9

202.1

76.5

Cash, cash equivalents, restricted cash, and restricted cash equivalents - end of year

$ 99.6

$ 220.9

$ 202.1

[1]	See Note 14 – Dividends for further discussion.

Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Common Shares, par value (USD per share)	$ 1.00	$ 1.00	$ 1.00
Common shares, dividends declared (USD per share)	$ 1.15	$ 0.40	$ 1.90
Voting Preferred Stock
Preferred shares, authorized (in shares)	5,000,000	5,000,000	5,000,000
Preferred shares, issued (in shares)	0	0	0
Serial Preferred Stock
Preferred shares, authorized (in shares)	20,000,000.0	20,000,000.0
Serial Preferred Stock \| Series B Preferred Stock
Preferred stock, par value	$ 0	$ 0	$ 0
Preferred shares, dividends declared (USD per share)	$ 60.354787	$ 53.75	$ 53.75
Preferred shares, authorized (in shares)	500,000	500,000
Preferred shares, issued (in shares)	500,000	500,000

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties

12 Months Ended

Dec. 31, 2023

SCHEDULE I - Summary Of Investments - Other Than Investments In Related Parties

SCHEDULE I — SUMMARY OF INVESTMENTS — OTHER THAN INVESTMENTS IN RELATED PARTIES

THE PROGRESSIVE CORPORATION AND SUBSIDIARIES

(millions)


	December 31, 2023
Type of Investment	Cost		Fair Value		Amount At Which Shown In The Balance Sheet
Fixed maturities:
Bonds:
United States Government and government agencies and authorities	$	37,823.2	$	36,869.4	$	36,869.4
States, municipalities, and political subdivisions	2,338.4		2,202.8		2,202.8
Foreign government obligations	17.3		16.3		16.3
Public utilities	1,378.5		1,352.3		1,352.3
Corporate and other debt securities	10,067.5		9,831.4		9,831.4
Asset-backed securities	10,629.3		9,932.3		9,932.3
Redeemable preferred stocks	187.7		173.7		173.7
Total fixed maturities	62,441.9		60,378.2		60,378.2
Equity securities:
Common stocks:
Public utilities	39.0		97.5		97.5
Banks, trusts, and insurance companies	130.8		480.0		480.0
Industrial, miscellaneous, and all other	536.2		2,350.9		2,350.9
Nonredeemable preferred stocks	977.1		902.1		902.1
Total equity securities	1,683.1		3,830.5		3,830.5
Short-term investments	1,789.9		1,789.9		1,789.9
Total investments	$	65,914.9	$	65,998.6	$	65,998.6

Progressive did not have 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 December 31, 2023.

SCHEDULE II - Condensed Financial Information Of Registrant

12 Months Ended

Dec. 31, 2023

SCHEDULE II - Condensed Financial Information Of Registrant

SCHEDULE II — CONDENSED FINANCIAL INFORMATION OF REGISTRANT

CONDENSED STATEMENTS OF COMPREHENSIVE INCOME

THE PROGRESSIVE CORPORATION (PARENT COMPANY)

(millions)


	Years Ended December 31,
	2023		2022		2021
Revenues
Dividends from subsidiaries	$	399.0	$	540.5	$	2,847.0
Undistributed income from subsidiaries	3,572.3		325.0		674.9
Equity in net income of subsidiaries	3,971.3		865.5		3,521.9
Intercompany investment income	204.3		92.7		4.5
Total revenues	4,175.6		958.2		3,526.4
Expenses
Interest expense	270.0		246.0		220.0
Deferred compensation1	20.4		25.3		8.8
Other operating costs and expenses	7.6		6.8		6.8
Total expenses	298.0		278.1		235.6
Income before income taxes	3,877.6		680.1		3,290.8
Benefit for income taxes	24.8		41.4		60.1
Net income	3,902.4		721.5		3,350.9
Other comprehensive income (loss)	1,186.3		(2,842.7)		(891.0)
Comprehensive income (loss)	$	5,088.7	$	(2,121.2)	$	2,459.9

1 See Note 4 – Employee Benefit Plans in these condensed financial statements.

See notes to condensed financial statements.

CONDENSED BALANCE SHEETS

THE PROGRESSIVE CORPORATION (PARENT COMPANY)

(millions - except per share amounts)


	December 31,
	2023		2022
Assets
Investment in affiliate	$	5.0	$	5.0
Investment in subsidiaries	23,409.9		17,911.8
Receivable from investment subsidiary	3,791.4		4,098.7
Intercompany receivable	886.7		466.2
Net federal deferred income taxes	65.6		64.3
Other assets	165.4		150.6
Total assets	$	28,324.0	$	22,696.6
Liabilities and Shareholders’ Equity
Accounts payable, accrued expenses, and other liabilities	$	1,158.3	$	417.3
Debt1	6,888.6		6,388.3
Total liabilities	8,046.9		6,805.6
Serial Preferred Shares (authorized 20.0)
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)2	493.9		493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 212.3 and 212.7)	585.3		584.9
Paid-in capital	2,013.1		1,893.0
Retained earnings	18,800.5		15,721.2
Total accumulated other comprehensive income (loss)	(1,615.7)		(2,802.0)
Total shareholders’ equity	20,277.1		15,891.0
Total liabilities and shareholders’ equity	$	28,324.0	$	22,696.6

1 Consists of long-term debt. See Note 4 – Debt in our Annual Report for further discussion.

2 See Note 7 – Subsequent Event in these condensed financial statements.

See notes to condensed financial statements.

CONDENSED STATEMENTS OF CASH FLOWS

THE PROGRESSIVE CORPORATION (PARENT COMPANY)

(millions)


	Years Ended December 31,
	2023		2022		2021
Cash Flows From Operating Activities:
Net income	$	3,902.4	$	721.5	$	3,350.9
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed income from subsidiaries	(3,572.3)		(325.0)		(674.9)
Amortization of equity-based compensation	3.3		3.2		3.1
Changes in:
Intercompany receivable	(420.5)		(79.0)		86.6
Accounts payable, accrued expenses, and other liabilities	12.5		(21.5)		23.8
Income taxes	301.2		28.9		(154.8)
Other, net	9.6		60.1		76.8
Net cash provided by operating activities	236.2		388.2		2,711.5
Cash Flows From Investing Activities:
Additional investments in equity securities of consolidated subsidiaries	(621.5)		(797.8)		(397.3)
Received from (paid to) investment subsidiary	307.3		(716.6)		2,519.6
Acquisition of Protective Insurance Corporation	0		0		(337.5)
Net cash provided by (used in) investing activities	(314.2)		(1,514.4)		1,784.8
Cash Flows From Financing Activities:
Dividends paid to common shareholders	(234.0)		(234.0)		(3,746.5)
Dividends paid to preferred shareholders	(43.6)		(26.8)		(26.8)
Acquisition of treasury shares for restricted stock tax liabilities	(95.0)		(76.7)		(67.2)
Acquisition of treasury shares acquired in open market	(45.7)		(22.3)		(155.8)
Net proceeds from debt issuance	496.3		1,486.0		0
Payments of debt	0		0		(500.0)
Net cash provided by (used in) financing activities	78.0		1,126.2		(4,496.3)
Change in cash	0		0		0
Cash - beginning of year	0		0		0
Cash - end of year	$	0	$	0	$	0

See notes to condensed financial statements.

NOTES TO CONDENSED FINANCIAL STATEMENTS

The accompanying condensed financial statements of The Progressive Corporation (parent company) should be read in conjunction with the consolidated financial statements and notes thereto in the Annual Report to Shareholders of The Progressive Corporation and its subsidiaries, which is included as Exhibit 13 to this Form 10-K.

Note 1. Statements of Cash Flows — For the purpose of the condensed statements of cash flows, cash includes only bank demand deposits. The Progressive Corporation does not hold any cash but has unrestricted access to funds maintained in a non-insurance investment subsidiary to meet its holding company obligations; at December 31, 2023, 2022, and 2021, $4.2 billion, $4.4 billion, and $4.2 billion, respectively, of marketable securities were available in this subsidiary.

For the years ended December 31, non-cash activity included the following:


(millions)	2023		2022		2021
Common share dividends1	$	497.9	$	58.5	$	58.5
Preferred share dividends1	0		13.4		13.4

1 Declared but unpaid. See Note 14 – Dividends in the Annual Report for further discussion.

For the years ended December 31, The Progressive Corporation paid the following:


(millions)	2023		2022		2021
Income taxes	$	800.0	$	705.0	$	815.0
Interest	264.9		228.9		223.9

Note 2. Income Taxes — The Progressive Corporation files a consolidated federal income tax return with its eligible subsidiaries and acts as an agent for the consolidated tax group when making payments to the Internal Revenue Service. The Progressive Corporation consolidated group’s net income taxes currently payable/recoverable are included in other liabilities/assets, respectively, in the accompanying condensed balance sheets based on the balance at the end of the year. The Progressive Corporation and its eligible subsidiaries have adopted, pursuant to a written agreement, a method of allocating consolidated federal income taxes. Amounts allocated to the eligible subsidiaries under the written agreement are included in intercompany receivable in the accompanying condensed balance sheets.

Note 3. Debt — The information relating to debt is incorporated by reference from Note 4 – Debt in our Annual Report.

Note 4. Employee Benefit Plans — The information relating to incentive compensation and deferred compensation plans is incorporated by reference from Note 9 – Employee Benefit Plans in our Annual Report.

Note 5. Other Comprehensive Income (Loss) — On the condensed statements of comprehensive income, other comprehensive income (loss) represents activity of the subsidiaries of The Progressive Corporation and includes net unrealized gains (losses) on fixed-maturity securities, net unrealized losses on forecasted transactions, and foreign currency translation adjustments.

Note 6. Dividends — The information relating to our dividend policy is incorporated by reference from Note 14 – Dividends in our Annual Report.Note 7. Subsequent Event — Pursuant to authorization from our Board of Directors, we redeemed all of the outstanding Serial Preferred Shares, Series B, at the stated amount of $1,000 per share, for an aggregate payout of $507.8 million, including accrued and unpaid dividends to, but excluding, February 22, 2024, which is the redemption date.

SCHEDULE III - Supplementary Insurance Information

12 Months Ended

Dec. 31, 2023

SCHEDULE III - Supplementary Insurance Information

SCHEDULE III — SUPPLEMENTARY INSURANCE INFORMATION

THE PROGRESSIVE CORPORATION AND SUBSIDIARIES

(millions)


Segment	Deferred policy acquisition costs1		Future policy benefits, losses, claims, and loss expenses1		Unearned premiums1		Other policy claims and benefits payable1		Premium revenue		Net investment income1,2		Benefits, claims, losses, and settlement expenses		Amortization of deferred policy acquisition costs		Other operating expenses1		Net premiums written
Year ended December 31, 2023:
Personal Lines									$	46,213.3			$	35,972.4	$	3,169.1	$	4,928.6	$	48,581.0
Commercial Lines									9,898.7				7,899.7		1,004.7		1,020.8		10,138.3
Property									2,551.4				1,776.3		491.0		281.4		2,830.6
Other indemnity									1.0				6.2		0.3		10.7		0.3
Total	$	1,687.4	$	34,389.2	$	20,133.7	$	0	$	58,664.4	$	1,865.6	$	45,654.6	$	4,665.1	$	6,241.5	$	61,550.2
Year ended December 31, 2022:
Personal Lines									$	37,880.2			$	29,680.8	$	2,592.1	$	4,668.9	$	39,278.5
Commercial Lines									9,088.3				6,544.7		913.3		947.7		9,398.8
Property									2,270.0				1,891.3		411.1		235.3		2,401.7
Other indemnity									2.7				5.9		0.5		7.7		2.1
Total	$	1,544.4	$	30,359.3	$	17,293.6	$	0	$	49,241.2	$	1,236.0	$	38,122.7	$	3,917.0	$	5,859.6	$	51,081.1
Year ended December 31, 2021:
Personal Lines									$	35,373.3			$	27,043.1	$	2,614.7	$	4,656.8	$	36,168.8
Commercial Lines									6,945.2				4,814.5		734.1		742.3		8,015.9
Property									2,042.5				1,764.6		362.9		253.0		2,216.2
Other indemnity									7.7				5.4		1.1		2.6		4.3
Total	$	1,355.6	$	26,164.1	$	15,615.8	$	0	$	44,368.7	$	835.4	$	33,627.6	$	3,712.8	$	5,654.7	$	46,405.2

1 Progressive does not allocate assets, liabilities, or investment income to operating segments. Expense allocations are based on certain assumptions and estimates primarily related to revenue and volume; stated segment operating results would change if different methods were applied.

2 Excludes total net realized gains (losses) on securities.

SCHEDULE IV - Reinsurance

12 Months Ended

Dec. 31, 2023

SCHEDULE IV - Reinsurance

SCHEDULE IV — REINSURANCE

THE PROGRESSIVE CORPORATION AND SUBSIDIARIES

(millions)


Year Ended:	Gross Amount		Ceded to Other Companies		Assumed From Other Companies		Net Amount		Percentage of Amount Assumed to Net
December 31, 2023
Premiums earned:
Property and liability insurance	$	59,881.1	$	1,216.7	$	0	$	58,664.4	0	%
December 31, 2022
Premiums earned:
Property and liability insurance	$	50,650.2	$	1,409.0	$	0	$	49,241.2	0	%
December 31, 2021
Premiums earned:
Property and liability insurance	$	46,018.6	$	1,649.9	$	0	$	44,368.7	0	%

Reporting and Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Reporting and Accounting Policies

REPORTING AND ACCOUNTING POLICIES

Nature of Operations The Progressive insurance organization began business in 1937. The financial results of The Progressive Corporation include its subsidiaries and affiliates (references to “subsidiaries” in these notes include affiliates as well). Our insurance subsidiaries write personal and commercial auto insurance, personal residential property insurance, business-related general liability and commercial property insurance predominantly for small businesses, workers’ compensation insurance primarily for the transportation industry, and other specialty property-casualty insurance and provide related services.

We report three operating segments. Our Personal Lines segment writes insurance for personal autos and recreational vehicles, which we refer to as 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. We operate our businesses throughout the United States, through both the independent agency and direct channels.

Basis of Consolidation and Reporting The accompanying consolidated financial statements include the accounts of The Progressive Corporation and our wholly owned insurance and non-insurance subsidiaries and affiliates in which we have a controlling financial interest. All intercompany accounts and transactions are eliminated in consolidation. All revenues are generated from external customers and we do not have a reliance on any major customer.

Estimates We are required to make estimates and assumptions when preparing our financial statements and accompanying notes in conformity with accounting principles generally accepted in the United States of America (GAAP). As estimates develop into fact, results may, and will likely, differ from those estimates.

Investments Our fixed-maturity securities and short-term investments are accounted for on an available-for-sale basis. Fixed-maturity securities include debt securities and redeemable preferred stocks, which may have fixed or variable principal payment schedules, may be held for indefinite periods of time, and may be used as a part of our asset/liability strategy or sold in response to changes in interest rates, anticipated prepayments, risk/reward characteristics, liquidity needs, or other economic factors.

These securities are carried at fair value with the corresponding unrealized gains (losses), net of deferred income taxes, reported in accumulated other comprehensive income.

Short-term investments may include commercial paper, repurchase transactions, and other securities expected to mature within one year. From time to time, we may also invest in municipal bonds that have maturity dates that are longer than one year but have either liquidity facilities or mandatory put features within one year.

Equity securities include common stocks, nonredeemable preferred stocks, and other risk investments. Common stocks and nonredeemable preferred stocks are carried at fair value, with the changes in fair value reported in net holding period gains (losses) on securities on the consolidated statements of comprehensive income. Our other risk investments are accounted for under the equity method of accounting. These securities are carried at cost and adjusted for our share of the investee’s earnings or losses, with the changes in carrying value reported in investment income.

We did not have any open derivative instruments at December 31, 2023, 2022, or 2021. From time to time, we entered into interest rate swaps to hedge the exposure to variable cash flows of a forecasted transaction (i.e., cash flow hedge).

Derivatives designated as hedges are required to be evaluated on established criteria to determine the effectiveness of their correlation to, and ability to reduce the designated risk of, specific securities or transactions. Effectiveness is required to be reassessed regularly. For cash flow hedges that are deemed to be effective, the changes in fair value of the hedge would be reported as a component of accumulated other comprehensive income and subsequently amortized into earnings over the life of the hedged transaction. If a hedge is deemed to become ineffective or discontinued, changes in fair value of the derivative instrument would be reported in income for the current period. See Note 4 – Debt for a summary of our closed debt issuance cash flow hedges.

Investment securities are exposed to various risks such as interest rate, market, credit, and liquidity risk. Fair values of securities fluctuate based on the nature and magnitude of changing market conditions; significant changes in market conditions could materially affect the portfolio’s value in the near term. We routinely monitor our fixed-maturity portfolio for pricing changes that might indicate potential credit losses exist and perform detailed reviews of

securities with unrealized losses. For an unrealized loss that we determined to be related to current market conditions, we will not record an allowance for credit losses or write off the unrealized loss for the securities we do not intend to sell. We will continue to monitor these securities to determine if the unrealized loss is due to credit deterioration. If we believe that a potential credit loss exists, we will record an allowance for the credit loss and recognize the realized loss as a component of realized gains (losses) in the income statement. Once a credit loss allowance has been established, we will continue to evaluate the security, at least quarterly, to determine if changes in conditions have created the need to either increase or decrease the allowance recorded. If we determine that a security with a credit loss allowance previously recorded is likely to be sold prior to the potential recovery of the credit loss, or if we determine that the loss is uncollectible, we will reverse the allowance and write down the security to its fair value.

Investment income consists of interest, dividends, accretion, and amortization. Interest is recognized on an accrual basis using the effective yield method, except for asset-backed securities, discussed below. Depending on the nature of the equity instruments, dividends are recorded at either the ex-dividend date or on an accrual basis.

Asset-backed securities, which are included in our fixed-maturity portfolio, are generally accounted for under the retrospective method. The retrospective method recalculates yield assumptions (based on changes in interest rates or cash flow expectations) historically to the inception of the investment holding period, and applies the required adjustment, if any, to the cost basis, with the offset recorded to investment income on a quarterly basis. The prospective method is used primarily for interest-only securities, asset-backed securities below high investment-grade status (i.e., below AA-), and certain asset-backed securities with sub-prime loan exposure or where there is a greater risk of non-performance and where it is possible the initial investment may not be substantially recovered. The prospective method requires a calculation of expected future repayments and resets the yield to allow for future period adjustments; no current period impact to investment income or the security’s cost is made based on the cash flow update. Prepayment assumptions are updated quarterly.

Realized gains (losses) on securities are computed based on the first-in first-out method. Realized gains (losses) also include holding period valuation changes on equity securities and hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument), as well as initial and subsequent changes in credit allowance losses and write-offs for losses deemed uncollectible or securities in a loss position that are expected to be sold prior to the recovery of the credit loss.

Insurance Premiums and Receivables Insurance premiums written are earned into income on a pro rata basis over the period of risk, based on a daily earnings convention. Accordingly, unearned premiums represent the portion of premiums written with unexpired risk. We write insurance and provide related services to individuals and commercial accounts and offer a variety of payment plans. Generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk.

For our Personal Lines and Commercial Lines businesses, we perform a policy-level evaluation to determine the extent to which the premiums receivable balance exceeds the unearned premiums balance. To determine an allowance for credit losses, we evaluate the collectibility of premiums receivables based on historical and current collections experience of the aged exposures, using actuarial analysis. Our estimate of the future recoverability of our projected ultimate at-risk exposures also takes into consideration any unusual circumstances that we may encounter, such as moratoriums or other programs that may suspend collections.

For our Property business, the risk of uncollectibility is relatively low. If premiums are unpaid by the policy due date, we provide advance notice of cancellation in accordance with each state’s requirements and, if the premiums remain unpaid after receipt of notice, we cancel the policy and write off any remaining balance.

The following table summarizes changes in our allowance for credit loss exposure on our premiums receivable:


(millions)	2023		2022
Balance at January 1	$	343.3	$	280.4
Increase in allowance1	540.3		471.1
Write-offs2	(514.5)		(408.2)
Balance at December 31	$	369.1	$	343.3

1 Represents the incremental increase in other underwriting expenses.

2 Represents the portion of allowance that is reversed when premiums receivables are written off. Premiums receivable balances are written off once we have exhausted our collection efforts.

Deferred Acquisition Costs Deferred acquisition costs include commissions, premium taxes, and other variable underwriting and direct sales costs incurred in connection with the successful acquisition or renewal of insurance contracts. These acquisition costs, net of ceding allowances, are deferred and amortized over the policy period in which the related premiums are earned. We consider anticipated investment income in determining recoverability of these costs. Management believes these costs will be fully recoverable in the near term.

We do not defer any advertising costs. Total advertising costs, which are expensed as incurred, for the years ended December 31, were:


(millions)	Advertising Costs
2023	$	1,599.7
2022	2,032.5
2021	2,139.5

Loss and Loss Adjustment Expense Reserves Loss reserves represent the estimated liability on claims reported to us, plus reserves for losses incurred but not recorded. These estimates are reported net of amounts estimated to be recoverable from salvage and subrogation. Loss adjustment expense reserves represent the estimated expenses required to settle these claims. The methods of making estimates and establishing these reserves are reviewed regularly and resulting adjustments are reflected in income in the current period. Such loss and loss adjustment expense reserves are susceptible to change.

Reinsurance Our reinsurance activity includes transactions which are categorized as Regulated and Non-Regulated. Regulated refers to plans in which we participate that are governed by insurance regulations and include state-provided reinsurance facilities (e.g., Michigan Catastrophic Claims Association, North Carolina Reinsurance Facility, Florida Hurricane Catastrophe Fund), as well as state-mandated involuntary plans for commercial vehicles (Commercial Automobile Insurance Procedures/Plans – CAIP) and federally regulated plans for flood (National Flood Insurance Program – NFIP); we act as a participant in the “Write Your Own” program for the NFIP.

Non-Regulated includes voluntary contractual arrangements primarily related to our Property business and to the transportation network company (TNC) business written by our Commercial Lines segment. Prepaid

reinsurance premiums are earned on a pro rata basis over the period of risk, based on a daily earnings convention, which is consistent with premiums earned. See Note 7 – Reinsurance for further discussion.

We routinely monitor changes in the credit quality and concentration risks of the reinsurers who are counterparties to our reinsurance recoverables to determine if an allowance for credit losses should be established.

Income Taxes The income tax provision is calculated under the balance sheet approach. Deferred tax assets and liabilities are recorded based on the temporary difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. The principal items giving rise to such differences include:

•unearned premiums reserves;

•investment securities (e.g., net unrealized gains (losses) and net holding period gains (losses) on securities);

•deferred acquisition costs;

•loss and loss adjustment expense reserves;

•non-deductible accruals;

•property and equipment; and

•software development costs.

We review our deferred tax assets regularly for recoverability. See Note 5 – Income Taxes for further discussion.

Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is recognized over the estimated useful lives of the assets using accelerated methods for computer equipment and the straight-line method for all other fixed assets. We evaluate impairment whenever events or circumstances warrant such a review and write off the impaired assets if appropriate.

The cost and useful lives for property and equipment at December 31, were:


($ in millions)	2023		2022		Useful Lives
Land	$	102.6	$	123.1	NA
Buildings, improvements, and integrated components	732.9		844.1		7-40 years
Capitalized software	467.5		475.4		3-10 years
Software licenses (internal use)	486.4		427.6		1-6 years
Computer equipment	353.3		318.1		3 years
All other property and equipment	393.2		396.8		3-10 years
Total cost	2,535.9		2,585.1
Accumulated depreciation	(1,655.1)		(1,551.1)
Balance at end of year	$	880.8	$	1,034.0
NA = Not applicable; land is not a depreciable asset.

Included in other assets in our consolidated balance sheets are “held for sale” properties of $77.2 million and $48.7 million at December 31, 2023 and 2022, respectively, and capitalized cloud computing arrangement implementation costs, net of amortization, of $88.1 million and $63.4 million. When properties are determined to be “held for sale,” they are written down to their fair values less the estimated costs to sell, as applicable.

Goodwill and Intangible Assets Goodwill is the excess of the purchase price over the estimated fair value of the assets and liabilities acquired and represents the future economic benefits arising from other assets acquired that could not be individually identified and separately recognized. At December 31, 2023 and 2022, we had goodwill of $227.9 million, which is primarily attributable to our Agency Personal Lines business and related to the April 1, 2015, acquisition of a controlling interest in ARX Holding Corp. (ARX). There were no changes to the carrying amount of goodwill during the year ended December 31, 2023.

We evaluate our goodwill for impairment at least annually using a qualitative approach. If events or changes in circumstances indicate that the carrying value of goodwill or intangible assets may not be recoverable, we will evaluate such items for impairment using a quantitative approach.

In 2022, we recorded an impairment loss of $224.8 million, related to the goodwill assigned to the ARX reporting unit of our Property operating segment. As a result of our annual impairment testing, we determined that impairment was necessary given the magnitude of weather events relative to forecasted expectations during the first half of 2022, as well as other factors impacting our plans to restore our Property business to target profitability in a timely fashion. There were no previously recorded goodwill impairment losses on any of the outstanding goodwill.

Intangible assets are non-financial assets lacking physical substance (e.g., customer and agency relationships, trade names, software rights) and represent the future economic benefit of those acquired assets. Amortization expense related to intangible assets was $14.2 million, $31.0 million, and $57.7 million for the years ended December 31, 2023, 2022, and 2021, respectively.

Goodwill and intangible assets are included in other assets in our consolidated balance sheets; the prior-year amounts, which were presented separately on the balance sheet in the prior year, were reclassified into this line item to conform to the current year presentation.

Guaranty Fund Assessments We are subject to state guaranty fund assessments, which provide for the payment of covered claims or other insurance obligations of insurance companies deemed insolvent. These assessments are accrued after a determination of insolvency has occurred, and we have written the premiums on which the assessments will be based. Assessments are expensed when incurred except for assessments that are available for recoupment from policyholders or are eligible to offset premiums taxes payable, which are capitalized to the extent allowable.

Fees and Other Revenues Fees and other revenues primarily represent fees collected from policyholders relating to installment charges in accordance with our bill

plans, as well as late payment and insufficient funds fees and revenue from ceding commissions, and are considered a part of our underwriting operations. Fees and other revenues are generally earned when invoiced, except for excess ceding commissions, which are earned over the policy period.

Service Revenues and Expenses Our service businesses provide insurance-related services. Service revenues and expenses from our commission-based businesses are recorded in the period in which they are earned or incurred.

Equity-Based Compensation We issue time-based and performance-based restricted stock unit awards to key members of management as our form of equity compensation and time-based restricted stock awards to non-employee directors. Collectively, we refer to these awards as restricted equity awards. Generally, restricted equity awards are expensed pro rata over their respective vesting periods (i.e., requisite service period), based on the market value of the awards at the time of grant, with accelerated expense for participants who satisfy qualified retirement eligibility. We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates.

We credit dividend equivalent units to our management restricted equity awards. Dividend equivalent units for both time-based and performance-based awards are based on the amount of common share dividends declared by the Board of Directors, credited to outstanding restricted stock unit awards at the time a dividend is paid to shareholders, and distributed upon, or after, vesting of the underlying award.

The total compensation expense recognized for equity-based compensation for the years ended December 31, was:


(millions)	2023		2022		2021
Pretax expense	$	121.3	$	122.7	$	100.7
Tax benefit1	17.0		16.0		14.1

1 Differs from statutory rate of 21% due to the expected disallowance of certain executive compensation deductions.

Earnings Per Common 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.

Basic earnings per common share is computed using the weighted average number of common shares outstanding during the reporting period, excluding unvested, non-employee director, time-based restricted stock awards. Diluted earnings per common share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents, which are calculated using the treasury stock method, include the incremental shares assumed to be issued for:

•earned but unvested time-based restricted equity awards, and

•performance-based restricted equity awards that satisfied certain contingency conditions for unvested common stock equivalents during the period and are highly likely to continue to satisfy the conditions until the date of vesting.

For periods when a net loss is reported, earnings per common share are calculated using basic average equivalent common shares since diluted earnings per share would be antidilutive.

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 overnight reverse repurchase commitments, which are not considered part of the investment portfolio, held by these subsidiaries at December 31, 2023, 2022, and 2021, were $68.2 million, $125.9 million, and $137.1 million, respectively. Restricted cash and restricted cash equivalents include collateral held against unpaid deductibles and cash that is restricted to pay flood claims under the NFIP’s “Write Your Own” program, for which certain subsidiaries are participants.

For the years ended December 31, non-cash activity included the following:


(millions)	2023		2022		2021
Common share dividends1	$	497.9	$	58.5	$	58.5
Preferred share dividends1	0		13.4		13.4
Operating lease liabilities2	114.3		36.2		86.7

1 Declared but unpaid. See Note 14 – Dividends for further discussion.

2 See Note 13 – Leases for further discussion.

For the years ended December 31, we paid the following:


(millions)	2023		2022		2021
Income taxes	$	820.8	$	719.0	$	842.4
Interest	264.9		228.9		224.0
Operating lease liabilities	77.2		82.5		88.6

Commitments and Contingencies We have certain noncancelable purchase obligations for goods and services with minimum commitments of $1,024.8 million at December 31, 2023, primarily consisting of software licenses, maintenance on information technology equipment, and media placements. Aggregate payments on these obligations for the years ended December 31, were as follows:


(millions)	Payments
2024	$	780.0
2025	139.5
2026	68.6
2027	26.5
2028	7.8
Thereafter	2.4
Total	$	1,024.8

In addition, we have several multiple-layer property catastrophe reinsurance contracts with various reinsurers with terms ranging from one to three years; the minimum commitment under these agreements at December 31, 2023, was $291.5 million. Pursuant to these contracts, $282.8 million, $8.1 million, and $0.6 million will be paid in 2024, 2025, and 2026, respectively.

New Accounting Standards

Adopted

We did not adopt any new accounting standards during the year ended December 31, 2023.

Issued

In March 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 is effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2023 (2024 for calendar-year companies). On January 1, 2024, we adopted this standard on the modified retrospective basis. This standard did not have a material impact on our financial condition or results of operations.

Investments

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

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 Unrealized Gains		Gross Unrealized Losses		Net Holding Period Gains (Losses)		Fair Value		% of Total Fair Value
December 31, 2023
Available-for-sale securities:
Fixed maturities:
U.S. government obligations	$	37,823.2	$	204.1	$	(1,157.9)	$	0	$	36,869.4	55.9	%
State and local government obligations	2,338.4		2.8		(138.4)		0		2,202.8		3.3
Foreign government obligations	17.3		0		(1.0)		0		16.3		0.1
Corporate debt securities	11,446.0		87.2		(332.3)		(17.2)		11,183.7		16.9
Residential mortgage-backed securities	426.9		0.2		(10.0)		0.1		417.2		0.6
Commercial mortgage-backed securities	4,535.2		2.2		(597.7)		0		3,939.7		6.0
Other asset-backed securities	5,667.2		15.7		(107.1)		(0.4)		5,575.4		8.4
Redeemable preferred stocks	187.7		0		(2.4)		(11.6)		173.7		0.3
Total fixed maturities	62,441.9		312.2		(2,346.8)		(29.1)		60,378.2		91.5
Short-term investments	1,789.9		0		0		0		1,789.9		2.7
Total available-for-sale securities	64,231.8		312.2		(2,346.8)		(29.1)		62,168.1		94.2
Equity securities:
Nonredeemable preferred stocks	977.1		0		0		(75.0)		902.1		1.4
Common equities	706.0		0		0		2,222.4		2,928.4		4.4
Total equity securities	1,683.1		0		0		2,147.4		3,830.5		5.8
Total portfolio1	$	65,914.9	$	312.2	$	(2,346.8)	$	2,118.3	$	65,998.6	100.0	%


($ in millions)	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Net Holding Period Gains (Losses)		Fair Value		% of Total Fair Value
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 portfolio1	$	55,316.0	$	13.9	$	(3,551.5)	$	1,769.9	$	53,548.3	100.0	%

1 At December 31, 2023 and 2022, we had $45.6 million and $34.4 million, respectively, of net unsettled security transactions included in other assets.

The total fair value of the portfolio at December 31, 2023 and 2022, included $4.2 billion and $4.4 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.

At December 31, 2023, bonds and certificates of deposit in the principal amount of $671.8 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 December 31, 2023 or 2022. At December 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 have any open repurchase or reverse repurchase transaction positions at December 31, 2023 or 2022, and did not enter into any such transactions during 2023. During 2022, we invested in repurchase transactions that had an immaterial impact on our results of operations and cash flows. 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 on 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 at December 31:


(millions)	2023		2022
Fixed Maturities:
Corporate debt securities	$	531.3	$	535.4
Residential mortgage-backed securities	323.9		509.6
Other asset-backed securities	13.9		42.0
Redeemable preferred stocks	141.2		134.7
Total hybrid securities	$	1,010.3	$	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 (losses).

Fixed Maturities The composition of fixed maturities by maturity at December 31, 2023, was:


(millions)	Cost		Fair Value
Less than one year	$	9,782.8	$	9,566.2
One to five years	37,948.6		36,796.2
Five to ten years	14,637.1		13,942.5
Ten years or greater	73.4		73.3
Total	$	62,441.9	$	60,378.2

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 Fair Value		Gross Unrealized Losses		Less than 12 Months					12 Months or Greater
($ in millions)						No. of Sec.	Fair Value		Gross Unrealized Losses		No. of Sec.	Fair Value		Gross Unrealized Losses
December 31, 2023
U.S. government obligations	147	$	28,225.0	$	(1,157.9)	25	$	11,890.0	$	(100.0)	122	$	16,335.0	$	(1,057.9)
State and local government obligations	324	1,846.2		(138.4)		31	169.9		(0.9)		293	1,676.3		(137.5)
Foreign government obligations	1	16.3		(1.0)		0	0		0		1	16.3		(1.0)
Corporate debt securities	313	6,642.4		(332.3)		26	617.2		(14.7)		287	6,025.2		(317.6)
Residential mortgage-backed securities	39	88.4		(10.0)		2	0.4		0		37	88.0		(10.0)
Commercial mortgage-backed securities	189	3,912.2		(597.7)		1	30.7		(2.5)		188	3,881.5		(595.2)
Other asset-backed securities	207	3,299.1		(107.1)		41	639.4		(1.2)		166	2,659.7		(105.9)
Redeemable preferred stocks	3	32.5		(2.4)		0	0		0		3	32.5		(2.4)
Total fixed maturities	1,223	$	44,062.1	$	(2,346.8)	126	$	13,347.6	$	(119.3)	1,097	$	30,714.5	$	(2,227.5)


	Total No. of Sec.	Total Fair Value		Gross Unrealized Losses		Less than 12 Months					12 Months or Greater
($ in millions)						No. of Sec.	Fair Value		Gross Unrealized Losses		No. of Sec.	Fair Value		Gross Unrealized Losses
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)

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.

We had 29 securities in fixed-maturity sectors, other than U.S. government obligations, that had their credit ratings downgraded, with a combined fair value of $447.9 million and an unrealized loss of $59.0 million as of December 31, 2023. Additionally, during 2023, the credit ratings of our U.S. government obligations were downgraded to AA+ from AAA due to downgrades by two major credit rating agencies.

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 2023 or 2022 and did not have a material credit loss allowance balance as of December 31, 2023 or 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 on any specific security, or in the 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 December 31, 2023 and 2022, we believe that 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 December 31, 2023 and 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 December 31, 2023 or 2022.

Realized Gains (Losses) The components of net realized gains (losses) for the years ended December 31, were:


(millions)	2023		2022		2021
Gross realized gains on security sales
Available-for-sale securities:
U.S. government obligations	$	12.1	$	10.8	$	105.8
State and local government obligations	0		0		51.2

Corporate and other debt securities	1.0		8.7		104.0
Residential mortgage-backed securities	0.9		0.7		0.3
Commercial mortgage-backed securities	0		0		41.9
Other asset-backed securities	0		0.2		1.2
Redeemable preferred stocks	0		0		1.5

Total available-for-sale securities	14.0		20.4		305.9
Equity securities:
Nonredeemable preferred stocks	0.3		17.6		28.0
Common equities	381.0		846.1		369.6
Total equity securities	381.3		863.7		397.6
Subtotal gross realized gains on security sales	395.3		884.1		703.5
Gross realized losses on security sales
Available-for-sale securities:
U.S. government obligations	(64.6)		(433.3)		(52.0)
State and local government obligations	0		(1.0)		(3.4)
Foreign government obligations	0		0		(0.1)
Corporate and other debt securities	(85.7)		(88.3)		(8.3)
Residential mortgage-backed securities	0		0		(1.1)
Commercial mortgage-backed securities	(106.8)		(72.4)		(1.9)
Other asset-backed securities	(5.6)		(4.4)		(0.6)

Short-term investments	(0.4)		(0.4)		0
Total available-for-sale securities	(263.1)		(599.8)		(67.4)
Equity securities:
Nonredeemable preferred stocks	(118.3)		(9.8)		(1.7)
Common equities	(21.8)		(78.0)		(20.1)
Total equity securities	(140.1)		(87.8)		(21.8)
Subtotal gross realized losses on security sales	(403.2)		(687.6)		(89.2)
Net realized gains (losses) on security sales
Available-for-sale securities:
U.S. government obligations	(52.5)		(422.5)		53.8
State and local government obligations	0		(1.0)		47.8
Foreign government obligations	0		0		(0.1)
Corporate and other debt securities	(84.7)		(79.6)		95.7
Residential mortgage-backed securities	0.9		0.7		(0.8)
Commercial mortgage-backed securities	(106.8)		(72.4)		40.0
Other asset-backed securities	(5.6)		(4.2)		0.6
Redeemable preferred stocks	0		0		1.5
Short-term investments	(0.4)		(0.4)		0
Total available-for-sale securities	(249.1)		(579.4)		238.5
Equity securities:
Nonredeemable preferred stocks	(118.0)		7.8		26.3
Common equities	359.2		768.1		349.5
Total equity securities	241.2		775.9		375.8

Subtotal net realized gains (losses) on security sales	(7.9)		196.5		614.3
Other assets
Gain	21.6		0		0
Impairment	(9.0)		(8.6)		(5.0)
Subtotal net realized gains (losses) on other assets	12.6		(8.6)		(5.0)
Net holding period gains (losses)
Hybrid securities	45.4		(82.0)		(7.7)
Equity securities	303.0		(2,018.1)		907.6

Subtotal net holding period gains (losses)	348.4		(2,100.1)		899.9
Total net realized gains (losses) on securities	$	353.1	$	(1,912.2)	$	1,509.2

During 2023 and 2022, 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 our then-current views of the potential for a more difficult economic environment in both years, while during 2021, the gross gains in common equities primarily reflected the sale of common stocks held outside of our indexed portfolio. During 2023, the gross losses were primarily related to: i) commercial mortgage-backed securities, as we reduced certain positions that we believed would be sensitive to potential future economic uncertainty; ii) corporate debt securities, as we sold some longer duration securities that had less attractive risk/reward profiles; and

iii) nonredeemable preferred stocks, predominantly due to the sale of certain holdings in U.S. bank preferred stocks. During 2022, we sold U.S. Treasury Notes to shorten duration and for tax planning purposes and recognized a gross loss on the sales. 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 for all three years was recorded as a result of our investment in a federal tax credit fund, which was entered into during the second quarter 2021, and is reported in other assets in our consolidated balance sheets.

The following table reflects our holding period realized gains (losses) recognized on equity securities held at the respective periods ended December 31:


(millions)	2023		2022		2021
Total net gains (losses) recognized during the period on equity securities	$	544.2	$	(1,242.2)	$	1,283.4
Less: Net gains (losses) recognized on equity securities sold during the period	241.2		775.9		375.8
Net holding period gains (losses) recognized during the period on equity securities held at period end	$	303.0	$	(2,018.1)	$	907.6

Net Investment Income The components of net investment income for the years ended December 31, were:


(millions)	2023		2022		2021
Available-for-sale securities:
Fixed maturities:
U.S. government obligations	$	864.0	$	339.1	$	149.5
State and local government obligations	47.6		39.7		44.1
Foreign government obligations	0.2		0.2		0.1
Corporate debt securities	365.4		288.8		301.1
Residential mortgage-backed securities	28.7		31.6		11.9
Commercial mortgage-backed securities	196.1		190.6		143.0
Other asset-backed securities	192.5		174.6		64.1
Redeemable preferred stocks	11.1		11.4		9.5
Total fixed maturities	1,705.6		1,076.0		723.3
Short-term investments	92.4		53.6		3.1
Total available-for-sale securities	1,798.0		1,129.6		726.4
Equity securities:
Nonredeemable preferred stocks	51.4		70.2		70.3
Common equities	42.4		60.5		64.2
Total equity securities	93.8		130.7		134.5
Investment income	1,891.8		1,260.3		860.9
Investment expenses	(26.2)		(24.3)		(25.5)
Net investment income	$	1,865.6	$	1,236.0	$	835.4

On a year-over-year basis, investment income (interest and dividends) increased 50% in 2023, compared to 2022, and increased 46% in 2022, compared to 2021, primarily due to increases during the periods in interest rates on floating-rate securities in our portfolio and purchases of new investments with higher coupon rates. The recurring

investment book yield increased 29% in 2023, compared to 2022, and increased 26% in 2022, compared to 2021, reflecting investing new cash and cash from maturities in higher interest rate securities given the rising interest rate environment in both periods.

Fair Value

12 Months Ended

Dec. 31, 2022

Fair Value Disclosures [Abstract]

FAIR VALUE

We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows:

•Level 1: Inputs are unadjusted, quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, which are continually priced on a daily basis, active exchange-traded equity securities, and certain short-term securities).

•Level 2: Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are

observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means.

•Level 3: Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments).

Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations.

The composition of the investment portfolio by major security type and our outstanding debt was:


	Fair Value
(millions)	Level 1		Level 2		Level 3		Total		Cost
December 31, 2023
Fixed maturities:
U.S. government obligations	$	36,869.4	$	0	$	0	$	36,869.4	$	37,823.2
State and local government obligations	0		2,202.8		0		2,202.8		2,338.4
Foreign government obligations	0		16.3		0		16.3		17.3
Corporate debt securities	0		11,180.7		3.0		11,183.7		11,446.0
Subtotal	36,869.4		13,399.8		3.0		50,272.2		51,624.9
Asset-backed securities:
Residential mortgage-backed	0		417.2		0		417.2		426.9
Commercial mortgage-backed	0		3,939.7		0		3,939.7		4,535.2
Other asset-backed	0		5,575.4		0		5,575.4		5,667.2
Subtotal asset-backed securities	0		9,932.3		0		9,932.3		10,629.3
Redeemable preferred stocks:
Financials	0		23.1		0		23.1		24.5
Utilities	0		9.4		0		9.4		10.4
Industrials	0		141.2		0		141.2		152.8
Subtotal redeemable preferred stocks	0		173.7		0		173.7		187.7
Total fixed maturities	36,869.4		23,505.8		3.0		60,378.2		62,441.9
Short-term investments	1,757.0		32.9		0		1,789.9		1,789.9
Total available-for-sale securities	38,626.4		23,538.7		3.0		62,168.1		64,231.8
Equity securities:
Nonredeemable preferred stocks:
Financials	0		802.7		49.2		851.9		922.1
Utilities	0		35.4		0		35.4		40.0
Industrials	0		0		14.8		14.8		15.0
Subtotal nonredeemable preferred stocks	0		838.1		64.0		902.1		977.1
Common equities:
Common stocks	2,885.3		0		22.5		2,907.8		685.4
Other risk investments	0		0		20.6		20.6		20.6
Subtotal common equities	2,885.3		0		43.1		2,928.4		706.0
Total equity securities	2,885.3		838.1		107.1		3,830.5		1,683.1
Total portfolio	$	41,511.7	$	24,376.8	$	110.1	$	65,998.6	$	65,914.9
Debt	$	0	$	6,431.3	$	0	$	6,431.3	$	6,888.6


	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 December 31, 2023, vendor-quoted prices represented 93% of our Level 1 classifications (excluding short-term investments), compared to 90% at December 31, 2022. 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. All Level 1 preferred stocks with active

exchange quotes were sold during 2023.

At December 31, 2023, vendor-quoted prices comprised 100% of our Level 2 classifications (excluding short-term investments and common stock), compared to 98% at year-

end 2022; the remaining 2% at December 31, 2022, were dealer-quoted prices. 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 our 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 our 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 our 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 at economic data as it relates to geographic location as an indication of price-to-call or maturity predictors. For municipal housing securities, we look at 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 for 2023 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 tables and categorize these securities as “pricing exemption securities” in the quantitative information tables.

During the fourth quarter 2023, we purchased a privately held fixed-maturity security that is classified as a Level 3 investment. At December 31, 2022, we did not have any securities in our fixed-maturity portfolio listed as Level 3.

During 2023, there were no material assets or liabilities measured at fair value on a nonrecurring basis. During 2022, we determined that the fair value of goodwill related to our ARX reporting unit was less than the carrying value and we wrote down $224.8 million of our total goodwill asset. No other material assets or liabilities were measured at fair value during 2022.

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 years ended December 31, 2023 and 2022:


	Level 3 Fair Value
(millions)	Fair Value at Dec. 31, 2022		Calls/ Maturities/ Paydowns/Other		Purchases		Sales		Net Realized (Gain)/Loss on Sales		Change in Valuation		Net Transfers In (Out)		Fair Value at Dec. 31, 2023
Fixed maturities:
Corporate debt securities	$	0	$	0	$	3.0	$	0	$	0	$	0	$	0	$	3.0



Equity securities:
Nonredeemable preferred stocks:
Financials	67.4		(8.1)		1.0		0		0		(11.1)		0		49.2
Industrials	16.4		0		0		0		0		(1.6)		0		14.8
Common equities:
Common stocks	18.3		8.1		0		(10.0)		8.9		(2.8)		0		22.5
Other risk investments	19.8		0.8		0		0		0		0		0		20.6
Total Level 3 securities	$	121.9	$	0.8	$	4.0	$	(10.0)	$	8.9	$	(15.5)	$	0	$	110.1


	Level 3 Fair Value
(millions)	Fair Value at Dec. 31, 2021		Calls/ Maturities/ Paydowns/Other		Purchases		Sales		Net Realized (Gain)/Loss on Sales		Change in Valuation		Net Transfers In (Out)1		Fair Value at Dec. 31, 2022




Equity securities:
Nonredeemable preferred stocks:
Financials	$	76.4	$	0	$	2.5	$	(15.0)	$	(17.2)	$	20.7	$	0	$	67.4
Industrials	34.4		(0.5)		0		0		0		(17.5)		0		16.4
Common equities:
Common stocks	0		0		0		0		0		0		18.3		18.3
Other risk investments	16.9		2.9		0		0		0		0		0		19.8
Total Level 3 securities	$	127.7	$	2.4	$	2.5	$	(15.0)	$	(17.2)	$	3.2	$	18.3	$	121.9

1The security was transferred into Level 3 due to a lack of observable market level inputs.

The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at December 31:

Quantitative Information about Level 3 Fair Value Measurements

($ in millions)

Fair Value at Dec. 31, 2023

Valuation Technique

Unobservable Input

Range of Input Values Increase (Decrease)

Weighted Average Increase (Decrease)

Fixed maturities:

Corporate debt securities

$

3.0

Market comparables

Weighted average market capitalization price change %

0.3% to 7.7%

2.6

%

Equity securities:

Nonredeemable preferred stocks

64.0

Market comparables

Weighted average market capitalization price change %

17.2% to 39.7%

21.7%

Common stocks

22.5

Market comparables

Weighted average market capitalization price change %

(45.8)% to 95.6%

39.7%

Subtotal Level 3 securities

89.5

Pricing exemption securities

20.6

Total Level 3 securities

$

110.1

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

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

Debt

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

DEBT

Debt at December 31, consisted of:


	2023				2022
(millions)	Carrying Value		Fair Value		Carrying Value		Fair Value
2.45% Senior Notes due 2027 (issued: $500.0, August 2016)	$	498.6	$	468.9	$	498.2	$	457.7
2.50% Senior Notes due 2027 (issued: $500.0, March 2022)	498.1		469.1		497.5		460.3
6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)	297.8		328.7		297.5		326.8
4.00% Senior Notes due 2029 (issued: $550.0, October 2018)	546.9		542.6		546.4		527.8
3.20% Senior Notes due 2030 (issued: $500.0, March 2020)	497.3		462.2		496.9		448.6
3.00% Senior Notes due 2032 (issued: $500.0, March 2022)	496.3		446.0		495.9		438.1
6.25% Senior Notes due 2032 (issued: $400.0, November 2002)	396.7		445.6		396.4		435.4
4.95% Senior Notes due 2033 (issued: $500.0, May 2023)	496.4		513.0		0		0
4.35% Senior Notes due 2044 (issued: $350.0, April 2014)	347.0		314.2		346.9		298.4
3.70% Senior Notes due 2045 (issued: $400.0, January 2015)	395.9		325.1		395.7		310.2
4.125% Senior Notes due 2047 (issued: $850.0, April 2017)	842.3		756.2		842.1		716.2
4.20% Senior Notes due 2048 (issued: $600.0, March 2018)	590.6		534.1		590.4		507.0
3.95% Senior Notes due 2050 (issued: $500.0, March 2020)	491.1		422.3		490.9		404.9
3.70% Senior Notes due 2052 (issued: $500.0, March 2022)	493.6		403.3		493.5		386.5
Total	$	6,888.6	$	6,431.3	$	6,388.3	$	5,717.9

All of the outstanding debt was issued by The Progressive Corporation and includes amounts that were borrowed for general corporate purposes, which may include contributions to the capital of its insurance subsidiaries, payments of debt at maturity, or may be used, or made available for use, for other business purposes. Fair values for these debt instruments are obtained from external sources. There are no restrictive financial covenants or credit rating triggers on the outstanding debt.

Interest on all debt is payable semiannually at the stated rates. All principal is due at the stated maturity. Each note is redeemable, in whole or in part, at any time; however, the redemption price will equal the greater of the principal amount of the note or a “make whole” amount calculated by reference to the present values of remaining scheduled principal and interest payments under the note. There was no short-term debt outstanding at December 31, 2023 or 2022.

We issued $500 million of 4.95% Senior Notes due 2033 in May 2023, in an underwritten public offering. The net proceeds from the issuance, after deducting underwriters’ discounts, commissions, and other issuance costs, were approximately $496.3 million.

Aggregate required principal payments on debt outstanding at December 31, 2023, were as follows:


(millions)	Payments
2024	$	0
2025	0
2026	0
2027	1,000.0
2028	0
Thereafter	5,950.0
Total	$	6,950.0

Prior to certain issuances of our debt securities, we entered into forecasted transactions to hedge against possible rises in interest rates. When the contracts were closed upon the issuance of the applicable debt securities, we recognized the unrealized gains (losses) on these contracts as part of accumulated other comprehensive income (see Note 1 – Reporting and Accounting Policies, Investments for further discussion). These unrealized gains (losses) are being amortized as adjustments to interest expense over the life of the related notes.

The following table shows the original gain (loss) recognized at debt issuance and the unamortized balance at December 31, 2023, on a pretax basis:


(millions)	Unrealized Gain (Loss) at Issuance		Unamortized Balance at December 31, 2023
6 5/8% Senior Notes due 2029	$	(4.2)	$	(1.5)
6.25% Senior Notes due 2032	5.1		2.6
4.35% Senior Notes due 2044	(1.6)		(1.3)
3.70% Senior Notes due 2045	(12.9)		(10.5)
4.125% Senior Notes due 2047	(8.0)		(7.0)

We reclassified $0.6 million in 2023, $0.5 million in 2022, and $0.9 million in 2021, of net pretax unrealized losses from accumulated other comprehensive income to interest expense on our closed debt issuance cash flow hedges.

During 2023, The Progressive Corporation amended its line of credit with PNC Bank, National Association (PNC), to increase the maximum principal amount to $300 million from the previous amount of $250 million and extend the expiration date to April 30, 2024. Subject to the terms and conditions of the line of credit documents, advances under the line of credit, if any, will bear interest at a variable rate equal to the 1-month term Secured Overnight Financing Rate (SOFR) plus 1.10%. Each advance must be repaid on the 30th day after the date of the advance or, if earlier, on April 30, 2024, the expiration date of the line of credit. Prepayments are permitted without penalty. The line of credit is uncommitted and, as such, all advances are subject to PNC’s discretion. We had no borrowings under either line of credit in 2023 or 2022.

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

INCOME TAXES

The components of our income tax provision for the years ended December 31, were as follows:


(millions)	2023		2022		2021
Current tax provision
Federal	$	1,102.5	$	733.2	$	739.5
State	18.7		12.7		20.7
Deferred tax expense (benefit)
Federal	(119.9)		(528.7)		98.6
State	0		(16.6)		0.3
Total income tax provision	$	1,001.3	$	200.6	$	859.1

The provision for income taxes in the consolidated statements of comprehensive income differed from the statutory rate for the years ended December 31, as follows:


	2023				2022				2021
(millions)	Expense (Benefit)		Rate Impact		Expense (Benefit)		Rate Impact		Expense (Benefit)		Rate Impact
Income before income taxes	$	4,903.7			$	922.1			$	4,210.0
Tax at statutory federal rate	$	1,029.8	21	%	$	193.6	21	%	$	884.1	21	%
Tax effect of:
Stock-based compensation	(21.7)		(1)		(18.1)		(2)		(19.4)		(1)
Tax credits	(16.4)		0		(14.8)		(2)		(9.9)		0
Tax-preferenced investment income	(10.2)		0		(12.7)		(1)		(13.2)		0
State income taxes, net of federal taxes	14.7		0		(3.1)		0		16.6		0
Nondeductible compensation expense	9.8		0		11.1		1		8.4		0
Tax-deductible dividends	(4.8)		0		(1.8)		0		(9.4)		0
Goodwill impairment1	0		0		47.2		5		0		0
Other items, net	0.1		0		(0.8)		0		1.9		0
Total income tax provision	$	1,001.3	20	%	$	200.6	22	%	$	859.1	20	%
1 The ARX acquisition did not create goodwill for income tax purposes. As a result, the impairment was not deductible for income tax purposes.

Deferred income taxes reflect the tax effects of temporary differences between the financial statement carrying amounts and the tax bases of assets and liabilities. The following table shows the components of the net deferred tax assets and liabilities at December 31:


(millions)	2023		2022
Federal deferred income tax assets:
Unearned premiums reserve	$	836.0	$	719.2
Net unrealized losses on fixed-maturity securities	427.3		742.9
Loss and loss adjustment expense reserves	292.7		239.9
Non-deductible accruals	238.2		225.9
Software development costs	66.0		37.8
Operating lease liabilities	37.2		28.8
Hedges on forecasted transactions	3.7		3.8
Investment basis differences	0.2		17.0
Other	13.4		12.7
Federal deferred income tax liabilities:
Net holding period gains on equity securities	(451.0)		(387.3)
Deferred acquisition costs	(354.4)		(324.3)
Property and equipment	(88.4)		(97.0)
Operating lease assets	(37.2)		(28.8)
Loss and loss adjustment expense reserve transition adjustment	(15.9)		(24.1)
Intangible assets	(8.7)		(11.1)
Prepaid expenses	(6.2)		(6.5)
Other	(16.9)		(17.4)
Net federal deferred income taxes	936.0		1,131.5
State deferred income tax assets1	39.9		42.2
State deferred income tax liabilities1	0		0
Total	$	975.9	$	1,173.7

1 State deferred assets and liabilities are recorded in other assets and accounts payable, accrued expenses, and other liabilities, respectively, on our consolidated balance sheets.

Although realization of the deferred tax assets is not assured, management believes that it is more likely than not that 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 and, therefore, no valuation allowance was needed at December 31, 2023 or 2022. We believe our deferred tax asset related to net unrealized losses on fixed-maturity securities will be realized based on the existence of prior-year capital gains and current temporary differences related to unrealized gains in our equity portfolio.

At December 31, 2023 and 2022, we had net current income taxes payable of $311.8 million and $10.9 million, respectively, which were reported in accounts payable, accrued expenses, and other liabilities on our consolidated balance sheets. The increase in income taxes payable was primarily driven by the portion of earnings generated during the fourth quarter relative to our annual earnings.

The Progressive Corporation and its subsidiaries file a consolidated federal income tax return. As a result of the acquisition of the Protective Insurance Corporation and

subsidiaries (Protective Insurance) in 2021, Protective Insurance was included in The Progressive Corporation consolidated federal income tax return for the period from the June 2021 acquisition date through the end of 2021. We filed a final consolidated federal income tax return for Protective Insurance for the period from the beginning of the year through the June 2021 acquisition date.

All federal income tax years prior to 2020 are generally closed to examination; however, for The Progressive Corporation, 2016 remains open for a tax credit partnership investment. The statute of limitations for state income tax purposes generally remains open for three to four years from the return filing date, depending upon the jurisdiction. There has been no significant state income tax audit activity.

For the years ended December 31, 2023, 2022, and 2021, we recognized $0.2 million, $0.1 million, and $0.1 million, respectively, of interest and penalties, as a component of the income tax provision. We have not recorded any unrecognized tax benefits, or related interest and penalties, as of December 31, 2023 and 2022.

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

Loss And Loss Adjustment Expense Reserves

Loss And Loss Adjustment Expense Reserves

12 Months Ended

Dec. 31, 2023

Insurance [Abstract]

LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES

We write personal and commercial auto insurance, personal residential property insurance, business-related general liability and commercial property insurance predominantly for small businesses, workers’ compensation insurance primarily for the transportation industry, and other specialty property-casualty insurance and provide related services throughout the United States. As a property-casualty insurance company, we are exposed to hurricanes or other catastrophes. We are unable to predict the frequency or severity of any such events that may occur in the near term or thereafter. To help mitigate this risk in our Property business, we currently maintain excess of loss reinsurance coverage, both on an aggregate and a per occurrence basis.

As we are primarily an insurer of motor vehicles and residential property, we have limited exposure to environmental and asbestos claims. We have established reserves for such exposures, which represented less than 1% of our total loss and loss adjustment expense reserves. We believe these reserves to be adequate based on information currently known. These claims are not expected to have a material effect on our liquidity, financial condition, cash flows, or results of operations.

Loss and Loss Adjustment Expense Reserves Loss and loss adjustment expense (LAE) reserves represent our best estimate of our ultimate liability for losses and LAE relating to events that occurred prior to the end of any given accounting period but have not yet been paid. For our Personal and Commercial Lines vehicle businesses, which represented about 92% of our total carried reserves, we establish loss and LAE reserves after completing reviews at a disaggregated level of grouping. Progressive’s actuarial staff reviews approximately 400 subsets of business data, which are at a combined state, product, and line coverage level, to calculate the needed loss and LAE reserves. During a reserve review, ultimate loss amounts are estimated using several industry standard actuarial projection methods. These methods take into account historical comparable loss data at the subset level and estimate the impact of various loss development factors, such as the frequency (number of losses per exposure), severity (dollars of loss per each claim), and average premium (dollars of premium per earned car year), as well as the frequency and severity of loss adjustment expense costs.

We begin our review of a set of data by producing multiple estimates of needed reserves, using both paid and incurred data, to determine if a reserve change is required. In the

event of a wide variation among results generated by the different projections, our actuarial group will further analyze the data using additional quantitative analysis. Each review develops a point estimate for a relatively small subset of the business, which allows us to establish meaningful reserve levels for that subset. We believe our comprehensive process of reviewing at a subset level provides us more meaningful estimates of our aggregate loss reserves.

The actuarial staff completes separate projections of needed case and incurred but not recorded (IBNR) reserves. Since a large majority of the parties involved in an accident report their claims within a short time period after the occurrence, we do not carry a significant amount of IBNR reserves for older accident years. Based on the methodology we use to estimate case reserves for our vehicle businesses, we generally do not have expected development on reported claims included in our IBNR reserves. We do, however, include anticipated salvage and subrogation recoveries in our IBNR reserves, which could result in negative carried IBNR reserves, primarily in our physical damage reserves.

Changes from historical data may reduce the predictiveness of our projected future loss costs. Internal considerations that are process-related, which generally result from changes in our claims organization’s activities, include claim closure rates, the number of claims that are closed without payment, and the level of the claims representatives’ estimates of the needed case reserve for each claim. These changes and their effect on the historical data are studied at the state level versus on a larger, less indicative, countrywide basis. External items considered include the litigation atmosphere, state-by-state changes in medical costs, and the availability of services to resolve claims. These also are better understood at the state level versus at a more macro, countrywide level. The actuarial staff takes these changes into consideration when making their assumptions to determine needed reserve levels.

Similar to our vehicle businesses, our actuarial staff analyzes loss and LAE data for our Commercial Lines non-vehicle business and our Property business on a claim occurrence period basis. Many of the methodologies and key parameters reviewed are similar. In addition, for Protective Insurance and our Property business, since claims adjusters primarily establish the case reserves, the actuarial staff includes expected development on case reserves as a component of the overall IBNR reserves.

Activity in the loss and LAE reserves is summarized as follows:


(millions)	2023		2022		2021
Balance at January 1	$	30,359.3	$	26,164.1	$	20,265.8
Less reinsurance recoverables on unpaid losses	5,559.2		4,733.6		3,798.2
Net balance at January 1	24,800.1		21,430.5		16,467.6
Net loss and loss adjustment expense reserves acquired1	0		0		729.2
Total beginning reserves	24,800.1		21,430.5		17,196.8
Incurred related to:
Current year	44,560.6		38,209.0		33,632.3
Prior years	1,094.0		(86.3)		(4.7)
Total incurred	45,654.6		38,122.7		33,627.6
Paid related to:
Current year	26,874.3		23,542.9		20,561.1
Prior years	13,980.2		11,210.2		8,832.8
Total paid	40,854.5		34,753.1		29,393.9
Net balance at December 31	29,600.2		24,800.1		21,430.5
Plus reinsurance recoverables on unpaid losses	4,789.0		5,559.2		4,733.6
Balance at December 31	$	34,389.2	$	30,359.3	$	26,164.1

1 Net reserves acquired in Protective Insurance acquisition.

We experienced unfavorable development of $1,094.0 million in 2023 and favorable reserve development of $86.3 million and $4.7 million in 2022 and 2021, respectively, which is reflected as “Incurred related to prior years” in the table above.

2023

•The unfavorable reserve development for 2023 included approximately $950 million attributable to accident year 2022 and $125 million to accident year 2021.

•Our personal auto products incurred about $715 million of unfavorable loss and LAE reserve development, with the Agency and Direct auto businesses each contributing about half. About half of this unfavorable development was attributable to higher than anticipated severity in auto property and physical damage coverages. The remaining unfavorable development was primarily due to increased loss costs in Florida injury and medical coverages and, to a lesser extent, higher than anticipated late reported injury claims; partially offset by lower than expected LAE.

•Our Commercial Lines business experienced about $365 million of unfavorable development, primarily driven by higher than anticipated severity and frequency of late reported injury claims and large loss emergence on injury claims, with about half attributable to our transportation network company (TNC) business.

2022

•The favorable reserve development for 2022, reflected approximately $22 million of favorable prior year reserve development that was attributable to accident year 2021, $47 million to accident year 2020, and the remainder to accident years 2019 and prior.

•Our personal auto products incurred $157 million of favorable loss and LAE reserve development, with the Agency and Direct auto businesses each contributing about half. The favorable development was primarily attributable to more subrogation and salvage recoveries and lower LAE than originally anticipated, partially offset by higher than anticipated severity and frequency of auto property damage payments on previously closed claims and late reported injury claims.

•Our Commercial Lines business experienced $82 million of unfavorable development, primarily driven by our TNC business, due to higher than anticipated severity of injury case reserves and higher than anticipated severity and frequency of late reported claims.

2021

•The slightly favorable reserve development for 2021, reflected approximately $140 million of favorable prior year reserve development that was attributable to accident year 2020, offset by $87 million of unfavorable development attributable to accident year 2019, with the remainder of the unfavorable development attributable to 2018 and prior accident years.

•Our personal auto products incurred $113 million of favorable loss and LAE reserve development, with about $80 million attributable to the Direct auto business, primarily attributable to revised estimates of our per claim settlement costs and fewer late reports than originally anticipated, partially offset by higher than anticipated bodily injury severity.

•Our Commercial Lines business experienced $87 million of unfavorable development, primarily due to increased injury severity and the emergence of large injury claims at rates higher than originally anticipated, primarily in Texas and Florida.

•Our Property business experienced $36 million of unfavorable development primarily due to higher than anticipated severity and claims that were previously closed being reopened in Florida.

Incurred and Paid Claims Development by Accident Year The following tables present our incurred, net of reinsurance, and paid claims development by accident year for the number of years that generally have historically represented the maximum development period for claims in any of our segment categories. The tables below include inception-to-date information for companies acquired and wholly exclude companies disposed of, rather than including information from the date of acquisition, or until the date of disposition. We believe the most meaningful presentation of claims development is through the retrospective approach by presenting all relevant historical information for all periods presented.

We have elected to present our incurred and paid claims development consistent with our GAAP reportable segments (see Note 10 – Segment Information for a discussion of our segment reporting), with a further disaggregation of our Personal Lines and Commercial Lines auto business claims development between liability and physical damage, since the loss patterns are

significantly different between them. The Commercial Lines other business includes Protective Insurance coverages other than liability and physical damage. Reserves for our run-off products are not considered material and, therefore, are not included in a separate claims development table.

Only 2023 is audited; all prior years are considered required supplementary information and, therefore, are unaudited. Expected development on our case reserves is excluded from the IBNR reserves on our vehicle businesses, as discussed above. For the Property business and the Commercial Lines other business, the IBNR reserves include expected case development based on the methodology used in establishing the case reserves for that segment. The cumulative number of incurred claims are based on accident coverages (e.g., bodily injury, collision, comprehensive, personal injury protection, property damage) related to opened claims. Coverage counts related to claims closed without payment are excluded from the cumulative number of incurred claims.


Personal Lines - Agency - Liability
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	5,885.0	$	5,886.9	$	5,918.2	$	5,959.9	$	5,879.2	$	0	916,543
2020			5,433.8		5,405.4		5,385.7		5,458.1		142.8		757,024
2021					6,716.4		6,861.8		6,936.4		174.2		885,607
2022							7,076.9		7,301.5		402.8		838,763
2023									8,615.9		1,715.2		883,430
							Total		$	34,191.1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	2,715.2	$	4,533.2	$	5,272.8	$	5,626.6	$	5,779.3
2020			2,383.0		4,112.2		4,796.8		5,122.0
2021					2,855.4		5,239.4		6,183.1
2022							3,018.8		5,564.1
2023									3,526.5
							Total		$	26,175.0
	All outstanding liabilities before 2019, net of reinsurance1								92.9
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	8,109.0

1 Required supplementary information (unaudited)


Personal Lines - Agency - Physical Damage
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	3,277.9	$	3,254.7	$	3,261.1	$	3,259.0	$	3,268.1	$	0.4	1,879,041
2020			3,328.5		3,319.8		3,327.3		3,323.3		(8.4)		1,785,036
2021					4,708.3		4,624.3		4,628.5		8.9		2,105,540
2022							5,429.4		5,544.6		(13.3)		2,031,717
2023									5,774.5		(298.0)		2,091,830
							Total		$	22,539.0
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	3,242.5	$	3,259.2	$	3,255.9	$	3,260.9	$	3,263.7
2020			3,250.1		3,322.5		3,323.0		3,328.0
2021					4,438.1		4,620.9		4,611.5
2022							5,176.2		5,542.0
2023									5,584.2
							Total		$	22,329.4
	All outstanding liabilities before 2019, net of reinsurance1								3.7
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	213.3

1 Required supplementary information (unaudited)


Personal Lines - Direct - Liability
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	5,756.5	$	5,811.7	$	5,837.9	$	5,870.0	$	5,802.1	$	0.1	957,826
2020			5,356.9		5,322.7		5,301.5		5,343.1		126.4		789,952
2021					6,964.7		7,180.3		7,244.1		164.5		981,424
2022							7,563.4		7,869.6		398.5		970,145
2023									9,627.9		1,763.6		1,080,475
							Total		$	35,886.8
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	2,630.3	$	4,452.5	$	5,218.8	$	5,568.8	$	5,716.3
2020			2,301.3		4,018.7		4,721.4		5,035.9
2021					2,915.0		5,460.5		6,487.9
2022							3,131.8		5,982.6
2023									3,925.5
							Total		$	27,148.2
	All outstanding liabilities before 2019, net of reinsurance1								79.4
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	8,818.0

1 Required supplementary information (unaudited)


Personal Lines - Direct - Physical Damage
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	3,787.9	$	3,737.8	$	3,749.6	$	3,747.9	$	3,757.8	$	0.3	2,272,383
2020			3,775.6		3,753.3		3,765.9		3,762.0		(9.7)		2,139,045
2021					5,752.3		5,568.2		5,572.9		3.6		2,602,359
2022							6,613.3		6,724.2		(27.3)		2,606,698
2023									7,577.9		(459.8)		2,851,047
							Total		$	27,394.8
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	3,782.6	$	3,751.3	$	3,746.8	$	3,750.9	$	3,753.9
2020			3,720.0		3,765.9		3,762.2		3,767.4
2021					5,421.9		5,578.7		5,559.6
2022							6,325.7		6,731.9
2023									7,361.7
							Total		$	27,174.5
	All outstanding liabilities before 2019, net of reinsurance1								2.8
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	223.1

1 Required supplementary information (unaudited)


Commercial Lines - Liability
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	2,301.1	$	2,370.9	$	2,426.3	$	2,434.4	$	2,429.9	$	7.6	136,213
2020			2,335.7		2,388.8		2,418.9		2,436.5		58.6		117,614
2021					3,446.6		3,527.3		3,573.7		134.7		156,829
2022							4,526.1		4,834.5		406.2		180,500
2023									5,455.8		1,299.6		184,840
							Total		$	18,730.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	474.8	$	1,184.4	$	1,684.5	$	2,037.5	$	2,250.0
2020			440.8		1,110.4		1,628.9		2,043.5
2021					573.6		1,545.9		2,414.3
2022							749.2		2,086.4
2023									847.6
							Total		$	9,641.8
	All outstanding liabilities before 2019, net of reinsurance1								103.2
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	9,191.8

1 Required supplementary information (unaudited)


Commercial Lines - Physical Damage
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	633.1	$	628.3	$	626.6	$	625.9	$	626.4	$	0	99,508
2020			631.8		624.9		622.0		624.8		2.9		99,588
2021					920.9		909.8		910.1		3.6		121,900
2022							1,314.9		1,330.3		0.7		147,146
2023									1,351.8		(6.5)		164,859
							Total		$	4,843.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	561.1	$	625.1	$	624.8	$	625.3	$	625.4
2020			540.6		621.8		620.4		620.5
2021					764.2		903.1		901.5
2022							1,114.0		1,315.0
2023									1,184.4
							Total		$	4,646.8
	All outstanding liabilities before 2019, net of reinsurance1								0.8
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	197.4

1 Required supplementary information (unaudited)


Commercial Lines - Other
($ in millions)																					As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance																					December 31, 2023
	For the years ended December 31,																				Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20141		20151		20161		20171		20181		20191		20201		20211		20221		2023
2014	$	74.9	$	70.0	$	68.3	$	70.5	$	70.7	$	69.4	$	70.7	$	70.9	$	70.4	$	70.4	$	3.2	9,226
2015			51.2		45.4		46.1		48.3		47.0		44.8		45.1		44.6		44.8		3.4		9,527
2016					51.8		43.3		41.0		41.5		40.2		40.1		40.0		40.4		3.1		7,648
2017							62.6		54.6		51.1		48.8		46.2		48.0		55.1		10.2		17,675
2018									81.5		81.3		76.7		77.0		76.5		81.7		10.0		15,475
2019											80.7		83.1		85.4		88.3		87.7		10.3		10,709
2020													75.0		80.7		81.9		82.9		14.0		9,505
2021															84.1		87.3		88.8		24.4		9,367
2022																	84.0		80.9		26.3		7,660
2023																			85.0		45.2		6,795
																	Total		$	717.7
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20141		20151		20161		20171		20181		20191		20201		20211		20221		2023
2014	$	18.6	$	33.9	$	44.3	$	51.1	$	56.9	$	59.0	$	61.1	$	64.2	$	65.0	$	65.5
2015			6.5		18.1		26.5		30.9		33.9		36.1		37.1		37.8		38.7
2016					8.5		20.9		27.0		30.6		32.7		33.8		35.0		35.5
2017							9.6		24.4		30.8		34.5		36.9		39.7		41.6
2018									17.6		39.6		49.5		56.7		61.7		65.2
2019											20.0		42.4		56.0		64.6		70.8
2020													15.8		38.6		52.2		59.6
2021															16.9		39.6		52.4
2022																	18.4		39.7
2023																			18.4
																	Total		$	487.4
					All outstanding liabilities before 2014, net of reinsurance1														30.2
					Liabilities for claims and claim adjustment expenses, net of reinsurance														$	260.5

1 Required supplementary information (unaudited)


Property Business
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	971.7	$	965.2	$	962.8	$	965.8	$	964.8	$	9.0	73,051
2020			1,223.5		1,246.8		1,260.9		1,256.0		1.5		88,736
2021					1,539.6		1,516.3		1,503.2		23.6		89,864
2022							1,664.6		1,622.0		77.0		89,348
2023									1,582.5		392.4		75,812
							Total		$	6,928.5
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	708.0	$	930.4	$	950.5	$	959.3	$	962.2
2020			832.5		1,141.2		1,210.7		1,237.2
2021					1,035.4		1,374.5		1,444.0
2022							1,041.7		1,469.5
2023									1,078.3
							Total		$	6,191.2
	All outstanding liabilities before 2019, net of reinsurance1								7.4
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	744.7

1 Required supplementary information (unaudited)

The following table reconciles the net incurred and paid claims development tables to the liability for claims and claim adjustment expenses:


(millions)	2023		2022
Net outstanding liabilities
Personal Lines
Agency, Liability	$	8,109.0	$	6,791.2
Agency, Physical Damage	213.3		261.5
Direct, Liability	8,818.0		7,187.2
Direct, Physical Damage	223.1		284.7
Commercial Lines
Liability	9,191.8		7,177.0
Physical Damage	197.4		211.2
Other	260.5		242.5
Property	744.7		839.7
Other business	88.7		108.9
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	27,846.5		23,103.9
Reinsurance recoverables on unpaid claims
Personal Lines
Agency, Liability	875.1		894.1
Agency, Physical Damage	0		0
Direct, Liability	1,471.3		1,485.4
Direct, Physical Damage	0		0
Commercial Lines
Liability	1,077.7		1,273.7
Physical Damage	1.4		0.5
Other	216.0		204.6
Property	631.4		1,068.1
Other business	475.1		559.0
Total reinsurance recoverables on unpaid claims	4,748.0		5,485.4
Unallocated claims adjustment expense related to:
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	1,753.7		1,696.2
Reinsurance recoverables on unpaid claims	41.0		73.8
Total gross liability for unpaid claims and claim adjustment expense	$	34,389.2	$	30,359.3

The following table shows the average historical claims duration as of December 31, 2023:


(Required Supplementary Information - Unaudited)
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance	Years
	1	2	3	4	5
Personal Lines
Agency, Liability	42.4%	33.1%	13.0%	6.0%	2.6%
Agency, Physical Damage	96.2	3.8	(0.1)	0.2	0.1
Direct, Liability	41.5	34.0	13.6	6.0	2.5
Direct, Physical Damage	97.1	2.9	(0.2)	0.1	0.1
Commercial Lines
Liability	16.5	27.8	22.4	15.8	8.7
Physical Damage	86.0	13.9	(0.2)	0	0
Other	20.9	26.1	14.7	9.0	6.4
Property	67.8	24.3	4.3	1.6	0.3

Reinsurance

12 Months Ended

Dec. 31, 2023

Reinsurance Disclosures [Abstract]

Reinsurance

REINSURANCE

The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows:


	2023				2022				2021
(millions)	Written		Earned		Written		Earned		Written		Earned
Direct premiums	$	62,721.2	$	59,881.1	$	52,335.6	$	50,650.2	$	48,129.6	$	46,018.6
Ceded premiums:
Regulated	(535.0)		(545.3)		(621.5)		(674.8)		(674.5)		(650.2)
Non-Regulated	(636.0)		(671.4)		(633.0)		(734.2)		(1,049.9)		(999.7)
Total ceded premiums	(1,171.0)		(1,216.7)		(1,254.5)		(1,409.0)		(1,724.4)		(1,649.9)
Net premiums	$	61,550.2	$	58,664.4	$	51,081.1	$	49,241.2	$	46,405.2	$	44,368.7

Regulated refers to federal or state run plans and primarily includes the following:

•Federal reinsurance plan

◦National Flood Insurance Program (NFIP)

•State-provided reinsurance facilities

◦Michigan Catastrophic Claims Association (MCCA)

◦North Carolina Reinsurance Facility (NCRF)

◦Florida Hurricane Catastrophe Fund (FHCF)

•State-mandated involuntary plans

◦Commercial Automobile Insurance Procedures/Plans (CAIP)

Non-Regulated refers to voluntary external reinsurance contracts. We do not reinsure our Personal Lines business. In our Commercial Lines business, we reinsure our TNC

business, workers’ compensation insurance, and our fleet trucking product under quota-share reinsurance agreements. For our Property business, we have both multi-year catastrophic excess of loss and aggregate excess of loss reinsurance agreements.

The decrease in the ceded written and earned premiums in our Regulated plans during 2023 and 2022, primarily reflected our decision to non-renew our CAIP service carrier agreements in 2022. For the Non-Regulated reinsurance contracts, the year-over-year decreases in 2023 and 2022, reflected the changes that were made in 2022 to the reinsurance program structure of certain TNC products whereby we wrote less direct premiums and, therefore, ceded less premiums than in the prior year.

Our reinsurance recoverables and prepaid reinsurance premiums were comprised of the following at December 31:


	Reinsurance Recoverables								Prepaid Reinsurance Premiums
($ in millions)	2023				2022				2023				2022
Regulated:
MCCA	$	2,272.1	45	%	$	2,332.3	40	%	$	40.2	16	%	$	26.4	9	%
CAIP	539.1		10		626.8		11		0		0		50.4		17
FHCF	306.6		6		437.3		7		0		0		0		0
NCRF	184.7		4		143.2		2		74.6		30		54.5		18
NFIP	10.7		0		215.4		4		66.4		27		60.1		20
Other	3.8		0		2.9		0		1.3		0		1.5		1
Total Regulated	3,317.0		65		3,757.9		64		182.5		73		192.9		65
Non-Regulated:
Commercial Lines	1,385.7		27		1,544.3		27		56.3		23		91.0		31
Property	381.2		8		524.4		9		11.0		4		11.6		4
Other	10.0		0		5.5		0		0		0		0		0
Total Non-Regulated	1,776.9		35		2,074.2		36		67.3		27		102.6		35
Total	$	5,093.9	100	%	$	5,832.1	100	%	$	249.8	100	%	$	295.5	100	%

The decrease in our reinsurance recoverables in 2023, compared to 2022, for the FHCF, NFIP, and Property business were primarily due to the settlement of Hurricane Ian losses and allocated LAE that were incurred during 2022.

Our prepaid reinsurance premiums decreased in 2023 primarily due to our decision to non-renew our CAIP service contract in 2022 and changes that were made in 2022 to the reinsurance program structure of certain TNC products as discussed above.

Reinsurance contracts do not relieve us from our obligations to policyholders. Failure of reinsurers to honor their obligations could result in losses to us. Our exposure to losses from the failure of Regulated plans is minimal, since these plans are funded by the federal government or by mechanisms supported by insurance companies in applicable states.

For our Non-Regulated reinsurers, we routinely monitor changes in the credit quality and concentration risks of the reinsurers who are counterparties to our reinsurance recoverables to determine if an allowance for credit losses

should be established. For at-risk uncollateralized recoverable balances, we evaluate a number of reinsurer specific factors, including reinsurer credit quality rating, credit rating outlook, historical experience, reinsurer surplus, recoverable duration, and collateralization composition in respect to our net exposure (i.e., the reinsurance recoverable amount less premiums payable to the reinsurer, where the right to offset exists). At December 31, 2023 and 2022, the allowance for credit losses related to these contracts was not material to our financial condition or results of operations.

Statutory Financial Information	12 Months Ended
Statutory Financial Information	Dec. 31, 2023
Statutory Financial Information Disclosures [Abstract]
Statutory Financial Information	STATUTORY FINANCIAL INFORMATION Consolidated statutory surplus was $22,249.6 million and $17,879.9 million at December 31, 2023 and 2022, respectively. Statutory net income was $3,502.2 million, $2,763.5 million, and $2,283.9 million for the years ended December 31, 2023, 2022, and 2021, respectively. At December 31, 2023, $1,513.2 million of consolidated statutory surplus represented net admitted assets of our insurance subsidiaries and affiliates that are required to meet minimum statutory surplus requirements in such entities’ states of domicile. The companies may be licensed in states other than their states of domicile, which may have higher minimum statutory surplus requirements. Generally, the net admitted assets of insurance companies that, subject to other applicable insurance laws and regulations, are available for transfer to the parent company cannot include the net admitted assets required to meet the minimum statutory surplus requirements of the states where the companies are licensed. During 2023, the insurance subsidiaries paid aggregate dividends of $413.4 million to their parent company. Based on the dividend laws currently in effect, the insurance subsidiaries could pay aggregate dividends of $3,365.1 million in 2024, without prior approval from regulatory authorities, subject to other potential state specific limitations, capital requirements, and restrictions on the amount of dividends that can be paid within a 12-month period by the applicable subsidiary.

Employee Benefit Plans

12 Months Ended

Dec. 31, 2023

Employee Benefit Plans Disclosures [Abstract]

Employee Benefit Plans

EMPLOYEE BENEFIT PLANS

Retirement Plans Progressive has a defined contribution pension plan (401(k) Plan) that covers employees who have been employed with the company for at least 30 days. Under Progressive’s 401(k) Plan, we match up to a maximum of 6% of an employee’s eligible compensation contributed to the plan, with employees vesting in the company match after providing two years of service. Matching contributions to the 401(k) Plan for the years ended December 31, 2023, 2022, and 2021, were $205.9 million, $179.9 million, and $159.2 million, respectively.

Employee and company matching contributions are invested, at the direction of the employee, in a number of investment options available under the plan, including various mutual funds, a self-directed brokerage option, and a Progressive common stock fund. Progressive’s common stock fund is an employee stock ownership program (ESOP) within the 401(k) Plan. At December 31, 2023, the ESOP held 18.2 million of our common shares, all of which are included in shares outstanding. Dividends on these shares are reinvested in common shares or paid out in cash, at the election of the participant, and the related tax benefit is recorded as part of our tax provision.

Postemployment Benefits Progressive provides various postemployment benefits to former or inactive employees who meet eligibility requirements and to their beneficiaries and covered dependents. Postemployment benefits include salary continuation and disability-related benefits, including workers’ compensation and, if elected, continuation of health-care benefits for specified limited periods. The liability for these benefits was $18.7 million and $19.6 million at December 31, 2023 and 2022, respectively.

Incentive Compensation Plans – Employees Progressive’s incentive compensation programs include both non-equity incentive plans (cash) and equity incentive plans. Progressive’s cash incentive compensation includes an annual cash incentive program (Gainshare Program) for nearly all employees. Progressive’s equity incentive compensation plans provide for the granting of restricted stock unit awards to key members of management.

The amounts charged to expense for incentive compensation plans for the years ended December 31, were:


	2023				2022				2021
(millions)	Pretax		After Tax		Pretax		After Tax		Pretax		After Tax
Non-equity incentive plans – cash	$	897.3	$	708.9	$	380.8	$	300.8	$	619.3	$	489.2
Equity incentive plans1	121.3		104.3		122.7		106.7		100.7		86.6
1 After-tax amounts differ from the statutory rate of 21% due to the expected disallowance of certain executive compensation deductions.

Under Progressive’s 2015 Equity Incentive Plan, there are 17.0 million shares, in the aggregate, authorized for issuance. This plan provides for the granting of equity-based compensation to officers and other key employees.

The restricted equity awards are issued as either time-based or performance-based awards. Generally, equity awards are expensed pro rata over their respective vesting periods (i.e., requisite service period), based on the market value of the awards at the time of grant, with accelerated expense for participants who satisfy qualified retirement eligibility. The time-based awards vest in equal installments upon the lapse of specified periods of time, typically three, four, and five years, subject to the retirement provisions of the applicable award agreements.

Performance-based awards that contain variable vesting criteria are expensed based on management’s expectation of the percentage of the award, if any, that will ultimately vest. These estimates can change periodically throughout the measurement period. Vesting of performance-based awards is contingent upon the achievement of predetermined performance goals within specified time periods.

In addition to their time-based awards, performance-based awards are granted to executives and other senior managers to provide additional incentive to achieve pre-established profitability and growth targets or relative investment performance. The targets for the performance-based awards, as well as the number of units that ultimately may vest, vary by grant.

The following shows the performance measurement criteria for our performance-based equity awards outstanding at December 31, 2023:


Performance Measurement	Year(s) of Grant	Vesting range (as a percentage of target)
Growth of our personal auto and commercial auto businesses, both compared to its respective market	2023	0-250%
Growth of our personal auto and commercial auto businesses and homeowners multi-peril business, each compared to its respective market	2021-2022	0-250%
Investment results relative to peer group	2021-2023	0-200%

All restricted equity awards are settled at or after vesting in Progressive common shares from existing treasury shares on a one-to-one basis.

A summary of all employee restricted equity award activity during the years ended December 31, follows:


	2023			2022			2021
Restricted Equity Awards	Number of Shares1	Weighted Average Grant Date Fair Value		Number of Shares1	Weighted Average Grant Date Fair Value		Number of Shares1	Weighted Average Grant Date Fair Value
Beginning of year	3,198,150	$	81.71	3,539,022	$	67.24	3,570,271	$	57.68
Add (deduct):
Granted2	1,080,658	110.93		1,154,838	96.54		1,476,802	70.11
Vested	(1,338,466)	63.10		(1,378,070)	57.79		(1,452,353)	46.88
Forfeited	(46,600)	84.86		(117,640)	72.44		(55,698)	60.81
End of year3,4	2,893,742	$	101.18	3,198,150	$	81.71	3,539,022	$	67.24

1 Includes restricted stock units. All performance-based awards are included at their target amounts.

2 We reinvest dividend equivalents on restricted stock units. For 2023, 2022, and 2021, the number of units “granted” shown in the table above includes 36,656, 44,327, and 237,582 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0, since the dividends were factored into the grant date fair value of the original grant.

3 At December 31, 2023, the number of shares included 557,119 performance-based units at their target amounts. We expect 1,204,918 units to vest based upon our current estimates of the likelihood of achieving the predetermined performance measures applicable to each award.

4 At December 31, 2023, the total unrecognized compensation cost related to unvested equity awards was $93.3 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into our consolidated statements of comprehensive income over the weighted average vesting period of 2.2 years.

The aggregate fair value of the restricted equity awards that vested during the years ended December 31, 2023, 2022, and 2021, was $195.2 million, $154.4 million, and $139.1 million, respectively, based on the actual stock price on the applicable vesting date.

Incentive Compensation Plans – Directors Progressive’s Amended and Restated 2017 Directors Equity Incentive Plan, which was approved by shareholders in 2022, provides for the granting of equity-based awards, including restricted stock awards, to non-employee directors. Under the amended and restated plan, an additional 150,000 shares are eligible to be granted, bringing the total authorized shares under the directors plan to 650,000 shares.

The Progressive Corporation permits each non-employee director to indicate a preference to receive either 100% of their compensation in the form of a restricted stock award or 60% in the form of a restricted stock award and 40% in

the form of cash. If the director does not state a preference, it is presumed that they preferred to receive 100% of their compensation in the form of restricted stock. The Compensation Committee of the Board of Directors will consider such preferences when making a determination with respect to the allocation (restricted stock, or restricted stock and cash) and approval of the annual awards for each non-employee director.

The restricted stock awards are issued as time-based awards. The vesting period is typically 11 months from the date of each grant. To the extent a director is newly appointed during the year, or a director’s committee assignments change, the vesting period may be shorter. Both the restricted stock awards and cash, if elected, are expensed pro rata over their respective vesting periods based on the market value of the awards at the time of grant.

A summary of all directors’ restricted stock activity during the years ended December 31, follows:


	2023			2022			2021
Restricted Stock	Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value
Beginning of year	30,439	$	109.75	29,206	$	105.16	39,403	$	74.77
Add (deduct):
Granted	25,075	133.43		30,439	109.75		29,206	105.16
Vested	(30,439)	109.75		(29,206)	105.16		(39,403)	74.77
End of year1	25,075	$	133.43	30,439	$	109.75	29,206	$	105.16

1 At December 31, 2023, 2022, and 2021, the remaining unrecognized compensation cost related to restricted stock awards was $1.0 million, $1.0 million, and $0.9 million, respectively.

The aggregate fair value of the restricted stock vested during the years ended December 31, 2023, 2022, and 2021, was $4.2 million, $3.4 million, and $3.8 million, respectively, based on the actual stock price at time of vesting.

Deferred Compensation The Progressive Corporation Executive Deferred Compensation Plan (Deferral Plan) permits eligible Progressive executives to defer receipt of some or all of their annual cash incentive payments and all of their annual equity awards. Deferred cash compensation is deemed invested in one or more investment funds, including Progressive common shares, offered under the Deferral Plan and elected by the participant. All Deferral Plan distributions attributable to deferred cash compensation will be paid in cash.

For all equity awards granted in or after March 2005, and deferred pursuant to the Deferral Plan, the deferred amounts are deemed invested in our common shares and are ineligible for transfer to other investment funds in the Deferral Plan; distributions of these deferred awards will be made in Progressive common shares. For all restricted stock awards granted prior to that date, the deferred amounts are eligible to be transferred to any of the investment funds in the Deferral Plan; distributions of

these deferred awards will be made in cash. We reserved 11.1 million of our common shares for issuance under the Deferral Plan.

An irrevocable grantor trust has been established to provide a source of funds to assist us in meeting our liabilities under the Deferral Plan. The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31:


(millions)	2023		2022
Progressive common shares1	$	118.5	$	131.0
Other investment funds2	165.1		150.4
Total	$	283.6	$	281.4

1 Included 1.6 million and 2.0 million common shares as of December 31, 2023 and 2022, respectively, to be distributed in common shares, and are reported at grant date fair value.

2 Amount is included in other assets on our consolidated balance sheets.

Segment Information

12 Months Ended

Dec. 31, 2023

Segment Reporting [Abstract]

Segment Information

SEGMENT INFORMATION

We write personal and commercial auto insurance, personal residential property insurance, business-related general liability and commercial property insurance predominantly for small businesses, workers’ compensation insurance primarily for the transportation industry, and other specialty property-casualty insurance and provide related services throughout the United States.

We report our operating segments based on product. Our segments include Personal Lines, Commercial Lines, and Property.

Our Personal Lines segment writes insurance for personal autos and recreational vehicles (our special lines products). The Personal Lines segment is comprised of both the Agency and Direct businesses. The Agency business includes business written by our network of more than 40,000 independent insurance agencies, including brokerages in New York and California, and strategic alliance business relationships (including other insurance companies, financial institutions, and national agencies). The Direct business includes business written directly by us online, through the Progressive mobile app, or by phone. We operate our Personal Lines segment throughout the United States.

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. This segment operates throughout the United States and is distributed through both the independent agency, including brokerages, and direct channels.

Our Property segment writes residential property insurance for homeowners, other property owners, and renters, and umbrella insurance through both the independent agency and direct channels, and writes flood insurance through the “Write Your Own” program for the National Flood Insurance Program. Our Property segment operates throughout the majority of the United States.

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. In 2022, our service contract to act as a servicing agent for CAIP expired and we did not renew the contract.

We evaluate segment profitability based on pretax underwriting profit (loss). 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.

Service business pretax profit (loss) is the difference between service business revenues and service business expenses.

Assets and income taxes are not allocated to operating segments, as such allocation would be impractical. Expense allocations are based on certain assumptions and estimates primarily related to revenue and volume; stated segment operating results would change if different methods were applied. We also do not separately identify

depreciation expense by segment. Companywide depreciation expense for 2023, 2022, and 2021, was $285.5 million, $305.6 million, and $279.7 million, respectively. The accounting policies of the operating segments are consistent with those described in Note 1 – Reporting and Accounting Policies.

Following are the operating results for the years ended December 31:


	2023				2022				2021
(millions)	Revenues		Pretax Profit (Loss)		Revenues		Pretax Profit (Loss)		Revenues		Pretax Profit (Loss)
Personal Lines
Agency	$	21,198.2	$	1,029.2	$	17,744.7	$	734.1	$	16,881.0	$	992.1
Direct	25,015.1		1,828.2		20,135.5		769.4		18,492.3		619.2
Total Personal Lines1	46,213.3		2,857.4		37,880.2		1,503.5		35,373.3		1,611.3
Commercial Lines	9,898.7		123.0		9,088.3		810.3		6,945.2		767.8
Property2	2,551.4		28.1		2,270.0		(238.4)		2,042.5		(312.3)
Other indemnity3	1.0		(16.2)		2.7		(11.4)		7.7		(1.4)
Total underwriting operations	58,664.4		2,992.3		49,241.2		2,064.0		44,368.7		2,065.4
Fees and other revenues4	889.1		NA		722.1		NA		691.8		NA
Service businesses	310.1		(38.9)		299.3		2.6		271.4		18.6
Investments5	2,244.9		2,218.7		(651.9)		(676.2)		2,370.1		2,344.6
Interest expense	NA		(268.4)		NA		(243.5)		NA		(218.6)
Property - Goodwill impairment2	NA		0		NA		(224.8)		NA		0
Consolidated total	$	62,108.5	$	4,903.7	$	49,610.7	$	922.1	$	47,702.0	$	4,210.0

NA = Not applicable

1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned in 2023, 2022, and 2021; 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 The total pretax loss, including goodwill impairment, for the Property segment was $463.2 million for 2022.

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, as defined above. The underwriting margin is the pretax underwriting profit (loss) expressed as a percentage of net premiums earned (i.e., revenues from underwriting operations). Combined ratio is the complement of the underwriting margin. Following are the underwriting margins and combined ratios for our underwriting operations for the years ended December 31:


	2023			2022			2021
	Underwriting Margin		Combined Ratio	Underwriting Margin		Combined Ratio	Underwriting Margin		Combined Ratio
Personal Lines
Agency	4.9	%	95.1	4.1	%	95.9	5.9	%	94.1
Direct	7.3		92.7	3.8		96.2	3.4		96.6
Total Personal Lines	6.2		93.8	4.0		96.0	4.6		95.4
Commercial Lines	1.2		98.8	8.9		91.1	11.1		88.9
Property	1.1		98.9	(10.5)		110.5	(15.3)		115.3
Total underwriting operations	5.1		94.9	4.2		95.8	4.7		95.3

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-42

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 40
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-40

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//280/tableOfContent

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 26
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-26

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 34
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-34

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 41
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-41

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-21

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Other Comprehensive Income (Loss)

Other Comprehensive Income (Loss)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

OTHER COMPREHENSIVE INCOME (LOSS)

The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, for the years ended December 31, were as follows:


							Components of Changes in Accumulated Other Comprehensive Income (after tax)
(millions)	Pretax total accumulated other comprehensive income (loss)		Total tax (provision) benefit		After tax total accumulated other comprehensive income (loss)		Total net unrealized gains (losses) on securities		Net unrealized gains (losses) on forecasted transactions		Foreign currency translation adjustment
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	1,256.1		(265.6)		990.5		990.5		0		0
Foreign currency translation adjustment	0.4		(0.1)		0.3		0		0		0.3
Total other comprehensive income (loss) before reclassifications	1,256.5		(265.7)		990.8		990.5		0		0.3
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net realized gains (losses) on securities	(246.9)		51.9		(195.0)		(195.0)		0		0
Interest expense	(0.6)		0.1		(0.5)		0		(0.5)		0
Total reclassification adjustment for amounts realized in net income	(247.5)		52.0		(195.5)		(195.0)		(0.5)		0
Total other comprehensive income (loss)	1,504.0		(317.7)		1,186.3		1,185.5		0.5		0.3
Balance at December 31, 2023	$	(2,052.9)	$	437.2	$	(1,615.7)	$	(1,600.8)	$	(14.0)	$	(0.9)


							Components of Changes in Accumulated Other Comprehensive Income (after tax)
(millions)	Pretax total accumulated other comprehensive income (loss)		Total tax (provision) benefit		After tax total accumulated other comprehensive income (loss)		Total net unrealized gains (losses) on securities		Net unrealized gains (losses) on forecasted transactions		Foreign currency translation adjustment
Balance at December 31, 2021	$	52.3	$	(11.6)	$	40.7	$	56.2	$	(14.9)	$	(0.6)
Other comprehensive income (loss) before reclassifications:
Investment securities	(4,168.4)		878.7		(3,289.7)		(3,289.7)		0		0
Foreign currency translation adjustment	(0.7)		0.1		(0.6)		0		0		(0.6)
Total other comprehensive income (loss) before reclassifications	(4,169.1)		878.8		(3,290.3)		(3,289.7)		0		(0.6)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net realized gains (losses) on securities	(559.4)		112.2		(447.2)		(447.2)		0		0
Interest expense	(0.5)		0.1		(0.4)		0		(0.4)		0
Total reclassification adjustment for amounts realized in net income	(559.9)		112.3		(447.6)		(447.2)		(0.4)		0
Total other comprehensive income (loss)	(3,609.2)		766.5		(2,842.7)		(2,842.5)		0.4		(0.6)
Balance at December 31, 2022	$	(3,556.9)	$	754.9	$	(2,802.0)	$	(2,786.3)	$	(14.5)	$	(1.2)


							Components of Changes in Accumulated Other Comprehensive Income (after tax)
(millions)	Pretax total accumulated other comprehensive income (loss)		Total tax (provision) benefit		After tax total accumulated other comprehensive income (loss)		Total net unrealized gains (losses) on securities		Net unrealized gains (losses) on forecasted transactions		Foreign currency translation adjustment
Balance at December 31, 2020	$	1,187.4	$	(255.7)	$	931.7	$	947.3	$	(15.6)	$	0
Other comprehensive income (loss) before reclassifications:
Investment securities	(892.4)		193.0		(699.4)		(699.4)		0		0
Foreign currency translation adjustment	(0.8)		0.2		(0.6)		0		0		(0.6)
Total other comprehensive income (loss) before reclassifications	(893.2)		193.2		(700.0)		(699.4)		0		(0.6)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net realized gains (losses) on securities	242.8		(51.1)		191.7		191.7		0		0
Interest expense	(0.9)		0.2		(0.7)		0		(0.7)		0
Total reclassification adjustment for amounts realized in net income	241.9		(50.9)		191.0		191.7		(0.7)		0
Total other comprehensive income (loss)	(1,135.1)		244.1		(891.0)		(891.1)		0.7		(0.6)
Balance at December 31, 2021	$	52.3	$	(11.6)	$	40.7	$	56.2	$	(14.9)	$	(0.6)

In an effort to manage interest rate risk, we entered into forecasted transactions on Progressive’s debt issuances. During the next 12 months, we expect to reclassify $0.6 million (pretax) into interest expense, related to net unrealized losses on forecasted transactions (see Note 4 – Debt for further discussion).

Litigation	12 Months Ended
Litigation	Dec. 31, 2023
Litigation Disclosures [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 insurance subsidiaries are named as defendants in a number of class action or individual lawsuits that challenge certain of the operations of the subsidiaries. We describe litigation contingencies for which a loss is probable. In addition, we establish accruals for these lawsuits when we can reasonably estimate potential loss exposure, which may include a range of loss, and we will disclose such amount or range of loss if material. As to lawsuits for which the loss is considered probable but not estimable, we do not establish an accrual. Nevertheless, we continue to evaluate this 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. We also describe litigation contingencies for which a loss is reasonably possible (but not probable). When disclosing reasonably possible litigation contingencies, we will disclose the amount or range of possible loss, if we are able to make that determination and if material. We review all reasonably possible losses on an ongoing basis to determine whether the likelihood of incurring a loss has become probable, or whether the circumstances have changed such that we may now reasonably estimate a range of loss. We may also be exposed to litigation contingencies that are remote. Remote litigation contingencies are those for which the likelihood of a loss is slight at the balance sheet date. We do not disclose, or establish accruals for, remote litigation contingencies, but we evaluate these contingencies on an ongoing basis to determine whether the likelihood of a loss has increased. Each year, certain of our pending litigation matters may be brought to conclusion. For cases that have settled, but for which settlement is not complete, an accrual is established at our best estimate of the loss exposure. We regularly review these and other accruals to ensure they are adequate. Settlements that are complete are fully reflected in our financial statements. The amounts accrued and/or paid for settlements during the periods presented were not material to our consolidated financial condition, cash flows, or results of operations. The pending lawsuits summarized below are in various stages of development, and the outcomes are uncertain until final disposition or, if probable and estimable, are accrued and immaterial as of December 31, 2023. At year end, except to the extent an immaterial accrual has been established, we do not consider the losses from these pending cases to be both probable and estimable, and we are unable to estimate a range of loss at this time. It is not possible to determine loss exposure for a number of reasons, including, without limitation, one or more of the following: •liability appears to be remote; •putative class action lawsuits generally pose immaterial exposure until a class is actually certified, which, historically, has not been granted by courts in the vast majority of our cases in which class certification has been sought; •even certified class action lawsuits are subject to decertification, denial of liability, and/or appeal; •class definitions are often indefinite and preclude detailed exposure analysis; and •complaints rarely state an amount sought as relief, and when such amount is stated, it often is a function of pleading requirements and may be unrelated to the potential exposure. We plan to contest these suits vigorously, but may pursue settlement negotiations in some cases, as we deem appropriate. In the event that any one or more of these cases results in a substantial judgment against us, or settlement by us, or if our accruals (if any) prove to be inadequate, the resulting liability could have a material adverse effect on our consolidated financial condition, cash flows, and/or results of operations. Lawsuits arising from insurance policies and operations, including but not limited to allegations involving claims adjustment and vehicle valuation, may be filed contemporaneously in multiple states. As of December 31, 2023, we are named as defendants in class action lawsuits pending in multiple states alleging that we improperly value total loss vehicle physical damage claims through the application of a negotiation adjustment in calculating such valuations. At December 31, 2023, this includes four states in which classes have been certified, and lawsuits styled as putative class actions pending in additional states. These lawsuits, which were filed at different times by different plaintiffs, feature certain similar claims and also include different allegations and are subject to various state laws. While we believe we have meritorious defenses and we are vigorously contesting these lawsuits, an unfavorable result in, or a settlement of, a significant number of these lawsuits could, in aggregation, have a material adverse effect on our financial condition, cash flows, and/or results of operations. Based on information known at December 31, 2023, we determined that losses from these lawsuits are reasonably possible but neither probable nor reasonably estimable. At December 31, 2023, the pending lawsuits summarized below, including those discussed above, are in various stages of development, and the outcomes are uncertain until final disposition or, if probable and estimable, are accrued and immaterial: Lawsuits seeking class/collective action status alleging that: •we improperly handle, adjust, and pay physical damage claims, including how we value total loss claims, the application of a negotiation adjustment in calculating total loss valuations, the payment of fees and taxes associated with total losses, and the payment of diminution of value damages. •we improperly adjust personal injury protection (PIP) claims in Florida. •we improperly adjust medical bills submitted by insureds or medical providers in medical claims. •we improperly pay and reimburse Medicare Advantage Plans or Medicaid on first party medical, PIP, and bodily injury claims. •we sell illusory underinsured motorist coverage. •we wrongfully withheld or delayed payments owed to insureds under uninsured/underinsured motorist coverage. •we provided an insufficient amount of premium relief to California insureds in response to the COVID-19 pandemic. •we improperly use marital status as a rating factor when setting premium in California. •we fail to timely and fully refund premiums to insureds upon taking title to vehicles that have been deemed total losses. •we mistitle vehicles by failing to include a salvage designation. •we improperly pay post-arbitration award interest. •we improperly prorate the deductible amount returned to the insured after subrogation. •we improperly funded a grant program for small businesses. •we improperly raised insureds’ premiums during their current policy term. •we failed, based on a vendor data security incident, to properly secure and safeguard personally identifiable information. Lawsuits certified or conditionally certified as class/collective actions alleging that: •we improperly value total loss claims by applying a negotiation adjustment in Colorado, Georgia, New York, and Pennsylvania. •we improperly fail to pay fees and taxes associated with total losses in 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. •we improperly reduce or deny PIP benefits when medical expenses are paid initially by health insurance. Non-class/collective/representative lawsuits filed by different plaintiffs and subject to various state laws, alleging that certain business operations, commercial matters, and/or employment policies, practices, or decisions are improper.

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

LEASES

Included in our consolidated balance sheets are certain operating leases for office space, computer equipment, and vehicles. The leased assets represent our right to use an underlying asset for the lease term and the lease liabilities represent our obligation to make lease payments arising from the lease using an incremental borrowing rate to calculate the present value of the remaining lease payments. Leased assets and leased liabilities are reported as a component of other assets and accounts payable, accrued expenses, and other liabilities, respectively, in our consolidated balance sheets.

Contracts are reviewed at inception to determine if it contains a lease and whether the lease qualifies as an operating or financing lease. We do not have material financing leases.

Operating leases are expensed on a straight-line basis over the term of the lease. In determining the lease term, we consider the probability of exercising renewal options. We elected to account for leases with both lease and non-lease components as a single lease component and to apply a portfolio approach to account for our vehicle leases.

The following table summarizes the carrying amounts of our operating leased assets and liabilities at December 31, along with key inputs used to discount our lease liabilities:


(millions)	2023			2022
Operating lease assets	$	172.5		$	130.5
Operating lease liabilities	$	177.2		$	137.2
Weighted-average remaining term	3.2 years			2.5 years
Weighted-average discount rate	5.1		%	2.0		%

At December 31, 2023, the following table shows our operating lease liabilities, on an undiscounted basis for the periods indicated:


(millions)	Commitments
2024	$	74.0
2025	54.6
2026	37.6
2027	15.8
2028	6.0
Thereafter	4.8
Total	192.8
Interest	(15.6)
Present value of lease liabilities	$	177.2

The operating lease expense for the years ended December 31, was as follows:


(millions)	Expense
2023	$	94.4
2022	89.1
2021	90.4

Dividends

12 Months Ended

Dec. 31, 2023

Dividends [Abstract]

Dividends

DIVIDENDS

Following is a summary of our common and preferred share dividends that were declared and/or paid in the last three years:


(millions, except per share amounts)		Amount
Declared	Payable	Per Share		Accrued/Paid1
Common - Annual-Variable Dividends:
December 2023	January 2024	$	0.75	$	439.3
December 2021	December 2021	1.50		876.5
December 2020	January 2021	4.50		2,635.9

Common - Quarterly Dividends:
December 2023	January 2024	0.10		58.6
August 2023	October 2023	0.10		58.5
May 2023	July 2023	0.10		58.5
March 2023	April 2023	0.10		58.5
December 2022	January 2023	0.10		58.5
August 2022	October 2022	0.10		58.5
May 2022	July 2022	0.10		58.5
March 2022	April 2022	0.10		58.5
December 2021	January 2022	0.10		58.5
August 2021	October 2021	0.10		58.5
May 2021	July 2021	0.10		58.5
March 2021	April 2021	0.10		58.5
December 2020	January 2021	0.10		58.6

Preferred Dividends:
October 2023	December 2023	20.753157		10.4
August 2023	September 2023	20.67700		10.3
May 2023	June 2023	18.92463		9.5
December 2022	March 2023	26.875		13.4
August 2022	September 2022	26.875		13.4
December 2021	March 2022	26.875		13.4
August 2021	September 2021	26.875		13.4
December 2020	March 2021	26.875		13.4

1 The 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 our consolidated balance sheets until paid.

Common Share Dividends The Board of Directors adopted a policy of declaring regular quarterly common share dividends, and on at least an annual basis, to consider declaring an additional, variable common share dividend. For 2022, the Board decided not to declare an annual-variable dividend after assessing our capital position, existing capital resources, and expected future capital needs.

Preferred Share Dividends During 2018, we issued 500,000 Series B Fixed-to-Floating Rate Cumulative Perpetual Serial Preferred Shares, without par value (the Series B Preferred Shares), with a liquidation preference of $1,000 per share (the stated amount). Beginning March 15, 2023 and up until redemption (the floating-rate period), holders of the Series B Preferred Shares are entitled to receive cumulative cash dividends quarterly, if and when declared by the Board of Directors, at a floating annual dividend rate equal to the three-month London Interbank Offered Rate (LIBOR) plus a spread of 2.539% applied to the stated amount per share.

We, as calculation agent under our Series B Preferred Shares, determined that the reference rate for the Series B Preferred Shares, for any determination date after June 30, 2023, shall be the sum of (i) 3-Month CME Term SOFR plus (ii) a tenor spread adjustment of 0.26161%, and (iii) a spread of 2.539%. The new reference rate became effective for the dividend period determination date commencing September 15, 2023. The reference rate was determined in accordance with the successor base rate provisions of the Series B Preferred Shares and the Adjustable Interest Rate (LIBOR) Act and the regulation issued by the Board of Governors of the Federal Reserve System on December 16, 2022, implementing the LIBOR Act. The Board did not declare a dividend in December 2023 as they had in prior years.

Prior to the floating-rate period, dividends were payable semiannually in March and September, if and when declared by the Board of Directors, at a fixed annual dividend rate of 5.375% of the stated amount per share.

The Series B Preferred Shares are perpetual and have no stated maturity date. During the first quarter 2024, we redeemed all of the outstanding Series B Preferred Shares at the stated amount of $1,000 per share, for an aggregate payout of $507.8 million, including accrued and unpaid dividends to, but excluding February 22, 2024, which is the redemption date.

Pay vs Performance Disclosure - USD ($) $ in Millions	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net income	$ 3,902.4	$ 721.5	$ 3,350.9

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-3

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 20: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(B))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 30: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 32: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 34: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483499/205-20-50-7

Reference 35: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 36: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1A

Reference 37: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

Reference 38: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 39: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

Premium Receivable, Allowance for Credit Loss

Insider Trading Arrangements	3 Months Ended	12 Months Ended
Insider Trading Arrangements	Dec. 31, 2023 shares	Dec. 31, 2023 shares
Karen B. Bailo [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On November 21, 2023, Karen B. Bailo, our Commercial Lines President, entered into a Rule 10b5-1 trading arrangement that is intended to satisfy the affirmative defense of Rule 10b5-1(c). The plan provides for (i) the sale of all shares vested during the duration of the plan pursuant to certain equity awards previously granted to Ms. Bailo, excluding any shares withheld by the company to satisfy tax withholding obligations, and (ii) 3,212 shares of the company’s common stock. Ms. Bailo’s plan will expire on November 29, 2024, subject to the plan’s earlier expiration or completion in accordance with its terms.
Name	Karen B. Bailo
Title	Commercial Lines President
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	November 21, 2023
Termination Date	November 29, 2024
Arrangement Duration	374 days
Aggregate Available	3,212	3,212
Patrick K. Callahan [Member]
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		On October 16, 2023, Patrick K. Callahan, our Personal Lines President, entered into a Rule 10b5-1 trading arrangement that is intended to satisfy the affirmative defense of Rule 10b5-1(c). The plan provides for the sale of all shares vested during the duration of the plan pursuant to certain equity awards previously granted to Mr. Callahan, excluding any shares withheld by the company to satisfy tax withholding obligations. Mr. Callahan’s plan will expire on September 30, 2024, subject to the plan’s earlier expiration or completion in accordance with its terms.
Name	Patrick K. Callahan
Title	Personal Lines President
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	October 16, 2023
Termination Date	September 30, 2024
Arrangement Duration	350 days

Reporting and Accounting Policies (Policies)	12 Months Ended
Reporting and Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Nature of Operations	Nature of Operations The Progressive insurance organization began business in 1937. The financial results of The Progressive Corporation include its subsidiaries and affiliates (references to “subsidiaries” in these notes include affiliates as well). Our insurance subsidiaries write personal and commercial auto insurance, personal residential property insurance, business-related general liability and commercial property insurance predominantly for small businesses, workers’ compensation insurance primarily for the transportation industry, and other specialty property-casualty insurance and provide related services. We report three operating segments. Our Personal Lines segment writes insurance for personal autos and recreational vehicles, which we refer to as 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. We operate our businesses throughout the United States, through both the independent agency and direct channels.
Basis of Consolidation and Reporting	Basis of Consolidation and Reporting The accompanying consolidated financial statements include the accounts of The Progressive Corporation and our wholly owned insurance and non-insurance subsidiaries and affiliates in which we have a controlling financial interest. All intercompany accounts and transactions are eliminated in consolidation. All revenues are generated from external customers and we do not have a reliance on any major customer.
Estimates	Estimates We are required to make estimates and assumptions when preparing our financial statements and accompanying notes in conformity with accounting principles generally accepted in the United States of America (GAAP). As estimates develop into fact, results may, and will likely, differ from those estimates.
Investments	Investments Our fixed-maturity securities and short-term investments are accounted for on an available-for-sale basis. Fixed-maturity securities include debt securities and redeemable preferred stocks, which may have fixed or variable principal payment schedules, may be held for indefinite periods of time, and may be used as a part of our asset/liability strategy or sold in response to changes in interest rates, anticipated prepayments, risk/reward characteristics, liquidity needs, or other economic factors. These securities are carried at fair value with the corresponding unrealized gains (losses), net of deferred income taxes, reported in accumulated other comprehensive income. Short-term investments may include commercial paper, repurchase transactions, and other securities expected to mature within one year. From time to time, we may also invest in municipal bonds that have maturity dates that are longer than one year but have either liquidity facilities or mandatory put features within one year. Equity securities include common stocks, nonredeemable preferred stocks, and other risk investments. Common stocks and nonredeemable preferred stocks are carried at fair value, with the changes in fair value reported in net holding period gains (losses) on securities on the consolidated statements of comprehensive income. Our other risk investments are accounted for under the equity method of accounting. These securities are carried at cost and adjusted for our share of the investee’s earnings or losses, with the changes in carrying value reported in investment income. We did not have any open derivative instruments at December 31, 2023, 2022, or 2021. From time to time, we entered into interest rate swaps to hedge the exposure to variable cash flows of a forecasted transaction (i.e., cash flow hedge). Derivatives designated as hedges are required to be evaluated on established criteria to determine the effectiveness of their correlation to, and ability to reduce the designated risk of, specific securities or transactions. Effectiveness is required to be reassessed regularly. For cash flow hedges that are deemed to be effective, the changes in fair value of the hedge would be reported as a component of accumulated other comprehensive income and subsequently amortized into earnings over the life of the hedged transaction. If a hedge is deemed to become ineffective or discontinued, changes in fair value of the derivative instrument would be reported in income for the current period. See Note 4 – Debt for a summary of our closed debt issuance cash flow hedges. Investment securities are exposed to various risks such as interest rate, market, credit, and liquidity risk. Fair values of securities fluctuate based on the nature and magnitude of changing market conditions; significant changes in market conditions could materially affect the portfolio’s value in the near term. We routinely monitor our fixed-maturity portfolio for pricing changes that might indicate potential credit losses exist and perform detailed reviews of securities with unrealized losses. For an unrealized loss that we determined to be related to current market conditions, we will not record an allowance for credit losses or write off the unrealized loss for the securities we do not intend to sell. We will continue to monitor these securities to determine if the unrealized loss is due to credit deterioration. If we believe that a potential credit loss exists, we will record an allowance for the credit loss and recognize the realized loss as a component of realized gains (losses) in the income statement. Once a credit loss allowance has been established, we will continue to evaluate the security, at least quarterly, to determine if changes in conditions have created the need to either increase or decrease the allowance recorded. If we determine that a security with a credit loss allowance previously recorded is likely to be sold prior to the potential recovery of the credit loss, or if we determine that the loss is uncollectible, we will reverse the allowance and write down the security to its fair value. Investment income consists of interest, dividends, accretion, and amortization. Interest is recognized on an accrual basis using the effective yield method, except for asset-backed securities, discussed below. Depending on the nature of the equity instruments, dividends are recorded at either the ex-dividend date or on an accrual basis. Asset-backed securities, which are included in our fixed-maturity portfolio, are generally accounted for under the retrospective method. The retrospective method recalculates yield assumptions (based on changes in interest rates or cash flow expectations) historically to the inception of the investment holding period, and applies the required adjustment, if any, to the cost basis, with the offset recorded to investment income on a quarterly basis. The prospective method is used primarily for interest-only securities, asset-backed securities below high investment-grade status (i.e., below AA-), and certain asset-backed securities with sub-prime loan exposure or where there is a greater risk of non-performance and where it is possible the initial investment may not be substantially recovered. The prospective method requires a calculation of expected future repayments and resets the yield to allow for future period adjustments; no current period impact to investment income or the security’s cost is made based on the cash flow update. Prepayment assumptions are updated quarterly. Realized gains (losses) on securities are computed based on the first-in first-out method. Realized gains (losses) also include holding period valuation changes on equity securities and hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument), as well as initial and subsequent changes in credit allowance losses and write-offs for losses deemed uncollectible or securities in a loss position that are expected to be sold prior to the recovery of the credit loss.
Insurance Premiums and Receivables	Insurance Premiums and Receivables Insurance premiums written are earned into income on a pro rata basis over the period of risk, based on a daily earnings convention. Accordingly, unearned premiums represent the portion of premiums written with unexpired risk. We write insurance and provide related services to individuals and commercial accounts and offer a variety of payment plans. Generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk. For our Personal Lines and Commercial Lines businesses, we perform a policy-level evaluation to determine the extent to which the premiums receivable balance exceeds the unearned premiums balance. To determine an allowance for credit losses, we evaluate the collectibility of premiums receivables based on historical and current collections experience of the aged exposures, using actuarial analysis. Our estimate of the future recoverability of our projected ultimate at-risk exposures also takes into consideration any unusual circumstances that we may encounter, such as moratoriums or other programs that may suspend collections. For our Property business, the risk of uncollectibility is relatively low. If premiums are unpaid by the policy due date, we provide advance notice of cancellation in accordance with each state’s requirements and, if the premiums remain unpaid after receipt of notice, we cancel the policy and write off any remaining balance.
Deferred Acquisition Costs	Deferred Acquisition Costs Deferred acquisition costs include commissions, premium taxes, and other variable underwriting and direct sales costs incurred in connection with the successful acquisition or renewal of insurance contracts. These acquisition costs, net of ceding allowances, are deferred and amortized over the policy period in which the related premiums are earned. We consider anticipated investment income in determining recoverability of these costs. Management believes these costs will be fully recoverable in the near term.
Loss and Loss Adjustment Expense Reserves	Loss and Loss Adjustment Expense Reserves Loss reserves represent the estimated liability on claims reported to us, plus reserves for losses incurred but not recorded. These estimates are reported net of amounts estimated to be recoverable from salvage and subrogation. Loss adjustment expense reserves represent the estimated expenses required to settle these claims. The methods of making estimates and establishing these reserves are reviewed regularly and resulting adjustments are reflected in income in the current period. Such loss and loss adjustment expense reserves are susceptible to change.
Reinsurance	Reinsurance Our reinsurance activity includes transactions which are categorized as Regulated and Non-Regulated. Regulated refers to plans in which we participate that are governed by insurance regulations and include state-provided reinsurance facilities (e.g., Michigan Catastrophic Claims Association, North Carolina Reinsurance Facility, Florida Hurricane Catastrophe Fund), as well as state-mandated involuntary plans for commercial vehicles (Commercial Automobile Insurance Procedures/Plans – CAIP) and federally regulated plans for flood (National Flood Insurance Program – NFIP); we act as a participant in the “Write Your Own” program for the NFIP. Non-Regulated includes voluntary contractual arrangements primarily related to our Property business and to the transportation network company (TNC) business written by our Commercial Lines segment. Prepaid reinsurance premiums are earned on a pro rata basis over the period of risk, based on a daily earnings convention, which is consistent with premiums earned. See Note 7 – Reinsurance for further discussion. We routinely monitor changes in the credit quality and concentration risks of the reinsurers who are counterparties to our reinsurance recoverables to determine if an allowance for credit losses should be established.
Income Taxes	Income Taxes The income tax provision is calculated under the balance sheet approach. Deferred tax assets and liabilities are recorded based on the temporary difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. The principal items giving rise to such differences include: •unearned premiums reserves; •investment securities (e.g., net unrealized gains (losses) and net holding period gains (losses) on securities); •deferred acquisition costs; •loss and loss adjustment expense reserves; •non-deductible accruals; •property and equipment; and •software development costs. We review our deferred tax assets regularly for recoverability. See Note 5 – Income Taxes for further discussion.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is recognized over the estimated useful lives of the assets using accelerated methods for computer equipment and the straight-line method for all other fixed assets. We evaluate impairment whenever events or circumstances warrant such a review and write off the impaired assets if appropriate.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill is the excess of the purchase price over the estimated fair value of the assets and liabilities acquired and represents the future economic benefits arising from other assets acquired that could not be individually identified and separately recognized. At December 31, 2023 and 2022, we had goodwill of $227.9 million, which is primarily attributable to our Agency Personal Lines business and related to the April 1, 2015, acquisition of a controlling interest in ARX Holding Corp. (ARX). There were no changes to the carrying amount of goodwill during the year ended December 31, 2023. We evaluate our goodwill for impairment at least annually using a qualitative approach. If events or changes in circumstances indicate that the carrying value of goodwill or intangible assets may not be recoverable, we will evaluate such items for impairment using a quantitative approach. In 2022, we recorded an impairment loss of $224.8 million, related to the goodwill assigned to the ARX reporting unit of our Property operating segment. As a result of our annual impairment testing, we determined that impairment was necessary given the magnitude of weather events relative to forecasted expectations during the first half of 2022, as well as other factors impacting our plans to restore our Property business to target profitability in a timely fashion. There were no previously recorded goodwill impairment losses on any of the outstanding goodwill. Intangible assets are non-financial assets lacking physical substance (e.g., customer and agency relationships, trade names, software rights) and represent the future economic benefit of those acquired assets. Amortization expense related to intangible assets was $14.2 million, $31.0 million, and $57.7 million for the years ended December 31, 2023, 2022, and 2021, respectively. Goodwill and intangible assets are included in other assets in our consolidated balance sheets; the prior-year amounts, which were presented separately on the balance sheet in the prior year, were reclassified into this line item to conform to the current year presentation.
Guaranty Fund Assessments	Guaranty Fund Assessments We are subject to state guaranty fund assessments, which provide for the payment of covered claims or other insurance obligations of insurance companies deemed insolvent. These assessments are accrued after a determination of insolvency has occurred, and we have written the premiums on which the assessments will be based. Assessments are expensed when incurred except for assessments that are available for recoupment from policyholders or are eligible to offset premiums taxes payable, which are capitalized to the extent allowable.
Fees and Other Revenues	Fees and Other Revenues Fees and other revenues primarily represent fees collected from policyholders relating to installment charges in accordance with our bill plans, as well as late payment and insufficient funds fees and revenue from ceding commissions, and are considered a part of our underwriting operations. Fees and other revenues are generally earned when invoiced, except for excess ceding commissions, which are earned over the policy period
Service Revenues and Expenses	Service Revenues and Expenses Our service businesses provide insurance-related services. Service revenues and expenses from our commission-based businesses are recorded in the period in which they are earned or incurred.
Equity-Based Compensation	Equity-Based Compensation We issue time-based and performance-based restricted stock unit awards to key members of management as our form of equity compensation and time-based restricted stock awards to non-employee directors. Collectively, we refer to these awards as restricted equity awards. Generally, restricted equity awards are expensed pro rata over their respective vesting periods (i.e., requisite service period), based on the market value of the awards at the time of grant, with accelerated expense for participants who satisfy qualified retirement eligibility. We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates. We credit dividend equivalent units to our management restricted equity awards. Dividend equivalent units for both time-based and performance-based awards are based on the amount of common share dividends declared by the Board of Directors, credited to outstanding restricted stock unit awards at the time a dividend is paid to shareholders, and distributed upon, or after, vesting of the underlying award.
Earnings Per Common Share	Earnings Per Common 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. Basic earnings per common share is computed using the weighted average number of common shares outstanding during the reporting period, excluding unvested, non-employee director, time-based restricted stock awards. Diluted earnings per common share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents, which are calculated using the treasury stock method, include the incremental shares assumed to be issued for: •earned but unvested time-based restricted equity awards, and •performance-based restricted equity awards that satisfied certain contingency conditions for unvested common stock equivalents during the period and are highly likely to continue to satisfy the conditions until the date of vesting. For periods when a net loss is reported, earnings per common share are calculated using basic average equivalent common shares since diluted earnings per share would be antidilutive.
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 overnight reverse repurchase commitments, which are not considered part of the investment portfolio, held by these subsidiaries at December 31, 2023, 2022, and 2021, were $68.2 million, $125.9 million, and $137.1 million, respectively. Restricted cash and restricted cash equivalents include collateral held against unpaid deductibles and cash that is restricted to pay flood claims under the NFIP’s “Write Your Own” program, for which certain subsidiaries are participants.
Commitments and Contingencies	Commitments and Contingencies We have certain noncancelable purchase obligations for goods and services with minimum commitments of $1,024.8 million at December 31, 2023, primarily consisting of software licenses, maintenance on information technology equipment, and media placements. In addition, we have several multiple-layer property catastrophe reinsurance contracts with various reinsurers with terms ranging from one to three years; the minimum commitment under these agreements at December 31, 2023, was $291.5 million. Pursuant to these contracts, $282.8 million, $8.1 million, and $0.6 million will be paid in 2024, 2025, and 2026, respectively.
New Accounting Standards	New Accounting Standards Adopted We did not adopt any new accounting standards during the year ended December 31, 2023. Issued In March 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 is effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2023 (2024 for calendar-year companies). On January 1, 2024, we adopted this standard on the modified retrospective basis. This standard did not have a material impact on our financial condition or results of operations.

Reporting and Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

The following table summarizes changes in our allowance for credit loss exposure on our premiums receivable:


(millions)	2023		2022
Balance at January 1	$	343.3	$	280.4
Increase in allowance1	540.3		471.1
Write-offs2	(514.5)		(408.2)
Balance at December 31	$	369.1	$	343.3

1 Represents the incremental increase in other underwriting expenses.

2 Represents the portion of allowance that is reversed when premiums receivables are written off. Premiums receivable balances are written off once we have exhausted our collection efforts.

Advertising Costs

Total advertising costs, which are expensed as incurred, for the years ended December 31, were:


(millions)	Advertising Costs
2023	$	1,599.7
2022	2,032.5
2021	2,139.5

Property and Equipment

The cost and useful lives for property and equipment at December 31, were:


($ in millions)	2023		2022		Useful Lives
Land	$	102.6	$	123.1	NA
Buildings, improvements, and integrated components	732.9		844.1		7-40 years
Capitalized software	467.5		475.4		3-10 years
Software licenses (internal use)	486.4		427.6		1-6 years
Computer equipment	353.3		318.1		3 years
All other property and equipment	393.2		396.8		3-10 years
Total cost	2,535.9		2,585.1
Accumulated depreciation	(1,655.1)		(1,551.1)
Balance at end of year	$	880.8	$	1,034.0
NA = Not applicable; land is not a depreciable asset.

Equity Based Compensation and Related Tax Benefits

The total compensation expense recognized for equity-based compensation for the years ended December 31, was:


(millions)	2023		2022		2021
Pretax expense	$	121.3	$	122.7	$	100.7
Tax benefit1	17.0		16.0		14.1

1 Differs from statutory rate of 21% due to the expected disallowance of certain executive compensation deductions.

Non cash activity

For the years ended December 31, non-cash activity included the following:


(millions)	2023		2022		2021
Common share dividends1	$	497.9	$	58.5	$	58.5
Preferred share dividends1	0		13.4		13.4
Operating lease liabilities2	114.3		36.2		86.7

1 Declared but unpaid. See Note 14 – Dividends for further discussion.

2 See Note 13 – Leases for further discussion.

Supplemental Cash Flow Information

For the years ended December 31, we paid the following:


(millions)	2023		2022		2021
Income taxes	$	820.8	$	719.0	$	842.4
Interest	264.9		228.9		224.0
Operating lease liabilities	77.2		82.5		88.6

Unrecorded Unconditional Purchase Obligations Disclosure

Aggregate payments on these obligations for the years ended December 31, were as follows:


(millions)	Payments
2024	$	780.0
2025	139.5
2026	68.6
2027	26.5
2028	7.8
Thereafter	2.4
Total	$	1,024.8

Investments (Tables)

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Investment Portfolio by Major Security Type

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 Unrealized Gains		Gross Unrealized Losses		Net Holding Period Gains (Losses)		Fair Value		% of Total Fair Value
December 31, 2023
Available-for-sale securities:
Fixed maturities:
U.S. government obligations	$	37,823.2	$	204.1	$	(1,157.9)	$	0	$	36,869.4	55.9	%
State and local government obligations	2,338.4		2.8		(138.4)		0		2,202.8		3.3
Foreign government obligations	17.3		0		(1.0)		0		16.3		0.1
Corporate debt securities	11,446.0		87.2		(332.3)		(17.2)		11,183.7		16.9
Residential mortgage-backed securities	426.9		0.2		(10.0)		0.1		417.2		0.6
Commercial mortgage-backed securities	4,535.2		2.2		(597.7)		0		3,939.7		6.0
Other asset-backed securities	5,667.2		15.7		(107.1)		(0.4)		5,575.4		8.4
Redeemable preferred stocks	187.7		0		(2.4)		(11.6)		173.7		0.3
Total fixed maturities	62,441.9		312.2		(2,346.8)		(29.1)		60,378.2		91.5
Short-term investments	1,789.9		0		0		0		1,789.9		2.7
Total available-for-sale securities	64,231.8		312.2		(2,346.8)		(29.1)		62,168.1		94.2
Equity securities:
Nonredeemable preferred stocks	977.1		0		0		(75.0)		902.1		1.4
Common equities	706.0		0		0		2,222.4		2,928.4		4.4
Total equity securities	1,683.1		0		0		2,147.4		3,830.5		5.8
Total portfolio1	$	65,914.9	$	312.2	$	(2,346.8)	$	2,118.3	$	65,998.6	100.0	%


($ in millions)	Cost		Gross Unrealized Gains		Gross Unrealized Losses		Net Holding Period Gains (Losses)		Fair Value		% of Total Fair Value
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 portfolio1	$	55,316.0	$	13.9	$	(3,551.5)	$	1,769.9	$	53,548.3	100.0	%

1 At December 31, 2023 and 2022, we had $45.6 million and $34.4 million, respectively, of net unsettled security transactions included in other assets.

The total fair value of the portfolio at December 31, 2023 and 2022, included $4.2 billion and $4.4 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.

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 at December 31:


(millions)	2023		2022
Fixed Maturities:
Corporate debt securities	$	531.3	$	535.4
Residential mortgage-backed securities	323.9		509.6
Other asset-backed securities	13.9		42.0
Redeemable preferred stocks	141.2		134.7
Total hybrid securities	$	1,010.3	$	1,221.7

Composition of Fixed Maturities by Maturity

The composition of fixed maturities by maturity at December 31, 2023, was:


(millions)	Cost		Fair Value
Less than one year	$	9,782.8	$	9,566.2
One to five years	37,948.6		36,796.2
Five to ten years	14,637.1		13,942.5
Ten years or greater	73.4		73.3
Total	$	62,441.9	$	60,378.2

Gross Unrealized Losses by Major Security

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 Fair Value		Gross Unrealized Losses		Less than 12 Months					12 Months or Greater
($ in millions)						No. of Sec.	Fair Value		Gross Unrealized Losses		No. of Sec.	Fair Value		Gross Unrealized Losses
December 31, 2023
U.S. government obligations	147	$	28,225.0	$	(1,157.9)	25	$	11,890.0	$	(100.0)	122	$	16,335.0	$	(1,057.9)
State and local government obligations	324	1,846.2		(138.4)		31	169.9		(0.9)		293	1,676.3		(137.5)
Foreign government obligations	1	16.3		(1.0)		0	0		0		1	16.3		(1.0)
Corporate debt securities	313	6,642.4		(332.3)		26	617.2		(14.7)		287	6,025.2		(317.6)
Residential mortgage-backed securities	39	88.4		(10.0)		2	0.4		0		37	88.0		(10.0)
Commercial mortgage-backed securities	189	3,912.2		(597.7)		1	30.7		(2.5)		188	3,881.5		(595.2)
Other asset-backed securities	207	3,299.1		(107.1)		41	639.4		(1.2)		166	2,659.7		(105.9)
Redeemable preferred stocks	3	32.5		(2.4)		0	0		0		3	32.5		(2.4)
Total fixed maturities	1,223	$	44,062.1	$	(2,346.8)	126	$	13,347.6	$	(119.3)	1,097	$	30,714.5	$	(2,227.5)


	Total No. of Sec.	Total Fair Value		Gross Unrealized Losses		Less than 12 Months					12 Months or Greater
($ in millions)						No. of Sec.	Fair Value		Gross Unrealized Losses		No. of Sec.	Fair Value		Gross Unrealized Losses
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)

Components of Net Realized Gains (Losses)

The components of net realized gains (losses) for the years ended December 31, were:


(millions)	2023		2022		2021
Gross realized gains on security sales
Available-for-sale securities:
U.S. government obligations	$	12.1	$	10.8	$	105.8
State and local government obligations	0		0		51.2

Corporate and other debt securities	1.0		8.7		104.0
Residential mortgage-backed securities	0.9		0.7		0.3
Commercial mortgage-backed securities	0		0		41.9
Other asset-backed securities	0		0.2		1.2
Redeemable preferred stocks	0		0		1.5

Total available-for-sale securities	14.0		20.4		305.9
Equity securities:
Nonredeemable preferred stocks	0.3		17.6		28.0
Common equities	381.0		846.1		369.6
Total equity securities	381.3		863.7		397.6
Subtotal gross realized gains on security sales	395.3		884.1		703.5
Gross realized losses on security sales
Available-for-sale securities:
U.S. government obligations	(64.6)		(433.3)		(52.0)
State and local government obligations	0		(1.0)		(3.4)
Foreign government obligations	0		0		(0.1)
Corporate and other debt securities	(85.7)		(88.3)		(8.3)
Residential mortgage-backed securities	0		0		(1.1)
Commercial mortgage-backed securities	(106.8)		(72.4)		(1.9)
Other asset-backed securities	(5.6)		(4.4)		(0.6)

Short-term investments	(0.4)		(0.4)		0
Total available-for-sale securities	(263.1)		(599.8)		(67.4)
Equity securities:
Nonredeemable preferred stocks	(118.3)		(9.8)		(1.7)
Common equities	(21.8)		(78.0)		(20.1)
Total equity securities	(140.1)		(87.8)		(21.8)
Subtotal gross realized losses on security sales	(403.2)		(687.6)		(89.2)
Net realized gains (losses) on security sales
Available-for-sale securities:
U.S. government obligations	(52.5)		(422.5)		53.8
State and local government obligations	0		(1.0)		47.8
Foreign government obligations	0		0		(0.1)
Corporate and other debt securities	(84.7)		(79.6)		95.7
Residential mortgage-backed securities	0.9		0.7		(0.8)
Commercial mortgage-backed securities	(106.8)		(72.4)		40.0
Other asset-backed securities	(5.6)		(4.2)		0.6
Redeemable preferred stocks	0		0		1.5
Short-term investments	(0.4)		(0.4)		0
Total available-for-sale securities	(249.1)		(579.4)		238.5
Equity securities:
Nonredeemable preferred stocks	(118.0)		7.8		26.3
Common equities	359.2		768.1		349.5
Total equity securities	241.2		775.9		375.8

Subtotal net realized gains (losses) on security sales	(7.9)		196.5		614.3
Other assets
Gain	21.6		0		0
Impairment	(9.0)		(8.6)		(5.0)
Subtotal net realized gains (losses) on other assets	12.6		(8.6)		(5.0)
Net holding period gains (losses)
Hybrid securities	45.4		(82.0)		(7.7)
Equity securities	303.0		(2,018.1)		907.6

Subtotal net holding period gains (losses)	348.4		(2,100.1)		899.9
Total net realized gains (losses) on securities	$	353.1	$	(1,912.2)	$	1,509.2

Components of Equity Realized Gains (Losses)

December 31:


(millions)	2023		2022		2021
Total net gains (losses) recognized during the period on equity securities	$	544.2	$	(1,242.2)	$	1,283.4
Less: Net gains (losses) recognized on equity securities sold during the period	241.2		775.9		375.8
Net holding period gains (losses) recognized during the period on equity securities held at period end	$	303.0	$	(2,018.1)	$	907.6

Components of Net Investment Income

The components of net investment income for the years ended December 31, were:


(millions)	2023		2022		2021
Available-for-sale securities:
Fixed maturities:
U.S. government obligations	$	864.0	$	339.1	$	149.5
State and local government obligations	47.6		39.7		44.1
Foreign government obligations	0.2		0.2		0.1
Corporate debt securities	365.4		288.8		301.1
Residential mortgage-backed securities	28.7		31.6		11.9
Commercial mortgage-backed securities	196.1		190.6		143.0
Other asset-backed securities	192.5		174.6		64.1
Redeemable preferred stocks	11.1		11.4		9.5
Total fixed maturities	1,705.6		1,076.0		723.3
Short-term investments	92.4		53.6		3.1
Total available-for-sale securities	1,798.0		1,129.6		726.4
Equity securities:
Nonredeemable preferred stocks	51.4		70.2		70.3
Common equities	42.4		60.5		64.2
Total equity securities	93.8		130.7		134.5
Investment income	1,891.8		1,260.3		860.9
Investment expenses	(26.2)		(24.3)		(25.5)
Net investment income	$	1,865.6	$	1,236.0	$	835.4

Fair Value (Tables)

12 Months Ended

Dec. 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
December 31, 2023
Fixed maturities:
U.S. government obligations	$	36,869.4	$	0	$	0	$	36,869.4	$	37,823.2
State and local government obligations	0		2,202.8		0		2,202.8		2,338.4
Foreign government obligations	0		16.3		0		16.3		17.3
Corporate debt securities	0		11,180.7		3.0		11,183.7		11,446.0
Subtotal	36,869.4		13,399.8		3.0		50,272.2		51,624.9
Asset-backed securities:
Residential mortgage-backed	0		417.2		0		417.2		426.9
Commercial mortgage-backed	0		3,939.7		0		3,939.7		4,535.2
Other asset-backed	0		5,575.4		0		5,575.4		5,667.2
Subtotal asset-backed securities	0		9,932.3		0		9,932.3		10,629.3
Redeemable preferred stocks:
Financials	0		23.1		0		23.1		24.5
Utilities	0		9.4		0		9.4		10.4
Industrials	0		141.2		0		141.2		152.8
Subtotal redeemable preferred stocks	0		173.7		0		173.7		187.7
Total fixed maturities	36,869.4		23,505.8		3.0		60,378.2		62,441.9
Short-term investments	1,757.0		32.9		0		1,789.9		1,789.9
Total available-for-sale securities	38,626.4		23,538.7		3.0		62,168.1		64,231.8
Equity securities:
Nonredeemable preferred stocks:
Financials	0		802.7		49.2		851.9		922.1
Utilities	0		35.4		0		35.4		40.0
Industrials	0		0		14.8		14.8		15.0
Subtotal nonredeemable preferred stocks	0		838.1		64.0		902.1		977.1
Common equities:
Common stocks	2,885.3		0		22.5		2,907.8		685.4
Other risk investments	0		0		20.6		20.6		20.6
Subtotal common equities	2,885.3		0		43.1		2,928.4		706.0
Total equity securities	2,885.3		838.1		107.1		3,830.5		1,683.1
Total portfolio	$	41,511.7	$	24,376.8	$	110.1	$	65,998.6	$	65,914.9
Debt	$	0	$	6,431.3	$	0	$	6,431.3	$	6,888.6


	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

Summary of Changes in Fair Value Associated With Level 3 Assets

The following tables provide a summary of changes in fair value associated with Level 3 assets for the years ended December 31, 2023 and 2022:


	Level 3 Fair Value
(millions)	Fair Value at Dec. 31, 2022		Calls/ Maturities/ Paydowns/Other		Purchases		Sales		Net Realized (Gain)/Loss on Sales		Change in Valuation		Net Transfers In (Out)		Fair Value at Dec. 31, 2023
Fixed maturities:
Corporate debt securities	$	0	$	0	$	3.0	$	0	$	0	$	0	$	0	$	3.0



Equity securities:
Nonredeemable preferred stocks:
Financials	67.4		(8.1)		1.0		0		0		(11.1)		0		49.2
Industrials	16.4		0		0		0		0		(1.6)		0		14.8
Common equities:
Common stocks	18.3		8.1		0		(10.0)		8.9		(2.8)		0		22.5
Other risk investments	19.8		0.8		0		0		0		0		0		20.6
Total Level 3 securities	$	121.9	$	0.8	$	4.0	$	(10.0)	$	8.9	$	(15.5)	$	0	$	110.1


	Level 3 Fair Value
(millions)	Fair Value at Dec. 31, 2021		Calls/ Maturities/ Paydowns/Other		Purchases		Sales		Net Realized (Gain)/Loss on Sales		Change in Valuation		Net Transfers In (Out)1		Fair Value at Dec. 31, 2022




Equity securities:
Nonredeemable preferred stocks:
Financials	$	76.4	$	0	$	2.5	$	(15.0)	$	(17.2)	$	20.7	$	0	$	67.4
Industrials	34.4		(0.5)		0		0		0		(17.5)		0		16.4
Common equities:
Common stocks	0		0		0		0		0		0		18.3		18.3
Other risk investments	16.9		2.9		0		0		0		0		0		19.8
Total Level 3 securities	$	127.7	$	2.4	$	2.5	$	(15.0)	$	(17.2)	$	3.2	$	18.3	$	121.9

1The security was transferred into Level 3 due to a lack of observable market level inputs.

Summary of Quantitative Information about Level 3 Fair Value Measurements

The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at December 31:

Quantitative Information about Level 3 Fair Value Measurements

($ in millions)

Fair Value at Dec. 31, 2023

Valuation Technique

Unobservable Input

Range of Input Values Increase (Decrease)

Weighted Average Increase (Decrease)

Fixed maturities:

Corporate debt securities

$

3.0

Market comparables

Weighted average market capitalization price change %

0.3% to 7.7%

2.6

%

Equity securities:

Nonredeemable preferred stocks

64.0

Market comparables

Weighted average market capitalization price change %

17.2% to 39.7%

21.7%

Common stocks

22.5

Market comparables

Weighted average market capitalization price change %

(45.8)% to 95.6%

39.7%

Subtotal Level 3 securities

89.5

Pricing exemption securities

20.6

Total Level 3 securities

$

110.1

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)

12 Months Ended

Dec. 31, 2023

Debt Table

Debt at December 31, consisted of:


	2023				2022
(millions)	Carrying Value		Fair Value		Carrying Value		Fair Value
2.45% Senior Notes due 2027 (issued: $500.0, August 2016)	$	498.6	$	468.9	$	498.2	$	457.7
2.50% Senior Notes due 2027 (issued: $500.0, March 2022)	498.1		469.1		497.5		460.3
6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)	297.8		328.7		297.5		326.8
4.00% Senior Notes due 2029 (issued: $550.0, October 2018)	546.9		542.6		546.4		527.8
3.20% Senior Notes due 2030 (issued: $500.0, March 2020)	497.3		462.2		496.9		448.6
3.00% Senior Notes due 2032 (issued: $500.0, March 2022)	496.3		446.0		495.9		438.1
6.25% Senior Notes due 2032 (issued: $400.0, November 2002)	396.7		445.6		396.4		435.4
4.95% Senior Notes due 2033 (issued: $500.0, May 2023)	496.4		513.0		0		0
4.35% Senior Notes due 2044 (issued: $350.0, April 2014)	347.0		314.2		346.9		298.4
3.70% Senior Notes due 2045 (issued: $400.0, January 2015)	395.9		325.1		395.7		310.2
4.125% Senior Notes due 2047 (issued: $850.0, April 2017)	842.3		756.2		842.1		716.2
4.20% Senior Notes due 2048 (issued: $600.0, March 2018)	590.6		534.1		590.4		507.0
3.95% Senior Notes due 2050 (issued: $500.0, March 2020)	491.1		422.3		490.9		404.9
3.70% Senior Notes due 2052 (issued: $500.0, March 2022)	493.6		403.3		493.5		386.5
Total	$	6,888.6	$	6,431.3	$	6,388.3	$	5,717.9

Aggregate Principal Payments on Debt Outstanding

Aggregate required principal payments on debt outstanding at December 31, 2023, were as follows:


(millions)	Payments
2024	$	0
2025	0
2026	0
2027	1,000.0
2028	0
Thereafter	5,950.0
Total	$	6,950.0

Cash Flow Hedging

Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges Included in Accumulated Other Comprehensive Income

The following table shows the original gain (loss) recognized at debt issuance and the unamortized balance at December 31, 2023, on a pretax basis:


(millions)	Unrealized Gain (Loss) at Issuance		Unamortized Balance at December 31, 2023
6 5/8% Senior Notes due 2029	$	(4.2)	$	(1.5)
6.25% Senior Notes due 2032	5.1		2.6
4.35% Senior Notes due 2044	(1.6)		(1.3)
3.70% Senior Notes due 2045	(12.9)		(10.5)
4.125% Senior Notes due 2047	(8.0)		(7.0)

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69E

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-3

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482925/835-30-45-2

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482925/835-30-45-1A

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-3

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482949/835-30-55-8

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480848/942-470-50-3

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-8

Reference 11: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-6

Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-7

Components of Income Tax Provision

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

The components of our income tax provision for the years ended December 31, were as follows:


(millions)	2023		2022		2021
Current tax provision
Federal	$	1,102.5	$	733.2	$	739.5
State	18.7		12.7		20.7
Deferred tax expense (benefit)
Federal	(119.9)		(528.7)		98.6
State	0		(16.6)		0.3
Total income tax provision	$	1,001.3	$	200.6	$	859.1

Reconciliation of Provision (Benefit) for Income Taxes Reported in Consolidated Statements of Income with Tax at Statutory Rate

The provision for income taxes in the consolidated statements of comprehensive income differed from the statutory rate for the years ended December 31, as follows:


	2023				2022				2021
(millions)	Expense (Benefit)		Rate Impact		Expense (Benefit)		Rate Impact		Expense (Benefit)		Rate Impact
Income before income taxes	$	4,903.7			$	922.1			$	4,210.0
Tax at statutory federal rate	$	1,029.8	21	%	$	193.6	21	%	$	884.1	21	%
Tax effect of:
Stock-based compensation	(21.7)		(1)		(18.1)		(2)		(19.4)		(1)
Tax credits	(16.4)		0		(14.8)		(2)		(9.9)		0
Tax-preferenced investment income	(10.2)		0		(12.7)		(1)		(13.2)		0
State income taxes, net of federal taxes	14.7		0		(3.1)		0		16.6		0
Nondeductible compensation expense	9.8		0		11.1		1		8.4		0
Tax-deductible dividends	(4.8)		0		(1.8)		0		(9.4)		0
Goodwill impairment1	0		0		47.2		5		0		0
Other items, net	0.1		0		(0.8)		0		1.9		0
Total income tax provision	$	1,001.3	20	%	$	200.6	22	%	$	859.1	20	%
1 The ARX acquisition did not create goodwill for income tax purposes. As a result, the impairment was not deductible for income tax purposes.

Components of Net Deferred Tax Assets

The following table shows the components of the net deferred tax assets and liabilities at December 31:


(millions)	2023		2022
Federal deferred income tax assets:
Unearned premiums reserve	$	836.0	$	719.2
Net unrealized losses on fixed-maturity securities	427.3		742.9
Loss and loss adjustment expense reserves	292.7		239.9
Non-deductible accruals	238.2		225.9
Software development costs	66.0		37.8
Operating lease liabilities	37.2		28.8
Hedges on forecasted transactions	3.7		3.8
Investment basis differences	0.2		17.0
Other	13.4		12.7
Federal deferred income tax liabilities:
Net holding period gains on equity securities	(451.0)		(387.3)
Deferred acquisition costs	(354.4)		(324.3)
Property and equipment	(88.4)		(97.0)
Operating lease assets	(37.2)		(28.8)
Loss and loss adjustment expense reserve transition adjustment	(15.9)		(24.1)
Intangible assets	(8.7)		(11.1)
Prepaid expenses	(6.2)		(6.5)
Other	(16.9)		(17.4)
Net federal deferred income taxes	936.0		1,131.5
State deferred income tax assets1	39.9		42.2
State deferred income tax liabilities1	0		0
Total	$	975.9	$	1,173.7

1 State deferred assets and liabilities are recorded in other assets and accounts payable, accrued expenses, and other liabilities, respectively, on our consolidated balance sheets.

Loss And Loss Adjustment Expense Reserves (Tables)

12 Months Ended

Dec. 31, 2023

Insurance [Abstract]

Activity in Loss and Loss Adjustment Expense Reserves

Activity in the loss and LAE reserves is summarized as follows:


(millions)	2023		2022		2021
Balance at January 1	$	30,359.3	$	26,164.1	$	20,265.8
Less reinsurance recoverables on unpaid losses	5,559.2		4,733.6		3,798.2
Net balance at January 1	24,800.1		21,430.5		16,467.6
Net loss and loss adjustment expense reserves acquired1	0		0		729.2
Total beginning reserves	24,800.1		21,430.5		17,196.8
Incurred related to:
Current year	44,560.6		38,209.0		33,632.3
Prior years	1,094.0		(86.3)		(4.7)
Total incurred	45,654.6		38,122.7		33,627.6
Paid related to:
Current year	26,874.3		23,542.9		20,561.1
Prior years	13,980.2		11,210.2		8,832.8
Total paid	40,854.5		34,753.1		29,393.9
Net balance at December 31	29,600.2		24,800.1		21,430.5
Plus reinsurance recoverables on unpaid losses	4,789.0		5,559.2		4,733.6
Balance at December 31	$	34,389.2	$	30,359.3	$	26,164.1

1 Net reserves acquired in Protective Insurance acquisition.

Short-duration Insurance Contracts, Claims Development

Only 2023 is audited; all prior years are considered required supplementary information and, therefore, are unaudited. Expected development on our case reserves is excluded from the IBNR reserves on our vehicle businesses, as discussed above. For the Property business and the Commercial Lines other business, the IBNR reserves include expected case development based on the methodology used in establishing the case reserves for that segment. The cumulative number of incurred claims are based on accident coverages (e.g., bodily injury, collision, comprehensive, personal injury protection, property damage) related to opened claims. Coverage counts related to claims closed without payment are excluded from the cumulative number of incurred claims.


Personal Lines - Agency - Liability
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	5,885.0	$	5,886.9	$	5,918.2	$	5,959.9	$	5,879.2	$	0	916,543
2020			5,433.8		5,405.4		5,385.7		5,458.1		142.8		757,024
2021					6,716.4		6,861.8		6,936.4		174.2		885,607
2022							7,076.9		7,301.5		402.8		838,763
2023									8,615.9		1,715.2		883,430
							Total		$	34,191.1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	2,715.2	$	4,533.2	$	5,272.8	$	5,626.6	$	5,779.3
2020			2,383.0		4,112.2		4,796.8		5,122.0
2021					2,855.4		5,239.4		6,183.1
2022							3,018.8		5,564.1
2023									3,526.5
							Total		$	26,175.0
	All outstanding liabilities before 2019, net of reinsurance1								92.9
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	8,109.0

1 Required supplementary information (unaudited)


Personal Lines - Agency - Physical Damage
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	3,277.9	$	3,254.7	$	3,261.1	$	3,259.0	$	3,268.1	$	0.4	1,879,041
2020			3,328.5		3,319.8		3,327.3		3,323.3		(8.4)		1,785,036
2021					4,708.3		4,624.3		4,628.5		8.9		2,105,540
2022							5,429.4		5,544.6		(13.3)		2,031,717
2023									5,774.5		(298.0)		2,091,830
							Total		$	22,539.0
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	3,242.5	$	3,259.2	$	3,255.9	$	3,260.9	$	3,263.7
2020			3,250.1		3,322.5		3,323.0		3,328.0
2021					4,438.1		4,620.9		4,611.5
2022							5,176.2		5,542.0
2023									5,584.2
							Total		$	22,329.4
	All outstanding liabilities before 2019, net of reinsurance1								3.7
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	213.3

1 Required supplementary information (unaudited)


Personal Lines - Direct - Liability
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	5,756.5	$	5,811.7	$	5,837.9	$	5,870.0	$	5,802.1	$	0.1	957,826
2020			5,356.9		5,322.7		5,301.5		5,343.1		126.4		789,952
2021					6,964.7		7,180.3		7,244.1		164.5		981,424
2022							7,563.4		7,869.6		398.5		970,145
2023									9,627.9		1,763.6		1,080,475
							Total		$	35,886.8
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	2,630.3	$	4,452.5	$	5,218.8	$	5,568.8	$	5,716.3
2020			2,301.3		4,018.7		4,721.4		5,035.9
2021					2,915.0		5,460.5		6,487.9
2022							3,131.8		5,982.6
2023									3,925.5
							Total		$	27,148.2
	All outstanding liabilities before 2019, net of reinsurance1								79.4
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	8,818.0

1 Required supplementary information (unaudited)


Personal Lines - Direct - Physical Damage
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	3,787.9	$	3,737.8	$	3,749.6	$	3,747.9	$	3,757.8	$	0.3	2,272,383
2020			3,775.6		3,753.3		3,765.9		3,762.0		(9.7)		2,139,045
2021					5,752.3		5,568.2		5,572.9		3.6		2,602,359
2022							6,613.3		6,724.2		(27.3)		2,606,698
2023									7,577.9		(459.8)		2,851,047
							Total		$	27,394.8
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	3,782.6	$	3,751.3	$	3,746.8	$	3,750.9	$	3,753.9
2020			3,720.0		3,765.9		3,762.2		3,767.4
2021					5,421.9		5,578.7		5,559.6
2022							6,325.7		6,731.9
2023									7,361.7
							Total		$	27,174.5
	All outstanding liabilities before 2019, net of reinsurance1								2.8
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	223.1

1 Required supplementary information (unaudited)


Commercial Lines - Liability
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	2,301.1	$	2,370.9	$	2,426.3	$	2,434.4	$	2,429.9	$	7.6	136,213
2020			2,335.7		2,388.8		2,418.9		2,436.5		58.6		117,614
2021					3,446.6		3,527.3		3,573.7		134.7		156,829
2022							4,526.1		4,834.5		406.2		180,500
2023									5,455.8		1,299.6		184,840
							Total		$	18,730.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	474.8	$	1,184.4	$	1,684.5	$	2,037.5	$	2,250.0
2020			440.8		1,110.4		1,628.9		2,043.5
2021					573.6		1,545.9		2,414.3
2022							749.2		2,086.4
2023									847.6
							Total		$	9,641.8
	All outstanding liabilities before 2019, net of reinsurance1								103.2
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	9,191.8

1 Required supplementary information (unaudited)


Commercial Lines - Physical Damage
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	633.1	$	628.3	$	626.6	$	625.9	$	626.4	$	0	99,508
2020			631.8		624.9		622.0		624.8		2.9		99,588
2021					920.9		909.8		910.1		3.6		121,900
2022							1,314.9		1,330.3		0.7		147,146
2023									1,351.8		(6.5)		164,859
							Total		$	4,843.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	561.1	$	625.1	$	624.8	$	625.3	$	625.4
2020			540.6		621.8		620.4		620.5
2021					764.2		903.1		901.5
2022							1,114.0		1,315.0
2023									1,184.4
							Total		$	4,646.8
	All outstanding liabilities before 2019, net of reinsurance1								0.8
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	197.4

1 Required supplementary information (unaudited)


Commercial Lines - Other
($ in millions)																					As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance																					December 31, 2023
	For the years ended December 31,																				Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20141		20151		20161		20171		20181		20191		20201		20211		20221		2023
2014	$	74.9	$	70.0	$	68.3	$	70.5	$	70.7	$	69.4	$	70.7	$	70.9	$	70.4	$	70.4	$	3.2	9,226
2015			51.2		45.4		46.1		48.3		47.0		44.8		45.1		44.6		44.8		3.4		9,527
2016					51.8		43.3		41.0		41.5		40.2		40.1		40.0		40.4		3.1		7,648
2017							62.6		54.6		51.1		48.8		46.2		48.0		55.1		10.2		17,675
2018									81.5		81.3		76.7		77.0		76.5		81.7		10.0		15,475
2019											80.7		83.1		85.4		88.3		87.7		10.3		10,709
2020													75.0		80.7		81.9		82.9		14.0		9,505
2021															84.1		87.3		88.8		24.4		9,367
2022																	84.0		80.9		26.3		7,660
2023																			85.0		45.2		6,795
																	Total		$	717.7
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20141		20151		20161		20171		20181		20191		20201		20211		20221		2023
2014	$	18.6	$	33.9	$	44.3	$	51.1	$	56.9	$	59.0	$	61.1	$	64.2	$	65.0	$	65.5
2015			6.5		18.1		26.5		30.9		33.9		36.1		37.1		37.8		38.7
2016					8.5		20.9		27.0		30.6		32.7		33.8		35.0		35.5
2017							9.6		24.4		30.8		34.5		36.9		39.7		41.6
2018									17.6		39.6		49.5		56.7		61.7		65.2
2019											20.0		42.4		56.0		64.6		70.8
2020													15.8		38.6		52.2		59.6
2021															16.9		39.6		52.4
2022																	18.4		39.7
2023																			18.4
																	Total		$	487.4
					All outstanding liabilities before 2014, net of reinsurance1														30.2
					Liabilities for claims and claim adjustment expenses, net of reinsurance														$	260.5

1 Required supplementary information (unaudited)


Property Business
($ in millions)											As of
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance											December 31, 2023
	For the years ended December 31,										Total of IBNR Liabilities Plus Expected Development on Reported Claims		Cumulative Number of Incurred Claim Counts
Accident Year	20191		20201		20211		20221		2023
2019	$	971.7	$	965.2	$	962.8	$	965.8	$	964.8	$	9.0	73,051
2020			1,223.5		1,246.8		1,260.9		1,256.0		1.5		88,736
2021					1,539.6		1,516.3		1,503.2		23.6		89,864
2022							1,664.6		1,622.0		77.0		89,348
2023									1,582.5		392.4		75,812
							Total		$	6,928.5
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance
	For the years ended December 31,
Accident Year	20191		20201		20211		20221		2023
2019	$	708.0	$	930.4	$	950.5	$	959.3	$	962.2
2020			832.5		1,141.2		1,210.7		1,237.2
2021					1,035.4		1,374.5		1,444.0
2022							1,041.7		1,469.5
2023									1,078.3
							Total		$	6,191.2
	All outstanding liabilities before 2019, net of reinsurance1								7.4
	Liabilities for claims and claim adjustment expenses, net of reinsurance								$	744.7

1 Required supplementary information (unaudited)

Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability

The following table reconciles the net incurred and paid claims development tables to the liability for claims and claim adjustment expenses:


(millions)	2023		2022
Net outstanding liabilities
Personal Lines
Agency, Liability	$	8,109.0	$	6,791.2
Agency, Physical Damage	213.3		261.5
Direct, Liability	8,818.0		7,187.2
Direct, Physical Damage	223.1		284.7
Commercial Lines
Liability	9,191.8		7,177.0
Physical Damage	197.4		211.2
Other	260.5		242.5
Property	744.7		839.7
Other business	88.7		108.9
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	27,846.5		23,103.9
Reinsurance recoverables on unpaid claims
Personal Lines
Agency, Liability	875.1		894.1
Agency, Physical Damage	0		0
Direct, Liability	1,471.3		1,485.4
Direct, Physical Damage	0		0
Commercial Lines
Liability	1,077.7		1,273.7
Physical Damage	1.4		0.5
Other	216.0		204.6
Property	631.4		1,068.1
Other business	475.1		559.0
Total reinsurance recoverables on unpaid claims	4,748.0		5,485.4
Unallocated claims adjustment expense related to:
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	1,753.7		1,696.2
Reinsurance recoverables on unpaid claims	41.0		73.8
Total gross liability for unpaid claims and claim adjustment expense	$	34,389.2	$	30,359.3

Short-duration Insurance Contracts, Schedule of Historical Claims Duration

The following table shows the average historical claims duration as of December 31, 2023:


(Required Supplementary Information - Unaudited)
Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance	Years
	1	2	3	4	5
Personal Lines
Agency, Liability	42.4%	33.1%	13.0%	6.0%	2.6%
Agency, Physical Damage	96.2	3.8	(0.1)	0.2	0.1
Direct, Liability	41.5	34.0	13.6	6.0	2.5
Direct, Physical Damage	97.1	2.9	(0.2)	0.1	0.1
Commercial Lines
Liability	16.5	27.8	22.4	15.8	8.7
Physical Damage	86.0	13.9	(0.2)	0	0
Other	20.9	26.1	14.7	9.0	6.4
Property	67.8	24.3	4.3	1.6	0.3

Reinsurance (Tables)

12 Months Ended

Dec. 31, 2023

Reinsurance Disclosures [Abstract]

Effect of Reinsurance on Premiums Written and Earned

The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows:


	2023				2022				2021
(millions)	Written		Earned		Written		Earned		Written		Earned
Direct premiums	$	62,721.2	$	59,881.1	$	52,335.6	$	50,650.2	$	48,129.6	$	46,018.6
Ceded premiums:
Regulated	(535.0)		(545.3)		(621.5)		(674.8)		(674.5)		(650.2)
Non-Regulated	(636.0)		(671.4)		(633.0)		(734.2)		(1,049.9)		(999.7)
Total ceded premiums	(1,171.0)		(1,216.7)		(1,254.5)		(1,409.0)		(1,724.4)		(1,649.9)
Net premiums	$	61,550.2	$	58,664.4	$	51,081.1	$	49,241.2	$	46,405.2	$	44,368.7

Prepaid Reinsurance Premiums and Reinsurance Recoverables

Our reinsurance recoverables and prepaid reinsurance premiums were comprised of the following at December 31:


	Reinsurance Recoverables								Prepaid Reinsurance Premiums
($ in millions)	2023				2022				2023				2022
Regulated:
MCCA	$	2,272.1	45	%	$	2,332.3	40	%	$	40.2	16	%	$	26.4	9	%
CAIP	539.1		10		626.8		11		0		0		50.4		17
FHCF	306.6		6		437.3		7		0		0		0		0
NCRF	184.7		4		143.2		2		74.6		30		54.5		18
NFIP	10.7		0		215.4		4		66.4		27		60.1		20
Other	3.8		0		2.9		0		1.3		0		1.5		1
Total Regulated	3,317.0		65		3,757.9		64		182.5		73		192.9		65
Non-Regulated:
Commercial Lines	1,385.7		27		1,544.3		27		56.3		23		91.0		31
Property	381.2		8		524.4		9		11.0		4		11.6		4
Other	10.0		0		5.5		0		0		0		0		0
Total Non-Regulated	1,776.9		35		2,074.2		36		67.3		27		102.6		35
Total	$	5,093.9	100	%	$	5,832.1	100	%	$	249.8	100	%	$	295.5	100	%

Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Employee Benefit Plans Disclosures [Abstract]

Amounts Charged to Income for Employees Incentive Compensation Plans

The amounts charged to expense for incentive compensation plans for the years ended December 31, were:


	2023				2022				2021
(millions)	Pretax		After Tax		Pretax		After Tax		Pretax		After Tax
Non-equity incentive plans – cash	$	897.3	$	708.9	$	380.8	$	300.8	$	619.3	$	489.2
Equity incentive plans1	121.3		104.3		122.7		106.7		100.7		86.6
1 After-tax amounts differ from the statutory rate of 21% due to the expected disallowance of certain executive compensation deductions.

Share Based Compensation Performance Share Awards Targets

The following shows the performance measurement criteria for our performance-based equity awards outstanding at December 31, 2023:


Performance Measurement	Year(s) of Grant	Vesting range (as a percentage of target)
Growth of our personal auto and commercial auto businesses, both compared to its respective market	2023	0-250%
Growth of our personal auto and commercial auto businesses and homeowners multi-peril business, each compared to its respective market	2021-2022	0-250%
Investment results relative to peer group	2021-2023	0-200%

Summary of Restricted Stock Activity

A summary of all employee restricted equity award activity during the years ended December 31, follows:


	2023			2022			2021
Restricted Equity Awards	Number of Shares1	Weighted Average Grant Date Fair Value		Number of Shares1	Weighted Average Grant Date Fair Value		Number of Shares1	Weighted Average Grant Date Fair Value
Beginning of year	3,198,150	$	81.71	3,539,022	$	67.24	3,570,271	$	57.68
Add (deduct):
Granted2	1,080,658	110.93		1,154,838	96.54		1,476,802	70.11
Vested	(1,338,466)	63.10		(1,378,070)	57.79		(1,452,353)	46.88
Forfeited	(46,600)	84.86		(117,640)	72.44		(55,698)	60.81
End of year3,4	2,893,742	$	101.18	3,198,150	$	81.71	3,539,022	$	67.24

1 Includes restricted stock units. All performance-based awards are included at their target amounts.

2 We reinvest dividend equivalents on restricted stock units. For 2023, 2022, and 2021, the number of units “granted” shown in the table above includes 36,656, 44,327, and 237,582 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0, since the dividends were factored into the grant date fair value of the original grant.

3 At December 31, 2023, the number of shares included 557,119 performance-based units at their target amounts. We expect 1,204,918 units to vest based upon our current estimates of the likelihood of achieving the predetermined performance measures applicable to each award.

4 At December 31, 2023, the total unrecognized compensation cost related to unvested equity awards was $93.3 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into our consolidated statements of comprehensive income over the weighted average vesting period of 2.2 years.

A summary of all directors’ restricted stock activity during the years ended December 31, follows:


	2023			2022			2021
Restricted Stock	Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value		Number of Shares	Weighted Average Grant Date Fair Value
Beginning of year	30,439	$	109.75	29,206	$	105.16	39,403	$	74.77
Add (deduct):
Granted	25,075	133.43		30,439	109.75		29,206	105.16
Vested	(30,439)	109.75		(29,206)	105.16		(39,403)	74.77
End of year1	25,075	$	133.43	30,439	$	109.75	29,206	$	105.16

1 At December 31, 2023, 2022, and 2021, the remaining unrecognized compensation cost related to restricted stock awards was $1.0 million, $1.0 million, and $0.9 million, respectively.

Assets Held in Deferral Plan Irrevocable Grantor Trust Account

The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31:


(millions)	2023		2022
Progressive common shares1	$	118.5	$	131.0
Other investment funds2	165.1		150.4
Total	$	283.6	$	281.4

1 Included 1.6 million and 2.0 million common shares as of December 31, 2023 and 2022, respectively, to be distributed in common shares, and are reported at grant date fair value.

2 Amount is included in other assets on our consolidated balance sheets.

Segment Information (Tables)

12 Months Ended

Dec. 31, 2023

Dec. 31, 2019

Segment Reporting [Abstract]

Reconciliation of Revenue and Operating Income from Segments to Consolidated

Following are the operating results for the years ended December 31:


	2023				2022				2021
(millions)	Revenues		Pretax Profit (Loss)		Revenues		Pretax Profit (Loss)		Revenues		Pretax Profit (Loss)
Personal Lines
Agency	$	21,198.2	$	1,029.2	$	17,744.7	$	734.1	$	16,881.0	$	992.1
Direct	25,015.1		1,828.2		20,135.5		769.4		18,492.3		619.2
Total Personal Lines1	46,213.3		2,857.4		37,880.2		1,503.5		35,373.3		1,611.3
Commercial Lines	9,898.7		123.0		9,088.3		810.3		6,945.2		767.8
Property2	2,551.4		28.1		2,270.0		(238.4)		2,042.5		(312.3)
Other indemnity3	1.0		(16.2)		2.7		(11.4)		7.7		(1.4)
Total underwriting operations	58,664.4		2,992.3		49,241.2		2,064.0		44,368.7		2,065.4
Fees and other revenues4	889.1		NA		722.1		NA		691.8		NA
Service businesses	310.1		(38.9)		299.3		2.6		271.4		18.6
Investments5	2,244.9		2,218.7		(651.9)		(676.2)		2,370.1		2,344.6
Interest expense	NA		(268.4)		NA		(243.5)		NA		(218.6)
Property - Goodwill impairment2	NA		0		NA		(224.8)		NA		0
Consolidated total	$	62,108.5	$	4,903.7	$	49,610.7	$	922.1	$	47,702.0	$	4,210.0

NA = Not applicable

1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned in 2023, 2022, and 2021; 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 The total pretax loss, including goodwill impairment, for the Property segment was $463.2 million for 2022.

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 years ended December 31:


	2023			2022			2021
	Underwriting Margin		Combined Ratio	Underwriting Margin		Combined Ratio	Underwriting Margin		Combined Ratio
Personal Lines
Agency	4.9	%	95.1	4.1	%	95.9	5.9	%	94.1
Direct	7.3		92.7	3.8		96.2	3.4		96.6
Total Personal Lines	6.2		93.8	4.0		96.0	4.6		95.4
Commercial Lines	1.2		98.8	8.9		91.1	11.1		88.9
Property	1.1		98.9	(10.5)		110.5	(15.3)		115.3
Total underwriting operations	5.1		94.9	4.2		95.8	4.7		95.3

Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Dec. 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, for the years ended December 31, were as follows:


							Components of Changes in Accumulated Other Comprehensive Income (after tax)
(millions)	Pretax total accumulated other comprehensive income (loss)		Total tax (provision) benefit		After tax total accumulated other comprehensive income (loss)		Total net unrealized gains (losses) on securities		Net unrealized gains (losses) on forecasted transactions		Foreign currency translation adjustment
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	1,256.1		(265.6)		990.5		990.5		0		0
Foreign currency translation adjustment	0.4		(0.1)		0.3		0		0		0.3
Total other comprehensive income (loss) before reclassifications	1,256.5		(265.7)		990.8		990.5		0		0.3
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net realized gains (losses) on securities	(246.9)		51.9		(195.0)		(195.0)		0		0
Interest expense	(0.6)		0.1		(0.5)		0		(0.5)		0
Total reclassification adjustment for amounts realized in net income	(247.5)		52.0		(195.5)		(195.0)		(0.5)		0
Total other comprehensive income (loss)	1,504.0		(317.7)		1,186.3		1,185.5		0.5		0.3
Balance at December 31, 2023	$	(2,052.9)	$	437.2	$	(1,615.7)	$	(1,600.8)	$	(14.0)	$	(0.9)


							Components of Changes in Accumulated Other Comprehensive Income (after tax)
(millions)	Pretax total accumulated other comprehensive income (loss)		Total tax (provision) benefit		After tax total accumulated other comprehensive income (loss)		Total net unrealized gains (losses) on securities		Net unrealized gains (losses) on forecasted transactions		Foreign currency translation adjustment
Balance at December 31, 2021	$	52.3	$	(11.6)	$	40.7	$	56.2	$	(14.9)	$	(0.6)
Other comprehensive income (loss) before reclassifications:
Investment securities	(4,168.4)		878.7		(3,289.7)		(3,289.7)		0		0
Foreign currency translation adjustment	(0.7)		0.1		(0.6)		0		0		(0.6)
Total other comprehensive income (loss) before reclassifications	(4,169.1)		878.8		(3,290.3)		(3,289.7)		0		(0.6)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net realized gains (losses) on securities	(559.4)		112.2		(447.2)		(447.2)		0		0
Interest expense	(0.5)		0.1		(0.4)		0		(0.4)		0
Total reclassification adjustment for amounts realized in net income	(559.9)		112.3		(447.6)		(447.2)		(0.4)		0
Total other comprehensive income (loss)	(3,609.2)		766.5		(2,842.7)		(2,842.5)		0.4		(0.6)
Balance at December 31, 2022	$	(3,556.9)	$	754.9	$	(2,802.0)	$	(2,786.3)	$	(14.5)	$	(1.2)


							Components of Changes in Accumulated Other Comprehensive Income (after tax)
(millions)	Pretax total accumulated other comprehensive income (loss)		Total tax (provision) benefit		After tax total accumulated other comprehensive income (loss)		Total net unrealized gains (losses) on securities		Net unrealized gains (losses) on forecasted transactions		Foreign currency translation adjustment
Balance at December 31, 2020	$	1,187.4	$	(255.7)	$	931.7	$	947.3	$	(15.6)	$	0
Other comprehensive income (loss) before reclassifications:
Investment securities	(892.4)		193.0		(699.4)		(699.4)		0		0
Foreign currency translation adjustment	(0.8)		0.2		(0.6)		0		0		(0.6)
Total other comprehensive income (loss) before reclassifications	(893.2)		193.2		(700.0)		(699.4)		0		(0.6)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net realized gains (losses) on securities	242.8		(51.1)		191.7		191.7		0		0
Interest expense	(0.9)		0.2		(0.7)		0		(0.7)		0
Total reclassification adjustment for amounts realized in net income	241.9		(50.9)		191.0		191.7		(0.7)		0
Total other comprehensive income (loss)	(1,135.1)		244.1		(891.0)		(891.1)		0.7		(0.6)
Balance at December 31, 2021	$	52.3	$	(11.6)	$	40.7	$	56.2	$	(14.9)	$	(0.6)

(Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Operating Assets and Liabilities, Weighted-Average Remaining Term and Discount Rate, Lessee

The following table summarizes the carrying amounts of our operating leased assets and liabilities at December 31, along with key inputs used to discount our lease liabilities:


(millions)	2023			2022
Operating lease assets	$	172.5		$	130.5
Operating lease liabilities	$	177.2		$	137.2
Weighted-average remaining term	3.2 years			2.5 years
Weighted-average discount rate	5.1		%	2.0		%

Minimum Commitments under Noncancelable Operating Lease Agreements

At December 31, 2023, the following table shows our operating lease liabilities, on an undiscounted basis for the periods indicated:


(millions)	Commitments
2024	$	74.0
2025	54.6
2026	37.6
2027	15.8
2028	6.0
Thereafter	4.8
Total	192.8
Interest	(15.6)
Present value of lease liabilities	$	177.2

Lease, Cost

The operating lease expense for the years ended December 31, was as follows:


(millions)	Expense
2023	$	94.4
2022	89.1
2021	90.4

Dividends (Tables)

12 Months Ended

Dec. 31, 2023

Dividends [Abstract]

Dividends

Following is a summary of our common and preferred share dividends that were declared and/or paid in the last three years:


(millions, except per share amounts)		Amount
Declared	Payable	Per Share		Accrued/Paid1
Common - Annual-Variable Dividends:
December 2023	January 2024	$	0.75	$	439.3
December 2021	December 2021	1.50		876.5
December 2020	January 2021	4.50		2,635.9

Common - Quarterly Dividends:
December 2023	January 2024	0.10		58.6
August 2023	October 2023	0.10		58.5
May 2023	July 2023	0.10		58.5
March 2023	April 2023	0.10		58.5
December 2022	January 2023	0.10		58.5
August 2022	October 2022	0.10		58.5
May 2022	July 2022	0.10		58.5
March 2022	April 2022	0.10		58.5
December 2021	January 2022	0.10		58.5
August 2021	October 2021	0.10		58.5
May 2021	July 2021	0.10		58.5
March 2021	April 2021	0.10		58.5
December 2020	January 2021	0.10		58.6

Preferred Dividends:
October 2023	December 2023	20.753157		10.4
August 2023	September 2023	20.67700		10.3
May 2023	June 2023	18.92463		9.5
December 2022	March 2023	26.875		13.4
August 2022	September 2022	26.875		13.4
December 2021	March 2022	26.875		13.4
August 2021	September 2021	26.875		13.4
December 2020	March 2021	26.875		13.4

1 The 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 our consolidated balance sheets until paid.

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties Summary Of Investments - Other than Investments In Related Parties (Detail) $ in Millions	Dec. 31, 2023 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	$ 65,914.9
Fair Value	65,998.6
Amount At Which Shown In The Balance Sheet	65,998.6
Fixed maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	62,441.9
Fair Value	60,378.2
Amount At Which Shown In The Balance Sheet	60,378.2
Fixed maturities \| US Government Agencies and Authorities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	37,823.2
Fair Value	36,869.4
Amount At Which Shown In The Balance Sheet	36,869.4
Fixed maturities \| State and local government obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,338.4
Fair Value	2,202.8
Amount At Which Shown In The Balance Sheet	2,202.8
Fixed maturities \| Foreign government obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	17.3
Fair Value	16.3
Amount At Which Shown In The Balance Sheet	16.3
Fixed maturities \| Public Utilities, Bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,378.5
Fair Value	1,352.3
Amount At Which Shown In The Balance Sheet	1,352.3
Fixed maturities \| Corporate And Other Debt Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	10,067.5
Fair Value	9,831.4
Amount At Which Shown In The Balance Sheet	9,831.4
Fixed maturities \| Asset-backed Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	10,629.3
Fair Value	9,932.3
Amount At Which Shown In The Balance Sheet	9,932.3
Fixed maturities \| Redeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	187.7
Fair Value	173.7
Amount At Which Shown In The Balance Sheet	173.7
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,683.1
Fair Value	3,830.5
Amount At Which Shown In The Balance Sheet	3,830.5
Equity securities \| Utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	39.0
Fair Value	97.5
Amount At Which Shown In The Balance Sheet	97.5
Equity securities \| Financials
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	130.8
Fair Value	480.0
Amount At Which Shown In The Balance Sheet	480.0
Equity securities \| Industrials
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	536.2
Fair Value	2,350.9
Amount At Which Shown In The Balance Sheet	2,350.9
Equity securities \| Nonredeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	977.1
Fair Value	902.1
Amount At Which Shown In The Balance Sheet	902.1
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,789.9
Fair Value	1,789.9
Amount At Which Shown In The Balance Sheet	$ 1,789.9

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Comprehensive Income (Parent Company) (Detail) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Revenues

Total revenues

$ 62,108.5

$ 49,610.7

$ 47,702.0

Expenses

Interest expense

268.4

243.5

218.6

Total expenses

57,204.8

48,688.6

43,492.0

Income before income taxes

4,903.7

922.1

4,210.0

Benefit for income taxes

(1,001.3)

(200.6)

(859.1)

3,902.4

721.5

3,350.9

Comprehensive income (loss)

1,186.3

(2,842.7)

(891.0)

5,088.7

(2,121.2)

2,459.9

Parent Company

Revenues

Dividends from subsidiaries

399.0

540.5

2,847.0

Undistributed income from subsidiaries

3,572.3

325.0

674.9

Equity in net income of subsidiaries

3,971.3

865.5

3,521.9

Intercompany investment income

204.3

92.7

4.5

Total revenues

4,175.6

958.2

3,526.4

Expenses

Interest expense

270.0

246.0

220.0

Deferred compensation

^[1]

20.4

25.3

8.8

Other operating costs and expenses

7.6

6.8

Total expenses

298.0

278.1

235.6

Income before income taxes

3,877.6

680.1

3,290.8

Benefit for income taxes

24.8

41.4

60.1

3,902.4

721.5

3,350.9

Comprehensive income (loss)

1,186.3

(2,842.7)

(891.0)

$ 5,088.7

$ (2,121.2)

$ 2,459.9

[1]	See Note 4 – Employee Benefit Plans in these condensed financial statements.

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Balance Sheets (Parent Company) (Detail) - USD ($)
$ / shares in Units, $ in Millions

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Dec. 31, 2020

Dec. 31, 2018

Assets

Other assets

$ 1,348.5

$ 1,158.9

Total assets

88,690.8

75,465.0

Accounts payable, accrued expenses, and other liabilities

^[1]

7,002.2

5,532.8

Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)

^[2]

6,888.6

6,388.3

Total liabilities

68,413.7

59,574.0

493.9

Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 212.3 and 212.7)

585.3

584.9

Paid-in capital

2,013.1

1,893.0

Retained earnings

18,800.5

15,721.2

Total accumulated other comprehensive income (loss)

(1,615.7)

(2,802.0)

$ 40.7

$ 931.7

Total shareholders’ equity

20,277.1

15,891.0

$ 18,231.6

Total liabilities and shareholders’ equity

$ 88,690.8

$ 75,465.0

Common Shares, par value (USD per share)

$ 1.00

Common Shares, authorized (shares)

900,000,000.0

Common Shares, issued (shares)

797,600,000

Treasury Stock, Common, Shares

212,300,000

212,700,000

Series B Preferred Stock

Preferred Stock, Liquidation Preference Per Share

$ 1,000

Preferred shares, issued (in shares)

500,000

Serial Preferred Stock

Serial Preferred Stock | Series B Preferred Stock

20,000,000.0

Preferred stock, par value

500,000

$ 0

Preferred Stock, Liquidation Preference Per Share

$ 1,000

Preferred shares, issued (in shares)

500,000

Preferred Stock, Shares Outstanding (in shares)

500,000

Parent Company

Assets

Investment in affiliate

$ 5.0

Investment in subsidiaries

23,409.9

17,911.8

Receivable from investment subsidiary

3,791.4

4,098.7

Intercompany receivable

886.7

466.2

Net federal deferred income taxes

65.6

64.3

Other assets

165.4

150.6

Total assets

28,324.0

22,696.6

Accounts payable, accrued expenses, and other liabilities

1,158.3

417.3

Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)

^[3]

6,888.6

6,388.3

Total liabilities

8,046.9

6,805.6

^[4]

493.9

Common shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 212.3 and 212.7)

585.3

584.9

Paid-in capital

2,013.1

1,893.0

Retained earnings

18,800.5

15,721.2

Total accumulated other comprehensive income (loss)

(1,615.7)

(2,802.0)

Total shareholders’ equity

20,277.1

15,891.0

Total liabilities and shareholders’ equity

$ 28,324.0

$ 22,696.6

Common Shares, par value (USD per share)

$ 1.00

Common Shares, authorized (shares)

900,000,000.0

Common Shares, issued (shares)

797,600,000

Treasury Stock, Common, Shares

212,300,000

212,700,000

Parent Company | Serial Preferred Stock

Parent Company | Serial Preferred Stock | Series B Preferred Stock

20,000,000.0

Preferred stock, par value

500,000

$ 0

Preferred Stock, Liquidation Preference Per Share

$ 1,000

Preferred shares, issued (in shares)

500,000

Preferred Stock, Shares Outstanding (in shares)

500,000

[1]	See Note 1 – Reporting and Accounting Policies, Commitments and Contingencies and Note 12 – Litigation for further discussion.
[2]	Consists of long-term debt. See Note 4 – Debt for further discussion.
[3]	Consists of long-term debt. See Note 4 – Debt in our Annual Report for further discussion.
[4]	See Note 7 – Subsequent Event in these condensed financial statements.

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Cash Flows (Parent Company) (Detail) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Cash Flows From Operating Activities:

Adjustments to reconcile net income to net cash provided by operating activities:

$ 3,902.4

$ 721.5

$ 3,350.9

121.3

122.7

100.7

Accounts payable, accrued expenses, and other liabilities

699.6

199.5

399.7

Income taxes

181.2

(515.3)

(86.0)

Net cash provided by operating activities

(255.0)

(104.7)

26.1

10,643.3

6,848.8

7,761.7

Cash Flows From Investing Activities:

Acquisition of Protective

0.0

(313.2)

Net Cash Provided by (Used in) Investing Activities

(10,842.6)

(7,956.2)

(3,119.8)

Cash Flows From Financing Activities:

Dividends paid to common shareholders

^[1]

(234.0)

(3,746.5)

Dividends paid to preferred shareholders

^[1]

(43.6)

(26.8)

Acquisition of treasury shares for restricted stock tax liabilities

(95.0)

(76.7)

(67.2)

Acquisition of treasury shares acquired in open market

(45.7)

(22.3)

(155.8)

Net proceeds from debt issuance

496.3

1,486.0

0.0

Repayments of Long-term Debt

0.0

(500.0)

Net cash provided by (used in) financing activities

78.0

1,126.2

(4,516.3)

Change in cash, cash equivalents, and restricted cash

(121.3)

18.8

125.6

Cash, cash equivalents, restricted cash, and restricted cash equivalents - beginning of year

220.9

202.1

76.5

Cash, cash equivalents, restricted cash, and restricted cash equivalents - end of year

99.6

220.9

202.1

Parent Company

Cash Flows From Operating Activities:

Adjustments to reconcile net income to net cash provided by operating activities:

3,902.4

721.5

3,350.9

Undistributed income from subsidiaries

(3,572.3)

(325.0)

(674.9)

3.3

3.2

3.1

Accounts payable, accrued expenses, and other liabilities

Intercompany receivable

(420.5)

(79.0)

86.6

12.5

(21.5)

23.8

Income taxes

301.2

28.9

(154.8)

Net cash provided by operating activities

9.6

60.1

76.8

236.2

388.2

2,711.5

Cash Flows From Investing Activities:

Additional investments in equity securities of consolidated subsidiaries

(621.5)

(797.8)

(397.3)

Received from (paid to) investment subsidiary

307.3

(716.6)

2,519.6

Acquisition of Protective

0.0

(337.5)

Net Cash Provided by (Used in) Investing Activities

(314.2)

(1,514.4)

1,784.8

Cash Flows From Financing Activities:

Dividends paid to common shareholders

(234.0)

(3,746.5)

Dividends paid to preferred shareholders

(43.6)

(26.8)

Acquisition of treasury shares for restricted stock tax liabilities

(95.0)

(76.7)

(67.2)

Acquisition of treasury shares acquired in open market

(45.7)

(22.3)

(155.8)

Net proceeds from debt issuance

496.3

1,486.0

0.0

Repayments of Long-term Debt

0.0

(500.0)

Net cash provided by (used in) financing activities

78.0

1,126.2

(4,496.3)

Change in cash, cash equivalents, and restricted cash

0.0

Cash, cash equivalents, restricted cash, and restricted cash equivalents - beginning of year

0.0

Cash, cash equivalents, restricted cash, and restricted cash equivalents - end of year

$ 0.0

[1]	See Note 14 – Dividends for further discussion.

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Financial Information Of Registrant - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Mar. 31, 2024	Feb. 22, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Securities held in consolidated non-insurance subsidiary			$ 4,200.0	$ 4,400.0
Series B Preferred Stock
Significant Accounting Policies [Line Items]
Preferred Stock, Liquidation Preference Per Share						$ 1,000
Series B Preferred Stock \| Subsequent Event
Significant Accounting Policies [Line Items]
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Preferred Stock, Redemption Amount	$ 507.8
Parent Company
Significant Accounting Policies [Line Items]
Securities held in consolidated non-insurance subsidiary			$ 4,200.0	$ 4,400.0	$ 4,200.0
Parent Company \| Series B Preferred Stock \| Subsequent Event
Significant Accounting Policies [Line Items]
Preferred Stock, Liquidation Preference Per Share		$ 1,000
Preferred Stock, Redemption Amount		$ 507.8

SCHEDULE II - Condensed Financial Information Of Registrant Progressive Corporation Non Cash Transactions (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Series B Preferred Stock
Other Significant Noncash Transactions [Line Items]
Dividends Payable	$ 0.0	$ 13.4	$ 13.4
Common equities
Other Significant Noncash Transactions [Line Items]
Dividends Payable	497.9	58.5	58.5
Parent Company \| Series B Preferred Stock
Other Significant Noncash Transactions [Line Items]
Dividends Payable	0.0	13.4	13.4
Parent Company \| Common equities
Other Significant Noncash Transactions [Line Items]
Dividends Payable	$ 497.9	$ 58.5	$ 58.5

SCHEDULE II - Condensed Financial Information Of Registrant Progressive Corporation Cash Paid (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income taxes	$ 820.8	$ 719.0	$ 842.4
Parent Company
Income taxes	800.0	705.0	815.0
Interest	$ 264.9	$ 228.9	$ 223.9

SCHEDULE III - Supplementary Insurance Information Supplementary Insurance Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 1,687.4	$ 1,544.4	$ 1,355.6
Future policy benefits, losses, claims, and loss expenses	34,389.2	30,359.3	26,164.1
Unearned premiums	20,133.7	17,293.6	15,615.8
Other policy claims and benefits payable	0.0	0.0	0.0
Premium revenue	58,664.4	49,241.2	44,368.7
Net investment income	1,865.6	1,236.0	835.4
Benefits, claims, losses, and settlement expenses	45,654.6	38,122.7	33,627.6
Amortization of deferred policy acquisition costs	4,665.1	3,917.0	3,712.8
Other operating expenses	6,241.5	5,859.6	5,654.7
Net premiums written	61,550.2	51,081.1	46,405.2
Personal Lines Segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	46,213.3	37,880.2	35,373.3
Benefits, claims, losses, and settlement expenses	35,972.4	29,680.8	27,043.1
Amortization of deferred policy acquisition costs	3,169.1	2,592.1	2,614.7
Other operating expenses	4,928.6	4,668.9	4,656.8
Net premiums written	48,581.0	39,278.5	36,168.8
Commercial Lines Segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	9,898.7	9,088.3	6,945.2
Benefits, claims, losses, and settlement expenses	7,899.7	6,544.7	4,814.5
Amortization of deferred policy acquisition costs	1,004.7	913.3	734.1
Other operating expenses	1,020.8	947.7	742.3
Net premiums written	10,138.3	9,398.8	8,015.9
Property Segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	2,551.4	2,270.0	2,042.5
Benefits, claims, losses, and settlement expenses	1,776.3	1,891.3	1,764.6
Amortization of deferred policy acquisition costs	491.0	411.1	362.9
Other operating expenses	281.4	235.3	253.0
Net premiums written	2,830.6	2,401.7	2,216.2
Other Indemnity
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	1.0	2.7	7.7
Benefits, claims, losses, and settlement expenses	6.2	5.9	5.4
Amortization of deferred policy acquisition costs	0.3	0.5	1.1
Other operating expenses	10.7	7.7	2.6
Net premiums written	$ 0.3	$ 2.1	$ 4.3

SCHEDULE IV - Reinsurance Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	$ 59,881.1	$ 50,650.2	$ 46,018.6
Ceded to Other Companies	1,216.7	1,409.0	1,649.9
Property, Liability and Casualty Insurance Product Line
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	59,881.1	50,650.2	46,018.6
Ceded to Other Companies	1,216.7	1,409.0	1,649.9
Assumed From Other Companies	0.0	0.0	0.0
Net Amount	$ 58,664.4	$ 49,241.2	$ 44,368.7
Percentage of Amount Assumed to Net	0.00%	0.00%	0.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reporting and Accounting Policies - Allowance for Credit Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Allowance for Credit Loss [Abstract]
Balance at January 1	$ 343.3	$ 280.4
Increase in allowance	540.3	471.1
Write-offs	(514.5)	(408.2)
Balance at December 31	$ 369.1	$ 343.3

Reporting and Accounting Policies - Advertising Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Advertising costs	$ 1,599.7	$ 2,032.5	$ 2,139.5

Reporting and Accounting Policies Property, Plant, and Equipment (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total cost	$ 2,535.9	$ 2,585.1
Accumulated depreciation	(1,655.1)	(1,551.1)
Balance at end of year	880.8	1,034.0
Land
Property, Plant and Equipment [Line Items]
Total cost	102.6	123.1
Buildings, improvements, and integrated components
Property, Plant and Equipment [Line Items]
Total cost	732.9	844.1
Capitalized software
Property, Plant and Equipment [Line Items]
Total cost	467.5	475.4
Software licenses (internal use)
Property, Plant and Equipment [Line Items]
Total cost	486.4	427.6
Computer equipment
Property, Plant and Equipment [Line Items]
Total cost	$ 353.3	318.1
Useful Lives	3 years
All other property and equipment
Property, Plant and Equipment [Line Items]
Total cost	$ 393.2	$ 396.8
Lower Limit \| Buildings, improvements, and integrated components
Property, Plant and Equipment [Line Items]
Useful Lives	7 years
Lower Limit \| Capitalized software
Property, Plant and Equipment [Line Items]
Useful Lives	3 years
Lower Limit \| Software licenses (internal use)
Property, Plant and Equipment [Line Items]
Useful Lives	1 year
Lower Limit \| All other property and equipment
Property, Plant and Equipment [Line Items]
Useful Lives	3 years
Upper Limit \| Buildings, improvements, and integrated components
Property, Plant and Equipment [Line Items]
Useful Lives	40 years
Upper Limit \| Capitalized software
Property, Plant and Equipment [Line Items]
Useful Lives	10 years
Upper Limit \| Software licenses (internal use)
Property, Plant and Equipment [Line Items]
Useful Lives	6 years
Upper Limit \| All other property and equipment
Property, Plant and Equipment [Line Items]
Useful Lives	10 years

Reporting and Accounting Policies - Compensation Expense Recognized for Equity-Based Compensation (Details) - Stock compensation plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax expense	$ 121.3	$ 122.7	$ 100.7
Tax benefit	$ 17.0	$ 16.0	$ 14.1

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(v)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reporting and Accounting Policies - Supplemental Cash Flow Information, non-cash activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Other Significant Noncash Transactions [Line Items]
Operating Lease Liabilities	$ 114.3	$ 36.2	$ 86.7
Series B Preferred Stock
Other Significant Noncash Transactions [Line Items]
Dividends Payable	0.0	13.4	13.4
Common equities
Other Significant Noncash Transactions [Line Items]
Dividends Payable	$ 497.9	$ 58.5	$ 58.5

Reporting and Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Income taxes	$ 820.8	$ 719.0	$ 842.4
Interest	264.9	228.9	224.0
Operating lease liabilities	$ 77.2	$ 82.5	$ 88.6

Reporting and Accounting Policies - Unrecorded Unconditional Purchase Obligations (Details) $ in Millions	Dec. 31, 2023 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2024	$ 780.0
2025	139.5
2026	68.6
2027	26.5
2028	7.8
Thereafter	2.4
Total	$ 1,024.8

Reporting and Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) segment security	Dec. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security	Jun. 30, 2022 USD ($)
Property, Plant and Equipment [Line Items]
Number of Operating Segments \| segment	3
Derivative, Number of Instruments Held \| security	0	0	0
Held for sale property	$ 77,200,000	$ 48,700,000
Other assets	1,348,500,000	1,158,900,000
Goodwill	227,900,000	227,900,000
Goodwill, Other Increase (Decrease)	0
Goodwill impairment	0	224,800,000	$ 0
Goodwill, Impaired, Accumulated Impairment Loss				$ 0
Amortization of intangible assets	14,200,000	31,000,000	57,700,000
Open reverse repurchase commitments	0	0
Noncancelable purchase obligation, minimum commitments	1,024,800,000
2024	780,000,000.0
2025	139,500,000
2026	68,600,000
Property Segment
Property, Plant and Equipment [Line Items]
Goodwill impairment		224,800,000
Software licenses (internal use)
Property, Plant and Equipment [Line Items]
Other assets	88,100,000	63,400,000
Cash and Cash Equivalents
Property, Plant and Equipment [Line Items]
Open reverse repurchase commitments	68,200,000	$ 125,900,000	$ 137,100,000
Unrecorded unconditional purchase obligations reinsurance
Property, Plant and Equipment [Line Items]
2024	282,800,000
2025	8,100,000
2026	$ 600,000
Unrecorded unconditional purchase obligations reinsurance \| Lower Limit
Property, Plant and Equipment [Line Items]
Other Commitments, Term	1 year
Other reinsurance contracts, minimum commitment	$ 291,500,000
Unrecorded unconditional purchase obligations reinsurance \| Upper Limit
Property, Plant and Equipment [Line Items]
Other Commitments, Term	3 years

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Available-for-sale securities, at fair value:
Cost	$ 64,231.8	$ 53,125.7
Gross Unrealized Gains	312.2	13.9
Gross Unrealized Losses	(2,346.8)	(3,551.5)
Net Holding Period Gains (Losses)	(29.1)	(74.5)
Fair Value	$ 62,168.1	$ 49,513.6
% of Total Fair Value	94.20%	92.50%
Equity securities, at fair value:
Cost	$ 1,683.1	$ 2,190.3
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Net Holding Period Gains (Losses)	2,147.4	1,844.4
Fair Value	$ 3,830.5	$ 4,034.7
% of Total Fair Value	5.80%	7.50%
Debt and Equity Securities, at Fair Value
Cost	$ 65,914.9	$ 55,316.0
Gross Unrealized Gains	312.2	13.9
Gross Unrealized Losses	(2,346.8)	(3,551.5)
Net Holding Period Gains (Losses)	2,118.3	1,769.9
Fair value	$ 65,998.6	$ 53,548.3
% of Total Fair Value	100.00%	100.00%
Other Receivable from Broker-Dealer and Clearing Organization	$ 45.6	$ 34.4
Securities held in consolidated non-insurance subsidiary	4,200.0	4,400.0
Nonredeemable preferred stocks
Equity securities, at fair value:
Cost	977.1	1,364.2
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Net Holding Period Gains (Losses)	(75.0)	(151.0)
Fair Value	$ 902.1	$ 1,213.2
% of Total Fair Value	1.40%	2.30%
Common equities
Equity securities, at fair value:
Cost	$ 706.0	$ 826.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Net Holding Period Gains (Losses)	2,222.4	1,995.4
Fair Value	$ 2,928.4	$ 2,821.5
% of Total Fair Value	4.40%	5.20%
Fixed maturities
Available-for-sale securities, at fair value:
Cost	$ 62,441.9	$ 50,264.0
Gross Unrealized Gains	312.2	13.9
Gross Unrealized Losses	(2,346.8)	(3,551.5)
Net Holding Period Gains (Losses)	(29.1)	(74.5)
Fair Value	$ 60,378.2	$ 46,651.9
% of Total Fair Value	91.50%	87.10%
Fixed maturities \| U.S. government obligations
Available-for-sale securities, at fair value:
Cost	$ 37,823.2	$ 26,770.7
Gross Unrealized Gains	204.1	1.4
Gross Unrealized Losses	(1,157.9)	(1,604.7)
Net Holding Period Gains (Losses)	0.0	0.0
Fair Value	$ 36,869.4	$ 25,167.4
% of Total Fair Value	55.90%	47.00%
Fixed maturities \| State and local government obligations
Available-for-sale securities, at fair value:
Cost	$ 2,338.4	$ 2,180.0
Gross Unrealized Gains	2.8	0.0
Gross Unrealized Losses	(138.4)	(202.9)
Net Holding Period Gains (Losses)	0.0	0.0
Fair Value	$ 2,202.8	$ 1,977.1
% of Total Fair Value	3.30%	3.70%
Fixed maturities \| Foreign government obligations
Available-for-sale securities, at fair value:
Cost	$ 17.3	$ 16.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(1.0)	(1.3)
Net Holding Period Gains (Losses)	0.0	0.0
Fair Value	$ 16.3	$ 15.5
% of Total Fair Value	0.10%	0.10%
Fixed maturities \| Corporate debt securities
Available-for-sale securities, at fair value:
Cost	$ 11,446.0	$ 10,125.8
Gross Unrealized Gains	87.2	9.8
Gross Unrealized Losses	(332.3)	(676.1)
Net Holding Period Gains (Losses)	(17.2)	(46.8)
Fair Value	$ 11,183.7	$ 9,412.7
% of Total Fair Value	16.90%	17.60%
Fixed maturities \| Residential mortgage-backed securities
Available-for-sale securities, at fair value:
Cost	$ 426.9	$ 696.1
Gross Unrealized Gains	0.2	0.3
Gross Unrealized Losses	(10.0)	(17.5)
Net Holding Period Gains (Losses)	0.1	(12.1)
Fair Value	$ 417.2	$ 666.8
% of Total Fair Value	0.60%	1.20%
Fixed maturities \| Commercial mortgage-backed securities
Available-for-sale securities, at fair value:
Cost	$ 4,535.2	$ 5,446.0
Gross Unrealized Gains	2.2	1.5
Gross Unrealized Losses	(597.7)	(784.0)
Net Holding Period Gains (Losses)	0.0	0.0
Fair Value	$ 3,939.7	$ 4,663.5
% of Total Fair Value	6.00%	8.70%
Fixed maturities \| Other asset-backed securities
Available-for-sale securities, at fair value:
Cost	$ 5,667.2	$ 4,826.0
Gross Unrealized Gains	15.7	0.9
Gross Unrealized Losses	(107.1)	(260.5)
Net Holding Period Gains (Losses)	(0.4)	(1.8)
Fair Value	$ 5,575.4	$ 4,564.6
% of Total Fair Value	8.40%	8.50%
Fixed maturities \| Redeemable preferred stocks
Available-for-sale securities, at fair value:
Cost	$ 187.7	$ 202.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(2.4)	(4.5)
Net Holding Period Gains (Losses)	(11.6)	(13.8)
Fair Value	$ 173.7	$ 184.3
% of Total Fair Value	0.30%	0.30%
Short-term investments
Available-for-sale securities, at fair value:
Cost	$ 1,789.9	$ 2,861.7
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Net Holding Period Gains (Losses)	0.0	0.0
Fair Value	$ 1,789.9	$ 2,861.7
% of Total Fair Value	2.70%	5.40%

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Hybrid Securities [Line Items]
Hybrid securities	$ 1,010.3	$ 1,221.7
Corporate debt securities
Hybrid Securities [Line Items]
Hybrid securities	531.3	535.4
Residential mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	323.9	509.6
Other asset-backed securities
Hybrid Securities [Line Items]
Hybrid securities	13.9	42.0
Redeemable preferred stocks
Hybrid Securities [Line Items]
Hybrid securities	$ 141.2	$ 134.7

Investments Composition of Fixed Maturities by Maturity (Detail) - Fixed maturities $ in Millions	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 9,782.8
One to five years	37,948.6
Five to ten years	14,637.1
Ten years or greater	73.4
Cost	62,441.9
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Less than one year	9,566.2
One to five years	36,796.2
Five to ten years	13,942.5
Ten years or greater	73.3
Debt Securities, Available-for-Sale	$ 60,378.2

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Number of Securities
Total \| security	1,223	1,468
Less than 12 Months \| security	126	873
12 Months or Greater \| security	1,097	595
Fair Value
Total	$ 44,062.1	$ 44,315.9
Less than 12 Months	13,347.6	28,119.4
12 Month or Greater	30,714.5	16,196.5
Gross Unrealized Losses
Total	2,346.8	3,551.5
Less than 12 Months	119.3	1,505.0
12 Months or Greater	$ 2,227.5	$ 2,046.5
U.S. government obligations
Number of Securities
Total \| security	147	160
Less than 12 Months \| security	25	90
12 Months or Greater \| security	122	70
Fair Value
Total	$ 28,225.0	$ 24,802.5
Less than 12 Months	11,890.0	17,327.2
12 Month or Greater	16,335.0	7,475.3
Gross Unrealized Losses
Total	1,157.9	1,604.7
Less than 12 Months	100.0	699.2
12 Months or Greater	$ 1,057.9	$ 905.5
State and local government obligations
Number of Securities
Total \| security	324	348
Less than 12 Months \| security	31	239
12 Months or Greater \| security	293	109
Fair Value
Total	$ 1,846.2	$ 1,948.8
Less than 12 Months	169.9	1,124.2
12 Month or Greater	1,676.3	824.6
Gross Unrealized Losses
Total	138.4	202.9
Less than 12 Months	0.9	76.8
12 Months or Greater	$ 137.5	$ 126.1
Foreign government obligations
Number of Securities
Total \| security	1	1
Less than 12 Months \| security	0	0
12 Months or Greater \| security	1	1
Fair Value
Total	$ 16.3	$ 15.5
Less than 12 Months	0.0	0.0
12 Month or Greater	16.3	15.5
Gross Unrealized Losses
Total	1.0	1.3
Less than 12 Months	0.0	0.0
12 Months or Greater	$ 1.0	$ 1.3
Corporate debt securities
Number of Securities
Total \| security	313	422
Less than 12 Months \| security	26	285
12 Months or Greater \| security	287	137
Fair Value
Total	$ 6,642.4	$ 8,449.6
Less than 12 Months	617.2	5,717.6
12 Month or Greater	6,025.2	2,732.0
Gross Unrealized Losses
Total	332.3	676.1
Less than 12 Months	14.7	426.1
12 Months or Greater	$ 317.6	$ 250.0
Residential mortgage-backed securities
Number of Securities
Total \| security	39	45
Less than 12 Months \| security	2	27
12 Months or Greater \| security	37	18
Fair Value
Total	$ 88.4	$ 151.0
Less than 12 Months	0.4	65.1
12 Month or Greater	88.0	85.9
Gross Unrealized Losses
Total	10.0	17.5
Less than 12 Months	0.0	6.8
12 Months or Greater	$ 10.0	$ 10.7
Commercial mortgage-backed securities
Number of Securities
Total \| security	189	226
Less than 12 Months \| security	1	99
12 Months or Greater \| security	188	127
Fair Value
Total	$ 3,912.2	$ 4,651.1
Less than 12 Months	30.7	1,702.0
12 Month or Greater	3,881.5	2,949.1
Gross Unrealized Losses
Total	597.7	784.0
Less than 12 Months	2.5	192.1
12 Months or Greater	$ 595.2	$ 591.9
Other asset-backed securities
Number of Securities
Total \| security	207	262
Less than 12 Months \| security	41	130
12 Months or Greater \| security	166	132
Fair Value
Total	$ 3,299.1	$ 4,247.8
Less than 12 Months	639.4	2,144.8
12 Month or Greater	2,659.7	2,103.0
Gross Unrealized Losses
Total	107.1	260.5
Less than 12 Months	1.2	100.9
12 Months or Greater	$ 105.9	$ 159.6
Redeemable preferred stocks
Number of Securities
Total \| security	3	4
Less than 12 Months \| security	0	3
12 Months or Greater \| security	3	1
Fair Value
Total	$ 32.5	$ 49.6
Less than 12 Months	0.0	38.5
12 Month or Greater	32.5	11.1
Gross Unrealized Losses
Total	2.4	4.5
Less than 12 Months	0.0	3.1
12 Months or Greater	$ 2.4	$ 1.4

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	$ 14.0	$ 20.4	$ 305.9
Equity Securities, FV-NI, Realized Gain	381.3	863.7	397.6
Debt and Equity Securities, Realized Gains	395.3	884.1	703.5
Debt Securities, Available-for-Sale, Realized Loss	(263.1)	(599.8)	(67.4)
Equity Securities, FV-NI, Realized Loss	(140.1)	(87.8)	(21.8)
Debt and Equity Securities, Realized Losses	(403.2)	(687.6)	(89.2)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(249.1)	(579.4)	238.5
Equity Securities, FV-NI, Realized Gain (Loss)	241.2	775.9	375.8
Net realized gains (losses) on security sales	(7.9)	196.5	614.3
Realized Gain (Loss) on Security Sales, Other Assets	21.6	0.0	0.0
Net impairment losses recognized in earnings	(9.0)	(8.6)	(5.0)
Realized Gains (Losses), Other Assets	12.6	(8.6)	(5.0)
Unrealized Gain (Loss) on Hybrid Instrument, Net	45.4	(82.0)	(7.7)
Equity Securities, FV-NI, Unrealized Gain (Loss)	303.0	(2,018.1)	907.6
Net holding period gains (losses) on securities	348.4	(2,100.1)	899.9
Total net realized gains (losses) on securities	353.1	(1,912.2)	1,509.2
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	12.1	10.8	105.8
Debt Securities, Available-for-Sale, Realized Loss	(64.6)	(433.3)	(52.0)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(52.5)	(422.5)	53.8
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	0.0	0.0	51.2
Debt Securities, Available-for-Sale, Realized Loss	0.0	(1.0)	(3.4)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	0.0	(1.0)	47.8
Foreign government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Loss	0.0	0.0	(0.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	0.0	0.0	(0.1)
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	1.0	8.7	104.0
Debt Securities, Available-for-Sale, Realized Loss	(85.7)	(88.3)	(8.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(84.7)	(79.6)	95.7
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	0.9	0.7	0.3
Debt Securities, Available-for-Sale, Realized Loss	0.0	0.0	(1.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	0.9	0.7	(0.8)
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	0.0	0.0	41.9
Debt Securities, Available-for-Sale, Realized Loss	(106.8)	(72.4)	(1.9)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(106.8)	(72.4)	40.0
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	0.0	0.2	1.2
Debt Securities, Available-for-Sale, Realized Loss	(5.6)	(4.4)	(0.6)
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(5.6)	(4.2)	0.6
Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Gain	0.0	0.0	1.5
Debt Securities, Available-for-Sale, Realized Gain (Loss)	0.0	0.0	1.5
Short-term investments
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Realized Loss	(0.4)	(0.4)	0.0
Debt Securities, Available-for-Sale, Realized Gain (Loss)	(0.4)	(0.4)	0.0
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain	0.3	17.6	28.0
Equity Securities, FV-NI, Realized Loss	(118.3)	(9.8)	(1.7)
Equity Securities, FV-NI, Realized Gain (Loss)	(118.0)	7.8	26.3
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain	381.0	846.1	369.6
Equity Securities, FV-NI, Realized Loss	(21.8)	(78.0)	(20.1)
Equity Securities, FV-NI, Realized Gain (Loss)	$ 359.2	$ 768.1	$ 349.5

Investments Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Equity Securities, FV-NI, Gain (Loss)	$ 544.2	$ (1,242.2)	$ 1,283.4
Equity Securities, FV-NI, Realized Gain (Loss)	241.2	775.9	375.8
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 303.0	$ (2,018.1)	$ 907.6

Investments Components of Net Investment Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Investment Income [Line Items]
Investment income	$ 1,891.8	$ 1,260.3	$ 860.9
Investment expenses	(26.2)	(24.3)	(25.5)
Net investment income	1,865.6	1,236.0	835.4
Available-for-sale Securities
Net Investment Income [Line Items]
Investment income	1,798.0	1,129.6	726.4
Equity securities
Net Investment Income [Line Items]
Investment income	93.8	130.7	134.5
Equity securities \| Nonredeemable preferred stocks
Net Investment Income [Line Items]
Investment income	51.4	70.2	70.3
Equity securities \| Common equities
Net Investment Income [Line Items]
Investment income	42.4	60.5	64.2
Fixed maturities
Net Investment Income [Line Items]
Investment income	1,705.6	1,076.0	723.3
Fixed maturities \| U.S. government obligations
Net Investment Income [Line Items]
Investment income	864.0	339.1	149.5
Fixed maturities \| State and local government obligations
Net Investment Income [Line Items]
Investment income	47.6	39.7	44.1
Fixed maturities \| Foreign government obligations
Net Investment Income [Line Items]
Investment income	0.2	0.2	0.1
Fixed maturities \| Corporate debt securities
Net Investment Income [Line Items]
Investment income	365.4	288.8	301.1
Fixed maturities \| Residential mortgage-backed securities
Net Investment Income [Line Items]
Investment income	28.7	31.6	11.9
Fixed maturities \| Commercial mortgage-backed securities
Net Investment Income [Line Items]
Investment income	196.1	190.6	143.0
Fixed maturities \| Other asset-backed securities
Net Investment Income [Line Items]
Investment income	192.5	174.6	64.1
Fixed maturities \| Redeemable preferred stocks
Net Investment Income [Line Items]
Investment income	11.1	11.4	9.5
Short-term investments
Net Investment Income [Line Items]
Investment income	$ 92.4	$ 53.6	$ 3.1

Investments - Additional Information (Detail)	12 Months Ended
Investments - Additional Information (Detail)	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($)
Investments, Debt and Equity Securities [Abstract]
Principal amount of bonds and certificates of deposit on deposit to meet state insurance regulatory and/or rating agency requirements	$ 671,800,000
Securities exceeding 10% of Shareholders' Equity	0	$ 0
Fair value of fixed-maturity securities that were non-income producing during the preceding 12 months	0
Securities sold under agreements to repurchase	0	0
Open reverse repurchase commitments	$ 0	0
Securities with credit ratings downgraded \| security	29
Value of securities with credit rating downgraded	$ 447,900,000
Unrealized loss on securities with credit downgraded	59,000,000
Allowance for credit losses, securities	0	0
Credit loss allowance balance, available-for-sale securities	0	0
Write off of accrued income	$ 0	$ 0
Recovery of Impairment, Other Assets, Number of Positions \| security	3
Percent change in investment income	50.00%	46.00%
Percent change in book yield	29.00%	26.00%

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 65,998.6	$ 53,548.3
Debt, fair value	6,431.3	5,717.9
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	62,168.1	49,513.6
Available-for-sale Securities \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	60,378.2	46,651.9
Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	50,272.2	36,572.7
Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	36,869.4	25,167.4
Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,202.8	1,977.1
Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	16.3	15.5
Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	11,183.7	9,412.7
Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	9,932.3	9,894.9
Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	417.2	666.8
Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3,939.7	4,663.5
Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	5,575.4	4,564.6
Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	173.7	184.3
Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	23.1	40.5
Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	9.4	9.1
Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	141.2	134.7
Available-for-sale Securities \| Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,789.9	2,861.7
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3,830.5	4,034.7
Equity securities \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	902.1	1,213.2
Equity securities \| Nonredeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	851.9	1,100.8
Equity securities \| Nonredeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	35.4	71.2
Equity securities \| Nonredeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	14.8	41.2
Equity securities \| Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,928.4	2,821.5
Equity securities \| Common equities \| Common Stocks, by Industry
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,907.8	2,801.7
Equity securities \| Common equities \| Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	20.6	19.8
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	41,511.7	30,799.7
Debt, fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	38,626.4	27,977.3
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	36,869.4	25,176.6
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	36,869.4	25,167.4
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	36,869.4	25,167.4
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	9.2
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	9.2
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]
Fair value	1,757.0	2,800.7
Fair Value, Inputs, Level 1 \| Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,885.3	2,822.4
Fair Value, Inputs, Level 1 \| Equity securities \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	39.0
Fair Value, Inputs, Level 1 \| Equity securities \| Nonredeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	39.0
Fair Value, Inputs, Level 1 \| Equity securities \| Nonredeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Equity securities \| Nonredeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 1 \| Equity securities \| Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,885.3	2,783.4
Fair Value, Inputs, Level 1 \| Equity securities \| Common equities \| Common Stocks, by Industry
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,885.3	2,783.4
Fair Value, Inputs, Level 1 \| Equity securities \| Common equities \| Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	24,376.8	22,626.7
Debt, fair value	6,431.3	5,717.9
Fair Value, Inputs, Level 2 \| Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	23,538.7	21,536.3
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	23,505.8	21,475.3
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	13,399.8	11,405.3
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,202.8	1,977.1
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	16.3	15.5
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	11,180.7	9,412.7
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	9,932.3	9,894.9
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	417.2	666.8
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3,939.7	4,663.5
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	5,575.4	4,564.6
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	173.7	175.1
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	23.1	40.5
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	9.4	9.1
Fair Value, Inputs, Level 2 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	141.2	125.5
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]
Fair value	32.9	61.0
Fair Value, Inputs, Level 2 \| Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	838.1	1,090.4
Fair Value, Inputs, Level 2 \| Equity securities \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	838.1	1,090.4
Fair Value, Inputs, Level 2 \| Equity securities \| Nonredeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	802.7	994.4
Fair Value, Inputs, Level 2 \| Equity securities \| Nonredeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	35.4	71.2
Fair Value, Inputs, Level 2 \| Equity securities \| Nonredeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	24.8
Fair Value, Inputs, Level 2 \| Equity securities \| Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 2 \| Equity securities \| Common equities \| Common Stocks, by Industry
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 2 \| Equity securities \| Common equities \| Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	110.1	121.9
Debt, fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value		0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	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]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	107.1	121.9
Fair Value, Inputs, Level 3 \| Equity securities \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	64.0	83.8
Fair Value, Inputs, Level 3 \| Equity securities \| Nonredeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	49.2	67.4
Fair Value, Inputs, Level 3 \| Equity securities \| Nonredeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	0.0	0.0
Fair Value, Inputs, Level 3 \| Equity securities \| Nonredeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	14.8	16.4
Fair Value, Inputs, Level 3 \| Equity securities \| Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	43.1	38.1
Fair Value, Inputs, Level 3 \| Equity securities \| Common equities \| Common Stocks, by Industry
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	22.5	18.3
Fair Value, Inputs, Level 3 \| Equity securities \| Common equities \| Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	20.6	19.8
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	65,914.9	55,316.0
Carrying value	6,888.6	6,388.3
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	64,231.8	53,125.7
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	62,441.9	50,264.0
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	51,624.9	39,093.3
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	37,823.2	26,770.7
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,338.4	2,180.0
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	17.3	16.8
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Debt Securities [Member] \| Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	11,446.0	10,125.8
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	10,629.3	10,968.1
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	426.9	696.1
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,535.2	5,446.0
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Asset-backed Securities \| Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	5,667.2	4,826.0
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	187.7	202.6
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	24.5	43.6
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	10.4	10.5
Carrying (Reported) Amount, Fair Value Disclosure \| Available-for-sale Securities \| Fixed maturities \| Redeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	152.8	148.5
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]
Fair value	1,789.9	2,861.7
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,683.1	2,190.3
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	977.1	1,364.2
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Nonredeemable preferred stocks \| Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	922.1	1,244.2
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Nonredeemable preferred stocks \| Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	40.0	79.9
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Nonredeemable preferred stocks \| Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	15.0	40.1
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	706.0	826.1
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Common equities \| Common Stocks, by Industry
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	685.4	806.3
Carrying (Reported) Amount, Fair Value Disclosure \| Equity securities \| Common equities \| Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 20.6	$ 19.8

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	$ 121.9	$ 127.7
Calls/ Maturities/ Paydowns	0.8	2.4
Purchases	4.0	2.5
Sales	(10.0)	(15.0)
Net Realized (Gain)/Loss on Sales	8.9	(17.2)
Change in Valuation	(15.5)	3.2
Net Transfers In (Out)	0.0	18.3
Ending Fair value	110.1	$ 121.9
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Net realized gains (losses) on security sales
Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.0
Calls/ Maturities/ Paydowns	0.0
Purchases	3.0
Sales	0.0
Net Realized (Gain)/Loss on Sales	0.0
Change in Valuation	0.0
Net Transfers In (Out)	0.0
Ending Fair value	3.0	$ 0.0
Nonredeemable preferred stocks \| Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	67.4	76.4
Calls/ Maturities/ Paydowns	(8.1)	0.0
Purchases	1.0	2.5
Sales	0.0	(15.0)
Net Realized (Gain)/Loss on Sales	0.0	(17.2)
Change in Valuation	(11.1)	20.7
Net Transfers In (Out)	0.0	0.0
Ending Fair value	49.2	67.4
Nonredeemable preferred stocks \| Industrials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	16.4	34.4
Calls/ Maturities/ Paydowns	0.0	(0.5)
Purchases	0.0	0.0
Sales	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0
Change in Valuation	(1.6)	(17.5)
Net Transfers In (Out)	0.0	0.0
Ending Fair value	14.8	16.4
Common equities \| Common Stocks, by Industry
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	18.3	0.0
Calls/ Maturities/ Paydowns	8.1	0.0
Purchases	0.0	0.0
Sales	(10.0)	0.0
Net Realized (Gain)/Loss on Sales	8.9	0.0
Change in Valuation	(2.8)	0.0
Net Transfers In (Out)	0.0	18.3
Ending Fair value	22.5	18.3
Common equities \| Other risk investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	19.8	16.9
Calls/ Maturities/ Paydowns	0.8	2.9
Purchases	0.0	0.0
Sales	0.0	0.0
Net Realized (Gain)/Loss on Sales	0.0	0.0
Change in Valuation	0.0	0.0
Net Transfers In (Out)	0.0	0.0
Ending Fair value	$ 20.6	$ 19.8

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 65,998.6	$ 53,548.3
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	110.1	121.9
Fair Value, Inputs, Level 3 \| Total Quantitative Level Three Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	89.5	102.1
Fair Value, Inputs, Level 3 \| Third Party Pricing Exemption Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	20.6	19.8
Fair Value, Inputs, Level 3 \| Corporate debt securities \| Total Quantitative Level Three Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 3.0
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum	0.30%
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum	7.70%
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average	2.60%
Fair Value, Inputs, Level 3 \| Nonredeemable preferred stocks \| Total Quantitative Level Three Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 64.0	$ 83.8
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum	17.20%	(0.60%)
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum	39.70%	19.90%
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average	21.70%	10.50%
Fair Value, Inputs, Level 3 \| Common equities \| Total Quantitative Level Three Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 22.5	$ 18.3
Fair Value Inputs, Market Cap Price Change Percentage, Range, Minimum	(45.80%)	(42.50%)
Fair Value Inputs, Market Cap Price Change Percentage, Range, Maximum	95.60%	59.10%
Fair Value Inputs, Market Cap Price Change Percentage, Weighted Average	39.70%	30.00%

Fair Value - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 65,998.6	$ 53,548.3
Goodwill impairment	$ 0.0	224.8	$ 0.0
Property Segment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill impairment		$ 224.8
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vendor quoted prices, percent of FV hierarchy level	93.00%	90.00%
Fair value	$ 41,511.7	$ 30,799.7
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vendor quoted prices, percent of FV hierarchy level	100.00%	98.00%
Dealer quoted prices, percent of FV hierarchy level		2.00%
Fair value	$ 24,376.8	$ 22,626.7
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 110.1	121.9
Fair Value, Inputs, Level 3 \| Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value		$ 0.0

Debt (Detail) - USD ($)

Dec. 31, 2023

May 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, Long-term and Short-term, Combined Amount

$ 6,431,300,000

$ 5,717,900,000

^[1]

6,888,600,000

6,388,300,000

2.45% Senior Notes Due 2027

498,600,000

498,200,000

468,900,000

457,700,000

2.45%

2.50% Senior Notes due 2027

$ 500,000,000.0

498,100,000

497,500,000

469,100,000

460,300,000

2.50%

6 5/8% Senior Notes due 2029

$ 500,000,000.0

297,800,000

297,500,000

328,700,000

326,800,000

6.625%

4.00% Senior Notes due 2029

$ 300,000,000.0

546,900,000

546,400,000

542,600,000

527,800,000

4.00%

3.20% Senior Notes due 2030

$ 550,000,000.0

497,300,000

496,900,000

462,200,000

448,600,000

3.20%

3.00% Senior Notes due 2032

$ 500,000,000.0

496,300,000

495,900,000

446,000,000.0

438,100,000

3.00%

6.25% Senior Notes due 2032

$ 500,000,000.0

396,700,000

396,400,000

445,600,000

435,400,000

6.25%

4.95% Senior Notes due 2033

$ 400,000,000.0

496,400,000

0

513,000,000.0

0

4.95%

4.35% Senior Notes due 2044

$ 500,000,000.0

347,000,000.0

346,900,000

314,200,000

298,400,000

4.35%

3.70% Senior Notes due 2045

$ 350,000,000.0

395,900,000

395,700,000

325,100,000

310,200,000

3.70%

4.125% Senior Notes due 2047

$ 400,000,000.0

842,300,000

842,100,000

756,200,000

716,200,000

4.125%

4.20% Senior Notes due 2048

$ 850,000,000.0

590,600,000

590,400,000

534,100,000

507,000,000.0

4.20%

3.95% Senior Notes due 2050

$ 600,000,000.0

491,100,000

490,900,000

422,300,000

404,900,000

3.95%

3.70% Senior Notes due 2052

$ 500,000,000.0

493,600,000

493,500,000

$ 403,300,000

$ 386,500,000

3.70%

$ 500,000,000.0

[1]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Debt Aggregate Principal Payments On Debt Outstanding (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
Debt Instrument, Periodic Payment, Principal in Next Twelve Months	$ 0.0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0.0
Long-Term Debt, Maturities, Repayments of Principal in Year Three	0.0
Long-Term Debt, Maturities, Repayments of Principal in Year Four	1,000.0
Long-Term Debt, Maturities, Repayments of Principal in Year Five	0.0
Long-Term Debt, Maturities, Repayments of Principal after Year Five	5,950.0
Total	$ 6,950.0

Debt Unrealized Gains (Losses) From Debt Hedges Included In Accumulated Other (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Apr. 30, 2017	Jan. 31, 2015	Apr. 30, 2014	Nov. 30, 2002	Mar. 31, 1999
Debt Instrument [Line Items]
Net unrealized losses on forecasted transactions	$ (14.0)	$ (14.5)
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Unrealized Gain (Loss)							$ (4.2)
Net unrealized losses on forecasted transactions	(1.5)
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Unrealized Gain (Loss)						$ 5.1
Net unrealized losses on forecasted transactions	2.6
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Unrealized Gain (Loss)					$ (1.6)
Net unrealized losses on forecasted transactions	(1.3)
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Unrealized Gain (Loss)				$ (12.9)
Net unrealized losses on forecasted transactions	(10.5)
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Unrealized Gain (Loss)			$ (8.0)
Net unrealized losses on forecasted transactions	$ (7.0)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482900/835-30-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69C

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69E

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69F

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Debt - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
Debt - Additional Information (Detail) - USD ($)	May 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Long-term Debt, Current Maturities		$ 0	$ 0
Proceeds from debt invested	$ 496,300,000
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax		600,000	500,000	$ 900,000
Discretionary Line of Credit
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 300,000,000	250,000,000
Discretionary Line of Credit Repayment Period		30 days
Proceeds from Lines of Credit		$ 0	$ 0
Discretionary Line of Credit \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.10%
4.95% Senior Notes due 2033
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000,000.0
Debt Instrument, Interest Rate, Stated Percentage	4.95%

Income Taxes Components of Income Tax Provision (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)	$ 1,102.5	$ 733.2	$ 739.5
Current State and Local Tax Expense (Benefit)	18.7	12.7	20.7
Deferred Federal Income Tax Expense (Benefit)	(119.9)	(528.7)	98.6
Deferred State and Local Income Tax Expense (Benefit)	0.0	(16.6)	0.3
Provision for income taxes	$ 1,001.3	$ 200.6	$ 859.1

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Income Taxes Reconciliation of Provision (Benefit) for income Taxes Reported in Consolidated Statements Of Income with Tax at Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income before income taxes	$ 4,903.7	$ 922.1	$ 4,210.0
Tax at statutory federal rate	1,029.8	193.6	884.1
Stock-based compensation	(21.7)	(18.1)	(19.4)
Tax credits	(16.4)	(14.8)	(9.9)
Tax-preferenced investment income	(10.2)	(12.7)	(13.2)
State income taxes, net of federal taxes	14.7	(3.1)	16.6
Nondeductible compensation expense	9.8	11.1	8.4
Tax-deductible dividends	(4.8)	(1.8)	(9.4)
Goodwill impairment	0.0	47.2	0.0
Other items, net	0.1	(0.8)	1.9
Provision for income taxes	$ 1,001.3	$ 200.6	$ 859.1
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Tax at statutory federal rate	21.00%	21.00%	21.00%
Stock-based compensation	(1.00%)	(2.00%)	(1.00%)
Tax credits	0.00%	(2.00%)	0.00%
Tax-preferenced investment income	0.00%	(1.00%)	0.00%
State income taxes, net of federal taxes	0.00%	0.00%	0.00%
Nondeductible compensation expense	0.00%	1.00%	0.00%
Tax-deductible dividends	0.00%	0.00%	0.00%
Goodwill impairment	0.00%	5.00%	0.00%
Other items, net	0.00%	0.00%	0.00%
Total income tax provision	20.00%	22.00%	20.00%

Income Taxes Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Federal deferred income tax assets:
Unearned premiums reserve	$ 836.0	$ 719.2
Net unrealized losses on fixed-maturity securities	427.3	742.9
Loss and loss adjustment expense reserves	292.7	239.9
Non-deductible accruals	238.2	225.9
Software development costs	66.0	37.8
Operating lease liabilities	37.2	28.8
Hedges on forecasted transactions	3.7	3.8
Investment basis differences	0.2	17.0
Other	13.4	12.7
Federal deferred income tax liabilities:
Net holding period gains on equity securities	(451.0)	(387.3)
Deferred acquisition costs	(354.4)	(324.3)
Property and equipment	(88.4)	(97.0)
Operating lease assets	(37.2)	(28.8)
Loss and loss adjustment expense reserve transition adjustment	(15.9)	(24.1)
Intangible assets	(8.7)	(11.1)
Prepaid expenses	(6.2)	(6.5)
Other	(16.9)	(17.4)
Net federal deferred income taxes	936.0	1,131.5
State deferred income tax assets	39.9	42.2
State deferred income tax liabilities	0.0	0.0
Total	$ 975.9	$ 1,173.7

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Deferred tax assets valuation allowance	$ 0	$ 0
Net taxes payable	311,800,000	10,900,000
Provision for income taxes	1,001,300,000	200,600,000	$ 859,100,000
Unrecognized Tax Benefits	0	0
Interest and Penalties
Income Taxes [Line Items]
Provision for income taxes	$ 200,000	$ 100,000	$ 100,000

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Loss And Loss Adjustment Expense Reserves Activity in Loss and loss Adjustment Expense Reserves (Detail) - USD ($) $ in Millions				12 Months Ended
	Jan. 01, 2022	Jan. 01, 2021	Jan. 01, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 26,164.1	$ 20,265.8		$ 30,359.3	$ 26,164.1	$ 20,265.8
Less reinsurance recoverables on unpaid losses	4,733.6	3,798.2		5,559.2	4,733.6	3,798.2
Liability for Unpaid Claims and Claims Adjustment Expense, Business Acquisitions	0.0	0.0	$ 729.2
Net balance at beginning of period	21,430.5	16,467.6		24,800.1	21,430.5	16,467.6
Incurred related to:
Current year				44,560.6	38,209.0	33,632.3
Prior years				1,094.0	(86.3)	(4.7)
Total incurred				45,654.6	38,122.7	33,627.6
Paid related to:
Current year				26,874.3	23,542.9	20,561.1
Prior years				13,980.2	11,210.2	8,832.8
Total paid				40,854.5	34,753.1	29,393.9
Net balance at ending of period	$ 24,800.1	$ 21,430.5	$ 17,196.8	29,600.2	24,800.1	21,430.5
Plus reinsurance recoverables on unpaid losses				4,789.0	5,559.2	4,733.6
Balance at ending of period				$ 34,389.2	$ 30,359.3	$ 26,164.1

Loss And Loss Adjustment Expense Reserves Loss And Loss Adjustment Expense Reserves - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) data_subset	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Number of subsets of business data reviewed (over) \| data_subset	400
Reserve development, prior years	$ 1,094.0	$ (86.3)	$ (4.7)
2022
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	950.0
2021
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	125.0	(22.0)
2020
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years		(47.0)	(140.0)
2019
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			87.0
Commercial Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ 365.0	82.0	87.0
Property Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			36.0
environmental and asbestos \| Upper Limit
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of reserves	1.00%
Auto
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of reserves	92.00%
Personal Auto \| Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ 715.0	$ (157.0)	(113.0)
Direct Channel \| Personal Auto \| Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			$ (80.0)

Loss And Loss Adjustment Expense Reserves Incurred and Paid Claims Development with IBNR and Claim Counts (Details) $ in Millions	Dec. 31, 2023 USD ($) claim	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 27,846.5	$ 23,103.9
Commercial Lines - Liability \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	18,730.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	9,641.8
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	103.2
Liabilities for claims and claim adjustment expenses, net of reinsurance	9,191.8	7,177.0
Commercial Lines - Physical Damage \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,843.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,646.8
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	0.8
Liabilities for claims and claim adjustment expenses, net of reinsurance	197.4	211.2
Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	717.7
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	487.4
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	30.2
Liabilities for claims and claim adjustment expenses, net of reinsurance	260.5	242.5
Property \| Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,928.5
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,191.2
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	7.4
Liabilities for claims and claim adjustment expenses, net of reinsurance	744.7	839.7
2014 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	70.4	70.4	$ 70.9	$ 70.7	$ 69.4	$ 70.7	$ 70.5	$ 68.3	$ 70.0	$ 74.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 3.2
Cumulative Number of Incurred Claim Counts \| claim	9,226
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 65.5	65.0	64.2	61.1	59.0	56.9	51.1	44.3	33.9	$ 18.6
2015 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	44.8	44.6	45.1	44.8	47.0	48.3	46.1	45.4	51.2
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 3.4
Cumulative Number of Incurred Claim Counts \| claim	9,527
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 38.7	37.8	37.1	36.1	33.9	30.9	26.5	18.1	$ 6.5
2016 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	40.4	40.0	40.1	40.2	41.5	41.0	43.3	51.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 3.1
Cumulative Number of Incurred Claim Counts \| claim	7,648
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 35.5	35.0	33.8	32.7	30.6	27.0	20.9	$ 8.5
2017 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	55.1	48.0	46.2	48.8	51.1	54.6	62.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 10.2
Cumulative Number of Incurred Claim Counts \| claim	17,675
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 41.6	39.7	36.9	34.5	30.8	24.4	$ 9.6
2018 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	81.7	76.5	77.0	76.7	81.3	81.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 10.0
Cumulative Number of Incurred Claim Counts \| claim	15,475
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 65.2	61.7	56.7	49.5	39.6	$ 17.6
2019 \| Commercial Lines - Liability \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,429.9	2,434.4	2,426.3	2,370.9	2,301.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 7.6
Cumulative Number of Incurred Claim Counts \| claim	136,213
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,250.0	2,037.5	1,684.5	1,184.4	474.8
2019 \| Commercial Lines - Physical Damage \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	626.4	625.9	626.6	628.3	633.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0.0
Cumulative Number of Incurred Claim Counts \| claim	99,508
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 625.4	625.3	624.8	625.1	561.1
2019 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	87.7	88.3	85.4	83.1	80.7
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 10.3
Cumulative Number of Incurred Claim Counts \| claim	10,709
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 70.8	64.6	56.0	42.4	20.0
2019 \| Property \| Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	964.8	965.8	962.8	965.2	971.7
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 9.0
Cumulative Number of Incurred Claim Counts \| claim	73,051
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 962.2	959.3	950.5	930.4	708.0
2020 \| Commercial Lines - Liability \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,436.5	2,418.9	2,388.8	2,335.7
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 58.6
Cumulative Number of Incurred Claim Counts \| claim	117,614
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,043.5	1,628.9	1,110.4	440.8
2020 \| Commercial Lines - Physical Damage \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	624.8	622.0	624.9	631.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 2.9
Cumulative Number of Incurred Claim Counts \| claim	99,588
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 620.5	620.4	621.8	540.6
2020 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	82.9	81.9	80.7	75.0
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 14.0
Cumulative Number of Incurred Claim Counts \| claim	9,505
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 59.6	52.2	38.6	15.8
2020 \| Property \| Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,256.0	1,260.9	1,246.8	1,223.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 1.5
Cumulative Number of Incurred Claim Counts \| claim	88,736
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,237.2	1,210.7	1,141.2	832.5
2021 \| Commercial Lines - Liability \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,573.7	3,527.3	3,446.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 134.7
Cumulative Number of Incurred Claim Counts \| claim	156,829
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,414.3	1,545.9	573.6
2021 \| Commercial Lines - Physical Damage \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	910.1	909.8	920.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 3.6
Cumulative Number of Incurred Claim Counts \| claim	121,900
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 901.5	903.1	764.2
2021 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	88.8	87.3	84.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 24.4
Cumulative Number of Incurred Claim Counts \| claim	9,367
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 52.4	39.6	16.9
2021 \| Property \| Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,503.2	1,516.3	1,539.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 23.6
Cumulative Number of Incurred Claim Counts \| claim	89,864
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,444.0	1,374.5	1,035.4
2022 \| Commercial Lines - Liability \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,834.5	4,526.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 406.2
Cumulative Number of Incurred Claim Counts \| claim	180,500
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,086.4	749.2
2022 \| Commercial Lines - Physical Damage \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,330.3	1,314.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0.7
Cumulative Number of Incurred Claim Counts \| claim	147,146
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,315.0	1,114.0
2022 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	80.9	84.0
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 26.3
Cumulative Number of Incurred Claim Counts \| claim	7,660
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 39.7	18.4
2022 \| Property \| Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,622.0	1,664.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 77.0
Cumulative Number of Incurred Claim Counts \| claim	89,348
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,469.5	1,041.7
2023 \| Commercial Lines - Liability \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,455.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 1,299.6
Cumulative Number of Incurred Claim Counts \| claim	184,840
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 847.6
2023 \| Commercial Lines - Physical Damage \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,351.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (6.5)
Cumulative Number of Incurred Claim Counts \| claim	164,859
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,184.4
2023 \| Commercial Lines - Other \| Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	85.0
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 45.2
Cumulative Number of Incurred Claim Counts \| claim	6,795
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 18.4
2023 \| Property \| Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,582.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 392.4
Cumulative Number of Incurred Claim Counts \| claim	75,812
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,078.3
Agency Channel \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	34,191.1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	26,175.0
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	92.9
Liabilities for claims and claim adjustment expenses, net of reinsurance	8,109.0	6,791.2
Agency Channel \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	22,539.0
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	22,329.4
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	3.7
Liabilities for claims and claim adjustment expenses, net of reinsurance	213.3	261.5
Agency Channel \| 2019 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,879.2	5,959.9	5,918.2	5,886.9	5,885.0
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0.0
Cumulative Number of Incurred Claim Counts \| claim	916,543
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,779.3	5,626.6	5,272.8	4,533.2	2,715.2
Agency Channel \| 2019 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,268.1	3,259.0	3,261.1	3,254.7	3,277.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0.4
Cumulative Number of Incurred Claim Counts \| claim	1,879,041
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,263.7	3,260.9	3,255.9	3,259.2	3,242.5
Agency Channel \| 2020 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,458.1	5,385.7	5,405.4	5,433.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 142.8
Cumulative Number of Incurred Claim Counts \| claim	757,024
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,122.0	4,796.8	4,112.2	2,383.0
Agency Channel \| 2020 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,323.3	3,327.3	3,319.8	3,328.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (8.4)
Cumulative Number of Incurred Claim Counts \| claim	1,785,036
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,328.0	3,323.0	3,322.5	3,250.1
Agency Channel \| 2021 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,936.4	6,861.8	6,716.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 174.2
Cumulative Number of Incurred Claim Counts \| claim	885,607
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 6,183.1	5,239.4	2,855.4
Agency Channel \| 2021 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,628.5	4,624.3	4,708.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 8.9
Cumulative Number of Incurred Claim Counts \| claim	2,105,540
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,611.5	4,620.9	4,438.1
Agency Channel \| 2022 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,301.5	7,076.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 402.8
Cumulative Number of Incurred Claim Counts \| claim	838,763
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,564.1	3,018.8
Agency Channel \| 2022 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,544.6	5,429.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (13.3)
Cumulative Number of Incurred Claim Counts \| claim	2,031,717
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,542.0	5,176.2
Agency Channel \| 2023 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	8,615.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 1,715.2
Cumulative Number of Incurred Claim Counts \| claim	883,430
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,526.5
Agency Channel \| 2023 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,774.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (298.0)
Cumulative Number of Incurred Claim Counts \| claim	2,091,830
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,584.2
Direct Channel \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	35,886.8
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,148.2
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	79.4
Liabilities for claims and claim adjustment expenses, net of reinsurance	8,818.0	7,187.2
Direct Channel \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,394.8
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	27,174.5
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net, Not Separately Presented	2.8
Liabilities for claims and claim adjustment expenses, net of reinsurance	223.1	284.7
Direct Channel \| 2019 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,802.1	5,870.0	5,837.9	5,811.7	5,756.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0.1
Cumulative Number of Incurred Claim Counts \| claim	957,826
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,716.3	5,568.8	5,218.8	4,452.5	2,630.3
Direct Channel \| 2019 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,757.8	3,747.9	3,749.6	3,737.8	3,787.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0.3
Cumulative Number of Incurred Claim Counts \| claim	2,272,383
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,753.9	3,750.9	3,746.8	3,751.3	$ 3,782.6
Direct Channel \| 2020 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,343.1	5,301.5	5,322.7	5,356.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 126.4
Cumulative Number of Incurred Claim Counts \| claim	789,952
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,035.9	4,721.4	4,018.7	2,301.3
Direct Channel \| 2020 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,762.0	3,765.9	3,753.3	3,775.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (9.7)
Cumulative Number of Incurred Claim Counts \| claim	2,139,045
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,767.4	3,762.2	3,765.9	$ 3,720.0
Direct Channel \| 2021 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,244.1	7,180.3	6,964.7
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 164.5
Cumulative Number of Incurred Claim Counts \| claim	981,424
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 6,487.9	5,460.5	2,915.0
Direct Channel \| 2021 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,572.9	5,568.2	5,752.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 3.6
Cumulative Number of Incurred Claim Counts \| claim	2,602,359
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,559.6	5,578.7	$ 5,421.9
Direct Channel \| 2022 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,869.6	7,563.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 398.5
Cumulative Number of Incurred Claim Counts \| claim	970,145
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 5,982.6	3,131.8
Direct Channel \| 2022 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,724.2	6,613.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (27.3)
Cumulative Number of Incurred Claim Counts \| claim	2,606,698
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 6,731.9	$ 6,325.7
Direct Channel \| 2023 \| Personal Lines - Liability \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	9,627.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 1,763.6
Cumulative Number of Incurred Claim Counts \| claim	1,080,475
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,925.5
Direct Channel \| 2023 \| Personal Lines - Physical Damage \| Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	7,577.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (459.8)
Cumulative Number of Incurred Claim Counts \| claim	2,851,047
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 7,361.7

Loss And Loss Adjustment Expense Reserves Reconciliation of the Claims Development to the Liability for Claims and Claim Adjustment Expenses (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	$ 27,846.5	$ 23,103.9
Total reinsurance recoverables on unpaid claims	4,748.0	5,485.4
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	1,753.7	1,696.2
Reinsurance recoverables on unpaid claims	41.0	73.8
Total gross liability for unpaid claims and claim adjustment expense	34,389.2	30,359.3	$ 26,164.1	$ 20,265.8
Other business
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	88.7	108.9
Total reinsurance recoverables on unpaid claims	475.1	559.0
Commercial Lines Segment \| Commercial Lines - Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	9,191.8	7,177.0
Total reinsurance recoverables on unpaid claims	1,077.7	1,273.7
Commercial Lines Segment \| Commercial Lines - Physical Damage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	197.4	211.2
Total reinsurance recoverables on unpaid claims	1.4	0.5
Commercial Lines Segment \| Commercial Lines - Other
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	260.5	242.5
Total reinsurance recoverables on unpaid claims	216.0	204.6
Property Segment \| Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	744.7	839.7
Total reinsurance recoverables on unpaid claims	631.4	1,068.1
Agency Channel \| Personal Lines Segment \| Personal Lines - Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	8,109.0	6,791.2
Total reinsurance recoverables on unpaid claims	875.1	894.1
Agency Channel \| Personal Lines Segment \| Personal Lines - Physical Damage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	213.3	261.5
Total reinsurance recoverables on unpaid claims	0.0	0.0
Direct Channel \| Personal Lines Segment \| Personal Lines - Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	8,818.0	7,187.2
Total reinsurance recoverables on unpaid claims	1,471.3	1,485.4
Direct Channel \| Personal Lines Segment \| Personal Lines - Physical Damage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	223.1	284.7
Total reinsurance recoverables on unpaid claims	$ 0.0	$ 0.0

Loss And Loss Adjustment Expense Reserves Historical Claims Duration (Details)	Dec. 31, 2023
Personal Lines Segment \| Agency Channel \| Personal Lines - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	42.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	33.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	13.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	6.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.60%
Personal Lines Segment \| Agency Channel \| Personal Lines - Physical Damage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	96.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	3.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.10%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.10%
Personal Lines Segment \| Direct Channel \| Personal Lines - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	41.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	34.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	13.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	6.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.50%
Personal Lines Segment \| Direct Channel \| Personal Lines - Physical Damage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	97.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	2.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.20%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.10%
Commercial Lines Segment \| Commercial Lines - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	16.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	27.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	22.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	15.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	8.70%
Commercial Lines Segment \| Commercial Lines - Physical Damage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	86.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	13.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.20%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.00%
Commercial Lines Segment \| Commercial Lines - Other
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	20.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	26.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	14.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	9.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.40%
Property Segment \| Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	67.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	24.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	4.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	1.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.30%

Reinsurance Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct premiums written	$ 62,721.2	$ 52,335.6	$ 48,129.6
Ceded written	(1,171.0)	(1,254.5)	(1,724.4)
Net premiums written	61,550.2	51,081.1	46,405.2
Direct premiums earned	59,881.1	50,650.2	46,018.6
Ceded earned	(1,216.7)	(1,409.0)	(1,649.9)
Net premiums earned	58,664.4	49,241.2	44,368.7
non regulated reinsurance plan
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded written	(636.0)	(633.0)	(1,049.9)
Ceded earned	(671.4)	(734.2)	(999.7)
Regulated reinsurance plan
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded written	(535.0)	(621.5)	(674.5)
Ceded earned	$ (545.3)	$ (674.8)	$ (650.2)

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reinsurance Prepaid Reinsurance Premiums and Reinsurance Recoverables (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 5,093.9	$ 5,832.1
Percentage Of Total Reinsurance Recoverables	100.00%	100.00%
Prepaid reinsurance premiums	$ 249.8	$ 295.5
Percentage Of Total Prepaid Reinsurance Premiums	100.00%	100.00%
Commercial Lines reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 1,385.7	$ 1,544.3
Percentage Of Total Reinsurance Recoverables	27.00%	27.00%
Prepaid reinsurance premiums	$ 56.3	$ 91.0
Percentage Of Total Prepaid Reinsurance Premiums	23.00%	31.00%
Property reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 381.2	$ 524.4
Percentage Of Total Reinsurance Recoverables	8.00%	9.00%
Prepaid reinsurance premiums	$ 11.0	$ 11.6
Percentage Of Total Prepaid Reinsurance Premiums	4.00%	4.00%
Other reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 10.0	$ 5.5
Percentage Of Total Reinsurance Recoverables	0.00%	0.00%
Prepaid reinsurance premiums	$ 0.0	$ 0.0
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	0.00%
Non State Reinsurance Plans
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 1,776.9	$ 2,074.2
Percentage Of Total Reinsurance Recoverables	35.00%	36.00%
Prepaid reinsurance premiums	$ 67.3	$ 102.6
Percentage Of Total Prepaid Reinsurance Premiums	27.00%	35.00%
State Reinsurance Plans
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 3,317.0	$ 3,757.9
Percentage Of Total Reinsurance Recoverables	65.00%	64.00%
Prepaid reinsurance premiums	$ 182.5	$ 192.9
Percentage Of Total Prepaid Reinsurance Premiums	73.00%	65.00%
State Reinsurance Plans \| Michigan Catastrophic Claims Association
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 2,272.1	$ 2,332.3
Percentage Of Total Reinsurance Recoverables	45.00%	40.00%
Prepaid reinsurance premiums	$ 40.2	$ 26.4
Percentage Of Total Prepaid Reinsurance Premiums	16.00%	9.00%
State Reinsurance Plans \| Commercial Auto Insurance Procedures Plans
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 539.1	$ 626.8
Percentage Of Total Reinsurance Recoverables	10.00%	11.00%
Prepaid reinsurance premiums	$ 0.0	$ 50.4
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	17.00%
State Reinsurance Plans \| Florida Hurricane Catastrophe Fund
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 306.6	$ 437.3
Percentage Of Total Reinsurance Recoverables	6.00%	7.00%
Prepaid reinsurance premiums	$ 0.0	$ 0.0
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	0.00%
State Reinsurance Plans \| North Carolina Reinsurance Facility
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 184.7	$ 143.2
Percentage Of Total Reinsurance Recoverables	4.00%	2.00%
Prepaid reinsurance premiums	$ 74.6	$ 54.5
Percentage Of Total Prepaid Reinsurance Premiums	30.00%	18.00%
State Reinsurance Plans \| Other reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 3.8	$ 2.9
Percentage Of Total Reinsurance Recoverables	0.00%	0.00%
Prepaid reinsurance premiums	$ 1.3	$ 1.5
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	1.00%
Federal Reinsurance Plans \| National Flood Insurance Program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 10.7	$ 215.4
Percentage Of Total Reinsurance Recoverables	0.00%	4.00%
Prepaid reinsurance premiums	$ 66.4	$ 60.1
Percentage Of Total Prepaid Reinsurance Premiums	27.00%	20.00%

Statutory Financial Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statutory Financial Information Disclosures [Abstract]
Consolidated statutory policyholders' surplus	$ 22,249.6	$ 17,879.9
Statutory net income	3,502.2	$ 2,763.5	$ 2,283.9
Consolidated statutory policyholders' surplus, net admitted assets of insurance subsidiaries and affiliate that are required to meet minimum statutory surplus requirements in such entities' states of domicile	1,513.2
Cash and Non-Cash Dividends Paid To Parent Company	413.4
Maximum aggregate dividend amount subsidiaries could pay without prior approval from regulatory authorities	$ 3,365.1

Employee Benefit Plans - Additional Information (Detail) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Benefits Disclosure [Line Items]
Minimum employment period for benefits	30 days
Postemployment benefits liability	$ 18.7	$ 19.6
Compensation, Percentage	100.00%
Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Aggregate fair value of the restricted equity awards that vested during the period	$ 195.2	154.4	$ 139.1
Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	11 months
Total pretax intrinsic value of options exercised and restricted stock vested	$ 4.2	$ 3.4	3.8
Non Employee Director Restricted Equity Awards \| 2017 Directors Equity Incentive Plan
Employee Benefits Disclosure [Line Items]
Shares authorized		650
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Additional Shares Authorized		150
Executive Deferred Compensation Plan
Employee Benefits Disclosure [Line Items]
Common shares reserved for issuance under executive deferred compensation plan	11,100
Equity Incentive Plan Twenty Fifteen
Employee Benefits Disclosure [Line Items]
Shares authorized	17,000
Defined Contribution Pension Plan 401k
Employee Benefits Disclosure [Line Items]
Defined Contribution Plan, Requisite Service Period	2 years
Matching contributions	$ 205.9	$ 179.9	$ 159.2
Defined Contribution Pension Plan 401k \| Upper Limit
Employee Benefits Disclosure [Line Items]
Matching contribution to defined contribution pension plan	6.00%
Cash
Employee Benefits Disclosure [Line Items]
Compensation, Percentage	40.00%
Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Compensation, Percentage	60.00%
Vesting tranche one \| Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	3 years
Vesting tranche two \| Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	4 years
Vesting tranche three \| Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	5 years
Common equities
Employee Benefits Disclosure [Line Items]
Employee Stock Ownership Plan Shares held	18,200

Employee Benefit Plans Amounts Charged to Income for employees Incentive Compensation Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Incentive Compensation Cash Award
Incentive Compensation Plans Expense [Line Items]
Pretax	$ 897.3	$ 380.8	$ 619.3
After Tax	708.9	300.8	489.2
Employee Stock
Incentive Compensation Plans Expense [Line Items]
Pretax	121.3	122.7	100.7
After Tax	$ 104.3	$ 106.7	$ 86.6

Employee Benefit Plans - Vesting ranges of outstanding performance based equity awards (Details) - Performance Shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Insurance Operating Results \| Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	0.00%	0.00%	0.00%
Insurance Operating Results \| Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	250.00%	250.00%	250.00%
Investment Results \| Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	0.00%	0.00%	0.00%
Investment Results \| Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	200.00%	200.00%	200.00%

Employee Benefit Plans Summary of All Employee Restricted Equity Award Activity (Detail) - Employee Restricted Equity Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Number of Shares
Beginning of year	3,198,150	3,539,022	3,570,271
Add (deduct):
Granted	1,080,658	1,154,838	1,476,802
Vested	(1,338,466)	(1,378,070)	(1,452,353)
Forfeited	(46,600)	(117,640)	(55,698)
End of year	2,893,742	3,198,150	3,539,022
Weighted Average Grant Date Fair Value
Beginning of year	$ 81.71	$ 67.24	$ 57.68
Granted	110.93	96.54	70.11
Vested	63.10	57.79	46.88
Forfeited	84.86	72.44	60.81
End of year	$ 101.18	$ 81.71	$ 67.24
Unrecognized compensation cost related to unvested equity awards	$ 93.3
Period of recognition of compensation expense related to unvested equity awards	2 years 2 months 12 days
Dividend Equivalent Units
Add (deduct):
Granted	36,656	44,327	237,582
Weighted Average Grant Date Fair Value
Granted	$ 0	$ 0	$ 0
Performance Shares
Weighted Average Grant Date Fair Value
Target shares	557,119
Units expected to vest	1,204,918

Employee Benefit Plans Summary of all Directors' Restricted Stock Activity (Detail) - Non Employee Director Restricted Equity Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested equity awards	$ 1.0	$ 1.0	$ 0.9
Number of Shares
Beginning of year	30,439	29,206	39,403
Add (deduct):
Granted	25,075	30,439	29,206
Vested	(30,439)	(29,206)	(39,403)
End of year	25,075	30,439	29,206
Weighted Average Grant Date Fair Value
Beginning of year	$ 109.75	$ 105.16	$ 74.77
Granted	133.43	109.75	105.16
Vested	109.75	105.16	74.77
End of year	$ 133.43	$ 109.75	$ 105.16

Employee Benefit Plans Assets Held in Deferral Plan Irrevocable Grantor Trust Account (Detail) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$ 283.6	$ 281.4
Other Investment Funds
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	165.1	150.4
Common equities \| Progressive common shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$ 118.5	$ 131.0
Deferred Compensation Arrangement with Individual, Shares Authorized for Issuance	1.6	2.0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(v)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Payments of Ordinary Dividends, Common Stock

Segment Information Operating Results (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 62,108.5	$ 49,610.7	$ 47,702.0
Pretax Profit (Loss)	4,903.7	922.1	4,210.0
Goodwill impairment	0.0	224.8	0.0
Amortization of intangible assets	14.2	31.0	57.7
Personal Lines Segment \| Agency Channel \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	21,198.2	17,744.7	16,881.0
Pretax Profit (Loss)	1,029.2	734.1	992.1
Personal Lines Segment \| Direct Channel \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	25,015.1	20,135.5	18,492.3
Pretax Profit (Loss)	1,828.2	769.4	619.2
Property Segment
Segment Reporting Information [Line Items]
Goodwill impairment		224.8
Operating Segments \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	58,664.4	49,241.2	44,368.7
Pretax Profit (Loss)	2,992.3	2,064.0	2,065.4
Operating Segments \| Personal Lines Segment \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	46,213.3	37,880.2	35,373.3
Pretax Profit (Loss)	$ 2,857.4	$ 1,503.5	$ 1,611.3
Personal auto insurance percentage of the total personal lines segment net premiums earned	94.00%	94.00%	94.00%
Operating Segments \| Commercial Lines Segment \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	$ 9,898.7	$ 9,088.3	$ 6,945.2
Pretax Profit (Loss)	123.0	810.3	767.8
Operating Segments \| Property Segment
Segment Reporting Information [Line Items]
Pretax Profit (Loss)		(463.2)
Goodwill impairment	0.0	(224.8)	0.0
Operating Segments \| Property Segment \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	2,551.4	2,270.0	2,042.5
Pretax Profit (Loss)	28.1	(238.4)	(312.3)
Operating Segments \| Other Indemnity \| Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	1.0	2.7	7.7
Pretax Profit (Loss)	(16.2)	(11.4)	(1.4)
Segment Reconciling Items
Segment Reporting Information [Line Items]
Interest Expense	(268.4)	(243.5)	(218.6)
Segment Reconciling Items \| Fees And Other Revenues
Segment Reporting Information [Line Items]
Revenues	889.1	722.1	691.8
Segment Reconciling Items \| Service Businesses
Segment Reporting Information [Line Items]
Revenues	310.1	299.3	271.4
Pretax Profit (Loss)	(38.9)	2.6	18.6
Segment Reconciling Items \| Investments Member
Segment Reporting Information [Line Items]
Revenues	2,244.9	(651.9)	2,370.1
Pretax Profit (Loss)	$ 2,218.7	$ (676.2)	$ 2,344.6

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Details) - Underwriting Operations	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Personal Lines Segment \| Agency Channel
Segment Reporting Information [Line Items]
Underwriting Margin	4.90%	4.10%	5.90%
Combined Ratio	95.10%	95.90%	94.10%
Personal Lines Segment \| Direct Channel
Segment Reporting Information [Line Items]
Underwriting Margin	7.30%	3.80%	3.40%
Combined Ratio	92.70%	96.20%	96.60%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	5.10%	4.20%	4.70%
Combined Ratio	94.90%	95.80%	95.30%
Operating Segments \| Personal Lines Segment
Segment Reporting Information [Line Items]
Underwriting Margin	6.20%	4.00%	4.60%
Combined Ratio	93.80%	96.00%	95.40%
Operating Segments \| Commercial Lines Segment
Segment Reporting Information [Line Items]
Underwriting Margin	1.20%	8.90%	11.10%
Combined Ratio	98.80%	91.10%	88.90%
Operating Segments \| Property Segment
Segment Reporting Information [Line Items]
Underwriting Margin	1.10%	(10.50%)	(15.30%)
Combined Ratio	98.90%	110.50%	115.30%

Segment Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Entity	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Depreciation \| $	$ 285.5	$ 305.6	$ 279.7
Operating Segments \| Personal Lines Segment \| Agency Channel \| Lower Limit
Segment Reporting Information [Line Items]
Independent insurance agencies and brokerages \| Entity	40,000

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ (3,556.9)	$ 52.3	$ 1,187.4
Unrealized Holding Gain (Loss) on Securities Arising During the Period, before tax	1,256.1	(4,168.4)	(892.4)
Foreign Currently Translation Adjustment, before tax	0.4	(0.7)	(0.8)
Total other comprehensive income (loss) before reclassifications, before tax	1,256.5	(4,169.1)	(893.2)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(246.9)	(559.4)	242.8
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(0.6)	(0.5)	(0.9)
Total reclassification adjustment for amounts realized in net income, before tax	(247.5)	(559.9)	241.9
Total other comprehensive income, before tax	1,504.0	(3,609.2)	(1,135.1)
AOCI before Tax, Attributable to Parent, ending balance	(2,052.9)	(3,556.9)	52.3
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	754.9	(11.6)	(255.7)
Unrealized Holding Gain (Loss) on Securities Arising During the Period, tax	(265.6)	878.7	193.0
Foreign currency translation adjustment, tax	(0.1)	0.1	0.2
Total Other Comprehensive Income (Loss), before Reclassification Adjustments, Tax	(265.7)	878.8	193.2
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	51.9	112.2	(51.1)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax	0.1	0.1	0.2
Total reclassification adjustment for amounts realized in net income, Total tax (provisions) benefit	52.0	112.3	(50.9)
Total other comprehensive income, Total tax (provision) benefit	(317.7)	766.5	244.1
AOCI Tax, Attributable to Parent, ending balance	437.2	754.9	(11.6)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(2,802.0)	40.7	931.7
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	990.5	(3,289.7)	(699.4)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0.3	(0.6)	(0.6)
Total other comprehensive income (loss), before reclassifications, after tax	990.8	(3,290.3)	(700.0)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(195.0)	(447.2)	191.7
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.5)	(0.4)	(0.7)
Total reclassification adjustment for amounts realized in net income, Net of tax	(195.5)	(447.6)	191.0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	1,186.3	(2,842.7)	(891.0)
After tax total accumulated other comprehensive income, ending balance	(1,615.7)	(2,802.0)	40.7
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	947.3
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	990.5	(3,289.7)	(699.4)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0.0	0.0	0.0
Total other comprehensive income (loss), before reclassifications, after tax	990.5	(3,289.7)	(699.4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(195.0)	(447.2)	191.7
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0.0	0.0	0.0
Total reclassification adjustment for amounts realized in net income, Net of tax	(195.0)	(447.2)	191.7
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	1,185.5	(2,842.5)	(891.1)
After tax total accumulated other comprehensive income, ending balance	(1,600.8)	(2,786.3)	56.2
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(14.5)	(14.9)	(15.6)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0.0	0.0	0.0
Total other comprehensive income (loss), before reclassifications, after tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.5)	(0.4)	(0.7)
Total reclassification adjustment for amounts realized in net income, Net of tax	(0.5)	(0.4)	(0.7)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.5	0.4	0.7
After tax total accumulated other comprehensive income, ending balance	(14.0)	(14.5)	(14.9)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(1.2)	(0.6)	0.0
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0.3	(0.6)	(0.6)
Total other comprehensive income (loss), before reclassifications, after tax	0.3	(0.6)	(0.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	0.0	0.0	0.0
Total reclassification adjustment for amounts realized in net income, Net of tax	0.0	0.0	0.0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.3	(0.6)	(0.6)
After tax total accumulated other comprehensive income, ending balance	$ (0.9)	$ (1.2)	$ (0.6)

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement Additional Information (Detail) $ in Millions	Dec. 31, 2023 USD ($)
Statement of Comprehensive Income [Abstract]
Net unrealized losses on forecasted transactions, expected to reclassify into interest expense within the next 12 months	$ (0.6)

Litigation - Additional Information (Details)	Dec. 31, 2023 segment
Loss Contingency, Information about Litigation Matters [Abstract]
Number of States, Classes Certified	4

Leases - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Accounts payable, accrued expenses, and other liabilities	Accounts payable, accrued expenses, and other liabilities
Operating lease assets	$ 172.5	$ 130.5
Operating lease liabilities	$ 177.2	$ 137.2
Weighted-average remaining term	3 years 2 months 12 days	2 years 6 months
Weighted-average discount rate	5.10%	2.00%

Leases - Schedule of operating lease maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 74.0
2025	54.6
2026	37.6
2027	15.8
2028	6.0
Thereafter	4.8
Total	192.8
Interest	(15.6)
Present value of lease liabilities	$ 177.2	$ 137.2

Leases Expenses Incurred for Leases (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Expense	$ 94.4	$ 89.1	$ 90.4

Dividends Dividends (Details) - USD ($)
$ / shares in Units, $ in Millions

1 Months Ended

12 Months Ended

Dec. 31, 2023

Oct. 31, 2023

Sep. 30, 2023

Jul. 31, 2023

Jun. 30, 2023

Apr. 30, 2023

Mar. 31, 2023

Jan. 31, 2023

Oct. 31, 2022

Sep. 30, 2022

Jul. 31, 2022

Apr. 30, 2022

Mar. 31, 2022

Jan. 31, 2022

Dec. 31, 2021

Oct. 31, 2021

Sep. 30, 2021

Jul. 31, 2021

Apr. 30, 2021

Mar. 31, 2021

Jan. 31, 2021

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

^[1]

$ 234.0

$ 3,746.5

Common shares, dividends declared (USD per share)

$ 1.15

$ 0.40

$ 1.90

Payments of Ordinary Dividends, Preferred Stock and Preference Stock

^[1]

$ 43.6

$ 26.8

Annual variable dividend

Common Stock, Dividends, Per Share, Cash Paid

$ 1.50

$ 4.50

Payments of Ordinary Dividends, Common Stock

$ 876.5

$ 2,635.9

Common shares, dividends declared (USD per share)

$ 0.75

Quarterly dividend

Common Stock, Dividends, Per Share, Cash Paid

$ 0.10

Payments of Ordinary Dividends, Common Stock

$ 58.5

$ 58.6

Common shares, dividends declared (USD per share)

$ 0.10

Series B Preferred Stock

Preferred Stock, Dividends, Per Share, Cash Paid

$ 0.0

13.4

0.0

13.4

$ 20.753157

$ 20.67700

$ 18.92463

$ 26.875

Payments of Ordinary Dividends, Preferred Stock and Preference Stock

$ 10.4

$ 10.3

$ 9.5

$ 13.4

Common equities

Common equities | Annual variable dividend

497.9

$ 58.5

497.9

$ 58.5

Common equities | Quarterly dividend

439.3