The Progressive Corporation (PGR) 10-K 1 Mar 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-09518
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	34-0963169
Entity Address, Address Line One	6300 Wilson Mills Road,
Entity Address, City or Town	Mayfield Village,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	44143
City Area Code	440
Local Phone Number	461-5000
Title of 12(b) Security	Common Shares, $1.00 Par Value
Trading Symbol	PGR
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 46,424,173,990
Entity Common Stock, Shares Outstanding		585,747,728
Entity Central Index Key	0000080661
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Amendment Flag	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s Proxy Statement for the Annual Meeting of Shareholders to be held on May 7, 2021, and the Annual Report to Shareholders of The Progressive Corporation and subsidiaries for the year ended December 31, 2020, included as Exhibit 13 to this Form 10-K, are incorporated by reference in Parts I, II, III, and IV hereof.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Net premiums earned	$ 39,261.6	$ 36,192.4	$ 30,933.3
Investment income	936.6	1,042	820.5
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales	914.7	334.6	170.7
Net holding period gains (losses) on securities	715.3	757.9	(507.9)
Net impairment losses recognized in earnings	0	(63.3)	(68.3)
Total net realized gains (losses) on securities	1,630	1,029.2	(405.5)
Fees and other revenues	603.5	563.7	472.2
Service revenues	226.4	195	158.5
Total revenues	42,658.1	39,022.3	31,979
Expenses
Losses and loss adjustment expenses	25,121.8	25,470.5	21,721
Policy acquisition costs	3,273.2	3,023.2	2,573.7
Other underwriting expenses	5,570	4,975.1	4,195.8
Policyholder credit expense	1,077.4	0	0
Investment expenses	20	24.6	24.3
Service expenses	205.5	178.9	134.1
Interest expense	217	189.7	166.5
Total expenses	35,484.9	33,862	28,815.4
Net Income
Income before income taxes	7,173.2	5,160.3	3,163.6
Provision for income taxes	1,468.6	1,180.3	542.6
Net income	5,704.6	3,980	2,621
Net income attributable to noncontrolling interest (NCI)	0	(9.7)	(5.7)
Net income attributable to Progressive	5,704.6	3,970.3	2,615.3
Changes in:
Total net unrealized gains (losses) on fixed-maturity securities	586.5	466.4	(99.3)
Net unrealized losses on forecasted transactions	0.8	0.8	0.8
Other comprehensive income (loss)	587.3	467.2	(98.5)
Other comprehensive (income) loss attributable to NCI	0	(4.6)	3.3
Comprehensive income attributable to Progressive	6,291.9	4,432.9	2,520.1
Computation of Earnings Per Common Share
Net income attributable to Progressive	5,704.6	3,970.3	2,615.3
Less: Preferred share dividends	26.9	26.9	21.4
Net income available to common shareholders	$ 5,677.7	$ 3,943.4	$ 2,593.9
Average common shares outstanding - Basic	584.9	583.8	582.4
Net effect of dilutive stock-based compensation	2.7	3.4	4.3
Total average equivalent common shares - Diluted	587.6	587.2	586.7
Basic: Earnings per share (usd per share)	$ 9.71	$ 6.75	$ 4.45
Diluted: Earnings per share (usd per share)	$ 9.66	$ 6.72	$ 4.42

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Assets
Fixed maturities (amortized cost: $35,589.1 and $32,643.1)		$ 36,810.9	$ 33,110.3
Short-term investments (amortized cost: $5,218.5 and $1,798.8)		5,218.5	1,798.8
Total available-for-sale securities		42,029.4	34,909.1
Nonredeemable preferred stocks		1,447.9	1,038.9
Common equities		4,053	3,306.3
Total equity securities		5,500.9	4,345.2
Total investments		47,530.3	39,254.3
Cash and cash equivalents		76.5	226.2
Restricted cash		0	1.2
Total cash, cash equivalents, and restricted cash		76.5	227.4
Accrued investment income		176.4	181.3
Premiums receivable, net of allowance for credit losses of $356.2 and $283.2		8,160.1	7,507.3
Reinsurance recoverables		4,019.4	3,378.9
Prepaid reinsurance premiums		368.1	626.5
Deferred acquisition costs		1,237.2	1,056.5
Property and equipment, net of accumulated depreciation of $1,291.4 and $1,138.1		1,106	1,213.7
Goodwill		452.7	452.7
Intangible assets, net of accumulated amortization of $326.1 and $314.0		171.4	228.3
Other assets		800.2	783.6
Total assets		64,098.3	54,910.5
Liabilities
Unearned premiums		13,437.5	12,388.8
Loss and loss adjustment expense reserves		20,265.8	18,105.4
Deferred Tax Liability, Federal Tax		310	118
Dividends payable on common shares		2,694.5	1,375.4
Accounts payable, accrued expenses, and other liabilities1	[1]	4,955.8	4,617
Debt	[2]	5,396.1	4,407.1
Total liabilities		47,059.7	41,011.7
Redeemable noncontrolling interest (NCI)	[3]	0	225.6
Shareholders’ Equity
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)		493.9	493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 212.3 and 212.9)		585.2	584.6
Paid-in capital		1,672.9	1,573.4
Retained earnings		13,354.9	10,679.6
Accumulated other comprehensive income (loss):
Net unrealized gains (losses) on fixed-maturity securities		947.3	360.8
Net unrealized losses on forecasted transactions		(15.6)	(16.4)
Accumulated other comprehensive income attributable to NCI		0	(2.7)
Total accumulated other comprehensive income (loss) attributable to Progressive		931.7	341.7
Total shareholders’ equity		17,038.6	13,673.2
Total liabilities, redeemable NCI, and shareholders’ equity		$ 64,098.3	$ 54,910.5
[1]	See Note 1 – Reporting and Accounting Policies for Commitments and Contingencies and Note 12 – Litigation
[2]	Consists of both short-term and long-term debt. See Note 4 – Debt for further discussion .
[3]	See Note 15 – Redeemable Noncontrolling Interest for further discussion .

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fixed maturities, amortized cost	$ 35,589.1	$ 32,643.1
Short-term investments, amortized cost	5,218.5	1,798.8
Nonredeemable preferred stocks, cost	1,358.7	971.3
Equity Securities Common Equities Cost	1,187.3	1,125.5
Premium receivable, allowance for credit loss	356.2	283.2
Property and equipment, accumulated depreciation	1,291.4	1,138.1
Intangible assets, accumulated amortization	$ 326.1	$ 314
Common Shares, par value (USD per share)	$ 1	$ 1
Common Shares, authorized (shares)	900,000,000	900,000,000
Common Shares, issued (shares)	797,500,000	797,500,000
Common Shares, treasury shares (shares)	212,300,000	212,900,000
Serial Preferred Stock
Preferred shares, authorized (in shares)	20,000,000	20,000,000
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	500,000	500,000

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Millions		Total	Voting Preferred Stock	Preferred Shares, No Par Value	Common Shares, $1.00 Par Value	Paid-In Capital	Retained Earnings	Retained EarningsCumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss) Attributable to Progressive	Accumulated Other Comprehensive Income (Loss) Attributable to ProgressiveCumulative Effect, Period of Adoption, Adjustment	Serial Preferred Stock	Serial Preferred StockSeries B Preferred Stock
Reclassification of disproportionate tax effects		$ (7.7)
Balance, beginning of year at Dec. 31, 2017				$ 0	$ 581.7	$ 1,389.2	$ 6,031.7		$ 1,282.2
Issuance of Serial Preferred Shares, Series B				493.9
Treasury shares purchased					(1.4)	(3.3)	(74.3)
Net restricted equity awards issued/vested					2.9	(2.9)
Amortization of equity-based compensation						76.2
Reinvested dividends on restricted stock units						12.2	(12.2)
Adjustment to carrying amount of redeemable noncontrolling interest		(2.8)				7.6
Net income attributable to Progressive		2,615.3					2,615.3
Cash dividends declared on common shares ($4.90, $2.65, and $2.5140 per share)1	[1]						(1,466)
Cash dividends declared on Serial Preferred Shares, Series B ($80.625, $53.75, and $27.024 per share)1	[1]						(13.5)
Other, net							1.1
Attributable to noncontrolling interest		3.3							(0.1)
Other comprehensive income (loss)									(98.5)
Balance, end of year at Dec. 31, 2018		$ 10,821.8		493.9	583.2	1,479	8,386.6		(120.9)
Balance, end of year (Accounting Standards Update 2016-01) at Dec. 31, 2018								$ 1,300.2		$ (1,300.2)
Common shares, dividends declared (USD per share)		$ 2.5140
Preferred shares, dividends declared (USD per share)												$ 27.024
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02							4.3		(4.3)
Preferred shares, authorized (in shares)			5,000,000
Preferred shares, issued (in shares)			0
Issuance of Serial Preferred Shares, Series B				0
Treasury shares purchased					(1.3)	(3.2)	(86.8)
Net restricted equity awards issued/vested					2.7	(2.7)
Amortization of equity-based compensation						90.1
Reinvested dividends on restricted stock units						10.6	(10.6)
Adjustment to carrying amount of redeemable noncontrolling interest		$ 0.3				(0.4)
Net income attributable to Progressive		3,970.3					3,970.3
Cash dividends declared on common shares ($4.90, $2.65, and $2.5140 per share)1	[1]						(1,548.4)
Cash dividends declared on Serial Preferred Shares, Series B ($80.625, $53.75, and $27.024 per share)1	[1]						(26.8)
Other, net							(4.7)
Attributable to noncontrolling interest		(4.6)							(4.6)
Other comprehensive income (loss)									467.2
Balance, end of year at Dec. 31, 2019		$ 13,673.2		493.9	584.6	1,573.4	10,679.6		341.7
Balance, end of year (Accounting Standards Update 2016-01) at Dec. 31, 2019								0		0
Common shares, dividends declared (USD per share)		$ 2.65
Preferred shares, dividends declared (USD per share)												53.75
Reclassification of disproportionate tax effects		$ 2.7
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02							0		0
Preferred stock, par value												$ 0
Common Shares, par value (USD per share)		$ 1
Preferred shares, authorized (in shares)			5,000,000								20,000,000	500,000
Preferred shares, issued (in shares)			0									500,000
Issuance of Serial Preferred Shares, Series B				0
Treasury shares purchased					(1.3)	(3.6)	(106.7)
Net restricted equity awards issued/vested					1.9	(1.9)
Amortization of equity-based compensation						89.4
Reinvested dividends on restricted stock units						18.2	(18.2)
Adjustment to carrying amount of redeemable noncontrolling interest		$ 0				(2.6)
Net income attributable to Progressive		5,704.6					5,704.6
Cash dividends declared on common shares ($4.90, $2.65, and $2.5140 per share)1	[1]						(2,865.9)
Cash dividends declared on Serial Preferred Shares, Series B ($80.625, $53.75, and $27.024 per share)1	[1]						(40.2)
Other, net							1.7
Attributable to noncontrolling interest		0							2.7
Other comprehensive income (loss)									587.3
Balance, end of year at Dec. 31, 2020		$ 17,038.6		$ 493.9	$ 585.2	$ 1,672.9	13,354.9		931.7
Balance, end of year (Accounting Standards Update 2016-01) at Dec. 31, 2020								$ 0		$ 0
Common shares, dividends declared (USD per share)		$ 4.90
Preferred shares, dividends declared (USD per share)												$ 80.625
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02							$ 0		$ 0
Preferred stock, par value												$ 0
Common Shares, par value (USD per share)		$ 1
Preferred shares, authorized (in shares)			5,000,000								20,000,000	500,000
Preferred shares, issued (in shares)			0									500,000
[1]	See Note 14 – Dividends for further discussion.

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Cash Flows [Abstract]
Net income	$ 5,704.6	$ 3,980	$ 2,621
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	274.9	239.8	190.4
Amortization of intangible assets	56.9	66.3	72
Net amortization of fixed-income securities	100.9	33.3	34.3
Amortization of equity-based compensation	89.4	90.2	77.2
Net realized (gains) losses on securities	(1,630)	(1,029.2)	405.5
Net (gains) losses on disposition of property and equipment	12.5	11	32.1
Changes in:
Premiums receivable	(652.8)	(1,010.2)	(1,074.6)
Reinsurance recoverables	(640.5)	(682.8)	(422.7)
Prepaid reinsurance premiums	258.4	(316.8)	(106.4)
Deferred acquisition costs	(180.7)	(104.9)	(171.1)
Income taxes	(23.1)	227.2	(158.7)
Unearned premiums	1,048.7	1,702.3	1,783
Loss and loss adjustment expense reserves	2,160.4	2,704.6	2,313.9
Accounts payable, accrued expenses, and other liabilities	328.9	611.6	746.6
Other, net	(2.9)	(260.8)	(57.7)
Net cash provided by operating activities	6,905.6	6,261.6	6,284.8
Purchases:
Fixed maturities	(32,037.5)	(28,765.2)	(21,153)
Equity securities	(951.2)	(379.9)	(538.8)
Sales:
Fixed maturities	22,727.2	18,412.7	7,835.6
Equity securities	431.8	471.4	823.5
Maturities, paydowns, calls, and other:
Fixed maturities	7,109.4	6,145.5	5,099.8
Equity securities	113.8	49.9	26.6
Net (purchases) sales of short-term investments	(3,393.2)	31.5	1,116.3
Net unsettled security transactions	83.6	6	11.7
Purchases of property and equipment	(223.5)	(363.5)	(266)
Sales of property and equipment	21.9	53.3	9.4
Net cash used in investing activities	(6,117.7)	(4,338.3)	(7,034.9)
Cash Flows From Financing Activities
Dividends paid to common shareholders	(1,551)	(1,643.2)	(654.9)
Dividends paid to preferred shareholders	(26.8)	(26.8)	(13.5)
Acquisition of treasury shares for restricted stock tax liabilities	(68.7)	(84.4)	(78.6)
Acquisition of treasury shares acquired in open market	(42.9)	(6.9)	(0.4)
Acquisition of additional shares of ARX Holding Corp.	(243)	(11.2)	(296.9)
Net proceeds from debt issuance	986.3	0	1,134
Proceeds from exercise of equity options	7.3	1.6	3.3
Net proceeds from issuance of Serial Preferred Shares, Series B	0	0	493.9
Payments of debt	0	0	(37.1)
Net cash provided by (used in) financing activities	(938.8)	(1,770.9)	549.8
Increase (decrease) in cash, cash equivalents, and restricted cash	(150.9)	152.4	(200.3)
Cash, cash equivalents, and restricted cash - beginning of year	227.4	75	275.3
Cash, cash equivalents, and restricted cash - end of year	$ 76.5	$ 227.4	$ 75

SCHEDULE I - Summary Of Investm

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
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, 2020 Type of Investment Cost Fair Value Amount At Fixed maturities: Bonds: United States Government and government agencies and authorities $ 12,437.9 $ 12,740.0 $ 12,740.0 States, municipalities, and political subdivisions 3,099.4 3,221.8 3,221.8 Public utilities 577.8 619.9 619.9 Corporate and other debt securities 9,001.9 9,565.3 9,565.3 Asset-backed securities 10,290.9 10,469.2 10,469.2 Redeemable preferred stocks 181.2 194.7 194.7 Total fixed maturities 35,589.1 36,810.9 36,810.9 Equity securities: Common stocks: Public utilities 73.5 164.0 164.0 Banks, trusts, and insurance companies 220.1 658.3 658.3 Industrial, miscellaneous, and all other 893.7 3,230.7 3,230.7 Nonredeemable preferred stocks 1,358.7 1,447.9 1,447.9 Total equity securities 2,546.0 5,500.9 5,500.9 Short-term investments 5,218.5 5,218.5 5,218.5 Total investments $ 43,353.6 $ 47,530.3 $ 47,530.3 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, 2020.

SCHEDULE II - Condensed Financi

SCHEDULE II - Condensed Financial Information Of Registrant	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
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, 2020 2019 2018 Revenues Dividends from subsidiaries $ 4,096.5 $ 2,277.9 $ 939.1 Undistributed income from subsidiaries 1,774.4 1,821.3 1,770.7 Equity in net income of subsidiaries 5,870.9 4,099.2 2,709.8 Intercompany investment income 16.5 31.1 39.4 Total revenues 5,887.4 4,130.3 2,749.2 Expenses Interest expense 218.1 190.4 166.8 Deferred compensation 1 33.9 16.6 7.5 Other operating costs and expenses 7.2 5.5 5.1 Total expenses 259.2 212.5 179.4 Income before income taxes 5,628.2 3,917.8 2,569.8 Benefit for income taxes 76.4 52.5 45.5 Net income attributable to Progressive 5,704.6 3,970.3 2,615.3 Other comprehensive income (loss) 587.3 462.6 (95.2) Comprehensive income attributable to Progressive $ 6,291.9 $ 4,432.9 $ 2,520.1 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) December 31, 2020 2019 Assets Investment in affiliate $ 5.0 $ 5.0 Investment in subsidiaries 18,895.9 16,186.8 Receivable from investment subsidiary 5,901.7 2,912.0 Intercompany receivable 473.8 678.6 Net federal deferred income taxes 86.9 70.3 Other assets 270.9 303.8 Total assets $ 25,634.2 $ 20,156.5 Liabilities Accounts payable, accrued expenses, and other liabilities $ 505.0 $ 475.2 Dividends payable on common shares 2,694.5 1,375.4 Debt 1 5,396.1 4,407.1 Total liabilities 8,595.6 6,257.7 Redeemable noncontrolling interest (NCI) 0 225.6 Shareholders’ Equity 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) 493.9 493.9 Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 212.3 and 212.9) 585.2 584.6 Paid-in capital 1,672.9 1,573.4 Retained earnings 13,354.9 10,679.6 Total accumulated other comprehensive income attributable to Progressive 931.7 341.7 Total shareholders’ equity 17,038.6 13,673.2 Total liabilities, redeemable NCI, and shareholders’ equity $ 25,634.2 $ 20,156.5 1 Consists of both short-term and long-term debt. See Note 4 – Debt in our Annual Report for further discussion. See notes to condensed financial statements. CONDENSED STATEMENTS OF CASH FLOWS THE PROGRESSIVE CORPORATION (PARENT COMPANY) (millions) Years Ended December 31, 2020 2019 2018 Cash Flows From Operating Activities: Net income attributable to Progressive $ 5,704.6 $ 3,970.3 $ 2,615.3 Adjustments to reconcile net income attributable to Progressive to net cash provided by operating activities: Undistributed income from subsidiaries (1,774.4) (1,821.3) (1,770.7) Amortization of equity-based compensation 2.9 2.9 2.4 Changes in: Intercompany receivable (20.2) (14.1) 77.5 Accounts payable, accrued expenses, and other liabilities 52.0 47.1 (29.6) Income taxes (52.2) 175.5 (14.2) Other, net 40.4 (179.8) 47.8 Net cash provided by operating activities 3,953.1 2,180.6 928.5 Cash Flows From Investing Activities: Additional investments in equity securities of consolidated subsidiaries (27.1) (152.8) (178.3) Acquisition of additional shares - ARX (233.2) (5.4) (287.9) (Paid to) received from investment subsidiary (2,989.7) (253.1) (1,192.8) Net cash used in investing activities (3,250.0) (411.3) (1,659.0) Cash Flows From Financing Activities: Net proceeds from debt issuance 986.3 0 1,134.0 Net proceeds from preferred stock issuance 0 0 493.9 Dividends paid to common shareholders (1,551.0) (1,643.2) (654.9) Dividends paid to preferred shareholders (26.8) (26.8) (13.5) Acquisition of treasury shares for restricted stock tax liabilities (68.7) (84.4) (78.6) Acquisition of treasury shares acquired in open market (42.9) (6.9) (0.4) Loan to ARX Holding Corp. 0 (8.0) (150.0) Net cash provided by (used in) financing activities (703.1) (1,769.3) 730.5 Change in cash, cash equivalents, and restricted cash 0 0 0 Cash, cash equivalents, restricted cash - beginning of year 0 0 0 Cash, cash equivalents, restricted 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 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, 2020, 2019, and 2018, $6.2 billion, $3.2 billion, and $2.9 billion, respectively, of marketable securities were available in this subsidiary. For the year ended December 31, 2020, non-cash activity includes declared but unpaid common share dividends of $2,694.5 million and preferred share dividends of $13.4 million, and $225.0 million of loans made by The Progressive Corporation to ARX Holding Corp.(ARX) that were converted to a capital contribution upon acquisition of the remaining outstanding stock of ARX; see Note 14 – Dividends and Note 15 – Redeemable Noncontrolling Interest in the Annual Report for further discussion. For the years ended December 31, The Progressive Corporation paid the following: (millions) 2020 2019 2018 Income taxes $ 1,411.0 $ 925.0 $ 679.2 Interest 206.0 184.9 153.6 Note 2. Income Taxes — The Progressive Corporation files a consolidated federal income tax return with its 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 — On the condensed Statements of Comprehensive Income, other comprehensive income represents activity of the subsidiaries of The Progressive Corporation and includes net unrealized gains (losses) on securities and net unrealized gains on forecasted transactions. Note 6. Dividends — The information relating to our dividend policy is incorporated by reference from Note 14 – Dividends

SCHEDULE III - Supplementary In

SCHEDULE III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
SCHEDULE III - Supplementary Insurance Information	SCHEDULE III — SUPPLEMENTARY INSURANCE INFORMATION THE PROGRESSIVE CORPORATION AND SUBSIDIARIES (millions) Segment Deferred 1 Future 1 Unearned premiums 1 Other 1 Premium revenue Net 1,2 Benefits, Amortization Other 1 Net premiums Year ended December 31, 2020: Personal Lines 3 $ 32,620.1 $ 20,611.7 $ 2,437.3 $ 5,762.0 $ 33,342.6 Commercial Lines 4,875.8 3,146.0 525.7 647.5 5,315.3 Property 1,765.7 1,364.1 310.2 237.9 1,910.8 Other indemnity 0 0 0 0 0 Total $ 1,237.2 $ 20,265.8 $ 13,437.5 $ 0 $ 39,261.6 $ 916.6 $ 25,121.8 $ 3,273.2 $ 6,647.4 $ 40,568.7 Year ended December 31, 2019: Personal Lines $ 30,210.0 $ 21,329.7 $ 2,273.6 $ 4,227.6 $ 31,102.2 Commercial Lines 4,427.6 3,034.8 481.2 523.5 4,791.8 Property 1,554.8 1,106.0 268.4 224.0 1,683.9 Other indemnity 0 0 0 0 0 Total $ 1,056.5 $ 18,105.4 $ 12,388.8 $ 0 $ 36,192.4 $ 1,017.4 $ 25,470.5 $ 3,023.2 $ 4,975.1 $ 37,577.9 Year ended December 31, 2018: Personal Lines $ 26,034.7 $ 18,389.8 $ 1,964.4 $ 3,563.3 $ 27,157.6 Commercial Lines 3,610.9 2,394.0 396.0 396.0 3,996.4 Property 1,287.7 937.0 213.3 237.2 1,455.9 Other indemnity 0 0.2 0 (0.7) 0 Total $ 951.6 $ 15,400.8 $ 10,686.5 $ 0 $ 30,933.3 $ 796.2 $ 21,721.0 $ 2,573.7 $ 4,195.8 $ 32,609.9 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. 3 Other operating expenses includes $1,077.4 million of policyholder credits issued to personal auto customers.

SCHEDULE IV - Reinsurance

SCHEDULE IV - Reinsurance	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
SCHEDULE IV - Reinsurance	SCHEDULE IV — REINSURANCE THE PROGRESSIVE CORPORATION AND SUBSIDIARIES (millions) Year Ended: Gross Amount Ceded to Assumed Net Amount Percentage December 31, 2020 Premiums earned: Property and liability insurance $ 40,687.7 $ 1,426.1 $ 0 $ 39,261.6 0 % December 31, 2019 Premiums earned: Property and liability insurance $ 37,519.7 $ 1,327.3 $ 0 $ 36,192.4 0 % December 31, 2018 Premiums earned: Property and liability insurance $ 31,970.2 $ 1,036.9 $ 0 $ 30,933.3 0 %

Reporting and Accounting Polici

Reporting and Accounting Policies	12 Months Ended
	Dec. 31, 2020
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 provide personal and commercial auto insurance, personal residential and commercial property insurance, general liability insurance, and other specialty property-casualty insurance and related services. 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 primary liability and physical damage insurance, and general liability and property insurance, predominately for small businesses. 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, 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 Eurodollar deposits, 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. These securities are carried at fair value, with the changes in fair value reported as a component of net holding period gains (losses) on securities reported in net income. Derivative instruments may include futures, options, forward positions, interest rate swap agreements, and credit default swaps and may be used in the portfolio for general investment purposes or to hedge the exposure to variable cash flows of a forecasted transaction (cash flow hedge). We did not have any derivatives outstanding at December 31, 2020 or 2019. To the extent we have derivatives held for general investment purposes, these derivative instruments would be recognized as either assets or liabilities and measured at fair value, with changes in fair value recognized in net income as a component of net holding period gains (losses) on securities. 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. For derivatives settled through a clearinghouse, collateral is required to post initial margin and is subject to increases in margin beyond changes in fair value. Exposure to credit risk is limited to the carrying value; collateral may be required to limit credit risk. For bi-lateral derivative positions, net cash requirements are limited to changes in fair values, which may vary as a result of changes in interest rates, currency exchange rates, and other factors. We have elected not to offset fair value amounts that arise from derivative positions with the same counterparty under a master netting arrangement. 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 a write-off of the fair value for 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 and 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-off the security to its fair value. Investment income consists of interest, dividends, and accretion (net of 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. 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 includes holding period valuation changes on equity securities, hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument), and derivatives, as well as initial credit allowance losses, subsequent changes in credit loss allowances, 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 that are applicable to the unexpired risk. We provide insurance and 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. We then age this exposure to establish an allowance for credit losses based on prior experience. 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, cancel the policy and write off any remaining balance. To determine an allowance for credit losses, we evaluate the collectibility of premiums receivables based on historical and current collections experience 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. The following table summarizes changes in our allowance for credit loss exposure on our premium receivables: (millions) 2020 2019 Balance at January 1 $ 283.2 $ 252.1 Increase in allowance 1 472.0 433.5 Write-offs 2 (399.0) (402.4) Balance at December 31 $ 356.2 $ 283.2 1 Represents the incremental increase in other underwriting expenses. 2 Represents the portion of allowance that is reversed when premium receivables are written off. Premiums receivable balances are written off once we have exhausted our collection efforts. The increase in the allowance during 2020 in part reflects the greater potential for credit losses due to financial hardships of policyholders as a result of the economic impacts related to the spread of the novel coronavirus, COVID-19. 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 the 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 2020 $ 2,175.7 2019 1,837.3 2018 1,422.4 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 (IBNR). 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 in the near term. 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 servicing agent for CAIP and 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 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 counter parties 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 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 are investment securities (e.g., net unrealized gains (losses), net holding period gains (losses) on securities, write-downs on securities determined to be other-than-temporarily impaired), loss and loss adjustment expense reserves, unearned premiums reserves, deferred acquisition costs, property and equipment, intangible assets, and non-deductible accruals. 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) 2020 2019 Useful Lives Land $ 151.6 $ 161.6 NA Buildings, improvements, and integrated components 872.7 927.1 7-40 years Capitalized software 392.6 367.1 3-10 years Software licenses (internal use) 335.5 286.8 1-5 years Computer equipment 253.8 223.3 3 years All other property and equipment 391.2 385.9 3-10 years Total cost 2,397.4 2,351.8 Accumulated depreciation (1,291.4) (1,138.1) Balance at end of year $ 1,106.0 $ 1,213.7 NA = Not applicable; land is not a depreciable asset. Included in other assets in the consolidated balance sheets are “held for sale” property, which represents the fair value of these properties less the estimated costs to sell, of $56.6 million and $32.9 million at December 31, 2020 and 2019, respectively, and capitalized cloud computing arrangement implementation costs, net of amortization, of $25.3 million at December 31, 2020. We adopted the new accounting standard for cloud computing arrangements in January 2020; see New Accounting Standards below in this Note 1 for further discussion. 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. Intangible assets are non-financial assets lacking physical substance, such as customer and agency relationships and software rights, and represent the future economic benefit of those acquired assets. See Note 16 – Goodwill and Intangible Assets for further discussion. 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. 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 formal determination of insolvency has occurred, and we have written the premiums on which the assessments will be based. Assessments that are available for recoupment from policyholders are capitalized when incurred; all other assessments are expensed. 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. 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. Service revenues generated from processing business for involuntary CAIP plans are earned on a pro rata basis over the term of the related policies. Service expenses related to these CAIP plans are expensed as 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.” Compensation expense for time-based restricted equity awards with installment vesting is recognized over each respective vesting period. For performance-based restricted equity awards, compensation expense is recognized over the estimated vesting periods. Dividend equivalent units are credited to outstanding restricted stock unit awards, both time-based and performance-based, at the time a dividend is paid to shareholders and paid upon vesting of the underlying award. We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates. The total compensation expense recognized for equity-based compensation for the years ended December 31, was: (millions) 2020 2019 2018 Pretax expense $ 89.4 $ 90.2 $ 77.2 Tax benefit 18.8 18.9 16.2 Earnings Per Common Share Net income attributable to Progressive 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 time-based restricted stock awards. Diluted earnings per common share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents 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. 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, and are not considered part of the investment portfolio. The amount of reverse repurchase commitments held by these subsidiaries at December 31, 2020, 2019, and 2018, were $93.5 million, $46.3 million, and $117.3 million, respectively. Restricted cash on our consolidated balance sheets represents cash that is restricted to pay flood claims under the NFIP’s “Write Your Own” program, for which certain subsidiaries are administrators. For the year ended December 31, 2020, non-cash activity includes declared but unpaid common share dividends of $2,694.5 million and preferred share dividends of $13.4 million, and operating lease liabilities arising from obtaining right-of-use assets of $60.3 million (see Note 13 – Leases and Note 14 – Dividends for further discussion). For the years ended December 31, we paid the following: (millions) 2020 2019 2018 Income taxes $ 1,446.3 $ 954.3 $ 702.6 Interest 206.0 184.9 154.0 Operating lease liabilities 86.5 84.0 NA NA = Not applicable prior to the adoption of the new accounting standard in 2019. Commitments and Contingencies We have certain noncancelable purchase obligations for goods and services with minimum commitments of $830.4 million at December 31, 2020, 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 New Accounting Standards On January 1, 2020, we adopted the following new Accounting Standards Updates (ASU). Cloud Computing Arrangements This ASU, which provides guidance on the requirements for capitalizing and amortizing implementation costs incurred in a cloud computing arrangement that does not include a software license, was adopted on a prospective basis. See the Property and Equipment discussion above for the cloud computing arrangement implementation cost capitalized at December 31, 2020. Fair Value Measurements We early adopted a portion of this ASU in 2018 and the remaining provisions in 2020. This ASU amended the disclosure requirements for fair value measurements to require companies to disclose the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and removed current disclosure requirements for the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels, and the valuation processes for Level 3 fair value measurements. The adoption of this ASU had no impact on our financial condition, cash flows, or results of operations. Goodwill Impairment Test Simplification The ASU eliminated the requirement to determine the implied fair value of goodwill in measuring an impairment loss and now requires the measurement of a goodwill impairment to represent the excess of the reporting unit’s carrying value over fair value, limited to the carrying value of goodwill. The adoption of this ASU had no impact on our financial condition, cash flows, or results of operations. Measurement of Credit Losses on Financial Instruments This ASU modified the existing accounting guidance related to the impairment evaluation for our available-for-sale debt securities, reinsurance recoverables, and premiums receivable. The ASU is intended to improve the timing, and enhance the accounting and disclosure, of credit losses on financial assets. To the extent a credit loss is determined to exist, an allowance for credit losses would be required to be recorded as a contra asset, with changes to the credit loss allowance recorded prospectively. Based on our analysis for available-for-sale debt securities and reinsurance recoverables as described in Note 2– Investments and Note 7– Reinsurance , respectively, no adjustment to the beginning balance of retained earnings was required upon adoption. See the Insurance Premiums and Receivables discussion above for changes in the allowance for credit losses related to the premiums receivable balance.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	INVESTMENTS The following tables present the composition of our investment portfolio by major security type, consistent with our classification of how we manage, monitor, and measure the portfolio. 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, net of deferred income taxes, in our consolidated balance sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value of the securities. The changes in the net holding period gains (losses) between periods for the hybrid securities and equity securities are recorded as a component of net realized gains (losses) on securities in our consolidated statements of comprehensive income. ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair Value December 31, 2020 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 12,437.9 $ 305.8 $ (3.7) $ 0 $ 12,740.0 26.8 % State and local government obligations 3,099.4 123.1 (0.7) 0 3,221.8 6.8 Corporate debt securities 9,579.7 601.7 (0.1) 3.9 10,185.2 21.4 Residential mortgage-backed securities 503.3 7.1 (0.9) 0 509.5 1.1 Commercial mortgage-backed securities 6,042.6 142.5 (10.0) 0 6,175.1 13.0 Other asset-backed securities 3,745.0 40.1 (0.5) 0 3,784.6 7.9 Redeemable preferred stocks 181.2 3.6 (1.4) 11.3 194.7 0.4 Total fixed maturities 35,589.1 1,223.9 (17.3) 15.2 36,810.9 77.4 Short-term investments 5,218.5 0 0 0 5,218.5 11.0 Total available-for-sale securities 40,807.6 1,223.9 (17.3) 15.2 42,029.4 88.4 Equity securities: Nonredeemable preferred stocks 1,358.7 0 0 89.2 1,447.9 3.1 Common equities 1,187.3 0 0 2,865.7 4,053.0 8.5 Total equity securities 2,546.0 0 0 2,954.9 5,500.9 11.6 Total portfolio 1 $ 43,353.6 $ 1,223.9 $ (17.3) $ 2,970.1 $ 47,530.3 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair Value December 31, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,100.7 $ 194.1 $ (43.7) $ 0 $ 13,251.1 33.7 % State and local government obligations 1,686.0 30.0 (2.7) 0 1,713.3 4.4 Corporate debt securities 6,860.3 206.6 (0.5) 1.3 7,067.7 18.0 Residential mortgage-backed securities 625.0 4.5 (2.0) 0 627.5 1.6 Commercial mortgage-backed securities 5,020.7 61.5 (6.0) 0 5,076.2 12.9 Other asset-backed securities 5,164.7 16.2 (1.4) 0 5,179.5 13.2 Redeemable preferred stocks 185.7 4.1 (1.3) 6.5 195.0 0.5 Total fixed maturities 32,643.1 517.0 (57.6) 7.8 33,110.3 84.3 Short-term investments 1,798.8 0 0 0 1,798.8 4.6 Total available-for-sale securities 34,441.9 517.0 (57.6) 7.8 34,909.1 88.9 Equity securities: Nonredeemable preferred stocks 971.3 0 0 67.6 1,038.9 2.7 Common equities 1,125.5 0 0 2,180.8 3,306.3 8.4 Total equity securities 2,096.8 0 0 2,248.4 4,345.2 11.1 Total portfolio 1 $ 36,538.7 $ 517.0 $ (57.6) $ 2,256.2 $ 39,254.3 100.0 % 1 Our portfolio reflects the effect of net unsettled security transactions; at December 31, 2020, $95.5 million was included in “other liabilities,” compared to $11.9 million at December 31, 2019. The total fair value of the portfolio at December 31, 2020 and 2019 included $6.2 billion and $3.2 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. A portion of these investments were sold and proceeds used to pay our common share dividends; see Note 14 – Dividends for additional information. At December 31, 2020, bonds and certificates of deposit in the principal amount of $298.2 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, 2020 or 2019. At December 31, 2020, we did not hold any debt securities that were non-income producing during the preceding 12 months. Short-Term Investments Our short-term investments may include commercial paper and other investments that are expected to mature or are redeemable within one year. We invested in repurchase and reverse repurchase transactions during 2020 and 2019, but did not have any open positions at December 31, 2020 or 2019. 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 maturities 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) 2020 2019 Fixed Maturities: State and local government obligations $ 0 $ 3.5 Corporate debt securities 188.4 91.2 Other asset-backed securities 34.8 2.6 Redeemable preferred stocks 131.4 92.1 Total hybrid securities $ 354.6 $ 189.4 Since the embedded derivatives (e.g., change-in-control put option, debt-to-equity conversion, or any other feature unrelated to the credit quality or risk of default of the issuer that could impact the amount or timing of our expected future cash flows) do not have observable intrinsic values, we have elected to record the changes in fair value of these securities through income as a component of net realized gains or losses. Fixed Maturities The composition of fixed maturities by maturity at December 31, 2020, was: (millions) Cost Fair Value Less than one year $ 5,734.9 $ 5,765.4 One to five years 20,769.2 21,377.3 Five to ten years 8,939.8 9,512.2 Ten years or greater 145.2 156.0 Total $ 35,589.1 $ 36,810.9 Asset-backed securities are classified in the maturity distribution table based upon their projected cash flows. All other securities that do not have a single maturity date are reported based upon expected average maturity. Contractual maturities may differ from expected maturities because the issuers of the securities may have the right to call or prepay obligations. Gross Unrealized Losses The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses December 31, 2020 U.S. government obligations 9 $ 1,511.0 $ (3.7) 9 $ 1,511.0 $ (3.7) 0 $ 0 $ 0 State and local government obligations 30 208.7 (0.7) 30 208.7 (0.7) 0 0 0 Corporate debt securities 7 129.4 (0.1) 7 129.4 (0.1) 0 0 0 Residential mortgage-backed securities 21 44.4 (0.9) 0 0 0 21 44.4 (0.9) Commercial mortgage-backed securities 43 893.3 (10.0) 9 93.6 (0.3) 34 799.7 (9.7) Other asset-backed securities 22 183.7 (0.5) 9 74.4 (0.1) 13 109.3 (0.4) Redeemable preferred stocks 1 11.0 (1.4) 0 0 0 1 11.0 (1.4) Total fixed maturities 133 $ 2,981.5 $ (17.3) 64 $ 2,017.1 $ (4.9) 69 $ 964.4 $ (12.4) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized December 31, 2019 U.S. government obligations 23 $ 5,152.4 $ (43.7) 19 $ 5,057.2 $ (43.6) 4 $ 95.2 $ (0.1) State and local government obligations 67 314.3 (2.7) 52 287.5 (2.6) 15 26.8 (0.1) Corporate debt securities 16 247.6 (0.5) 12 191.4 (0.5) 4 56.2 0 Residential mortgage-backed securities 41 292.8 (2.0) 12 163.7 (0.9) 29 129.1 (1.1) Commercial mortgage-backed securities 98 1,742.4 (6.0) 79 1,400.0 (5.3) 19 342.4 (0.7) Other asset-backed securities 61 1,000.6 (1.4) 43 938.5 (0.9) 18 62.1 (0.5) Redeemable preferred stocks 1 11.2 (1.3) 0 0 0 1 11.2 (1.3) Total fixed maturities 307 $ 8,761.3 $ (57.6) 217 $ 8,038.3 $ (53.8) 90 $ 723.0 $ (3.8) During 2020, we had seven securities that had their credit ratings downgraded, with a combined fair value of $65.0 million and an unrealized loss of $1.6 million as of December 31, 2020, comprised of residential and commercial mortgage-backed securities. A review of the securities in an unrealized loss position indicated that the issuers were current with respect to their interest obligations and that there was no evidence of deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. Allowance For Credit and Uncollectible Losses We are required to measure the amount of potential credit losses for all fixed-maturity securities in an unrealized loss position. We did not record any allowances for credit losses or any write-offs for amounts deemed to be uncollectible during 2020 and did not have a credit loss allowance balance as of December 31, 2020. We considered several factors and inputs related to the individual securities as part of our analysis. The methodology and significant inputs used to measure the amount of credit losses in our portfolio included: • current performance indicators on the business model or underlying assets (e.g., delinquency rates, foreclosure rates, and default rates); • credit support (via current levels of subordination); • historical credit ratings; and • updated cash flow expectations based upon these performance indicators. In order to determine the amount of credit loss, if any, we initially reviewed securities in a loss position to determine whether it was likely that we would be required, or intended, to sell any of the securities prior to the recovery of their respective cost bases (which could be maturity). If we were likely to, or intended to, sell prior to a potential recovery, we would write off the unrealized loss. For those securities that we determined we were not likely to, or did not intend to, sell prior to a potential recovery, we calculated the net present value (NPV) of the cash flows expected (i.e., expected recovery value) using the current book yield for each security. The NPV was then compared to the security’s current amortized value to determine if a credit loss existed. In the event that the NPV was below the amortized value, and the amount was determined to be material individually, or in aggregate, a credit loss would be deemed to exist, and either an allowance for credit losses would be created, or if an allowance currently existed, either a recovery of the previous allowance, or an incremental loss, would be recorded to net realized gains (losses) on securities. As of December 31, 2020, we believe none of the unrealized losses relate to material credit losses on any specific securities, or in the aggregate, based on our review. 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, 2020, 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, 2020. Realized Gains (Losses) The components of net realized gains (losses) for the years ended December 31, were: (millions) 2020 2019 2018 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 612.5 $ 164.4 $ 6.7 State and local government obligations 102.4 6.1 9.5 Corporate and other debt securities 161.9 100.1 2.4 Residential mortgage-backed securities 0 0.2 0 Commercial mortgage-backed securities 23.7 8.1 2.0 Other asset-backed securities 0.2 0.8 0.1 Redeemable preferred stocks 0 2.2 4.5 Total available-for-sale securities 900.7 281.9 25.2 Equity securities: Nonredeemable preferred stocks 24.4 36.2 4.1 Common equities 88.6 61.7 286.6 Total equity securities 113.0 97.9 290.7 Subtotal gross realized gains on security sales 1,013.7 379.8 315.9 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (9.6) (20.4) (98.7) State and local government obligations (0.7) (0.7) (2.9) Corporate and other debt securities (6.5) (7.9) (10.4) Residential mortgage-backed securities 0 (2.3) (0.1) Commercial mortgage-backed securities (12.8) (2.2) (6.3) Other asset-backed securities 0 (0.1) (1.1) Redeemable preferred stocks 0 (0.4) (0.1) Total available-for-sale securities (29.6) (34.0) (119.6) Equity securities: Nonredeemable preferred stocks (8.7) (3.2) (3.9) Common equities (60.7) (8.0) (21.7) Total equity securities (69.4) (11.2) (25.6) Subtotal gross realized losses on security sales (99.0) (45.2) (145.2) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 602.9 144.0 (92.0) State and local government obligations 101.7 5.4 6.6 Corporate and other debt securities 155.4 92.2 (8.0) Residential mortgage-backed securities 0 (2.1) (0.1) Commercial mortgage-backed securities 10.9 5.9 (4.3) Other asset-backed securities 0.2 0.7 (1.0) Redeemable preferred stocks 0 1.8 4.4 Total available-for-sale securities 871.1 247.9 (94.4) Equity securities: Nonredeemable preferred stocks 15.7 33.0 0.2 Common equities 27.9 53.7 264.9 Total equity securities 43.6 86.7 265.1 Subtotal net realized gains (losses) on security sales 914.7 334.6 170.7 Net holding period gains (losses) Hybrid securities 7.4 18.0 (10.4) Equity securities 706.5 739.9 (497.5) Derivatives 1.4 0 0 Subtotal net holding period gains (losses) 715.3 757.9 (507.9) Other-than-temporary impairment losses Other asset impairment 0 (63.3) (68.3) Subtotal other-than-temporary impairment losses 0 (63.3) (68.3) Total net realized gains (losses) on securities $ 1,630.0 $ 1,029.2 $ (405.5) Realized gains (losses) on securities sold are computed using the first-in-first-out method. During 2020, we sold U.S. Treasury securities in order to selectively increase holdings across the remainder of the portfolio, predominantly in our corporate debt securities. For 2019 and 2018, the other asset impairment losses related to federal renewable energy tax credit fund investments, which were reported in other assets on the consolidated balance sheets, and are based on an analysis that our investments in those funds will not generate the cash flows that we anticipated. The following table reflects our holding period realized gains (losses) on equity securities recognized for the respective years ended December 31, for equity securities held at the respective year end: (millions) 2020 2019 2018 Total net gains (losses) recognized during the period on equity securities $ 750.1 $ 826.6 $ (232.4) Less: Net gains (losses) recognized on equity securities sold during the period 43.6 86.7 265.1 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 706.5 $ 739.9 $ (497.5) Net Investment Income The components of net investment income for the years ended December 31, were: (millions) 2020 2019 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 166.3 $ 268.6 $ 196.8 State and local government obligations 62.7 36.5 37.7 Corporate debt securities 284.0 268.9 217.9 Residential mortgage-backed securities 11.8 21.6 27.6 Commercial mortgage-backed securities 152.9 150.1 93.9 Other asset-backed securities 96.7 117.3 75.7 Redeemable preferred stocks 14.9 19.0 12.3 Total fixed maturities 789.3 882.0 661.9 Short-term investments 29.0 41.7 52.9 Total available-for-sale securities 818.3 923.7 714.8 Equity securities: Nonredeemable preferred stocks 60.6 61.8 45.9 Common equities 57.7 56.5 59.8 Total equity securities 118.3 118.3 105.7 Investment income 936.6 1,042.0 820.5 Investment expenses (20.0) (24.6) (24.3) Net investment income $ 916.6 $ 1,017.4 $ 796.2

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value	FAIR VALUE We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows: • Level 1 : Inputs are unadjusted, quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, which are continually priced on a daily basis, active exchange-traded equity securities, and certain short-term securities). • Level 2 : Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 : Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments). Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations. The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2020 Fixed maturities: U.S. government obligations $ 12,740.0 $ 0 $ 0 $ 12,740.0 $ 12,437.9 State and local government obligations 0 3,221.8 0 3,221.8 3,099.4 Corporate debt securities 0 10,185.2 0 10,185.2 9,579.7 Subtotal 12,740.0 13,407.0 0 26,147.0 25,117.0 Asset-backed securities: Residential mortgage-backed 0 509.5 0 509.5 503.3 Commercial mortgage-backed 0 6,175.1 0 6,175.1 6,042.6 Other asset-backed 0 3,784.6 0 3,784.6 3,745.0 Subtotal asset-backed securities 0 10,469.2 0 10,469.2 10,290.9 Redeemable preferred stocks: Financials 0 51.6 0 51.6 51.1 Utilities 0 11.7 0 11.7 10.0 Industrials 10.8 120.6 0 131.4 120.1 Subtotal redeemable preferred stocks 10.8 183.9 0 194.7 181.2 Total fixed maturities 12,750.8 24,060.1 0 36,810.9 35,589.1 Short-term investments 4,704.9 513.6 0 5,218.5 5,218.5 Total available-for-sale securities 17,455.7 24,573.7 0 42,029.4 40,807.6 Equity securities: Nonredeemable preferred stocks: Financials 117.7 1,212.3 35.0 1,365.0 1,278.6 Utilities 0 41.9 0 41.9 40.0 Industrials 0 24.3 16.7 41.0 40.1 Subtotal nonredeemable preferred stocks 117.7 1,278.5 51.7 1,447.9 1,358.7 Common equities: Common stocks 4,049.9 0 0 4,049.9 1,184.2 Other risk investments 0 0 3.1 3.1 3.1 Subtotal common equities 4,049.9 0 3.1 4,053.0 1,187.3 Total equity securities 4,167.6 1,278.5 54.8 5,500.9 2,546.0 Total portfolio $ 21,623.3 $ 25,852.2 $ 54.8 $ 47,530.3 $ 43,353.6 Debt $ 0 $ 6,793.5 $ 0 $ 6,793.5 $ 5,396.1 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2019 Fixed maturities: U.S. government obligations $ 13,251.1 $ 0 $ 0 $ 13,251.1 $ 13,100.7 State and local government obligations 0 1,713.3 0 1,713.3 1,686.0 Corporate debt securities 0 7,067.7 0 7,067.7 6,860.3 Subtotal 13,251.1 8,781.0 0 22,032.1 21,647.0 Asset-backed securities: Residential mortgage-backed 0 627.5 0 627.5 625.0 Commercial mortgage-backed 0 5,076.2 0 5,076.2 5,020.7 Other asset-backed 0 5,179.5 0 5,179.5 5,164.7 Subtotal asset-backed securities 0 10,883.2 0 10,883.2 10,810.4 Redeemable preferred stocks: Financials 0 51.7 0 51.7 51.5 Utilities 0 11.1 0 11.1 10.0 Industrials 11.1 121.1 0 132.2 124.2 Subtotal redeemable preferred stocks 11.1 183.9 0 195.0 185.7 Total fixed maturities 13,262.2 19,848.1 0 33,110.3 32,643.1 Short-term investments 1,797.4 1.4 0 1,798.8 1,798.8 Total fixed maturities and short-term 15,059.6 19,849.5 0 34,909.1 34,441.9 Equity securities: Nonredeemable preferred stocks: Financials 77.4 850.7 27.1 955.2 891.3 Utilities 0 42.3 0 42.3 39.9 Industrials 0 25.4 16.0 41.4 40.1 Subtotal nonredeemable preferred stocks 77.4 918.4 43.1 1,038.9 971.3 Common equities: Common stocks 3,306.0 0 0 3,306.0 1,125.2 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,306.0 0 0.3 3,306.3 1,125.5 Total equity securities 3,383.4 918.4 43.4 4,345.2 2,096.8 Total available-for-sale portfolio $ 18,443.0 $ 20,767.9 $ 43.4 $ 39,254.3 $ 36,538.7 Debt $ 0 $ 5,119.6 $ 0 $ 5,119.6 $ 4,407.1 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, 2020, vendor-quoted prices represented 76% of our Level 1 classifications (excluding short-term investments), compared to 80% at December 31, 2019. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. At both December 31, 2020 and 2019, vendor-quoted prices comprised 99% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented 1%. 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 to economic data as it relates to geographic location as an indication of price-to-call or maturity predictors. For municipal housing securities, we look to changes in cash flow projections, both historical and reasonably estimable projections, to understand yield changes and their effect on valuation. Lastly, for our 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. Except as described below, our Level 3 securities are also 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. Certain private equity investments included in the Level 3 category are valued using external pricing supplemented by internal review and analysis. After all the valuations are received and our review is complete, if the inputs used by vendors are determined to not contain sufficient observable market information, we will reclassify the affected security valuations to Level 3. At December 31, 2020 and 2019, we did not have any securities in our fixed-maturity portfolio listed as Level 3. At December 31, 2020, we owned four private nonredeemable preferred securities that were priced internally or by a pricing firm, and we held three private nonredeemable preferred securities at December 31, 2019. At December 31, 2020, we held two Level 3 other risk investments that were priced using the cost method, compared to one Level 3 other risk investment at December 31, 2019. To the extent we receive prices from external sources for the Level 3 securities, we would review those prices for reasonableness using internally developed assumptions and then compare our derived prices to the prices we received. During 2020 or 2019, there were no material assets or liabilities measured at fair value on a nonrecurring basis. Based on our review, all prices received from external sources remained unadjusted. 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, 2020 and 2019: Level 3 Fair Value (millions) Fair Value at Dec. 31, 2019 Calls/ Purchases Sales Net Realized Change in Net Transfers In (Out) Fair Value at Dec. 31, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ (27.1) $ 35.0 $ 0 $ 0 $ 0 $ 0 $ 35.0 Industrials 16.0 0 0 0 0 0.7 0 16.7 Common equities: Other risk investments 0.3 0 2.8 0 0 0 0 3.1 Total Level 3 securities $ 43.4 $ (27.1) $ 37.8 $ 0 $ 0 $ 0.7 $ 0 $ 54.8 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2018 Calls/ Purchases Sales Net Realized Change in Net Fair Value at Dec. 31, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 10.0 0 0 1.0 0 16.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 30.4 $ 0 $ 12.0 $ 0 $ 0 $ 1.0 $ 0 $ 43.4 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, 2020 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 25.0 Internal price Unadjusted purchase price per share 3.7 Financials 2 10.0 Internal price Unadjusted purchase price per share 16.9 Industrials 6.9 Pricing firm Market Approach (Guideline Public Company Method) 5.4 Industrials 9.8 Pricing firm Market Approach (Guideline Public Company Method) 4.8 Subtotal Level 3 securities 51.7 Pricing exemption securities 3.1 Total Level 3 securities $ 54.8 1 This security was purchased in May 2020. 2 This security was purchased in November 2020. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 Pricing firm Recent transaction price per share 9.0 Industrials 6.0 Pricing firm Performance-based transaction price adjustment per share 4.8 Industrials 1 10.0 Internal price Unadjusted purchase price per share 4.9 Subtotal Level 3 securities 43.1 Pricing exemption securities 0.3 Total Level 3 securities $ 43.4

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	DEBT Debt at December 31, consisted of: 2020 2019 (millions) Carrying Fair Carrying Fair 3.75% Senior Notes due 2021 (issued: $500.0, August 2011) $ 499.8 $ 510.9 $ 499.4 $ 515.6 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) 497.3 541.1 496.9 501.5 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 296.9 409.4 296.6 392.5 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 545.5 660.4 545.0 614.3 3.20% Senior Notes due 2030 (issued: $500.0, March 2020) 496.1 575.5 0 0 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 396.0 582.0 395.7 552.6 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.7 459.7 346.7 417.0 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.5 481.0 395.4 434.2 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 841.7 1,113.1 841.6 986.1 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 590.0 806.7 589.8 705.8 3.95% Senior Notes due 2050 (issued: $500.0, March 2020) 490.6 653.7 0 0 Total $ 5,396.1 $ 6,793.5 $ 4,407.1 $ 5,119.6 All of the outstanding debt was issued by The Progressive Corporation and includes amounts that were borrowed and contributed to the capital of its insurance subsidiaries or 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. We issued $500 million of 3.20% Senior Notes due 2030 and $500 million of 3.95% Senior Notes due 2050 in March 2020, in an underwritten public offering. The net proceeds from these issuances, after deducting underwriters’ discounts, commissions, and other issuance costs, were approximately $986.3 million in aggregate. Aggregate required principal payments on debt outstanding at December 31, 2020, were as follows: (millions) Year Payments 2021 $ 500 2022 0 2023 0 2024 0 2025 0 Thereafter 4,950 Total $ 5,450 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 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, 2020, on a pretax basis: (millions) Unrealized Unamortized 3.75% Senior Notes $ (5.1) $ (0.4) 6 5/8% Senior Notes (4.2) (2.2) 6.25% Senior Notes 5.1 3.2 4.35% Senior Notes (1.6) (1.4) 3.70% Senior Notes (12.9) (11.4) 4.125% Senior Notes (8.0) (7.5) We reclassified $1.1 million in 2020, and $1.0 million in 2019 and 2018, of net unrealized losses from accumulated other comprehensive income to interest expense on our closed debt issuance cash flow hedges. During 2020, we renewed the line of credit with PNC Bank, National Association (PNC), in the maximum principal amount of $250 million. 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 higher of PNC’s Prime Rate or the sum of the Federal Funds Open Rate plus 175 basis points. Each advance must be repaid on the 30th day after the advance or, if earlier, on April 30, 2021, the expiration date of the line of credit. Prepayments are permitted without penalty.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
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) 2020 2019 2018 Current tax provision Federal $ 1,395.7 $ 1,133.2 $ 673.1 State 35.6 27.3 21.5 Deferred tax expense (benefit) Federal 35.8 16.8 (145.9) State 1.5 3.0 (6.1) Total income tax provision $ 1,468.6 $ 1,180.3 $ 542.6 The provision for income taxes in the accompanying consolidated statements of comprehensive income differed from the statutory rate for the years ended December 31, as follows: (millions) 2020 2019 2018 Income before income taxes $ 7,173.2 $ 5,160.3 $ 3,163.6 Tax at statutory federal rate $ 1,506.4 21 % $ 1,083.7 21 % $ 664.4 21 % Tax effect of: Reversal of prior year tax credits 0 0 163.2 3 0 0 Tax credits 1 (5.4) 0 (43.9) (1) (76.3) (2) Stock-based compensation (22.7) (1) (25.9) (1) (25.1) (1) Tax-deductible dividends (25.1) (1) (14.6) 0 (14.6) 0 Tax-preferenced investment income (15.2) 0 (14.0) 0 (15.6) (1) Nondeductible compensation expense 6.4 0 8.1 0 (0.2) 0 State income taxes, net of federal taxes 29.3 1 24.0 1 12.2 0 Other items, net (5.1) 0 (0.3) 0 (2.2) 0 Total income tax provision $ 1,468.6 20 % $ 1,180.3 23 % $ 542.6 17 % 1 Includes $0, $38.1 million, and $71.0 million for 2020, 2019, and 2018, respectively, of benefits on investments in federal renewable energy tax credit funds. In late December 2018, we learned of allegations of potential fraudulent conduct by the sponsor of three tax credit fund investments we made from 2016 through 2018, including information about ongoing federal investigations. Based on our investigations and other information that became available to us, we concluded the sponsor had committed fraud through these tax credit funds and that all the tax credits and other tax benefits related to those investments were not valid. As a result, during 2019, we increased our provision for income taxes by $163.2 million ($252.0 million current income taxes payable, offset by $88.8 million reduction of deferred tax liability), principally reflecting the total reversal of the tax credits and other tax benefits previously recognized from certain renewable energy investments, plus interest. In addition, we paid $100.0 million related to the 2018 tax year, which reduced net taxes payable, and made protective deposits of $152.1 million for tax years 2017 and 2016. During 2020, $48.8 million of this deposit was applied against our 2016 tax liability, including interest. The remaining protective deposit of $103.3 million is included in other assets on our consolidated balance sheets. The principals of the sponsor and various other individuals have pleaded guilty to federal criminal charges relating to the fraudulent tax credit funds. Deferred income taxes reflect the effect for financial statement reporting purposes 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 asset (liability) at December 31, 2020 and 2019, respectively. (millions) 2020 2019 Federal deferred income tax assets: Unearned premiums reserve $ 552.5 $ 498.2 Non-deductible accruals 238.2 181.8 Loss and loss adjustment expense reserves 170.0 153.3 Operating lease liabilities 37.4 42.3 Investment basis difference 18.6 27.4 Hedges on forecasted transactions 4.1 4.4 Other 25.8 15.3 Federal deferred income tax liabilities: Net holding period gains on equity securities (620.5) (472.2) Deferred acquisition costs (259.8) (221.9) Net unrealized gains on fixed-maturity securities (253.4) (96.5) Property and equipment (105.6) (108.6) Loss and loss adjustment expense reserve transition adjustment (39.3) (47.2) Operating lease assets (37.4) (42.3) Intangible assets (27.6) (38.9) Prepaid expenses (5.5) (4.8) Other (7.5) (8.3) Net federal deferred income taxes (310.0) (118.0) State deferred income tax assets 1 11.9 15.2 State deferred income tax liabilities 1 (4.0) (1.2) Total $ (302.1) $ (104.0) 1 Recorded in “other assets” and “accounts payable, accrued expenses, and other liabilities,” respectively, on the consolidated balance sheets; the prior year amounts were reclassified into these line items from “net federal deferred income taxes” to conform to the current year presentation. 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, 2020 or 2019. At December 31, 2020 and 2019, we had $163.5 million and $224.0 million, respectively, of net taxes payable (included in other liabilities on our consolidated balance sheets). Net taxes payable included the impact from the reversal of the tax credit benefits for 2017 and 2016. The Progressive Corporation and its subsidiaries file a consolidated federal income tax return. Effective April 2018, we acquired additional shares of ARX Holding Corp. (“ARX”) to increase our ownership above 80%. As a result, ARX and its subsidiaries were first included in The Progressive Corporation consolidated federal income tax return for the period from April 2018 to December 31, 2018. ARX filed a final consolidated federal income tax return with its subsidiaries for the period from January to March 2018. The Progressive Corporation and its eligible subsidiaries participated in the Compliance Assurance Program (CAP) from 2007 through 2018. Under CAP, the IRS begins its examination process for the tax year before the tax return is filed, by examining significant transactions and events as they occur; however, a CAP examination does not include equity investments in pass-through entities in which the taxpayer owns less than 100% (e.g., partnerships, joint ventures, etc.). The goal of the CAP program is to expedite the exam process and to reduce the level of uncertainty regarding a taxpayer’s tax filing positions. All federal income tax years prior to 2017 are closed to examination for The Progressive Corporation. The IRS CAP exams for 2017 and 2018 for The Progressive Corporation have been completed and the returns were accepted as filed. We consider these years to be effectively settled (other than with respect to equity investments in pass-through entities). The 2019 and 2020 tax years remain open to examination. For the tax year ended March 2018, and for 2017 and prior years, ARX and its eligible subsidiaries filed their own consolidated federal income tax returns. All tax years prior to 2017 are closed and the 2017 and short 2018 tax years remain open to examination. 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.

Loss And Loss Adjustment Expens

Loss And Loss Adjustment Expense Reserves	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Loss And Loss Adjustment Expense Reserves	LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES We write personal and commercial auto insurance, residential property insurance, and other specialty property-casualty insurance and 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, and had aggregate stop-loss reinsurance coverage covering accident years 2017 to 2019. As we are primarily an insurer of motor vehicles and residential property, we have limited exposure to environmental, asbestos, and general liability claims. We have established reserves for such exposures, which represent about 0.1% 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 represent about 94% 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 over 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 earned car year), 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 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 Property business on an accident period basis. Many of the methodologies and key parameters reviewed are similar. In addition, for 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) 2020 2019 2018 Balance at January 1 $ 18,105.4 $ 15,400.8 $ 13,086.9 Less reinsurance recoverables on unpaid losses 3,212.2 2,572.7 2,170.1 Net balance at January 1 14,893.2 12,828.1 10,916.8 Incurred related to: Current year 24,926.5 25,238.2 21,632.5 Prior years 195.3 232.3 88.5 Total incurred 25,121.8 25,470.5 21,721.0 Paid related to: Current year 15,584.4 16,105.0 13,792.1 Prior years 7,963.0 7,300.4 6,017.6 Total paid 23,547.4 23,405.4 19,809.7 Net balance at December 31 16,467.6 14,893.2 12,828.1 Plus reinsurance recoverables on unpaid losses 3,798.2 3,212.2 2,572.7 Balance at December 31 $ 20,265.8 $ 18,105.4 $ 15,400.8 We experienced unfavorable reserve development of $195.3 million, $232.3 million, and $88.5 million in 2020, 2019, and 2018, respectively, which is reflected as “Incurred related to prior years” in the table above. 2020 • Approximately $59 million of the unfavorable prior year reserve development was attributable to accident year 2019, $107 million to accident year 2018, and the remainder to 2017 and prior accident years. • Our personal auto products incurred about $136 million of unfavorable loss and LAE reserve development, with the Agency and Direct auto businesses each contributing about half, primarily attributable to higher than anticipated frequency of reopened personal injury protection (PIP) claims, primarily in Florida, updated estimates of our per claim settlement costs, and late reported losses occurring toward the end of 2019 but not reported until 2020, which was partially offset by higher than anticipated salvage and subrogation recoveries. • Our Commercial Lines business experienced about $98 million of unfavorable development, primarily due to increased injury severity and the emergence of large injury claims at rates higher than originally anticipated. • Our special lines and Property businesses experienced about $25 million and $14 million, respectively, of favorable development driven by favorable case development across all products, as severity was lower than expected. 2019 • Approximately $131 million of the unfavorable prior year reserve development was attributable to accident year 2018, $73 million to accident year 2017, and the remainder to 2016 and prior accident years. • Our personal auto products incurred about $121 million of unfavorable loss and LAE reserve development, with the Agency and Direct auto businesses each contributing about half, primarily reflecting increased injury severity, a higher than anticipated frequency of reopened PIP claims, primarily in Florida, and late reported losses occurring late 2018 but not reported until 2019. • Our Commercial Lines business experienced about $83 million of unfavorable development, primarily due to increased injury severity and more emergence of large injury claims than originally anticipated. • Our special lines business experienced about $14 million of unfavorable development, primarily due to less salvage and subrogation recoveries than originally anticipated and increased severity of late reported claims. • Our Property businesses experienced about $12 million of unfavorable development, primarily due to higher than originally anticipated homeowner and dwelling costs and fire liability costs. 2018 • Approximately $99 million of unfavorable prior year reserve development was attributable to accident years 2017 and 2016. This unfavorable development was offset by about $10 million of favorable development attributable to accident year 2015 and prior accident years. • Our personal auto products incurred almost $85 million of unfavorable loss and LAE reserve development, with approximately 70% attributable to the Agency business and 30% attributable to the Direct business, primarily reflecting unfavorable development from reopened Florida PIP claims. • Our special lines and Property businesses experienced about $5 million and $3 million of unfavorable development, respectively, while our commercial auto products had about $4 million of favorable reserve development. 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 last five years, which generally represents the maximum development period for claims in any of our segments. 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 claims development between liability and physical damage, since the loss patterns are significantly different between them. The other business primarily includes reserves for our run-off products, which are not considered material, and, therefore, we are not including separate claims development tables. Only 2020 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, 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 4,082.9 $ 4,130.0 $ 4,152.0 $ 4,177.3 $ 4,137.8 $ 0 740,535 2017 4,474.8 4,485.8 4,511.1 4,546.4 72.3 779,303 2018 5,141.8 5,182.1 5,192.7 100.0 856,108 2019 5,885.0 5,886.9 264.3 913,063 2020 5,433.8 926.8 750,654 Total $ 25,197.6 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 1,941.6 $ 3,231.5 $ 3,723.1 $ 3,969.5 $ 4,062.5 2017 2,074.0 3,478.5 4,048.5 4,285.5 2018 2,378.0 4,028.7 4,635.0 2019 2,715.2 4,533.2 2020 2,383.0 Total $ 19,899.2 All outstanding liabilities before 2016, net of reinsurance 1 80.3 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 5,378.7 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,423.4 $ 2,398.9 $ 2,401.8 $ 2,400.1 $ 2,402.8 $ 0 1,399,156 2017 2,635.5 2,638.5 2,643.5 2,640.6 (4.0) 1,514,873 2018 2,819.0 2,822.6 2,821.7 (3.4) 1,694,997 2019 3,277.9 3,254.7 (13.4) 1,876,942 2020 3,328.5 (183.4) 1,768,482 Total $ 14,448.3 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,391.0 $ 2,406.9 $ 2,402.1 $ 2,402.2 $ 2,401.8 2017 2,599.8 2,643.2 2,640.9 2,640.8 2018 2,769.1 2,827.4 2,819.9 2019 3,242.5 3,259.2 2020 3,250.1 Total $ 14,371.8 All outstanding liabilities before 2016, net of reinsurance 1 5.9 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 82.4 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 3,819.0 $ 3,843.9 $ 3,871.2 $ 3,897.8 $ 3,866.1 $ 0 735,791 2017 4,209.5 4,209.9 4,229.3 4,254.4 61.3 772,986 2018 4,904.8 4,980.9 5,003.2 88.0 870,978 2019 5,756.5 5,811.7 243.5 954,209 2020 5,356.9 901.1 786,809 Total $ 24,292.3 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 1,780.6 $ 2,991.1 $ 3,476.9 $ 3,714.6 $ 3,799.1 2017 1,912.6 3,255.2 3,808.3 4,035.6 2018 2,235.1 3,863.5 4,481.7 2019 2,630.3 4,452.5 2020 2,301.3 Total $ 19,070.2 All outstanding liabilities before 2016, net of reinsurance 1 55.2 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 5,277.3 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,521.0 $ 2,475.4 $ 2,477.7 $ 2,475.6 $ 2,478.5 $ 0 1,676,396 2017 2,750.6 2,743.7 2,749.0 2,745.6 (5.1) 1,791,582 2018 3,202.3 3,181.9 3,182.0 (5.1) 2,069,684 2019 3,787.9 3,737.8 (22.7) 2,269,857 2020 3,775.6 (264.5) 2,137,810 Total $ 15,919.5 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,505.0 $ 2,485.8 $ 2,479.3 $ 2,478.5 $ 2,477.8 2017 2,742.1 2,753.5 2,748.4 2,747.6 2018 3,170.0 3,193.8 3,183.0 2019 3,782.6 3,751.3 2020 3,720.0 Total $ 15,879.7 All outstanding liabilities before 2016, net of reinsurance 1 0.8 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 40.6 1 Required supplementary information (unaudited) Commercial Lines - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 1,185.8 $ 1,204.8 $ 1,231.1 $ 1,238.9 $ 1,224.9 $ 0 92,688 2017 1,374.1 1,366.6 1,393.3 1,374.6 18.3 97,448 2018 1,700.8 1,736.5 1,789.7 41.5 111,767 2019 2,103.1 2,175.6 116.3 126,959 2020 2,161.8 369.8 105,900 Total $ 8,726.6 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 298.6 $ 639.9 $ 886.0 $ 1,073.3 $ 1,153.4 2017 325.8 712.9 1,027.3 1,183.6 2018 382.7 913.4 1,290.5 2019 455.4 1,120.1 2020 427.6 Total $ 5,175.2 All outstanding liabilities before 2016, net of reinsurance 1 34.9 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 3,586.3 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 379.6 $ 379.8 $ 378.2 $ 377.8 $ 378.1 $ 0 74,199 2017 415.4 412.1 411.0 409.9 (0.9) 77,170 2018 475.0 478.2 476.6 (1.4) 82,134 2019 577.8 574.2 (3.3) 88,897 2020 575.2 (14.1) 87,333 Total $ 2,414.0 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 336.7 $ 376.9 $ 376.8 $ 377.5 $ 377.6 2017 369.0 409.4 409.2 409.4 2018 426.0 475.1 475.3 2019 516.9 571.5 2020 497.9 Total $ 2,331.7 All outstanding liabilities before 2016, net of reinsurance 1 0.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 82.7 1 Required supplementary information (unaudited) Property Business ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 568.6 $ 541.2 $ 537.1 $ 536.5 $ 535.5 $ 2.4 53,693 2017 672.8 680.9 683.4 681.3 1.3 74,140 2018 839.0 845.2 845.4 18.2 63,722 2019 971.7 965.2 11.7 72,396 2020 1,223.5 252.4 80,820 Total $ 4,250.9 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 415.2 $ 498.2 $ 516.9 $ 526.4 $ 530.8 2017 506.7 647.1 670.1 675.0 2018 595.9 781.2 812.6 2019 708.0 930.4 2020 832.5 Total $ 3,781.3 All outstanding liabilities before 2016, net of reinsurance 1 5.1 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 474.7 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) 2020 2019 Net outstanding liabilities Personal Lines Agency, Liability $ 5,378.7 $ 5,117.4 Agency, Physical Damage 82.4 32.4 Direct, Liability 5,277.3 4,936.8 Direct, Physical Damage 40.6 (7.7) Commercial Lines Liability 3,586.3 3,080.8 Physical Damage 82.7 66.6 Property 474.7 357.2 Other business 66.7 30.8 Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 14,989.4 13,614.3 Reinsurance recoverable on unpaid claims Personal Lines Agency, Liability 959.6 930.7 Agency, Physical Damage 0 0 Direct, Liability 1,475.8 1,314.1 Direct, Physical Damage 0 0 Commercial Lines Liability 758.5 482.6 Physical Damage (0.3) 0.5 Property 226.9 184.1 Other business 358.6 288.1 Total reinsurance recoverable on unpaid claims 3,779.1 3,200.1 Unallocated claims adjustment expense related to: Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 1,478.2 1,278.9 Reinsurance recoverable on unpaid claims 19.1 12.1 Total gross liability for unpaid claims and claim adjustment expense $ 20,265.8 $ 18,105.4 The following table shows the average historical claims duration as of December 31, 2020: (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 45.6% 31.2% 12.0% 5.6% 2.2% Agency, Physical Damage 98.6 1.2 (0.2) 0 0 Direct, Liability 44.7 31.7 12.6 5.7 2.2 Direct, Physical Damage 100.0 (0.1) (0.3) 0 0 Commercial Lines Liability 21.7 29.3 21.4 13.2 6.5 Physical Damage 88.9 10.0 0 0.1 0 Property 71.9 20.8 3.5 1.2 0.8

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2020
Reinsurance Disclosures [Abstract]
Reinsurance	REINSURANCE The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows: 2020 2019 2018 (millions) Written Earned Written Earned Written Earned Direct premiums $ 41,736.4 $ 40,687.7 $ 39,222.0 $ 37,519.7 $ 33,753.1 $ 31,970.2 Ceded premiums: Regulated (648.2) (686.5) (711.1) (670.8) (596.4) (557.5) Non-Regulated (519.5) (739.6) (933.0) (656.5) (546.8) (479.4) Total ceded premiums (1,167.7) (1,426.1) (1,644.1) (1,327.3) (1,143.2) (1,036.9) Net premiums $ 40,568.7 $ 39,261.6 $ 37,577.9 $ 36,192.4 $ 32,609.9 $ 30,933.3 Regulated refers to federal or state run plans and primarily include 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 represents voluntary external reinsurance contracts entered into by the company. These include amounts ceded on our Commercial Lines business primarily related to transportation network company (TNC) business under quota-share reinsurance agreements and amounts ceded on our Property business under catastrophic occurrence excess of loss, aggregate excess of loss, beginning January 1, 2020, and, for accident years 2017-2019, aggregate stop-loss reinsurance agreements. At December 31, 2020, we wrote TNC business in 20 states and the District of Columbia, compared to 17 states and 4 states at year-end 2019 and 2018, respectively. While expanding our footprint in the TNC business increased our ceded written premium in 2019, during 2020 the impact of this expansion was mitigated by a significant decrease in vehicle miles driven, which was attributable to COVID-19 restrictions. Premiums written on TNC policies are estimated based on projections of miles driven during the policy term, and such estimates are revised monthly based on actual miles driven and revised estimates of miles driven for the remaining policy term. The increase in ceded earned premiums in both 2020 and 2019 reflects the growth in the TNC business. Our reinsurance recoverables and prepaid reinsurance premiums were comprised of the following at December 31: Reinsurance Recoverables Prepaid Reinsurance Premiums ($ in millions) 2020 2019 2020 2019 Regulated: MCCA $ 2,428.8 60 % $ 2,247.1 67 % $ 33.3 9 % $ 71.8 12 % CAIP 397.8 10 332.4 10 84.7 23 93.8 15 NCRF 88.6 2 84.4 2 41.9 11 33.8 5 FHCF 54.8 1 86.0 3 0 0 0 0 NFIP 24.2 1 11.6 0 60.7 17 58.7 9 Other 3.2 0 3.1 0 1.3 0 1.0 0 Total Regulated 2,997.4 74 2,764.6 82 221.9 60 259.1 41 Non-Regulated: Commercial Lines 753.2 19 459.5 14 134.5 37 352.9 56 Property 261.7 7 146.8 4 11.7 3 14.5 3 Other 7.1 0 8.0 0 0 0 0 0 Total Non-Regulated 1,022.0 26 614.3 18 146.2 40 367.4 59 Total $ 4,019.4 100 % $ 3,378.9 100 % $ 368.1 100 % $ 626.5 100 % The increase in our reinsurance recoverables on our Commercial Lines business primarily reflects the growth in the TNC business, while the decrease in the prepaid reinsurance premiums is due to the reduction of premiums written due to the COVID-19 restrictions 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. We evaluate the financial condition of our other reinsurers and monitor concentrations of credit risk to minimize our exposure to significant losses from reinsurer insolvencies. We routinely monitor changes in the credit quality and concentration risks of the reinsurers who are counter

Statutory Financial Information

Statutory Financial Information	12 Months Ended
	Dec. 31, 2020
Statutory Financial Information Disclosures [Abstract]
Statutory Financial Information	STATUTORY FINANCIAL INFORMATION Consolidated statutory surplus was $15,194.6 million and $13,671.1 million at December 31, 2020 and 2019, respectively. Statutory net income was $4,911.4 million, $3,489.7 million, and $2,643.0 million for the years ended December 31, 2020, 2019, and 2018, respectively. At December 31, 2020, $1,142.0 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

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2020
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. 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, 2020, the ESOP held 21.5 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. Matching contributions to these plans for the years ended December 31, 2020, 2019, and 2018 were $131.2 million, $120.8 million, and $106.8 million, respectively. 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 $24.1 million and $22.2 million at December 31, 2020 and 2019, 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 included an annual cash incentive program (i.e., Gainsharing Program) for virtually 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: 2020 2019 2018 (millions) Pretax After Tax Pretax After Tax Pretax After Tax Non-equity incentive plans – cash $ 688.8 $ 544.2 $ 598.4 $ 472.7 $ 539.5 $ 426.2 Equity incentive plans: Equity awards 89.4 70.6 90.1 71.2 76.2 60.2 Liability awards 1 0 0 0.1 0.1 1.0 0.8 1 Relates to stock options granted to key employees of ARX, which were exercised in 2020. See Note 15 – Redeemable Noncontrolling Interest for further discussion. Under Progressive’s 2015 Equity Incentive Plan, which provides for the granting of equity-based compensation to officers and other key employees, 17.0 million shares, in the aggregate, were authorized for issuance. 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, based on the market value of the awards at the time of grant, with accelerated expense for participants who reach qualified retirement provisions. The time-based awards vest in equal installments upon the lapse of specified periods of time, typically three four 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 pre-determined performance goals within specified time periods. The performance-based awards were granted to executives and other senior managers in 2020, in addition to their time-based awards, 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 details of the performance-based equity awards that were outstanding at December 31, 2020, are as follows: Performance Measurement Year(s) of Grant Vesting range (as a percentage of target) Growth of our personal auto and commercial auto businesses and homeowners multi-peril business, each compared to its respective market 2018-2020 0-250% Investment results relative to peer group 2018-2020 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: 2020 2019 2018 Restricted Equity Awards Number of Shares 1 Weighted Number of Shares 1 Weighted Number of Shares 1 Weighted Beginning of year 3,879,077 $ 48.28 4,856,356 $ 38.56 5,858,848 $ 30.47 Add (deduct): Granted 2 1,629,534 55.28 1,835,145 49.61 1,876,109 45.55 Vested (1,861,442) 36.19 (2,691,337) 31.85 (2,811,070) 26.41 Forfeited (76,898) 52.79 (121,087) 43.98 (67,531) 36.10 End of year 3,4 3,570,271 $ 57.68 3,879,077 $ 48.28 4,856,356 $ 38.56 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 2020, 2019, and 2018, the number of units “granted” shown in the table above includes 144,389, 210,159, and 144,688 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, 2020, the number of shares included 707,293 performance-based units at their target amounts. We expect 1,658,308 units to vest based upon our current estimates of the likelihood of achieving the pre-determined performance goals applicable to each award. 4 At December 31, 2020, the total unrecognized compensation cost related to unvested equity awards was $102.1 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the consolidated statements of comprehensive income over the weighted average vesting period of 2.3 years. The aggregate fair value of the restricted equity awards that vested during the years ended December 31, 2020, 2019, and 2018, was $148.9 million, $191.6 million, and $162.7 million, respectively, based on the actual stock price on the applicable vesting date. Incentive Compensation Plans – Directors Progressive’s 2017 Directors Equity Incentive Plan, which provides for the granting of equity-based awards, including restricted stock awards, to non-employee directors, was approved by shareholders in 2017 and originally authorized awards for up to 0.5 million 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 he or she preferred to receive 100% of their compensation in the form of restricted stock. After considering such preferences, the Compensation Committee of the Board of Directors determines the awards (restricted stock, or restricted stock and cash) for each non-employee director. The restricted stock awards are issued as time-based awards. The vesting period (i.e., requisite service 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: 2020 2019 2018 Restricted Stock Number of Weighted Number of Weighted Number of Weighted Beginning of year 38,451 $ 73.43 41,706 $ 62.23 53,284 $ 40.54 Add (deduct): Granted 39,403 74.77 38,451 73.43 41,706 62.23 Vested (38,451) 73.43 (41,706) 62.23 (53,284) 40.54 End of year 1 39,403 $ 74.77 38,451 $ 73.43 41,706 $ 62.23 1 At December 31, 2020, 2019, and 2018, the remaining unrecognized compensation cost related to restricted stock awards was $0.9 million, $0.8 million, and $0.9 million, respectively. The aggregate fair value of the restricted stock vested during the years ended December 31, 2020, 2019, and 2018, was $3.0 million, $3.0 million, and $3.2 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 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) 2020 2019 Progressive common shares 1 $ 134.2 $ 121.6 Other investment funds 2 167.2 151.2 Total $ 301.4 $ 272.8 1 Included 2.8 million and 3.2 million common shares as of December 31, 2020 and 2019, respectively, to be distributed in common shares, and are reported at grant date fair value. 2 Amount is included in other assets on the consolidated balance sheets.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION We write personal and commercial auto insurance, personal residential and commercial property insurance, general liability insurance, and other specialty property-casualty insurance and related services. 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, by phone, or on mobile devices. We operate our Personal Lines businesses throughout the United States. Our Commercial Lines segment writes auto-related primary liability and physical damage insurance, and general liability and property insurance, predominately for small businesses. This segment operates throughout the United States and is distributed through both the independent agency and direct channels. Our Property segment writes residential property insurance for homeowners, other property owners, and renters through both the independent agency and direct channel, and writes flood insurance through the “Write Your Own” program for the National Flood Insurance Program, through the agency channel. Our Property segment operates throughout the majority of the United States. Our service businesses provide insurance-related services, including processing CAIP business and serving as an agent for homeowners, general liability, and workers’ compensation insurance, among other products, through programs in our direct Personal Lines and Commercial Lines businesses. We evaluate profitability based on pretax underwriting profit (loss) for the Personal Lines, Commercial Lines, and Property segments. 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 do not separately identify depreciation expense by segment. Companywide depreciation expense was $274.9 million in 2020, $239.8 million in 2019, and $190.4 million in 2018. The accounting policies of the operating segments are the same as those described in Note 1 – Reporting and Accounting Policies . Following are the operating results for the years ended December 31: 2020 2019 2018 (millions) Revenues Pretax Revenues Pretax Revenues Pretax Personal Lines Agency $ 15,789.5 $ 2,236.5 $ 14,904.1 $ 1,673.2 $ 13,017.2 $ 1,435.7 Direct 16,830.6 2,076.5 15,305.9 1,181.4 13,017.5 1,088.5 Total Personal Lines 1 32,620.1 4,313.0 30,210.0 2,854.6 26,034.7 2,524.2 Commercial Lines 4,875.8 634.8 4,427.6 458.8 3,610.9 478.6 Property 2 1,765.7 (125.1) 1,554.8 (26.1) 1,287.7 (88.7) Other indemnity 0 0 0 0 0 0.9 Total underwriting operations 39,261.6 4,822.7 36,192.4 3,287.3 30,933.3 2,915.0 Fees and other revenues 3 603.5 NA 563.7 NA 472.2 NA Service businesses 226.4 20.9 195.0 16.1 158.5 24.4 Investments 4 2,566.6 2,546.6 2,071.2 2,046.6 415.0 390.7 Interest expense NA (217.0) NA (189.7) NA (166.5) Consolidated total $ 42,658.1 $ 7,173.2 $ 39,022.3 $ 5,160.3 $ 31,979.0 $ 3,163.6 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned in 2020, 2019, and 2018; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 During 2020, 2019, and 2018, pretax profit (loss) includes $56.9 million, $66.3 million, and $72.0 million, respectively, of amortization expense predominately associated with intangible assets. See Note 16 - Goodwill and Intangible Assets for further discussion. 3 Pretax profit (loss) for fees and other revenues is allocated to operating segments. 4 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit 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: 2020 2019 2018 Underwriting Combined Underwriting Combined Underwriting Combined Personal Lines Agency 14.2 % 85.8 11.2 % 88.8 11.0 % 89.0 Direct 12.3 87.7 7.7 92.3 8.4 91.6 Total Personal Lines 13.2 86.8 9.5 90.5 9.7 90.3 Commercial Lines 13.0 87.0 10.4 89.6 13.3 86.7 Property 1 (7.1) 107.1 (1.7) 101.7 (6.9) 106.9 Total underwriting operations 12.3 87.7 9.1 90.9 9.4 90.6 1 Included in 2020, 2019, and 2018, are 3.2 points, 4.3 points, and 5.6 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Other Comprehensive Income (Loss)	OTHER COMPREHENSIVE INCOME (LOSS) The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, for the years ended December 31, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized (Income) loss attributable to NCI Balance at December 31, 2019 $ 435.7 $ (94.0) $ 341.7 $ 360.8 $ (16.4) $ (2.7) Reclassification of disproportionate amounts 1 3.4 (0.7) 2.7 0 0 2.7 Adjusted balance at December 31, 2019 439.1 (94.7) 344.4 360.8 (16.4) 0 Other comprehensive income (loss) before reclassifications: Investment securities 1,557.2 (306.1) 1,251.1 1,251.1 0 0 Loss attributable to noncontrolling interest (NCI) 0 0 0 0 0 0 Total other comprehensive income (loss) before reclassifications 1,557.2 (306.1) 1,251.1 1,251.1 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 810.0 (145.4) 664.6 664.6 0 0 Interest expense (1.1) 0.3 (0.8) 0 (0.8) 0 Total reclassification adjustment for amounts realized in net income 808.9 (145.1) 663.8 664.6 (0.8) 0 Total other comprehensive income (loss) 748.3 (161.0) 587.3 586.5 0.8 0 Balance at December 31, 2020 $ 1,187.4 $ (255.7) $ 931.7 $ 947.3 $ (15.6) $ 0 1 Adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the purchase transaction (See Note 15 - Redeemable Noncontrolling Interest for additional information). Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized (Income) loss attributable to NCI Balance at December 31, 2018 $ (153.0) $ 32.1 $ (120.9) $ (105.6) $ (17.2) $ 1.9 Other comprehensive income (loss) before reclassifications: Investment securities 825.8 (174.9) 650.9 650.9 0 0 Loss attributable to noncontrolling interest (NCI) (5.9) 1.3 (4.6) 0 0 (4.6) Total other comprehensive income (loss) before reclassifications 819.9 (173.6) 646.3 650.9 0 (4.6) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 232.2 (47.7) 184.5 184.5 0 0 Interest expense (1.0) 0.2 (0.8) 0 (0.8) 0 Total reclassification adjustment for amounts realized in net income 231.2 (47.5) 183.7 184.5 (0.8) 0 Total other comprehensive income (loss) 588.7 (126.1) 462.6 466.4 0.8 (4.6) Balance at December 31, 2019 $ 435.7 $ (94.0) $ 341.7 $ 360.8 $ (16.4) $ (2.7) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized (Income) loss attributable to NCI Balance at December 31, 2017 $ 1,977.8 $ (695.6) $ 1,282.2 $ 1,295.0 $ (14.8) $ 2.0 Cumulative effect adjustment 1 (2,006.0) 705.8 (1,300.2) (1,300.2) 0 0 Reclassification of disproportionate amounts 2 (4.3) (3.4) (7.7) (1.1) (3.2) (3.4) Adjusted balance at December 31, 2017 (32.5) 6.8 (25.7) (6.3) (18.0) (1.4) Other comprehensive income (loss) before reclassifications: Investment securities (224.1) 47.0 (177.1) (177.1) 0 0 Loss attributable to noncontrolling interest (NCI) 4.3 (1.0) 3.3 0 0 3.3 Total other comprehensive income (loss) before reclassifications (219.8) 46.0 (173.8) (177.1) 0 3.3 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (98.3) 20.5 (77.8) (77.8) 0 0 Interest expense (1.0) 0.2 (0.8) 0 (0.8) 0 Total reclassification adjustment for amounts realized in net income (99.3) 20.7 (78.6) (77.8) (0.8) 0 Total other comprehensive income (loss) (120.5) 25.3 (95.2) (99.3) 0.8 3.3 Total at December 31, 2018 $ (153.0) $ 32.1 $ (120.9) $ (105.6) $ (17.2) $ 1.9 1 Reflects the fair value changes on equity securities as of December 31, 2017, which are reported as realized gains (losses) under the new accounting guidance. See Note 1 - Reporting and Accounting Policies for additional information. 2 Reflects the effect of the change in U.S. federal tax rate on our available-for-sale fixed-maturity securities and our hedges on forecasted transactions as of December 31, 2017 (see Note 1 - Reporting and Accounting Policies for additional information) and the adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the “put” transaction (see Note 15 - Redeemable Noncontrolling Interest for additional information). In an effort to manage interest rate risk, we may enter into forecasted transactions on Progressive’s debt issuances. We expect to reclassify $0.9 million (pretax) into interest expense during the next 12 months, related to net unrealized losses on forecasted transactions (see Note 4 – Debt

Litigation

Litigation	12 Months Ended
	Dec. 31, 2020
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 subsidiaries are named as defendants in a number of class action or individual lawsuits that challenge certain of the operations of the subsidiaries. Other insurance companies face many of these same issues. 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 period end. 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 are 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 or, if probable and estimable, are accrued and immaterial as of December 31, 2020. At period 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. Based on information currently known, we do not believe that the outcome of any pending cases described below will have a material impact on our consolidated financial condition, cash flows, and/or results of operations. At December 31, 2020, pending lawsuits as described above that challenge certain of the operations of our subsidiaries included: Lawsuits seeking class/collective action status: • alleging we sell or charge insureds for illusory coverage or coverage lower than amounts allowed by law for PIP coverage and pay related claims at levels lower than allowed by law. • challenging how physical damage claims are handled, adjusted, and ultimately paid, including how we value total loss claims, the payment of fees and taxes associated with total losses, and the payment of diminution damages. • challenging our practices in Florida of adjusting PIP claims. • challenging our use of used original equipment manufacturer parts in the repair of a leased vehicle. • challenging our adjustment of medical bills submitted by insureds or medical providers in medical claims. • challenging our payment and reimbursement practices to Medicare Advantage Plans on first party medical, PIP, and bodily injury claims. • challenging our acceptance of uninsured motorist rejection. • alleging we sell illusory underinsured motorist coverage. • alleging we wrongfully withheld payments owed to insureds under uninsured/underinsured motorist coverage. • alleging that we wrongly pursue subrogation of medical payments paid directly to providers and not to insureds. • alleging that we must pay an insured the pre-loss actual cash value of a totaled vehicle in addition to the value of the salvage vehicle if we take ownership of the salvage vehicle. • alleging that we improperly calculate basic economic loss as it relates to wage loss coverage. • alleging that we violated the Telephone Consumer Protection Act. • alleging that we provided an insufficient amount of premium relief to Illinois insureds in response to the COVID-19 pandemic. • challenging certain of our pay practices and overtime payment practices. • alleging that we fail to pay overtime to certain employees who we classify as exempt from overtime pay requirements. Lawsuits certified or conditionally certified as class/collective actions: • alleging we improperly sell secondary PIP coverage to Medicare and Medicaid beneficiaries in New Jersey. • challenging how we value total loss claims in Florida and Louisiana. • challenging the payment of fees and taxes associated with total losses in Florida.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	LEASES Included in our consolidated balance sheets are certain operating leases for office space, computer equipment, and vehicles that are reported as a component of other assets accounts payable, accrued expenses, and other liabilities 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. An incremental borrowing rate is used to calculate the present value of the remaining lease payments. Each contract is 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) 2020 2019 Operating lease assets $ 165.5 $ 188.2 Operating lease liabilities $ 179.0 $ 201.5 Weighted-average remaining term 3.0 years 3.3 years Weighted-average discount rate 2.5 % 3.0 % At December 31, 2020, the following table shows our operating lease liabilities, on an undiscounted basis for the periods indicated: (millions) Commitments 2021 $ 78.9 2022 48.7 2023 29.1 2024 18.4 2025 9.8 Thereafter 0.5 Total 185.4 Interest (6.4) Present value of lease liabilities $ 179.0 The operating lease expense for the years ended December 31, was as follows: (millions) Expense 2020 $ 95.4 2019 102.0 2018 77.3

Dividends

Dividends	12 Months Ended
	Dec. 31, 2020
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 1 Common - Annual Variable Dividends: December 2020 January 2021 $ 4.50 $ 2,635.9 December 2019 January 2020 2.25 1,316.9 December 2018 February 2019 2.5140 1,467.9 December 2017 February 2018 1.1247 655.1 Common - Quarterly Dividends: December 2020 January 2021 0.10 58.6 August 2020 October 2020 0.10 58.6 May 2020 July 2020 0.10 58.5 February 2020 April 2020 0.10 58.5 December 2019 January 2020 0.10 58.5 August 2019 October 2019 0.10 58.5 May 2019 July 2019 0.10 58.4 February 2019 April 2019 0.10 58.4 Preferred Dividends: December 2020 March 2021 26.875 13.4 August 2020 September 2020 26.875 13.4 February 2020 March 2020 26.875 13.4 August 2019 September 2019 26.875 13.4 February 2019 March 2019 26.875 13.4 August 2018 September 2018 27.024 13.5 1 The accrual is based on an estimate of shares outstanding as of the record date and the common share accrual is recorded as “dividends payable on common shares” on the Consolidated Balance Sheets; the prior year common share amount was reclassified into this line item from “accounts payable, accrued expenses, and other liabilities” to conform to the current year presentation. 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 common share dividend, which was effective beginning in 2019. Prior to 2019, we maintained a policy of paying an annual variable dividend. Under the policy, the dividend was based on a target percentage of 33-1/3%, as determined by the Board, of after-tax underwriting income multiplied by a performance factor (Gainshare factor). The Gainshare factor was 1.91 and 1.79 for the dividends declared in 2018 and 2017, respectively. Preferred Share Dividends In March 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

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest	12 Months Ended
	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interest	REDEEMABLE NONCONTROLLING INTEREST In connection with the April 2015 acquisition of a controlling interest in ARX, The Progressive Corporation entered into a stockholders’ agreement with the other ARX stockholders. During 2018, minority ARX stockholders put 204,527 shares, including 5,483 shares that were issued upon the exercise of outstanding stock options. Progressive acquired these additional shares, in a cash transaction, for a total cost of $295.9 million. On April 1, 2020, Progressive purchased all remaining outstanding stock, including shares from exercised stock options, of ARX under a separately negotiated purchase agreement at a total cost of $243.0 million. Since these securities were redeemable upon the occurrence of an event that was not solely within the control of Progressive, we recorded the redeemable noncontrolling interest (NCI) as mezzanine equity on our consolidated balance sheets, representing the minority shares at the current estimated purchase price pursuant to the put and call provisions of the stockholders’ agreement. The changes in the components of redeemable NCI during the years ended December 31, were: (millions) 2020 2019 2018 Balance, beginning of year $ 225.6 $ 214.5 $ 503.7 Net income attributable to NCI 0 9.7 5.7 Other comprehensive income (loss) attributable to NCI 1 0 4.6 (3.3) Exercise of stock options 16.0 7.7 9.4 Purchase/change of ARX minority shares (241.6) (11.2) (298.2) Change in redemption value 0 0.3 (2.8) Balance, end of year $ 0 $ 225.6 $ 214.5 1 Amount represents the other comprehensive income (loss) attributable to NCI, as reflected on the consolidated statements of comprehensive income; changes in accumulated other comprehensive income (loss) attributable to NCI due to a change in the minority ownership percentage does not impact the amount of redeemable NCI .

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	GOODWILL AND INTANGIBLE ASSETS Goodwill Goodwill recorded at December 31, 2020, and 2019, was $452.7 million. The majority of the goodwill recorded as of December 31, 2020 and 2019, relates to the April 1, 2015, acquisition of a controlling interest in ARX. No impairment losses have been recorded on any of the outstanding goodwill. Intangible Assets The following table is a summary of the net carrying amount of other intangible assets as of December 31: (millions) 2020 2019 Intangible assets subject to amortization $ 159.0 $ 215.9 Indefinite-lived intangible assets 1 12.4 12.4 Total $ 171.4 $ 228.3 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for both years presented. Intangible assets subject to amortization for the years ended December 31, consisted of the following: (millions) 2020 2019 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 210.4 $ 45.8 $ 256.2 $ 173.9 $ 82.3 Agency relationships 159.2 65.4 93.8 159.2 54.0 105.2 Software rights 69.1 49.7 19.4 79.1 50.7 28.4 Trade name 0 0 0 34.8 34.8 0 Total $ 484.5 $ 325.5 $ 159.0 $ 529.3 $ 313.4 $ 215.9 Amortization expense was $56.9 million, $66.3 million, and $72.0 million for the years ended December 31, 2020, 2019, and 2018, respectively. During 2020, one software rights intangible asset, with a gross carrying value of $10.0 million, was fully amortized. The estimated aggregate amortization on these intangible assets for each of the next five years as of December 31, 2020, follows: (millions) Year Amortization 2021 $ 56.6 2022 29.2 2023 13.5 2024 11.4 2025 11.4

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event	SUBSEQUENT EVENTOn February 16, 2021, we announced that we have entered into a definitive agreement with Protective Insurance Corporation (“Protective”) to acquire all of Protective’s outstanding Class A and Class B common shares for $23.30 per share in cash, or approximately $338 million in aggregate. This transaction is expected to close prior to the end of the third quarter 2021, subject to customary closing conditions, including the receipt of certain required regulatory approvals and approval of Protective’s Class A shareholders

Reporting and Accounting Poli_2

Reporting and Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
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 provide personal and commercial auto insurance, personal residential and commercial property insurance, general liability insurance, and other specialty property-casualty insurance and related services. 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 primary liability and physical damage insurance, and general liability and property insurance, predominately for small businesses. 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, 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 Eurodollar deposits, 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. These securities are carried at fair value, with the changes in fair value reported as a component of net holding period gains (losses) on securities reported in net income. Derivative instruments may include futures, options, forward positions, interest rate swap agreements, and credit default swaps and may be used in the portfolio for general investment purposes or to hedge the exposure to variable cash flows of a forecasted transaction (cash flow hedge). We did not have any derivatives outstanding at December 31, 2020 or 2019. To the extent we have derivatives held for general investment purposes, these derivative instruments would be recognized as either assets or liabilities and measured at fair value, with changes in fair value recognized in net income as a component of net holding period gains (losses) on securities. 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. For derivatives settled through a clearinghouse, collateral is required to post initial margin and is subject to increases in margin beyond changes in fair value. Exposure to credit risk is limited to the carrying value; collateral may be required to limit credit risk. For bi-lateral derivative positions, net cash requirements are limited to changes in fair values, which may vary as a result of changes in interest rates, currency exchange rates, and other factors. We have elected not to offset fair value amounts that arise from derivative positions with the same counterparty under a master netting arrangement. 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 a write-off of the fair value for 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 and 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-off the security to its fair value. Investment income consists of interest, dividends, and accretion (net of 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. 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 includes holding period valuation changes on equity securities, hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument), and derivatives, as well as initial credit allowance losses, subsequent changes in credit loss allowances, and write-offs for losses deemed uncollectible or securities in a 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 that are applicable to the unexpired risk. We provide insurance and 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. We then age this exposure to establish an allowance for credit losses based on prior experience. 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, cancel the policy and write off any remaining balance.
Allowance for credit losses	To determine an allowance for credit losses, we evaluate the collectibility of premiums receivables based on historical and current collections experience 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. The following table summarizes changes in our allowance for credit loss exposure on our premium receivables: (millions) 2020 2019 Balance at January 1 $ 283.2 $ 252.1 Increase in allowance 1 472.0 433.5 Write-offs 2 (399.0) (402.4) Balance at December 31 $ 356.2 $ 283.2 1 Represents the incremental increase in other underwriting expenses. 2 Represents the portion of allowance that is reversed when premium receivables are written off.
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
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 (IBNR). 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 in the near term.
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 servicing agent for CAIP and 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 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.
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 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 are investment securities (e.g., net unrealized gains (losses), net holding period gains (losses) on securities, write-downs on securities determined to be other-than-temporarily impaired), loss and loss adjustment expense reserves, unearned premiums reserves, deferred acquisition costs, property and equipment, intangible assets, and non-deductible accruals. 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. The cost and useful lives for property and equipment at December 31, were: ($ in millions) 2020 2019 Useful Lives Land $ 151.6 $ 161.6 NA Buildings, improvements, and integrated components 872.7 927.1 7-40 years Capitalized software 392.6 367.1 3-10 years Software licenses (internal use) 335.5 286.8 1-5 years Computer equipment 253.8 223.3 3 years All other property and equipment 391.2 385.9 3-10 years Total cost 2,397.4 2,351.8 Accumulated depreciation (1,291.4) (1,138.1) Balance at end of year $ 1,106.0 $ 1,213.7 NA = Not applicable; land is not a depreciable asset. Included in other assets in the consolidated balance sheets are “held for sale” property, which represents the fair value of these properties less the estimated costs to sell, of $56.6 million and $32.9 million at December 31, 2020 and 2019, respectively, and capitalized cloud computing arrangement implementation costs, net of amortization, of $25.3 million at December 31, 2020. We adopted the new accounting standard for cloud computing arrangements in January 2020; see New Accounting Standards below in this Note 1 for further discussion.
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. Intangible assets are non-financial assets lacking physical substance, such as customer and agency relationships and software rights, and represent the future economic benefit of those acquired assets. See Note 16 – Goodwill and Intangible Assets for further discussion. 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.
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 formal determination of insolvency has occurred, and we have written the premiums on which the assessments will be based. Assessments that are available for recoupment from policyholders are capitalized when incurred; all other assessments are expensed.
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. 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. Service revenues generated from processing business for involuntary CAIP plans are earned on a pro rata basis over the term of the related policies. Service expenses related to these CAIP plans are expensed as 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.” Compensation expense for time-based restricted equity awards with installment vesting is recognized over each respective vesting period. For performance-based restricted equity
Earnings Per Common Share	Earnings Per Common Share Net income attributable to Progressive 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 time-based restricted stock awards. Diluted earnings per common share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents 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.
Cash Flow Supplemental Disclosure	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, and are not considered part of the investment portfolio. The amount of reverse repurchase commitments held by these subsidiaries at December 31, 2020, 2019, and 2018, were $93.5 million, $46.3 million, and $117.3 million, respectively. Restricted cash on our consolidated balance sheets represents cash that is restricted to pay flood claims under the NFIP’s “Write Your Own” program, for which certain subsidiaries are administrators. For the year ended December 31, 2020, non-cash activity includes declared but unpaid common share dividends of $2,694.5 million and preferred share dividends of $13.4 million, and operating lease liabilities arising from obtaining right-of-use assets of $60.3 million (see Note 13 – Leases and Note 14 – Dividends for further discussion). For the years ended December 31, we paid the following: (millions) 2020 2019 2018 Income taxes $ 1,446.3 $ 954.3 $ 702.6 Interest 206.0 184.9 154.0 Operating lease liabilities 86.5 84.0 NA NA = Not applicable prior to the adoption of the new accounting standard in 2019.
Commitments and Contingencies	Commitments and Contingencies We have certain noncancelable purchase obligations for goods and services with minimum commitments of $830.4 million at December 31, 2020, 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
New Accounting Standards	New Accounting Standards On January 1, 2020, we adopted the following new Accounting Standards Updates (ASU). Cloud Computing Arrangements This ASU, which provides guidance on the requirements for capitalizing and amortizing implementation costs incurred in a cloud computing arrangement that does not include a software license, was adopted on a prospective basis. See the Property and Equipment discussion above for the cloud computing arrangement implementation cost capitalized at December 31, 2020. Fair Value Measurements We early adopted a portion of this ASU in 2018 and the remaining provisions in 2020. This ASU amended the disclosure requirements for fair value measurements to require companies to disclose the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and removed current disclosure requirements for the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels, and the valuation processes for Level 3 fair value measurements. The adoption of this ASU had no impact on our financial condition, cash flows, or results of operations. Goodwill Impairment Test Simplification The ASU eliminated the requirement to determine the implied fair value of goodwill in measuring an impairment loss and now requires the measurement of a goodwill impairment to represent the excess of the reporting unit’s carrying value over fair value, limited to the carrying value of goodwill. The adoption of this ASU had no impact on our financial condition, cash flows, or results of operations. Measurement of Credit Losses on Financial Instruments This ASU modified the existing accounting guidance related to the impairment evaluation for our available-for-sale debt securities, reinsurance recoverables, and premiums receivable. The ASU is intended to improve the timing, and enhance the accounting and disclosure, of credit losses on financial assets. To the extent a credit loss is determined to exist, an allowance for credit losses would be required to be recorded as a contra asset, with changes to the credit loss allowance recorded prospectively. Based on our analysis for available-for-sale debt securities and reinsurance recoverables as described in Note 2– Investments and Note 7– Reinsurance , respectively, no adjustment to the beginning balance of retained earnings was required upon adoption. See the Insurance Premiums and Receivables discussion above for changes in the allowance for credit losses related to the premiums receivable balance.

Reporting and Accounting Poli_3

Reporting and Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table summarizes changes in our allowance for credit loss exposure on our premium receivables: (millions) 2020 2019 Balance at January 1 $ 283.2 $ 252.1 Increase in allowance 1 472.0 433.5 Write-offs 2 (399.0) (402.4) Balance at December 31 $ 356.2 $ 283.2 1 Represents the incremental increase in other underwriting expenses. 2 Represents the portion of allowance that is reversed when premium receivables are written off.
Advertising Costs	Total advertising costs, which are expensed as incurred, for the years ended December 31, were: (millions) Advertising Costs 2020 $ 2,175.7 2019 1,837.3 2018 1,422.4
Property and Equipment	The cost and useful lives for property and equipment at December 31, were: ($ in millions) 2020 2019 Useful Lives Land $ 151.6 $ 161.6 NA Buildings, improvements, and integrated components 872.7 927.1 7-40 years Capitalized software 392.6 367.1 3-10 years Software licenses (internal use) 335.5 286.8 1-5 years Computer equipment 253.8 223.3 3 years All other property and equipment 391.2 385.9 3-10 years Total cost 2,397.4 2,351.8 Accumulated depreciation (1,291.4) (1,138.1) Balance at end of year $ 1,106.0 $ 1,213.7 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) 2020 2019 2018 Pretax expense $ 89.4 $ 90.2 $ 77.2 Tax benefit 18.8 18.9 16.2
Supplemental Cash Flow Information	For the years ended December 31, we paid the following: (millions) 2020 2019 2018 Income taxes $ 1,446.3 $ 954.3 $ 702.6 Interest 206.0 184.9 154.0 Operating lease liabilities 86.5 84.0 NA NA = Not applicable prior to the adoption of the new accounting standard in 2019.

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
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, consistent with our classification of how we manage, monitor, and measure the portfolio. 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, net of deferred income taxes, in our consolidated balance sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value of the securities. The changes in the net holding period gains (losses) between periods for the hybrid securities and equity securities are recorded as a component of net realized gains (losses) on securities in our consolidated statements of comprehensive income. ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair Value December 31, 2020 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 12,437.9 $ 305.8 $ (3.7) $ 0 $ 12,740.0 26.8 % State and local government obligations 3,099.4 123.1 (0.7) 0 3,221.8 6.8 Corporate debt securities 9,579.7 601.7 (0.1) 3.9 10,185.2 21.4 Residential mortgage-backed securities 503.3 7.1 (0.9) 0 509.5 1.1 Commercial mortgage-backed securities 6,042.6 142.5 (10.0) 0 6,175.1 13.0 Other asset-backed securities 3,745.0 40.1 (0.5) 0 3,784.6 7.9 Redeemable preferred stocks 181.2 3.6 (1.4) 11.3 194.7 0.4 Total fixed maturities 35,589.1 1,223.9 (17.3) 15.2 36,810.9 77.4 Short-term investments 5,218.5 0 0 0 5,218.5 11.0 Total available-for-sale securities 40,807.6 1,223.9 (17.3) 15.2 42,029.4 88.4 Equity securities: Nonredeemable preferred stocks 1,358.7 0 0 89.2 1,447.9 3.1 Common equities 1,187.3 0 0 2,865.7 4,053.0 8.5 Total equity securities 2,546.0 0 0 2,954.9 5,500.9 11.6 Total portfolio 1 $ 43,353.6 $ 1,223.9 $ (17.3) $ 2,970.1 $ 47,530.3 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair Value December 31, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,100.7 $ 194.1 $ (43.7) $ 0 $ 13,251.1 33.7 % State and local government obligations 1,686.0 30.0 (2.7) 0 1,713.3 4.4 Corporate debt securities 6,860.3 206.6 (0.5) 1.3 7,067.7 18.0 Residential mortgage-backed securities 625.0 4.5 (2.0) 0 627.5 1.6 Commercial mortgage-backed securities 5,020.7 61.5 (6.0) 0 5,076.2 12.9 Other asset-backed securities 5,164.7 16.2 (1.4) 0 5,179.5 13.2 Redeemable preferred stocks 185.7 4.1 (1.3) 6.5 195.0 0.5 Total fixed maturities 32,643.1 517.0 (57.6) 7.8 33,110.3 84.3 Short-term investments 1,798.8 0 0 0 1,798.8 4.6 Total available-for-sale securities 34,441.9 517.0 (57.6) 7.8 34,909.1 88.9 Equity securities: Nonredeemable preferred stocks 971.3 0 0 67.6 1,038.9 2.7 Common equities 1,125.5 0 0 2,180.8 3,306.3 8.4 Total equity securities 2,096.8 0 0 2,248.4 4,345.2 11.1 Total portfolio 1 $ 36,538.7 $ 517.0 $ (57.6) $ 2,256.2 $ 39,254.3 100.0 % 1 Our portfolio reflects the effect of net unsettled security transactions; at December 31, 2020, $95.5 million was included in “other liabilities,” compared to $11.9 million at December 31, 2019. The total fair value of the portfolio at December 31, 2020 and 2019 included $6.2 billion and $3.2 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. A portion of these investments were sold and proceeds used to pay our common share dividends; see Note 14 – Dividends
Hybrid Securities	Certain securities in our fixed maturities 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) 2020 2019 Fixed Maturities: State and local government obligations $ 0 $ 3.5 Corporate debt securities 188.4 91.2 Other asset-backed securities 34.8 2.6 Redeemable preferred stocks 131.4 92.1 Total hybrid securities $ 354.6 $ 189.4
Composition of Fixed Maturities by Maturity	The composition of fixed maturities by maturity at December 31, 2020, was: (millions) Cost Fair Value Less than one year $ 5,734.9 $ 5,765.4 One to five years 20,769.2 21,377.3 Five to ten years 8,939.8 9,512.2 Ten years or greater 145.2 156.0 Total $ 35,589.1 $ 36,810.9
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 Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses December 31, 2020 U.S. government obligations 9 $ 1,511.0 $ (3.7) 9 $ 1,511.0 $ (3.7) 0 $ 0 $ 0 State and local government obligations 30 208.7 (0.7) 30 208.7 (0.7) 0 0 0 Corporate debt securities 7 129.4 (0.1) 7 129.4 (0.1) 0 0 0 Residential mortgage-backed securities 21 44.4 (0.9) 0 0 0 21 44.4 (0.9) Commercial mortgage-backed securities 43 893.3 (10.0) 9 93.6 (0.3) 34 799.7 (9.7) Other asset-backed securities 22 183.7 (0.5) 9 74.4 (0.1) 13 109.3 (0.4) Redeemable preferred stocks 1 11.0 (1.4) 0 0 0 1 11.0 (1.4) Total fixed maturities 133 $ 2,981.5 $ (17.3) 64 $ 2,017.1 $ (4.9) 69 $ 964.4 $ (12.4) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized December 31, 2019 U.S. government obligations 23 $ 5,152.4 $ (43.7) 19 $ 5,057.2 $ (43.6) 4 $ 95.2 $ (0.1) State and local government obligations 67 314.3 (2.7) 52 287.5 (2.6) 15 26.8 (0.1) Corporate debt securities 16 247.6 (0.5) 12 191.4 (0.5) 4 56.2 0 Residential mortgage-backed securities 41 292.8 (2.0) 12 163.7 (0.9) 29 129.1 (1.1) Commercial mortgage-backed securities 98 1,742.4 (6.0) 79 1,400.0 (5.3) 19 342.4 (0.7) Other asset-backed securities 61 1,000.6 (1.4) 43 938.5 (0.9) 18 62.1 (0.5) Redeemable preferred stocks 1 11.2 (1.3) 0 0 0 1 11.2 (1.3) Total fixed maturities 307 $ 8,761.3 $ (57.6) 217 $ 8,038.3 $ (53.8) 90 $ 723.0 $ (3.8)
Components of Net Realized Gains (Losses)	The components of net realized gains (losses) for the years ended December 31, were: (millions) 2020 2019 2018 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 612.5 $ 164.4 $ 6.7 State and local government obligations 102.4 6.1 9.5 Corporate and other debt securities 161.9 100.1 2.4 Residential mortgage-backed securities 0 0.2 0 Commercial mortgage-backed securities 23.7 8.1 2.0 Other asset-backed securities 0.2 0.8 0.1 Redeemable preferred stocks 0 2.2 4.5 Total available-for-sale securities 900.7 281.9 25.2 Equity securities: Nonredeemable preferred stocks 24.4 36.2 4.1 Common equities 88.6 61.7 286.6 Total equity securities 113.0 97.9 290.7 Subtotal gross realized gains on security sales 1,013.7 379.8 315.9 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (9.6) (20.4) (98.7) State and local government obligations (0.7) (0.7) (2.9) Corporate and other debt securities (6.5) (7.9) (10.4) Residential mortgage-backed securities 0 (2.3) (0.1) Commercial mortgage-backed securities (12.8) (2.2) (6.3) Other asset-backed securities 0 (0.1) (1.1) Redeemable preferred stocks 0 (0.4) (0.1) Total available-for-sale securities (29.6) (34.0) (119.6) Equity securities: Nonredeemable preferred stocks (8.7) (3.2) (3.9) Common equities (60.7) (8.0) (21.7) Total equity securities (69.4) (11.2) (25.6) Subtotal gross realized losses on security sales (99.0) (45.2) (145.2) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 602.9 144.0 (92.0) State and local government obligations 101.7 5.4 6.6 Corporate and other debt securities 155.4 92.2 (8.0) Residential mortgage-backed securities 0 (2.1) (0.1) Commercial mortgage-backed securities 10.9 5.9 (4.3) Other asset-backed securities 0.2 0.7 (1.0) Redeemable preferred stocks 0 1.8 4.4 Total available-for-sale securities 871.1 247.9 (94.4) Equity securities: Nonredeemable preferred stocks 15.7 33.0 0.2 Common equities 27.9 53.7 264.9 Total equity securities 43.6 86.7 265.1 Subtotal net realized gains (losses) on security sales 914.7 334.6 170.7 Net holding period gains (losses) Hybrid securities 7.4 18.0 (10.4) Equity securities 706.5 739.9 (497.5) Derivatives 1.4 0 0 Subtotal net holding period gains (losses) 715.3 757.9 (507.9) Other-than-temporary impairment losses Other asset impairment 0 (63.3) (68.3) Subtotal other-than-temporary impairment losses 0 (63.3) (68.3) Total net realized gains (losses) on securities $ 1,630.0 $ 1,029.2 $ (405.5)
Components of Equity Realized Gains (Losses)	The following table reflects our holding period realized gains (losses) on equity securities recognized for the respective years ended December 31, for equity securities held at the respective year end: (millions) 2020 2019 2018 Total net gains (losses) recognized during the period on equity securities $ 750.1 $ 826.6 $ (232.4) Less: Net gains (losses) recognized on equity securities sold during the period 43.6 86.7 265.1 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 706.5 $ 739.9 $ (497.5)
Components of Net Investment Income	The components of net investment income for the years ended December 31, were: (millions) 2020 2019 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 166.3 $ 268.6 $ 196.8 State and local government obligations 62.7 36.5 37.7 Corporate debt securities 284.0 268.9 217.9 Residential mortgage-backed securities 11.8 21.6 27.6 Commercial mortgage-backed securities 152.9 150.1 93.9 Other asset-backed securities 96.7 117.3 75.7 Redeemable preferred stocks 14.9 19.0 12.3 Total fixed maturities 789.3 882.0 661.9 Short-term investments 29.0 41.7 52.9 Total available-for-sale securities 818.3 923.7 714.8 Equity securities: Nonredeemable preferred stocks 60.6 61.8 45.9 Common equities 57.7 56.5 59.8 Total equity securities 118.3 118.3 105.7 Investment income 936.6 1,042.0 820.5 Investment expenses (20.0) (24.6) (24.3) Net investment income $ 916.6 $ 1,017.4 $ 796.2

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 Fixed maturities: U.S. government obligations $ 12,740.0 $ 0 $ 0 $ 12,740.0 $ 12,437.9 State and local government obligations 0 3,221.8 0 3,221.8 3,099.4 Corporate debt securities 0 10,185.2 0 10,185.2 9,579.7 Subtotal 12,740.0 13,407.0 0 26,147.0 25,117.0 Asset-backed securities: Residential mortgage-backed 0 509.5 0 509.5 503.3 Commercial mortgage-backed 0 6,175.1 0 6,175.1 6,042.6 Other asset-backed 0 3,784.6 0 3,784.6 3,745.0 Subtotal asset-backed securities 0 10,469.2 0 10,469.2 10,290.9 Redeemable preferred stocks: Financials 0 51.6 0 51.6 51.1 Utilities 0 11.7 0 11.7 10.0 Industrials 10.8 120.6 0 131.4 120.1 Subtotal redeemable preferred stocks 10.8 183.9 0 194.7 181.2 Total fixed maturities 12,750.8 24,060.1 0 36,810.9 35,589.1 Short-term investments 4,704.9 513.6 0 5,218.5 5,218.5 Total available-for-sale securities 17,455.7 24,573.7 0 42,029.4 40,807.6 Equity securities: Nonredeemable preferred stocks: Financials 117.7 1,212.3 35.0 1,365.0 1,278.6 Utilities 0 41.9 0 41.9 40.0 Industrials 0 24.3 16.7 41.0 40.1 Subtotal nonredeemable preferred stocks 117.7 1,278.5 51.7 1,447.9 1,358.7 Common equities: Common stocks 4,049.9 0 0 4,049.9 1,184.2 Other risk investments 0 0 3.1 3.1 3.1 Subtotal common equities 4,049.9 0 3.1 4,053.0 1,187.3 Total equity securities 4,167.6 1,278.5 54.8 5,500.9 2,546.0 Total portfolio $ 21,623.3 $ 25,852.2 $ 54.8 $ 47,530.3 $ 43,353.6 Debt $ 0 $ 6,793.5 $ 0 $ 6,793.5 $ 5,396.1 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2019 Fixed maturities: U.S. government obligations $ 13,251.1 $ 0 $ 0 $ 13,251.1 $ 13,100.7 State and local government obligations 0 1,713.3 0 1,713.3 1,686.0 Corporate debt securities 0 7,067.7 0 7,067.7 6,860.3 Subtotal 13,251.1 8,781.0 0 22,032.1 21,647.0 Asset-backed securities: Residential mortgage-backed 0 627.5 0 627.5 625.0 Commercial mortgage-backed 0 5,076.2 0 5,076.2 5,020.7 Other asset-backed 0 5,179.5 0 5,179.5 5,164.7 Subtotal asset-backed securities 0 10,883.2 0 10,883.2 10,810.4 Redeemable preferred stocks: Financials 0 51.7 0 51.7 51.5 Utilities 0 11.1 0 11.1 10.0 Industrials 11.1 121.1 0 132.2 124.2 Subtotal redeemable preferred stocks 11.1 183.9 0 195.0 185.7 Total fixed maturities 13,262.2 19,848.1 0 33,110.3 32,643.1 Short-term investments 1,797.4 1.4 0 1,798.8 1,798.8 Total fixed maturities and short-term 15,059.6 19,849.5 0 34,909.1 34,441.9 Equity securities: Nonredeemable preferred stocks: Financials 77.4 850.7 27.1 955.2 891.3 Utilities 0 42.3 0 42.3 39.9 Industrials 0 25.4 16.0 41.4 40.1 Subtotal nonredeemable preferred stocks 77.4 918.4 43.1 1,038.9 971.3 Common equities: Common stocks 3,306.0 0 0 3,306.0 1,125.2 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,306.0 0 0.3 3,306.3 1,125.5 Total equity securities 3,383.4 918.4 43.4 4,345.2 2,096.8 Total available-for-sale portfolio $ 18,443.0 $ 20,767.9 $ 43.4 $ 39,254.3 $ 36,538.7 Debt $ 0 $ 5,119.6 $ 0 $ 5,119.6 $ 4,407.1
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, 2020 and 2019: Level 3 Fair Value (millions) Fair Value at Dec. 31, 2019 Calls/ Purchases Sales Net Realized Change in Net Transfers In (Out) Fair Value at Dec. 31, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ (27.1) $ 35.0 $ 0 $ 0 $ 0 $ 0 $ 35.0 Industrials 16.0 0 0 0 0 0.7 0 16.7 Common equities: Other risk investments 0.3 0 2.8 0 0 0 0 3.1 Total Level 3 securities $ 43.4 $ (27.1) $ 37.8 $ 0 $ 0 $ 0.7 $ 0 $ 54.8 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2018 Calls/ Purchases Sales Net Realized Change in Net Fair Value at Dec. 31, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 10.0 0 0 1.0 0 16.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 30.4 $ 0 $ 12.0 $ 0 $ 0 $ 1.0 $ 0 $ 43.4
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, 2020 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 25.0 Internal price Unadjusted purchase price per share 3.7 Financials 2 10.0 Internal price Unadjusted purchase price per share 16.9 Industrials 6.9 Pricing firm Market Approach (Guideline Public Company Method) 5.4 Industrials 9.8 Pricing firm Market Approach (Guideline Public Company Method) 4.8 Subtotal Level 3 securities 51.7 Pricing exemption securities 3.1 Total Level 3 securities $ 54.8 1 This security was purchased in May 2020. 2 This security was purchased in November 2020. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 Pricing firm Recent transaction price per share 9.0 Industrials 6.0 Pricing firm Performance-based transaction price adjustment per share 4.8 Industrials 1 10.0 Internal price Unadjusted purchase price per share 4.9 Subtotal Level 3 securities 43.1 Pricing exemption securities 0.3 Total Level 3 securities $ 43.4

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Table	Debt at December 31, consisted of: 2020 2019 (millions) Carrying Fair Carrying Fair 3.75% Senior Notes due 2021 (issued: $500.0, August 2011) $ 499.8 $ 510.9 $ 499.4 $ 515.6 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) 497.3 541.1 496.9 501.5 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 296.9 409.4 296.6 392.5 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 545.5 660.4 545.0 614.3 3.20% Senior Notes due 2030 (issued: $500.0, March 2020) 496.1 575.5 0 0 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 396.0 582.0 395.7 552.6 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.7 459.7 346.7 417.0 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.5 481.0 395.4 434.2 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 841.7 1,113.1 841.6 986.1 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 590.0 806.7 589.8 705.8 3.95% Senior Notes due 2050 (issued: $500.0, March 2020) 490.6 653.7 0 0 Total $ 5,396.1 $ 6,793.5 $ 4,407.1 $ 5,119.6
Aggregate Principal Payments on Debt Outstanding	Aggregate required principal payments on debt outstanding at December 31, 2020, were as follows: (millions) Year Payments 2021 $ 500 2022 0 2023 0 2024 0 2025 0 Thereafter 4,950 Total $ 5,450
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, 2020, on a pretax basis: (millions) Unrealized Unamortized 3.75% Senior Notes $ (5.1) $ (0.4) 6 5/8% Senior Notes (4.2) (2.2) 6.25% Senior Notes 5.1 3.2 4.35% Senior Notes (1.6) (1.4) 3.70% Senior Notes (12.9) (11.4) 4.125% Senior Notes (8.0) (7.5)

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Components of Income Tax Provision	The components of our income tax provision for the years ended December 31, were as follows: (millions) 2020 2019 2018 Current tax provision Federal $ 1,395.7 $ 1,133.2 $ 673.1 State 35.6 27.3 21.5 Deferred tax expense (benefit) Federal 35.8 16.8 (145.9) State 1.5 3.0 (6.1) Total income tax provision $ 1,468.6 $ 1,180.3 $ 542.6
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 accompanying consolidated statements of comprehensive income differed from the statutory rate for the years ended December 31, as follows: (millions) 2020 2019 2018 Income before income taxes $ 7,173.2 $ 5,160.3 $ 3,163.6 Tax at statutory federal rate $ 1,506.4 21 % $ 1,083.7 21 % $ 664.4 21 % Tax effect of: Reversal of prior year tax credits 0 0 163.2 3 0 0 Tax credits 1 (5.4) 0 (43.9) (1) (76.3) (2) Stock-based compensation (22.7) (1) (25.9) (1) (25.1) (1) Tax-deductible dividends (25.1) (1) (14.6) 0 (14.6) 0 Tax-preferenced investment income (15.2) 0 (14.0) 0 (15.6) (1) Nondeductible compensation expense 6.4 0 8.1 0 (0.2) 0 State income taxes, net of federal taxes 29.3 1 24.0 1 12.2 0 Other items, net (5.1) 0 (0.3) 0 (2.2) 0 Total income tax provision $ 1,468.6 20 % $ 1,180.3 23 % $ 542.6 17 % 1 Includes $0, $38.1 million, and $71.0 million for 2020, 2019, and 2018, respectively, of benefits on investments in federal renewable energy tax credit funds.
Components of Net Deferred Tax Assets	The following table shows the components of the net deferred tax asset (liability) at December 31, 2020 and 2019, respectively. (millions) 2020 2019 Federal deferred income tax assets: Unearned premiums reserve $ 552.5 $ 498.2 Non-deductible accruals 238.2 181.8 Loss and loss adjustment expense reserves 170.0 153.3 Operating lease liabilities 37.4 42.3 Investment basis difference 18.6 27.4 Hedges on forecasted transactions 4.1 4.4 Other 25.8 15.3 Federal deferred income tax liabilities: Net holding period gains on equity securities (620.5) (472.2) Deferred acquisition costs (259.8) (221.9) Net unrealized gains on fixed-maturity securities (253.4) (96.5) Property and equipment (105.6) (108.6) Loss and loss adjustment expense reserve transition adjustment (39.3) (47.2) Operating lease assets (37.4) (42.3) Intangible assets (27.6) (38.9) Prepaid expenses (5.5) (4.8) Other (7.5) (8.3) Net federal deferred income taxes (310.0) (118.0) State deferred income tax assets 1 11.9 15.2 State deferred income tax liabilities 1 (4.0) (1.2) Total $ (302.1) $ (104.0) 1 Recorded in “other assets” and “accounts payable, accrued expenses, and other liabilities,” respectively, on the consolidated balance sheets; the prior year amounts were reclassified into these line items from “net federal deferred income taxes” to conform to the current year presentation.

Loss And Loss Adjustment Expe_2

Loss And Loss Adjustment Expense Reserves (Tables)	12 Months Ended
	Dec. 31, 2020
Insurance [Abstract]
Activity in Loss and Loss Adjustment Expense Reserves	Activity in the loss and LAE reserves is summarized as follows: (millions) 2020 2019 2018 Balance at January 1 $ 18,105.4 $ 15,400.8 $ 13,086.9 Less reinsurance recoverables on unpaid losses 3,212.2 2,572.7 2,170.1 Net balance at January 1 14,893.2 12,828.1 10,916.8 Incurred related to: Current year 24,926.5 25,238.2 21,632.5 Prior years 195.3 232.3 88.5 Total incurred 25,121.8 25,470.5 21,721.0 Paid related to: Current year 15,584.4 16,105.0 13,792.1 Prior years 7,963.0 7,300.4 6,017.6 Total paid 23,547.4 23,405.4 19,809.7 Net balance at December 31 16,467.6 14,893.2 12,828.1 Plus reinsurance recoverables on unpaid losses 3,798.2 3,212.2 2,572.7 Balance at December 31 $ 20,265.8 $ 18,105.4 $ 15,400.8
Short-duration Insurance Contracts, Claims Development	Only 2020 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, 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 4,082.9 $ 4,130.0 $ 4,152.0 $ 4,177.3 $ 4,137.8 $ 0 740,535 2017 4,474.8 4,485.8 4,511.1 4,546.4 72.3 779,303 2018 5,141.8 5,182.1 5,192.7 100.0 856,108 2019 5,885.0 5,886.9 264.3 913,063 2020 5,433.8 926.8 750,654 Total $ 25,197.6 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 1,941.6 $ 3,231.5 $ 3,723.1 $ 3,969.5 $ 4,062.5 2017 2,074.0 3,478.5 4,048.5 4,285.5 2018 2,378.0 4,028.7 4,635.0 2019 2,715.2 4,533.2 2020 2,383.0 Total $ 19,899.2 All outstanding liabilities before 2016, net of reinsurance 1 80.3 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 5,378.7 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,423.4 $ 2,398.9 $ 2,401.8 $ 2,400.1 $ 2,402.8 $ 0 1,399,156 2017 2,635.5 2,638.5 2,643.5 2,640.6 (4.0) 1,514,873 2018 2,819.0 2,822.6 2,821.7 (3.4) 1,694,997 2019 3,277.9 3,254.7 (13.4) 1,876,942 2020 3,328.5 (183.4) 1,768,482 Total $ 14,448.3 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,391.0 $ 2,406.9 $ 2,402.1 $ 2,402.2 $ 2,401.8 2017 2,599.8 2,643.2 2,640.9 2,640.8 2018 2,769.1 2,827.4 2,819.9 2019 3,242.5 3,259.2 2020 3,250.1 Total $ 14,371.8 All outstanding liabilities before 2016, net of reinsurance 1 5.9 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 82.4 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 3,819.0 $ 3,843.9 $ 3,871.2 $ 3,897.8 $ 3,866.1 $ 0 735,791 2017 4,209.5 4,209.9 4,229.3 4,254.4 61.3 772,986 2018 4,904.8 4,980.9 5,003.2 88.0 870,978 2019 5,756.5 5,811.7 243.5 954,209 2020 5,356.9 901.1 786,809 Total $ 24,292.3 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 1,780.6 $ 2,991.1 $ 3,476.9 $ 3,714.6 $ 3,799.1 2017 1,912.6 3,255.2 3,808.3 4,035.6 2018 2,235.1 3,863.5 4,481.7 2019 2,630.3 4,452.5 2020 2,301.3 Total $ 19,070.2 All outstanding liabilities before 2016, net of reinsurance 1 55.2 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 5,277.3 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,521.0 $ 2,475.4 $ 2,477.7 $ 2,475.6 $ 2,478.5 $ 0 1,676,396 2017 2,750.6 2,743.7 2,749.0 2,745.6 (5.1) 1,791,582 2018 3,202.3 3,181.9 3,182.0 (5.1) 2,069,684 2019 3,787.9 3,737.8 (22.7) 2,269,857 2020 3,775.6 (264.5) 2,137,810 Total $ 15,919.5 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 2,505.0 $ 2,485.8 $ 2,479.3 $ 2,478.5 $ 2,477.8 2017 2,742.1 2,753.5 2,748.4 2,747.6 2018 3,170.0 3,193.8 3,183.0 2019 3,782.6 3,751.3 2020 3,720.0 Total $ 15,879.7 All outstanding liabilities before 2016, net of reinsurance 1 0.8 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 40.6 1 Required supplementary information (unaudited) Commercial Lines - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 1,185.8 $ 1,204.8 $ 1,231.1 $ 1,238.9 $ 1,224.9 $ 0 92,688 2017 1,374.1 1,366.6 1,393.3 1,374.6 18.3 97,448 2018 1,700.8 1,736.5 1,789.7 41.5 111,767 2019 2,103.1 2,175.6 116.3 126,959 2020 2,161.8 369.8 105,900 Total $ 8,726.6 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 298.6 $ 639.9 $ 886.0 $ 1,073.3 $ 1,153.4 2017 325.8 712.9 1,027.3 1,183.6 2018 382.7 913.4 1,290.5 2019 455.4 1,120.1 2020 427.6 Total $ 5,175.2 All outstanding liabilities before 2016, net of reinsurance 1 34.9 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 3,586.3 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, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 379.6 $ 379.8 $ 378.2 $ 377.8 $ 378.1 $ 0 74,199 2017 415.4 412.1 411.0 409.9 (0.9) 77,170 2018 475.0 478.2 476.6 (1.4) 82,134 2019 577.8 574.2 (3.3) 88,897 2020 575.2 (14.1) 87,333 Total $ 2,414.0 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 336.7 $ 376.9 $ 376.8 $ 377.5 $ 377.6 2017 369.0 409.4 409.2 409.4 2018 426.0 475.1 475.3 2019 516.9 571.5 2020 497.9 Total $ 2,331.7 All outstanding liabilities before 2016, net of reinsurance 1 0.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 82.7 1 Required supplementary information (unaudited) Property Business ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2020 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 568.6 $ 541.2 $ 537.1 $ 536.5 $ 535.5 $ 2.4 53,693 2017 672.8 680.9 683.4 681.3 1.3 74,140 2018 839.0 845.2 845.4 18.2 63,722 2019 971.7 965.2 11.7 72,396 2020 1,223.5 252.4 80,820 Total $ 4,250.9 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2016 1 2017 1 2018 1 2019 1 2020 2016 $ 415.2 $ 498.2 $ 516.9 $ 526.4 $ 530.8 2017 506.7 647.1 670.1 675.0 2018 595.9 781.2 812.6 2019 708.0 930.4 2020 832.5 Total $ 3,781.3 All outstanding liabilities before 2016, net of reinsurance 1 5.1 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 474.7 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) 2020 2019 Net outstanding liabilities Personal Lines Agency, Liability $ 5,378.7 $ 5,117.4 Agency, Physical Damage 82.4 32.4 Direct, Liability 5,277.3 4,936.8 Direct, Physical Damage 40.6 (7.7) Commercial Lines Liability 3,586.3 3,080.8 Physical Damage 82.7 66.6 Property 474.7 357.2 Other business 66.7 30.8 Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 14,989.4 13,614.3 Reinsurance recoverable on unpaid claims Personal Lines Agency, Liability 959.6 930.7 Agency, Physical Damage 0 0 Direct, Liability 1,475.8 1,314.1 Direct, Physical Damage 0 0 Commercial Lines Liability 758.5 482.6 Physical Damage (0.3) 0.5 Property 226.9 184.1 Other business 358.6 288.1 Total reinsurance recoverable on unpaid claims 3,779.1 3,200.1 Unallocated claims adjustment expense related to: Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 1,478.2 1,278.9 Reinsurance recoverable on unpaid claims 19.1 12.1 Total gross liability for unpaid claims and claim adjustment expense $ 20,265.8 $ 18,105.4
Short-duration Insurance Contracts, Schedule of Historical Claims Duration	The following table shows the average historical claims duration as of December 31, 2020: (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 45.6% 31.2% 12.0% 5.6% 2.2% Agency, Physical Damage 98.6 1.2 (0.2) 0 0 Direct, Liability 44.7 31.7 12.6 5.7 2.2 Direct, Physical Damage 100.0 (0.1) (0.3) 0 0 Commercial Lines Liability 21.7 29.3 21.4 13.2 6.5 Physical Damage 88.9 10.0 0 0.1 0 Property 71.9 20.8 3.5 1.2 0.8

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2020
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: 2020 2019 2018 (millions) Written Earned Written Earned Written Earned Direct premiums $ 41,736.4 $ 40,687.7 $ 39,222.0 $ 37,519.7 $ 33,753.1 $ 31,970.2 Ceded premiums: Regulated (648.2) (686.5) (711.1) (670.8) (596.4) (557.5) Non-Regulated (519.5) (739.6) (933.0) (656.5) (546.8) (479.4) Total ceded premiums (1,167.7) (1,426.1) (1,644.1) (1,327.3) (1,143.2) (1,036.9) Net premiums $ 40,568.7 $ 39,261.6 $ 37,577.9 $ 36,192.4 $ 32,609.9 $ 30,933.3
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) 2020 2019 2020 2019 Regulated: MCCA $ 2,428.8 60 % $ 2,247.1 67 % $ 33.3 9 % $ 71.8 12 % CAIP 397.8 10 332.4 10 84.7 23 93.8 15 NCRF 88.6 2 84.4 2 41.9 11 33.8 5 FHCF 54.8 1 86.0 3 0 0 0 0 NFIP 24.2 1 11.6 0 60.7 17 58.7 9 Other 3.2 0 3.1 0 1.3 0 1.0 0 Total Regulated 2,997.4 74 2,764.6 82 221.9 60 259.1 41 Non-Regulated: Commercial Lines 753.2 19 459.5 14 134.5 37 352.9 56 Property 261.7 7 146.8 4 11.7 3 14.5 3 Other 7.1 0 8.0 0 0 0 0 0 Total Non-Regulated 1,022.0 26 614.3 18 146.2 40 367.4 59 Total $ 4,019.4 100 % $ 3,378.9 100 % $ 368.1 100 % $ 626.5 100 %

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2020
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: 2020 2019 2018 (millions) Pretax After Tax Pretax After Tax Pretax After Tax Non-equity incentive plans – cash $ 688.8 $ 544.2 $ 598.4 $ 472.7 $ 539.5 $ 426.2 Equity incentive plans: Equity awards 89.4 70.6 90.1 71.2 76.2 60.2 Liability awards 1 0 0 0.1 0.1 1.0 0.8
Assets Held in Deferral Plan Irrevocable Grantor Trust Account	The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31: (millions) 2020 2019 Progressive common shares 1 $ 134.2 $ 121.6 Other investment funds 2 167.2 151.2 Total $ 301.4 $ 272.8 1 Included 2.8 million and 3.2 million common shares as of December 31, 2020 and 2019, respectively, to be distributed in common shares, and are reported at grant date fair value. 2 Amount is included in other assets on the consolidated balance sheets.
Employee
Summary of Restricted Stock Activity	A summary of all employee restricted equity award activity during the years ended December 31, follows: 2020 2019 2018 Restricted Equity Awards Number of Shares 1 Weighted Number of Shares 1 Weighted Number of Shares 1 Weighted Beginning of year 3,879,077 $ 48.28 4,856,356 $ 38.56 5,858,848 $ 30.47 Add (deduct): Granted 2 1,629,534 55.28 1,835,145 49.61 1,876,109 45.55 Vested (1,861,442) 36.19 (2,691,337) 31.85 (2,811,070) 26.41 Forfeited (76,898) 52.79 (121,087) 43.98 (67,531) 36.10 End of year 3,4 3,570,271 $ 57.68 3,879,077 $ 48.28 4,856,356 $ 38.56 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 2020, 2019, and 2018, the number of units “granted” shown in the table above includes 144,389, 210,159, and 144,688 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, 2020, the number of shares included 707,293 performance-based units at their target amounts. We expect 1,658,308 units to vest based upon our current estimates of the likelihood of achieving the pre-determined performance goals applicable to each award. 4 At December 31, 2020, the total unrecognized compensation cost related to unvested equity awards was $102.1 million, which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the consolidated statements of comprehensive income over the weighted average vesting period of 2.3 years.
Director
Summary of Restricted Stock Activity	A summary of all directors’ restricted stock activity during the years ended December 31, follows: 2020 2019 2018 Restricted Stock Number of Weighted Number of Weighted Number of Weighted Beginning of year 38,451 $ 73.43 41,706 $ 62.23 53,284 $ 40.54 Add (deduct): Granted 39,403 74.77 38,451 73.43 41,706 62.23 Vested (38,451) 73.43 (41,706) 62.23 (53,284) 40.54 End of year 1 39,403 $ 74.77 38,451 $ 73.43 41,706 $ 62.23 1 At December 31, 2020, 2019, and 2018, the remaining unrecognized compensation cost related to restricted stock awards was $0.9 million, $0.8 million, and $0.9 million, respectively.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2020	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: 2020 2019 2018 (millions) Revenues Pretax Revenues Pretax Revenues Pretax Personal Lines Agency $ 15,789.5 $ 2,236.5 $ 14,904.1 $ 1,673.2 $ 13,017.2 $ 1,435.7 Direct 16,830.6 2,076.5 15,305.9 1,181.4 13,017.5 1,088.5 Total Personal Lines 1 32,620.1 4,313.0 30,210.0 2,854.6 26,034.7 2,524.2 Commercial Lines 4,875.8 634.8 4,427.6 458.8 3,610.9 478.6 Property 2 1,765.7 (125.1) 1,554.8 (26.1) 1,287.7 (88.7) Other indemnity 0 0 0 0 0 0.9 Total underwriting operations 39,261.6 4,822.7 36,192.4 3,287.3 30,933.3 2,915.0 Fees and other revenues 3 603.5 NA 563.7 NA 472.2 NA Service businesses 226.4 20.9 195.0 16.1 158.5 24.4 Investments 4 2,566.6 2,546.6 2,071.2 2,046.6 415.0 390.7 Interest expense NA (217.0) NA (189.7) NA (166.5) Consolidated total $ 42,658.1 $ 7,173.2 $ 39,022.3 $ 5,160.3 $ 31,979.0 $ 3,163.6 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned in 2020, 2019, and 2018; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 During 2020, 2019, and 2018, pretax profit (loss) includes $56.9 million, $66.3 million, and $72.0 million, respectively, of amortization expense predominately associated with intangible assets. See Note 16 - Goodwill and Intangible Assets for further discussion. 3 Pretax profit (loss) for fees and other revenues is allocated to operating segments. 4 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit 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: 2020 2019 2018 Underwriting Combined Underwriting Combined Underwriting Combined Personal Lines Agency 14.2 % 85.8 11.2 % 88.8 11.0 % 89.0 Direct 12.3 87.7 7.7 92.3 8.4 91.6 Total Personal Lines 13.2 86.8 9.5 90.5 9.7 90.3 Commercial Lines 13.0 87.0 10.4 89.6 13.3 86.7 Property 1 (7.1) 107.1 (1.7) 101.7 (6.9) 106.9 Total underwriting operations 12.3 87.7 9.1 90.9 9.4 90.6 1 Included in 2020, 2019, and 2018, are 3.2 points, 4.3 points, and 5.6 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2020
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 (millions) Pretax total Total tax After tax total Total net Net unrealized (Income) loss attributable to NCI Balance at December 31, 2019 $ 435.7 $ (94.0) $ 341.7 $ 360.8 $ (16.4) $ (2.7) Reclassification of disproportionate amounts 1 3.4 (0.7) 2.7 0 0 2.7 Adjusted balance at December 31, 2019 439.1 (94.7) 344.4 360.8 (16.4) 0 Other comprehensive income (loss) before reclassifications: Investment securities 1,557.2 (306.1) 1,251.1 1,251.1 0 0 Loss attributable to noncontrolling interest (NCI) 0 0 0 0 0 0 Total other comprehensive income (loss) before reclassifications 1,557.2 (306.1) 1,251.1 1,251.1 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 810.0 (145.4) 664.6 664.6 0 0 Interest expense (1.1) 0.3 (0.8) 0 (0.8) 0 Total reclassification adjustment for amounts realized in net income 808.9 (145.1) 663.8 664.6 (0.8) 0 Total other comprehensive income (loss) 748.3 (161.0) 587.3 586.5 0.8 0 Balance at December 31, 2020 $ 1,187.4 $ (255.7) $ 931.7 $ 947.3 $ (15.6) $ 0 1 Adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the purchase transaction (See Note 15 - Redeemable Noncontrolling Interest for additional information). Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized (Income) loss attributable to NCI Balance at December 31, 2018 $ (153.0) $ 32.1 $ (120.9) $ (105.6) $ (17.2) $ 1.9 Other comprehensive income (loss) before reclassifications: Investment securities 825.8 (174.9) 650.9 650.9 0 0 Loss attributable to noncontrolling interest (NCI) (5.9) 1.3 (4.6) 0 0 (4.6) Total other comprehensive income (loss) before reclassifications 819.9 (173.6) 646.3 650.9 0 (4.6) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 232.2 (47.7) 184.5 184.5 0 0 Interest expense (1.0) 0.2 (0.8) 0 (0.8) 0 Total reclassification adjustment for amounts realized in net income 231.2 (47.5) 183.7 184.5 (0.8) 0 Total other comprehensive income (loss) 588.7 (126.1) 462.6 466.4 0.8 (4.6) Balance at December 31, 2019 $ 435.7 $ (94.0) $ 341.7 $ 360.8 $ (16.4) $ (2.7) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net unrealized (Income) loss attributable to NCI Balance at December 31, 2017 $ 1,977.8 $ (695.6) $ 1,282.2 $ 1,295.0 $ (14.8) $ 2.0 Cumulative effect adjustment 1 (2,006.0) 705.8 (1,300.2) (1,300.2) 0 0 Reclassification of disproportionate amounts 2 (4.3) (3.4) (7.7) (1.1) (3.2) (3.4) Adjusted balance at December 31, 2017 (32.5) 6.8 (25.7) (6.3) (18.0) (1.4) Other comprehensive income (loss) before reclassifications: Investment securities (224.1) 47.0 (177.1) (177.1) 0 0 Loss attributable to noncontrolling interest (NCI) 4.3 (1.0) 3.3 0 0 3.3 Total other comprehensive income (loss) before reclassifications (219.8) 46.0 (173.8) (177.1) 0 3.3 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (98.3) 20.5 (77.8) (77.8) 0 0 Interest expense (1.0) 0.2 (0.8) 0 (0.8) 0 Total reclassification adjustment for amounts realized in net income (99.3) 20.7 (78.6) (77.8) (0.8) 0 Total other comprehensive income (loss) (120.5) 25.3 (95.2) (99.3) 0.8 3.3 Total at December 31, 2018 $ (153.0) $ 32.1 $ (120.9) $ (105.6) $ (17.2) $ 1.9 1 Reflects the fair value changes on equity securities as of December 31, 2017, which are reported as realized gains (losses) under the new accounting guidance. See Note 1 - Reporting and Accounting Policies for additional information. 2 Reflects the effect of the change in U.S. federal tax rate on our available-for-sale fixed-maturity securities and our hedges on forecasted transactions as of December 31, 2017 (see Note 1 - Reporting and Accounting Policies for additional information) and the adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the “put” transaction (see Note 15 - Redeemable Noncontrolling Interest for additional information).

(Tables)

(Tables)	12 Months Ended
	Dec. 31, 2020
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) 2020 2019 Operating lease assets $ 165.5 $ 188.2 Operating lease liabilities $ 179.0 $ 201.5 Weighted-average remaining term 3.0 years 3.3 years Weighted-average discount rate 2.5 % 3.0 %
Minimum Commitments under Noncancelable Operating Lease Agreements	At December 31, 2020, the following table shows our operating lease liabilities, on an undiscounted basis for the periods indicated: (millions) Commitments 2021 $ 78.9 2022 48.7 2023 29.1 2024 18.4 2025 9.8 Thereafter 0.5 Total 185.4 Interest (6.4) Present value of lease liabilities $ 179.0
Lease, Cost	The operating lease expense for the years ended December 31, was as follows: (millions) Expense 2020 $ 95.4 2019 102.0 2018 77.3

Dividends (Tables)

Dividends (Tables)	12 Months Ended
	Dec. 31, 2020
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 1 Common - Annual Variable Dividends: December 2020 January 2021 $ 4.50 $ 2,635.9 December 2019 January 2020 2.25 1,316.9 December 2018 February 2019 2.5140 1,467.9 December 2017 February 2018 1.1247 655.1 Common - Quarterly Dividends: December 2020 January 2021 0.10 58.6 August 2020 October 2020 0.10 58.6 May 2020 July 2020 0.10 58.5 February 2020 April 2020 0.10 58.5 December 2019 January 2020 0.10 58.5 August 2019 October 2019 0.10 58.5 May 2019 July 2019 0.10 58.4 February 2019 April 2019 0.10 58.4 Preferred Dividends: December 2020 March 2021 26.875 13.4 August 2020 September 2020 26.875 13.4 February 2020 March 2020 26.875 13.4 August 2019 September 2019 26.875 13.4 February 2019 March 2019 26.875 13.4 August 2018 September 2018 27.024 13.5 1 The accrual is based on an estimate of shares outstanding as of the record date and the common share accrual is recorded as “dividends payable on common shares” on the Consolidated Balance Sheets; the prior year common share amount was reclassified into this line item from “accounts payable, accrued expenses, and other liabilities” to conform to the current year presentation.

Redeemable Noncontrolling Int_2

Redeemable Noncontrolling Interest (Tables)	12 Months Ended
	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interest	The changes in the components of redeemable NCI during the years ended December 31, were: (millions) 2020 2019 2018 Balance, beginning of year $ 225.6 $ 214.5 $ 503.7 Net income attributable to NCI 0 9.7 5.7 Other comprehensive income (loss) attributable to NCI 1 0 4.6 (3.3) Exercise of stock options 16.0 7.7 9.4 Purchase/change of ARX minority shares (241.6) (11.2) (298.2) Change in redemption value 0 0.3 (2.8) Balance, end of year $ 0 $ 225.6 $ 214.5 1 Amount represents the other comprehensive income (loss) attributable to NCI, as reflected on the consolidated statements of comprehensive income; changes in accumulated other comprehensive income (loss) attributable to NCI due to a change in the minority ownership percentage does not impact the amount of redeemable NCI .

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Net Carrying Amount of Other Intangible Assets	The following table is a summary of the net carrying amount of other intangible assets as of December 31: (millions) 2020 2019 Intangible assets subject to amortization $ 159.0 $ 215.9 Indefinite-lived intangible assets 1 12.4 12.4 Total $ 171.4 $ 228.3 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for both years presented.
Intangible Assets Subject to Amortization	Intangible assets subject to amortization for the years ended December 31, consisted of the following: (millions) 2020 2019 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 210.4 $ 45.8 $ 256.2 $ 173.9 $ 82.3 Agency relationships 159.2 65.4 93.8 159.2 54.0 105.2 Software rights 69.1 49.7 19.4 79.1 50.7 28.4 Trade name 0 0 0 34.8 34.8 0 Total $ 484.5 $ 325.5 $ 159.0 $ 529.3 $ 313.4 $ 215.9
Amortization on Intangible Assets	The estimated aggregate amortization on these intangible assets for each of the next five years as of December 31, 2020, follows: (millions) Year Amortization 2021 $ 56.6 2022 29.2 2023 13.5 2024 11.4 2025 11.4

SCHEDULE I - Summary Of Inves_2

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, 2020USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	$ 43,353.6
Fair Value	47,530.3
Amount At Which Shown In The Balance Sheet	47,530.3
Fixed maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	35,589.1
Fair Value	36,810.9
Amount At Which Shown In The Balance Sheet	36,810.9
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	12,437.9
Fair Value	12,740
Amount At Which Shown In The Balance Sheet	12,740
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	3,099.4
Fair Value	3,221.8
Amount At Which Shown In The Balance Sheet	3,221.8
Fixed maturities | Public Utilities, Bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	577.8
Fair Value	619.9
Amount At Which Shown In The Balance Sheet	619.9
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	9,001.9
Fair Value	9,565.3
Amount At Which Shown In The Balance Sheet	9,565.3
Fixed maturities | Asset-backed Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	10,290.9
Fair Value	10,469.2
Amount At Which Shown In The Balance Sheet	10,469.2
Fixed maturities | Redeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	181.2
Fair Value	194.7
Amount At Which Shown In The Balance Sheet	194.7
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,546
Fair Value	5,500.9
Amount At Which Shown In The Balance Sheet	5,500.9
Equity securities | Utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	73.5
Fair Value	164
Amount At Which Shown In The Balance Sheet	164
Equity securities | Financials
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	220.1
Fair Value	658.3
Amount At Which Shown In The Balance Sheet	658.3
Equity securities | Industrials
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	893.7
Fair Value	3,230.7
Amount At Which Shown In The Balance Sheet	3,230.7
Equity securities | Nonredeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,358.7
Fair Value	1,447.9
Amount At Which Shown In The Balance Sheet	1,447.9
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	5,218.5
Fair Value	5,218.5
Amount At Which Shown In The Balance Sheet	$ 5,218.5

SCHEDULE II - Condensed Finan_2

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Comprehensive Income (Parent Company) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Total revenues	$ 42,658.1	$ 39,022.3	$ 31,979
Expenses
Interest expense	217	189.7	166.5
Total expenses	35,484.9	33,862	28,815.4
Income before income taxes	7,173.2	5,160.3	3,163.6
Benefit for income taxes	(1,468.6)	(1,180.3)	(542.6)
Net income attributable to Progressive	5,704.6	3,970.3	2,615.3
Comprehensive income attributable to Progressive	6,291.9	4,432.9	2,520.1
Parent Company
Revenues
Dividends from subsidiaries	4,096.5	2,277.9	939.1
Undistributed income (loss) from subsidiaries	1,774.4	1,821.3	1,770.7
Equity in net income of subsidiaries	5,870.9	4,099.2	2,709.8
Intercompany investment income	16.5	31.1	39.4
Total revenues	5,887.4	4,130.3	2,749.2
Expenses
Interest expense	218.1	190.4	166.8
Deferred compensation	33.9	16.6	7.5
Other operating costs and expenses	7.2	5.5	5.1
Total expenses	259.2	212.5	179.4
Income before income taxes	5,628.2	3,917.8	2,569.8
Benefit for income taxes	76.4	52.5	45.5
Net income attributable to Progressive	5,704.6	3,970.3	2,615.3
Other comprehensive income (loss)	587.3	462.6	(95.2)
Comprehensive income attributable to Progressive	$ 6,291.9	$ 4,432.9	$ 2,520.1

SCHEDULE II - Condensed Finan_3

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Balance Sheets (Parent Company) (Detail) - USD ($) $ / shares in Units, $ in Millions		Dec. 31, 2020		Aug. 31, 2020	Feb. 29, 2020	Dec. 31, 2019		Aug. 31, 2019	Feb. 28, 2019	Dec. 31, 2018	Aug. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Other assets		$ 800.2				$ 783.6
Total assets		64,098.3				54,910.5
Liabilities and Shareholders' Equity
Accounts payable, accrued expenses, and other liabilities1	[1]	4,955.8				4,617
Dividends payable on common shares		2,694.5				1,375.4
Debt	[2]	5,396.1				4,407.1
Total liabilities		47,059.7				41,011.7
Redeemable noncontrolling interest (NCI)		0	[3]			225.6	[3]			$ 214.5			$ 503.7
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)		493.9				493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 212.3 and 212.9)		585.2				584.6
Paid-in capital		1,672.9				1,573.4
Retained earnings		13,354.9				10,679.6
Total accumulated other comprehensive income attributable to Progressive		931.7				341.7				(120.9)			$ 1,282.2
Total shareholders’ equity		17,038.6				13,673.2				$ 10,821.8
Total liabilities, redeemable NCI, and shareholders’ equity		$ 64,098.3				$ 54,910.5
Common Shares, par value (USD per share)		$ 1				$ 1
Common Shares, authorized (shares)		900,000,000				900,000,000
Common Shares, issued (shares)		797,500,000				797,500,000
Common Shares, treasury shares (shares)		212,300,000				212,900,000
Series B Preferred Stock
Liabilities and Shareholders' Equity
Dividends payable on common shares		$ 13.4		$ 13.4	$ 13.4			$ 13.4	$ 13.4		$ 13.5
Preferred Stock, Liquidation Preference Per Share												$ 1,000
Preferred shares, issued (in shares)												500,000
Serial Preferred Stock
Liabilities and Shareholders' Equity
Preferred shares, authorized (in shares)		20,000,000				20,000,000
Serial Preferred Stock | Series B Preferred Stock
Liabilities and Shareholders' Equity
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		500,000				500,000
Parent Company
Assets
Investment in affiliate		$ 5				$ 5
Investment in subsidiaries		18,895.9				16,186.8
Receivable from investment subsidiary		5,901.7				2,912
Intercompany receivable		473.8				678.6
Deferred Income Tax Assets, Net		86.9				70.3
Other assets		270.9				303.8
Total assets		25,634.2				20,156.5
Liabilities and Shareholders' Equity
Accounts payable, accrued expenses, and other liabilities1		505				475.2
Dividends payable on common shares		2,694.5				1,375.4
Debt		5,396.1				4,407.1
Total liabilities		8,595.6				6,257.7
Redeemable noncontrolling interest (NCI)		0				225.6
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference of $1,000 per share) (authorized, issued, and outstanding 0.5)		493.9				493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 212.3 and 212.9)		585.2				584.6
Paid-in capital		1,672.9				1,573.4
Retained earnings		13,354.9				10,679.6
Total accumulated other comprehensive income attributable to Progressive		931.7				341.7
Total shareholders’ equity		17,038.6				13,673.2
Total liabilities, redeemable NCI, and shareholders’ equity		$ 25,634.2				$ 20,156.5
Common Shares, par value (USD per share)		$ 1				$ 1
Common Shares, authorized (shares)		900,000,000				900,000,000
Common Shares, issued (shares)		797,500,000				797,500,000
Common Shares, treasury shares (shares)		212,300,000				212,900,000
Parent Company | Series B Preferred Stock
Liabilities and Shareholders' Equity
Dividends payable on common shares		$ 13.4
Parent Company | Serial Preferred Stock
Liabilities and Shareholders' Equity
Preferred shares, authorized (in shares)		20,000,000				20,000,000
Parent Company | Serial Preferred Stock | Series B Preferred Stock
Liabilities and Shareholders' Equity
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		500,000				500,000
[1]	See Note 1 – Reporting and Accounting Policies for Commitments and Contingencies and Note 12 – Litigation
[2]	Consists of both short-term and long-term debt. See Note 4 – Debt for further discussion .
[3]	See Note 15 – Redeemable Noncontrolling Interest for further discussion .

SCHEDULE II - Condensed Finan_4

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Cash Flows (Parent Company) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows From Operating Activities:
Net income attributable to Progressive	$ 5,704.6	$ 3,970.3	$ 2,615.3
Adjustments to reconcile net income attributable to Progressive to net cash provided by operating activities:
Amortization of equity-based compensation	89.4	90.2	77.2
Changes in:
Accounts payable, accrued expenses, and other liabilities	328.9	611.6	746.6
Income taxes	(23.1)	227.2	(158.7)
Other, net	(2.9)	(260.8)	(57.7)
Net cash provided by operating activities	6,905.6	6,261.6	6,284.8
Cash Flows From Investing Activities:
Net cash used in investing activities	(6,117.7)	(4,338.3)	(7,034.9)
Cash Flows From Financing Activities:
Proceeds from exercise of equity options	7.3	1.6	3.3
Net proceeds from debt issuance	986.3	0	1,134
Net proceeds from preferred stock issuance	0	0	493.9
Dividends paid to common shareholders	(1,551)	(1,643.2)	(654.9)
Dividends paid to preferred shareholders	(26.8)	(26.8)	(13.5)
Acquisition of treasury shares for restricted stock tax liabilities	(68.7)	(84.4)	(78.6)
Acquisition of treasury shares acquired in open market	(42.9)	(6.9)	(0.4)
Net cash provided by (used in) financing activities	(938.8)	(1,770.9)	549.8
Change in cash, cash equivalents, and restricted cash	(150.9)	152.4	(200.3)
Cash, cash equivalents, and restricted cash - beginning of year	227.4	75	275.3
Cash, cash equivalents, and restricted cash - end of year	76.5	227.4	75
Acquisition of additional shares of ARX Holding Corp.	(243)	(11.2)	(296.9)
Parent Company
Cash Flows From Operating Activities:
Net income attributable to Progressive	5,704.6	3,970.3	2,615.3
Adjustments to reconcile net income attributable to Progressive to net cash provided by operating activities:
Undistributed (income) loss from subsidiaries	(1,774.4)	(1,821.3)	(1,770.7)
Amortization of equity-based compensation	2.9	2.9	2.4
Changes in:
Intercompany receivable	(20.2)	(14.1)	77.5
Accounts payable, accrued expenses, and other liabilities	52	47.1	(29.6)
Income taxes	(52.2)	175.5	(14.2)
Other, net	40.4	(179.8)	47.8
Net cash provided by operating activities	3,953.1	2,180.6	928.5
Cash Flows From Investing Activities:
Additional investments in equity securities of consolidated subsidiaries	(27.1)	(152.8)	(178.3)
(Paid to) received from investment subsidiary	(2,989.7)	(253.1)	(1,192.8)
Net cash used in investing activities	(3,250)	(411.3)	(1,659)
Cash Flows From Financing Activities:
Net proceeds from debt issuance	986.3	0	1,134
Net proceeds from preferred stock issuance	0	0	493.9
Dividends paid to common shareholders	(1,551)	(1,643.2)	(654.9)
Dividends paid to preferred shareholders	(26.8)	(26.8)	(13.5)
Acquisition of treasury shares for restricted stock tax liabilities	(68.7)	(84.4)	(78.6)
Acquisition of treasury shares acquired in open market	(42.9)	(6.9)	(0.4)
Loan to ARX Holding Corp.	0	(8)	(150)
Net cash provided by (used in) financing activities	(703.1)	(1,769.3)	730.5
Change in cash, cash equivalents, and restricted cash	0	0	0
Cash, cash equivalents, and restricted cash - beginning of year	0	0	0
Cash, cash equivalents, and restricted cash - end of year	0	0	0
Acquisition of additional shares of ARX Holding Corp.	$ (233.2)	$ (5.4)	$ (287.9)

SCHEDULE II - Condensed Finan_5

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Financial Information Of Registrant - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 31, 2020	Feb. 29, 2020	Aug. 31, 2019	Feb. 28, 2019	Aug. 31, 2018
Significant Accounting Policies [Line Items]
Securities held in consolidated non-insurance subsidiary	$ 6,200	$ 3,200
Dividends payable on common shares	2,694.5	1,375.4
Common equities
Significant Accounting Policies [Line Items]
Dividends payable on common shares	2,694.5
Series B Preferred Stock
Significant Accounting Policies [Line Items]
Dividends payable on common shares	13.4			$ 13.4	$ 13.4	$ 13.4	$ 13.4	$ 13.5
Parent Company
Significant Accounting Policies [Line Items]
Securities held in consolidated non-insurance subsidiary	6,200	3,200	$ 2,900
Dividends payable on common shares	2,694.5	1,375.4
Origination of Notes Receivable from Related Parties	0	$ 8	$ 150
Other Significant Noncash Transaction, Value of Consideration Received	225
Parent Company | Series B Preferred Stock
Significant Accounting Policies [Line Items]
Dividends payable on common shares	13.4
Parent Company | Common equities
Significant Accounting Policies [Line Items]
Dividends payable on common shares	$ 2,694.5

SCHEDULE II - Condensed Finan_6

SCHEDULE II - Condensed Financial Information Of Registrant Progressive Corporation Cash Paid (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income taxes	$ 1,446.3	$ 954.3	$ 702.6
Interest	206	184.9	154
Parent Company
Income taxes	1,411	925	679.2
Interest	$ 206	$ 184.9	$ 153.6

SCHEDULE III - Supplementary _2

SCHEDULE III - Supplementary Insurance Information Supplementary Insurance Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 1,237.2	$ 1,056.5	$ 951.6
Future policy benefits, losses, claims, and loss expenses	20,265.8	18,105.4	15,400.8
Unearned premiums	13,437.5	12,388.8	10,686.5
Other policy claims and benefits payable	0	0	0
Premium revenue	39,261.6	36,192.4	30,933.3
Net investment income	916.6	1,017.4	796.2
Benefits, claims, losses, and settlement expenses	25,121.8	25,470.5	21,721
Amortization of deferred policy acquisition costs	3,273.2	3,023.2	2,573.7
Other operating expenses	6,647.4	4,975.1	4,195.8
Net premiums written	40,568.7	37,577.9	32,609.9
Policyholder credit expense	1,077.4	0	0
Personal Lines Segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	32,620.1	30,210	26,034.7
Benefits, claims, losses, and settlement expenses	20,611.7	21,329.7	18,389.8
Amortization of deferred policy acquisition costs	2,437.3	2,273.6	1,964.4
Other operating expenses	5,762	4,227.6	3,563.3
Net premiums written	33,342.6	31,102.2	27,157.6
Commercial Lines Segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	4,875.8	4,427.6	3,610.9
Benefits, claims, losses, and settlement expenses	3,146	3,034.8	2,394
Amortization of deferred policy acquisition costs	525.7	481.2	396
Other operating expenses	647.5	523.5	396
Net premiums written	5,315.3	4,791.8	3,996.4
Property Segment
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	1,765.7	1,554.8	1,287.7
Benefits, claims, losses, and settlement expenses	1,364.1	1,106	937
Amortization of deferred policy acquisition costs	310.2	268.4	213.3
Other operating expenses	237.9	224	237.2
Net premiums written	1,910.8	1,683.9	1,455.9
Other Indemnity
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue	0	0	0
Benefits, claims, losses, and settlement expenses	0	0	0.2
Amortization of deferred policy acquisition costs	0	0	0
Other operating expenses	0	0	(0.7)
Net premiums written	$ 0	$ 0	$ 0

SCHEDULE IV - Reinsurance Reins

SCHEDULE IV - Reinsurance Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	$ 40,687.7	$ 37,519.7	$ 31,970.2
Ceded to Other Companies	1,426.1	1,327.3	1,036.9
Property, Liability and Casualty Insurance Product Line
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	40,687.7	37,519.7	31,970.2
Ceded to Other Companies	1,426.1	1,327.3	1,036.9
Assumed From Other Companies	0	0	0
Net Amount	$ 39,261.6	$ 36,192.4	$ 30,933.3
Percentage of Amount Assumed to Net	0.00%	0.00%	0.00%

Reporting and Accounting Poli_4

Reporting and Accounting Policies - Allowance for Credit Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Allowance for Credit Loss [Abstract]
Balance at January 1	$ 283.2	$ 252.1
Increase in allowance	472	433.5
Write-offs	(399)	(402.4)
Balance at December 31	$ 356.2	$ 283.2

Reporting and Accounting Poli_5

Reporting and Accounting Policies - Advertising Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Advertising costs	$ 2,175.7	$ 1,837.3	$ 1,422.4

Reporting and Accounting Poli_6

Reporting and Accounting Policies Property, Plant, and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total cost	$ 2,397.4	$ 2,351.8
Accumulated depreciation	(1,291.4)	(1,138.1)
Balance at end of year	1,106	1,213.7
Land
Property, Plant and Equipment [Line Items]
Total cost	151.6	161.6
Buildings, improvements, and integrated components
Property, Plant and Equipment [Line Items]
Total cost	872.7	927.1
Capitalized software
Property, Plant and Equipment [Line Items]
Total cost	392.6	367.1
Software licenses (internal use)
Property, Plant and Equipment [Line Items]
Total cost	335.5	286.8
Computer equipment
Property, Plant and Equipment [Line Items]
Total cost	$ 253.8	223.3
Useful Lives	3 years
All other property and equipment
Property, Plant and Equipment [Line Items]
Total cost	$ 391.2	$ 385.9
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	5 years
Upper Limit | All other property and equipment
Property, Plant and Equipment [Line Items]
Useful Lives	10 years

Reporting and Accounting Poli_7

Reporting and Accounting Policies - Compensation Expense Recognized for Equity-Based Compensation (Details) - Stock compensation plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax expense	$ 89.4	$ 90.2	$ 77.2
Tax benefit	$ 18.8	$ 18.9	$ 16.2

Reporting and Accounting Poli_8

Reporting and Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Income taxes	$ 1,446.3	$ 954.3	$ 702.6
Interest	206	184.9	$ 154
Operating lease liabilities	$ 86.5	$ 84

Reporting and Accounting Poli_9

Reporting and Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Aug. 31, 2020	Feb. 29, 2020	Dec. 31, 2019	Aug. 31, 2019	Feb. 28, 2019	Dec. 31, 2018	Aug. 31, 2018
Property, Plant and Equipment [Line Items]
Outstanding derivatives	$ 0			$ 0			$ 0
Held for sale property	56,600,000			32,900,000
Open reverse repurchase commitments	0			0
Dividends payable on common shares	2,694,500,000			1,375,400,000
Right-of-use asset	60,300,000
Noncancelable purchase obligations, minimum commitment	830,400,000
Other assets	800,200,000			783,600,000
Software licenses (internal use)
Property, Plant and Equipment [Line Items]
Other assets	25,300,000
Series B Preferred Stock
Property, Plant and Equipment [Line Items]
Dividends payable on common shares	13,400,000	$ 13,400,000	$ 13,400,000		$ 13,400,000	$ 13,400,000		$ 13,500,000
Cash and Cash Equivalents | ARX Holding Corp.
Property, Plant and Equipment [Line Items]
Open reverse repurchase commitments	93,500,000			$ 46,300,000			$ 117,300,000
Common equities
Property, Plant and Equipment [Line Items]
Dividends payable on common shares	2,694,500,000
Unrecorded unconditional purchase obligations reinsurance | Lower Limit
Property, Plant and Equipment [Line Items]
Other reinsurance contracts, minimum commitment	$ 191,100,000
Other Commitments, Term	1 year
Unrecorded unconditional purchase obligations reinsurance | Upper Limit
Property, Plant and Equipment [Line Items]
Other Commitments, Term	3 years

Investments Investment Portfoli

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 40,807.6	$ 34,441.9
Gross Unrealized Gains	1,223.9	517
Gross Unrealized Losses	(17.3)	(57.6)
Net Holding Period Gains (Losses)	15.2	7.8
Fair Value	$ 42,029.4	$ 34,909.1
% of Total Fair Value	88.40%	88.90%
Equity Securities, at Fair Value
Cost	$ 2,546	$ 2,096.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Net Holding Period Gains (Losses)	2,954.9	2,248.4
Fair Value	$ 5,500.9	$ 4,345.2
% of Total Fair Value	11.60%	11.10%
Debt and Equity Securities, at Fair Value
Cost	$ 43,353.6	$ 36,538.7
Gross Unrealized Gains	1,223.9	517
Gross Unrealized Losses	(17.3)	(57.6)
Net Holding Period Gains (Losses)	2,970.1	2,256.2
Fair value	$ 47,530.3	$ 39,254.3
% of Total Fair Value	100.00%	100.00%
Other Payables to Broker-Dealers and Clearing Organizations	$ 95.5	$ 11.9
Securities held in consolidated non-insurance subsidiary	6,200	3,200
Nonredeemable preferred stocks
Equity Securities, at Fair Value
Cost	1,358.7	971.3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Net Holding Period Gains (Losses)	89.2	67.6
Fair Value	$ 1,447.9	$ 1,038.9
% of Total Fair Value	3.10%	2.70%
Common equities
Equity Securities, at Fair Value
Cost	$ 1,187.3	$ 1,125.5
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Net Holding Period Gains (Losses)	2,865.7	2,180.8
Fair Value	$ 4,053	$ 3,306.3
% of Total Fair Value	8.50%	8.40%
Fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 35,589.1	$ 32,643.1
Gross Unrealized Gains	1,223.9	517
Gross Unrealized Losses	(17.3)	(57.6)
Net Holding Period Gains (Losses)	15.2	7.8
Fair Value	$ 36,810.9	$ 33,110.3
% of Total Fair Value	77.40%	84.30%
Fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 12,437.9	$ 13,100.7
Gross Unrealized Gains	305.8	194.1
Gross Unrealized Losses	(3.7)	(43.7)
Net Holding Period Gains (Losses)	0	0
Fair Value	$ 12,740	$ 13,251.1
% of Total Fair Value	26.80%	33.70%
Fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 3,099.4	$ 1,686
Gross Unrealized Gains	123.1	30
Gross Unrealized Losses	(0.7)	(2.7)
Net Holding Period Gains (Losses)	0	0
Fair Value	$ 3,221.8	$ 1,713.3
% of Total Fair Value	6.80%	4.40%
Fixed maturities | Corporate debt securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 9,579.7	$ 6,860.3
Gross Unrealized Gains	601.7	206.6
Gross Unrealized Losses	(0.1)	(0.5)
Net Holding Period Gains (Losses)	3.9	1.3
Fair Value	$ 10,185.2	$ 7,067.7
% of Total Fair Value	21.40%	18.00%
Fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 503.3	$ 625
Gross Unrealized Gains	7.1	4.5
Gross Unrealized Losses	(0.9)	(2)
Net Holding Period Gains (Losses)	0	0
Fair Value	$ 509.5	$ 627.5
% of Total Fair Value	1.10%	1.60%
Fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 6,042.6	$ 5,020.7
Gross Unrealized Gains	142.5	61.5
Gross Unrealized Losses	(10)	(6)
Net Holding Period Gains (Losses)	0	0
Fair Value	$ 6,175.1	$ 5,076.2
% of Total Fair Value	13.00%	12.90%
Fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 3,745	$ 5,164.7
Gross Unrealized Gains	40.1	16.2
Gross Unrealized Losses	(0.5)	(1.4)
Net Holding Period Gains (Losses)	0	0
Fair Value	$ 3,784.6	$ 5,179.5
% of Total Fair Value	7.90%	13.20%
Fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 181.2	$ 185.7
Gross Unrealized Gains	3.6	4.1
Gross Unrealized Losses	(1.4)	(1.3)
Net Holding Period Gains (Losses)	11.3	6.5
Fair Value	$ 194.7	$ 195
% of Total Fair Value	0.40%	0.50%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 5,218.5	$ 1,798.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Net Holding Period Gains (Losses)	0	0
Fair Value	$ 5,218.5	$ 1,798.8
% of Total Fair Value	11.00%	4.60%

Investments Hybrid Securities (

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Hybrid Securities [Line Items]
Hybrid securities	$ 354.6	$ 189.4
State and local government obligations
Hybrid Securities [Line Items]
Hybrid securities	0	3.5
Corporate debt securities
Hybrid Securities [Line Items]
Hybrid securities	188.4	91.2
Other asset-backed securities
Hybrid Securities [Line Items]
Hybrid securities	34.8	2.6
Redeemable preferred stocks
Hybrid Securities [Line Items]
Hybrid securities	$ 131.4	$ 92.1

Investments Composition of Fixe

Investments Composition of Fixed Maturities by Maturity (Detail) - Fixed maturities $ in Millions	Dec. 31, 2020USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 5,734.9
One to five years	20,769.2
Five to ten years	8,939.8
Ten years or greater	145.2
Cost	35,589.1
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Less than one year	5,765.4
One to five years	21,377.3
Five to ten years	9,512.2
Ten years or greater	156
Debt Securities, Available-for-Sale	$ 36,810.9

Investments Gross Unrealized lo

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Dec. 31, 2020USD ($)security	Dec. 31, 2019USD ($)security
Number of Securities
Total | security	133	307
Less than 12 Months | security	64	217
12 Months or Greater | security	69	90
Fair Value
Total	$ 2,981.5	$ 8,761.3
Less than 12 Months	2,017.1	8,038.3
12 Month or Greater	964.4	723
Gross Unrealized Losses
Total	17.3	57.6
Less than 12 Months	4.9	53.8
12 Months or Greater	$ 12.4	$ 3.8
U.S. government obligations
Number of Securities
Total | security	9	23
Less than 12 Months | security	9	19
12 Months or Greater | security	0	4
Fair Value
Total	$ 1,511	$ 5,152.4
Less than 12 Months	1,511	5,057.2
12 Month or Greater	0	95.2
Gross Unrealized Losses
Total	3.7	43.7
Less than 12 Months	3.7	43.6
12 Months or Greater	$ 0	$ 0.1
State and local government obligations
Number of Securities
Total | security	30	67
Less than 12 Months | security	30	52
12 Months or Greater | security	0	15
Fair Value
Total	$ 208.7	$ 314.3
Less than 12 Months	208.7	287.5
12 Month or Greater	0	26.8
Gross Unrealized Losses
Total	0.7	2.7
Less than 12 Months	0.7	2.6
12 Months or Greater	$ 0	$ 0.1
Corporate debt securities
Number of Securities
Total | security	7	16
Less than 12 Months | security	7	12
12 Months or Greater | security	0	4
Fair Value
Total	$ 129.4	$ 247.6
Less than 12 Months	129.4	191.4
12 Month or Greater	0	56.2
Gross Unrealized Losses
Total	0.1	0.5
Less than 12 Months	0.1	0.5
12 Months or Greater	$ 0	$ 0
Residential mortgage-backed securities
Number of Securities
Total | security	21	41
Less than 12 Months | security	0	12
12 Months or Greater | security	21	29
Fair Value
Total	$ 44.4	$ 292.8
Less than 12 Months	0	163.7
12 Month or Greater	44.4	129.1
Gross Unrealized Losses
Total	0.9	2
Less than 12 Months	0	0.9
12 Months or Greater	$ 0.9	$ 1.1
Commercial mortgage-backed securities
Number of Securities
Total | security	43	98
Less than 12 Months | security	9	79
12 Months or Greater | security	34	19
Fair Value
Total	$ 893.3	$ 1,742.4
Less than 12 Months	93.6	1,400
12 Month or Greater	799.7	342.4
Gross Unrealized Losses
Total	10	6
Less than 12 Months	0.3	5.3
12 Months or Greater	$ 9.7	$ 0.7
Other asset-backed securities
Number of Securities
Total | security	22	61
Less than 12 Months | security	9	43
12 Months or Greater | security	13	18
Fair Value
Total	$ 183.7	$ 1,000.6
Less than 12 Months	74.4	938.5
12 Month or Greater	109.3	62.1
Gross Unrealized Losses
Total	0.5	1.4
Less than 12 Months	0.1	0.9
12 Months or Greater	$ 0.4	$ 0.5
Redeemable preferred stocks
Number of Securities
Total | security	1	1
Less than 12 Months | security	0	0
12 Months or Greater | security	1	1
Fair Value
Total	$ 11	$ 11.2
Less than 12 Months	0	0
12 Month or Greater	11	11.2
Gross Unrealized Losses
Total	1.4	1.3
Less than 12 Months	0	0
12 Months or Greater	$ 1.4	$ 1.3

Investments Components of Net R

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	$ 900.7	$ 281.9	$ 25.2
Total equity securities	113	97.9	290.7
Subtotal gross realized gains on security sales	1,013.7	379.8	315.9
Total available-for-sale securities	(29.6)	(34)	(119.6)
Total equity securities	(69.4)	(11.2)	(25.6)
Subtotal gross realized losses on security sales	(99)	(45.2)	(145.2)
Total available-for-sale securities	871.1	247.9	(94.4)
Total equity securities	43.6	86.7	265.1
Net realized gains (losses) on security sales	914.7	334.6	170.7
Hybrid securities	7.4	18	(10.4)
Equity securities	706.5	739.9	(497.5)
Derivatives	1.4	0	0
Net holding period gains (losses) on securities	715.3	757.9	(507.9)
Net impairment losses recognized in earnings	0	(63.3)	(68.3)
Total net realized gains (losses) on securities	1,630	1,029.2	(405.5)
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	612.5	164.4	6.7
Total available-for-sale securities	(9.6)	(20.4)	(98.7)
Total available-for-sale securities	602.9	144	(92)
State and local government obligations
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	102.4	6.1	9.5
Total available-for-sale securities	(0.7)	(0.7)	(2.9)
Total available-for-sale securities	101.7	5.4	6.6
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	161.9	100.1	2.4
Total available-for-sale securities	(6.5)	(7.9)	(10.4)
Total available-for-sale securities	155.4	92.2	(8)
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	0	0.2	0
Total available-for-sale securities	0	(2.3)	(0.1)
Total available-for-sale securities	0	(2.1)	(0.1)
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	23.7	8.1	2
Total available-for-sale securities	(12.8)	(2.2)	(6.3)
Total available-for-sale securities	10.9	5.9	(4.3)
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	0.2	0.8	0.1
Total available-for-sale securities	0	(0.1)	(1.1)
Total available-for-sale securities	0.2	0.7	(1)
Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Total available-for-sale securities	0	2.2	4.5
Total available-for-sale securities	0	(0.4)	(0.1)
Total available-for-sale securities	0	1.8	4.4
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Total equity securities	24.4	36.2	4.1
Total equity securities	(8.7)	(3.2)	(3.9)
Total equity securities	15.7	33	0.2
Common equities
Gain (Loss) on Securities [Line Items]
Total equity securities	88.6	61.7	286.6
Total equity securities	(60.7)	(8)	(21.7)
Total equity securities	27.9	53.7	264.9
Other Assets
Gain (Loss) on Securities [Line Items]
Net impairment losses recognized in earnings	$ 0	$ (63.3)	$ (68.3)

Investments Components of Equit

Investments Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Total net gains (losses) recognized during the period on equity securities	$ 750.1	$ 826.6	$ (232.4)
Less: Net gains (losses) recognized on equity securities sold during the period	706.5	739.9	(497.5)
Net holding period gains (losses) recognized during the period on equity securities held at period end	$ 43.6	$ 86.7	$ 265.1

Investments Components of Net I

Investments Components of Net Investment Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 936.6	$ 1,042	$ 820.5
Investment expenses	(20)	(24.6)	(24.3)
Net investment income	916.6	1,017.4	796.2
Available-for-sale Securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	818.3	923.7	714.8
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	789.3	882	661.9
Fixed maturities | U.S. government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	166.3	268.6	196.8
Fixed maturities | State and local government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	62.7	36.5	37.7
Fixed maturities | Corporate debt securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	284	268.9	217.9
Fixed maturities | Residential mortgage-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	11.8	21.6	27.6
Fixed maturities | Commercial mortgage-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	152.9	150.1	93.9
Fixed maturities | Other asset-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	96.7	117.3	75.7
Fixed maturities | Redeemable preferred stocks
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	14.9	19	12.3
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	29	41.7	52.9
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	118.3	118.3	105.7
Equity securities | Nonredeemable preferred stocks
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	60.6	61.8	45.9
Equity securities | Common equities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Investment income	$ 57.7	$ 56.5	$ 59.8

Investments - Additional Inform

Investments - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)security	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
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		$ 298,200,000
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		7
Value of securities with credit rating downgraded		$ 65,000,000
Unrealized loss on securities with credit downgraded		1,600,000
Allowance for credit losses, securities		0
Credit loss allowance balance, available-for-sale securities		0
Write off of accrued income		$ 0
Percent change in investment income		10.00%
Percent change in book yield		23.00%
Proceeds from debt invested	$ 986,300,000
Derivatives		$ 1,400,000	0	$ 0
Maximum notional value		114,600,000
Open derivative positions		$ 0	$ 0	$ 0

Fair Value Composition of Inves

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 47,530.3	$ 39,254.3
Debt, fair value	6,793.5	5,119.6
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	42,029.4	34,909.1
Available-for-sale Securities | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	36,810.9	33,110.3
Available-for-sale Securities | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	26,147	22,032.1
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	12,740	13,251.1
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	3,221.8	1,713.3
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	10,185.2	7,067.7
Available-for-sale Securities | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	10,469.2	10,883.2
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	509.5	627.5
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	6,175.1	5,076.2
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	3,784.6	5,179.5
Available-for-sale Securities | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	194.7	195
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	51.6	51.7
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	11.7	11.1
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	131.4	132.2
Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	5,218.5	1,798.8
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	5,500.9	4,345.2
Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,447.9	1,038.9
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,365	955.2
Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	41.9	42.3
Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	41	41.4
Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,053	3,306.3
Equity securities | Common equities | Common Stocks, by Industry
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,049.9	3,306
Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3.1	0.3
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	21,623.3	18,443
Debt, fair value	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	17,455.7	15,059.6
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	12,750.8	13,262.2
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	12,740	13,251.1
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	12,740	13,251.1
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
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
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
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
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
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
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	10.8	11.1
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
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
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	10.8	11.1
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	4,704.9	1,797.4
Fair Value, Inputs, Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,167.6	3,383.4
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	117.7	77.4
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	117.7	77.4
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
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
Fair Value, Inputs, Level 1 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	4,049.9	3,306
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	4,049.9	3,306
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
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	25,852.2	20,767.9
Debt, fair value	6,793.5	5,119.6
Fair Value, Inputs, Level 2 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	24,573.7	19,849.5
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	24,060.1	19,848.1
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	13,407	8,781
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
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	3,221.8	1,713.3
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	10,185.2	7,067.7
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	10,469.2	10,883.2
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	509.5	627.5
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	6,175.1	5,076.2
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	3,784.6	5,179.5
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	183.9	183.9
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	51.6	51.7
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	11.7	11.1
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	120.6	121.1
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	513.6	1.4
Fair Value, Inputs, Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	1,278.5	918.4
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	1,278.5	918.4
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	1,212.3	850.7
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	41.9	42.3
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	24.3	25.4
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
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
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
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	54.8	43.4
Debt, 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	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	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	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
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
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	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
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
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
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
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
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
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
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
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
Fair Value, Inputs, Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	54.8	43.4
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	51.7	43.1
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	35	27.1
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
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	16.7	16
Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	3.1	0.3
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	0	0
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	3.1	0.3
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	43,353.6	36,538.7
Carrying value	5,396.1	4,407.1
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	40,807.6	34,441.9
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	35,589.1	32,643.1
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	25,117	21,647
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	12,437.9	13,100.7
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	3,099.4	1,686
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	9,579.7	6,860.3
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	10,290.9	10,810.4
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	503.3	625
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	6,042.6	5,020.7
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	3,745	5,164.7
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	181.2	185.7
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	51.1	51.5
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	10
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	120.1	124.2
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	5,218.5	1,798.8
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	2,546	2,096.8
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	1,358.7	971.3
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	1,278.6	891.3
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	39.9
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	40.1	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	1,187.3	1,125.5
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	1,184.2	1,125.2
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	$ 3.1	$ 0.3

Fair Value Summary of Changes i

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	$ 43.4	$ 30.4
Calls/ Maturities/ Paydowns	(27.1)	0
Purchases	37.8	12
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0.7	1
Net Transfers In (Out)	0	0
Ending Fair value	54.8	43.4
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	27.1	25.1
Calls/ Maturities/ Paydowns	(27.1)	0
Purchases	35	2
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	35	27.1
Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	16	5
Calls/ Maturities/ Paydowns	0	0
Purchases	0	10
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0.7	1
Net Transfers In (Out)	0	0
Ending Fair value	16.7	16
Equity securities | Common equities | Other risk investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.3	0.3
Calls/ Maturities/ Paydowns	0	0
Purchases	2.8	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	$ 3.1	$ 0.3

Fair Value Summary of Quantitat

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 47,530.3	$ 39,254.3
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	54.8	43.4
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	3.1	0.3
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	51.7	43.1
Financials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Internal Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 25
Fair value inputs, original issue price	$ 3.7
Financials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Unadjusted Purchase Price
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 10
Fair value inputs, original issue price	$ 16.9
Financials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Third Party Pricing Firm
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value		$ 27.1
Fair value inputs, recent transaction price		$ 9
Industrials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Internal Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value		$ 10
Fair value inputs, original issue price		$ 4.9
Industrials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Third Party Pricing Firm
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 6.9	$ 6
Fair value inputs, guideline public company method	$ 5.4
Fair value inputs, performance based price adjustment		$ 4.8
Industrials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Guideline Public Company Method
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 9.8
Fair value inputs, guideline public company method	$ 4.8

Fair Value - Additional Informa

Fair Value - Additional Information (Detail) - security	Dec. 31, 2020	Dec. 31, 2019
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	76.00%	80.00%
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	99.00%	99.00%
Dealer quoted prices, percent of FV hierarchy level	1.00%	1.00%
Fixed maturities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities	0	0
Nonredeemable preferred stocks | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities	4	3
Common equities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities	2	1

Debt (Detail)

Debt (Detail) - USD ($)		Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Fair Value		$ 6,793,500,000		$ 5,119,600,000
Debt, Long-term and Short-term, Combined Amount	[1]	5,396,100,000		4,407,100,000
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Carrying value		499,800,000		499,400,000
Fair Value		510,900,000		515,600,000
Debt Instrument, Face Amount		$ 500,000,000		500,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.75%
2.45% Senior Notes Due 2027
Debt Instrument [Line Items]
Carrying value		$ 497,300,000		496,900,000
Fair Value		541,100,000		501,500,000
Debt Instrument, Face Amount		$ 500,000,000		500,000,000
Debt Instrument, Interest Rate, Stated Percentage		2.45%
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Carrying value		$ 296,900,000		296,600,000
Fair Value		409,400,000		392,500,000
Debt Instrument, Face Amount		$ 300,000,000		300,000,000
Debt Instrument, Interest Rate, Stated Percentage		6.625%
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Carrying value		$ 545,500,000		545,000,000
Fair Value		660,400,000		614,300,000
Debt Instrument, Face Amount		$ 550,000,000		550,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.00%
3.20% Senior Notes due 2030
Debt Instrument [Line Items]
Carrying value		$ 496,100,000		0
Fair Value		575,500,000		0
Debt Instrument, Face Amount		$ 500,000,000	$ 500,000,000	500,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.20%	3.20%
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Carrying value		$ 396,000,000		395,700,000
Fair Value		582,000,000		552,600,000
Debt Instrument, Face Amount		$ 400,000,000		400,000,000
Debt Instrument, Interest Rate, Stated Percentage		6.25%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Carrying value		$ 346,700,000		346,700,000
Fair Value		459,700,000		417,000,000
Debt Instrument, Face Amount		$ 350,000,000		350,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.35%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Carrying value		$ 395,500,000		395,400,000
Fair Value		481,000,000		434,200,000
Debt Instrument, Face Amount		$ 400,000,000		400,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.70%
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Carrying value		$ 841,700,000		841,600,000
Fair Value		1,113,100,000		986,100,000
Debt Instrument, Face Amount		$ 850,000,000		850,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.125%
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Carrying value		$ 590,000,000		589,800,000
Fair Value		806,700,000		705,800,000
Debt Instrument, Face Amount		$ 600,000,000		600,000,000
Debt Instrument, Interest Rate, Stated Percentage		4.20%
3.95% Senior Notes due 2050
Debt Instrument [Line Items]
Carrying value		$ 490,600,000		0
Fair Value		653,700,000		0
Debt Instrument, Face Amount		$ 500,000,000	$ 500,000,000	$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage		3.95%	3.95%
[1]	Consists of both short-term and long-term debt. See Note 4 – Debt for further discussion .

Debt Aggregate Principal Paymen

Debt Aggregate Principal Payments On Debt Outstanding (Detail) $ in Millions	Dec. 31, 2020USD ($)
Debt Disclosure [Abstract]
Debt Instrument, Periodic Payment, Principal in Next Twelve Months	$ 500
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-Term Debt, Maturities, Repayments of Principal in Year Three	0
Long-Term Debt, Maturities, Repayments of Principal in Year Four	0
Long-Term Debt, Maturities, Repayments of Principal in Year Five	0
Long-Term Debt, Maturities, Repayments of Principal after Year Five	4,950
Total	$ 5,450

Debt Unrealized Gains (Losses)

Debt Unrealized Gains (Losses) From Debt Hedges Included In Accumulated Other (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Apr. 30, 2017	Jan. 31, 2015	Apr. 30, 2014	Aug. 31, 2011	Nov. 30, 2002	Mar. 31, 1999
Debt Instrument [Line Items]
Unrealized Gain (Loss)	$ (15.6)	$ (16.4)
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(0.4)					$ (5.1)
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(2.2)							$ (4.2)
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Unrealized Gain (Loss)	3.2						$ 5.1
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(1.4)				$ (1.6)
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(11.4)			$ (12.9)
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Unrealized Gain (Loss)	$ (7.5)		$ (8)

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Proceeds from debt invested	$ 986,300,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax		$ 1,100,000	$ 1,000,000	$ 1,000,000
Discretionary Line of Credit
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 250,000,000
Debt Instrument, Term		30 days
Proceeds from Lines of Credit		$ 0	0
3.20% Senior Notes due 2030
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000,000	$ 500,000,000	500,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.20%	3.20%
3.95% Senior Notes due 2050
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000,000	$ 500,000,000	$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.95%	3.95%
Federal Funds Rate | Discretionary Line of Credit
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate		1.75%

Income Taxes Components of Inco

Income Taxes Components of Income Tax Provision (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)	$ 1,395.7	$ 1,133.2	$ 673.1
Current State and Local Tax Expense (Benefit)	35.6	27.3	21.5
Deferred Federal Income Tax Expense (Benefit)	35.8	16.8	(145.9)
Deferred State and Local Income Tax Expense (Benefit)	1.5	3	(6.1)
Provision for income taxes	$ 1,468.6	$ 1,180.3	$ 542.6

Income Taxes Reconciliation of

Income Taxes Reconciliation of Provision (Benefit) for income Taxes Reported in Consolidated Statements Of Income with Tax at Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income before income taxes	$ 7,173.2	$ 5,160.3	$ 3,163.6
Tax at statutory federal rate	1,506.4	1,083.7	664.4
Tax Adjustments, Settlements, and Unusual Provisions	0	163.2	0
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	(5.4)	(43.9)	(76.3)
Stock-based compensation	(22.7)	(25.9)	(25.1)
Tax-deductible dividends	(25.1)	(14.6)	(14.6)
Tax-preferenced investment income	(15.2)	(14)	(15.6)
Nondeductible compensation expense	6.4	8.1	(0.2)
State income taxes, net of federal taxes	29.3	24	12.2
Other items, net	(5.1)	(0.3)	(2.2)
Provision for income taxes	$ 1,468.6	$ 1,180.3	$ 542.6
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Tax at statutory federal rate	21.00%	21.00%	21.00%
Tax adjustments, settlements, and unusual provisions, percentage	0.00%	3.00%	0.00%
Tax credits	0.00%	(1.00%)	(2.00%)
Stock-based compensation	(1.00%)	(1.00%)	(1.00%)
Tax-deductible dividends	(1.00%)	0.00%	0.00%
Tax-preferenced investment income	0.00%	0.00%	(1.00%)
Nondeductible compensation expense	0.00%	0.00%	0.00%
State income taxes, net of federal taxes	1.00%	1.00%	0.00%
Other items, net	0.00%	0.00%	0.00%
Total income tax provision	20.00%	23.00%	17.00%

Income Taxes Components of Net

Income Taxes Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Federal deferred income tax assets:
Unearned premiums reserve	$ 552.5	$ 498.2
Non-deductible accruals	238.2	181.8
Loss and loss adjustment expense reserves	170	153.3
Operating lease liabilities	37.4	42.3
Investment basis difference	18.6	27.4
Hedges on forecasted transactions	4.1	4.4
Other	25.8	15.3
Federal deferred income tax liabilities:
Net holding period gains on equity securities	(620.5)	(472.2)
Deferred acquisition costs	(259.8)	(221.9)
Net unrealized gains on fixed-maturity securities	(253.4)	(96.5)
Property and equipment	(105.6)	(108.6)
Loss and loss adjustment expense reserve transition adjustment	(39.3)	(47.2)
Operating lease assets	(37.4)	(42.3)
Intangible assets	(27.6)	(38.9)
Prepaid expenses	(5.5)	(4.8)
Other	(7.5)	(8.3)
Deferred Tax Liability, Federal Tax	(310)	(118)
Deferred Tax Assets, State Taxes	11.9	15.2
Deferred Tax Liabilities, State Taxes	(4)	(1.2)
Deferred Tax Liabilities, Net	$ (302.1)	$ (104)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Mar. 31, 2019Investment	Apr. 01, 2018
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	$ 5,400,000	$ 43,900,000	$ 76,300,000
Tax Adjustments, Settlements, and Unusual Provisions	0	163,200,000	0
Net taxes payable	163,500,000	224,000,000
Provision for income taxes	1,468,600,000	1,180,300,000	542,600,000
Deferred tax assets valuation allowance	0	0
Interest and Penalties
Income Taxes [Line Items]
Provision for income taxes	0	9,900,000	0
ARX Holding Corp. | Lower Limit
Income Taxes [Line Items]
Equity interest percentage					80.00%
Alternative Energy
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	0	38,100,000	$ 71,000,000
Number of Investments | Investment				3
Tax Adjustments, Settlements, and Unusual Provisions		163,200,000
Net taxes payable		252,000,000
Net deferred income taxes		88,800,000
Provision for income taxes		100,000,000
Protective Deposits		$ 152,100,000
Alternative Energy | Tax Year 2016
Income Taxes [Line Items]
Protective Deposits	48,800,000
Alternative Energy | Other Assets
Income Taxes [Line Items]
Protective Deposits	$ 103,300,000

Loss And Loss Adjustment Expe_3

Loss And Loss Adjustment Expense Reserves Activity in Loss and loss Adjustment Expense Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 18,105.4	$ 15,400.8	$ 13,086.9
Less reinsurance recoverables on unpaid losses	3,212.2	2,572.7	2,170.1
Net balance at beginning of period	14,893.2	12,828.1	10,916.8
Incurred related to:
Current year	24,926.5	25,238.2	21,632.5
Prior years	195.3	232.3	88.5
Total incurred	25,121.8	25,470.5	21,721
Paid related to:
Current year	15,584.4	16,105	13,792.1
Prior years	7,963	7,300.4	6,017.6
Total paid	23,547.4	23,405.4	19,809.7
Net balance at ending of period	16,467.6	14,893.2	12,828.1
Plus reinsurance recoverables on unpaid losses	3,798.2	3,212.2	2,572.7
Balance at ending of period	$ 20,265.8	$ 18,105.4	$ 15,400.8

Loss And Loss Adjustment Expe_4

Loss And Loss Adjustment Expense Reserves Loss And Loss Adjustment Expense Reserves - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)data_subset	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
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	$ 195.3	$ 232.3	$ 88.5
2018
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	107	131
2017
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years		73
Short-duration Insurance Contracts, Accident Years 2017 and 2016
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			99
2019
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	59
Short-duration Insurance Contracts, Accident Years 2015 and Prior
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			(10)
Commercial Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	98	83	(4)
Property Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ (14)	12	3
Environmental, asbestos, and general liability
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of reserves	0.10%
Auto
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of reserves	94.00%
Personal Auto | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ 136	121	85
Special Lines | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ (25)	$ 14	$ 5
Agency Channel | Personal Auto | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percent of personal auto Prior Year Claims and Claims Adjustment Expense			70.00%
Direct Channel | Personal Auto | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percent of personal auto Prior Year Claims and Claims Adjustment Expense			30.00%

Loss And Loss Adjustment Expe_5

Loss And Loss Adjustment Expense Reserves Incurred and Paid Claims Development with IBNR and Claim Counts (Details) $ in Millions	Dec. 31, 2020USD ($)claim	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 14,989.4	$ 13,614.3
Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,414
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,331.7
All outstanding liabilities before 2016, net of reinsurance1	0.4
Liabilities for claims and claim adjustment expenses, net of reinsurance	82.7	66.6
Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	8,726.6
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,175.2
All outstanding liabilities before 2016, net of reinsurance1	34.9
Liabilities for claims and claim adjustment expenses, net of reinsurance	3,586.3	3,080.8
Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,250.9
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,781.3
All outstanding liabilities before 2016, net of reinsurance1	5.1
Liabilities for claims and claim adjustment expenses, net of reinsurance	474.7	357.2
2016 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	378.1	377.8	$ 378.2	$ 379.8	$ 379.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	74,199
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 377.6	377.5	376.8	376.9	336.7
2016 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,224.9	1,238.9	1,231.1	1,204.8	1,185.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	92,688
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,153.4	1,073.3	886	639.9	298.6
2016 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	535.5	536.5	537.1	541.2	568.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 2.4
Cumulative Number of Incurred Claim Counts | claim	53,693
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 530.8	526.4	516.9	498.2	415.2
2017 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	409.9	411	412.1	415.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (0.9)
Cumulative Number of Incurred Claim Counts | claim	77,170
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 409.4	409.2	409.4	369
2017 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,374.6	1,393.3	1,366.6	1,374.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 18.3
Cumulative Number of Incurred Claim Counts | claim	97,448
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,183.6	1,027.3	712.9	325.8
2017 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	681.3	683.4	680.9	672.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 1.3
Cumulative Number of Incurred Claim Counts | claim	74,140
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 675	670.1	647.1	506.7
2018 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	476.6	478.2	475
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (1.4)
Cumulative Number of Incurred Claim Counts | claim	82,134
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 475.3	475.1	426
2018 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,789.7	1,736.5	1,700.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 41.5
Cumulative Number of Incurred Claim Counts | claim	111,767
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,290.5	913.4	382.7
2018 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	845.4	845.2	839
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 18.2
Cumulative Number of Incurred Claim Counts | claim	63,722
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 812.6	781.2	595.9
2019 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	574.2	577.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (3.3)
Cumulative Number of Incurred Claim Counts | claim	88,897
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 571.5	516.9
2019 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,175.6	2,103.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 116.3
Cumulative Number of Incurred Claim Counts | claim	126,959
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,120.1	455.4
2019 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	965.2	971.7
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 11.7
Cumulative Number of Incurred Claim Counts | claim	72,396
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 930.4	708
2020 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	575.2
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (14.1)
Cumulative Number of Incurred Claim Counts | claim	87,333
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 497.9
2020 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,161.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 369.8
Cumulative Number of Incurred Claim Counts | claim	105,900
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 427.6
2020 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,223.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 252.4
Cumulative Number of Incurred Claim Counts | claim	80,820
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 832.5
Agency Channel | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	25,197.6
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	19,899.2
All outstanding liabilities before 2016, net of reinsurance1	80.3
Liabilities for claims and claim adjustment expenses, net of reinsurance	5,378.7	5,117.4
Agency Channel | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	14,448.3
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	14,371.8
All outstanding liabilities before 2016, net of reinsurance1	5.9
Liabilities for claims and claim adjustment expenses, net of reinsurance	82.4	32.4
Agency Channel | 2016 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,137.8	4,177.3	4,152	4,130	4,082.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	740,535
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,062.5	3,969.5	3,723.1	3,231.5	1,941.6
Agency Channel | 2016 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,402.8	2,400.1	2,401.8	2,398.9	2,423.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	1,399,156
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,401.8	2,402.2	2,402.1	2,406.9	2,391
Agency Channel | 2017 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,546.4	4,511.1	4,485.8	4,474.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 72.3
Cumulative Number of Incurred Claim Counts | claim	779,303
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,285.5	4,048.5	3,478.5	2,074
Agency Channel | 2017 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,640.6	2,643.5	2,638.5	2,635.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (4)
Cumulative Number of Incurred Claim Counts | claim	1,514,873
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,640.8	2,640.9	2,643.2	2,599.8
Agency Channel | 2018 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,192.7	5,182.1	5,141.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 100
Cumulative Number of Incurred Claim Counts | claim	856,108
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,635	4,028.7	2,378
Agency Channel | 2018 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,821.7	2,822.6	2,819
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (3.4)
Cumulative Number of Incurred Claim Counts | claim	1,694,997
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,819.9	2,827.4	2,769.1
Agency Channel | 2019 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,886.9	5,885
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 264.3
Cumulative Number of Incurred Claim Counts | claim	913,063
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 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	3,254.7	3,277.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (13.4)
Cumulative Number of Incurred Claim Counts | claim	1,876,942
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 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	5,433.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 926.8
Cumulative Number of Incurred Claim Counts | claim	750,654
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,383
Agency Channel | 2020 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,328.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (183.4)
Cumulative Number of Incurred Claim Counts | claim	1,768,482
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,250.1
Direct Channel | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	24,292.3
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	19,070.2
All outstanding liabilities before 2016, net of reinsurance1	55.2
Liabilities for claims and claim adjustment expenses, net of reinsurance	5,277.3	4,936.8
Direct Channel | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,919.5
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,879.7
All outstanding liabilities before 2016, net of reinsurance1	0.8
Liabilities for claims and claim adjustment expenses, net of reinsurance	40.6	(7.7)
Direct Channel | 2016 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,866.1	3,897.8	3,871.2	3,843.9	3,819
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	735,791
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,799.1	3,714.6	3,476.9	2,991.1	1,780.6
Direct Channel | 2016 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,478.5	2,475.6	2,477.7	2,475.4	2,521
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	1,676,396
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,477.8	2,478.5	2,479.3	2,485.8	$ 2,505
Direct Channel | 2017 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,254.4	4,229.3	4,209.9	4,209.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 61.3
Cumulative Number of Incurred Claim Counts | claim	772,986
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,035.6	3,808.3	3,255.2	1,912.6
Direct Channel | 2017 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,745.6	2,749	2,743.7	2,750.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (5.1)
Cumulative Number of Incurred Claim Counts | claim	1,791,582
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,747.6	2,748.4	2,753.5	$ 2,742.1
Direct Channel | 2018 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,003.2	4,980.9	4,904.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 88
Cumulative Number of Incurred Claim Counts | claim	870,978
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 4,481.7	3,863.5	2,235.1
Direct Channel | 2018 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,182	3,181.9	3,202.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (5.1)
Cumulative Number of Incurred Claim Counts | claim	2,069,684
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,183	3,193.8	$ 3,170
Direct Channel | 2019 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,811.7	5,756.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 243.5
Cumulative Number of Incurred Claim Counts | claim	954,209
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 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	3,737.8	3,787.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (22.7)
Cumulative Number of Incurred Claim Counts | claim	2,269,857
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 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	5,356.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 901.1
Cumulative Number of Incurred Claim Counts | claim	786,809
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 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	3,775.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (264.5)
Cumulative Number of Incurred Claim Counts | claim	2,137,810
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,720

Loss And Loss Adjustment Expe_6

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, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	$ 14,989.4	$ 13,614.3
Total reinsurance recoverable on unpaid claims	3,779.1	3,200.1
Unallocated claims adjustment expense related to liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	1,478.2	1,278.9
Unallocated claims adjustment expense related to reinsurance recoverable on unpaid claims	19.1	12.1
Total gross liability for unpaid claims and claim adjustment expense	20,265.8	18,105.4	$ 15,400.8	$ 13,086.9
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	66.7	30.8
Total reinsurance recoverable on unpaid claims	358.6	288.1
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	3,586.3	3,080.8
Total reinsurance recoverable on unpaid claims	758.5	482.6
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	82.7	66.6
Total reinsurance recoverable on unpaid claims	(0.3)	0.5
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	474.7	357.2
Total reinsurance recoverable on unpaid claims	226.9	184.1
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	5,378.7	5,117.4
Total reinsurance recoverable on unpaid claims	959.6	930.7
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	82.4	32.4
Total reinsurance recoverable on unpaid claims	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	5,277.3	4,936.8
Total reinsurance recoverable on unpaid claims	1,475.8	1,314.1
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	40.6	(7.7)
Total reinsurance recoverable on unpaid claims	$ 0	$ 0

Loss And Loss Adjustment Expe_7

Loss And Loss Adjustment Expense Reserves Historical Claims Duration (Details)	Dec. 31, 2020
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	45.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	31.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	12.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	5.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.20%
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	98.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	1.20%
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%
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	44.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	31.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	12.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	5.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.20%
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	100.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	(0.10%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.30%)
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 - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	21.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	29.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	21.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	13.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.50%
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	88.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	10.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	0.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.00%
Property Segment | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	71.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	20.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	3.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	1.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.80%

Reinsurance Effect of Reinsuran

Reinsurance Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct premiums written	$ 41,736.4	$ 39,222	$ 33,753.1
Ceded written	(1,167.7)	(1,644.1)	(1,143.2)
Net premiums written	40,568.7	37,577.9	32,609.9
Direct premiums earned	40,687.7	37,519.7	31,970.2
Ceded earned	(1,426.1)	(1,327.3)	(1,036.9)
Net premiums earned	39,261.6	36,192.4	30,933.3
non regulated reinsurance plan
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded written	(519.5)	(933)	(546.8)
Ceded earned	(739.6)	(656.5)	(479.4)
Regulated reinsurance plan
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded written	(648.2)	(711.1)	(596.4)
Ceded earned	$ (686.5)	$ (670.8)	$ (557.5)

Reinsurance Prepaid Reinsurance

Reinsurance Prepaid Reinsurance Premiums and Reinsurance Recoverables (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 4,019.4	$ 3,378.9
Percentage Of Total Reinsurance Recoverables	100.00%	100.00%
Prepaid reinsurance premiums	$ 368.1	$ 626.5
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	$ 753.2	$ 459.5
Percentage Of Total Reinsurance Recoverables	19.00%	14.00%
Prepaid reinsurance premiums	$ 134.5	$ 352.9
Percentage Of Total Prepaid Reinsurance Premiums	37.00%	56.00%
Property reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 261.7	$ 146.8
Percentage Of Total Reinsurance Recoverables	7.00%	4.00%
Prepaid reinsurance premiums	$ 11.7	$ 14.5
Percentage Of Total Prepaid Reinsurance Premiums	3.00%	3.00%
Other reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 7.1	$ 8
Percentage Of Total Reinsurance Recoverables	0.00%	0.00%
Prepaid reinsurance premiums	$ 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	$ 1,022	$ 614.3
Percentage Of Total Reinsurance Recoverables	26.00%	18.00%
Prepaid reinsurance premiums	$ 146.2	$ 367.4
Percentage Of Total Prepaid Reinsurance Premiums	40.00%	59.00%
State Reinsurance Plans
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 2,997.4	$ 2,764.6
Percentage Of Total Reinsurance Recoverables	74.00%	82.00%
Prepaid reinsurance premiums	$ 221.9	$ 259.1
Percentage Of Total Prepaid Reinsurance Premiums	60.00%	41.00%
State Reinsurance Plans | Michigan Catastrophic Claims Association
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 2,428.8	$ 2,247.1
Percentage Of Total Reinsurance Recoverables	60.00%	67.00%
Prepaid reinsurance premiums	$ 33.3	$ 71.8
Percentage Of Total Prepaid Reinsurance Premiums	9.00%	12.00%
State Reinsurance Plans | Commercial Auto Insurance Procedures Plans
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 397.8	$ 332.4
Percentage Of Total Reinsurance Recoverables	10.00%	10.00%
Prepaid reinsurance premiums	$ 84.7	$ 93.8
Percentage Of Total Prepaid Reinsurance Premiums	23.00%	15.00%
State Reinsurance Plans | Florida Hurricane Catastrophe Fund
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 54.8	$ 86
Percentage Of Total Reinsurance Recoverables	1.00%	3.00%
Prepaid reinsurance premiums	$ 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	$ 88.6	$ 84.4
Percentage Of Total Reinsurance Recoverables	2.00%	2.00%
Prepaid reinsurance premiums	$ 41.9	$ 33.8
Percentage Of Total Prepaid Reinsurance Premiums	11.00%	5.00%
State Reinsurance Plans | Other reinsurance program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 3.2	$ 3.1
Percentage Of Total Reinsurance Recoverables	0.00%	0.00%
Prepaid reinsurance premiums	$ 1.3	$ 1
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	0.00%
Federal Reinsurance Plans | National Flood Insurance Program
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 24.2	$ 11.6
Percentage Of Total Reinsurance Recoverables	1.00%	0.00%
Prepaid reinsurance premiums	$ 60.7	$ 58.7
Percentage Of Total Prepaid Reinsurance Premiums	17.00%	9.00%

Reinsurance - Additional Inform

Reinsurance - Additional Information (Detail) - state	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Transportation Network Company
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Number of States in which Entity Operates	20	17	4

Statutory Financial Informati_2

Statutory Financial Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statutory Financial Information Disclosures [Abstract]
Consolidated statutory policyholders' surplus	$ 15,194.6	$ 13,671.1
Statutory net income	4,911.4	$ 3,489.7	$ 2,643
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	1,142
Aggregate cash dividends paid to the parent company by subsidiaries	4,096.5
Maximum aggregate dividend amount subsidiaries could pay without prior approval from regulatory authorities	$ 4,612.6

Employee Benefit Plans Amounts

Employee Benefit Plans Amounts Charged to Income for employees Incentive Compensation Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Incentive Compensation Cash Award
Incentive Compensation Plans Expense [Line Items]
Pretax	$ 688.8	$ 598.4	$ 539.5
After Tax	544.2	472.7	426.2
Employee Stock
Incentive Compensation Plans Expense [Line Items]
Pretax	89.4	90.1	76.2
After Tax	70.6	71.2	60.2
Employee Stock Option
Incentive Compensation Plans Expense [Line Items]
Pretax	0	0.1	1
After Tax	$ 0	$ 0.1	$ 0.8

Employee Benefit Plans Summary

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Beginning of year	3,879,077	4,856,356	5,858,848
Add (deduct):
Granted	1,629,534	1,835,145	1,876,109
Vested	(1,861,442)	(2,691,337)	(2,811,070)
Forfeited	(76,898)	(121,087)	(67,531)
End of year	3,570,271	3,879,077	4,856,356
Weighted Average Grant Date Fair Value
Beginning of year	$ 48.28	$ 38.56	$ 30.47
Granted	55.28	49.61	45.55
Vested	36.19	31.85	26.41
Forfeited	52.79	43.98	36.10
End of year	$ 57.68	$ 48.28	$ 38.56
Unrecognized compensation cost related to unvested equity awards	$ 102.1
Period of recognition of compensation expense related to unvested equity awards	2 years 3 months 18 days
Dividend Equivalent Units
Add (deduct):
Granted	144,389	210,159	144,688
Weighted Average Grant Date Fair Value
Granted	$ 0	$ 0	$ 0
Performance Shares
Weighted Average Grant Date Fair Value
Target shares	707,293
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Expected To Vest Number	1,658,308

Employee Benefit Plans Summar_2

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested equity awards	$ 0.9	$ 0.8	$ 0.9
Number of Shares
Beginning of year	38,451	41,706	53,284
Add (deduct):
Granted	39,403	38,451	41,706
Vested	(38,451)	(41,706)	(53,284)
End of year	39,403	38,451	41,706
Weighted Average Grant Date Fair Value
Beginning of year	$ 73.43	$ 62.23	$ 40.54
Granted	74.77	73.43	62.23
Vested	73.43	62.23	40.54
End of year	$ 74.77	$ 73.43	$ 62.23

Employee Benefit Plans Assets H

Employee Benefit Plans Assets Held in Deferral Plan Irrevocable Grantor Trust Account (Detail) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$ 301.4	$ 272.8
Other Investment Funds
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	167.2	151.2
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	$ 134.2	$ 121.6
Deferred Compensation Arrangement with Individual, Shares Authorized for Issuance	2.8	3.2

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Benefits Disclosure [Line Items]
Minimum employment period for benefits	30 days
Postemployment benefits liability	$ 24.1	$ 22.2
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	$ 148.9	191.6	$ 162.7
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	$ 3	$ 3	$ 3.2
Executive Deferred Compensation Plan
Employee Benefits Disclosure [Line Items]
Common shares reserved for issuance under executive deferred compensation plan	11.1
2017 Directors Equity Incentive Plan | Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Shares authorized	0.5
Equity Incentive Plan Twenty Fifteen
Employee Benefits Disclosure [Line Items]
Shares authorized	17
Performance Based Restricted Equity Awards | 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%
Performance Based Restricted Equity Awards | 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%
Performance Based Restricted Equity Awards | 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%
Performance Based Restricted Equity Awards | 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%
Defined Contribution Pension Plan 401k
Employee Benefits Disclosure [Line Items]
Matching contributions	$ 131.2	$ 120.8	$ 106.8
Defined Contribution Pension Plan 401k | Upper Limit
Employee Benefits Disclosure [Line Items]
Matching contribution to defined contribution pension plan	6.00%
Cash [Member]
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	21.5

Segment Information Operating R

Segment Information Operating Results (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues	$ 42,658.1	$ 39,022.3	$ 31,979
Pretax Profit (Loss)	7,173.2	5,160.3	3,163.6
Amortization of intangible assets	56.9	66.3	72
Personal Lines Segment | Agency Channel | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	15,789.5	14,904.1	13,017.2
Pretax Profit (Loss)	2,236.5	1,673.2	1,435.7
Personal Lines Segment | Direct Channel | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	16,830.6	15,305.9	13,017.5
Pretax Profit (Loss)	2,076.5	1,181.4	1,088.5
Operating Segments | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	39,261.6	36,192.4	30,933.3
Pretax Profit (Loss)	4,822.7	3,287.3	2,915
Operating Segments | Personal Lines Segment | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	32,620.1	30,210	26,034.7
Pretax Profit (Loss)	$ 4,313	$ 2,854.6	$ 2,524.2
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	$ 4,875.8	$ 4,427.6	$ 3,610.9
Pretax Profit (Loss)	634.8	458.8	478.6
Operating Segments | Property Segment | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	1,765.7	1,554.8	1,287.7
Pretax Profit (Loss)	(125.1)	(26.1)	(88.7)
Amortization of intangible assets	56.9	66.3	72
Operating Segments | Other Indemnity | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	0	0	0
Pretax Profit (Loss)	0	0	0.9
Segment Reconciling Items | Investments
Segment Reporting Information [Line Items]
Revenues	2,566.6	2,071.2	415
Pretax Profit (Loss)	2,546.6	2,046.6	390.7
Segment Reconciling Items | Interest Expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	(217)	(189.7)	(166.5)
Segment Reconciling Items | Fees And Other Revenues
Segment Reporting Information [Line Items]
Revenues	603.5	563.7	472.2
Segment Reconciling Items | Service Businesses
Segment Reporting Information [Line Items]
Revenues	226.4	195	158.5
Pretax Profit (Loss)	$ 20.9	$ 16.1	$ 24.4

Segment Information Underwritin

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Details) - Underwriting Operations	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Personal Lines Segment | Agency Channel
Segment Reporting Information [Line Items]
Underwriting Margin	14.20%	11.20%	11.00%
Combined Ratio	85.80%	88.80%	89.00%
Personal Lines Segment | Direct Channel
Segment Reporting Information [Line Items]
Underwriting Margin	12.30%	7.70%	8.40%
Combined Ratio	87.70%	92.30%	91.60%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	12.30%	9.10%	9.40%
Combined Ratio	87.70%	90.90%	90.60%
Operating Segments | Personal Lines Segment
Segment Reporting Information [Line Items]
Underwriting Margin	13.20%	9.50%	9.70%
Combined Ratio	86.80%	90.50%	90.30%
Operating Segments | Commercial Lines Segment
Segment Reporting Information [Line Items]
Underwriting Margin	13.00%	10.40%	13.30%
Combined Ratio	87.00%	89.60%	86.70%
Operating Segments | Property Segment
Segment Reporting Information [Line Items]
Underwriting Margin	(7.10%)	(1.70%)	(6.90%)
Combined Ratio	107.10%	101.70%	106.90%
Combined ratio amortization points	0.032	0.043	0.056

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)Entity	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Depreciation | $	$ 274.9	$ 239.8	$ 190.4
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 (L_3

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ 435.7	$ (153)	$ 1,977.8
Pretax Cumulative Effect of New Accounting Principal in Period of Adoption			(2,006)
Pretax Reclassification of Stranded Amounts in AOCI to Equity	3.4		(4.3)
AOCI before Tax, Attributable to Parent, After Reclassification of Stranded Amounts	439.1
AOCI before Tax, Attributable to Parent, after Cumulative Effect Adjustment and Reclassification of Stranded Amounts			(32.5)
Unrealized Holding Gain (Loss) on Securities Arising During the Period, before tax	1,557.2	825.8	(224.1)
Portion Attributable to Noncontrolling Interest, before tax	0	(5.9)	4.3
Total other comprehensive income (loss) before reclassifications, before tax	1,557.2	819.9	(219.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	810	232.2	(98.3)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	(1.1)	(1)	(1)
Total reclassification adjustment for amounts realized in net income, before tax	808.9	231.2	(99.3)
Total other comprehensive income, before tax	748.3	588.7	(120.5)
AOCI before Tax, Attributable to Parent, ending balance	1,187.4	435.7	(153)
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	(94)	32.1	(695.6)
Tax, Cumulative Effect of New Accounting Principal in Period of Adoption			705.8
Tax, Reclassification of Stranded Amounts in AOCI to Equity	(0.7)		(3.4)
AOCI Tax, Attributable to Parent, After Reclassification of Stranded Amounts	(94.7)
AOCI Tax, Attributable to Parent, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts			6.8
Unrealized Holding Gain (Loss) on Securities Arising During the Period, tax	(306.1)	(174.9)	47
Portion Attributable to Noncontrolling Interest, tax	0	1.3	(1)
Total Other Comprehensive Income (Loss), before Reclassification Adjustments, Tax	(306.1)	(173.6)	46
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(145.4)	(47.7)	20.5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	0.3	0.2	0.2
Total reclassification adjustment for amounts realized in net income, Total tax (provisions) benefit	(145.1)	(47.5)	20.7
Total other comprehensive income, Total tax (provision) benefit	(161)	(126.1)	25.3
AOCI Tax, Attributable to Parent, ending balance	(255.7)	(94)	32.1
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	341.7	(120.9)	1,282.2
Cumulative Effect of New Accounting Principal in Period of Adoption			(1,300.2)
Reclassification of Stranded Amounts in AOCI to Equity	2.7		(7.7)
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	344.4
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts			(25.7)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	1,251.1	650.9	(177.1)
Other comprehensive (income) loss attributable to NCI	0	(4.6)	3.3
Total other comprehensive income (loss), before reclassifications, after tax	1,251.1	646.3	(173.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	664.6	184.5	(77.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.8)	(0.8)	(0.8)
Total reclassification adjustment for amounts realized in net income, Net of tax	663.8	183.7	(78.6)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	587.3	462.6	(95.2)
After tax total accumulated other comprehensive income, ending balance	931.7	341.7	(120.9)
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	360.8	(105.6)	1,295
Cumulative Effect of New Accounting Principal in Period of Adoption			(1,300.2)
Reclassification of Stranded Amounts in AOCI to Equity	0		(1.1)
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	360.8
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts			(6.3)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	1,251.1	650.9	(177.1)
Other comprehensive (income) loss attributable to NCI	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	1,251.1	650.9	(177.1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	664.6	184.5	(77.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0
Total reclassification adjustment for amounts realized in net income, Net of tax	664.6	184.5	(77.8)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	586.5	466.4	(99.3)
After tax total accumulated other comprehensive income, ending balance	947.3	360.8	(105.6)
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	(16.4)	(17.2)	(14.8)
Cumulative Effect of New Accounting Principal in Period of Adoption			0
Reclassification of Stranded Amounts in AOCI to Equity	0		(3.2)
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	(16.4)
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts			(18)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0	0	0
Other comprehensive (income) loss attributable to NCI	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.8)	(0.8)	(0.8)
Total reclassification adjustment for amounts realized in net income, Net of tax	(0.8)	(0.8)	(0.8)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.8	0.8	0.8
After tax total accumulated other comprehensive income, ending balance	(15.6)	(16.4)	(17.2)
Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(2.7)	1.9	2
Cumulative Effect of New Accounting Principal in Period of Adoption			0
Reclassification of Stranded Amounts in AOCI to Equity	2.7		(3.4)
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	0
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts			(1.4)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0	0	0
Other comprehensive (income) loss attributable to NCI	0	(4.6)	3.3
Total other comprehensive income (loss), before reclassifications, after tax	0	(4.6)	3.3
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0
Total reclassification adjustment for amounts realized in net income, Net of tax	0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	(4.6)	3.3
After tax total accumulated other comprehensive income, ending balance	$ 0	$ (2.7)	$ 1.9

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement Additional Information (Detail) $ in Millions	Dec. 31, 2020USD ($)
Statement of Comprehensive Income [Abstract]
Net unrealized losses on forecasted transactions, expected to reclassify into interest expense within the next 12 months	$ 0.9

- Additional Information (Detai

- Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating Lease, Right-of-Use Asset	$ 165.5	$ 188.2
Operating Lease, Liability	$ 179	$ 201.5
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
Weighted-average remaining term	3 years	3 years 3 months 18 days
Weighted-average discount rate	2.50%	3.00%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets	us-gaap:OtherAssets

Leases - Schedule of operating

Leases - Schedule of operating lease maturities (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 78.9
2022	48.7
2023	29.1
2024	18.4
2025	9.8
Thereafter	0.5
Total	185.4
Interest	(6.4)
Present value of lease liabilities	$ 179	$ 201.5

Leases Expenses Incurred for Le

Leases Expenses Incurred for Leases (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Expense	$ 95.4	$ 102	$ 77.3

Dividends Dividends (Details)

Dividends Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended															12 Months Ended
	Dec. 31, 2020	Oct. 31, 2020	Sep. 30, 2020	Jul. 31, 2020	Apr. 30, 2020	Mar. 31, 2020	Jan. 31, 2020	Oct. 31, 2019	Sep. 30, 2019	Jul. 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Feb. 28, 2019	Sep. 30, 2018	Feb. 28, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 31, 2020	Jun. 30, 2020	Feb. 29, 2020	Aug. 31, 2019	Jun. 30, 2019	Aug. 31, 2018	Dec. 31, 2017
Common shares, dividends declared (USD per share)																$ 4.90	$ 2.65	$ 2.5140
Dividends payable on common shares	$ 2,694.5															$ 2,694.5	$ 1,375.4
Quarterly dividend
Common shares, dividends declared (USD per share)	$ 0.10
Common Stock, Dividends, Per Share, Cash Paid		$ 0.10		$ 0.10	$ 0.10		$ 0.10	$ 0.10		$ 0.10	$ 0.10
Annual variable dividend
Common shares, dividends declared (USD per share)	$ 4.50
Common Stock, Dividends, Per Share, Cash Paid							$ 2.25						$ 2.5140		$ 1.1247
Series B Preferred Stock
Dividends payable on common shares	$ 13.4												$ 13.4			13.4			$ 13.4		$ 13.4	$ 13.4		$ 13.5
Preferred shares, dividends declared (USD per share)	$ 26.875
Preferred Stock, Dividends, Per Share, Cash Paid			$ 26.875			$ 26.875			$ 26.875			$ 26.875		$ 27.024
Common equities
Dividends payable on common shares	$ 2,694.5															2,694.5
Common equities | Quarterly dividend
Dividends payable on common shares	58.6		$ 58.6			$ 58.5			$ 58.5			$ 58.4				58.6	58.5			$ 58.5			$ 58.4
Common equities | Annual variable dividend
Dividends payable on common shares	$ 2,635.9															$ 2,635.9	$ 1,316.9	$ 1,467.9							$ 655.1

Dividends-Additional Informatio

Dividends-Additional Information (Details) - $ / shares	1 Months Ended	60 Months Ended
	Mar. 31, 2023	Mar. 14, 2023	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Dividends Payable [Line Items]
Target percentage used to determine annual variable dividend			33.33%		33.33%
Gainshare factor used to determine annual variable dividend			1.91		1.79
Series B Preferred Stock
Dividends Payable [Line Items]
Preferred shares, issued (in shares)				500,000
Preferred Stock, Liquidation Preference Per Share				$ 1,000
Forecast | Series B Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividend Rate, Percentage		5.375%
London Interbank Offered Rate (LIBOR) | Forecast | Series B Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Basis Spread on Variable Rate	2.539%

Redeemable Noncontrolling Int_3

Redeemable Noncontrolling Interest (Details) $ in Millions	Apr. 01, 2020USD ($)	Dec. 31, 2020USD ($)		Dec. 31, 2019USD ($)		Dec. 31, 2018USD ($)shares
Redeemable Noncontrolling Interest [Line Items]
Payments for Repurchase of Redeemable Noncontrolling Interest		$ 243		$ 11.2		$ 296.9
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, Beginning of year		225.6	[1]	214.5		503.7
Net income attributable to NCI		0		9.7		5.7
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest		0		4.6		(3.3)
Stock Issued During Period, Value, Stock Options Exercised Attributable to Redeemable Noncontrolling Interest		16		7.7		9.4
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		(241.6)		(11.2)		(298.2)
Adjustment to carrying amount of redeemable noncontrolling interest		0		0.3		(2.8)
Balance, End of year		$ 0	[1]	$ 225.6	[1]	$ 214.5
ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Number of Shares Put Pursuant to Stockholders' Agreement | shares						204,527
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | shares						5,483
Payments to Acquire Interest in Subsidiaries and Affiliates						$ 295.9
Payments for Repurchase of Redeemable Noncontrolling Interest	$ 243
[1]	See Note 15 – Redeemable Noncontrolling Interest for further discussion .

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Intangible assets, accumulated amortization	$ 326.1	$ 314
Indefinite-lived Intangible Assets (Excluding Goodwill)	12.4	12.4
Total	171.4	228.3
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, accumulated amortization	325.5	313.4
Intangible assets subject to amortization	159	215.9
Licenses
Finite-Lived Intangible Assets [Line Items]
Intangible assets, accumulated amortization	$ 0.6	$ 0.6

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 326.1	$ 314
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2
Accumulated Amortization	210.4	173.9
Net Carrying Amount	45.8	82.3
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2
Accumulated Amortization	65.4	54
Net Carrying Amount	93.8	105.2
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	69.1	79.1
Accumulated Amortization	49.7	50.7
Net Carrying Amount	19.4	28.4
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	34.8
Accumulated Amortization	0	34.8
Net Carrying Amount	0	0
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	484.5	529.3
Accumulated Amortization	325.5	313.4
Net Carrying Amount	$ 159	$ 215.9

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets Goodwill and Intangible Assets - Amortization (Details) $ in Millions	Dec. 31, 2020USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Finite- Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 56.6
Finite-Lived Intangible Assets, Amortization Expense, Year Two	29.2
Finite-Lived Intangible Assets, Amortization Expense, Year Three	13.5
Finite-Lived Intangible Assets, Amortization Expense, Year Four	11.4
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 11.4

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets Goodwill (Details)	12 Months Ended
	Dec. 31, 2020USD ($)intangible_asset	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Goodwill [Line Items]
Goodwill	$ 452,700,000	$ 452,700,000
Goodwill, Impaired, Accumulated Impairment Loss	0
Amortization of intangible assets	56,900,000	66,300,000	$ 72,000,000
Software rights
Goodwill [Line Items]
Gross Carrying Amount	$ 69,100,000	$ 79,100,000
Number of Intangible Assets | intangible_asset	1
Fully Amortized | Software rights
Goodwill [Line Items]
Gross Carrying Amount	$ 10,000,000

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent Event $ / shares in Units, $ in Millions	Feb. 16, 2021USD ($)$ / shares
Subsequent Event [Line Items]
Business Acquisition, Share Price | $ / shares	$ 23.30
Business Acquisition, Amount | $	$ 338