The Progressive Corporation (PGR) 10-Q 3 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2020shares
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-09518
Entity Incorporation, State or Country Code	OH
Entity Tax Identification Number	34-0963169
Entity Address, Address Line One	6300 Wilson Mills Road,
Entity Address, City or Town	Mayfield Village,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	44143
City Area Code	440
Local Phone Number	461-5000
Entity Information, Former Legal or Registered Name	Not Applicable
Title of 12(b) Security	Common Shares, $1.00 Par Value
Trading Symbol	PGR
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	585,597,988
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	0000080661
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues
Net premiums earned	$ 9,973.5	$ 9,012.2	$ 29,052.8	$ 26,296.7
Investment income	230.5	263	715.5	777.2
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales	195.9	71.7	771.1	185.3
Net holding period gains (losses) on securities	336.7	31.8	98.7	536.9
Net impairment losses recognized in earnings	0	(38.1)	0	(62.4)
Total net realized gains (losses) on securities	532.6	65.4	869.8	659.8
Fees and other revenues	151.8	138.4	434.8	403.4
Service revenues	58.8	51.5	169.4	144.1
Total revenues	10,947.2	9,530.5	31,242.3	28,281.2
Expenses
Losses and loss adjustment expenses	6,713.1	6,426.3	18,189.7	18,323.4
Policy acquisition costs	835.2	751.5	2,413.5	2,200.7
Other underwriting expenses	1,330.9	1,240.3	4,179.7	3,643
Policyholder credit expense	29	0	1,062.4	0
Investment expenses	4.7	5.9	14.5	18.3
Service expenses	54.4	48.7	154.7	132.1
Interest expense	56.4	47.5	160.8	142.3
Total expenses	9,023.7	8,520.2	26,175.3	24,459.8
Net Income
Income before income taxes	1,923.5	1,010.3	5,067	3,821.4
Provision for income taxes	392.7	166.7	1,046.7	916
Net income	1,530.8	843.6	4,020.3	2,905.4
Net (income) loss attributable to noncontrolling interest (NCI)	0	(1.9)	0	(5.9)
Net income attributable to Progressive	1,530.8	841.7	4,020.3	2,899.5
Other Comprehensive Income (Loss)
Total net unrealized gains (losses) on fixed-maturity securities	(24.6)	58.1	605.6	636.6
Net unrealized losses on forecasted transactions	0.2	0.2	0.6	0.6
Other comprehensive income (loss)	(24.4)	58.3	606.2	637.2
Other comprehensive (income) loss attributable to NCI	0	(0.9)	0	(5.8)
Comprehensive income attributable to Progressive	1,506.4	899.1	4,626.5	3,530.9
Computation of Earnings Per Common Share
Net income attributable to Progressive	1,530.8	841.7	4,020.3	2,899.5
Less: Preferred share dividends	6.7	6.7	20.1	20.1
Net income available to common shareholders	$ 1,524.1	$ 835	$ 4,000.2	$ 2,879.4
Average common shares outstanding - Basic	585.1	584.1	584.9	583.7
Net effect of dilutive stock-based compensation	2.7	3	2.8	3.6
Total average equivalent common shares - Diluted	587.8	587.1	587.7	587.3
Basic: Earnings per common share	$ 2.60	$ 1.43	$ 6.84	$ 4.93
Diluted: Earnings per common share	$ 2.59	$ 1.42	$ 6.81	$ 4.90

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)		Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Assets
Fixed maturities (amortized cost: $35,082.8, $32,134.9, and $32,643.1)		$ 36,313,500,000	$ 33,110,300,000	$ 32,812,700,000
Short-term investments (amortized cost: $4,667.8, $1,467.4, and $1,798.8)		4,667,800,000	1,798,800,000	1,467,400,000
Total available-for-sale securities		40,981,300,000	34,909,100,000	34,280,100,000
Nonredeemable preferred stocks (cost: $1,302.7, $1,054.2, and $971.3)		1,323,200,000	1,038,900,000	1,128,500,000
Common equities (cost: $1,130.0, $1,210.3, and $1,125.5)		3,459,800,000	3,306,300,000	3,165,100,000
Total equity securities		4,783,000,000	4,345,200,000	4,293,600,000
Total investments		45,764,300,000	39,254,300,000	38,573,700,000
Cash and cash equivalents		90,100,000	226,200,000	45,900,000
Restricted cash		1,000,000	1,200,000	300,000
Cash and cash equivalents		91,100,000	227,400,000	46,200,000
Accrued investment income		181,500,000	181,300,000	182,500,000
Premiums receivable, net of allowance of $313.2, $258.8, and $283.2		8,574,300,000	7,507,300,000	7,687,200,000
Reinsurance recoverables		3,987,300,000	3,378,900,000	3,298,400,000
Prepaid reinsurance premiums		463,400,000	626,500,000	458,800,000
Deferred acquisition costs		1,265,000,000	1,056,500,000	1,093,700,000
Property and equipment, net of accumulated depreciation of $1,264.5, $1,085.3, and $1,138.1		1,181,600,000	1,213,700,000	1,214,200,000
Goodwill		452,700,000	452,700,000	452,700,000
Intangible assets, net of accumulated amortization of $312.0, $299.4, and $314.0		185,500,000	228,300,000	242,900,000
Other assets		744,100,000	768,400,000	757,800,000
Total assets		62,890,800,000	54,895,300,000	54,008,100,000
Liabilities
Unearned premiums		14,199,300,000	12,388,800,000	12,526,500,000
Loss and loss adjustment expense reserves		19,589,200,000	18,105,400,000	17,370,000,000
Net deferred income taxes		213,900,000	132,500,000	136,000,000
Accounts payable, accrued expenses, and other liabilities		5,405,800,000	5,962,700,000	5,222,900,000
Debt	[1]	5,395,400,000	4,407,100,000	4,406,500,000
Total liabilities		44,803,600,000	40,996,500,000	39,661,900,000
Redeemable noncontrolling interest (NCI)	[2]	0	225,600,000	222,900,000
Shareholders’ Equity
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5)		493,900,000	493,900,000	493,900,000
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 211.9, 212.9, and 212.9)		585,600,000	584,600,000	584,600,000
Paid-in capital		1,629,400,000	1,573,400,000	1,539,100,000
Retained earnings		14,427,700,000	10,679,600,000	10,995,200,000
Accumulated other comprehensive income (loss):
Net unrealized gains (losses) on fixed-maturity securities		966,400,000	360,800,000	531,000,000
Net unrealized losses on forecasted transactions		(15,800,000)	(16,400,000)	(16,600,000)
Accumulated other comprehensive (income) loss attributable to NCI		0	(2,700,000)	(3,900,000)
Total accumulated other comprehensive income (loss) attributable to Progressive		950,600,000	341,700,000	510,500,000
Total shareholders’ equity		18,087,200,000	13,673,200,000	14,123,300,000
Total liabilities, redeemable NCI, and shareholders’ equity		$ 62,890,800,000	$ 54,895,300,000	$ 54,008,100,000
3.75% Senior Notes due 2021
Debt, stated interest rate		3.75%
Debt, face amount		$ 500,000,000
Senior Notes Three Point Two Zero Percent Due Twenty Thirty [Member]
Debt, stated interest rate		3.20%
[1]	Consists of both short-term and long-term debt, including $500 million principal amount of 3.75% Senior Notes due August 2021. See Note 4 – Debt for further discussion.
[2]	See Note 12 – Redeemable Noncontrolling Interest for further discussion .

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fixed maturities, amortized cost	$ 35,082.8	$ 32,643.1	$ 32,134.9
Nonredeemable preferred stocks, cost	1,302.7	971.3	1,054.2
Common equities, cost	1,130	1,125.5	1,210.3
Short-term investments, amortized cost	4,667.8	1,798.8	1,467.4
Premiums receivable, allowance for doubtful accounts	313.2	283.2	258.8
Intangible Assets, Accumulated Amortization	312	314	299.4
Property and equipment, accumulated depreciation	$ 1,264.5	$ 1,138.1	$ 1,085.3
Common Shares, par value (USD per share)	$ 1	$ 1	$ 1
Common Shares, authorized (shares)	900,000,000	900,000,000	900,000,000
Common Shares, issued (shares)	797,500,000	797,500,000	797,500,000
Common Shares, treasury shares (shares)	211,900,000	212,900,000	212,900,000
Serial Preferred Stock
Preferred Stock, Shares Authorized (shares)	20,000,000	20,000,000	20,000,000
Series B Preferred Stock | Serial Preferred Stock
Preferred Stock, No Par Value	$ 0	$ 0	$ 0
Preferred Stock, Shares Authorized (shares)	500,000	500,000	500,000
Preferred Stock, Shares Issued (shares)	500,000	500,000	500,000
Preferred Stock, Shares Outstanding (shares)	500,000	500,000	500,000
Preferred Stock, Liquidation Preference Per Share (USD per share)	$ 1,000	$ 1,000	$ 1,000

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Serial Preferred Stock	Preferred Shares, No Par Value	Common Shares, $1.00 Par Value	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss) Attributable to Progressive	Series B Preferred StockSerial Preferred Stock	Voting Preference Shares
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 53.750
Balance, Beginning of period at Dec. 31, 2018			$ 493.9	$ 583.2	$ 1,479	$ 8,386.6	$ (120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 2,899.5					2,899.5
Treasury shares purchased				(1.2)	(3.1)	(83.8)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(175)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $53.750, and $53.750 per share)						(26.8)
Reinvested dividends on restricted stock units					1.3	(1.3)
Net restricted equity awards issued/vested				2.6	(2.6)
Amortization of equity-based compensation					64.7
Adjustment to carrying amount of redeemable noncontrolling interest	0.2				(0.2)
Attributable to noncontrolling interest	(5.8)						(5.8)
Other comprehensive income							637.2
Other, net						(4)
Balance, End of period at Sep. 30, 2019	14,123.3		493.9	584.6	1,539.1	10,995.2	510.5
Balance, Beginning of period at Dec. 31, 2018			493.9	583.2	1,479	8,386.6	(120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to carrying amount of redeemable noncontrolling interest	0.3
Attributable to noncontrolling interest	(4.6)
Balance, End of period at Dec. 31, 2019	$ 13,673.2		493.9	584.6	1,573.4	10,679.6	341.7
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2019			493.9	584.1	1,523.3	10,276.4	453.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 841.7					841.7
Treasury shares purchased				(0.7)	(2)	(57)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $53.750, and $53.750 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Net restricted equity awards issued/vested				1.2	(1.2)
Amortization of equity-based compensation					18.6
Adjustment to carrying amount of redeemable noncontrolling interest					0
Attributable to noncontrolling interest	(0.9)						(0.9)
Other comprehensive income							58.3
Other, net						6.3
Balance, End of period at Sep. 30, 2019	$ 14,123.3		493.9	584.6	1,539.1	10,995.2	510.5
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000	5,000,000
Preferred Stock, Shares Issued (shares)								500,000	0
Common Shares, par value (USD per share)	$ 1
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000
Preferred Stock, Shares Issued (shares)								500,000
Common Shares, par value (USD per share)	1
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 53.750
Balance, Beginning of period at Dec. 31, 2019	$ 13,673.2		493.9	584.6	1,573.4	10,679.6	341.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	4,020.3					4,020.3
Treasury shares purchased				(0.9)	(2.5)	(71.1)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(175.3)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $53.750, and $53.750 per share)						(26.8)
Reinvested dividends on restricted stock units					1.1	(1.1)
Net restricted equity awards issued/vested				1.9	(1.9)
Amortization of equity-based compensation					61.9
Adjustment to carrying amount of redeemable noncontrolling interest	0				(2.6)
Attributable to noncontrolling interest	0						2.7
Other comprehensive income							606.2
Other, net						2.1
Balance, End of period at Sep. 30, 2020	$ 18,087.2		493.9	585.6	1,629.4	14,427.7	950.6
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2020			493.9	585.4	1,614.5	13,001.8	975
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 1,530.8					1,530.8
Treasury shares purchased				(0.5)	(1.5)	(43.4)
Cash dividends declared on common shares ($0.10, $0.10, $0.30, and $0.30 per share)						(58.5)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $26.875, $53.750, and $53.750 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Net restricted equity awards issued/vested				0.7	(0.7)
Amortization of equity-based compensation					16.7
Adjustment to carrying amount of redeemable noncontrolling interest					0
Attributable to noncontrolling interest	0						0
Other comprehensive income							(24.4)
Other, net						10.8
Balance, End of period at Sep. 30, 2020	$ 18,087.2		$ 493.9	$ 585.6	$ 1,629.4	$ 14,427.7	$ 950.6
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000	5,000,000
Preferred Stock, Shares Issued (shares)								500,000	0
Common Shares, par value (USD per share)	$ 1

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Statement of Cash Flows [Abstract]
Net income	$ 4,020.3	$ 2,905.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	201.2	171
Amortization of intangible assets	42.8	51.7
Net amortization of fixed-income securities	72.4	14.1
Amortization of equity-based compensation	61.9	64.7
Net realized (gains) losses on securities	(869.8)	(659.8)
Net (gains) losses on disposition of property and equipment	4.8	(0.1)
Changes in:
Premiums receivable	(1,067)	(1,190.1)
Reinsurance recoverables	(608.4)	(602.3)
Prepaid reinsurance premiums	163.1	(149.1)
Deferred acquisition costs	(208.5)	(142.1)
Income taxes	(78.1)	179.7
Unearned premiums	1,810.5	1,840
Loss and loss adjustment expense reserves	1,483.8	1,969.2
Accounts payable, accrued expenses, and other liabilities	319.7	920.5
Other, net	9.6	(239.4)
Net cash provided by operating activities	5,358.3	5,133.4
Purchases:
Fixed maturities	(25,974.9)	(20,105.3)
Equity securities	(781.8)	(291.9)
Sales:
Fixed maturities	18,412.9	12,112.9
Equity securities	396.2	175.7
Maturities, paydowns, calls, and other:
Fixed maturities	5,766.8	4,236.7
Fixed maturities	79	22.8
Net (purchases) sales of short-term investments	(2,844.1)	356.8
Net unsettled security transactions	457.3	280.6
Purchases of property and equipment	(176.4)	(281.2)
Sales of property and equipment	13.5	39.9
Net cash used in investing activities	(4,651.5)	(3,453)
Cash Flows From Financing Activities
Dividends paid to common shareholders	(1,492.4)	(1,584.7)
Dividends paid to preferred shareholders	(26.8)	(26.8)
Acquisition of treasury shares for restricted stock tax liabilities	(67)	(81.2)
Payments for Repurchase of Common Stock in the Open Market	(7.5)	(6.9)
Acquisition of additional shares of ARX Holding Corp.	243	11.2
Net proceeds from debt issuances	986.3	0
Proceeds from exercise of equity options	7.3	1.6
Net cash used in financing activities	(843.1)	(1,709.2)
Decrease in cash, cash equivalents, and restricted cash	(136.3)	(28.8)
Cash, cash equivalents, and restricted cash – January 1	227.4	75
Cash, cash equivalents, and restricted cash – September 30	$ 91.1	$ 46.2

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying consolidated financial statements include the accounts of The Progressive Corporation, its wholly owned insurance and non-insurance subsidiaries, and affiliates. On April 1, 2020, The Progressive Corporation acquired the remaining outstanding stock of ARX Holding Corp. (ARX), bringing Progressive’s ownership interest of the outstanding capital stock of ARX to 100.0%, compared to 87.1% at September 30, 2019 and December 31, 2019. See Note 12 – Redeemable Noncontrolling Interest for further discussion. The consolidated financial statements reflect all normal recurring adjustments that, in the opinion of management, were necessary for a fair statement of the results for the interim periods presented. The results of operations for the period ended September 30, 2020, are not necessarily indicative of the results expected for the full year. These consolidated financial statements and the notes thereto should be read in conjunction with Progressive’s audited financial statements and accompanying notes included in Exhibit 13 to our Annual Report on Form 10-K for the year ended December 31, 2019 (“2019 Annual Report to Shareholders”). We perform analyses to evaluate our premium receivables for expected credit losses. As part of these analyses, we determine historical collectability rates and modify those rates based on current economic assumptions, to establish estimates on default. These rates are applied to the stratified subsets of our consumer receivable balances, based on the age of the receivable, to establish an allowance for credit loss. Progressive’s premiums receivable are short-term in nature and, generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk. The following table summarizes changes in our allowance for credit loss exposure on our premium receivables: (millions) Three Months Ended September 30, 2020 Nine Months Ended September 30, 2020 Allowance for credit loss, beginning of period $ 437.9 $ 283.2 Increase (decrease) in allowance 1 (3.6) 362.9 Write-offs 2 (121.1) (332.9) Allowance for credit loss, end of period $ 313.2 $ 313.2 1 Represents the incremental period increase (decrease) in other underwriting expenses. 2 Represents portion of allowance that is reversed when premium receivables are written off. To measure the amount of potential credit losses on our premiums receivable balances, we analyze our ultimate at-risk exposure of the receivables and apply actuarially determined factors to calculate our estimated credit loss based on historical and current collections experience, taking into account any unusual circumstances, such as moratoriums or other programs that may suspend collections. During the first and second quarters of 2020, we estimated the allowance for credit losses considering the impact from the moratoriums and billing leniency efforts that we put in place from mid-March through mid-May 2020, to help policyholders who may have been experiencing financial hardships as a result of the spread of the novel coronavirus, COVID-19, and federal, state, and local social distancing and shelter-in-place restrictions (“COVID-19 restrictions”). During the third quarter, we reduced the allowance based on the actual collections that were recognized once the moratoriums and billing leniency efforts were lifted. Premiums receivable balances are written off once we have exhausted our collection efforts. Other assets on the consolidated balance sheets include certain long-lived assets that are considered “ held for sale. ” The fair value of these held for sale assets, less the estimated sales costs, was $27.1 million at September 30, 2020, $43.7 million at September 30, 2019, and $32.9 million at December 31, 2019. Included on our consolidated balance sheets are certain operating leases for office space, computer equipment, and vehicles. The leased assets represent our right to use an underlying asset for the lease term and are included as a component of other assets, and the lease liabilities, represent our obligation to make lease payments arising from the leases and are included as a component of accounts payable, accrued expenses, and other liabilities. The following table summarizes the carrying amounts of our operating leased assets and liabilities: (millions) September 30, 2020 September 30, 2019 December 31, 2019 Operating lease assets $ 174.1 $ 190.5 $ 188.2 Operating lease liabilities 186.2 204.1 201.5 Note 13 – Leases in our 2019 Annual Report to Shareholders for further discussion.

Investments

Investments	9 Months Ended
	Sep. 30, 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. During the third quarter 2020, the portfolio’s valuation rose as markets continued to recover from their first quarter declines. ($ in millions) Cost Gross Gross Net Fair % of September 30, 2020 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,835.1 $ 370.3 $ (1.6) $ 0 $ 10,203.8 22.3 % State and local government obligations 4,382.1 148.2 (0.5) 0 4,529.8 9.9 Corporate debt securities 10,038.7 574.7 (3.6) 2.2 10,612.0 23.2 Residential mortgage-backed securities 525.4 7.0 (1.4) 0 531.0 1.2 Commercial mortgage-backed securities 5,964.4 117.1 (27.9) 0 6,053.6 13.2 Other asset-backed securities 4,155.8 46.8 (2.3) 0 4,200.3 9.2 Redeemable preferred stocks 181.3 2.5 (3.2) 2.4 183.0 0.4 Total fixed maturities 35,082.8 1,266.6 (40.5) 4.6 36,313.5 79.4 Short-term investments 4,667.8 0 0 0 4,667.8 10.2 Total available-for-sale securities 39,750.6 1,266.6 (40.5) 4.6 40,981.3 89.6 Equity securities: Nonredeemable preferred stocks 1,302.7 0 0 20.5 1,323.2 2.9 Common equities 1,130.0 0 0 2,329.8 3,459.8 7.5 Total equity securities 2,432.7 0 0 2,350.3 4,783.0 10.4 Total portfolio 1,2 $ 42,183.3 $ 1,266.6 $ (40.5) $ 2,354.9 $ 45,764.3 100.0 % ($ in millions) Cost Gross Gross Net Fair % of September 30, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,387.6 $ 300.3 $ (9.2) $ 0 $ 13,678.7 35.4 % State and local government obligations 1,652.2 32.6 (1.1) 0 1,683.7 4.4 Corporate debt securities 7,048.9 231.6 (0.4) 1.0 7,281.1 18.9 Residential mortgage-backed securities 677.5 5.5 (1.5) 0 681.5 1.8 Commercial mortgage-backed securities 4,547.9 93.0 (1.9) 0 4,639.0 12.0 Other asset-backed securities 4,601.0 21.5 (0.6) 0 4,621.9 12.0 Redeemable preferred stocks 219.8 4.4 (2.5) 5.1 226.8 0.6 Total fixed maturities 32,134.9 688.9 (17.2) 6.1 32,812.7 85.1 Short-term investments 1,467.4 0 0 0 1,467.4 3.8 Total available-for-sale securities 33,602.3 688.9 (17.2) 6.1 34,280.1 88.9 Equity securities: Nonredeemable preferred stocks 1,054.2 0 0 74.3 1,128.5 2.9 Common equities 1,210.3 0 0 1,954.8 3,165.1 8.2 Total equity securities 2,264.5 0 0 2,029.1 4,293.6 11.1 Total portfolio 1,2 $ 35,866.8 $ 688.9 $ (17.2) $ 2,035.2 $ 38,573.7 100.0 % ($ in millions) Cost Gross Gross Net Fair % of 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 1,2 $ 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 September 30, 2020, we had $469.2 million in other liabilities, compared to $286.5 million and $11.9 million at September 30, 2019 and December 31, 2019, respectively. 2 The total fair value of the portfolio at September 30, 2020 and 2019, and December 31, 2019, included $2.8 billion, $1.5 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. At September 30, 2020, bonds and certificates of deposit in the principal amount of $281.1 million were on deposit to meet state insurance regulatory requirements. We did not hold any securities of any one issuer, excluding U.S. government obligations, with an aggregate cost or fair value exceeding 10% of total shareholders’ equity at September 30, 2020 and 2019, or December 31, 2019. At September 30, 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. Although we invest in repurchase and reverse repurchase transactions from time to time, we did not have any open positions at September 30, 2020 or December 31, 2019, and had $400.0 million in open reverse repurchase positions at September 30, 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 Included in our fixed-maturity securities are hybrid securities, which are reported at fair value: September 30, (millions) 2020 2019 December 31, 2019 Fixed maturities: State and local government obligations $ 0 $ 3.5 $ 3.5 Corporate debt securities 101.0 91.3 91.2 Other asset-backed securities 18.7 3.0 2.6 Redeemable preferred stocks 122.5 90.7 92.1 Total hybrid securities $ 242.2 $ 188.5 $ 189.4 Certain securities in our 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. 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 realized gains or losses. Fixed Maturities The composition of fixed maturities by maturity at September 30, 2020, was: (millions) Cost Fair Value Less than one year $ 5,794.9 $ 5,827.6 One to five years 19,507.0 20,100.9 Five to ten years 9,319.7 9,900.1 Ten years or greater 461.2 484.9 Total $ 35,082.8 $ 36,313.5 Asset-backed securities are classified in the maturity distribution table based upon their projected cash flows. All other securities, which do not have a single maturity date, are reported based upon expected average maturity. Contractual maturities may differ from expected maturities because the issuers of the securities may have the right to call or prepay obligations. Gross Unrealized Losses The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized September 30, 2020 Fixed maturities: U.S. government obligations 13 $ 1,993.8 $ (1.6) 13 $ 1,993.8 $ (1.6) 0 $ 0 $ 0 State and local government obligations 45 320.1 (0.5) 45 320.1 (0.5) 0 0 0 Corporate debt securities 28 537.8 (3.6) 28 537.8 (3.6) 0 0 0 Residential mortgage-backed securities 28 86.7 (1.4) 9 38.7 (1.0) 19 48.0 (0.4) Commercial mortgage-backed securities 77 1,794.8 (27.9) 46 1,170.4 (17.3) 31 624.4 (10.6) Other asset-backed securities 22 191.5 (2.3) 11 146.5 (2.1) 11 45.0 (0.2) Redeemable preferred stocks 1 9.3 (3.2) 0 0 0 1 9.3 (3.2) Total fixed maturities 214 $ 4,934.0 $ (40.5) 152 $ 4,207.3 $ (26.1) 62 $ 726.7 $ (14.4) 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 September 30, 2019 Fixed maturities: U.S. government obligations 14 $ 2,708.0 $ (9.2) 7 $ 2,534.4 $ (8.9) 7 $ 173.6 $ (0.3) State and local government obligations 60 228.3 (1.1) 25 100.4 (0.7) 35 127.9 (0.4) Corporate debt securities 24 245.5 (0.4) 5 77.2 (0.1) 19 168.3 (0.3) Residential mortgage-backed securities 39 301.0 (1.5) 5 138.7 (0.1) 34 162.3 (1.4) Commercial mortgage-backed securities 48 743.3 (1.9) 26 361.9 (0.8) 22 381.4 (1.1) Other asset-backed securities 55 529.4 (0.6) 20 359.1 (0.2) 35 170.3 (0.4) Redeemable preferred stocks 3 57.2 (2.5) 2 45.9 (1.3) 1 11.3 (1.2) Total fixed maturities 243 $ 4,812.7 $ (17.2) 90 $ 3,617.6 $ (12.1) 153 $ 1,195.1 $ (5.1) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized December 31, 2019 Fixed maturities: 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) For securities in the table, during the third quarter 2020, we had no securities with credit rating upgrades and four securities that had their credit ratings downgraded, including two state and local government obligations and two commercial mortgage-backed securities, with a combined fair value of $47.5 million and an unrealized loss of $1.5 million as of September 30, 2020. A review of all securities in the table above indicated that the issuers were current with respect to their interest obligations and that there was no evidence of significant 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 for the first nine months of 2020 and did not have a credit loss allowance balance as of September 30, 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 intended 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 net present value 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 realized gains (losses). As of September 30, 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 September 30, 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 September 30, 2020. Realized Gains (Losses) The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2020 2019 2020 2019 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 90.2 $ 41.5 $ 565.8 $ 113.0 State and local government obligations 43.9 1.8 58.9 4.0 Corporate and other debt securities 58.8 21.3 125.5 68.5 Residential mortgage-backed securities 0 0 0 0.2 Commercial mortgage-backed securities 5.0 2.6 15.4 6.2 Other asset-backed securities 0.2 0.1 0.2 0.8 Total available-for-sale securities 198.1 67.3 765.8 192.7 Equity securities: Nonredeemable preferred stocks 0.3 3.6 20.0 20.2 Common equities 2.0 4.7 77.1 9.4 Total equity securities 2.3 8.3 97.1 29.6 Subtotal gross realized gains on security sales 200.4 75.6 862.9 222.3 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (1.5) (1.5) (4.8) (13.9) State and local government obligations 0 0 0 (0.7) Corporate and other debt securities 0 (0.2) (6.5) (7.7) Residential mortgage-backed securities 0 0 0 (2.3) Commercial mortgage-backed securities (2.9) 0 (12.7) (2.1) Other asset-backed securities 0 0 0 (0.1) Redeemable preferred stocks 0 (0.2) 0 (0.3) Total available-for-sale securities (4.4) (1.9) (24.0) (27.1) Equity securities: Nonredeemable preferred stocks (0.1) (2.0) (7.5) (2.0) Common equities 0 0 (60.3) (7.9) Total equity securities (0.1) (2.0) (67.8) (9.9) Subtotal gross realized losses on security sales (4.5) (3.9) (91.8) (37.0) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 88.7 40.0 561.0 99.1 State and local government obligations 43.9 1.8 58.9 3.3 Corporate and other debt securities 58.8 21.1 119.0 60.8 Residential mortgage-backed securities 0 0 0 (2.1) Commercial mortgage-backed securities 2.1 2.6 2.7 4.1 Other asset-backed securities 0.2 0.1 0.2 0.7 Redeemable preferred stocks 0 (0.2) 0 (0.3) Total available-for-sale securities 193.7 65.4 741.8 165.6 Equity securities: Nonredeemable preferred stocks 0.2 1.6 12.5 18.2 Common equities 2.0 4.7 16.8 1.5 Total equity securities 2.2 6.3 29.3 19.7 Subtotal net realized gains (losses) on security sales 195.9 71.7 771.1 185.3 Net holding period gains (losses) Hybrid securities 3.2 4.2 (3.2) 16.3 Equity securities 333.5 27.6 101.9 520.6 Subtotal net holding period gains (losses) 336.7 31.8 98.7 536.9 Impairment losses Other asset impairment 0 (38.1) 0 (62.4) Subtotal impairment losses 0 (38.1) 0 (62.4) Total net realized gains (losses) on securities $ 532.6 $ 65.4 $ 869.8 $ 659.8 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. The sales in our common stock portfolio were the result of rebalancing the indexed equity portfolio. In addition, during the third quarter 2020, our common and nonredeemable preferred stocks’ valuations continued to experience a significant recovery. For 2019, 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, 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 three and nine months ended September 30, 2020 and 2019, for equity securities held at the respective quarter end: Three Months Nine Months (millions) 2020 2019 2020 2019 Total net gains (losses) recognized during the period on equity securities $ 335.7 $ 33.9 $ 131.2 $ 540.3 Less: Net gains (losses) recognized on equity securities sold during the period 2.2 6.3 29.3 19.7 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 333.5 $ 27.6 $ 101.9 $ 520.6 Net Investment Income The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2020 2019 2020 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 36.7 $ 75.8 $ 135.0 $ 198.7 State and local government obligations 18.5 8.7 44.2 26.9 Corporate debt securities 76.6 65.1 211.2 209.8 Residential mortgage-backed securities 0.8 5.4 8.8 16.6 Commercial mortgage-backed securities 37.3 35.6 114.2 100.7 Other asset-backed securities 22.6 31.4 76.6 85.5 Redeemable preferred stocks 2.5 3.9 12.5 16.1 Total fixed maturities 195.0 225.9 602.5 654.3 Short-term investments 6.2 7.1 26.9 34.3 Total available-for-sale securities 201.2 233.0 629.4 688.6 Equity securities: Nonredeemable preferred stocks 15.8 15.9 44.3 47.3 Common equities 13.5 14.1 41.8 41.3 Total equity securities 29.3 30.0 86.1 88.6 Investment income 230.5 263.0 715.5 777.2 Investment expenses (4.7) (5.9) (14.5) (18.3) Net investment income $ 225.8 $ 257.1 $ 701.0 $ 758.9 The amount of investment income (interest and dividends) we earn varies based on the average assets held during the year and the book yields of the securities in our portfolio. On a year-over-year basis, investment income decreased 12% for the third quarter and 8% for the first nine months, compared to the same periods last year, due to a decrease in the portfolio yield, which was partially offset by an increase in average assets. The recurring investment book yield decreased about 25% in the third quarter 2020 and 21% for the first nine months of 2020, compared to the same period in 2019, as a result of investing cash from operations and reinvesting cash from sales, maturities, paydowns, and other redemptions at market yields that were significantly lower than the portfolio’s overall yield. The income reduction from the negative yield change was partially offset by an increase in income earned as a result of investing the $1.0 billion of proceeds from the debt issued during March 2020, as well as strong premium growth and underwriting profitability, net of common and preferred stock dividends. The portfolio’s duration at September 30, 2020 was 3.0 years, compared to 2.9 years at September 30, 2019. The decrease in investment expenses for both periods in 2020, compared to 2019, primarily reflects lower expenses incurred due to our decision to no longer maintain an actively managed portfolio, and lower incentive-based compensation recognized.

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 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 September 30, 2020 Fixed maturities: U.S. government obligations $ 10,203.8 $ 0 $ 0 $ 10,203.8 $ 9,835.1 State and local government obligations 0 4,529.8 0 4,529.8 4,382.1 Corporate debt securities 0 10,612.0 0 10,612.0 10,038.7 Subtotal 10,203.8 15,141.8 0 25,345.6 24,255.9 Asset-backed securities: Residential mortgage-backed 0 531.0 0 531.0 525.4 Commercial mortgage-backed 0 6,053.6 0 6,053.6 5,964.4 Other asset-backed 0 4,200.3 0 4,200.3 4,155.8 Subtotal asset-backed securities 0 10,784.9 0 10,784.9 10,645.6 Redeemable preferred stocks: Financials 0 49.2 0 49.2 51.2 Utilities 0 11.3 0 11.3 10.0 Industrials 10.1 112.4 0 122.5 120.1 Subtotal redeemable preferred stocks 10.1 172.9 0 183.0 181.3 Total fixed maturities 10,213.9 26,099.6 0 36,313.5 35,082.8 Short-term investments 4,506.2 161.6 0 4,667.8 4,667.8 Total available-for-sale securities 14,720.1 26,261.2 0 40,981.3 39,750.6 Equity securities: Nonredeemable preferred stocks: Financials 112.6 1,096.1 38.1 1,246.8 1,222.7 Utilities 0 40.7 0 40.7 39.9 Industrials 0 20.5 15.2 35.7 40.1 Subtotal nonredeemable preferred stocks 112.6 1,157.3 53.3 1,323.2 1,302.7 Common equities: Common stocks 3,457.1 0 0 3,457.1 1,127.3 Other risk investments 0 0 2.7 2.7 2.7 Subtotal common equities 3,457.1 0 2.7 3,459.8 1,130.0 Total equity securities 3,569.7 1,157.3 56.0 4,783.0 2,432.7 Total portfolio $ 18,289.8 $ 27,418.5 $ 56.0 $ 45,764.3 $ 42,183.3 Debt $ 0 $ 6,687.4 $ 0 $ 6,687.4 $ 5,395.4 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2019 Fixed maturities: U.S. government obligations $ 13,678.7 $ 0 $ 0 $ 13,678.7 $ 13,387.6 State and local government obligations 0 1,683.7 0 1,683.7 1,652.2 Corporate debt securities 0 7,281.1 0 7,281.1 7,048.9 Subtotal 13,678.7 8,964.8 0 22,643.5 22,088.7 Asset-backed securities: Residential mortgage-backed 0 681.5 0 681.5 677.5 Commercial mortgage-backed 0 4,639.0 0 4,639.0 4,547.9 Other asset-backed 0 4,621.9 0 4,621.9 4,601.0 Subtotal asset-backed securities 0 9,942.4 0 9,942.4 9,826.4 Redeemable preferred stocks: Financials 0 51.7 0 51.7 51.7 Utilities 0 10.9 0 10.9 10.0 Industrials 11.2 153.0 0 164.2 158.1 Subtotal redeemable preferred stocks 11.2 215.6 0 226.8 219.8 Total fixed maturities 13,689.9 19,122.8 0 32,812.7 32,134.9 Short-term investments 1,464.9 2.5 0 1,467.4 1,467.4 Total available-for-sale securities 15,154.8 19,125.3 0 34,280.1 33,602.3 Equity securities: Nonredeemable preferred stocks: Financials 82.2 967.1 27.1 1,076.4 1,004.3 Utilities 0 42.1 0 42.1 39.9 Industrials 0 5.0 5.0 10.0 10.0 Subtotal nonredeemable preferred stocks 82.2 1,014.2 32.1 1,128.5 1,054.2 Common equities: Common stocks 3,164.8 0 0 3,164.8 1,210.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,164.8 0 0.3 3,165.1 1,210.3 Total equity securities 3,247.0 1,014.2 32.4 4,293.6 2,264.5 Total portfolio $ 18,401.8 $ 20,139.5 $ 32.4 $ 38,573.7 $ 35,866.8 Debt $ 0 $ 5,113.3 $ 0 $ 5,113.3 $ 4,406.5 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 available-for-sale securities 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 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 September 30, 2020, vendor-quoted prices represented 75% of our Level 1 classifications (excluding short-term investments), compared to 81% and 80% at September 30, 2019 and December 31, 2019, respectively. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded, and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. At September 30, 2020 and 2019, and December 31, 2019, vendor-quoted prices comprised 99% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented the remaining 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 at least 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 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 explain significant price changes (i.e., greater than 2%) as known events occur in the marketplace and affect a 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 September 30, 2020 and 2019, and December 31, 2019, we did not have any securities in our fixed-maturity portfolio listed as Level 3. At September 30, 2020, we held four private nonredeemable preferred securities that were priced internally or by a pricing firm, compared to two securities at September 30, 2019 and three securities at December 31, 2019. At September 30, 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 both September 30, 2019 and 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 and 2019, there were no material assets or liabilities measured at fair value on a nonrecurring basis. During the second quarter 2020, we purchased a new Level 3 nonredeemable preferred security and we determined that the fair value at September 30, 2020 should continue to be the unadjusted purchase price. The remaining Level 3 nonredeemable preferred securities were priced in-house, using a capitalization-based model of similarly structured public company competitors and a weighted average capitalization formula (i.e., guideline public company method) to calculate a valuation change for our securities. We utilized this methodology at March 31, 2020, rather than having our external pricing source update their valuation models, due to the timing of the market decline relative to the end of the first quarter. Based on subsequent market evaluations, we determined the same valuation methodology was still appropriate at both June 30, and September 30, 2020. Based on our review, all prices received from external sources for 2019 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 three and nine months ended September 30, 2020 and 2019: Level 3 Fair Value (millions) Fair Value at June 30, 2020 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 38.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 38.1 Industrials 15.2 0 0 0 0 0 0 15.2 Common equities: Other risk investments 0.3 0 2.4 0 0 0 0 2.7 Total Level 3 securities $ 53.6 $ 0 $ 2.4 $ 0 $ 0 $ 0 $ 0 $ 56.0 Level 3 Fair Value (millions) Fair Value at June 30, 2019 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 32.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 32.4 Level 3 Fair Value (millions) Fair Value at December 31, 2019 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 25.0 $ 0 $ 0 $ (14.0) $ 0 $ 38.1 Industrials 16.0 0 0 0 0 (0.8) 0 15.2 Common equities: Other risk investments 0.3 0 2.4 0 0 0 0 2.7 Total Level 3 securities $ 43.4 $ 0 $ 27.4 $ 0 $ 0 $ (14.8) $ 0 $ 56.0 Level 3 Fair Value (millions) Fair Value at December 31, 2018 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 30.4 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 32.4 The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2020 and 2019, and December 31, 2019: Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2020 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials $ 13.1 Guideline public company method Weighted average capitalization % (51.5) Financials 1 25.0 Internal price Unadjusted purchase price per share 3.7 Industrials 15.2 Guideline public company method Weighted average capitalization % (19.2) Subtotal Level 3 securities 53.3 Pricing exemption securities 2.7 Total Level 3 securities $ 56.0 1 The security was purchased in May 2020 and the valuation remained the same at September 30, 2020. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 27.1 Internal price Unadjusted purchase price per share 9.0 Industrials 5.0 Internal price Price-to-sales ratio 5.5 Subtotal Level 3 securities 32.1 Pricing exemption securities 0.3 Total Level 3 securities $ 32.4 1 The security was purchased in December 2018. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at December 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 1 The security was purchased in November 2019.

Debt

Debt	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt	Debt — Debt at each of the balance sheet periods consisted of: September 30, 2020 September 30, 2019 December 31, 2019 (millions) Carrying Fair Carrying Fair Carrying Fair 3.75% Senior Notes due 2021 $ 499.7 $ 515.3 $ 499.3 $ 516.5 $ 499.4 $ 515.6 2.45% Senior Notes due 2027 497.2 532.0 496.8 502.1 496.9 501.5 6 5/8% Senior Notes due 2029 296.8 411.4 296.5 392.2 296.6 392.5 4.00% Senior Notes due 2029 545.3 662.5 544.9 617.0 545.0 614.3 3.20% Senior Notes due 2030 496.0 572.4 0 0 0 0 6.25% Senior Notes due 2032 395.9 587.2 395.7 547.2 395.7 552.6 4.35% Senior Notes due 2044 346.7 450.5 346.6 414.7 346.7 417.0 3.70% Senior Notes due 2045 395.5 473.5 395.4 431.8 395.4 434.2 4.125% Senior Notes due 2047 841.7 1,078.5 841.5 987.4 841.6 986.1 4.20% Senior Notes due 2048 590.0 775.3 589.8 704.4 589.8 705.8 3.95% Senior Notes due 2050 490.6 628.8 0 0 0 0 Total $ 5,395.4 $ 6,687.4 $ 4,406.5 $ 5,113.3 $ 4,407.1 $ 5,119.6 The Progressive Corporation issued $500 million of 3.20% Senior Notes due 2030 (the “3.20% Senior Notes”) and $500 million of 3.95% Senior Notes due 2050 (the “3.95% Senior Notes”) in March 2020, in an underwritten public offering. The net proceeds from the issuances, after deducting underwriters’ discounts, commissions, and other issuance costs, were approximately $986.3 million in aggregate. Consistent with the other senior notes issued by Progressive, interest on the 3.20% and 3.95% Senior Notes is payable semiannually, principal is due at maturity, and the notes are redeemable, in whole or in part, at any time, subject to treasury “make whole” provisions. During the second quarter 2020, The Progressive Corporation renewed the line of credit with PNC Bank, National Association (PNC), in the maximum principal amount of $250 million, that expired in April 2020. 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. The line of credit is uncommitted and, as such, all advances are subject to PNC’s discretion. We had no borrowings under either line of credit during the periods presented.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes — Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. We review our deferred tax assets regularly for recoverability. At September 30, 2020 and 2019, and December 31, 2019, we determined that we did not need a valuation allowance on our gross deferred tax assets. Although realization of the deferred tax assets is not assured, management believes that it is more likely than not the deferred tax assets will be realized based on our expectation that we will be able to fully utilize the deductions that are ultimately recognized for tax purposes. For the nine months ended September 30, 2020, there have been no material changes in our reserve for uncertain tax positions. The effective tax rate for the three and nine months ended September 30, 2020, was 20.4% and 20.7%, respectively, compared to 16.5% and 24.0% for the same periods last year. For the three months ended September 30, 2019, the lower effective rate was due primarily to renewable energy investment tax credits and the vesting of employee stock based compensation awards. For the nine months ended September 30, 2019, the higher effective rate was due primarily to the reversal of certain tax credits, unrelated to those impacting the quarter, and other tax benefits previously recognized from certain renewable energy investments, where the sponsor pled guilty to fraud through these investments and the tax credits and other benefits related to those investments were not valid. See Note 5 – Income Taxes in our 2019 Annual Report to Shareholders for further discussion.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	9 Months Ended
	Sep. 30, 2020
Loss and Loss Adjustment Expenses Reserves [Abstract]
Loss and Loss Adjustment Expenses Reserves	Loss and Loss Adjustment Expense Reserves — Activity in the loss and loss adjustment expense reserves is summarized as follows: September 30, (millions) 2020 2019 Balance at January 1 $ 18,105.4 $ 15,400.8 Less reinsurance recoverables on unpaid losses 3,212.2 2,572.7 Net balance at January 1 14,893.2 12,828.1 Incurred related to: Current year 18,073.6 18,108.2 Prior years 116.1 215.2 Total incurred 18,189.7 18,323.4 Paid related to: Current year 10,615.2 10,864.9 Prior years 6,682.8 6,061.7 Total paid 17,298.0 16,926.6 Net balance at September 30 15,784.9 14,224.9 Plus reinsurance recoverables on unpaid losses 3,804.3 3,145.1 Balance at September 30 $ 19,589.2 $ 17,370.0 We experienced unfavorable reserve development of $116.1 million and $215.2 million during the first nine months of 2020 and 2019, respectively, which is reflected as “Incurred related to prior years ” in the table above. Year-to-date September 30, 2020 • Approximately 80% of the unfavorable prior year reserve development was attributable to accident year 2018, with the remainder primarily related to accident year 2017 and prior accident years. During the second and third quarter 2020, we experienced favorable development on accident year 2019, primarily due to higher than anticipated salvage and subrogation recoveries, which almost fully offset the unfavorable development related to accident year 2019 we experienced during the first quarter 2020. • Our personal auto products incurred about $47 million of unfavorable loss and loss adjustment expense (LAE) reserve development, with the Agency and Direct auto business each contributing about half. The unfavorable LAE development was primarily attributable to revised estimates of our per claim settlement costs taken during the first quarter. We also experienced higher than anticipated frequency of reopened personal injury protection (PIP) claims, primarily in Florida, and late reported losses occurring toward the end 2019 but not reported until 2020, which was partially offset by higher than anticipated salvage and subrogation recoveries. • Our Commercial Lines business experienced about $104 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 $22 million and $13 million, respectively, of favorable development. Year-to-date September 30, 2019 • About 50% of the unfavorable prior year reserve development was attributable to accident year 2018, 30% to accident year 2017, and the remainder to accident years 2016 and prior. • Our personal auto products incurred about $108 million of unfavorable loss and LAE reserve development, with the Agency and Direct auto businesses each contributing about half. The unfavorable development was primarily attributable to 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 $71 million of unfavorable development, primarily due to increased injury severity and more emergence of large injury claims than originally anticipated. • Our Property business experienced about $19 million of unfavorable development, primarily due to higher than originally anticipated homeowner and dwelling costs and fire liability costs. • Our special lines business experienced about $17 million of unfavorable development, primarily due to less salvage and subrogation recoveries than originally anticipated.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information — Cash and cash equivalents include bank demand deposits and daily overnight reverse repurchase commitments used to safeguard funds held in those bank demand deposit accounts, and are not considered part of the investment portfolio. The amount of these reverse repurchase commitments held at September 30, 2020 and 2019, and December 31, 2019, were $77.2 million, $62.8 million, and $46.3 million, respectively. Restricted cash on our consolidated balance sheets represents cash that is restricted to pay flood claims under the National Flood Insurance Program’s “Write Your Own” program, for which subsidiaries of our Property business are administrators. During the nine months ended September 30, 2020, non-cash activity includes declared but unpaid common share dividends of $58.6 million (see Note 9 – Dividends for further discussion) and changes in operating lease liabilities arising from obtaining right-of-use assets of $48.5 million. We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2020 2019 Income taxes $ 1,079.2 $ 738.7 Interest 168.4 147.3 Operating lease liabilities 66.6 61.2 Our consolidated statement of cash flows for the nine months ended September 30, 2019, was revised to correct the classification of our acquisition of additional shares of ARX from an investing activity to a financing activity; there was no overall impact on the increase in cash, cash equivalents, and restricted cash that was reported for September 30, 2019.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Segment Information	Segment Information — Our Personal Lines segment writes insurance for personal autos and recreational vehicles (our special lines products). Our Commercial Lines segment writes auto-related primary liability and physical damage insurance, general liability, and property insurance, predominately for small businesses. Our Property segment writes residential property insurance for homeowners, other property owners, and renters. Our service businesses provide insurance-related services, including processing Commercial Automobile Insurance Procedures/Plans (CAIP) business and serving as an agent for homeowners, general liability, and workers’ compensation insurance, among other products, through our programs with unaffiliated insurance companies. All segment revenues are generated from external customers; all intercompany transactions are eliminated in consolidation. Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (millions) Revenues Pretax Revenues Pretax Revenues Pretax Revenues Pretax Personal Lines Agency $ 4,001.6 $ 596.5 $ 3,703.4 $ 380.2 $ 11,749.3 $ 1,748.7 $ 10,851.5 $ 1,267.9 Direct 4,309.8 517.6 3,804.0 291.7 12,470.1 1,637.8 11,113.7 940.2 Total Personal Lines 1 8,311.4 1,114.1 7,507.4 671.9 24,219.4 3,386.5 21,965.2 2,208.1 Commercial Lines 1,214.8 155.9 1,106.9 69.7 3,532.8 448.2 3,190.4 360.7 Property 2 447.3 (52.9) 397.9 (9.1) 1,300.6 (192.4) 1,141.1 (35.8) Total underwriting operations 9,973.5 1,217.1 9,012.2 732.5 29,052.8 3,642.3 26,296.7 2,533.0 Fees and other revenues 3 151.8 NA 138.4 NA 434.8 NA 403.4 NA Service businesses 58.8 4.4 51.5 2.8 169.4 14.7 144.1 12.0 Investments 4 763.1 758.4 328.4 322.5 1,585.3 1,570.8 1,437.0 1,418.7 Interest expense NA (56.4) NA (47.5) NA (160.8) NA (142.3) Consolidated total $ 10,947.2 $ 1,923.5 $ 9,530.5 $ 1,010.3 $ 31,242.3 $ 5,067.0 $ 28,281.2 $ 3,821.4 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three and nine months ended September 30, 2020 and 2019; 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 For the three and nine months ended September 30, 2020, pretax profit (loss) includes $14.2 million and $42.8 million, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $15.8 million and $51.7 million for the same periods in 2019. See Note 13 – 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 expense. Our management uses underwriting margin and combined ratio as primary measures of underwriting profitability. Underwriting profitability is calculated by subtracting losses and loss adjustment expenses, policy acquisition costs, other underwriting expenses, and policyholder credits from the total of net premiums earned and fees and other revenues. 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 respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Under-writing Combined Under-writing Combined Under-writing Combined Under-writing Combined Personal Lines Agency 14.9 % 85.1 10.3 % 89.7 14.9 % 85.1 11.7 % 88.3 Direct 12.0 88.0 7.7 92.3 13.1 86.9 8.5 91.5 Total Personal Lines 13.4 86.6 9.0 91.0 14.0 86.0 10.1 89.9 Commercial Lines 12.8 87.2 6.3 93.7 12.7 87.3 11.3 88.7 Property 1 (11.8) 111.8 (2.3) 102.3 (14.8) 114.8 (3.1) 103.1 Total underwriting operations 12.2 87.8 8.1 91.9 12.5 87.5 9.6 90.4 1 Included in the three and nine months ended September 30, 2020, is 3.2 points and 3.3 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 4.0 points and 4.5 points, respectively, for the three and nine months ended September 30, 2019.

Dividends

Dividends	9 Months Ended
	Sep. 30, 2020
Dividends [Abstract]
Dividends	Dividends — Following is a summary of our common and preferred share dividends that were declared and/or paid during the nine months ended September 30, 2020 and 2019: (millions, except per share amounts) Amount Declared Payable Per Share Accrued 1 Common - Quarterly Dividends: 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 Common - Annual Variable Dividends: December 2019 January 2020 2.25 1,316.9 December 2018 February 2019 2.5140 1,467.9 Preferred Dividends: 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 1 The accrual is based on an estimate of shares outstanding as of the record date and is recorded as a component of accounts payable, accrued expenses, and other liabilities on the consolidated balance sheets. See Note 14 – Dividends

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 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, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) Balance at June 30, 2020 $ 1,237.3 $ (262.3) $ 975.0 $ 991.0 $ (16.0) $ 0 Reclassification of disproportionate amounts 0 0 0 0 0 0 Adjusted balance at June 30, 2020 1,237.3 (262.3) 975.0 991.0 (16.0) 0 Other comprehensive income (loss) before reclassifications: Investment securities 163.3 (34.4) 128.9 128.9 0 0 Loss attributable to noncontrolling interest (NCI) 0 0 0 0 0 0 Total other comprehensive income (loss) before reclassifications 163.3 (34.4) 128.9 128.9 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 194.3 (40.8) 153.5 153.5 0 0 Interest expense (0.3) 0.1 (0.2) 0 (0.2) 0 Total reclassification adjustment for amounts realized in net income 194.0 (40.7) 153.3 153.5 (0.2) 0 Total other comprehensive income (loss) (30.7) 6.3 (24.4) (24.6) 0.2 0 Balance at September 30, 2020 $ 1,206.6 $ (256.0) $ 950.6 $ 966.4 $ (15.8) $ 0 Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) Balance at June 30, 2019 $ 573.6 $ (120.5) $ 453.1 $ 472.9 $ (16.8) $ (3.0) Other comprehensive income (loss) before reclassifications: Investment securities 134.3 (28.2) 106.1 106.1 0 0 Loss attributable to noncontrolling interest (NCI) (1.2) 0.3 (0.9) 0 0 (0.9) Total other comprehensive income (loss) before reclassifications 133.1 (27.9) 105.2 106.1 0 (0.9) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 60.7 (12.7) 48.0 48.0 0 0 Interest expense (0.3) 0.1 (0.2) 0 (0.2) 0 Total reclassification adjustment for amounts realized in net income 60.4 (12.6) 47.8 48.0 (0.2) 0 Total other comprehensive income (loss) 72.7 (15.3) 57.4 58.1 0.2 (0.9) Balance at September 30, 2019 $ 646.3 $ (135.8) $ 510.5 $ 531.0 $ (16.6) $ (3.9) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) 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 1,447.7 (304.1) 1,143.6 1,143.6 0 0 Loss attributable to noncontrolling interest (NCI) 0 0 0 0 0 0 Total other comprehensive income (loss) before reclassifications 1,447.7 (304.1) 1,143.6 1,143.6 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 681.0 (143.0) 538.0 538.0 0 0 Interest expense (0.8) 0.2 (0.6) 0 (0.6) 0 Total reclassification adjustment for amounts realized in net income 680.2 (142.8) 537.4 538.0 (0.6) 0 Total other comprehensive income (loss) 767.5 (161.3) 606.2 605.6 0.6 0 Balance at September 30, 2020 $ 1,206.6 $ (256.0) $ 950.6 $ 966.4 $ (15.8) $ 0 1 Adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the purchase transaction (See Note 12 – Redeemable Noncontrolling Interest for additional information). Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) 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 953.5 (200.2) 753.3 753.3 0 0 Loss attributable to noncontrolling interest (NCI) (7.4) 1.6 (5.8) 0 0 (5.8) Total other comprehensive income (loss) before reclassifications 946.1 (198.6) 747.5 753.3 0 (5.8) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 147.6 (30.9) 116.7 116.7 0 0 Interest expense (0.8) 0.2 (0.6) 0 (0.6) 0 Total reclassification adjustment for amounts realized in net income 146.8 (30.7) 116.1 116.7 (0.6) 0 Total other comprehensive income (loss) 799.3 (167.9) 631.4 636.6 0.6 (5.8) Balance at September 30, 2019 $ 646.3 $ (135.8) $ 510.5 $ 531.0 $ (16.6) $ (3.9) In an effort to manage interest rate risk, we entered into forecasted transactions on Progressive’s debt issuances prior to 2018. We expect to reclassify $1.0 million (pretax) into interest expense during the next 12 months, related to net unrealized losses on forecasted transactions (see Note 4 – Debt in our 2019 Annual Report to Shareholders for further discussion).

Litigation

Litigation	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Litigation	Litigation — The Progressive Corporation and/or its insurance subsidiaries are named as defendants in various lawsuits arising out of claims made under insurance policies written by our insurance subsidiaries in the ordinary course of business. We consider all legal actions relating to such claims in establishing our loss and loss adjustment expense reserves. In addition, The Progressive Corporation and/or its subsidiaries are named as defendants in a number of class action or individual lawsuits that challenge certain of the operations of the subsidiaries. Other insurance companies face many of these same issues. These cases include those alleging damages as a result of our subsidiaries’ practices in evaluating or paying medical or injury claims or benefits, including, but not limited to, personal injury protection, medical payments, and bodily injury benefits; the utilization, content, or appearance of policy documents; labor rates paid to auto body repair shops; wage and hour issues; and cases challenging other aspects of our subsidiaries’ claims, marketing, or sales practices, or other business operations. Other insurance companies face many of these same issues. The nature and volume of litigation to which The Progressive Corporation is subject is similar to that which was disclosed in Note 12 – Litigation in our 2019 Annual Report to Shareholders. We plan to contest the pending lawsuits vigorously, but may pursue settlement negotiations in some cases, as we deem appropriate. The outcomes of pending cases are uncertain at this time. We establish accruals for these lawsuits when it is probable that a loss has been or will be incurred and we can reasonably estimate potential loss exposure, which may include a range of loss. As to lawsuits for which the loss is considered neither probable or estimable, or 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. With respect to our pending lawsuits that are not related to claims under insurance policies, the accruals that we have established, if any, were not material at September 30, 2020 or 2019, and there were no material settlements during 2019 or the first nine months of 2020. For most of these lawsuits, we do not consider any losses to be both probable and estimable, and we are unable to estimate a meaningful range of loss, if any, at this time, due to the factors discussed in Note 12 – Litigation in our 2019 Annual Report to Shareholders. In the event that any one or more of these lawsuits results in a substantial judgment against or settlement by us, or if our accruals (if any) prove to be inadequate by a significant amount, the resulting liability could have a material adverse effect on our consolidated financial condition, cash flows, and/or results of operations. For a further discussion on our pending litigation and related reserving policies, see Note 12 – Litigation in our 2019 Annual Report to Shareholders.

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest	9 Months Ended
	Sep. 30, 2020
Temporary Equity Disclosure [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. 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. The changes in the components of redeemable NCI were: Nine Months Ended September 30, Year Ended (millions) 2020 2019 December 31, 2019 Balance, beginning of period $ 225.6 $ 214.5 $ 214.5 Net income attributable to NCI 0 5.9 9.7 Other comprehensive income (loss) attributable to NCI 1 0 5.8 4.6 Exercise of employee stock options 16.0 7.7 7.7 Purchase/change of ARX minority shares (241.6) (11.2) (11.2) Change in redemption value of NCI 0 0.2 0.3 Balance, end of period $ 0 $ 222.9 $ 225.6 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	9 Months Ended
	Sep. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill During the nine months ended September 30, 2020, there were no changes to the carrying amount of goodwill. No accumulated goodwill impairment losses exist. Intangible Assets The following table is a summary of the net carrying amount of other intangible assets: (millions) September 30, 2020 September 30, 2019 December 31, 2019 Intangible assets subject to amortization $ 173.1 $ 230.5 $ 215.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 185.5 $ 242.9 $ 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 all periods presented. Intangible assets subject to amortization consisted of the following: (millions) September 30, 2020 September 30, 2019 December 31, 2019 Category Gross Accumulated Net Gross Accumulated Net Gross Accumulated Net Policies in force $ 256.2 $ 201.3 $ 54.9 $ 256.2 $ 164.7 $ 91.5 $ 256.2 $ 173.9 $ 82.3 Agency relationships 159.2 62.6 96.6 159.2 51.2 108.0 159.2 54.0 105.2 Software rights 69.1 47.5 21.6 79.1 48.1 31.0 79.1 50.7 28.4 Trade name 0 0 0 34.8 34.8 0 34.8 34.8 0 Total $ 484.5 $ 311.4 $ 173.1 $ 529.3 $ 298.8 $ 230.5 $ 529.3 $ 313.4 $ 215.9 Amortization expense was $14.2 million and $42.8 million for the three and nine months ended September 30, 2020, respectively, compared to $15.8 million and $51.7 million during the same periods last year. During the first quarter 2020, one software rights intangible asset, with a gross carrying value of $10.0 million, was fully amortized.

New Accounting Standards

New Accounting Standards	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
New Accounting Standards	New Accounting Standards — On January 1, 2020, we adopted the Accounting Standards Update (ASU), on a prospective basis, 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. For the nine months ended September 30, 2020, we capitalized $21.7 million of cloud computing arrangement implementation costs, which is included in other assets on our consolidated balance sheet. On January 1, 2020, we adopted the ASU which amends the disclosure requirements for fair value measurements. The ASU requires 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. The ASU also removes 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. As permitted by the ASU, we elected to partially early adopt the removal of the then current disclosure requirements in 2018 and adopted the remaining disclosure requirements as of January 1, 2020. As this only affects disclosure requirements, there was no impact on our financial condition, cash flows, or results of operations. On January 1, 2020, we adopted the ASU which eliminates the requirement to determine the implied fair value of goodwill in measuring an impairment loss. The standard 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. On January 1, 2020, we adopted the ASU intended to improve the timing, and enhance the accounting and disclosure, of credit losses on financial assets. This update modified the existing accounting guidance related to the impairment evaluation for available-for-sale debt securities and resulted in the creation of an allowance for credit losses as a contra asset account. The ASU requires prospective changes to previously recorded impairments. To determine the existence of any credit-related impairment losses on our available-for-sale debt securities, we reviewed all such securities by applying estimates of future cash flows and performance of those securities in a loss position and identifying market-related versus performance-related losses. For our reinsurance recoverables, we assessed the current credit quality and credit outlook for reinsurers with at-risk uncollateralized recoverables. Based on these analyses, we determined that our allowance for credit losses was not material relative to our available-for-sale debt securities and reinsurance recoverables upon adoption of the ASU. In assessing premium receivables, which are short-term in nature, we assessed customer balances leveraging our current process for analyzing the collectibility of premium receivables. Based on our analysis, no adjustment to the beginning balance of retained earnings was required upon adoption. See Note 1 – Basis of Presentation for changes in the allowance for doubtful accounts related to the premiums receivable balance.

Organization, Consolidation and

Organization, Consolidation and Presentation of Financial Statements (Tables)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Premium Receivable, Allowance for Credit Loss	The following table summarizes changes in our allowance for credit loss exposure on our premium receivables: (millions) Three Months Ended September 30, 2020 Nine Months Ended September 30, 2020 Allowance for credit loss, beginning of period $ 437.9 $ 283.2 Increase (decrease) in allowance 1 (3.6) 362.9 Write-offs 2 (121.1) (332.9) Allowance for credit loss, end of period $ 313.2 $ 313.2 1 Represents the incremental period increase (decrease) in other underwriting expenses. 2 Represents portion of allowance that is reversed when premium receivables are written off.
Assets and Liabilities, Lessee	The following table summarizes the carrying amounts of our operating leased assets and liabilities: (millions) September 30, 2020 September 30, 2019 December 31, 2019 Operating lease assets $ 174.1 $ 190.5 $ 188.2 Operating lease liabilities 186.2 204.1 201.5

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Schedule of Debt and Equity Securities Reconciliation	The following tables present the composition of our investment portfolio by major security type, 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. During the third quarter 2020, the portfolio’s valuation rose as markets continued to recover from their first quarter declines. ($ in millions) Cost Gross Gross Net Fair % of September 30, 2020 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,835.1 $ 370.3 $ (1.6) $ 0 $ 10,203.8 22.3 % State and local government obligations 4,382.1 148.2 (0.5) 0 4,529.8 9.9 Corporate debt securities 10,038.7 574.7 (3.6) 2.2 10,612.0 23.2 Residential mortgage-backed securities 525.4 7.0 (1.4) 0 531.0 1.2 Commercial mortgage-backed securities 5,964.4 117.1 (27.9) 0 6,053.6 13.2 Other asset-backed securities 4,155.8 46.8 (2.3) 0 4,200.3 9.2 Redeemable preferred stocks 181.3 2.5 (3.2) 2.4 183.0 0.4 Total fixed maturities 35,082.8 1,266.6 (40.5) 4.6 36,313.5 79.4 Short-term investments 4,667.8 0 0 0 4,667.8 10.2 Total available-for-sale securities 39,750.6 1,266.6 (40.5) 4.6 40,981.3 89.6 Equity securities: Nonredeemable preferred stocks 1,302.7 0 0 20.5 1,323.2 2.9 Common equities 1,130.0 0 0 2,329.8 3,459.8 7.5 Total equity securities 2,432.7 0 0 2,350.3 4,783.0 10.4 Total portfolio 1,2 $ 42,183.3 $ 1,266.6 $ (40.5) $ 2,354.9 $ 45,764.3 100.0 % ($ in millions) Cost Gross Gross Net Fair % of September 30, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,387.6 $ 300.3 $ (9.2) $ 0 $ 13,678.7 35.4 % State and local government obligations 1,652.2 32.6 (1.1) 0 1,683.7 4.4 Corporate debt securities 7,048.9 231.6 (0.4) 1.0 7,281.1 18.9 Residential mortgage-backed securities 677.5 5.5 (1.5) 0 681.5 1.8 Commercial mortgage-backed securities 4,547.9 93.0 (1.9) 0 4,639.0 12.0 Other asset-backed securities 4,601.0 21.5 (0.6) 0 4,621.9 12.0 Redeemable preferred stocks 219.8 4.4 (2.5) 5.1 226.8 0.6 Total fixed maturities 32,134.9 688.9 (17.2) 6.1 32,812.7 85.1 Short-term investments 1,467.4 0 0 0 1,467.4 3.8 Total available-for-sale securities 33,602.3 688.9 (17.2) 6.1 34,280.1 88.9 Equity securities: Nonredeemable preferred stocks 1,054.2 0 0 74.3 1,128.5 2.9 Common equities 1,210.3 0 0 1,954.8 3,165.1 8.2 Total equity securities 2,264.5 0 0 2,029.1 4,293.6 11.1 Total portfolio 1,2 $ 35,866.8 $ 688.9 $ (17.2) $ 2,035.2 $ 38,573.7 100.0 % ($ in millions) Cost Gross Gross Net Fair % of 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 1,2 $ 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 September 30, 2020, we had $469.2 million in other liabilities, compared to $286.5 million and $11.9 million at September 30, 2019 and December 31, 2019, respectively.
Hybrid Instruments Table	Included in our fixed-maturity securities are hybrid securities, which are reported at fair value: September 30, (millions) 2020 2019 December 31, 2019 Fixed maturities: State and local government obligations $ 0 $ 3.5 $ 3.5 Corporate debt securities 101.0 91.3 91.2 Other asset-backed securities 18.7 3.0 2.6 Redeemable preferred stocks 122.5 90.7 92.1 Total hybrid securities $ 242.2 $ 188.5 $ 189.4
Investments Classified by Contractual Maturity Date	The composition of fixed maturities by maturity at September 30, 2020, was: (millions) Cost Fair Value Less than one year $ 5,794.9 $ 5,827.6 One to five years 19,507.0 20,100.9 Five to ten years 9,319.7 9,900.1 Ten years or greater 461.2 484.9 Total $ 35,082.8 $ 36,313.5
Schedule of Unrealized Loss on Investments	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized September 30, 2020 Fixed maturities: U.S. government obligations 13 $ 1,993.8 $ (1.6) 13 $ 1,993.8 $ (1.6) 0 $ 0 $ 0 State and local government obligations 45 320.1 (0.5) 45 320.1 (0.5) 0 0 0 Corporate debt securities 28 537.8 (3.6) 28 537.8 (3.6) 0 0 0 Residential mortgage-backed securities 28 86.7 (1.4) 9 38.7 (1.0) 19 48.0 (0.4) Commercial mortgage-backed securities 77 1,794.8 (27.9) 46 1,170.4 (17.3) 31 624.4 (10.6) Other asset-backed securities 22 191.5 (2.3) 11 146.5 (2.1) 11 45.0 (0.2) Redeemable preferred stocks 1 9.3 (3.2) 0 0 0 1 9.3 (3.2) Total fixed maturities 214 $ 4,934.0 $ (40.5) 152 $ 4,207.3 $ (26.1) 62 $ 726.7 $ (14.4) 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 September 30, 2019 Fixed maturities: U.S. government obligations 14 $ 2,708.0 $ (9.2) 7 $ 2,534.4 $ (8.9) 7 $ 173.6 $ (0.3) State and local government obligations 60 228.3 (1.1) 25 100.4 (0.7) 35 127.9 (0.4) Corporate debt securities 24 245.5 (0.4) 5 77.2 (0.1) 19 168.3 (0.3) Residential mortgage-backed securities 39 301.0 (1.5) 5 138.7 (0.1) 34 162.3 (1.4) Commercial mortgage-backed securities 48 743.3 (1.9) 26 361.9 (0.8) 22 381.4 (1.1) Other asset-backed securities 55 529.4 (0.6) 20 359.1 (0.2) 35 170.3 (0.4) Redeemable preferred stocks 3 57.2 (2.5) 2 45.9 (1.3) 1 11.3 (1.2) Total fixed maturities 243 $ 4,812.7 $ (17.2) 90 $ 3,617.6 $ (12.1) 153 $ 1,195.1 $ (5.1) Total No. of Sec. Total Gross Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized No. of Sec. Fair Unrealized December 31, 2019 Fixed maturities: 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)
Realized Gain (Loss) on Investments	The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2020 2019 2020 2019 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 90.2 $ 41.5 $ 565.8 $ 113.0 State and local government obligations 43.9 1.8 58.9 4.0 Corporate and other debt securities 58.8 21.3 125.5 68.5 Residential mortgage-backed securities 0 0 0 0.2 Commercial mortgage-backed securities 5.0 2.6 15.4 6.2 Other asset-backed securities 0.2 0.1 0.2 0.8 Total available-for-sale securities 198.1 67.3 765.8 192.7 Equity securities: Nonredeemable preferred stocks 0.3 3.6 20.0 20.2 Common equities 2.0 4.7 77.1 9.4 Total equity securities 2.3 8.3 97.1 29.6 Subtotal gross realized gains on security sales 200.4 75.6 862.9 222.3 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (1.5) (1.5) (4.8) (13.9) State and local government obligations 0 0 0 (0.7) Corporate and other debt securities 0 (0.2) (6.5) (7.7) Residential mortgage-backed securities 0 0 0 (2.3) Commercial mortgage-backed securities (2.9) 0 (12.7) (2.1) Other asset-backed securities 0 0 0 (0.1) Redeemable preferred stocks 0 (0.2) 0 (0.3) Total available-for-sale securities (4.4) (1.9) (24.0) (27.1) Equity securities: Nonredeemable preferred stocks (0.1) (2.0) (7.5) (2.0) Common equities 0 0 (60.3) (7.9) Total equity securities (0.1) (2.0) (67.8) (9.9) Subtotal gross realized losses on security sales (4.5) (3.9) (91.8) (37.0) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 88.7 40.0 561.0 99.1 State and local government obligations 43.9 1.8 58.9 3.3 Corporate and other debt securities 58.8 21.1 119.0 60.8 Residential mortgage-backed securities 0 0 0 (2.1) Commercial mortgage-backed securities 2.1 2.6 2.7 4.1 Other asset-backed securities 0.2 0.1 0.2 0.7 Redeemable preferred stocks 0 (0.2) 0 (0.3) Total available-for-sale securities 193.7 65.4 741.8 165.6 Equity securities: Nonredeemable preferred stocks 0.2 1.6 12.5 18.2 Common equities 2.0 4.7 16.8 1.5 Total equity securities 2.2 6.3 29.3 19.7 Subtotal net realized gains (losses) on security sales 195.9 71.7 771.1 185.3 Net holding period gains (losses) Hybrid securities 3.2 4.2 (3.2) 16.3 Equity securities 333.5 27.6 101.9 520.6 Subtotal net holding period gains (losses) 336.7 31.8 98.7 536.9 Impairment losses Other asset impairment 0 (38.1) 0 (62.4) Subtotal impairment losses 0 (38.1) 0 (62.4) Total net realized gains (losses) on securities $ 532.6 $ 65.4 $ 869.8 $ 659.8
Components of Equity Realized Gains (Losses)	The following table reflects our holding period realized gains (losses) on equity securities recognized for the three and nine months ended September 30, 2020 and 2019, for equity securities held at the respective quarter end: Three Months Nine Months (millions) 2020 2019 2020 2019 Total net gains (losses) recognized during the period on equity securities $ 335.7 $ 33.9 $ 131.2 $ 540.3 Less: Net gains (losses) recognized on equity securities sold during the period 2.2 6.3 29.3 19.7 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 333.5 $ 27.6 $ 101.9 $ 520.6
Components of Net Investment Income	The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2020 2019 2020 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 36.7 $ 75.8 $ 135.0 $ 198.7 State and local government obligations 18.5 8.7 44.2 26.9 Corporate debt securities 76.6 65.1 211.2 209.8 Residential mortgage-backed securities 0.8 5.4 8.8 16.6 Commercial mortgage-backed securities 37.3 35.6 114.2 100.7 Other asset-backed securities 22.6 31.4 76.6 85.5 Redeemable preferred stocks 2.5 3.9 12.5 16.1 Total fixed maturities 195.0 225.9 602.5 654.3 Short-term investments 6.2 7.1 26.9 34.3 Total available-for-sale securities 201.2 233.0 629.4 688.6 Equity securities: Nonredeemable preferred stocks 15.8 15.9 44.3 47.3 Common equities 13.5 14.1 41.8 41.3 Total equity securities 29.3 30.0 86.1 88.6 Investment income 230.5 263.0 715.5 777.2 Investment expenses (4.7) (5.9) (14.5) (18.3) Net investment income $ 225.8 $ 257.1 $ 701.0 $ 758.9

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 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 September 30, 2020 Fixed maturities: U.S. government obligations $ 10,203.8 $ 0 $ 0 $ 10,203.8 $ 9,835.1 State and local government obligations 0 4,529.8 0 4,529.8 4,382.1 Corporate debt securities 0 10,612.0 0 10,612.0 10,038.7 Subtotal 10,203.8 15,141.8 0 25,345.6 24,255.9 Asset-backed securities: Residential mortgage-backed 0 531.0 0 531.0 525.4 Commercial mortgage-backed 0 6,053.6 0 6,053.6 5,964.4 Other asset-backed 0 4,200.3 0 4,200.3 4,155.8 Subtotal asset-backed securities 0 10,784.9 0 10,784.9 10,645.6 Redeemable preferred stocks: Financials 0 49.2 0 49.2 51.2 Utilities 0 11.3 0 11.3 10.0 Industrials 10.1 112.4 0 122.5 120.1 Subtotal redeemable preferred stocks 10.1 172.9 0 183.0 181.3 Total fixed maturities 10,213.9 26,099.6 0 36,313.5 35,082.8 Short-term investments 4,506.2 161.6 0 4,667.8 4,667.8 Total available-for-sale securities 14,720.1 26,261.2 0 40,981.3 39,750.6 Equity securities: Nonredeemable preferred stocks: Financials 112.6 1,096.1 38.1 1,246.8 1,222.7 Utilities 0 40.7 0 40.7 39.9 Industrials 0 20.5 15.2 35.7 40.1 Subtotal nonredeemable preferred stocks 112.6 1,157.3 53.3 1,323.2 1,302.7 Common equities: Common stocks 3,457.1 0 0 3,457.1 1,127.3 Other risk investments 0 0 2.7 2.7 2.7 Subtotal common equities 3,457.1 0 2.7 3,459.8 1,130.0 Total equity securities 3,569.7 1,157.3 56.0 4,783.0 2,432.7 Total portfolio $ 18,289.8 $ 27,418.5 $ 56.0 $ 45,764.3 $ 42,183.3 Debt $ 0 $ 6,687.4 $ 0 $ 6,687.4 $ 5,395.4 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2019 Fixed maturities: U.S. government obligations $ 13,678.7 $ 0 $ 0 $ 13,678.7 $ 13,387.6 State and local government obligations 0 1,683.7 0 1,683.7 1,652.2 Corporate debt securities 0 7,281.1 0 7,281.1 7,048.9 Subtotal 13,678.7 8,964.8 0 22,643.5 22,088.7 Asset-backed securities: Residential mortgage-backed 0 681.5 0 681.5 677.5 Commercial mortgage-backed 0 4,639.0 0 4,639.0 4,547.9 Other asset-backed 0 4,621.9 0 4,621.9 4,601.0 Subtotal asset-backed securities 0 9,942.4 0 9,942.4 9,826.4 Redeemable preferred stocks: Financials 0 51.7 0 51.7 51.7 Utilities 0 10.9 0 10.9 10.0 Industrials 11.2 153.0 0 164.2 158.1 Subtotal redeemable preferred stocks 11.2 215.6 0 226.8 219.8 Total fixed maturities 13,689.9 19,122.8 0 32,812.7 32,134.9 Short-term investments 1,464.9 2.5 0 1,467.4 1,467.4 Total available-for-sale securities 15,154.8 19,125.3 0 34,280.1 33,602.3 Equity securities: Nonredeemable preferred stocks: Financials 82.2 967.1 27.1 1,076.4 1,004.3 Utilities 0 42.1 0 42.1 39.9 Industrials 0 5.0 5.0 10.0 10.0 Subtotal nonredeemable preferred stocks 82.2 1,014.2 32.1 1,128.5 1,054.2 Common equities: Common stocks 3,164.8 0 0 3,164.8 1,210.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,164.8 0 0.3 3,165.1 1,210.3 Total equity securities 3,247.0 1,014.2 32.4 4,293.6 2,264.5 Total portfolio $ 18,401.8 $ 20,139.5 $ 32.4 $ 38,573.7 $ 35,866.8 Debt $ 0 $ 5,113.3 $ 0 $ 5,113.3 $ 4,406.5 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 available-for-sale securities 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 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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	The following tables provide a summary of changes in fair value associated with Level 3 assets for the three and nine months ended September 30, 2020 and 2019: Level 3 Fair Value (millions) Fair Value at June 30, 2020 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 38.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 38.1 Industrials 15.2 0 0 0 0 0 0 15.2 Common equities: Other risk investments 0.3 0 2.4 0 0 0 0 2.7 Total Level 3 securities $ 53.6 $ 0 $ 2.4 $ 0 $ 0 $ 0 $ 0 $ 56.0 Level 3 Fair Value (millions) Fair Value at June 30, 2019 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 32.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 32.4 Level 3 Fair Value (millions) Fair Value at December 31, 2019 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 25.0 $ 0 $ 0 $ (14.0) $ 0 $ 38.1 Industrials 16.0 0 0 0 0 (0.8) 0 15.2 Common equities: Other risk investments 0.3 0 2.4 0 0 0 0 2.7 Total Level 3 securities $ 43.4 $ 0 $ 27.4 $ 0 $ 0 $ (14.8) $ 0 $ 56.0 Level 3 Fair Value (millions) Fair Value at December 31, 2018 Calls/ Purchases Sales Net Realized Change in Net Fair Value at September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 30.4 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 32.4
Fair Value Measurement Inputs and Valuation Techniques	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2020 and 2019, and December 31, 2019: Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2020 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials $ 13.1 Guideline public company method Weighted average capitalization % (51.5) Financials 1 25.0 Internal price Unadjusted purchase price per share 3.7 Industrials 15.2 Guideline public company method Weighted average capitalization % (19.2) Subtotal Level 3 securities 53.3 Pricing exemption securities 2.7 Total Level 3 securities $ 56.0 1 The security was purchased in May 2020 and the valuation remained the same at September 30, 2020. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 27.1 Internal price Unadjusted purchase price per share 9.0 Industrials 5.0 Internal price Price-to-sales ratio 5.5 Subtotal Level 3 securities 32.1 Pricing exemption securities 0.3 Total Level 3 securities $ 32.4 1 The security was purchased in December 2018. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at December 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 1 The security was purchased in November 2019.

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt Table	Debt at each of the balance sheet periods consisted of: September 30, 2020 September 30, 2019 December 31, 2019 (millions) Carrying Fair Carrying Fair Carrying Fair 3.75% Senior Notes due 2021 $ 499.7 $ 515.3 $ 499.3 $ 516.5 $ 499.4 $ 515.6 2.45% Senior Notes due 2027 497.2 532.0 496.8 502.1 496.9 501.5 6 5/8% Senior Notes due 2029 296.8 411.4 296.5 392.2 296.6 392.5 4.00% Senior Notes due 2029 545.3 662.5 544.9 617.0 545.0 614.3 3.20% Senior Notes due 2030 496.0 572.4 0 0 0 0 6.25% Senior Notes due 2032 395.9 587.2 395.7 547.2 395.7 552.6 4.35% Senior Notes due 2044 346.7 450.5 346.6 414.7 346.7 417.0 3.70% Senior Notes due 2045 395.5 473.5 395.4 431.8 395.4 434.2 4.125% Senior Notes due 2047 841.7 1,078.5 841.5 987.4 841.6 986.1 4.20% Senior Notes due 2048 590.0 775.3 589.8 704.4 589.8 705.8 3.95% Senior Notes due 2050 490.6 628.8 0 0 0 0 Total $ 5,395.4 $ 6,687.4 $ 4,406.5 $ 5,113.3 $ 4,407.1 $ 5,119.6

Loss and Loss Adjustment Expe_2

Loss and Loss Adjustment Expense Reserves (Tables)	9 Months Ended
	Sep. 30, 2020
Loss and Loss Adjustment Expenses Reserves [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	Activity in the loss and loss adjustment expense reserves is summarized as follows: September 30, (millions) 2020 2019 Balance at January 1 $ 18,105.4 $ 15,400.8 Less reinsurance recoverables on unpaid losses 3,212.2 2,572.7 Net balance at January 1 14,893.2 12,828.1 Incurred related to: Current year 18,073.6 18,108.2 Prior years 116.1 215.2 Total incurred 18,189.7 18,323.4 Paid related to: Current year 10,615.2 10,864.9 Prior years 6,682.8 6,061.7 Total paid 17,298.0 16,926.6 Net balance at September 30 15,784.9 14,224.9 Plus reinsurance recoverables on unpaid losses 3,804.3 3,145.1 Balance at September 30 $ 19,589.2 $ 17,370.0

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Table	We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2020 2019 Income taxes $ 1,079.2 $ 738.7 Interest 168.4 147.3 Operating lease liabilities 66.6 61.2

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Reconciliation of Revenue and operating Income from Segments to Consolidated	Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (millions) Revenues Pretax Revenues Pretax Revenues Pretax Revenues Pretax Personal Lines Agency $ 4,001.6 $ 596.5 $ 3,703.4 $ 380.2 $ 11,749.3 $ 1,748.7 $ 10,851.5 $ 1,267.9 Direct 4,309.8 517.6 3,804.0 291.7 12,470.1 1,637.8 11,113.7 940.2 Total Personal Lines 1 8,311.4 1,114.1 7,507.4 671.9 24,219.4 3,386.5 21,965.2 2,208.1 Commercial Lines 1,214.8 155.9 1,106.9 69.7 3,532.8 448.2 3,190.4 360.7 Property 2 447.3 (52.9) 397.9 (9.1) 1,300.6 (192.4) 1,141.1 (35.8) Total underwriting operations 9,973.5 1,217.1 9,012.2 732.5 29,052.8 3,642.3 26,296.7 2,533.0 Fees and other revenues 3 151.8 NA 138.4 NA 434.8 NA 403.4 NA Service businesses 58.8 4.4 51.5 2.8 169.4 14.7 144.1 12.0 Investments 4 763.1 758.4 328.4 322.5 1,585.3 1,570.8 1,437.0 1,418.7 Interest expense NA (56.4) NA (47.5) NA (160.8) NA (142.3) Consolidated total $ 10,947.2 $ 1,923.5 $ 9,530.5 $ 1,010.3 $ 31,242.3 $ 5,067.0 $ 28,281.2 $ 3,821.4 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three and nine months ended September 30, 2020 and 2019; 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 For the three and nine months ended September 30, 2020, pretax profit (loss) includes $14.2 million and $42.8 million, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $15.8 million and $51.7 million for the same periods in 2019. See Note 13 – 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 expense.
Underwriting Margins and Combined Ratios for our Underwriting Operations	Following are the underwriting margins and combined ratios for our underwriting operations for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Under-writing Combined Under-writing Combined Under-writing Combined Under-writing Combined Personal Lines Agency 14.9 % 85.1 10.3 % 89.7 14.9 % 85.1 11.7 % 88.3 Direct 12.0 88.0 7.7 92.3 13.1 86.9 8.5 91.5 Total Personal Lines 13.4 86.6 9.0 91.0 14.0 86.0 10.1 89.9 Commercial Lines 12.8 87.2 6.3 93.7 12.7 87.3 11.3 88.7 Property 1 (11.8) 111.8 (2.3) 102.3 (14.8) 114.8 (3.1) 103.1 Total underwriting operations 12.2 87.8 8.1 91.9 12.5 87.5 9.6 90.4 1 Included in the three and nine months ended September 30, 2020, is 3.2 points and 3.3 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 4.0 points and 4.5 points, respectively, for the three and nine months ended September 30, 2019.

Dividends (Tables)

Dividends (Tables)	9 Months Ended
	Sep. 30, 2020
Dividends [Abstract]
Dividends	Following is a summary of our common and preferred share dividends that were declared and/or paid during the nine months ended September 30, 2020 and 2019: (millions, except per share amounts) Amount Declared Payable Per Share Accrued 1 Common - Quarterly Dividends: 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 Common - Annual Variable Dividends: December 2019 January 2020 2.25 1,316.9 December 2018 February 2019 2.5140 1,467.9 Preferred Dividends: 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 1 The accrual is based on an estimate of shares outstanding as of the record date and is recorded as a component of accounts payable, accrued expenses, and other liabilities on the consolidated balance sheets.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Components of Other Comprehensive Income (Loss)	The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) Balance at June 30, 2020 $ 1,237.3 $ (262.3) $ 975.0 $ 991.0 $ (16.0) $ 0 Reclassification of disproportionate amounts 0 0 0 0 0 0 Adjusted balance at June 30, 2020 1,237.3 (262.3) 975.0 991.0 (16.0) 0 Other comprehensive income (loss) before reclassifications: Investment securities 163.3 (34.4) 128.9 128.9 0 0 Loss attributable to noncontrolling interest (NCI) 0 0 0 0 0 0 Total other comprehensive income (loss) before reclassifications 163.3 (34.4) 128.9 128.9 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 194.3 (40.8) 153.5 153.5 0 0 Interest expense (0.3) 0.1 (0.2) 0 (0.2) 0 Total reclassification adjustment for amounts realized in net income 194.0 (40.7) 153.3 153.5 (0.2) 0 Total other comprehensive income (loss) (30.7) 6.3 (24.4) (24.6) 0.2 0 Balance at September 30, 2020 $ 1,206.6 $ (256.0) $ 950.6 $ 966.4 $ (15.8) $ 0 Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) Balance at June 30, 2019 $ 573.6 $ (120.5) $ 453.1 $ 472.9 $ (16.8) $ (3.0) Other comprehensive income (loss) before reclassifications: Investment securities 134.3 (28.2) 106.1 106.1 0 0 Loss attributable to noncontrolling interest (NCI) (1.2) 0.3 (0.9) 0 0 (0.9) Total other comprehensive income (loss) before reclassifications 133.1 (27.9) 105.2 106.1 0 (0.9) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 60.7 (12.7) 48.0 48.0 0 0 Interest expense (0.3) 0.1 (0.2) 0 (0.2) 0 Total reclassification adjustment for amounts realized in net income 60.4 (12.6) 47.8 48.0 (0.2) 0 Total other comprehensive income (loss) 72.7 (15.3) 57.4 58.1 0.2 (0.9) Balance at September 30, 2019 $ 646.3 $ (135.8) $ 510.5 $ 531.0 $ (16.6) $ (3.9) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) 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 1,447.7 (304.1) 1,143.6 1,143.6 0 0 Loss attributable to noncontrolling interest (NCI) 0 0 0 0 0 0 Total other comprehensive income (loss) before reclassifications 1,447.7 (304.1) 1,143.6 1,143.6 0 0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 681.0 (143.0) 538.0 538.0 0 0 Interest expense (0.8) 0.2 (0.6) 0 (0.6) 0 Total reclassification adjustment for amounts realized in net income 680.2 (142.8) 537.4 538.0 (0.6) 0 Total other comprehensive income (loss) 767.5 (161.3) 606.2 605.6 0.6 0 Balance at September 30, 2020 $ 1,206.6 $ (256.0) $ 950.6 $ 966.4 $ (15.8) $ 0 1 Adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the purchase transaction (See Note 12 – Redeemable Noncontrolling Interest for additional information). Components of Changes in (millions) Pretax total Total tax After tax total Total net Net (Income) 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 953.5 (200.2) 753.3 753.3 0 0 Loss attributable to noncontrolling interest (NCI) (7.4) 1.6 (5.8) 0 0 (5.8) Total other comprehensive income (loss) before reclassifications 946.1 (198.6) 747.5 753.3 0 (5.8) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 147.6 (30.9) 116.7 116.7 0 0 Interest expense (0.8) 0.2 (0.6) 0 (0.6) 0 Total reclassification adjustment for amounts realized in net income 146.8 (30.7) 116.1 116.7 (0.6) 0 Total other comprehensive income (loss) 799.3 (167.9) 631.4 636.6 0.6 (5.8) Balance at September 30, 2019 $ 646.3 $ (135.8) $ 510.5 $ 531.0 $ (16.6) $ (3.9)

Redeemable Noncontrolling Int_2

Redeemable Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2020
Temporary Equity Disclosure [Abstract]
Redeemable Noncontrolling Interest	The changes in the components of redeemable NCI were: Nine Months Ended September 30, Year Ended (millions) 2020 2019 December 31, 2019 Balance, beginning of period $ 225.6 $ 214.5 $ 214.5 Net income attributable to NCI 0 5.9 9.7 Other comprehensive income (loss) attributable to NCI 1 0 5.8 4.6 Exercise of employee stock options 16.0 7.7 7.7 Purchase/change of ARX minority shares (241.6) (11.2) (11.2) Change in redemption value of NCI 0 0.2 0.3 Balance, end of period $ 0 $ 222.9 $ 225.6 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)	9 Months Ended
	Sep. 30, 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: (millions) September 30, 2020 September 30, 2019 December 31, 2019 Intangible assets subject to amortization $ 173.1 $ 230.5 $ 215.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 185.5 $ 242.9 $ 228.3
Intangible Assets Subject to Amortization	Intangible assets subject to amortization consisted of the following: (millions) September 30, 2020 September 30, 2019 December 31, 2019 Category Gross Accumulated Net Gross Accumulated Net Gross Accumulated Net Policies in force $ 256.2 $ 201.3 $ 54.9 $ 256.2 $ 164.7 $ 91.5 $ 256.2 $ 173.9 $ 82.3 Agency relationships 159.2 62.6 96.6 159.2 51.2 108.0 159.2 54.0 105.2 Software rights 69.1 47.5 21.6 79.1 48.1 31.0 79.1 50.7 28.4 Trade name 0 0 0 34.8 34.8 0 34.8 34.8 0 Total $ 484.5 $ 311.4 $ 173.1 $ 529.3 $ 298.8 $ 230.5 $ 529.3 $ 313.4 $ 215.9

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation-Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Business Acquisition [Line Items]
Assets held-for-sale	$ 27.1	$ 27.1	$ 32.9	$ 43.7
Operating lease, right-of-use asset	174.1	174.1	188.2	190.5
Operating lease, liability	$ 186.2	$ 186.2	$ 201.5	$ 204.1
Operating lease right-of-use asset, balance sheet location	us-gaap:OtherAssets	us-gaap:OtherAssets
Operating lease liability location on balance sheet	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Premium Receivable, Allowance for Credit Loss, Beginning Balance	$ 437.9	$ 283.2
Increase in premiums receivable, allowance for doubtful accounts	(3.6)	362.9
Reduction of premiums receivable, allowance for doubtful accounts	(121.1)	(332.9)
Premium Receivable, Allowance for Credit Loss, Ending Balance	$ 313.2	$ 313.2
ARX Holding Corp.
Business Acquisition [Line Items]
Percentage ownership	100.00%	100.00%	87.10%	87.10%

Investments Investment Portfoli

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 39,750.6	$ 34,441.9	$ 33,602.3
Gross Unrealized Gains	1,266.6	517	688.9
Gross Unrealized Losses	(40.5)	(57.6)	(17.2)
Net Holding Period Gains (Losses)	4.6	7.8	6.1
Total available-for-sale securities	$ 40,981.3	$ 34,909.1	$ 34,280.1
% of Total Fair Value	89.60%	88.90%	88.90%
Equity securities, at Fair Value
Cost	$ 2,432.7	$ 2,096.8	$ 2,264.5
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	2,350.3	2,248.4	2,029.1
Fair Value	$ 4,783	$ 4,345.2	$ 4,293.6
% of Total Fair Value	10.40%	11.10%	11.10%
Debt and Equity Securities, at Fair Value
Cost	$ 42,183.3	$ 36,538.7	$ 35,866.8
Gross Unrealized Gains	1,266.6	517	688.9
Gross Unrealized Losses	(40.5)	(57.6)	(17.2)
Net Holding Period Gains (Losses)	2,354.9	2,256.2	2,035.2
Fair Value	$ 45,764.3	$ 39,254.3	$ 38,573.7
% of Total Fair Value	100.00%	100.00%	100.00%
Unsettled security transactions, payable	$ 469.2	$ 11.9	$ 286.5
Total fair value of non-insurance subsidiary portfolio	2,800	3,200	1,500
Nonredeemable preferred stocks
Equity securities, at Fair Value
Cost	1,302.7	971.3	1,054.2
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	20.5	67.6	74.3
Fair Value	$ 1,323.2	$ 1,038.9	$ 1,128.5
% of Total Fair Value	2.90%	2.70%	2.90%
Common equities
Equity securities, at Fair Value
Cost	$ 1,130	$ 1,125.5	$ 1,210.3
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	2,329.8	2,180.8	1,954.8
Fair Value	$ 3,459.8	$ 3,306.3	$ 3,165.1
% of Total Fair Value	7.50%	8.40%	8.20%
Total fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 35,082.8	$ 32,643.1	$ 32,134.9
Gross Unrealized Gains	1,266.6	517	688.9
Gross Unrealized Losses	(40.5)	(57.6)	(17.2)
Net Holding Period Gains (Losses)	4.6	7.8	6.1
Total available-for-sale securities	$ 36,313.5	$ 33,110.3	$ 32,812.7
% of Total Fair Value	79.40%	84.30%	85.10%
Total fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 9,835.1	$ 13,100.7	$ 13,387.6
Gross Unrealized Gains	370.3	194.1	300.3
Gross Unrealized Losses	(1.6)	(43.7)	(9.2)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 10,203.8	$ 13,251.1	$ 13,678.7
% of Total Fair Value	22.30%	33.70%	35.40%
Total fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,382.1	$ 1,686	$ 1,652.2
Gross Unrealized Gains	148.2	30	32.6
Gross Unrealized Losses	(0.5)	(2.7)	(1.1)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 4,529.8	$ 1,713.3	$ 1,683.7
% of Total Fair Value	9.90%	4.40%	4.40%
Total fixed maturities | Corporate debt securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 10,038.7	$ 6,860.3	$ 7,048.9
Gross Unrealized Gains	574.7	206.6	231.6
Gross Unrealized Losses	(3.6)	(0.5)	(0.4)
Net Holding Period Gains (Losses)	2.2	1.3	1
Total available-for-sale securities	$ 10,612	$ 7,067.7	$ 7,281.1
% of Total Fair Value	23.20%	18.00%	18.90%
Total fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 525.4	$ 625	$ 677.5
Gross Unrealized Gains	7	4.5	5.5
Gross Unrealized Losses	(1.4)	(2)	(1.5)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 531	$ 627.5	$ 681.5
% of Total Fair Value	1.20%	1.60%	1.80%
Total fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 5,964.4	$ 5,020.7	$ 4,547.9
Gross Unrealized Gains	117.1	61.5	93
Gross Unrealized Losses	(27.9)	(6)	(1.9)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 6,053.6	$ 5,076.2	$ 4,639
% of Total Fair Value	13.20%	12.90%	12.00%
Total fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,155.8	$ 5,164.7	$ 4,601
Gross Unrealized Gains	46.8	16.2	21.5
Gross Unrealized Losses	(2.3)	(1.4)	(0.6)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 4,200.3	$ 5,179.5	$ 4,621.9
% of Total Fair Value	9.20%	13.20%	12.00%
Total fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 181.3	$ 185.7	$ 219.8
Gross Unrealized Gains	2.5	4.1	4.4
Gross Unrealized Losses	(3.2)	(1.3)	(2.5)
Net Holding Period Gains (Losses)	2.4	6.5	5.1
Total available-for-sale securities	$ 183	$ 195	$ 226.8
% of Total Fair Value	0.40%	0.50%	0.60%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,667.8	$ 1,798.8	$ 1,467.4
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 4,667.8	$ 1,798.8	$ 1,467.4
% of Total Fair Value	10.20%	4.60%	3.80%

Investments Hybrid Securities (

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Hybrid Instruments [Line Items]
Hybrid securities	$ 242.2	$ 189.4	$ 188.5
State and local government obligations
Hybrid Instruments [Line Items]
Hybrid securities	0	3.5	3.5
Corporate debt securities
Hybrid Instruments [Line Items]
Hybrid securities	101	91.2	91.3
Other asset-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	18.7	2.6	3
Redeemable preferred stocks
Hybrid Instruments [Line Items]
Hybrid securities	$ 122.5	$ 92.1	$ 90.7

Investments Composition of Fixe

Investments Composition of Fixed Maturities by Maturity (Detail) - Total fixed maturities $ in Millions	Sep. 30, 2020USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 5,794.9
One to five years	19,507
Five to ten years	9,319.7
Ten years or greater	461.2
Cost	35,082.8
Fair Value
Less than one year	5,827.6
One to five years	20,100.9
Five to ten years	9,900.1
Ten years or greater	484.9
Fair Value	$ 36,313.5

Investments Gross Unrealized lo

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Sep. 30, 2020USD ($)security	Dec. 31, 2019USD ($)security	Sep. 30, 2019USD ($)security
Number of Securities
Total | security	214	307	243
Less than 12 Months | security	152	217	90
12 Months or Greater | security	62	90	153
Fair Value
Total	$ 4,934	$ 8,761.3	$ 4,812.7
Less than 12 Months	4,207.3	8,038.3	3,617.6
12 Months or Greater	726.7	723	1,195.1
Unrealized Losses
Total	(40.5)	(57.6)	(17.2)
Less than 12 Months	(26.1)	(53.8)	(12.1)
12 Months or Greater	$ (14.4)	$ (3.8)	$ (5.1)
U.S. government obligations
Number of Securities
Total | security	13	23	14
Less than 12 Months | security	13	19	7
12 Months or Greater | security	0	4	7
Fair Value
Total	$ 1,993.8	$ 5,152.4	$ 2,708
Less than 12 Months	1,993.8	5,057.2	2,534.4
12 Months or Greater	0	95.2	173.6
Unrealized Losses
Total	(1.6)	(43.7)	(9.2)
Less than 12 Months	(1.6)	(43.6)	(8.9)
12 Months or Greater	$ 0	$ (0.1)	$ (0.3)
State and local government obligations
Number of Securities
Total | security	45	67	60
Less than 12 Months | security	45	52	25
12 Months or Greater | security	0	15	35
Fair Value
Total	$ 320.1	$ 314.3	$ 228.3
Less than 12 Months	320.1	287.5	100.4
12 Months or Greater	0	26.8	127.9
Unrealized Losses
Total	(0.5)	(2.7)	(1.1)
Less than 12 Months	(0.5)	(2.6)	(0.7)
12 Months or Greater	$ 0	$ (0.1)	$ (0.4)
Corporate debt securities
Number of Securities
Total | security	28	16	24
Less than 12 Months | security	28	12	5
12 Months or Greater | security	0	4	19
Fair Value
Total	$ 537.8	$ 247.6	$ 245.5
Less than 12 Months	537.8	191.4	77.2
12 Months or Greater	0	56.2	168.3
Unrealized Losses
Total	(3.6)	(0.5)	(0.4)
Less than 12 Months	(3.6)	(0.5)	(0.1)
12 Months or Greater	$ 0	$ 0	$ (0.3)
Residential mortgage-backed securities
Number of Securities
Total | security	28	41	39
Less than 12 Months | security	9	12	5
12 Months or Greater | security	19	29	34
Fair Value
Total	$ 86.7	$ 292.8	$ 301
Less than 12 Months	38.7	163.7	138.7
12 Months or Greater	48	129.1	162.3
Unrealized Losses
Total	(1.4)	(2)	(1.5)
Less than 12 Months	(1)	(0.9)	(0.1)
12 Months or Greater	$ (0.4)	$ (1.1)	$ (1.4)
Commercial mortgage-backed securities
Number of Securities
Total | security	77	98	48
Less than 12 Months | security	46	79	26
12 Months or Greater | security	31	19	22
Fair Value
Total	$ 1,794.8	$ 1,742.4	$ 743.3
Less than 12 Months	1,170.4	1,400	361.9
12 Months or Greater	624.4	342.4	381.4
Unrealized Losses
Total	(27.9)	(6)	(1.9)
Less than 12 Months	(17.3)	(5.3)	(0.8)
12 Months or Greater	$ (10.6)	$ (0.7)	$ (1.1)
Other asset-backed securities
Number of Securities
Total | security	22	61	55
Less than 12 Months | security	11	43	20
12 Months or Greater | security	11	18	35
Fair Value
Total	$ 191.5	$ 1,000.6	$ 529.4
Less than 12 Months	146.5	938.5	359.1
12 Months or Greater	45	62.1	170.3
Unrealized Losses
Total	(2.3)	(1.4)	(0.6)
Less than 12 Months	(2.1)	(0.9)	(0.2)
12 Months or Greater	$ (0.2)	$ (0.5)	$ (0.4)
Redeemable preferred stocks
Number of Securities
Total | security	1	1	3
Less than 12 Months | security	0	0	2
12 Months or Greater | security	1	1	1
Fair Value
Total	$ 9.3	$ 11.2	$ 57.2
Less than 12 Months	0	0	45.9
12 Months or Greater	9.3	11.2	11.3
Unrealized Losses
Total	(3.2)	(1.3)	(2.5)
Less than 12 Months	0	0	(1.3)
12 Months or Greater	$ (3.2)	$ (1.3)	$ (1.2)

Investments Components of Net R

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	$ 198.1	$ 67.3	$ 765.8	$ 192.7
Equity Securities, FV-NI, Gross Realized Gains on Sales	2.3	8.3	97.1	29.6
Debt and Equity Securities, Gross Realized Gains on Sales	200.4	75.6	862.9	222.3
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(4.4)	(1.9)	(24)	(27.1)
Equity Securities, FV-NI, Gross Realized Losses on Sales	(0.1)	(2)	(67.8)	(9.9)
Debt and Equity Securities, Gross Realized Losses on Sales	(4.5)	(3.9)	(91.8)	(37)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	193.7	65.4	741.8	165.6
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	2.2	6.3	29.3	19.7
Gross Realized Gain (Loss), excluding Holding Period and OTTI	195.9	71.7	771.1	185.3
Unrealized Gain (Loss) on Hybrid Instrument, Net	3.2	4.2	(3.2)	16.3
Net holding period gains (losses), equity securities	333.5	27.6	101.9	520.6
Net Holding Period Realized Gain (Loss)	336.7	31.8	98.7	536.9
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	0	(38.1)	0	(62.4)
Total net realized gains (losses) on securities	532.6	65.4	869.8	659.8
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	90.2	41.5	565.8	113
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(1.5)	(1.5)	(4.8)	(13.9)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	88.7	40	561	99.1
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	43.9	1.8	58.9	4
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	0	0	(0.7)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	43.9	1.8	58.9	3.3
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	58.8	21.3	125.5	68.5
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(0.2)	(6.5)	(7.7)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	58.8	21.1	119	60.8
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0	0	0.2
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	0	0	(2.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	0	0	(2.1)
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	5	2.6	15.4	6.2
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(2.9)	0	(12.7)	(2.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	2.1	2.6	2.7	4.1
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0.2	0.1	0.2	0.8
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	0	0	(0.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0.2	0.1	0.2	0.7
Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(0.2)	0	(0.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	(0.2)	0	(0.3)
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	0.3	3.6	20	20.2
Equity Securities, FV-NI, Gross Realized Losses on Sales	(0.1)	(2)	(7.5)	(2)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	0.2	1.6	12.5	18.2
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	2	4.7	77.1	9.4
Equity Securities, FV-NI, Gross Realized Losses on Sales	0	0	(60.3)	(7.9)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	2	4.7	16.8	1.5
Other Assets
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	$ 0	$ (38.1)	$ 0	$ (62.4)

Investments Components of Equit

Investments Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Realized Investment Gains (Losses)	$ 335.7	$ 33.9	$ 131.2	$ 540.3
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	2.2	6.3	29.3	19.7
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 333.5	$ 27.6	$ 101.9	$ 520.6

Investments Components of Net I

Investments Components of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Net Investment Income [Line Items]
Gross investment income	$ 230.5	$ 263	$ 715.5	$ 777.2
Investment expenses	(4.7)	(5.9)	(14.5)	(18.3)
Net Investment Income	225.8	257.1	701	758.9
Available-for-sale Securities
Net Investment Income [Line Items]
Gross investment income	201.2	233	629.4	688.6
Total equity securities
Net Investment Income [Line Items]
Gross investment income	29.3	30	86.1	88.6
Total equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	15.8	15.9	44.3	47.3
Total equity securities | Common equities
Net Investment Income [Line Items]
Gross investment income	13.5	14.1	41.8	41.3
Total fixed maturities
Net Investment Income [Line Items]
Gross investment income	195	225.9	602.5	654.3
Total fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Gross investment income	36.7	75.8	135	198.7
Total fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Gross investment income	18.5	8.7	44.2	26.9
Total fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Gross investment income	76.6	65.1	211.2	209.8
Total fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	0.8	5.4	8.8	16.6
Total fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	37.3	35.6	114.2	100.7
Total fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Gross investment income	22.6	31.4	76.6	85.5
Total fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	2.5	3.9	12.5	16.1
Short-term investments
Net Investment Income [Line Items]
Gross investment income	$ 6.2	$ 7.1	$ 26.9	$ 34.3

Investments - Additional Inform

Investments - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)security	Sep. 30, 2020USD ($)security	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Schedule of Debt and Equity Securities [Line Items]
Principal amount of bonds and certificates of deposit	$ 281,100,000	$ 281,100,000
Securities Exceeding 10% of Shareholders' Equity	0	0	$ 0	$ 0
Non-Income Producing Securities	0	0
Open reverse repurchase commitments	0	0	400,000,000	0
Securities Sold under Agreements to Repurchase	$ 0	$ 0	$ 0	$ 0
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Downgraded | security	4	4
Combined fair value of securities	$ 47,500,000	$ 47,500,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Downgrades in Period	1,500,000	1,500,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Not Previously Recorded		0
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0	0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff		$ 0
Percent Change in Investment Income	12.00%	8.00%
Percent Change in Book Yield	(25.00%)	(21.00%)
Investment Portfolio Duration		3 years	2 years 10 months 24 days
Corporate debt securities
Schedule of Debt and Equity Securities [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Downgraded | security	2	2
Commercial mortgage-backed securities
Schedule of Debt and Equity Securities [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Upgraded | security	0	0
Residential mortgage-backed securities
Schedule of Debt and Equity Securities [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Downgraded | security	2	2

Fair Value Composition of Inves

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 45,764.3	$ 39,254.3	$ 38,573.7
Fair Value	6,687.4	5,119.6	5,113.3
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	40,981.3	34,909.1	34,280.1
Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	36,313.5	33,110.3	32,812.7
Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	25,345.6	22,032.1	22,643.5
Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,203.8	13,251.1	13,678.7
Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,529.8	1,713.3	1,683.7
Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,612	7,067.7	7,281.1
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,784.9	10,883.2	9,942.4
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	531	627.5	681.5
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	6,053.6	5,076.2	4,639
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,200.3	5,179.5	4,621.9
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	183	195	226.8
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	49.2	51.7	51.7
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	11.3	11.1	10.9
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	122.5	132.2	164.2
Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,667.8	1,798.8	1,467.4
Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,783	4,345.2	4,293.6
Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,323.2	1,038.9	1,128.5
Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,246.8	955.2	1,076.4
Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	40.7	42.3	42.1
Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	35.7	41.4	10
Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,459.8	3,306.3	3,165.1
Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,457.1	3,306	3,164.8
Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2.7	0.3	0.3
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	18,289.8	18,443	18,401.8
Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	14,720.1	15,059.6	15,154.8
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,213.9	13,262.2	13,689.9
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,203.8	13,251.1	13,678.7
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,203.8	13,251.1	13,678.7
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10.1	11.1	11.2
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10.1	11.1	11.2
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,506.2	1,797.4	1,464.9
Fair Value, Inputs, Level 1 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,569.7	3,383.4	3,247
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	112.6	77.4	82.2
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	112.6	77.4	82.2
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,457.1	3,306	3,164.8
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,457.1	3,306	3,164.8
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	27,418.5	20,767.9	20,139.5
Fair Value	6,687.4	5,119.6	5,113.3
Fair Value, Inputs, Level 2 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	26,261.2	19,849.5	19,125.3
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	26,099.6	19,848.1	19,122.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	15,141.8	8,781	8,964.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,529.8	1,713.3	1,683.7
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,612	7,067.7	7,281.1
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,784.9	10,883.2	9,942.4
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	531	627.5	681.5
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	6,053.6	5,076.2	4,639
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,200.3	5,179.5	4,621.9
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	172.9	183.9	215.6
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	49.2	51.7	51.7
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	11.3	11.1	10.9
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	112.4	121.1	153
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	161.6	1.4	2.5
Fair Value, Inputs, Level 2 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,157.3	918.4	1,014.2
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,157.3	918.4	1,014.2
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,096.1	850.7	967.1
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	40.7	42.3	42.1
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	20.5	25.4	5
Fair Value, Inputs, Level 2 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	56	43.4	32.4
Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	56	43.4	32.4
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	53.3	43.1	32.1
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	38.1	27.1	27.1
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	15.2	16	5
Fair Value, Inputs, Level 3 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2.7	0.3	0.3
Fair Value, Inputs, Level 3 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 3 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2.7	0.3	0.3
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	42,183.3	36,538.7	35,866.8
Long-term Debt	5,395.4	4,407.1	4,406.5
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	39,750.6	34,441.9	33,602.3
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	35,082.8	32,643.1	32,134.9
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	24,255.9	21,647	22,088.7
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,835.1	13,100.7	13,387.6
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,382.1	1,686	1,652.2
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,038.7	6,860.3	7,048.9
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10,645.6	10,810.4	9,826.4
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	525.4	625	677.5
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	5,964.4	5,020.7	4,547.9
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,155.8	5,164.7	4,601
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	181.3	185.7	219.8
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	51.2	51.5	51.7
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10	10	10
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	120.1	124.2	158.1
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,667.8	1,798.8	1,467.4
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,432.7	2,096.8	2,264.5
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,302.7	971.3	1,054.2
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,222.7	891.3	1,004.3
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	39.9	39.9	39.9
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	40.1	40.1	10
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,130	1,125.5	1,210.3
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,127.3	1,125.2	1,210
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 2.7	$ 0.3	$ 0.3

Fair Value Summary of Changes i

Fair Value Summary of Changes in Fair Value Associated with Level 3 Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 53.6	$ 32.4	$ 43.4	$ 30.4
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	2.4	0	27.4	2
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	(14.8)	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	56	32.4	56	32.4
Total equity securities | Financials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	38.1	27.1	27.1	25.1
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	25	2
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	(14)	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	38.1	27.1	38.1	27.1
Total equity securities | Industrials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	15.2	5	16	5
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	(0.8)	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	15.2	5	15.2	5
Total equity securities | Other risk investments | Common equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	0.3	0.3	0.3	0.3
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	2.4	0	2.4	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	$ 2.7	$ 0.3	$ 2.7	$ 0.3

Fair Value Summary of Quantitat

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Details) $ / shares in Units, $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2020USD ($)$ / shares	Sep. 30, 2019USD ($)$ / shares	Dec. 31, 2019USD ($)$ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 45,764.3	$ 38,573.7	$ 39,254.3
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	56	32.4	43.4
Fair Value, Inputs, Level 3 | Guideline Public Company Method [Member] | Nonredeemable preferred stocks | Financials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 13.1
Fair Value Inputs, Guideline Public Company Method | $ / shares	$ (51.5)
Fair Value, Inputs, Level 3 | Guideline Public Company Method [Member] | Nonredeemable preferred stocks | Industrials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 15.2
Fair Value Inputs, Guideline Public Company Method | $ / shares	$ (19.2)
Fair Value, Inputs, Level 3 | Third Party Pricing Firm | Nonredeemable preferred stocks | Financials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value			$ 27.1
Fair Value Inputs, Recent Transaction Price | $ / shares			$ 9
Fair Value, Inputs, Level 3 | Third Party Pricing Firm | Nonredeemable preferred stocks | Industrials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value			$ 6
Fair Value Inputs, Performance Based Price Adjustment | $ / shares			$ 4.8
Fair Value, Inputs, Level 3 | Internal Pricing | Nonredeemable preferred stocks | Financials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 25	$ 27.1
Fair Value Inputs, Original Issue Price | $ / shares	$ 3.7	$ 9
Fair Value, Inputs, Level 3 | Internal Pricing | Nonredeemable preferred stocks | Industrials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value		$ 5	$ 10
Fair Value Inputs, Price-to-Sales Ratio		5.5
Fair Value Inputs, Original Issue Price | $ / shares			$ 4.9
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 53.3	$ 32.1	$ 43.1
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 2.7	$ 0.3	$ 0.3

Fair Value - Additional Informa

Fair Value - Additional Information (Detail)	Sep. 30, 2020USD ($)security	Dec. 31, 2019USD ($)security	Sep. 30, 2019USD ($)security
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 45,764,300,000	$ 39,254,300,000	$ 38,573,700,000
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	75.00%	80.00%	81.00%
Investments, Fair Value	$ 18,289,800,000	$ 18,443,000,000	$ 18,401,800,000
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	99.00%	99.00%	99.00%
Dealer Quoted Prices, Percent of FV Hierarchy Level	1.00%	1.00%	1.00%
Investments, Fair Value	$ 27,418,500,000	$ 20,767,900,000	$ 20,139,500,000
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	56,000,000	43,400,000	32,400,000
Total fixed maturities | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 0	$ 0	$ 0
Nonredeemable preferred stocks | Internal Pricing | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Number of securities | security	4	3	2
Common equities | Internal Pricing | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Number of securities | security	2	1	1

Debt (Detail)

Debt (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Debt Instrument [Line Items]
Fair Value		$ 6,687.4	$ 5,119.6	$ 5,113.3
Debt, Long-term and Short-term, Combined Amount	[1]	5,395.4	4,407.1	4,406.5
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term Debt		499.7	499.4	499.3
Fair Value		515.3	515.6	516.5
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Long-term Debt		497.2	496.9	496.8
Fair Value		532	501.5	502.1
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Long-term Debt		296.8	296.6	296.5
Fair Value		411.4	392.5	392.2
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Long-term Debt		545.3	545	544.9
Fair Value		662.5	614.3	617
Senior Notes Three Point Two Zero Percent Due Twenty Thirty [Member]
Debt Instrument [Line Items]
Long-term Debt		496	0	0
Fair Value		572.4	0	0
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Long-term Debt		395.9	395.7	395.7
Fair Value		587.2	552.6	547.2
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Long-term Debt		346.7	346.7	346.6
Fair Value		450.5	417	414.7
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Long-term Debt		395.5	395.4	395.4
Fair Value		473.5	434.2	431.8
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Long-term Debt		841.7	841.6	841.5
Fair Value		1,078.5	986.1	987.4
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Long-term Debt		590	589.8	589.8
Fair Value		775.3	705.8	704.4
Senior Notes Three Point Nine Five Percent Due Twenty Fifty [Member]
Debt Instrument [Line Items]
Long-term Debt		490.6	0	0
Fair Value		$ 628.8	$ 0	$ 0
[1]	Consists of both short-term and long-term debt, including $500 million principal amount of 3.75% Senior Notes due August 2021. See Note 4 – Debt for further discussion.

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	1 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Proceeds, net of underwriter's discounts and commissions	$ 986,300,000
Discretionary Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 250,000,000	$ 250,000,000
Debt term			30 days
Borrowings outstanding			$ 0	$ 0
Senior Notes Three Point Two Zero Percent Due Twenty Thirty [Member]
Debt Instrument [Line Items]
Debt, face amount	$ 500,000,000
Debt, stated interest rate	3.20%	3.20%	3.20%
Senior Notes Three Point Nine Five Percent Due Twenty Fifty [Member]
Debt Instrument [Line Items]
Debt, face amount	$ 500,000,000
Debt, stated interest rate	3.95%	3.95%	3.95%
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Debt, face amount		$ 500,000,000	$ 500,000,000
Debt, stated interest rate		3.75%	3.75%
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Debt, stated interest rate		2.45%	2.45%
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Debt, stated interest rate		4.20%	4.20%
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Debt, stated interest rate		6.625%	6.625%
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Debt, stated interest rate		6.25%	6.25%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Debt, stated interest rate		4.35%	4.35%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt, stated interest rate		3.70%	3.70%
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Debt, stated interest rate		4.125%	4.125%
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Debt, stated interest rate		4.00%	4.00%
Federal Funds Open Rate | Discretionary Line of Credit
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.75%

Income Taxes Additional Informa

Income Taxes Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Taxes [Line Items]
Valuation allowance	$ 0	$ 0	$ 0	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Percent	20.40%	16.50%	20.70%	24.00%

Loss and Loss Adjustment Expe_3

Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expense reserves	$ 19,589.2	$ 17,370	$ 18,105.4	$ 15,400.8
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments and Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item	3,804.3	3,145.1	3,212.2	2,572.7
Liability for Unpaid Claims and Claims Adjustment Expense, Net	15,784.9	14,224.9	$ 14,893.2	$ 12,828.1
Current Year Claims and Claims Adjustment Expense	18,073.6	18,108.2
Prior Year Claims and Claims Adjustment Expense	116.1	215.2
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	18,189.7	18,323.4
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	10,615.2	10,864.9
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	6,682.8	6,061.7
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	$ 17,298	$ 16,926.6
Short-duration Insurance Contracts, Accident Year 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of Prior Year Claims and Claims Adjustment Expense	80.00%	50.00%
Short-duration Insurance Contracts, Accident Year 2017 [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of Prior Year Claims and Claims Adjustment Expense		30.00%
Personal Lines | Personal auto businesses
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ 47	$ 108
Personal Lines | Special Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	(22)	17
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	104	71
Property
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (13)	$ 19

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019
Open reverse repurchase commitments	$ 0	$ 400,000,000			$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	48,500,000
Operating Lease, Payments	66,600,000	61,200,000
Income Taxes Paid	1,079,200,000	738,700,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	168,400,000	147,300,000
Cash and Cash Equivalents | ARX Holding Corp.
Open reverse repurchase commitments	77,200,000	62,800,000			46,300,000
Common equities | Quarterly dividend [Member]
Dividends payable	$ 58,600,000	$ 58,500,000	$ 58,500,000	$ 58,500,000	$ 58,500,000	$ 58,400,000	$ 58,400,000

Segment Information Operating R

Segment Information Operating Results (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 10,947.2	$ 9,530.5	$ 31,242.3	$ 28,281.2
Pretax Profit (Loss)	1,923.5	1,010.3	5,067	3,821.4
Amortization of intangible assets	14.2	15.8	42.8	51.7
Personal Lines | Agency | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	4,001.6	3,703.4	11,749.3	10,851.5
Pretax Profit (Loss)	596.5	380.2	1,748.7	1,267.9
Personal Lines | Direct | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	4,309.8	3,804	12,470.1	11,113.7
Pretax Profit (Loss)	517.6	291.7	1,637.8	940.2
Operating Segments | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	9,973.5	9,012.2	29,052.8	26,296.7
Pretax Profit (Loss)	1,217.1	732.5	3,642.3	2,533
Operating Segments | Personal Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	8,311.4	7,507.4	24,219.4	21,965.2
Pretax Profit (Loss)	$ 1,114.1	$ 671.9	$ 3,386.5	$ 2,208.1
Personal auto insurance percentage of the total personal lines segment net premiums earned	94.00%	94.00%	94.00%	94.00%
Operating Segments | Commercial Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	$ 1,214.8	$ 1,106.9	$ 3,532.8	$ 3,190.4
Pretax Profit (Loss)	155.9	69.7	448.2	360.7
Operating Segments | Property | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	447.3	397.9	1,300.6	1,141.1
Pretax Profit (Loss)	(52.9)	(9.1)	(192.4)	(35.8)
Amortization of intangible assets	14.2	15.8	42.8	51.7
Segment Reconciling Items | Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	151.8	138.4	434.8	403.4
Segment Reconciling Items | Service businesses
Segment Reporting Information [Line Items]
Revenues	58.8	51.5	169.4	144.1
Pretax Profit (Loss)	4.4	2.8	14.7	12
Segment Reconciling Items | Investment income
Segment Reporting Information [Line Items]
Revenues	763.1	328.4	1,585.3	1,437
Pretax Profit (Loss)	758.4	322.5	1,570.8	1,418.7
Segment Reconciling Items | Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (56.4)	$ (47.5)	$ (160.8)	$ (142.3)

Segment Information Underwritin

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Underwriting operations	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Personal Lines | Agency
Segment Reporting Information [Line Items]
Underwriting Margin	14.90%	10.30%	14.90%	11.70%
Combined Ratio	85.10%	89.70%	85.10%	88.30%
Personal Lines | Direct
Segment Reporting Information [Line Items]
Underwriting Margin	12.00%	7.70%	13.10%	8.50%
Combined Ratio	88.00%	92.30%	86.90%	91.50%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	12.20%	8.10%	12.50%	9.60%
Combined Ratio	87.80%	91.90%	87.50%	90.40%
Operating Segments | Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	13.40%	9.00%	14.00%	10.10%
Combined Ratio	86.60%	91.00%	86.00%	89.90%
Operating Segments | Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	12.80%	6.30%	12.70%	11.30%
Combined Ratio	87.20%	93.70%	87.30%	88.70%
Operating Segments | Property
Segment Reporting Information [Line Items]
Underwriting Margin	(11.80%)	(2.30%)	(14.80%)	(3.10%)
Combined Ratio	111.80%	102.30%	114.80%	103.10%
Combined ratio amortization points	0.032	0.040	0.033	0.045

Dividends (Details)

Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended												3 Months Ended		9 Months Ended
	Sep. 30, 2020	Aug. 31, 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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Feb. 29, 2020	Dec. 31, 2019	Aug. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Common Stock, Dividends, Per Share, Declared													$ 0.10	$ 0.10	$ 0.30	$ 0.30
Quarterly dividend [Member]
Common Stock, Dividends, Per Share, Declared		$ 0.10
Common Stock, Dividends, Per Share, Cash Paid			$ 0.10	$ 0.10		$ 0.10	$ 0.10		$ 0.10	$ 0.10
Annual variable dividend
Common Stock, Dividends, Per Share, Cash Paid						$ 2.25						$ 2.5140
Series B Preferred Stock
Preferred Stock, Dividends, Per Share, Cash Paid	$ 26.875				$ 26.875			$ 26.875			$ 26.875
Dividends payable		$ 13.4										$ 13.4						$ 13.4		$ 13.4
Common equities | Quarterly dividend [Member]
Dividends payable	$ 58.6				$ 58.5			$ 58.5			$ 58.4		$ 58.6	$ 58.5	$ 58.6	$ 58.5	$ 58.5		$ 58.5		$ 58.4
Common equities | Annual variable dividend
Dividends payable																			$ 1,316.9			$ 1,467.9

Dividends - Additional Informat

Dividends - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Aug. 31, 2020	Feb. 29, 2020	Aug. 31, 2019	Feb. 28, 2019
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.10	$ 0.10	$ 0.30	$ 0.30
Series B Preferred Stock
Class of Stock [Line Items]
Dividends payable					$ 13.4	$ 13.4	$ 13.4	$ 13.4

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ 1,237.3	$ 573.6	$ 435.7	$ (153)	$ (153)
Pretax Reclassification of Stranded Amounts in AOCI to Equity	0		3.4
AOCI before Tax, Attributable to Parent, After Reclassification of Stranded Amounts	1,237.3		439.1
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax	163.3	134.3	1,447.7	953.5
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Noncontrolling Interest	0	(1.2)	0	(7.4)
OCI, before Reclassifications, before Tax, Attributable to Parent	163.3	133.1	1,447.7	946.1
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	194.3	60.7	681	147.6
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	(0.3)	(0.3)	(0.8)	(0.8)
Total reclassification adjustment for amounts realized in net income, pre tax	194	60.4	680.2	146.8
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	(30.7)	72.7	767.5	799.3
AOCI before Tax, Attributable to Parent, ending balance	1,206.6	646.3	1,206.6	646.3	435.7
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	262.3	120.5	94	(32.1)	(32.1)
Tax, Reclassification of Stranded Amounts in AOCI to Equity	0		(0.7)
AOCI Tax, Attributable to Parent, After Reclassification of Stranded Amounts	(262.3)		(94.7)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, Tax	(34.4)	(28.2)	(304.1)	(200.2)
Other Comprehensive Income (Loss), Tax, Portion Attributable to Noncontrolling Interest	0	0.3	0	1.6
OCI, Debt Securities, Available-for-Sale, Gain (Loss), before Adjustment, Tax	(34.4)	(27.9)	(304.1)	(198.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(40.8)	(12.7)	(143)	(30.9)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	0.1	0.1	0.2	0.2
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	(40.7)	(12.6)	(142.8)	(30.7)
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	6.3	(15.3)	(161.3)	(167.9)
AOCI Tax, Attributable to Parent, ending balance	(256)	(135.8)	(256)	(135.8)	94
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	975	453.1	341.7	(120.9)	(120.9)
Reclassification of Stranded Amounts in AOCI to Equity	0		2.7
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	975		344.4
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	128.9	106.1	1,143.6	753.3
Other comprehensive (income) loss attributable to NCI	0	(0.9)	0	(5.8)	(4.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	128.9	105.2	1,143.6	747.5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	153.5	48	538	116.7
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)	(0.2)	(0.6)	(0.6)
Total reclassification adjustment for amounts realized in net income, after tax	153.3	47.8	537.4	116.1
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(24.4)	57.4	606.2	631.4
After tax total accumulated other comprehensive income, ending balance	950.6	510.5	950.6	510.5	341.7
Total net unrealized gains (losses) on securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	991	472.9	360.8	(105.6)	(105.6)
Reclassification of Stranded Amounts in AOCI to Equity	0		0
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	991		360.8
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	128.9	106.1	1,143.6	753.3
Other comprehensive (income) loss attributable to NCI	0	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	128.9	106.1	1,143.6	753.3
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	153.5	48	538	116.7
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0	0
Total reclassification adjustment for amounts realized in net income, after tax	153.5	48	538	116.7
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(24.6)	58.1	605.6	636.6
After tax total accumulated other comprehensive income, ending balance	966.4	531	966.4	531	360.8
Net unrealized gains (losses) on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(16)	(16.8)	(16.4)	(17.2)	(17.2)
Reclassification of Stranded Amounts in AOCI to Equity	0		0
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	(16)		(16.4)
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	0	0	0	0
Other comprehensive (income) loss attributable to NCI	0	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)	(0.2)	(0.6)	(0.6)
Total reclassification adjustment for amounts realized in net income, after tax	(0.2)	(0.2)	(0.6)	(0.6)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.2	0.2	0.6	0.6
After tax total accumulated other comprehensive income, ending balance	(15.8)	(16.6)	(15.8)	(16.6)	(16.4)
(Income) loss attributable to NCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	0	(3)	(2.7)	1.9	1.9
Reclassification of Stranded Amounts in AOCI to Equity	0		2.7
AOCI Net of Tax, Attributable to Parent, After Reclassification of Stranded Amounts	0		0
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax	0	0	0	0
Other comprehensive (income) loss attributable to NCI	0	(0.9)	0	(5.8)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	(0.9)	0	(5.8)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0	0
Total reclassification adjustment for amounts realized in net income, after tax	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	(0.9)	0	(5.8)
After tax total accumulated other comprehensive income, ending balance	$ 0	$ (3.9)	$ 0	$ (3.9)	$ (2.7)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement, Additional Information (Detail) $ in Millions	Sep. 30, 2020USD ($)
Statement of Comprehensive Income [Abstract]
Net unrealized gains on forecasted transactions, expected to reclassify into income within the next 12 months	$ 1

Redeemable Noncontrolling Int_3

Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended			12 Months Ended
		Apr. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Redeemable Noncontrolling Interest [Line Items]
Acquisition of additional shares of ARX Holding Corp.					$ 243		$ 11.2
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, beginning of period					225.6	[1]	214.5	$ 214.5
Net income attributable to NCI			$ 0	$ 1.9	0		5.9	9.7
Other comprehensive income (loss) attributable to NCI1			0	0.9	0		5.8	4.6
Exercise of employee stock options					16		7.7	7.7
Purchase/change of ARX minority shares					(241.6)		(11.2)	(11.2)
Change in redemption value of NCI					0		0.2	0.3
Balance, end of period	[1]		$ 0	$ 222.9	$ 0		$ 222.9	$ 225.6
ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Acquisition of additional shares of ARX Holding Corp.		$ 243
[1]	See Note 12 – Redeemable Noncontrolling Interest for further discussion .

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets Goodwill (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Mar. 31, 2020USD ($)intangible_asset	Dec. 31, 2019USD ($)
Goodwill [Line Items]
Goodwill, Acquired During Period			$ 0
Goodwill, Impaired, Accumulated Impairment Loss	$ 0		0
Amortization of intangible assets	14,200,000	$ 15,800,000	42,800,000	$ 51,700,000
Software rights
Goodwill [Line Items]
Number of Intangible Assets | intangible_asset					1
Gross Carrying Amount	69,100,000	79,100,000	69,100,000	79,100,000		$ 79,100,000
Trade name
Goodwill [Line Items]
Gross Carrying Amount	$ 0	$ 34,800,000	$ 0	$ 34,800,000		$ 34,800,000
Fully Amortized [Member] | Software rights
Goodwill [Line Items]
Gross Carrying Amount					$ 10,000,000

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Schedule of Other Intangible Assets [Line Items]
Indefinite lived intangible assets	$ 12.4	$ 12.4	$ 12.4
Total	185.5	228.3	242.9
Accumulated amortization	312	314	299.4
Licensing Agreements
Schedule of Other Intangible Assets [Line Items]
Accumulated amortization	0.6	0.6	0.6
Finite-Lived Intangible Assets
Schedule of Other Intangible Assets [Line Items]
Intangible assets subject to amortization	173.1	215.9	230.5
Accumulated amortization	$ 311.4	$ 313.4	$ 298.8

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 14.2	$ 15.8	$ 42.8	$ 51.7
Accumulated Amortization	312	299.4	312	299.4	$ 314
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2	256.2	256.2	256.2
Accumulated Amortization	201.3	164.7	201.3	164.7	173.9
Net Carrying Amount	54.9	91.5	54.9	91.5	82.3
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2	159.2	159.2
Accumulated Amortization	62.6	51.2	62.6	51.2	54
Net Carrying Amount	96.6	108	96.6	108	105.2
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	69.1	79.1	69.1	79.1	79.1
Accumulated Amortization	47.5	48.1	47.5	48.1	50.7
Net Carrying Amount	21.6	31	21.6	31	28.4
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	34.8	0	34.8	34.8
Accumulated Amortization	0	34.8	0	34.8	34.8
Net Carrying Amount	0	0	0	0	0
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	484.5	529.3	484.5	529.3	529.3
Accumulated Amortization	311.4	298.8	311.4	298.8	313.4
Net Carrying Amount	$ 173.1	$ 230.5	$ 173.1	$ 230.5	$ 215.9

New Accounting Standards Effect

New Accounting Standards Effect of Standard Change (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Other assets	$ 744.1	$ 768.4	$ 757.8
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Other assets	$ 21.7