The Progressive Corporation (PGR) 10-Q 5 May 20 2020 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2020shares
Cover [Abstract]
Document Quarterly Report	true
Document Transition Report	false
Security Exchange Name	NYSE
Title of 12(b) Security	Common Shares, $1.00 Par Value
City Area Code	440
Entity Incorporation, State or Country Code	OH
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	0000080661
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Entity File Number	001-09518
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	585,298,466
Trading Symbol	PGR
Entity Small Business	false
Entity Emerging Growth Company	false
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
Local Phone Number	461-5000
Entity Information, Former Legal or Registered Name	Not Applicable
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues
Net premiums earned	$ 9,430.7	$ 8,459.8
Investment income	241.2	252.9
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales	315.2	46.1
Net holding period gains (losses) on securities	(868.8)	392.7
Net impairment losses recognized in earnings	0	(24.3)
Total net realized gains (losses) on securities	(553.6)	414.5
Fees and other revenues	153.5	130.2
Service revenues	51.6	42.6
Total revenues	9,323.4	9,300
Expenses
Losses and loss adjustment expenses	6,155.2	5,759
Policy acquisition costs	782.8	710.6
Other underwriting expenses	1,409.9	1,171.2
Investment expenses	5.3	6.2
Service expenses	47.5	38.1
Interest expense	48	47.4
Total expenses	8,448.7	7,732.5
Net Income
Income before income taxes	874.7	1,567.5
Provision for income taxes	175.6	484.7
Net income	699.1	1,082.8
Net (income) loss attributable to noncontrolling interest (NCI)	(6.4)	(4.4)
Net income attributable to Progressive	692.7	1,078.4
Other Comprehensive Income (Loss)
Total net unrealized gains (losses) on fixed-maturity securities	62.8	301.1
Net unrealized losses on forecasted transactions	0.2	0.2
Other comprehensive income (loss)	63	301.3
Other comprehensive (income) loss attributable to NCI	(0.5)	(2.3)
Comprehensive income attributable to Progressive	755.2	1,377.4
Computation of Earnings Per Common Share
Net income attributable to Progressive	692.7	1,078.4
Less: Preferred share dividends	6.7	6.7
Net Income (Loss) Available to Common Stockholders, Basic	$ 686	$ 1,071.7
Average common shares outstanding - Basic	584.7	583.5
Net effect of dilutive stock-based compensation	2.2	3.1
Total average equivalent common shares - Diluted	586.9	586.6
Basic: Earnings per common share	$ 1.17	$ 1.84
Diluted: Earnings per common share	$ 1.17	$ 1.83

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Assets
Fixed maturities (amortized cost: $33,761.1, $27,574.5, and $32,643.1)		$ 34,276.6	$ 33,110.3	$ 27,821.9
Short-term investments (amortized cost: $2,524.2, $2,584.7, and $1,798.8)		2,524.2	1,798.8	2,584.7
Total available-for-sale securities		36,800.8	34,909.1	30,406.6
Nonredeemable preferred stocks (cost: $1,017.5, $1,021.1, and $971.3)		933.4	1,038.9	1,095.4
Common equities (cost: $1,113.2, $1,194.3, and $1,125.5)		2,608.1	3,306.3	3,010.5
Total equity securities		3,541.5	4,345.2	4,105.9
Total investments		40,342.3	39,254.3	34,512.5
Cash and cash equivalents		369.5	226.2	158
Restricted cash		0.9	1.2	0.7
Cash and cash equivalents		370.4	227.4	158.7
Accrued investment income		171.6	181.3	172.1
Premiums receivable, net of allowance for doubtful accounts of $344.7, $236.9, and $283.2		7,568.3	7,507.3	7,189.8
Reinsurance Recoverable for Paid and Unpaid Claims and Claims Adjustments		3,639.6	3,378.9	2,842.8
Prepaid reinsurance premiums		438.2	626.5	446.7
Deferred acquisition costs		1,095.8	1,056.5	999.1
Property and equipment, net of accumulated depreciation of $1,191.6, $1,064.9, and $1,138.1		1,215.1	1,213.7	1,127.3
Goodwill		452.7	452.7	452.7
Intangible assets, net of accumulated amortization of $328.5, $265.6, and $314.0		213.8	228.3	276.7
Deferred Income Tax Assets, Net		34.6	0	0
Other assets		722.8	768.4	671.9
Total assets		56,265.2	54,895.3	48,850.3
Liabilities
Unearned premiums		12,641.1	12,388.8	11,603.6
Loss and loss adjustment expense reserves		18,306.5	18,105.4	15,876.6
Deferred Income Tax Liabilities, Net		0	132.5	38.5
Accounts payable, accrued expenses, and other liabilities		5,346.5	5,962.7	4,594.3
Debt	[1]	5,394	4,407.1	4,405.4
Total liabilities		41,688.1	40,996.5	36,518.4
Redeemable noncontrolling interest (NCI)	[2]	225.6	225.6	221.2
Shareholders’ Equity
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5)		493.9	493.9	493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 212.2, 213.5, and 212.9)		585.3	584.6	584
Paid-in capital		1,601.9	1,573.4	1,496.6
Retained earnings		11,266.2	10,679.6	9,358.1
Accumulated other comprehensive income (loss):
Net unrealized gains (losses) on fixed-maturity securities		423.6	360.8	195.5
Net unrealized losses on forecasted transactions		(16.2)	(16.4)	(17)
Accumulated other comprehensive (income) loss attributable to NCI		(3.2)	(2.7)	(0.4)
Total accumulated other comprehensive income (loss) attributable to Progressive		404.2	341.7	178.1
Total shareholders’ equity		14,351.5	13,673.2	12,110.7
Total liabilities, redeemable NCI, and shareholders’ equity		$ 56,265.2	$ 54,895.3	$ 48,850.3
[1]	Consists of long-term debt. 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	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Fixed maturities, amortized cost	$ 33,761.1	$ 32,643.1	$ 27,574.5
Nonredeemable preferred stocks, cost	1,017.5	971.3	1,021.1
Common equities, cost	1,113.2	1,125.5	1,194.3
Short-term investments, amortized cost	2,524.2	1,798.8	2,584.7
Premiums receivable, allowance for doubtful accounts	344.7	283.2	236.9
Intangible Assets, Accumulated Amortization	328.5	314	265.6
Property and equipment, accumulated depreciation	$ 1,191.6	$ 1,138.1	$ 1,064.9
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)	212,200,000	212,900,000	213,500,000
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	$ 0.10
Preferred Stock, Dividends Per Share, Declared								$ 26.875
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	$ 1,078.4					1,078.4
Treasury shares purchased				(0.4)	(1.1)	(24.6)
Cash dividends declared on common shares ($0.10 per share)						(58.3)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875 per share)						(13.4)
Reinvested dividends on restricted stock units					0.3	(0.3)
Net restricted equity awards issued/vested				1.2	(1.2)
Amortization of equity-based compensation					19.6
Adjustment to carrying amount of redeemable noncontrolling interest	0				0
Attributable to noncontrolling interest	(2.3)						(2.3)
Other comprehensive income							301.3
Other, net						(10.3)
Balance, End of period at Mar. 31, 2019	12,110.7		493.9	584	1,496.6	9,358.1	178.1
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
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	$ 0.10
Preferred Stock, Dividends Per Share, Declared								$ 26.875
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 692.7					692.7
Treasury shares purchased				(0.3)	(1)	(25.2)
Cash dividends declared on common shares ($0.10 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875 per share)						(13.4)
Reinvested dividends on restricted stock units					0.3	(0.3)
Net restricted equity awards issued/vested				1	(1)
Amortization of equity-based compensation					23.3
Adjustment to carrying amount of redeemable noncontrolling interest	(6.9)				6.9
Attributable to noncontrolling interest	(0.5)						(0.5)
Other comprehensive income							63
Other, net						(8.8)
Balance, End of period at Mar. 31, 2020	$ 14,351.5		$ 493.9	$ 585.3	$ 1,601.9	$ 11,266.2	$ 404.2
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	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Cash Flows [Abstract]
Net income	$ 699.1	$ 1,082.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	62.6	52.6
Amortization of intangible assets	14.5	17.9
Net amortization of fixed-income securities	18.9	0.2
Amortization of equity-based compensation	23.3	19.2
Net realized (gains) losses on securities	553.6	(414.5)
Net (gains) losses on disposition of property and equipment	0.1	5.1
Changes in:
Premiums receivable	(61)	(692.7)
Reinsurance recoverables	(260.7)	(146.7)
Prepaid reinsurance premiums	188.3	(137)
Deferred acquisition costs	(39.3)	(47.5)
Income taxes	128.7	465.2
Unearned premiums	252.3	917.1
Loss and loss adjustment expense reserves	201.1	475.8
Accounts payable, accrued expenses, and other liabilities	(189.9)	291.5
Other, net	34.2	(20.5)
Net cash provided by operating activities	1,625.8	1,868.5
Purchases:
Fixed maturities	(10,433)	(4,711.1)
Equity securities	(366.6)	(93.6)
Sales:
Fixed maturities	7,415.9	4,214.7
Equity securities	281	39
Maturities, paydowns, calls, and other:
Fixed maturities	2,161.6	1,199.7
Fixed maturities	79	0
Net sales of short-term investments	(718.9)	(774.1)
Net unsettled security transactions	586.1	(82.4)
Purchases of property and equipment	(62.4)	(75.8)
Sales of property and equipment	3.5	6.2
Net cash used in investing activities	(1,053.8)	(277.4)
Cash Flows From Financing Activities
Dividends paid to common shareholders	(1,375.4)	(1,467.9)
Dividends paid to preferred shareholders	(13.4)	(13.4)
Acquisition of treasury shares for restricted stock tax liabilities	(26.5)	(26.1)
Net proceeds from debt issuances	986.3	0
Net cash used in financing activities	(429)	(1,507.4)
Increase in cash, cash equivalents, and restricted cash	143	83.7
Cash, cash equivalents, and restricted cash – January 1	227.4	75
Cash, cash equivalents, and restricted cash – March 31	$ 370.4	$ 158.7

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 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 and ARX Holding Corp. (ARX), and their respective wholly owned insurance and non-insurance subsidiaries and affiliates in which Progressive or ARX has a controlling financial interest. The Progressive Corporation owned 87.1% of the outstanding capital stock of ARX at March 31, 2020 and December 31, 2019, compared to 86.8% at March 31, 2019 . The Progressive Corporation acquired the remaining outstanding stock of ARX on April 1, 2020. See Note 15 – Subsequent Events 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 March 31, 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 an analysis to evaluate our premium receivables for expected credit losses. At March 31, 2020, we recorded an allowance for our credit loss exposure (i.e., allowance for doubtful accounts) on our premium receivables of $344.7 million . During the first quarter 2020, we increased our allowance by $170.3 million and reduced it by $108.8 million , which represents the receivables that were written off during the period. Our increase to the allowance for doubtful accounts during the first quarter 2020, included $71.0 million to reflect the estimated impact from the billing leniency efforts that we put in place during March 2020 to help policyholders who may be 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”) that were enacted during the period. See Note 15 – Subsequent Events for further discussion. 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 $31.8 million at March 31, 2020 , $52.6 million at March 31, 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 the lease liabilities represent our obligation to make lease payments arising from the leases. At March 31, 2020 , March 31, 2019, and December 31, 2019, we had operating lease assets of $176.6 million , $201.6 million , and $188.2 million , respectively, as a component of other assets; and operating lease liabilities of $189.3 million , $211.4 million , and $201.5 million , respectively, as a component of accounts payable, accrued expenses, and other liabilities. See Note 13 – Leases in our 2019 Annual Report to Shareholders for further discussion.

Investments

Investments	3 Months Ended
	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Investments	Investments — The following tables present the composition of our investment portfolio by major security type, consistent with our classification of how we manage, monitor, and measure the portfolio. Our securities are reported in our consolidated balance sheets at fair value. The changes in fair value for our fixed-maturity securities (other than hybrid securities) are reported as a component of accumulated other comprehensive income, net of deferred income taxes, in our consolidated balance sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value of the securities. The changes in the net holding period gains (losses) between periods for the hybrid securities and equity securities are recorded as a component of net realized gains (losses) on securities in our consolidated statements of comprehensive income. Our results for the first quarter were significantly impacted by the spread of the novel coronavirus, COVID-19 and COVID-19 restrictions that were enacted. ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value March 31, 2020 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 10,841.2 $ 654.5 $ 0 $ 0 $ 11,495.7 28.5 % State and local government obligations 2,243.9 64.8 (4.5 ) 0 2,304.2 5.7 Corporate debt securities 9,452.9 160.8 (120.1 ) (1.7 ) 9,491.9 23.5 Residential mortgage-backed securities 574.3 1.5 (19.2 ) 0 556.6 1.4 Commercial mortgage-backed securities 5,822.4 30.2 (188.3 ) 0 5,664.3 14.0 Other asset-backed securities 4,674.9 4.3 (40.0 ) (0.1 ) 4,639.1 11.5 Redeemable preferred stocks 151.5 0 (5.1 ) (21.6 ) 124.8 0.3 Total fixed maturities 33,761.1 916.1 (377.2 ) (23.4 ) 34,276.6 84.9 Short-term investments 2,524.2 0 0 0 2,524.2 6.3 Total available-for-sale securities 36,285.3 916.1 (377.2 ) (23.4 ) 36,800.8 91.2 Equity securities: Nonredeemable preferred stocks 1,017.5 0 0 (84.1 ) 933.4 2.3 Common equities 1,113.2 0 0 1,494.9 2,608.1 6.5 Total equity securities 2,130.7 0 0 1,410.8 3,541.5 8.8 Total portfolio 1,2 $ 38,416.0 $ 916.1 $ (377.2 ) $ 1,387.4 $ 40,342.3 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value March 31, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,685.6 $ 105.5 $ (20.6 ) $ 0 $ 9,770.5 28.3 % State and local government obligations 1,505.5 15.4 (5.1 ) 0 1,515.8 4.4 Corporate debt securities 7,870.1 126.3 (19.0 ) 0.6 7,978.0 23.1 Residential mortgage-backed securities 609.9 5.7 (2.6 ) 0 613.0 1.8 Commercial mortgage-backed securities 3,825.6 35.9 (7.9 ) 0 3,853.6 11.2 Other asset-backed securities 3,834.2 10.0 (4.5 ) 0.1 3,839.8 11.1 Redeemable preferred stocks 243.6 9.0 (1.2 ) (0.2 ) 251.2 0.7 Total fixed maturities 27,574.5 307.8 (60.9 ) 0.5 27,821.9 80.6 Short-term investments 2,584.7 0 0 0 2,584.7 7.5 Total available-for-sale securities 30,159.2 307.8 (60.9 ) 0.5 30,406.6 88.1 Equity securities: Nonredeemable preferred stocks 1,021.1 0 0 74.3 1,095.4 3.2 Common equities 1,194.3 0 0 1,816.2 3,010.5 8.7 Total equity securities 2,215.4 0 0 1,890.5 4,105.9 11.9 Total portfolio 1,2 $ 32,374.6 $ 307.8 $ (60.9 ) $ 1,891.0 $ 34,512.5 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value December 31, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,100.7 $ 194.1 $ (43.7 ) $ 0 $ 13,251.1 33.7 % State and local government obligations 1,686.0 30.0 (2.7 ) 0 1,713.3 4.4 Corporate debt securities 6,860.3 206.6 (0.5 ) 1.3 7,067.7 18.0 Residential mortgage-backed securities 625.0 4.5 (2.0 ) 0 627.5 1.6 Commercial mortgage-backed securities 5,020.7 61.5 (6.0 ) 0 5,076.2 12.9 Other asset-backed securities 5,164.7 16.2 (1.4 ) 0 5,179.5 13.2 Redeemable preferred stocks 185.7 4.1 (1.3 ) 6.5 195.0 0.5 Total fixed maturities 32,643.1 517.0 (57.6 ) 7.8 33,110.3 84.3 Short-term investments 1,798.8 0 0 0 1,798.8 4.6 Total available-for-sale securities 34,441.9 517.0 (57.6 ) 7.8 34,909.1 88.9 Equity securities: Nonredeemable preferred stocks 971.3 0 0 67.6 1,038.9 2.7 Common equities 1,125.5 0 0 2,180.8 3,306.3 8.4 Total equity securities 2,096.8 0 0 2,248.4 4,345.2 11.1 Total portfolio 1,2 $ 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; we had $598.0 million and $11.9 million in other liabilities at March 31, 2020 and December 31, 2019 , respectively, compared to $76.5 million in other assets at March 31, 2019 . 2 The total fair value of the portfolio at March 31, 2020 and 2019 , and December 31, 2019 , included $2.6 billion , $1.2 billion , and $3.2 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. During the first quarter 2020 , we paid $1.4 billion of common share dividends and issued $1.0 billion of senior notes, both of which impacted the amount held in this non-insurance subsidiary. At March 31, 2020 , bonds and certificates of deposit in the principal amount of $281.0 million were on deposit to meet state insurance regulatory requirements. 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 invested in repurchase and reverse repurchase transactions during the first three months of 2020 and throughout 2019, we did no t have any open positions at March 31, 2020 and 2019 , or December 31, 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: March 31, (millions) 2020 2019 December 31, 2019 Fixed maturities: State and local government obligations $ 3.4 $ 3.6 $ 3.5 Corporate debt securities 116.5 161.7 91.2 Other asset-backed securities 2.2 4.0 2.6 Redeemable preferred stocks 68.4 85.4 92.1 Total hybrid securities $ 190.5 $ 254.7 $ 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 March 31, 2020 , was: (millions) Cost Fair Value Less than one year $ 6,459.3 $ 6,407.6 One to five years 18,343.3 18,532.2 Five to ten years 8,170.4 8,519.9 Ten years or greater 788.1 816.9 Total $ 33,761.1 $ 34,276.6 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 Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses March 31, 2020 Fixed maturities: U.S. government obligations 1 $ 100.3 $ 0 1 $ 100.3 $ 0 0 $ 0 $ 0 State and local government obligations 89 528.4 (4.5 ) 78 507.7 (4.4 ) 11 20.7 (0.1 ) Corporate debt securities 233 4,205.6 (120.1 ) 233 4,205.6 (120.1 ) 0 0 0 Residential mortgage-backed securities 70 532.5 (19.2 ) 46 425.0 (11.9 ) 24 107.5 (7.3 ) Commercial mortgage-backed securities 204 4,441.5 (188.3 ) 187 4,109.2 (173.8 ) 17 332.3 (14.5 ) Other asset-backed securities 216 3,558.1 (40.0 ) 201 3,514.2 (39.0 ) 15 43.9 (1.0 ) Redeemable preferred stocks 4 56.3 (5.1 ) 3 45.2 (3.8 ) 1 11.1 (1.3 ) Total fixed maturities 817 $ 13,422.7 $ (377.2 ) 749 $ 12,907.2 $ (353.0 ) 68 $ 515.5 $ (24.2 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses March 31, 2019 Fixed maturities: U.S. government obligations 42 $ 3,174.0 $ (20.6 ) 1 $ 19.9 $ (0.1 ) 41 $ 3,154.1 $ (20.5 ) State and local government obligations 162 567.2 (5.1 ) 10 31.4 0 152 535.8 (5.1 ) Corporate debt securities 153 2,555.7 (19.0 ) 11 175.9 (1.1 ) 142 2,379.8 (17.9 ) Residential mortgage-backed securities 63 299.4 (2.6 ) 15 139.1 (1.1 ) 48 160.3 (1.5 ) Commercial mortgage-backed securities 76 1,294.3 (7.9 ) 13 229.1 (0.9 ) 63 1,065.2 (7.0 ) Other asset-backed securities 142 1,294.0 (4.5 ) 27 296.5 (0.7 ) 115 997.5 (3.8 ) Redeemable preferred stocks 2 31.1 (1.2 ) 0 0 0 2 31.1 (1.2 ) Total fixed maturities 640 $ 9,215.7 $ (60.9 ) 77 $ 891.9 $ (3.9 ) 563 $ 8,323.8 $ (57.0 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses December 31, 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 ) Since both March 31, 2019 and December 31, 2019 , the number of securities in our fixed-maturity portfolio with unrealized losses increased, primarily due to valuation decreases in nearly all non-U.S. Treasury sectors during the first three months of 2020 in response to the economic impact of COVID-19 restrictions and spread widening across the market. During the first quarter 2020, we had eight securities included in the table above that had their credit ratings downgraded as a result of COVID-19 market movement, including seven in our corporate debt portfolio and one in our residential mortgage-backed portfolio, with a combined fair value of $137.6 million and an unrealized loss of $5.2 million as of March 31, 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 no t record any allowances for credit losses or any write-offs for amounts deemed to be uncollectible for the first three months of 2020 and did no t have a credit loss allowance balance as of March 31, 2020 . We considered several factors and inputs related to the individual securities as part of our analysis. The methodology and significant inputs used to measure the amount of credit losses in our portfolio included: current performance indicators on the business model or underlying assets (e.g., delinquency rates, foreclosure rates, and default rates); credit support (via current levels of subordination); historical credit ratings; and updated cash flow expectations based upon these performance indicators. In order to determine the amount of credit loss, if any, the net present value of the cash flows expected (i.e., expected recovery value) was calculated using the current book yield for each security, and was compared to its current amortized value. In the event that the net present value was below the amortized value, a credit loss would be deemed to exist, and an allowance for credit losses would be created, or if a change in the current allowance has occurred, either a recovery of the previous allowance or an incremental loss would be recorded to realized gains (losses). We also deemed it is not likely that we will be required to sell the securities in an unrealized loss position prior to the recovery of their respective cost bases (which could be maturity). In addition to the analysis mentioned above, for corporate securities, we utilized a sector benchmark credit spread change analysis, as an additional evaluation to determine if a security’s valuation declined significantly more than would be considered a market related decline. We used this evaluation to determine if there was a need to further evaluate a specific security’s decline for a potential impairment allowance. Based on our analysis, we determined that the unrealized losses at March 31, 2020 , were primarily due to the significant market decline that occurred as a result of the economic impact of COVID-19 restrictions. As of quarter-end, we believe this to be driven by market valuations and not indicative of a credit loss on any specific security. Prior to the pandemic, we expected all the securities in our portfolio to pay their principal and interest obligations, and as of March 31, 2020 , our expectations have not changed. In addition, we reviewed our accrued investment income outstanding on those securities in an unrealized loss position at March 31, 2020, to determine if the accrued interest amounts were determined to be uncollectible. Based on our analysis, we believe the issuers have sufficient liquidity and capital reserves to meet their current interest, and future principal, obligations and, therefore, did no t write-off any accrued income as uncollectible at March 31, 2020. Realized Gains (Losses) The components of net realized gains (losses) for the three months ended March 31, were: Three Months (millions) 2020 2019 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 251.1 $ 36.6 State and local government obligations 2.0 1.6 Corporate and other debt securities 32.4 16.1 Commercial mortgage-backed securities 6.1 0.7 Total available-for-sale securities 291.6 55.0 Equity securities: Nonredeemable preferred stocks 19.6 4.9 Common equities 66.0 4.5 Total equity securities 85.6 9.4 Subtotal gross realized gains on security sales 377.2 64.4 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (2.7 ) (7.1 ) State and local government obligations 0 (0.6 ) Corporate and other debt securities (1.0 ) (6.1 ) Residential mortgage-backed securities 0 (2.3 ) Commercial mortgage-backed securities 0 (2.1 ) Other asset-backed securities 0 (0.1 ) Total available-for-sale securities (3.7 ) (18.3 ) Equity securities: Nonredeemable preferred stocks (4.4 ) 0 Common equities (53.9 ) 0 Total equity securities (58.3 ) 0 Subtotal gross realized losses on security sales (62.0 ) (18.3 ) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 248.4 29.5 State and local government obligations 2.0 1.0 Corporate and other debt securities 31.4 10.0 Residential mortgage-backed securities 0 (2.3 ) Commercial mortgage-backed securities 6.1 (1.4 ) Other asset-backed securities 0 (0.1 ) Total available-for-sale securities 287.9 36.7 Equity securities: Nonredeemable preferred stocks 15.2 4.9 Common equities 12.1 4.5 Total equity securities 27.3 9.4 Subtotal net realized gains (losses) on security sales 315.2 46.1 Net holding period gains (losses) Hybrid securities (31.2 ) 10.7 Equity securities (837.6 ) 382.0 Subtotal net holding period gains (losses) (868.8 ) 392.7 Impairment losses Other asset impairment 0 (24.3 ) Subtotal impairment losses 0 (24.3 ) Total net realized gains (losses) on securities $ (553.6 ) $ 414.5 Realized gains (losses) on securities sold are computed using the first-in-first-out method. Net holding period losses were the result of significant declines in our common and nonredeemable preferred stock valuations, due to the desire of investors to reduce exposure to risk and seek safety in the form of U.S. Treasury securities in response to the economic impact of COVID-19 restrictions. Net realized gains on security sales were primarily in U.S. Treasury securities, which were sold in order to selectively increase holdings across the remainder of the portfolio, predominantly in our corporate debt portfolio. The sales in our common stock portfolio were the result of rebalancing the indexed equity portfolio, which was intended to bring the tracking error within +/- 50 basis points of the index. We had net security gains on the sales of our common stocks due to the extensive holding periods of these investments, in some cases more than ten years, which created significant valuation increases that more than offset the decline experienced during the first quarter. For the first quarter 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, were 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 months ended March 31, 2020 and 2019 , for equity securities held at the respective quarter end: Three Months (millions) 2020 2019 Total net gains (losses) recognized during the period on equity securities $ (810.3 ) $ 391.4 Less: Net gains (losses) recognized on equity securities sold during the period 27.3 9.4 Net holding period gains (losses) recognized during the period on equity securities held at period end $ (837.6 ) $ 382.0 Net Investment Income The components of net investment income for the three months ended March 31, were: Three Months (millions) 2020 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 62.6 $ 53.7 State and local government obligations 9.6 9.3 Corporate debt securities 58.0 77.2 Residential mortgage-backed securities 4.2 6.6 Commercial mortgage-backed securities 34.3 31.7 Other asset-backed securities 29.2 26.0 Redeemable preferred stocks 7.9 3.7 Total fixed maturities 205.8 208.2 Short-term investments 7.0 16.0 Total available-for-sale securities 212.8 224.2 Equity securities: Nonredeemable preferred stocks 13.8 15.5 Common equities 14.6 13.2 Total equity securities 28.4 28.7 Investment income 241.2 252.9 Investment expenses (5.3 ) (6.2 ) Net investment income $ 235.9 $ 246.7 The amount of investment income (interest and dividends) we recognize varies based on the average assets held during the year and the book yields of the securities in our portfolio. We experienced an approximately 5% decrease in income during the first quarter 2020 compared to the same period in 2019, as interest rates significantly declined throughout the quarter due to the economic impact of COVID-19 restrictions, which impacted the portfolio’s yield from rates on new investments due to cash from operations, debt issuance proceeds, and reinvested cash from sales, maturities, paydowns, and other redemptions. Income declines based on yield reductions was approximately 17% while higher average assets increased income by approximately 12% during the first quarter 2020, when compared to the same period in 2019. The increase in average assets was a combination of strong premium growth, underwriting profitability, and the proceeds from the debt issuance, partially offset by common and preferred stock dividend payments and the slight negative returns for the total investment portfolio during the quarter. The portfolio duration at March 31, 2020 was 3.0 years , compared to 2.6 years at March 31, 2019 .

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value	Fair Value — We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows: • Level 1 : Inputs are unadjusted quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, which are continually priced on daily, 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 March 31, 2020 Fixed maturities: U.S. government obligations $ 11,495.7 $ 0 $ 0 $ 11,495.7 $ 10,841.2 State and local government obligations 0 2,304.2 0 2,304.2 2,243.9 Corporate debt securities 0 9,491.9 0 9,491.9 9,452.9 Subtotal 11,495.7 11,796.1 0 23,291.8 22,538.0 Asset-backed securities: Residential mortgage-backed 0 556.6 0 556.6 574.3 Commercial mortgage-backed 0 5,664.3 0 5,664.3 5,822.4 Other asset-backed 0 4,639.1 0 4,639.1 4,674.9 Subtotal asset-backed securities 0 10,860.0 0 10,860.0 11,071.6 Redeemable preferred stocks: Financials 0 47.2 0 47.2 51.4 Utilities 0 9.2 0 9.2 10.0 Industrials 7.3 61.1 0 68.4 90.1 Subtotal redeemable preferred stocks 7.3 117.5 0 124.8 151.5 Total fixed maturities 11,503.0 22,773.6 0 34,276.6 33,761.1 Short-term investments 2,438.4 85.8 0 2,524.2 2,524.2 Total available-for-sale securities 13,941.4 22,859.4 0 36,800.8 36,285.3 Equity securities: Nonredeemable preferred stocks: Financials 105.5 752.3 13.1 870.9 937.4 Utilities 0 32.0 0 32.0 40.0 Industrials 0 15.3 15.2 30.5 40.1 Subtotal nonredeemable preferred stocks 105.5 799.6 28.3 933.4 1,017.5 Common equities: Common stocks 2,607.8 0 0 2,607.8 1,112.9 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,607.8 0 0.3 2,608.1 1,113.2 Total equity securities 2,713.3 799.6 28.6 3,541.5 2,130.7 Total portfolio $ 16,654.7 $ 23,659.0 $ 28.6 $ 40,342.3 $ 38,416.0 Debt $ 0 $ 6,108.6 $ 0 $ 6,108.6 $ 5,394.0 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost March 31, 2019 Fixed maturities: U.S. government obligations $ 9,770.5 $ 0 $ 0 $ 9,770.5 $ 9,685.6 State and local government obligations 0 1,515.8 0 1,515.8 1,505.5 Corporate debt securities 0 7,978.0 0 7,978.0 7,870.1 Subtotal 9,770.5 9,493.8 0 19,264.3 19,061.2 Asset-backed securities: Residential mortgage-backed 0 613.0 0 613.0 609.9 Commercial mortgage-backed 0 3,853.6 0 3,853.6 3,825.6 Other asset-backed 0 3,839.8 0 3,839.8 3,834.2 Subtotal asset-backed securities 0 8,306.4 0 8,306.4 8,269.7 Redeemable preferred stocks: Financials 0 81.3 0 81.3 79.2 Utilities 0 0 0 0 0 Industrials 10.4 159.5 0 169.9 164.4 Subtotal redeemable preferred stocks 10.4 240.8 0 251.2 243.6 Total fixed maturities 9,780.9 18,041.0 0 27,821.9 27,574.5 Short-term investments 2,510.9 73.8 0 2,584.7 2,584.7 Total available-for-sale securities 12,291.8 18,114.8 0 30,406.6 30,159.2 Equity securities: Nonredeemable preferred stocks: Financials 69.6 955.0 25.1 1,049.7 976.1 Utilities 0 40.7 0 40.7 40.0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 69.6 995.7 30.1 1,095.4 1,021.1 Common equities: Common stocks 3,010.2 0 0 3,010.2 1,194.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,010.2 0 0.3 3,010.5 1,194.3 Total equity securities 3,079.8 995.7 30.4 4,105.9 2,215.4 Total portfolio $ 15,371.6 $ 19,110.5 $ 30.4 $ 34,512.5 $ 32,374.6 Debt $ 0 $ 4,734.8 $ 0 $ 4,734.8 $ 4,405.4 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 March 31, 2020 , vendor-quoted prices represented 82% of our Level 1 classifications (excluding short-term investments), compared to 77% and 80% at March 31, 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 March 31, 2020 , vendor-quoted prices comprised 98% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented the remaining 2% , compared to 99% and 1% , respectively, at both March 31, 2019 and December 31, 2019 . 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 March 31, 2020 and 2019 , and December 31, 2019 , we did no t have any securities in our fixed-maturity portfolio listed as Level 3. At March 31, 2020 and December 31, 2019 , we held three private nonredeemable preferred securities that were priced internally or by a pricing firm and we held two private nonredeemable preferred securities that were priced internally at March 31, 2019 . At March 31, 2020 and 2019 , and December 31, 2019 , we held one Level 3 other risk investment that was priced using the equity method. 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 first quarter 2020 , our Level 3 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, rather than having our external pricing source update their valuation models, due to the timing of the market decline, relative to our quarter end. 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 months ended March 31, 2020 and 2019 : Level 3 Fair Value (millions) Fair Value at December 31, 2019 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at March 31, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 0 $ 0 $ 0 $ (14.0 ) $ 0 $ 13.1 Industrials 16.0 0 0 0 0 (0.8 ) 0 15.2 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 43.4 $ 0 $ 0 $ 0 $ 0 $ (14.8 ) $ 0 $ 28.6 Level 3 Fair Value (millions) Fair Value at December 31, 2018 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at March 31, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 25.1 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 $ 0 $ 0 $ 0 $ 0 $ 0 $ 30.4 The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at March 31, 2020 and 2019 , and December 31, 2019 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 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 ) Industrials 15.2 Guideline public company method Weighted average capitalization % (19.2 ) Subtotal Level 3 securities 28.3 Pricing exemption securities 0.3 Total Level 3 securities $ 28.6 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 25.1 Internal price Unadjusted purchase price per share 9.0 Industrials 5.0 Internal price Price-to-sales ratio 5.5 Subtotal Level 3 securities 30.1 Pricing exemption securities 0.3 Total Level 3 securities $ 30.4 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	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt — Debt at each of the balance sheet periods consisted of: March 31, 2020 March 31, 2019 December 31, 2019 (millions) Carrying Value Fair Value Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 $ 499.5 $ 510.7 $ 499.2 $ 509.7 $ 499.4 $ 515.6 2.45% Senior Notes due 2027 497.0 488.2 496.6 475.6 496.9 501.5 6 5/8% Senior Notes due 2029 296.7 395.3 296.4 377.8 296.6 392.5 4.00% Senior Notes due 2029 545.1 605.7 544.6 587.9 545.0 614.3 3.20% Senior Notes due 2030 495.8 543.2 0 0 0 0 6.25% Senior Notes due 2032 395.8 539.6 395.6 508.5 395.7 552.6 4.35% Senior Notes due 2044 346.7 391.7 346.6 371.6 346.7 417.0 3.70% Senior Notes due 2045 395.4 406.2 395.3 389.7 395.4 434.2 4.125% Senior Notes due 2047 841.6 991.9 841.4 885.4 841.6 986.1 4.20% Senior Notes due 2048 589.9 675.8 589.7 628.6 589.8 705.8 3.95% Senior Notes due 2050 490.5 560.3 0 0 0 0 Total $ 5,394.0 $ 6,108.6 $ 4,405.4 $ 4,734.8 $ 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 a treasury “make whole” provision. During 2019, The Progressive Corporation renewed the line of credit with PNC Bank, National Association (PNC) in the maximum principal amount of $250 million . This line of credit replaced a previous line of credit that was entered into in April 2018. The line of credit is on the same terms and conditions as the previous line of credit. 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 50 basis points. Each advance must be repaid on the 30 th day after the advance or, if earlier, on April 30, 2020, 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 any of the periods presented. During April 2020, we renewed this line of credit in the same principal amount, 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, under otherwise similar terms and conditions.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 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 March 31, 2020 and 2019 , and December 31, 2019 , we determined that we did no t 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 three months ended March 31, 2020 , there have been no material changes in our reserve for uncertain tax positions. The effective tax rate for the three months ended March 31, 2020 , was 20.1% , compared to 30.9% for the same period last year. For the first quarter 2019, the higher effective rate was due primarily to the reversal of tax credits and other tax benefits previously recognized from certain renewable energy investments, where the sponsor plead 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	3 Months Ended
	Mar. 31, 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: March 31, (millions) 2020 2019 Balance, beginning of period $ 18,105.4 $ 15,400.8 Less reinsurance recoverables on unpaid losses 3,212.2 2,572.7 Net balance, beginning of period 14,893.2 12,828.1 Incurred related to: Current year 6,011.1 5,616.4 Prior years 144.1 142.6 Total incurred 6,155.2 5,759.0 Paid related to: Current year 2,916.4 2,517.5 Prior years 3,269.2 2,901.4 Total paid 6,185.6 5,418.9 Net balance, end of period 14,862.8 13,168.2 Plus reinsurance recoverables on unpaid losses 3,443.7 2,708.4 Balance, end of period $ 18,306.5 $ 15,876.6 We experienced unfavorable reserve development of $144.1 million and $142.6 million during the first three months of 2020 and 2019, respectively, which is reflected as “Incurred related to prior years ” in the table above. First Quarter 2020 • Approximately 52% of the unfavorable prior year reserve development was attributable to accident year 2019, 36% to accident year 2018, and the remainder to 2017 and prior accident years. • Our personal auto products incurred about $104 million of unfavorable loss and loss adjustment expense (LAE) reserve development, with the Agency and Direct auto businesses each contributing about half. The unfavorable development was primarily attributable to revised estimates of our per claim settlement costs and late reported losses occurring toward the end 2019 but not reported until 2020. • Our Commercial Lines business experienced about $54 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 business experienced about $14 million of favorable development and our Property business had minimal development during the first quarter. First Quarter 2019 • About 40% of the unfavorable prior year reserve development was attributable to accident year 2018, 15% to accident year 2017, and the remainder to accident years 2016 and prior. • Our personal auto products incurred about $111 million of unfavorable loss and loss adjustment expense reserve development, with the Agency and Direct auto businesses each contributing about half. The unfavorable development was primarily attributable to late reported losses occurring late 2018 but not reported until 2019, a higher than anticipated frequency of reopened personal injury protection (PIP) claims, primarily in Florida, and increased injury severity reflecting higher medical costs. • Our Commercial Lines and special lines businesses experienced about $22 million and $8 million of unfavorable development, respectively, and our Property business had minimal unfavorable development during the first quarter.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 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 of funds held in bank demand deposit accounts on ARX’s subsidiaries, and are not considered part of the investment portfolio. The amount of reverse repurchase commitments held by ARX’s subsidiaries at March 31, 2020 and 2019 , and December 31, 2019 , were $80.6 million , $185.6 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 ARX are administrators. During the first quarter 2020, non-cash activity includes declared but unpaid common share dividends of $58.5 million (see Note 9 – Dividends for further discussion) and operating lease liabilities arising from obtaining right-of-use assets of $9.7 million . We paid the following in the respective periods: Three Months Ended March 31, (millions) 2020 2019 Income taxes $ 0 $ 20.0 Interest 56.4 53.3 Operating lease liabilities 22.7 18.8

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 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 March 31, 2020 2019 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 3,828.7 $ 601.6 $ 3,508.5 $ 453.0 Direct 3,992.4 473.0 3,576.3 321.9 Total Personal Lines 1 7,821.1 1,074.6 7,084.8 774.9 Commercial Lines 1,189.0 112.5 1,013.0 166.6 Property 2 420.6 49.2 362.0 7.7 Total underwriting operations 9,430.7 1,236.3 8,459.8 949.2 Fees and other revenues 3 153.5 NA 130.2 NA Service businesses 51.6 4.1 42.6 4.5 Investments 4 (312.4 ) (317.7 ) 667.4 661.2 Interest expense NA (48.0 ) NA (47.4 ) Consolidated total $ 9,323.4 $ 874.7 $ 9,300.0 $ 1,567.5 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three months ended March 31, 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 months ended March 31, 2020 and 2019, pretax profit (loss) includes $14.5 million and $17.9 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX. Although this expense is included in our Property segment, it is not reported in the consolidated results of ARX and, therefore, does not affect the value of net income attributable to noncontrolling interest. 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, and other underwriting expenses 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 March 31, 2020 2019 Underwriting Combined Ratio Underwriting Combined Ratio Personal Lines Agency 15.7 % 84.3 12.9 % 87.1 Direct 11.9 88.1 9.0 91.0 Total Personal Lines 13.7 86.3 10.9 89.1 Commercial Lines 9.5 90.5 16.4 83.6 Property 1 11.7 88.3 2.1 97.9 Total underwriting operations 13.1 86.9 11.2 88.8 1 Included in the three months ended March 31, 2020 and 2019, is 3.4 points and 5.0 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX.

Dividends

Dividends	3 Months Ended
	Mar. 31, 2020
Dividends [Abstract]
Dividends	Dividends — Following is a summary of our common and preferred share dividends that were declared and/or paid during the three months ended March 31, 2020 and 2019: (millions, except per share amounts) Amount Declared Payable Per Share Accrued 1 Common - Quarterly Dividends: February 2020 April 2020 $ 0.10 $ 58.5 December 2019 January 2020 0.10 58.5 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: February 2020 March 2020 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)	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) — The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income (loss) Total tax (provision) benefit After tax total accumulated other comprehensive income (loss) Total net unrealized gains (losses) on securities Net unrealized gains (losses) on forecasted transactions (Income) loss attributable to NCI Balance at December 31, 2019 $ 435.7 $ (94.0 ) $ 341.7 $ 360.8 $ (16.4 ) $ (2.7 ) Other comprehensive income (loss) before reclassifications: Investment securities 318.2 (66.8 ) 251.4 251.4 0 0 Loss attributable to noncontrolling interest (NCI) (0.6 ) 0.1 (0.5 ) 0 0 (0.5 ) Total other comprehensive income (loss) before reclassifications 317.6 (66.7 ) 250.9 251.4 0 (0.5 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 238.7 (50.1 ) 188.6 188.6 0 0 Interest expense (0.3 ) 0.1 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income 238.4 (50.0 ) 188.4 188.6 (0.2 ) 0 Total other comprehensive income (loss) 79.2 (16.7 ) 62.5 62.8 0.2 (0.5 ) Balance at March 31, 2020 $ 514.9 $ (110.7 ) $ 404.2 $ 423.6 $ (16.2 ) $ (3.2 ) Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income (loss) Total tax (provision) benefit After tax total accumulated other comprehensive income (loss) Total net unrealized gains (losses) on securities Net (Income) loss attributable to NCI Balance at December 31, 2018 $ (153.0 ) $ 32.1 $ (120.9 ) $ (105.6 ) $ (17.2 ) $ 1.9 Other comprehensive income (loss) before reclassifications: Investment securities 414.5 (87.0 ) 327.5 327.5 0 0 Loss attributable to noncontrolling interest (NCI) (2.9 ) 0.6 (2.3 ) 0 0 (2.3 ) Total other comprehensive income (loss) before reclassifications 411.6 (86.4 ) 325.2 327.5 0 (2.3 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 33.4 (7.0 ) 26.4 26.4 0 0 Interest expense (0.3 ) 0.1 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income 33.1 (6.9 ) 26.2 26.4 (0.2 ) 0 Total other comprehensive income (loss) 378.5 (79.5 ) 299.0 301.1 0.2 (2.3 ) Balance at March 31, 2019 $ 225.5 $ (47.4 ) $ 178.1 $ 195.5 $ (17.0 ) $ (0.4 ) 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 $1.1 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	3 Months Ended
	Mar. 31, 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 March 31, 2020 or 2019 , and there were no material settlements during 2019 or the first three 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	3 Months Ended
	Mar. 31, 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. Pursuant to the stockholders’ agreement, the minority ARX stockholders, upon specified dates, had the right to “put ” all of their remaining shares to Progressive, and Progressive had the ability to “call ” all of the outstanding shares. On April 1, 2020, Progressive purchased all remaining outstanding stock of ARX under a separately negotiated purchase agreement. See Note 15 – Subsequent Events . In addition to these minority shares, at March 31, 2020 , ARX employees held options to purchase 10,438 ARX shares. These options and any shares issued upon exercise were subject to the stockholders’ agreement, including the “put ” and “call ” rights described above. As the options were not exercised at March 31, 2020, the underlying obligation of approximately $16.0 million is not recorded as part of redeemable NCI. See Note 9 – Employee Benefit Plans in our 2019 Annual Report to Shareholders for a discussion of ARX employee stock options. On April 1, 2020, the ARX employees exercised their stock options and Progressive purchased the exercised stock options under a separately negotiated purchase agreement. See Note 15 – Subsequent Events. The changes in the components of redeemable NCI were: Three Months Ended March 31, Year Ended (millions) 2020 2019 December 31, 2019 Balance, beginning of period $ 225.6 $ 214.5 $ 214.5 Net income attributable to NCI 6.4 4.4 9.7 Other comprehensive income (loss) attributable to NCI 1 0.5 2.3 4.6 Exercise of employee stock options 0 0 7.7 Purchase/change of ARX minority shares 0 0 (11.2 ) Change in redemption value of NCI 2 (6.9 ) 0 0.3 Balance, end of period $ 225.6 $ 221.2 $ 225.6 1 Amount represents the other comprehensive income (loss) attributable to NCI, as reflected on the 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. 2 For the three months ended March 31, 2020, amount represents the adjustment to the carrying amount of redeemable NCI, which was reclassified to paid-in capital, to reflect the amount due to acquire the remaining outstanding stock from ARX minority shareholders, based on a negotiated purchase agreement as discussed above. See Note 15 – Subsequent Events

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Mar. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill During the three months ended March 31, 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) March 31, 2020 March 31, 2019 December 31, 2019 Intangible assets subject to amortization $ 201.4 $ 264.3 $ 215.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 213.8 $ 276.7 $ 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) March 31, 2020 March 31, 2019 December 31, 2019 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 183.0 $ 73.2 $ 256.2 $ 146.4 $ 109.8 $ 256.2 $ 173.9 $ 82.3 Agency relationships 159.2 56.9 102.3 159.2 45.5 113.7 159.2 54.0 105.2 Software rights 79.1 53.2 25.9 79.1 42.7 36.4 79.1 50.7 28.4 Trade name 34.8 34.8 0 34.8 30.4 4.4 34.8 34.8 0 Total $ 529.3 $ 327.9 $ 201.4 $ 529.3 $ 265.0 $ 264.3 $ 529.3 $ 313.4 $ 215.9 Amortization expense was $14.5 million , compared to $17.9 million for the three months ended March 31, 2020 and 2019, respectively. During the first quarter 2020, one software rights intangible asset, with a gross carrying value of $10.0 million

New Accounting Standards

New Accounting Standards	3 Months Ended
	Mar. 31, 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 three months ended March 31, 2020, we capitalized $6.2 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 will require prospective changes on 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 uncollectibility 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.

Subsequent Event (Notes)

Subsequent Event (Notes)	3 Months Ended
	Mar. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events — On April 1, 2020, The Progressive Corporation acquired the remaining outstanding stock of ARX Holding Corp., bringing Progressive’s ownership interest to 100% . Under a separately negotiated purchase agreement, the cost of purchasing the remaining outstanding stock and shares from exercised stock options was $243.0 million in aggregate. In April 2020, in response to the expected reduction in auto accident frequency and the financial hardships imposed by the impact of COVID-19 restrictions throughout the United States, Progressive announced it will issue a credit to all personal auto customers who have a policy in force at the end of April and/or May 2020. These credits or payments, which will reduce our underwriting profitability during the second quarter 2020, will be made separately in May and June to customers with a policy in force on April 30 and May 31, 2020, respectively. Based on our current estimate of the number of customers who will have policies in force on the applicable dates, we estimate the credit will be approximately $1.0 billion in the aggregate.

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 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. Our results for the first quarter were significantly impacted by the spread of the novel coronavirus, COVID-19 and COVID-19 restrictions that were enacted. ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value March 31, 2020 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 10,841.2 $ 654.5 $ 0 $ 0 $ 11,495.7 28.5 % State and local government obligations 2,243.9 64.8 (4.5 ) 0 2,304.2 5.7 Corporate debt securities 9,452.9 160.8 (120.1 ) (1.7 ) 9,491.9 23.5 Residential mortgage-backed securities 574.3 1.5 (19.2 ) 0 556.6 1.4 Commercial mortgage-backed securities 5,822.4 30.2 (188.3 ) 0 5,664.3 14.0 Other asset-backed securities 4,674.9 4.3 (40.0 ) (0.1 ) 4,639.1 11.5 Redeemable preferred stocks 151.5 0 (5.1 ) (21.6 ) 124.8 0.3 Total fixed maturities 33,761.1 916.1 (377.2 ) (23.4 ) 34,276.6 84.9 Short-term investments 2,524.2 0 0 0 2,524.2 6.3 Total available-for-sale securities 36,285.3 916.1 (377.2 ) (23.4 ) 36,800.8 91.2 Equity securities: Nonredeemable preferred stocks 1,017.5 0 0 (84.1 ) 933.4 2.3 Common equities 1,113.2 0 0 1,494.9 2,608.1 6.5 Total equity securities 2,130.7 0 0 1,410.8 3,541.5 8.8 Total portfolio 1,2 $ 38,416.0 $ 916.1 $ (377.2 ) $ 1,387.4 $ 40,342.3 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value March 31, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,685.6 $ 105.5 $ (20.6 ) $ 0 $ 9,770.5 28.3 % State and local government obligations 1,505.5 15.4 (5.1 ) 0 1,515.8 4.4 Corporate debt securities 7,870.1 126.3 (19.0 ) 0.6 7,978.0 23.1 Residential mortgage-backed securities 609.9 5.7 (2.6 ) 0 613.0 1.8 Commercial mortgage-backed securities 3,825.6 35.9 (7.9 ) 0 3,853.6 11.2 Other asset-backed securities 3,834.2 10.0 (4.5 ) 0.1 3,839.8 11.1 Redeemable preferred stocks 243.6 9.0 (1.2 ) (0.2 ) 251.2 0.7 Total fixed maturities 27,574.5 307.8 (60.9 ) 0.5 27,821.9 80.6 Short-term investments 2,584.7 0 0 0 2,584.7 7.5 Total available-for-sale securities 30,159.2 307.8 (60.9 ) 0.5 30,406.6 88.1 Equity securities: Nonredeemable preferred stocks 1,021.1 0 0 74.3 1,095.4 3.2 Common equities 1,194.3 0 0 1,816.2 3,010.5 8.7 Total equity securities 2,215.4 0 0 1,890.5 4,105.9 11.9 Total portfolio 1,2 $ 32,374.6 $ 307.8 $ (60.9 ) $ 1,891.0 $ 34,512.5 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value December 31, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,100.7 $ 194.1 $ (43.7 ) $ 0 $ 13,251.1 33.7 % State and local government obligations 1,686.0 30.0 (2.7 ) 0 1,713.3 4.4 Corporate debt securities 6,860.3 206.6 (0.5 ) 1.3 7,067.7 18.0 Residential mortgage-backed securities 625.0 4.5 (2.0 ) 0 627.5 1.6 Commercial mortgage-backed securities 5,020.7 61.5 (6.0 ) 0 5,076.2 12.9 Other asset-backed securities 5,164.7 16.2 (1.4 ) 0 5,179.5 13.2 Redeemable preferred stocks 185.7 4.1 (1.3 ) 6.5 195.0 0.5 Total fixed maturities 32,643.1 517.0 (57.6 ) 7.8 33,110.3 84.3 Short-term investments 1,798.8 0 0 0 1,798.8 4.6 Total available-for-sale securities 34,441.9 517.0 (57.6 ) 7.8 34,909.1 88.9 Equity securities: Nonredeemable preferred stocks 971.3 0 0 67.6 1,038.9 2.7 Common equities 1,125.5 0 0 2,180.8 3,306.3 8.4 Total equity securities 2,096.8 0 0 2,248.4 4,345.2 11.1 Total portfolio 1,2 $ 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; we had $598.0 million and $11.9 million in other liabilities at March 31, 2020 and December 31, 2019 , respectively, compared to $76.5 million in other assets at March 31, 2019 . 2 The total fair value of the portfolio at March 31, 2020 and 2019 , and December 31, 2019 , included $2.6 billion , $1.2 billion , and $3.2 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. During the first quarter 2020 , we paid $1.4 billion of common share dividends and issued $1.0 billion of senior notes, both of which impacted the amount held in this non-insurance subsidiary.
Hybrid Instruments Table	Included in our fixed-maturity securities are hybrid securities, which are reported at fair value: March 31, (millions) 2020 2019 December 31, 2019 Fixed maturities: State and local government obligations $ 3.4 $ 3.6 $ 3.5 Corporate debt securities 116.5 161.7 91.2 Other asset-backed securities 2.2 4.0 2.6 Redeemable preferred stocks 68.4 85.4 92.1 Total hybrid securities $ 190.5 $ 254.7 $ 189.4
Investments Classified by Contractual Maturity Date	The composition of fixed maturities by maturity at March 31, 2020 , was: (millions) Cost Fair Value Less than one year $ 6,459.3 $ 6,407.6 One to five years 18,343.3 18,532.2 Five to ten years 8,170.4 8,519.9 Ten years or greater 788.1 816.9 Total $ 33,761.1 $ 34,276.6
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 Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses March 31, 2020 Fixed maturities: U.S. government obligations 1 $ 100.3 $ 0 1 $ 100.3 $ 0 0 $ 0 $ 0 State and local government obligations 89 528.4 (4.5 ) 78 507.7 (4.4 ) 11 20.7 (0.1 ) Corporate debt securities 233 4,205.6 (120.1 ) 233 4,205.6 (120.1 ) 0 0 0 Residential mortgage-backed securities 70 532.5 (19.2 ) 46 425.0 (11.9 ) 24 107.5 (7.3 ) Commercial mortgage-backed securities 204 4,441.5 (188.3 ) 187 4,109.2 (173.8 ) 17 332.3 (14.5 ) Other asset-backed securities 216 3,558.1 (40.0 ) 201 3,514.2 (39.0 ) 15 43.9 (1.0 ) Redeemable preferred stocks 4 56.3 (5.1 ) 3 45.2 (3.8 ) 1 11.1 (1.3 ) Total fixed maturities 817 $ 13,422.7 $ (377.2 ) 749 $ 12,907.2 $ (353.0 ) 68 $ 515.5 $ (24.2 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses March 31, 2019 Fixed maturities: U.S. government obligations 42 $ 3,174.0 $ (20.6 ) 1 $ 19.9 $ (0.1 ) 41 $ 3,154.1 $ (20.5 ) State and local government obligations 162 567.2 (5.1 ) 10 31.4 0 152 535.8 (5.1 ) Corporate debt securities 153 2,555.7 (19.0 ) 11 175.9 (1.1 ) 142 2,379.8 (17.9 ) Residential mortgage-backed securities 63 299.4 (2.6 ) 15 139.1 (1.1 ) 48 160.3 (1.5 ) Commercial mortgage-backed securities 76 1,294.3 (7.9 ) 13 229.1 (0.9 ) 63 1,065.2 (7.0 ) Other asset-backed securities 142 1,294.0 (4.5 ) 27 296.5 (0.7 ) 115 997.5 (3.8 ) Redeemable preferred stocks 2 31.1 (1.2 ) 0 0 0 2 31.1 (1.2 ) Total fixed maturities 640 $ 9,215.7 $ (60.9 ) 77 $ 891.9 $ (3.9 ) 563 $ 8,323.8 $ (57.0 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses December 31, 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 months ended March 31, were: Three Months (millions) 2020 2019 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 251.1 $ 36.6 State and local government obligations 2.0 1.6 Corporate and other debt securities 32.4 16.1 Commercial mortgage-backed securities 6.1 0.7 Total available-for-sale securities 291.6 55.0 Equity securities: Nonredeemable preferred stocks 19.6 4.9 Common equities 66.0 4.5 Total equity securities 85.6 9.4 Subtotal gross realized gains on security sales 377.2 64.4 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (2.7 ) (7.1 ) State and local government obligations 0 (0.6 ) Corporate and other debt securities (1.0 ) (6.1 ) Residential mortgage-backed securities 0 (2.3 ) Commercial mortgage-backed securities 0 (2.1 ) Other asset-backed securities 0 (0.1 ) Total available-for-sale securities (3.7 ) (18.3 ) Equity securities: Nonredeemable preferred stocks (4.4 ) 0 Common equities (53.9 ) 0 Total equity securities (58.3 ) 0 Subtotal gross realized losses on security sales (62.0 ) (18.3 ) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 248.4 29.5 State and local government obligations 2.0 1.0 Corporate and other debt securities 31.4 10.0 Residential mortgage-backed securities 0 (2.3 ) Commercial mortgage-backed securities 6.1 (1.4 ) Other asset-backed securities 0 (0.1 ) Total available-for-sale securities 287.9 36.7 Equity securities: Nonredeemable preferred stocks 15.2 4.9 Common equities 12.1 4.5 Total equity securities 27.3 9.4 Subtotal net realized gains (losses) on security sales 315.2 46.1 Net holding period gains (losses) Hybrid securities (31.2 ) 10.7 Equity securities (837.6 ) 382.0 Subtotal net holding period gains (losses) (868.8 ) 392.7 Impairment losses Other asset impairment 0 (24.3 ) Subtotal impairment losses 0 (24.3 ) Total net realized gains (losses) on securities $ (553.6 ) $ 414.5
Components of Equity Realized Gains (Losses)	The following table reflects our holding period realized gains (losses) on equity securities recognized for the three months ended March 31, 2020 and 2019 , for equity securities held at the respective quarter end: Three Months (millions) 2020 2019 Total net gains (losses) recognized during the period on equity securities $ (810.3 ) $ 391.4 Less: Net gains (losses) recognized on equity securities sold during the period 27.3 9.4 Net holding period gains (losses) recognized during the period on equity securities held at period end $ (837.6 ) $ 382.0
Components of Net Investment Income	The components of net investment income for the three months ended March 31, were: Three Months (millions) 2020 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 62.6 $ 53.7 State and local government obligations 9.6 9.3 Corporate debt securities 58.0 77.2 Residential mortgage-backed securities 4.2 6.6 Commercial mortgage-backed securities 34.3 31.7 Other asset-backed securities 29.2 26.0 Redeemable preferred stocks 7.9 3.7 Total fixed maturities 205.8 208.2 Short-term investments 7.0 16.0 Total available-for-sale securities 212.8 224.2 Equity securities: Nonredeemable preferred stocks 13.8 15.5 Common equities 14.6 13.2 Total equity securities 28.4 28.7 Investment income 241.2 252.9 Investment expenses (5.3 ) (6.2 ) Net investment income $ 235.9 $ 246.7

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Composition of Investment Portfolio by Major Security Type	The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost March 31, 2020 Fixed maturities: U.S. government obligations $ 11,495.7 $ 0 $ 0 $ 11,495.7 $ 10,841.2 State and local government obligations 0 2,304.2 0 2,304.2 2,243.9 Corporate debt securities 0 9,491.9 0 9,491.9 9,452.9 Subtotal 11,495.7 11,796.1 0 23,291.8 22,538.0 Asset-backed securities: Residential mortgage-backed 0 556.6 0 556.6 574.3 Commercial mortgage-backed 0 5,664.3 0 5,664.3 5,822.4 Other asset-backed 0 4,639.1 0 4,639.1 4,674.9 Subtotal asset-backed securities 0 10,860.0 0 10,860.0 11,071.6 Redeemable preferred stocks: Financials 0 47.2 0 47.2 51.4 Utilities 0 9.2 0 9.2 10.0 Industrials 7.3 61.1 0 68.4 90.1 Subtotal redeemable preferred stocks 7.3 117.5 0 124.8 151.5 Total fixed maturities 11,503.0 22,773.6 0 34,276.6 33,761.1 Short-term investments 2,438.4 85.8 0 2,524.2 2,524.2 Total available-for-sale securities 13,941.4 22,859.4 0 36,800.8 36,285.3 Equity securities: Nonredeemable preferred stocks: Financials 105.5 752.3 13.1 870.9 937.4 Utilities 0 32.0 0 32.0 40.0 Industrials 0 15.3 15.2 30.5 40.1 Subtotal nonredeemable preferred stocks 105.5 799.6 28.3 933.4 1,017.5 Common equities: Common stocks 2,607.8 0 0 2,607.8 1,112.9 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,607.8 0 0.3 2,608.1 1,113.2 Total equity securities 2,713.3 799.6 28.6 3,541.5 2,130.7 Total portfolio $ 16,654.7 $ 23,659.0 $ 28.6 $ 40,342.3 $ 38,416.0 Debt $ 0 $ 6,108.6 $ 0 $ 6,108.6 $ 5,394.0 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost March 31, 2019 Fixed maturities: U.S. government obligations $ 9,770.5 $ 0 $ 0 $ 9,770.5 $ 9,685.6 State and local government obligations 0 1,515.8 0 1,515.8 1,505.5 Corporate debt securities 0 7,978.0 0 7,978.0 7,870.1 Subtotal 9,770.5 9,493.8 0 19,264.3 19,061.2 Asset-backed securities: Residential mortgage-backed 0 613.0 0 613.0 609.9 Commercial mortgage-backed 0 3,853.6 0 3,853.6 3,825.6 Other asset-backed 0 3,839.8 0 3,839.8 3,834.2 Subtotal asset-backed securities 0 8,306.4 0 8,306.4 8,269.7 Redeemable preferred stocks: Financials 0 81.3 0 81.3 79.2 Utilities 0 0 0 0 0 Industrials 10.4 159.5 0 169.9 164.4 Subtotal redeemable preferred stocks 10.4 240.8 0 251.2 243.6 Total fixed maturities 9,780.9 18,041.0 0 27,821.9 27,574.5 Short-term investments 2,510.9 73.8 0 2,584.7 2,584.7 Total available-for-sale securities 12,291.8 18,114.8 0 30,406.6 30,159.2 Equity securities: Nonredeemable preferred stocks: Financials 69.6 955.0 25.1 1,049.7 976.1 Utilities 0 40.7 0 40.7 40.0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 69.6 995.7 30.1 1,095.4 1,021.1 Common equities: Common stocks 3,010.2 0 0 3,010.2 1,194.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,010.2 0 0.3 3,010.5 1,194.3 Total equity securities 3,079.8 995.7 30.4 4,105.9 2,215.4 Total portfolio $ 15,371.6 $ 19,110.5 $ 30.4 $ 34,512.5 $ 32,374.6 Debt $ 0 $ 4,734.8 $ 0 $ 4,734.8 $ 4,405.4 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 months ended March 31, 2020 and 2019 : Level 3 Fair Value (millions) Fair Value at December 31, 2019 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at March 31, 2020 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 0 $ 0 $ 0 $ (14.0 ) $ 0 $ 13.1 Industrials 16.0 0 0 0 0 (0.8 ) 0 15.2 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 43.4 $ 0 $ 0 $ 0 $ 0 $ (14.8 ) $ 0 $ 28.6 Level 3 Fair Value (millions) Fair Value at December 31, 2018 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at March 31, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 25.1 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 $ 0 $ 0 $ 0 $ 0 $ 0 $ 30.4
Fair Value Measurement Inputs and Valuation Techniques	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at March 31, 2020 and 2019 , and December 31, 2019 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 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 ) Industrials 15.2 Guideline public company method Weighted average capitalization % (19.2 ) Subtotal Level 3 securities 28.3 Pricing exemption securities 0.3 Total Level 3 securities $ 28.6 Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at March 31, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 25.1 Internal price Unadjusted purchase price per share 9.0 Industrials 5.0 Internal price Price-to-sales ratio 5.5 Subtotal Level 3 securities 30.1 Pricing exemption securities 0.3 Total Level 3 securities $ 30.4 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)	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Debt Table	Debt at each of the balance sheet periods consisted of: March 31, 2020 March 31, 2019 December 31, 2019 (millions) Carrying Value Fair Value Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 $ 499.5 $ 510.7 $ 499.2 $ 509.7 $ 499.4 $ 515.6 2.45% Senior Notes due 2027 497.0 488.2 496.6 475.6 496.9 501.5 6 5/8% Senior Notes due 2029 296.7 395.3 296.4 377.8 296.6 392.5 4.00% Senior Notes due 2029 545.1 605.7 544.6 587.9 545.0 614.3 3.20% Senior Notes due 2030 495.8 543.2 0 0 0 0 6.25% Senior Notes due 2032 395.8 539.6 395.6 508.5 395.7 552.6 4.35% Senior Notes due 2044 346.7 391.7 346.6 371.6 346.7 417.0 3.70% Senior Notes due 2045 395.4 406.2 395.3 389.7 395.4 434.2 4.125% Senior Notes due 2047 841.6 991.9 841.4 885.4 841.6 986.1 4.20% Senior Notes due 2048 589.9 675.8 589.7 628.6 589.8 705.8 3.95% Senior Notes due 2050 490.5 560.3 0 0 0 0 Total $ 5,394.0 $ 6,108.6 $ 4,405.4 $ 4,734.8 $ 4,407.1 $ 5,119.6

Loss and Loss Adjustment Expe_2

Loss and Loss Adjustment Expense Reserves (Tables)	3 Months Ended
	Mar. 31, 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: March 31, (millions) 2020 2019 Balance, beginning of period $ 18,105.4 $ 15,400.8 Less reinsurance recoverables on unpaid losses 3,212.2 2,572.7 Net balance, beginning of period 14,893.2 12,828.1 Incurred related to: Current year 6,011.1 5,616.4 Prior years 144.1 142.6 Total incurred 6,155.2 5,759.0 Paid related to: Current year 2,916.4 2,517.5 Prior years 3,269.2 2,901.4 Total paid 6,185.6 5,418.9 Net balance, end of period 14,862.8 13,168.2 Plus reinsurance recoverables on unpaid losses 3,443.7 2,708.4 Balance, end of period $ 18,306.5 $ 15,876.6

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2020
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Table	We paid the following in the respective periods: Three Months Ended March 31, (millions) 2020 2019 Income taxes $ 0 $ 20.0 Interest 56.4 53.3 Operating lease liabilities 22.7 18.8

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2020 2019 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 3,828.7 $ 601.6 $ 3,508.5 $ 453.0 Direct 3,992.4 473.0 3,576.3 321.9 Total Personal Lines 1 7,821.1 1,074.6 7,084.8 774.9 Commercial Lines 1,189.0 112.5 1,013.0 166.6 Property 2 420.6 49.2 362.0 7.7 Total underwriting operations 9,430.7 1,236.3 8,459.8 949.2 Fees and other revenues 3 153.5 NA 130.2 NA Service businesses 51.6 4.1 42.6 4.5 Investments 4 (312.4 ) (317.7 ) 667.4 661.2 Interest expense NA (48.0 ) NA (47.4 ) Consolidated total $ 9,323.4 $ 874.7 $ 9,300.0 $ 1,567.5 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three months ended March 31, 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 months ended March 31, 2020 and 2019, pretax profit (loss) includes $14.5 million and $17.9 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX. Although this expense is included in our Property segment, it is not reported in the consolidated results of ARX and, therefore, does not affect the value of net income attributable to noncontrolling interest. 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 March 31, 2020 2019 Underwriting Combined Ratio Underwriting Combined Ratio Personal Lines Agency 15.7 % 84.3 12.9 % 87.1 Direct 11.9 88.1 9.0 91.0 Total Personal Lines 13.7 86.3 10.9 89.1 Commercial Lines 9.5 90.5 16.4 83.6 Property 1 11.7 88.3 2.1 97.9 Total underwriting operations 13.1 86.9 11.2 88.8 1 Included in the three months ended March 31, 2020 and 2019, is 3.4 points and 5.0 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX.

Dividends Dividends (Tables)

Dividends Dividends (Tables)	3 Months Ended
	Mar. 31, 2020
Dividends [Abstract]
Dividends	Following is a summary of our common and preferred share dividends that were declared and/or paid during the three months ended March 31, 2020 and 2019: (millions, except per share amounts) Amount Declared Payable Per Share Accrued 1 Common - Quarterly Dividends: February 2020 April 2020 $ 0.10 $ 58.5 December 2019 January 2020 0.10 58.5 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: February 2020 March 2020 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)	3 Months Ended
	Mar. 31, 2020
Equity [Abstract]
Components of Other Comprehensive Income (Loss)	The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income (loss) Total tax (provision) benefit After tax total accumulated other comprehensive income (loss) Total net unrealized gains (losses) on securities Net unrealized gains (losses) on forecasted transactions (Income) loss attributable to NCI Balance at December 31, 2019 $ 435.7 $ (94.0 ) $ 341.7 $ 360.8 $ (16.4 ) $ (2.7 ) Other comprehensive income (loss) before reclassifications: Investment securities 318.2 (66.8 ) 251.4 251.4 0 0 Loss attributable to noncontrolling interest (NCI) (0.6 ) 0.1 (0.5 ) 0 0 (0.5 ) Total other comprehensive income (loss) before reclassifications 317.6 (66.7 ) 250.9 251.4 0 (0.5 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 238.7 (50.1 ) 188.6 188.6 0 0 Interest expense (0.3 ) 0.1 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income 238.4 (50.0 ) 188.4 188.6 (0.2 ) 0 Total other comprehensive income (loss) 79.2 (16.7 ) 62.5 62.8 0.2 (0.5 ) Balance at March 31, 2020 $ 514.9 $ (110.7 ) $ 404.2 $ 423.6 $ (16.2 ) $ (3.2 ) Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income (loss) Total tax (provision) benefit After tax total accumulated other comprehensive income (loss) Total net unrealized gains (losses) on securities Net (Income) loss attributable to NCI Balance at December 31, 2018 $ (153.0 ) $ 32.1 $ (120.9 ) $ (105.6 ) $ (17.2 ) $ 1.9 Other comprehensive income (loss) before reclassifications: Investment securities 414.5 (87.0 ) 327.5 327.5 0 0 Loss attributable to noncontrolling interest (NCI) (2.9 ) 0.6 (2.3 ) 0 0 (2.3 ) Total other comprehensive income (loss) before reclassifications 411.6 (86.4 ) 325.2 327.5 0 (2.3 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 33.4 (7.0 ) 26.4 26.4 0 0 Interest expense (0.3 ) 0.1 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income 33.1 (6.9 ) 26.2 26.4 (0.2 ) 0 Total other comprehensive income (loss) 378.5 (79.5 ) 299.0 301.1 0.2 (2.3 ) Balance at March 31, 2019 $ 225.5 $ (47.4 ) $ 178.1 $ 195.5 $ (17.0 ) $ (0.4 )

Redeemable Noncontrolling Int_2

Redeemable Noncontrolling Interest (Tables)	3 Months Ended
	Mar. 31, 2020
Temporary Equity Disclosure [Abstract]
Redeemable Noncontrolling Interest	The changes in the components of redeemable NCI were: Three Months Ended March 31, Year Ended (millions) 2020 2019 December 31, 2019 Balance, beginning of period $ 225.6 $ 214.5 $ 214.5 Net income attributable to NCI 6.4 4.4 9.7 Other comprehensive income (loss) attributable to NCI 1 0.5 2.3 4.6 Exercise of employee stock options 0 0 7.7 Purchase/change of ARX minority shares 0 0 (11.2 ) Change in redemption value of NCI 2 (6.9 ) 0 0.3 Balance, end of period $ 225.6 $ 221.2 $ 225.6 1 Amount represents the other comprehensive income (loss) attributable to NCI, as reflected on the 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. 2 For the three months ended March 31, 2020, amount represents the adjustment to the carrying amount of redeemable NCI, which was reclassified to paid-in capital, to reflect the amount due to acquire the remaining outstanding stock from ARX minority shareholders, based on a negotiated purchase agreement as discussed above. See Note 15 – Subsequent Events

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Net Carrying Amount of Other Intangible Assets	The following table is a summary of the net carrying amount of other intangible assets: (millions) March 31, 2020 March 31, 2019 December 31, 2019 Intangible assets subject to amortization $ 201.4 $ 264.3 $ 215.9 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 213.8 $ 276.7 $ 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	Intangible assets subject to amortization consisted of the following: (millions) March 31, 2020 March 31, 2019 December 31, 2019 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 183.0 $ 73.2 $ 256.2 $ 146.4 $ 109.8 $ 256.2 $ 173.9 $ 82.3 Agency relationships 159.2 56.9 102.3 159.2 45.5 113.7 159.2 54.0 105.2 Software rights 79.1 53.2 25.9 79.1 42.7 36.4 79.1 50.7 28.4 Trade name 34.8 34.8 0 34.8 30.4 4.4 34.8 34.8 0 Total $ 529.3 $ 327.9 $ 201.4 $ 529.3 $ 265.0 $ 264.3 $ 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
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Business Acquisition [Line Items]
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	$ 170.3
Premiums receivable, allowance for doubtful accounts	344.7	$ 283.2	$ 236.9
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	170.3
Premium Receivable, Allowance for Credit Loss, Writeoff	108.8
Assets Held-for-sale, Property, Plant and Equipment	31.8	32.9	52.6
Operating Lease, Right-of-Use Asset	176.6	188.2	201.6
Operating Lease, Liability	$ 189.3	$ 201.5	$ 211.4
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
ARX Holding Corp.
Business Acquisition [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage	87.10%	87.10%	86.80%
COVID-19 [Member]
Business Acquisition [Line Items]
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	$ 71
Premium Receivable, Allowance for Credit Loss, Period Increase (Decrease)	$ 71

Investments Investment Portfoli

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 36,285.3	$ 30,159.2	$ 34,441.9
Gross Unrealized Gains	916.1	307.8	517
Gross Unrealized Losses	(377.2)	(60.9)	(57.6)
Net Holding Period Gains (Losses)	(23.4)	0.5	7.8
Total available-for-sale securities	$ 36,800.8	$ 30,406.6	$ 34,909.1
% of Total Fair Value	91.20%	88.10%	88.90%
Equity securities, at Fair Value
Cost	$ 2,130.7	$ 2,215.4	$ 2,096.8
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	1,410.8	1,890.5	2,248.4
Fair Value	$ 3,541.5	$ 4,105.9	$ 4,345.2
% of Total Fair Value	8.80%	11.90%	11.10%
Debt and Equity Securities, at Fair Value
Cost	$ 38,416	$ 32,374.6	$ 36,538.7
Gross Unrealized Gains	916.1	307.8	517
Gross Unrealized Losses	(377.2)	(60.9)	(57.6)
Net Holding Period Gains (Losses)	1,387.4	1,891	2,256.2
Fair Value	$ 40,342.3	$ 34,512.5	$ 39,254.3
% of Total Fair Value	100.00%	100.00%	100.00%
Unsettled security transactions, payable	$ 598		$ 11.9
Other Receivables from Broker-Dealers and Clearing Organizations		$ 76.5
Total fair value of non-insurance subsidiary portfolio	2,600	1,200	3,200
Dividends paid to common shareholders	(1,375.4)	(1,467.9)
Proceeds from Issuance of Debt	986.3	0
Nonredeemable preferred stocks
Equity securities, at Fair Value
Cost	1,017.5	1,021.1	971.3
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	(84.1)	74.3	67.6
Fair Value	$ 933.4	$ 1,095.4	$ 1,038.9
% of Total Fair Value	2.30%	3.20%	2.70%
Common equities
Equity securities, at Fair Value
Cost	$ 1,113.2	$ 1,194.3	$ 1,125.5
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	1,494.9	1,816.2	2,180.8
Fair Value	$ 2,608.1	$ 3,010.5	$ 3,306.3
% of Total Fair Value	6.50%	8.70%	8.40%
Total fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 33,761.1	$ 27,574.5	$ 32,643.1
Gross Unrealized Gains	916.1	307.8	517
Gross Unrealized Losses	(377.2)	(60.9)	(57.6)
Net Holding Period Gains (Losses)	(23.4)	0.5	7.8
Total available-for-sale securities	$ 34,276.6	$ 27,821.9	$ 33,110.3
% of Total Fair Value	84.90%	80.60%	84.30%
Total fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 10,841.2	$ 9,685.6	$ 13,100.7
Gross Unrealized Gains	654.5	105.5	194.1
Gross Unrealized Losses	0	(20.6)	(43.7)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 11,495.7	$ 9,770.5	$ 13,251.1
% of Total Fair Value	28.50%	28.30%	33.70%
Total fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 2,243.9	$ 1,505.5	$ 1,686
Gross Unrealized Gains	64.8	15.4	30
Gross Unrealized Losses	(4.5)	(5.1)	(2.7)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 2,304.2	$ 1,515.8	$ 1,713.3
% of Total Fair Value	5.70%	4.40%	4.40%
Total fixed maturities | Corporate debt securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 9,452.9	$ 7,870.1	$ 6,860.3
Gross Unrealized Gains	160.8	126.3	206.6
Gross Unrealized Losses	(120.1)	(19)	(0.5)
Net Holding Period Gains (Losses)	(1.7)	0.6	1.3
Total available-for-sale securities	$ 9,491.9	$ 7,978	$ 7,067.7
% of Total Fair Value	23.50%	23.10%	18.00%
Total fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 574.3	$ 609.9	$ 625
Gross Unrealized Gains	1.5	5.7	4.5
Gross Unrealized Losses	(19.2)	(2.6)	(2)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 556.6	$ 613	$ 627.5
% of Total Fair Value	1.40%	1.80%	1.60%
Total fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 5,822.4	$ 3,825.6	$ 5,020.7
Gross Unrealized Gains	30.2	35.9	61.5
Gross Unrealized Losses	(188.3)	(7.9)	(6)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 5,664.3	$ 3,853.6	$ 5,076.2
% of Total Fair Value	14.00%	11.20%	12.90%
Total fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,674.9	$ 3,834.2	$ 5,164.7
Gross Unrealized Gains	4.3	10	16.2
Gross Unrealized Losses	(40)	(4.5)	(1.4)
Net Holding Period Gains (Losses)	(0.1)	0.1	0
Total available-for-sale securities	$ 4,639.1	$ 3,839.8	$ 5,179.5
% of Total Fair Value	11.50%	11.10%	13.20%
Total fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 151.5	$ 243.6	$ 185.7
Gross Unrealized Gains	0	9	4.1
Gross Unrealized Losses	(5.1)	(1.2)	(1.3)
Net Holding Period Gains (Losses)	(21.6)	(0.2)	6.5
Total available-for-sale securities	$ 124.8	$ 251.2	$ 195
% of Total Fair Value	0.30%	0.70%	0.50%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 2,524.2	$ 2,584.7	$ 1,798.8
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 2,524.2	$ 2,584.7	$ 1,798.8
% of Total Fair Value	6.30%	7.50%	4.60%

Investments Hybrid Securities (

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Hybrid Instruments [Line Items]
Hybrid securities	$ 190.5	$ 189.4	$ 254.7
State and local government obligations
Hybrid Instruments [Line Items]
Hybrid securities	3.4	3.5	3.6
Corporate debt securities
Hybrid Instruments [Line Items]
Hybrid securities	116.5	91.2	161.7
Other asset-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	2.2	2.6	4
Redeemable preferred stocks
Hybrid Instruments [Line Items]
Hybrid securities	$ 68.4	$ 92.1	$ 85.4

Investments Composition of Fixe

Investments Composition of Fixed Maturities by Maturity (Detail) - Total fixed maturities $ in Millions	Mar. 31, 2020USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 6,459.3
One to five years	18,343.3
Five to ten years	8,170.4
Ten years or greater	788.1
Cost	33,761.1
Fair Value
Less than one year	6,407.6
One to five years	18,532.2
Five to ten years	8,519.9
Ten years or greater	816.9
Fair Value	$ 34,276.6

Investments Gross Unrealized lo

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Mar. 31, 2020USD ($)security	Dec. 31, 2019USD ($)security	Mar. 31, 2019USD ($)security
Number of Securities
Total | security	817	307	640
Less than 12 Months | security	749	217	77
12 Months or Greater | security	68	90	563
Fair Value
Total	$ 13,422.7	$ 8,761.3	$ 9,215.7
Less than 12 Months	12,907.2	8,038.3	891.9
12 Months or Greater	515.5	723	8,323.8
Unrealized Losses
Total	(377.2)	(57.6)	(60.9)
Less than 12 Months	(353)	(53.8)	(3.9)
12 Months or Greater	$ (24.2)	$ (3.8)	$ (57)
U.S. government obligations
Number of Securities
Total | security	1	23	42
Less than 12 Months | security	1	19	1
12 Months or Greater | security	0	4	41
Fair Value
Total	$ 100.3	$ 5,152.4	$ 3,174
Less than 12 Months	100.3	5,057.2	19.9
12 Months or Greater	0	95.2	3,154.1
Unrealized Losses
Total	0	(43.7)	(20.6)
Less than 12 Months	0	(43.6)	(0.1)
12 Months or Greater	$ 0	$ (0.1)	$ (20.5)
State and local government obligations
Number of Securities
Total | security	89	67	162
Less than 12 Months | security	78	52	10
12 Months or Greater | security	11	15	152
Fair Value
Total	$ 528.4	$ 314.3	$ 567.2
Less than 12 Months	507.7	287.5	31.4
12 Months or Greater	20.7	26.8	535.8
Unrealized Losses
Total	(4.5)	(2.7)	(5.1)
Less than 12 Months	(4.4)	(2.6)	0
12 Months or Greater	$ (0.1)	$ (0.1)	$ (5.1)
Corporate debt securities
Number of Securities
Total | security	233	16	153
Less than 12 Months | security	233	12	11
12 Months or Greater | security	0	4	142
Fair Value
Total	$ 4,205.6	$ 247.6	$ 2,555.7
Less than 12 Months	4,205.6	191.4	175.9
12 Months or Greater	0	56.2	2,379.8
Unrealized Losses
Total	(120.1)	(0.5)	(19)
Less than 12 Months	(120.1)	(0.5)	(1.1)
12 Months or Greater	$ 0	$ 0	$ (17.9)
Residential mortgage-backed securities
Number of Securities
Total | security	70	41	63
Less than 12 Months | security	46	12	15
12 Months or Greater | security	24	29	48
Fair Value
Total	$ 532.5	$ 292.8	$ 299.4
Less than 12 Months	425	163.7	139.1
12 Months or Greater	107.5	129.1	160.3
Unrealized Losses
Total	(19.2)	(2)	(2.6)
Less than 12 Months	(11.9)	(0.9)	(1.1)
12 Months or Greater	$ (7.3)	$ (1.1)	$ (1.5)
Commercial mortgage-backed securities
Number of Securities
Total | security	204	98	76
Less than 12 Months | security	187	79	13
12 Months or Greater | security	17	19	63
Fair Value
Total	$ 4,441.5	$ 1,742.4	$ 1,294.3
Less than 12 Months	4,109.2	1,400	229.1
12 Months or Greater	332.3	342.4	1,065.2
Unrealized Losses
Total	(188.3)	(6)	(7.9)
Less than 12 Months	(173.8)	(5.3)	(0.9)
12 Months or Greater	$ (14.5)	$ (0.7)	$ (7)
Other asset-backed securities
Number of Securities
Total | security	216	61	142
Less than 12 Months | security	201	43	27
12 Months or Greater | security	15	18	115
Fair Value
Total	$ 3,558.1	$ 1,000.6	$ 1,294
Less than 12 Months	3,514.2	938.5	296.5
12 Months or Greater	43.9	62.1	997.5
Unrealized Losses
Total	(40)	(1.4)	(4.5)
Less than 12 Months	(39)	(0.9)	(0.7)
12 Months or Greater	$ (1)	$ (0.5)	$ (3.8)
Redeemable preferred stocks
Number of Securities
Total | security	4	1	2
Less than 12 Months | security	3	0	0
12 Months or Greater | security	1	1	2
Fair Value
Total	$ 56.3	$ 11.2	$ 31.1
Less than 12 Months	45.2	0	0
12 Months or Greater	11.1	11.2	31.1
Unrealized Losses
Total	(5.1)	(1.3)	(1.2)
Less than 12 Months	(3.8)	0	0
12 Months or Greater	$ (1.3)	$ (1.3)	$ (1.2)

Investments Components of Net R

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	$ 291.6	$ 55
Equity Securities, FV-NI, Gross Realized Gains on Sales	85.6	9.4
Debt and Equity Securities, Gross Realized Gains on Sales	377.2	64.4
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(3.7)	(18.3)
Equity Securities, FV-NI, Gross Realized Losses on Sales	(58.3)	0
Debt and Equity Securities, Gross Realized Losses on Sales	(62)	(18.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	287.9	36.7
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	27.3	9.4
Gross Realized Gain (Loss), excluding Holding Period and OTTI	315.2	46.1
Unrealized Gain (Loss) on Hybrid Instrument, Net	(31.2)	10.7
Net holding period gains (losses), equity securities	(837.6)	382
Net Holding Period Realized Gain (Loss)	(868.8)	392.7
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	0	(24.3)
Total net realized gains (losses) on securities	(553.6)	414.5
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	251.1	36.6
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(2.7)	(7.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	248.4	29.5
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	2	1.6
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(0.6)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	2	1
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	32.4	16.1
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(1)	(6.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	31.4	10
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(2.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	(2.3)
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	6.1	0.7
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(2.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	6.1	(1.4)
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(0.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	(0.1)
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	19.6	4.9
Equity Securities, FV-NI, Gross Realized Losses on Sales	(4.4)	0
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	15.2	4.9
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	66	4.5
Equity Securities, FV-NI, Gross Realized Losses on Sales	(53.9)	0
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	12.1	4.5
Other Assets
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	$ 0	$ (24.3)

Investments Components of Equit

Investments Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of Equity Realized Gains (Losses) [Line Items]
Realized Investment Gains (Losses)	$ (810.3)	$ 391.4
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	27.3	9.4
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ (837.6)	$ 382

Investments Components of Net I

Investments Components of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Net Investment Income [Line Items]
Gross investment income	$ 241.2	$ 252.9
Investment expenses	(5.3)	(6.2)
Net Investment Income	235.9	246.7
Total equity securities
Net Investment Income [Line Items]
Gross investment income	28.4	28.7
Total equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	13.8	15.5
Total equity securities | Common equities
Net Investment Income [Line Items]
Gross investment income	14.6	13.2
Available-for-sale Securities
Net Investment Income [Line Items]
Gross investment income	212.8	224.2
Short-term investments
Net Investment Income [Line Items]
Gross investment income	7	16
Total fixed maturities
Net Investment Income [Line Items]
Gross investment income	205.8	208.2
Total fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Gross investment income	62.6	53.7
Total fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Gross investment income	9.6	9.3
Total fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Gross investment income	58	77.2
Total fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	4.2	6.6
Total fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	34.3	31.7
Total fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Gross investment income	29.2	26
Total fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	$ 7.9	$ 3.7

Investments - Additional Inform

Investments - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2020USD ($)security	Mar. 31, 2019USD ($)	Dec. 31, 2019USD ($)
Schedule of Debt and Equity Securities [Line Items]
Deposit Assets	$ 281,000,000
Securities Sold under Agreements to Repurchase	0	$ 0	$ 0
Open reverse repurchase commitments	$ 0	$ 0	0
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Downgraded | security	8
Debt Securities, Available-for-sale, Unrealized Loss Position, Downgraded in Period	$ 137,600,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Downgrades in Period	5,200,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Not Previously Recorded	0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff	$ 0
Percent Change in Investment Income	5.00%
Percent Change in Investment Income, Change in Yield	17.00%
Percent Change in Investment Income, Change in Average Assets	12.00%
Investment Portfolio Duration	3 years	2 years 7 months 6 days
Derivative Assets (Liabilities), at Fair Value, Net		$ 0	$ 0
Corporate debt securities
Schedule of Debt and Equity Securities [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Downgraded | security	7
Residential mortgage-backed securities
Schedule of Debt and Equity Securities [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Positions Downgraded | security	1

Fair Value Composition of Inves

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 40,342.3	$ 39,254.3	$ 34,512.5
Fair Value	6,108.6	5,119.6	4,734.8
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	36,800.8	34,909.1	30,406.6
Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	34,276.6	33,110.3	27,821.9
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	23,291.8	22,032.1	19,264.3
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	11,495.7	13,251.1	9,770.5
Available-for-sale Securities | Total fixed maturities | Debt Securities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,304.2	1,713.3	1,515.8
Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,491.9	7,067.7	7,978
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	10,860	10,883.2	8,306.4
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	556.6	627.5	613
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	5,664.3	5,076.2	3,853.6
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	4,639.1	5,179.5	3,839.8
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	124.8	195	251.2
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	47.2	51.7	81.3
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	9.2	11.1	0
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	68.4	132.2	169.9
Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,524.2	1,798.8	2,584.7
Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,541.5	4,345.2	4,105.9
Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	933.4	1,038.9	1,095.4
Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	870.9	955.2	1,049.7
Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	32	42.3	40.7
Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	30.5	41.4	5
Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,608.1	3,306.3	3,010.5
Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,607.8	3,306	3,010.2
Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0.3	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	16,654.7	18,443	15,371.6
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	13,941.4	15,059.6	12,291.8
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	11,503	13,262.2	9,780.9
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	11,495.7	13,251.1	9,770.5
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	11,495.7	13,251.1	9,770.5
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	7.3	11.1	10.4
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	7.3	11.1	10.4
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,438.4	1,797.4	2,510.9
Fair Value, Inputs, Level 1 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,713.3	3,383.4	3,079.8
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	105.5	77.4	69.6
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	105.5	77.4	69.6
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,607.8	3,306	3,010.2
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,607.8	3,306	3,010.2
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	23,659	20,767.9	19,110.5
Fair Value	6,108.6	5,119.6	4,734.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,859.4	19,849.5	18,114.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,773.6	19,848.1	18,041
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	11,796.1	8,781	9,493.8
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	2,304.2	1,713.3	1,515.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Debt Securities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,491.9	7,067.7	7,978
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	10,860	10,883.2	8,306.4
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	556.6	627.5	613
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	5,664.3	5,076.2	3,853.6
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	4,639.1	5,179.5	3,839.8
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	117.5	183.9	240.8
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	47.2	51.7	81.3
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	9.2	11.1	0
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	61.1	121.1	159.5
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	85.8	1.4	73.8
Fair Value, Inputs, Level 2 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	799.6	918.4	995.7
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	799.6	918.4	995.7
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	752.3	850.7	955
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	32	42.3	40.7
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	15.3	25.4	0
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	28.6	43.4	30.4
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	28.6	43.4	30.4
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	28.3	43.1	30.1
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	13.1	27.1	25.1
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	0.3	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	0.3	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	38,416	36,538.7	32,374.6
Long-term Debt	5,394	4,407.1	4,405.4
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	36,285.3	34,441.9	30,159.2
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	33,761.1	32,643.1	27,574.5
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	22,538	21,647	19,061.2
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	10,841.2	13,100.7	9,685.6
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	2,243.9	1,686	1,505.5
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	9,452.9	6,860.3	7,870.1
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	11,071.6	10,810.4	8,269.7
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	574.3	625	609.9
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	5,822.4	5,020.7	3,825.6
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	4,674.9	5,164.7	3,834.2
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	151.5	185.7	243.6
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	51.4	51.5	79.2
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	0
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	90.1	124.2	164.4
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	2,524.2	1,798.8	2,584.7
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	2,130.7	2,096.8	2,215.4
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	1,017.5	971.3	1,021.1
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	937.4	891.3	976.1
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	40	39.9	40
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	5
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	1,113.2	1,125.5	1,194.3
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	1,112.9	1,125.2	1,194
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	$ 0.3	$ 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
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 43.4	$ 30.4
Calls/ Maturities/ Paydowns	0	0
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	(14.8)	0
Net Transfers In (Out)	0	0
Fair value, ending balance	28.6	30.4
Total equity securities | Financials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	27.1	25.1
Calls/ Maturities/ Paydowns	0	0
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	(14)	0
Net Transfers In (Out)	0	0
Fair value, ending balance	13.1	25.1
Total equity securities | Industrials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	16	5
Calls/ Maturities/ Paydowns	0	0
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	(0.8)	0
Net Transfers In (Out)	0	0
Fair value, ending balance	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
Calls/ Maturities/ Paydowns	0	0
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Fair value, ending balance	$ 0.3	$ 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	3 Months Ended		12 Months Ended
	Mar. 31, 2020USD ($)$ / shares	Mar. 31, 2019USD ($)$ / shares	Dec. 31, 2019USD ($)$ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 40,342.3	$ 34,512.5	$ 39,254.3
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	28.6	30.4	43.4
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	$ 13.1	$ 25.1
Fair Value Inputs, Original Issue Price | $ / shares		$ 9
Fair Value Inputs, Guideline Public Company Method | $ / shares	$ (51.5)
Fair Value, Inputs, Level 3 | Internal Pricing | Nonredeemable preferred stocks | Industrials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 15.2	$ 5	$ 10
Fair Value Inputs, Original Issue Price | $ / shares			$ 4.9
Fair Value Inputs, Guideline Public Company Method | $ / shares	$ (19.2)
Fair Value Inputs, Price-to-Sales Ratio		5.5
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 28.3	$ 30.1	$ 43.1
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 0.3	$ 0.3	$ 0.3

Fair Value - Additional Informa

Fair Value - Additional Information (Detail)	Mar. 31, 2020USD ($)security	Dec. 31, 2019USD ($)security	Mar. 31, 2019USD ($)security
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 40,342,300,000	$ 39,254,300,000	$ 34,512,500,000
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	82.00%	80.00%	77.00%
Investments, Fair Value	$ 16,654,700,000	$ 18,443,000,000	$ 15,371,600,000
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	98.00%	99.00%	99.00%
Dealer Quoted Prices, Percent of FV Hierarchy Level	2.00%	1.00%	1.00%
Investments, Fair Value	$ 23,659,000,000	$ 20,767,900,000	$ 19,110,500,000
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	28,600,000	43,400,000	30,400,000
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	3	3	2
Common equities | Internal Pricing | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Number of securities | security	1	1	1

Debt (Detail)

Debt (Detail) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Debt Instrument [Line Items]
Fair Value		$ 6,108.6	$ 5,119.6	$ 4,734.8
Debt, Long-term and Short-term, Combined Amount	[1]	5,394	4,407.1	4,405.4
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term Debt		499.5	499.4	499.2
Fair Value		510.7	515.6	509.7
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Long-term Debt		497	496.9	496.6
Fair Value		488.2	501.5	475.6
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Long-term Debt		296.7	296.6	296.4
Fair Value		395.3	392.5	377.8
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Long-term Debt		545.1	545	544.6
Fair Value		605.7	614.3	587.9
Senior Notes Three Point Two Zero Percent Due Twenty Thirty [Member]
Debt Instrument [Line Items]
Long-term Debt		495.8	0	0
Fair Value		543.2	0	0
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Long-term Debt		395.8	395.7	395.6
Fair Value		539.6	552.6	508.5
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Long-term Debt		346.7	346.7	346.6
Fair Value		391.7	417	371.6
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Long-term Debt		395.4	395.4	395.3
Fair Value		406.2	434.2	389.7
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Long-term Debt		841.6	841.6	841.4
Fair Value		991.9	986.1	885.4
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Long-term Debt		589.9	589.8	589.7
Fair Value		675.8	705.8	628.6
Senior Notes Three Point Nine Five Percent Due Twenty Fifty [Member]
Debt Instrument [Line Items]
Long-term Debt		490.5	0	0
Fair Value		$ 560.3	$ 0	$ 0
[1]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	Apr. 30, 2020	Mar. 31, 2020	Mar. 31, 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	$ 500,000,000
Debt, stated interest rate		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	$ 500,000,000
Debt, stated interest rate		3.95%	3.95%
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
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			0.50%
Subsequent Event [Member] | 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
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Income Taxes [Line Items]
Valuation allowance	$ 0	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Percent	20.10%	30.90%

Loss and Loss Adjustment Expe_3

Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expense reserves	$ 18,306.5	$ 15,876.6	$ 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	3,443.7	2,708.4	3,212.2	2,572.7
Liability for Unpaid Claims and Claims Adjustment Expense, Net	14,862.8	13,168.2	$ 14,893.2	$ 12,828.1
Current Year Claims and Claims Adjustment Expense	6,011.1	5,616.4
Prior Year Claims and Claims Adjustment Expense	(144.1)	(142.6)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	6,155.2	5,759
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	2,916.4	2,517.5
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	3,269.2	2,901.4
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	$ 6,185.6	$ 5,418.9
Short-Duration Insurance Contract, Accident Year 2019 [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of Prior Year Claims and Claims Adjustment Expense	52.00%
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	36.00%	40.00%
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		15.00%
Personal Lines | Personal auto businesses
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (104)	$ (111)
Personal Lines | Special Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	14	(8)
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ (54)	$ (22)

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Open reverse repurchase commitments	$ 0	$ 0	$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	9,700,000
Operating Lease, Payments	22,700,000	18,800,000
Income Taxes Paid	0	20,000,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	56,400,000	53,300,000
Cash and Cash Equivalents | ARX Holding Corp.
Open reverse repurchase commitments	80,600,000	185,600,000	46,300,000
Common Stock [Member] | Quarterly dividend [Member]
Dividends payable	$ 58,500,000	$ 58,400,000	$ 58,500,000

Segment Information Operating R

Segment Information Operating Results (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Revenues	$ 9,323.4	$ 9,300
Pretax Profit (Loss)	874.7	1,567.5
Amortization of intangible assets	14.5	17.9
Personal Lines | Agency | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	3,828.7	3,508.5
Pretax Profit (Loss)	601.6	453
Personal Lines | Direct | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	3,992.4	3,576.3
Pretax Profit (Loss)	473	321.9
Operating Segments | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	9,430.7	8,459.8
Pretax Profit (Loss)	1,236.3	949.2
Operating Segments | Personal Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	7,821.1	7,084.8
Pretax Profit (Loss)	$ 1,074.6	$ 774.9
Personal auto insurance percentage of the total personal lines segment net premiums earned	94.00%	94.00%
Operating Segments | Commercial Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	$ 1,189	$ 1,013
Pretax Profit (Loss)	112.5	166.6
Operating Segments | Property | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	420.6	362
Pretax Profit (Loss)	49.2	7.7
Amortization of intangible assets	14.5	17.9
Segment Reconciling Items | Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	153.5	130.2
Segment Reconciling Items | Service businesses
Segment Reporting Information [Line Items]
Revenues	51.6	42.6
Pretax Profit (Loss)	4.1	4.5
Segment Reconciling Items | Investment income
Segment Reporting Information [Line Items]
Revenues	(312.4)	667.4
Pretax Profit (Loss)	(317.7)	661.2
Segment Reconciling Items | Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (48)	$ (47.4)

Segment Information Underwritin

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Underwriting operations	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Personal Lines | Agency
Segment Reporting Information [Line Items]
Underwriting Margin	15.70%	12.90%
Combined Ratio	84.30%	87.10%
Personal Lines | Direct
Segment Reporting Information [Line Items]
Underwriting Margin	11.90%	9.00%
Combined Ratio	88.10%	91.00%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	13.10%	11.20%
Combined Ratio	86.90%	88.80%
Operating Segments | Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	13.70%	10.90%
Combined Ratio	86.30%	89.10%
Operating Segments | Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	9.50%	16.40%
Combined Ratio	90.50%	83.60%
Operating Segments | Property
Segment Reporting Information [Line Items]
Underwriting Margin	11.70%	2.10%
Combined Ratio	88.30%	97.90%
Combined ratio amortization points	0.034	0.050

Dividends (Details)

Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended					3 Months Ended
	Feb. 29, 2020	Jan. 31, 2020	Apr. 30, 2019	Mar. 31, 2019	Feb. 28, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Common Stock, Dividends, Per Share, Declared						$ 0.10	$ 0.10
Quarterly dividend [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.10
Common Stock, Dividends, Per Share, Cash Paid		$ 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
Dividends payable	$ 13.4				$ 13.4
Common Stock [Member] | Quarterly dividend [Member]
Dividends payable				$ 58.4		$ 58.5	$ 58.4	$ 58.5
Common Stock [Member] | 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
	Mar. 31, 2020	Mar. 31, 2019	Feb. 29, 2020	Feb. 28, 2019
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.10	$ 0.10
Series B Preferred Stock
Class of Stock [Line Items]
Dividends payable			$ 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		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ 435.7	$ (153)	$ (153)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax	318.2	414.5
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Noncontrolling Interest	(0.6)	(2.9)
OCI, before Reclassifications, before Tax, Attributable to Parent	317.6	411.6
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	238.7	33.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	(0.3)	(0.3)
Total reclassification adjustment for amounts realized in net income, pre tax	238.4	33.1
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	79.2	378.5
AOCI before Tax, Attributable to Parent, ending balance	514.9	225.5	435.7
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	(94)	32.1	32.1
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(66.8)	(87)
Other Comprehensive Income (Loss), Tax, Portion Attributable to Noncontrolling Interest	0.1	0.6
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax	(66.7)	(86.4)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(50.1)	(7)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	0.1	0.1
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	(50)	(6.9)
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	(16.7)	(79.5)
AOCI Tax, Attributable to Parent, ending balance	(110.7)	(47.4)	(94)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	341.7	(120.9)	(120.9)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	251.4	327.5
Other comprehensive (income) loss attributable to NCI	(0.5)	(2.3)	(4.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	250.9	325.2
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	188.6	26.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)	(0.2)
Total reclassification adjustment for amounts realized in net income, after tax	188.4	26.2
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	62.5	299
After tax total accumulated other comprehensive income, ending balance	404.2	178.1	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	360.8	(105.6)	(105.6)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	251.4	327.5
Other comprehensive (income) loss attributable to NCI	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	251.4	327.5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	188.6	26.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0
Total reclassification adjustment for amounts realized in net income, after tax	188.6	26.4
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	62.8	301.1
After tax total accumulated other comprehensive income, ending balance	423.6	195.5	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	(16.4)	(17.2)	(17.2)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0	0
Other comprehensive (income) loss attributable to NCI	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)	(0.2)
Total reclassification adjustment for amounts realized in net income, after tax	(0.2)	(0.2)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.2	0.2
After tax total accumulated other comprehensive income, ending balance	(16.2)	(17)	(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	(2.7)	1.9	1.9
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0	0
Other comprehensive (income) loss attributable to NCI	(0.5)	(2.3)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.5)	(2.3)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0
Total reclassification adjustment for amounts realized in net income, after tax	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(0.5)	(2.3)
After tax total accumulated other comprehensive income, ending balance	$ (3.2)	$ (0.4)	$ (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	Mar. 31, 2020USD ($)
Statement of Comprehensive Income [Abstract]
Net unrealized gains on forecasted transactions, expected to reclassify into income within the next 12 months	$ 1.1

Redeemable Noncontrolling Int_3

Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions		3 Months Ended			12 Months Ended
		Mar. 31, 2020		Mar. 31, 2019	Dec. 31, 2019
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, beginning of period		$ 225.6	[1]	$ 214.5	$ 214.5
Net income attributable to NCI		6.4		4.4	9.7
Other comprehensive income (loss) attributable to NCI1		0.5		2.3	4.6
Exercise of employee stock options		0		0	7.7
Purchase/change of ARX minority shares		0		0	(11.2)
Change in redemption value of NCI2		(6.9)		0	0.3
Balance, end of period	[1]	$ 225.6		$ 221.2	$ 225.6
ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Shares held in Employee Stock Option Plan, Suspense Shares		10,438
Employee Stock Ownership Plan (ESOP), Deferred Shares, Fair Value		$ 16
[1]	See Note 12 – Redeemable Noncontrolling Interest for further discussion .

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets Goodwill (Details)	3 Months Ended
	Mar. 31, 2020USD ($)intangible_asset	Mar. 31, 2019USD ($)	Dec. 31, 2019USD ($)
Goodwill [Line Items]
Goodwill, Acquired During Period	$ 0
Goodwill, Impaired, Accumulated Impairment Loss	0
Amortization of intangible assets	$ 14,500,000	$ 17,900,000
Software rights
Goodwill [Line Items]
Number of Intangible Assets | intangible_asset	1
Gross Carrying Amount	$ 79,100,000	79,100,000	$ 79,100,000
Trade name
Goodwill [Line Items]
Gross Carrying Amount	34,800,000	$ 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	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Schedule of Other Intangible Assets [Line Items]
Indefinite lived intangible assets	$ 12.4	$ 12.4	$ 12.4
Total	213.8	228.3	276.7
Accumulated amortization	328.5	314	265.6
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	201.4	215.9	264.3
Accumulated amortization	$ 327.9	$ 313.4	$ 265

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 328.5	$ 314	$ 265.6
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2	256.2
Accumulated Amortization	183	173.9	146.4
Net Carrying Amount	73.2	82.3	109.8
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2
Accumulated Amortization	56.9	54	45.5
Net Carrying Amount	102.3	105.2	113.7
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	79.1	79.1	79.1
Accumulated Amortization	53.2	50.7	42.7
Net Carrying Amount	25.9	28.4	36.4
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.8	34.8	34.8
Accumulated Amortization	34.8	34.8	30.4
Net Carrying Amount	0	0	4.4
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	529.3	529.3	529.3
Accumulated Amortization	327.9	313.4	265
Net Carrying Amount	$ 201.4	$ 215.9	$ 264.3

New Accounting Standards Effect

New Accounting Standards Effect of Standard Change (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Property, Plant and Equipment [Line Items]
Other assets	$ 722.8	$ 768.4	$ 671.9
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Other assets	$ 6.2

Subsequent Event (Details)

Subsequent Event (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended
	Apr. 30, 2020	May 31, 2020	Apr. 01, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Subsequent Event [Member]
Subsequent Event [Line Items]
Return of Premium		$ 1,000
ARX Holding Corp.
Subsequent Event [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage				87.10%	87.10%	86.80%
ARX Holding Corp. | Subsequent Event [Member]
Subsequent Event [Line Items]
Payments to Acquire Interest in Subsidiaries and Affiliates	$ 243
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage			100.00%