The Progressive Corporation (PGR) 10-Q 6 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Cover page.
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	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		584,630,089
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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Net premiums earned	$ 9,012.2	$ 7,930.5	$ 26,296.7	$ 22,738.7
Investment income	263	218.1	777.2	576.5
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales	71.7	108.4	185.3	205.8
Net holding period gains (losses) on securities	31.8	95.8	536.9	(5.9)
Net impairment losses recognized in earnings	(38.1)	(22.1)	(62.4)	(33.2)
Total net realized gains (losses) on securities	65.4	182.1	659.8	166.7
Fees and other revenues	138.4	122.6	403.4	342.4
Service revenues	51.5	42.5	144.1	119.6
Total revenues	9,530.5	8,495.8	28,281.2	23,943.9
Expenses
Losses and loss adjustment expenses	6,426.3	5,523.1	18,323.4	15,769.2
Policy acquisition costs	751.5	662.7	2,200.7	1,889.7
Other underwriting expenses	1,240.3	1,095.9	3,643	3,123
Investment expenses	5.9	5.8	18.3	18
Service expenses	48.7	35.8	132.1	102.1
Interest expense	47.5	42	142.3	120.5
Total expenses	8,520.2	7,365.3	24,459.8	21,022.5
Net Income
Income before income taxes	1,010.3	1,130.5	3,821.4	2,921.4
Provision for income taxes	166.7	200.3	916	560.2
Net income	843.6	930.2	2,905.4	2,361.2
Net (income) loss attributable to noncontrolling interest (NCI)	(1.9)	(1.8)	(5.9)	(10.6)
Net income attributable to Progressive	841.7	928.4	2,899.5	2,350.6
Other Comprehensive Income (Loss)
Total net unrealized gains (losses) on fixed-maturity securities	58.1	(39)	636.6	(243.6)
Net unrealized losses on forecasted transactions	0.2	0.2	0.6	0.6
Other comprehensive income (loss)	58.3	(38.8)	637.2	(243)
Other comprehensive (income) loss attributable to NCI	(0.9)	0.4	(5.8)	5
Comprehensive income attributable to Progressive	899.1	890	3,530.9	2,112.6
Computation of Earnings Per Common Share
Net income attributable to Progressive	841.7	928.4	2,899.5	2,350.6
Less: Preferred share dividends	6.7	6.7	20.1	14.6
Net Income (Loss) Available to Common Stockholders, Basic	$ 835	$ 921.7	$ 2,879.4	$ 2,336
Average common shares outstanding - Basic	584.1	582.7	583.7	582.2
Net effect of dilutive stock-based compensation	3	3.9	3.6	4.5
Total average equivalent common shares - Diluted	587.1	586.6	587.3	586.7
Basic: Earnings per common share	$ 1.43	$ 1.58	$ 4.93	$ 4.01
Diluted: Earnings per common share	$ 1.42	$ 1.57	$ 4.90	$ 3.98

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Assets
Fixed maturities (amortized cost: $32,134.9, $25,963.4, and $28,255.9)		$ 32,812.7	$ 28,111.5	$ 25,642.7
Short-term investments (amortized cost: $1,467.4, $2,809.7, and $1,795.9)		1,467.4	1,795.9	2,809.7
Total available-for-sale securities		34,280.1	29,907.4	28,452.4
Nonredeemable preferred stocks (cost: $1,054.2, $758.9, and $1,002.6)		1,128.5	1,033.9	840.9
Common equities (cost: $1,210.3, $1,135.0, and $1,148.9)		3,165.1	2,626.1	3,057.3
Total equity securities		4,293.6	3,660	3,898.2
Total investments		38,573.7	33,567.4	32,350.6
Cash and cash equivalents		45.9	69.5	121.9
Restricted cash		0.3	5.5	0.8
Cash and cash equivalents		46.2	75	122.7
Accrued investment income		182.5	190.8	159.5
Premiums receivable, net of allowance for doubtful accounts of $258.8, $230.1, and $252.1		7,687.2	6,497.1	6,776.6
Reinsurance recoverables		3,298.4	2,696.1	2,490.5
Prepaid reinsurance premiums		458.8	309.7	379.6
Deferred acquisition costs		1,093.7	951.6	962.7
Property and equipment, net of accumulated depreciation of $1,085.3, $1,004.6, and $1,033.2		1,214.2	1,131.7	1,139.3
Goodwill		452.7	452.7	452.7
Intangible assets, net of accumulated amortization of $299.4, $229.7, and $247.7		242.9	294.6	312.6
Net deferred income taxes		0	43.2	0
Other assets		757.8	365.1	396.9
Total assets		54,008.1	46,575	45,543.7
Liabilities
Unearned premiums		12,526.5	10,686.5	11,009.2
Loss and loss adjustment expense reserves		17,370	15,400.8	14,620.8
Net deferred income taxes		136	0	53.5
Accounts payable, accrued expenses, and other liabilities		5,222.9	5,046.5	3,924.1
Debt	[1]	4,406.5	4,404.9	3,859.9
Total liabilities		39,661.9	35,538.7	33,467.5
Redeemable noncontrolling interest (NCI)	[2]	222.9	214.5	217.4
Shareholders’ Equity
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5)		493.9	493.9	493.9
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 212.9, 214.4, and 214.3)		584.6	583.2	583.1
Paid-in capital		1,539.1	1,479	1,443.4
Retained earnings		10,995.2	8,386.6	9,602.1
Accumulated other comprehensive income (loss):
Net unrealized gains (losses) on fixed-maturity securities		531	(105.6)	(249.9)
Net unrealized losses on forecasted transactions		(16.6)	(17.2)	(17.4)
Accumulated other comprehensive (income) loss attributable to NCI		(3.9)	1.9	3.6
Total accumulated other comprehensive income (loss) attributable to Progressive		510.5	(120.9)	(263.7)
Total shareholders’ equity		14,123.3	10,821.8	11,858.8
Total liabilities, redeemable NCI, and shareholders’ equity		$ 54,008.1	$ 46,575	$ 45,543.7
[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	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fixed maturities, amortized cost	$ 32,134.9	$ 28,255.9	$ 25,963.4
Nonredeemable preferred stocks, cost	1,054.2	1,002.6	758.9
Common equities, cost	1,210.3	1,148.9	1,135
Short-term investments, amortized cost	1,467.4	1,795.9	2,809.7
Premiums receivable, allowance for doubtful accounts	258.8	252.1	230.1
Intangible Assets, Accumulated Amortization	299.4	247.7	229.7
Property and equipment, accumulated depreciation	$ 1,085.3	$ 1,033.2	$ 1,004.6
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)	212,900,000	214,300,000	214,400,000
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle	$ 1,300.2
Reclassification of disproportionate tax effects	$ 7.7
Common Stock, Dividends, Per Share, Declared	$ 0
Preferred Stock, Dividends Per Share, Declared								$ 27.024
Balance, Beginning of period at Dec. 31, 2017			$ 0	$ 581.7	$ 1,389.2	$ 6,031.7	$ 1,282.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 2,350.6					2,350.6
Treasury shares purchased				(1.4)	(3.3)	(74)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						0
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(13.5)
Reinvested dividends on restricted stock units					(0.8)	0.8
Issuance of Serial Preferred Shares, Series B			493.9
Net restricted equity awards issued/vested				2.8	(2.8)
Amortization of equity-based compensation					53.3
Adjustment to carrying amount of redeemable noncontrolling interest	(3.1)				7.8
Attributable to noncontrolling interest	5						1.6
Other comprehensive income							(243)
Other, net						2
Balance, End of period at Sep. 30, 2018	11,858.8		493.9	583.1	1,443.4	9,602.1	(263.7)
Balance, Beginning of period at Dec. 31, 2017			0	581.7	1,389.2	6,031.7	1,282.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to carrying amount of redeemable noncontrolling interest	(2.8)
Attributable to noncontrolling interest	3.3
Balance, End of period at Dec. 31, 2018	10,821.8		493.9	583.2	1,479	8,386.6	(120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of disproportionate tax effects	$ 3.4
Common Stock, Dividends, Per Share, Declared	$ 0
Preferred Stock, Dividends Per Share, Declared								27.024
Balance, Beginning of period at Jun. 30, 2018			493.9	582.5	1,425.9	8,720.4	(221.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 928.4					928.4
Treasury shares purchased				(0.7)	(1.6)	(37)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						0
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(13.5)
Reinvested dividends on restricted stock units					0	0
Issuance of Serial Preferred Shares, Series B			0
Net restricted equity awards issued/vested				1.3	(1.3)
Amortization of equity-based compensation					15.8
Adjustment to carrying amount of redeemable noncontrolling interest					4.6
Attributable to noncontrolling interest	0.4						(3)
Other comprehensive income							(38.8)
Other, net						3.8
Balance, End of period at Sep. 30, 2018	$ 11,858.8		493.9	583.1	1,443.4	9,602.1	(263.7)
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle | Accounting Standards Update 2016-01						0	0
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02						0	0
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000
Preferred Stock, Shares Issued (shares)								500,000
Common Shares, par value (USD per share)	1
Common Stock, Dividends, Per Share, Declared	$ 0.30
Preferred Stock, Dividends Per Share, Declared								$ 53.750
Balance, Beginning of period at Dec. 31, 2018	$ 10,821.8		493.9	583.2	1,479	8,386.6	(120.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	2,899.5					2,899.5
Treasury shares purchased				(1.2)	(3.1)	(83.8)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						(175)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(26.8)
Reinvested dividends on restricted stock units					1.3	(1.3)
Issuance of Serial Preferred Shares, Series B			0
Net restricted equity awards issued/vested				2.6	(2.6)
Amortization of equity-based compensation					64.7
Adjustment to carrying amount of redeemable noncontrolling interest	0.2				(0.2)
Attributable to noncontrolling interest	(5.8)						(5.8)
Other comprehensive income							637.2
Other, net						(4)
Balance, End of period at Sep. 30, 2019	$ 14,123.3		493.9	584.6	1,539.1	10,995.2	510.5
Common Stock, Dividends, Per Share, Declared	$ 0.10
Preferred Stock, Dividends Per Share, Declared								26.875
Balance, Beginning of period at Jun. 30, 2019			493.9	584.1	1,523.3	10,276.4	453.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 841.7					841.7
Treasury shares purchased				(0.7)	(2)	(57)
Cash dividends declared on common shares ($0.10, $0, $0.30, and $0 per share)						(58.4)
Cash dividends declared on Serial Preferred Shares, Series B ($26.875, $27.024, $53.750, and $27.024 per share)						(13.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Issuance of Serial Preferred Shares, Series B			0
Net restricted equity awards issued/vested				1.2	(1.2)
Amortization of equity-based compensation					18.6
Adjustment to carrying amount of redeemable noncontrolling interest					0
Attributable to noncontrolling interest	(0.9)						(0.9)
Other comprehensive income							58.3
Other, net						6.3
Balance, End of period at Sep. 30, 2019	$ 14,123.3		$ 493.9	$ 584.6	$ 1,539.1	10,995.2	510.5
Preferred Stock, No Par Value								$ 0
Preferred Stock, Shares Authorized (shares)		20,000,000						500,000	5,000,000
Preferred Stock, Shares Issued (shares)								500,000	0
Common Shares, par value (USD per share)	$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principle | Accounting Standards Update 2016-01						0	0
Reclassification of disproportionate tax effects | Accounting Standards Update 2018-02						$ 0	$ 0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Statement of Cash Flows [Abstract]
Net income	$ 2,905.4	$ 2,361.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	171	137.8
Amortization of intangible assets	51.7	54
Net amortization of fixed-income securities	14.1	29.7
Amortization of equity-based compensation	64.7	54
Net realized (gains) losses on securities	(659.8)	(166.7)
Net (gains) losses on disposition of property and equipment	(0.1)	7.4
Changes in:
Premiums receivable	(1,190.1)	(1,354.1)
Reinsurance recoverables	(602.3)	(217.1)
Prepaid reinsurance premiums	(149.1)	(176.3)
Deferred acquisition costs	(142.1)	(182.2)
Income taxes	179.7	25
Unearned premiums	1,840	2,105.7
Loss and loss adjustment expense reserves	1,969.2	1,533.9
Accounts payable, accrued expenses, and other liabilities	920.5	1,032.8
Other, net	(239.4)	(43.6)
Net cash provided by operating activities	5,133.4	5,201.5
Purchases:
Fixed maturities	(20,105.3)	(14,430.6)
Equity securities	(291.9)	(234.9)
Sales:
Fixed maturities	12,112.9	4,659.6
Equity securities	175.7	773.5
Maturities, paydowns, calls, and other:
Fixed maturities	4,236.7	3,911.5
Fixed maturities	22.8	15
Net sales of short-term investments	356.8	91.9
Net unsettled security transactions	280.6	11
Purchases of property and equipment	(281.2)	(164.8)
Sales of property and equipment	39.9	8.1
Acquisition of additional shares of ARX Holding Corp.	(11.2)	(296.9)
Net cash used in investing activities	(3,464.2)	(5,656.6)
Cash Flows From Financing Activities
Dividends paid to common shareholders	(1,584.7)	(654.9)
Dividends paid to preferred shareholders	(26.8)	(13.5)
Acquisition of treasury shares for restricted stock tax liabilities	(81.2)	(78.3)
Acquisition of treasury shares acquired in open market	(6.9)	(0.4)
Proceeds from exercise of equity options	1.6	3.3
Net proceeds from issuance of Serial Preferred Shares, Series B	0	493.9
Net proceeds from debt issuances	0	589.5
Payments of debt	0	(37.1)
Net cash provided by (used in) financing activities	(1,698)	302.5
Decrease in cash, cash equivalents, and restricted cash	(28.8)	(152.6)
Cash, cash equivalents, and restricted cash – January 1	75	275.3
Cash, cash equivalents, and restricted cash – September 30	$ 46.2	$ 122.7

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 , compared to 86.8% at September 30, 2018 and December 31, 2018. The consolidated financial statements reflect all normal recurring adjustments that, in the opinion of management, were necessary for a fair statement of the results for the interim periods presented. The results of operations for the period ended September 30, 2019 , 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, 2018 ( “ 2018 Annual Report to Shareholders ” ). 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 $43.7 million at September 30, 2019 , $20.5 million at September 30, 2018 , and $39.3 million

Investments

Investments	9 Months Ended
	Sep. 30, 2019
Investments Schedule [Abstract]
Investments	Investments — The following tables present the composition of our investment portfolio by major security type, consistent with our classification of how we manage, monitor, and measure the portfolio. Our securities are reported in our Consolidated Balance Sheets at fair value. The changes in fair value for our fixed-maturity securities (other than hybrid securities) are reported as a component of accumulated other comprehensive income, net of deferred income taxes, in our Consolidated Balance Sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value of the securities. The changes in the net holding period gains (losses) between periods for the hybrid securities and equity securities are recorded as a component of net realized gains (losses) on securities in our Consolidated Statements of Comprehensive Income. ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value September 30, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,387.6 $ 300.3 $ (9.2 ) $ 0 $ 13,678.7 35.4 % State and local government obligations 1,652.2 32.6 (1.1 ) 0 1,683.7 4.4 Corporate debt securities 7,048.9 231.6 (0.4 ) 1.0 7,281.1 18.9 Residential mortgage-backed securities 677.5 5.5 (1.5 ) 0 681.5 1.8 Commercial mortgage-backed securities 4,547.9 93.0 (1.9 ) 0 4,639.0 12.0 Other asset-backed securities 4,601.0 21.5 (0.6 ) 0 4,621.9 12.0 Redeemable preferred stocks 219.8 4.4 (2.5 ) 5.1 226.8 0.6 Total fixed maturities 32,134.9 688.9 (17.2 ) 6.1 32,812.7 85.1 Short-term investments 1,467.4 0 0 0 1,467.4 3.8 Total available-for-sale securities 33,602.3 688.9 (17.2 ) 6.1 34,280.1 88.9 Equity securities: Nonredeemable preferred stocks 1,054.2 0 0 74.3 1,128.5 2.9 Common equities 1,210.3 0 0 1,954.8 3,165.1 8.2 Total equity securities 2,264.5 0 0 2,029.1 4,293.6 11.1 Total portfolio 1,2 $ 35,866.8 $ 688.9 $ (17.2 ) $ 2,035.2 $ 38,573.7 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value September 30, 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,942.0 $ 0 $ (189.5 ) $ 0 $ 9,752.5 30.2 % State and local government obligations 1,610.1 1.9 (23.2 ) 0 1,588.8 4.9 Corporate debt securities 7,229.1 4.9 (85.2 ) (2.0 ) 7,146.8 22.1 Residential mortgage-backed securities 767.8 7.6 (5.6 ) 0 769.8 2.4 Commercial mortgage-backed securities 2,986.5 3.3 (30.5 ) 0 2,959.3 9.1 Other asset-backed securities 3,205.0 1.4 (13.6 ) 0.1 3,192.9 9.9 Redeemable preferred stocks 222.9 13.2 (1.4 ) (2.1 ) 232.6 0.7 Total fixed maturities 25,963.4 32.3 (349.0 ) (4.0 ) 25,642.7 79.3 Short-term investments 2,809.7 0 0 0 2,809.7 8.7 Total available-for-sale securities 28,773.1 32.3 (349.0 ) (4.0 ) 28,452.4 88.0 Equity securities: Nonredeemable preferred stocks 758.9 0 0 82.0 840.9 2.6 Common equities 1,135.0 0 0 1,922.3 3,057.3 9.4 Total equity securities 1,893.9 0 0 2,004.3 3,898.2 12.0 Total portfolio 1,2 $ 30,667.0 $ 32.3 $ (349.0 ) $ 2,000.3 $ 32,350.6 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value December 31, 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,897.4 $ 71.2 $ (52.1 ) $ 0 $ 9,916.5 29.5 % State and local government obligations 1,654.6 7.3 (12.8 ) 0 1,649.1 4.9 Corporate debt securities 8,808.5 13.6 (125.3 ) (2.5 ) 8,694.3 25.9 Residential mortgage-backed securities 733.5 6.0 (5.1 ) 0 734.4 2.2 Commercial mortgage-backed securities 3,332.8 7.8 (39.0 ) 0 3,301.6 9.8 Other asset-backed securities 3,585.4 3.6 (11.8 ) 0.1 3,577.3 10.7 Redeemable preferred stocks 243.7 5.9 (3.5 ) (7.8 ) 238.3 0.7 Total fixed maturities 28,255.9 115.4 (249.6 ) (10.2 ) 28,111.5 83.7 Short-term investments 1,795.9 0 0 0 1,795.9 5.4 Total available-for-sale securities 30,051.8 115.4 (249.6 ) (10.2 ) 29,907.4 89.1 Equity securities: Nonredeemable preferred stocks 1,002.6 0 0 31.3 1,033.9 3.1 Common equities 1,148.9 0 0 1,477.2 2,626.1 7.8 Total equity securities 2,151.5 0 0 1,508.5 3,660.0 10.9 Total portfolio 1,2 $ 32,203.3 $ 115.4 $ (249.6 ) $ 1,498.3 $ 33,567.4 100.0 % 1 Our portfolio reflects the effect of unsettled security transactions; at September 30, 2019 , we had $286.5 million included in “other liabilities,” compared to $5.2 million and $5.9 million at September 30, 2018 and December 31, 2018 , respectively. 2 The total fair value of the portfolio at September 30, 2019 and 2018 , and December 31, 2018 , included $1.5 billion , $1.8 billion , and $2.9 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. At September 30, 2019 , bonds and certificates of deposit in the principal amount of $261.0 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. Also included in short-term investments are reverse repurchase commitment transactions, where we loan cash to approved counterparties and receive U.S. Treasury Notes as collateral against the cash borrowed. Our exposure to credit risk is limited due to the nature of the collateral (i.e., U.S. Treasury Notes) received. We have counterparty exposure on these trades in the event of a counterparty default to the extent the collateral security’s value is below the amount of cash we delivered to acquire the collateral. The short-term duration of the transactions (primarily overnight) reduces that exposure. We had $400.0 million in open reverse repurchase positions at September 30, 2019 . Although we did invest in reverse repurchase transactions during 2018, we did no t have any open positions at September 30, 2018 or December 31, 2018 . We also participated in repurchase transactions during the first nine months of 2019 and at various times during 2018, but we did no t have any open positions at September 30, 2019 and 2018 , or December 31, 2018 . 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 balance sheets, despite the option to elect to offset these transactions as long as they were with the same counterparty and subject to an enforceable master netting arrangement. Hybrid Securities Included in our fixed-maturity securities are hybrid securities, which are reported at fair value: September 30, (millions) 2019 2018 December 31, 2018 Fixed maturities: State and local government obligations $ 3.5 $ 3.6 $ 3.6 Corporate debt securities 91.3 159.7 158.9 Other asset-backed securities 3.0 5.0 4.5 Redeemable preferred stocks 90.7 72.0 77.7 Total hybrid securities $ 188.5 $ 240.3 $ 244.7 Certain securities in our portfolio are accounted for as hybrid securities because they contain embedded derivatives that are not deemed to be clearly and closely related to the host investments. Since the embedded derivatives (e.g., change-in-control put option, debt-to-equity conversion, or any other feature unrelated to the credit quality or risk of default of the issuer that could impact the amount or timing of our expected future cash flows) do not have observable intrinsic values, we have elected to record the changes in fair value of these securities through income as realized gains or losses. Fixed Maturities The composition of fixed maturities by maturity at September 30, 2019 , was: (millions) Cost Fair Value Less than one year $ 5,620.9 $ 5,633.4 One to five years 18,862.6 19,203.2 Five to ten years 7,582.3 7,904.9 Ten years or greater 69.1 71.2 Total $ 32,134.9 $ 32,812.7 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 September 30, 2019 Fixed maturities: U.S. government obligations 14 $ 2,708.0 $ (9.2 ) 7 $ 2,534.4 $ (8.9 ) 7 $ 173.6 $ (0.3 ) State and local government obligations 60 228.3 (1.1 ) 25 100.4 (0.7 ) 35 127.9 (0.4 ) Corporate debt securities 24 245.5 (0.4 ) 5 77.2 (0.1 ) 19 168.3 (0.3 ) Residential mortgage-backed securities 39 301.0 (1.5 ) 5 138.7 (0.1 ) 34 162.3 (1.4 ) Commercial mortgage-backed securities 48 743.3 (1.9 ) 26 361.9 (0.8 ) 22 381.4 (1.1 ) Other asset-backed securities 55 529.4 (0.6 ) 20 359.1 (0.2 ) 35 170.3 (0.4 ) Redeemable preferred stocks 3 57.2 (2.5 ) 2 45.9 (1.3 ) 1 11.3 (1.2 ) Total fixed maturities 243 $ 4,812.7 $ (17.2 ) 90 $ 3,617.6 $ (12.1 ) 153 $ 1,195.1 $ (5.1 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses September 30, 2018 Fixed maturities: U.S. government obligations 91 $ 9,752.5 $ (189.5 ) 39 $ 5,025.0 $ (67.2 ) 52 $ 4,727.5 $ (122.3 ) State and local government obligations 459 1,394.3 (23.2 ) 227 680.5 (6.4 ) 232 713.8 (16.8 ) Corporate debt securities 369 5,959.2 (85.2 ) 221 3,963.9 (45.3 ) 148 1,995.3 (39.9 ) Residential mortgage-backed securities 234 521.7 (5.6 ) 44 325.0 (0.6 ) 190 196.7 (5.0 ) Commercial mortgage-backed securities 151 2,392.7 (30.5 ) 80 1,164.2 (8.3 ) 71 1,228.5 (22.2 ) Other asset-backed securities 219 2,828.6 (13.6 ) 111 1,821.8 (4.0 ) 108 1,006.8 (9.6 ) Redeemable preferred stocks 3 30.8 (1.4 ) 1 4.7 (0.1 ) 2 26.1 (1.3 ) Total fixed maturities 1,526 $ 22,879.8 $ (349.0 ) 723 $ 12,985.1 $ (131.9 ) 803 $ 9,894.7 $ (217.1 ) 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, 2018 Fixed maturities: U.S. government obligations 51 $ 4,438.0 $ (52.1 ) 2 $ 126.6 $ (0.1 ) 49 $ 4,311.4 $ (52.0 ) State and local government obligations 299 972.4 (12.8 ) 49 192.7 (0.3 ) 250 779.7 (12.5 ) Corporate debt securities 368 6,723.3 (125.3 ) 133 2,613.3 (33.4 ) 235 4,110.0 (91.9 ) Residential mortgage-backed securities 228 450.2 (5.1 ) 32 248.8 (0.8 ) 196 201.4 (4.3 ) Commercial mortgage-backed securities 140 2,328.5 (39.0 ) 48 741.2 (8.9 ) 92 1,587.3 (30.1 ) Other asset-backed securities 203 2,691.3 (11.8 ) 84 1,551.7 (3.2 ) 119 1,139.6 (8.6 ) Redeemable preferred stocks 3 48.5 (3.5 ) 1 18.9 (0.6 ) 2 29.6 (2.9 ) Total fixed maturities 1,292 $ 17,652.2 $ (249.6 ) 349 $ 5,493.2 $ (47.3 ) 943 $ 12,159.0 $ (202.3 ) Since both September 30, 2018 and December 31, 2018 , the number of securities in our fixed-maturity portfolio with unrealized losses decreased, primarily due to valuation increases in nearly all sectors as interest rates declined and credit spreads tightened. We had no material decreases in valuation as a result of credit rating downgrades. A review of the securities in the table above indicated that the issuers were current with respect to their interest obligations and that there was no evidence of deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. Other-Than-Temporary Impairment (OTTI) The following table shows the total non-credit portion of the OTTI recorded in accumulated other comprehensive income, reflecting the original non-credit loss at the time the credit impairment was determined (i.e., unadjusted for valuation changes subsequent to the original write-down): September 30, December 31, (millions) 2019 2018 Fixed maturities: Residential mortgage-backed securities $ (19.7 ) $ (19.7 ) $ (19.7 ) Commercial mortgage-backed securities (0.1 ) (0.1 ) (0.1 ) Total fixed maturities $ (19.8 ) $ (19.8 ) $ (19.8 ) The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended September 30, 2019 and 2018 , for which a portion of the OTTI losses were also recognized in accumulated other comprehensive income at the time the credit impairments were determined and recognized: Three Months Ended September 30, 2019 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2019 $ 0 $ 0.5 $ 0.5 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Balance at September 30, 2019 $ 0 $ 0.5 $ 0.5 Three Months Ended September 30, 2018 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2018 $ 0.3 $ 0.5 $ 0.8 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Balance at September 30, 2018 $ 0.3 $ 0.5 $ 0.8 Nine Months Ended September 30, 2019 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2018 $ 0 $ 0.5 $ 0.5 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Balance at September 30, 2019 $ 0 $ 0.5 $ 0.5 Nine Months Ended September 30, 2018 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2017 $ 0 $ 0.5 $ 0.5 Change in recoveries of future cash flows expected to be collected 1 0.3 0 0.3 Balance at September 30, 2018 $ 0.3 $ 0.5 $ 0.8 1 Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security. Although it is not likely that we will be required to sell the securities prior to the recovery of their respective cost bases (which could be maturity), we are required to measure the amount of potential credit losses on the securities that were in an unrealized loss position. In that process, we considered a number of factors and inputs related to the individual securities. 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 the security would be written down. We did no t have any credit impairment write-downs for the nine months ended September 30, 2019 or 2018 . Realized Gains (Losses) The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2019 2018 2019 2018 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 41.5 $ 0.1 $ 113.0 $ 1.8 State and local government obligations 1.8 0.2 4.0 9.4 Corporate and other debt securities 21.3 1.7 68.5 2.1 Residential mortgage-backed securities 0 0 0.2 0 Commercial mortgage-backed securities 2.6 0 6.2 2.0 Other asset-backed securities 0.1 0 0.8 0.1 Redeemable preferred stocks 0 0.2 0 4.5 Total available-for-sale securities 67.3 2.2 192.7 19.9 Equity securities: Nonredeemable preferred stocks 3.6 0.1 20.2 3.7 Common equities 4.7 126.8 9.4 265.2 Total equity securities 8.3 126.9 29.6 268.9 Subtotal gross realized gains on security sales 75.6 129.1 222.3 288.8 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (1.5 ) (7.6 ) (13.9 ) (46.4 ) State and local government obligations 0 (0.6 ) (0.7 ) (2.5 ) Corporate and other debt securities (0.2 ) (3.2 ) (7.7 ) (7.3 ) Residential mortgage-backed securities 0 0 (2.3 ) 0 Commercial mortgage-backed securities 0 0 (2.1 ) (6.3 ) Other asset-backed securities 0 (0.1 ) (0.1 ) (1.1 ) Redeemable preferred stocks (0.2 ) 0 (0.3 ) 0 Total available-for-sale securities (1.9 ) (11.5 ) (27.1 ) (63.6 ) Equity securities: Nonredeemable preferred stocks (2.0 ) 0 (2.0 ) (2.3 ) Common equities 0 (9.2 ) (7.9 ) (17.1 ) Total equity securities (2.0 ) (9.2 ) (9.9 ) (19.4 ) Subtotal gross realized losses on security sales (3.9 ) (20.7 ) (37.0 ) (83.0 ) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 40.0 (7.5 ) 99.1 (44.6 ) State and local government obligations 1.8 (0.4 ) 3.3 6.9 Corporate and other debt securities 21.1 (1.5 ) 60.8 (5.2 ) Residential mortgage-backed securities 0 0 (2.1 ) 0 Commercial mortgage-backed securities 2.6 0 4.1 (4.3 ) Other asset-backed securities 0.1 (0.1 ) 0.7 (1.0 ) Redeemable preferred stocks (0.2 ) 0.2 (0.3 ) 4.5 Total available-for-sale securities 65.4 (9.3 ) 165.6 (43.7 ) Equity securities: Nonredeemable preferred stocks 1.6 0.1 18.2 1.4 Common equities 4.7 117.6 1.5 248.1 Total equity securities 6.3 117.7 19.7 249.5 Subtotal net realized gains (losses) on security sales 71.7 108.4 185.3 205.8 Net holding period gains (losses) Hybrid securities 4.2 1.3 16.3 (4.2 ) Equity securities 27.6 94.5 520.6 (1.7 ) Subtotal net holding period gains (losses) 31.8 95.8 536.9 (5.9 ) Other-than-temporary impairment losses Other asset impairment (38.1 ) (22.1 ) (62.4 ) (33.2 ) Subtotal other-than-temporary impairment losses (38.1 ) (22.1 ) (62.4 ) (33.2 ) Total net realized gains (losses) on securities $ 65.4 $ 182.1 $ 659.8 $ 166.7 For both 2019 and 2018, the other asset impairment losses related to federal renewable energy tax credit fund investments, which were reported in “other assets” on the balance sheet, based on an analysis that our investments in those funds will not generate the cash flows that we anticipated. See Note 5 – Income Taxes for additional discussion related to 2019 activity. The following table reflects our holding period realized gains (losses) on equity securities recognized for the three and nine months ended September 30, 2019 and 2018 , for equity securities held at quarter end: Three Months Nine Months (millions) 2019 2018 2019 2018 Total net gains (losses) recognized during the period on equity securities $ 33.9 $ 212.2 $ 540.3 $ 247.8 Less: Net gains (losses) recognized on equity securities sold during the period 6.3 117.7 19.7 249.5 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 27.6 $ 94.5 $ 520.6 $ (1.7 ) Net Investment Income The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2019 2018 2019 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 75.8 $ 47.7 $ 198.7 $ 133.4 State and local government obligations 8.7 9.0 26.9 28.1 Corporate debt securities 65.1 62.1 209.8 150.1 Residential mortgage-backed securities 5.4 6.9 16.6 20.4 Commercial mortgage-backed securities 35.6 24.1 100.7 65.5 Other asset-backed securities 31.4 21.2 85.5 50.9 Redeemable preferred stocks 3.9 3.3 16.1 8.8 Total fixed maturities 225.9 174.3 654.3 457.2 Short-term investments 7.1 15.7 34.3 40.7 Total available-for-sale securities 233.0 190.0 688.6 497.9 Equity securities: Nonredeemable preferred stocks 15.9 11.2 47.3 32.5 Common equities 14.1 16.9 41.3 46.1 Total equity securities 30.0 28.1 88.6 78.6 Investment income 263.0 218.1 777.2 576.5 Investment expenses (5.9 ) (5.8 ) (18.3 ) (18.0 ) Net investment income $ 257.1 $ 212.3 $ 758.9 $ 558.5 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. The increase in net investment income on a year-over-year basis for the three and nine months ended September 30, 2019 , was due to a combination of an increase in average assets and an increase in portfolio yields. The increase in average assets was due to strong premium growth, underwriting profitability, and portfolio returns, as well as the proceeds from debt and preferred stock issuances during 2018, partially offset by our common and preferred share dividend payments during the first nine months of 2019. The increase in portfolio yields was a result of our decision to hold a short-duration portfolio, which allowed us to take advantage of opportunities to invest in higher yielding securities with cash from operations and portfolio maturities and paydowns. The portfolio duration at September 30, 2019 was 2.9 years , compared to 2.6 years at September 30, 2018 . Trading Securities At September 30, 2019 and 2018 , and December 31, 2018 , we did no t hold any trading securities and did no t have any net realized gains (losses) on trading securities for the three and nine months ended September 30, 2019 and 2018 . Derivative Instruments At September 30, 2019 and 2018 , and December 31, 2018 , we had no

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value	Fair Value — We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows: • Level 1 : Inputs are unadjusted quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, which are continually priced on a daily basis, active exchange-traded equity securities, and certain short-term securities). • Level 2 : Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 : Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments). Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations. The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2019 Fixed maturities: U.S. government obligations $ 13,678.7 $ 0 $ 0 $ 13,678.7 $ 13,387.6 State and local government obligations 0 1,683.7 0 1,683.7 1,652.2 Corporate debt securities 0 7,281.1 0 7,281.1 7,048.9 Subtotal 13,678.7 8,964.8 0 22,643.5 22,088.7 Asset-backed securities: Residential mortgage-backed 0 681.5 0 681.5 677.5 Commercial mortgage-backed 0 4,639.0 0 4,639.0 4,547.9 Other asset-backed 0 4,621.9 0 4,621.9 4,601.0 Subtotal asset-backed securities 0 9,942.4 0 9,942.4 9,826.4 Redeemable preferred stocks: Financials 0 51.7 0 51.7 51.7 Utilities 0 10.9 0 10.9 10.0 Industrials 11.2 153.0 0 164.2 158.1 Subtotal redeemable preferred stocks 11.2 215.6 0 226.8 219.8 Total fixed maturities 13,689.9 19,122.8 0 32,812.7 32,134.9 Short-term investments 1,464.9 2.5 0 1,467.4 1,467.4 Total available-for-sale securities 15,154.8 19,125.3 0 34,280.1 33,602.3 Equity securities: Nonredeemable preferred stocks: Financials 82.2 967.1 27.1 1,076.4 1,004.3 Utilities 0 42.1 0 42.1 39.9 Industrials 0 5.0 5.0 10.0 10.0 Subtotal nonredeemable preferred stocks 82.2 1,014.2 32.1 1,128.5 1,054.2 Common equities: Common stocks 3,164.8 0 0 3,164.8 1,210.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,164.8 0 0.3 3,165.1 1,210.3 Total equity securities 3,247.0 1,014.2 32.4 4,293.6 2,264.5 Total portfolio $ 18,401.8 $ 20,139.5 $ 32.4 $ 38,573.7 $ 35,866.8 Debt $ 0 $ 5,113.3 $ 0 $ 5,113.3 $ 4,406.5 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2018 Fixed maturities: U.S. government obligations $ 9,752.5 $ 0 $ 0 $ 9,752.5 $ 9,942.0 State and local government obligations 0 1,588.8 0 1,588.8 1,610.1 Corporate debt securities 0 7,146.8 0 7,146.8 7,229.1 Subtotal 9,752.5 8,735.6 0 18,488.1 18,781.2 Asset-backed securities: Residential mortgage-backed 0 769.8 0 769.8 767.8 Commercial mortgage-backed 0 2,959.3 0 2,959.3 2,986.5 Other asset-backed 0 3,192.9 0 3,192.9 3,205.0 Subtotal asset-backed securities 0 6,922.0 0 6,922.0 6,959.3 Redeemable preferred stocks: Financials 0 67.8 0 67.8 65.2 Utilities 0 4.7 0 4.7 4.8 Industrials 10.1 150.0 0 160.1 152.9 Subtotal redeemable preferred stocks 10.1 222.5 0 232.6 222.9 Total fixed maturities 9,762.6 15,880.1 0 25,642.7 25,963.4 Short-term investments 2,573.4 236.3 0 2,809.7 2,809.7 Total available-for-sale securities 12,336.0 16,116.4 0 28,452.4 28,773.1 Equity securities: Nonredeemable preferred stocks: Financials 76.3 724.0 0 800.3 718.9 Utilities 0 35.6 0 35.6 35.0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 76.3 759.6 5.0 840.9 758.9 Common equities: Common stocks 3,057.0 0 0 3,057.0 1,134.7 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,057.0 0 0.3 3,057.3 1,135.0 Total equity securities 3,133.3 759.6 5.3 3,898.2 1,893.9 Total portfolio $ 15,469.3 $ 16,876.0 $ 5.3 $ 32,350.6 $ 30,667.0 Debt $ 0 $ 3,926.9 $ 0 $ 3,926.9 $ 3,859.9 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2018 Fixed maturities: U.S. government obligations $ 9,916.5 $ 0 $ 0 $ 9,916.5 $ 9,897.4 State and local government obligations 0 1,649.1 0 1,649.1 1,654.6 Corporate debt securities 0 8,694.3 0 8,694.3 8,808.5 Subtotal 9,916.5 10,343.4 0 20,259.9 20,360.5 Asset-backed securities: Residential mortgage-backed 0 734.4 0 734.4 733.5 Commercial mortgage-backed 0 3,301.6 0 3,301.6 3,332.8 Other asset-backed 0 3,577.3 0 3,577.3 3,585.4 Subtotal asset-backed securities 0 7,613.3 0 7,613.3 7,651.7 Redeemable preferred stocks: Financials 0 78.2 0 78.2 79.3 Utilities 0 0 0 0 0 Industrials 9.5 150.6 0 160.1 164.4 Subtotal redeemable preferred stocks 9.5 228.8 0 238.3 243.7 Total fixed maturities 9,926.0 18,185.5 0 28,111.5 28,255.9 Short-term investments 1,722.1 73.8 0 1,795.9 1,795.9 Total available-for-sale securities 11,648.1 18,259.3 0 29,907.4 30,051.8 Equity securities: Nonredeemable preferred stocks: Financials 71.9 887.1 25.1 984.1 951.6 Utilities 0 44.8 0 44.8 46.0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 71.9 931.9 30.1 1,033.9 1,002.6 Common equities: Common stocks 2,625.8 0 0 2,625.8 1,148.6 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,625.8 0 0.3 2,626.1 1,148.9 Total equity securities 2,697.7 931.9 30.4 3,660.0 2,151.5 Total portfolio $ 14,345.8 $ 19,191.2 $ 30.4 $ 33,567.4 $ 32,203.3 Debt $ 0 $ 4,532.3 $ 0 $ 4,532.3 $ 4,404.9 Our portfolio valuations, excluding short-term investments, classified as either Level 1 or Level 2 in the above tables are priced exclusively by external sources, including: pricing vendors, dealers/market makers, and exchange-quoted prices. Our short-term investments classified as Level 1 are highly liquid, actively marketed, and have a very short duration, primarily 90 days or less to redemption. These securities are held at their original cost, adjusted for any accretion of discount, since that value very closely approximates what an active market participant would be willing to pay for such securities. The remainder of our short-term investments are classified as Level 2 and are not priced externally since these securities continually trade at par value. These securities are classified as Level 2 since they are primarily longer-dated securities issued by municipalities that contain either liquidity facilities or mandatory put features within one year. At September 30, 2019 , vendor-quoted prices represented 81% of our Level 1 classifications (excluding short-term investments), compared to 76% and 79% at September 30, 2018 and December 31, 2018 , respectively. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded, and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. At September 30, 2019 and 2018 and December 31, 2018 , vendor-quoted prices comprised 99% of our Level 2 classifications in each period (excluding short-term investments), while dealer-quoted prices represented the remaining 1% . In our process for selecting a source (e.g., dealer or pricing service) to provide pricing for securities in our portfolio, we reviewed documentation from the sources that detailed the pricing techniques and methodologies used by these sources and determined if their policies adequately considered market activity, either based on specific transactions for the particular security type or based on modeling of securities with similar credit quality, duration, yield, and structure that were recently transacted. Once a source is chosen, we continue to monitor any changes or modifications to their processes by reviewing their documentation on internal controls for pricing and market reviews. We review quality control measures of our sources as they become available to determine if any significant changes have occurred from period to period that might indicate issues or concerns regarding their evaluation or market coverage. As part of our pricing procedures, we obtain quotes from more than one source to help us fully evaluate the market price of securities. However, our internal pricing policy is to use a consistent source for individual securities in order to maintain the integrity of our valuation process. Quotes obtained from the sources are not considered binding offers to transact. Under our policy, when a review of the valuation received from our selected source appears to be outside of what is considered market level activity (which is defined as trading at spreads or yields significantly different than those of comparable securities or outside the general sector level movement without a reasonable explanation), we may use an alternate source’s price. To the extent we determine that it may be prudent to substitute one source’s price for another, we will contact the initial source to obtain an understanding of the factors that may be contributing to the significant price variance. To allow us to determine if our initial source is providing a price that is outside of a reasonable range, we review our portfolio pricing on 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 are able to explain significant price changes (i.e., greater than 2%) as known events occur in the marketplace and affect a particular security’s price at sale. This analysis provides us with additional comfort regarding the source’s process, the quality of its review, and its willingness to improve its analysis based on feedback from clients. We believe this effort helps ensure that we are reporting the most representative fair values for our securities. Except as described below, our Level 3 securities are also priced externally; however, due to several factors (e.g., nature of the securities, level of activity, and lack of similar securities trading to obtain observable market level inputs), these valuations are more subjective in nature. Certain private equity investments included in the Level 3 category are valued using external pricing supplemented by internal review and analysis. After all the valuations are received and our review is complete, if the inputs used by vendors are determined to not contain sufficient observable market information, we will reclassify the affected security valuations to Level 3. At September 30, 2019 and 2018 , and December 31, 2018 , we did no t have any securities in our fixed-maturity portfolio listed as Level 3. At September 30, 2019 and December 31, 2018 , we held two private nonredeemable preferred securities with a combined value of $32.1 million and $30.1 million , respectively, that were priced internally, and held one private nonredeemable preferred security with a value of $5.0 million that was priced internally at September 30, 2018 . At September 30, 2019 and 2018 , and December 31, 2018 , we held one Level 3 other risk investment with a value of $0.3 million . 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 2019 and 2018, there were no material assets or liabilities measured at fair value on a nonrecurring basis. Based on our review, all prices received from external sources remained unadjusted. Due to the relative size of the Level 3 securities’ fair values compared to the total portfolio’s fair value, any changes in pricing methodology would not have a significant change in valuation that would materially impact net or comprehensive income. The following tables provide a summary of changes in fair value associated with Level 3 assets for the three and nine months ended September 30, 2019 and 2018 : Level 3 Fair Value (millions) Fair Value at June 30, 2019 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 32.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 32.4 Level 3 Fair Value (millions) Fair Value at June 30, 2018 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2018 Equity securities: Nonredeemable preferred stocks: Financials $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 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 $ 5.3 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 5.3 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 September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 30.4 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 32.4 Level 3 Fair Value (millions) Fair Value at December 31, 2017 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2018 Equity securities: Nonredeemable preferred stocks: Financials $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 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 $ 5.3 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 5.3 The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2019 and 2018 , and December 31, 2018 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 27.1 internal price unadjusted purchase price per share 9.0 Industrials 2 5.0 internal price price-to-sales ratio 5.5 Subtotal Level 3 securities 32.1 Pricing exemption securities 3 0.3 Total Level 3 securities $ 32.4 1 The security was internally priced since it is a private equity. The security was initially purchased during December 2018 and additional shares were purchased during second quarter 2019. The value at September 30, 2019 reflects the unadjusted purchase price per share (all purchases were at the same price). 2 The security was internally priced since it is a private equity. The price at September 30, 2019 , was calculated using a price-to-sales ratio. 3 The unobservable input is not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2018 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials $ 0 NA NA NA Industrials 1 5.0 internal price unadjusted purchase price per share 3.9 Subtotal Level 3 securities 5.0 Pricing exemption securities 2 0.3 Total Level 3 securities $ 5.3 NA= Not applicable 1 The security was internally priced since it is a private equity. The value at September 30, 2018 reflects the unadjusted purchase price per share. 2 The unobservable input is not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at December 31, 2018 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 2 5.0 internal price price-to-sales ratio 5.5 Subtotal Level 3 securities 30.1 Pricing exemption securities 3 0.3 Total Level 3 securities $ 30.4 1 The security was internally priced since it is a private equity. The security was purchased during December 2018 and the value at December 31, 2018 reflects the unadjusted purchase price per share. 2 The security was internally priced since it is a private equity. The price at December 31, 2018, was calculated using a price-to-sales ratio. 3 The unobservable input is not reasonably available to us.

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Debt	Debt — Debt at each of the balance sheet periods consisted of: September 30, 2019 September 30, 2018 December 31, 2018 (millions) Carrying Value Fair Value Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 $ 499.3 $ 516.5 $ 499.0 $ 503.9 $ 499.1 $ 506.5 2.45% Senior Notes due 2027 496.8 502.1 496.4 453.3 496.5 455.5 6 5/8% Senior Notes due 2029 296.5 392.2 296.3 360.3 296.4 368.5 4.00% Senior Notes due 2029 544.9 617.0 0 0 544.5 562.4 6.25% Senior Notes due 2032 395.7 547.2 395.4 481.8 395.5 496.6 4.35% Senior Notes due 2044 346.6 414.7 346.6 349.7 346.6 350.2 3.70% Senior Notes due 2045 395.4 431.8 395.3 359.1 395.3 366.7 4.125% Senior Notes due 2047 841.5 987.4 841.3 828.4 841.4 831.9 4.20% Senior Notes due 2048 589.8 704.4 589.6 590.4 589.6 594.0 Total $ 4,406.5 $ 5,113.3 $ 3,859.9 $ 3,926.9 $ 4,404.9 $ 4,532.3 The Progressive Corporation issued $550 million of 4.00% Senior Notes due 2029 (the “ 4.00% Senior Notes”) in October 2018, in an underwritten public offering. The net proceeds from the issuance, after deducting underwriters’ discounts, commissions, and other issuance costs, was $544.5 million . Consistent with the other senior notes issued by Progressive, interest on the 4.00% Senior Notes is payable semiannually, principal is due at maturity, and the note is redeemable, in whole or in part, at any time, subject to a treasury “make whole” provision. During the second quarter 2019, The Progressive Corporation renewed its line of credit with PNC Bank, National Association (PNC) in the maximum principal amount of $250 million on the same terms and conditions. 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.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes — Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. We review our deferred tax assets regularly for recoverability. At September 30, 2019 and 2018 , and December 31, 2018 , 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 nine months ended September 30, 2019 , there have been no material changes in our reserve for uncertain tax positions. The effective tax rates for the three and nine months ended September 30, 2019 were 16.5% and 24.0% , respectively, compared to 17.7% and 19.2% for the same periods last year. From 2016 to 2018, we invested in federal renewable energy tax credit funds. The effective tax rates for 2018 were lower than the statutory rate due primarily to tax benefits related to the investments made during 2018, along with the vesting of employee stock-based compensation awards. In late December 2018 and during the first two months of 2019, we learned of allegations of potential fraudulent conduct by the sponsor of three of these tax credit fund investments, including information about ongoing federal investigations. Based on our continuing investigations and information that became available to us beginning late in the first quarter, we believe that the sponsor committed fraud through these tax credit funds and that all of the tax credits and other tax benefits related to those investments are not valid. Based on this information, during the first quarter 2019, we increased our provision for income taxes $156.1 million , principally reflecting the total reversal of the tax credits and other tax benefits previously recognized from certain renewable energy investments, plus interest, resulting in an effective tax rate higher than the statutory rate for the nine months ended September 30, 2019. For the third quarter 2019, the effective tax rate was lower than the statutory rate due primarily to tax benefits related to a renewable energy tax credit fund that is unrelated to the potentially fraudulent funds discussed above and the vesting of employee stock-based compensation awards during the quarter.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	9 Months Ended
	Sep. 30, 2019
Loss and Loss Adjustment Expenses Reserves [Abstract]
Loss and Loss Adjustment Expenses Reserves	Loss and Loss Adjustment Expense Reserves — Activity in the loss and loss adjustment expense reserves is summarized as follows: September 30, (millions) 2019 2018 Balance, Beginning of period $ 15,400.8 $ 13,086.9 Less reinsurance recoverables on unpaid losses 2,572.7 2,170.1 Net balance, Beginning of period 12,828.1 10,916.8 Incurred related to: Current year 18,108.2 15,722.2 Prior years 215.2 47.0 Total incurred 18,323.4 15,769.2 Paid related to: Current year 10,864.9 9,409.7 Prior years 6,061.7 5,031.9 Total paid 16,926.6 14,441.6 Net balance, End of period 14,224.9 12,244.4 Plus reinsurance recoverables on unpaid losses 3,145.1 2,376.4 Balance, End of period $ 17,370.0 $ 14,620.8 We experienced unfavorable reserve development of $215.2 million and $47.0 million for the first nine months of 2019 and 2018, respectively, which is reflected as “Incurred related to prior years ” in the table above. Year-to-date September 30, 2019 • About 50% of the unfavorable prior year reserve development was attributable to accident year 2018, 30% to accident year 2017, and the remainder to accident years 2016 and prior. • Our personal auto products incurred about $108 million of unfavorable loss and loss adjustment expense (LAE) reserve development, with the Agency and Direct auto businesses each contributing about half. The unfavorable development was primarily attributable to increased injury severity, a higher than anticipated frequency of reopened personal injury protection (PIP) claims, primarily in Florida, and late reported losses occurring late 2018 but not reported until 2019. • Our Commercial Lines business experienced about $71 million of unfavorable development, primarily due to increased injury severity and more emergence of large injury claims than originally anticipated. • Our Property business experienced about $19 million of unfavorable development, primarily due to higher than originally anticipated homeowner and dwelling costs and fire liability costs. • Our special lines business experienced about $17 million of unfavorable development, primarily due to less salvage and subrogation recoveries than originally anticipated. Year-to-date September 30, 2018 • Accident year 2016 had approximately $52 million of unfavorable prior year reserve development, which was in part offset by favorable development in 2017 as well as 2015 and prior accident years. • Our personal auto business incurred about $41 million of unfavorable loss and LAE reserve development, with the Agency and Direct auto businesses contributing about $30 million and $11 million , respectively, of unfavorable development. The unfavorable development was primarily due to an increase in reopened PIP claims. • Our Property business recognized unfavorable development of about $5 million . • Our special lines products and Commercial Lines business had minimal development during the first nine months of the year.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 and 2018 , and December 31, 2018 , were $62.8 million , $152.4 million , and $117.3 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 nine months ended September 30, 2019, 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 $43.4 million (see Note 14 – Leases for further discussion). We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2019 2018 Income taxes $ 738.7 $ 535.8 Interest 147.3 116.4 Operating lease liabilities 61.2 NA NA = Not applicable

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2019
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 primary liability, physical damage, and other auto-related insurance for automobiles and trucks owned and/or operated predominantly by small businesses in the business auto, for-hire transportation, contractor, for-hire specialty, tow, and for-hire livery markets. Our Property segment writes residential property insurance for homeowners, other property owners, and renters. Our other indemnity businesses include our run-off businesses. 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 ASI and unaffiliated insurance companies. All segment revenues are generated from external customers; all intercompany transactions are eliminated in consolidation. Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 3,703.4 $ 380.2 $ 3,318.2 $ 372.2 $ 10,851.5 $ 1,267.9 $ 9,607.7 $ 1,142.2 Direct 3,804.0 291.7 3,337.2 294.4 11,113.7 940.2 9,565.3 880.3 Total Personal Lines 1 7,507.4 671.9 6,655.4 666.6 21,965.2 2,208.1 19,173.0 2,022.5 Commercial Lines 1,106.9 69.7 939.6 112.7 3,190.4 360.7 2,632.5 307.8 Property 2 397.9 (9.1 ) 335.5 (7.8 ) 1,141.1 (35.8 ) 933.2 (31.2 ) Other indemnity 0 0 0 (0.1 ) 0 0 0 0.1 Total underwriting operations 9,012.2 732.5 7,930.5 771.4 26,296.7 2,533.0 22,738.7 2,299.2 Fees and other revenues 3 138.4 NA 122.6 NA 403.4 NA 342.4 NA Service businesses 51.5 2.8 42.5 6.7 144.1 12.0 119.6 17.5 Investments 4 328.4 322.5 400.2 394.4 1,437.0 1,418.7 743.2 725.2 Interest expense NA (47.5 ) NA (42.0 ) NA (142.3 ) NA (120.5 ) Consolidated total $ 9,530.5 $ 1,010.3 $ 8,495.8 $ 1,130.5 $ 28,281.2 $ 3,821.4 $ 23,943.9 $ 2,921.4 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three and nine months ended September 30, 2019 and 2018 ; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 For the three and nine months ended September 30, 2019 , pretax profit (loss) includes $15.8 million and $51.7 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $18.0 million and $54.0 million for the same periods in 2018. 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. 3 Pretax profit (loss) for fees and other revenues is attributable 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 September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Under-writing Combined Ratio Under-writing Combined Ratio Under-writing Combined Ratio Under-writing Combined Ratio Personal Lines Agency 10.3 % 89.7 11.2 % 88.8 11.7 % 88.3 11.9 % 88.1 Direct 7.7 92.3 8.8 91.2 8.5 91.5 9.2 90.8 Total Personal Lines 9.0 91.0 10.0 90.0 10.1 89.9 10.5 89.5 Commercial Lines 6.3 93.7 12.0 88.0 11.3 88.7 11.7 88.3 Property 1 (2.3 ) 102.3 (2.3 ) 102.3 (3.1 ) 103.1 (3.3 ) 103.3 Total underwriting operations 8.1 91.9 9.7 90.3 9.6 90.4 10.1 89.9 1 Included in the three and nine months ended September 30, 2019 , is 4.0 points and 4.5 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 5.4 points and 5.8 points, respectively, for the three and nine months ended September 30, 2018 .

Dividends

Dividends	9 Months Ended
	Sep. 30, 2019
Dividends [Abstract]
Dividends	Dividends — Following is a summary of our common and preferred share dividends that were declared and/or paid during the nine months ended September 30, 2019 and 2018: (millions, except per share amounts) Amount Dividend Type Declared Payable Per Share Accrued 1 Common - Quarterly August 2019 October 2019 $ 0.10 $ 58.5 Preferred - Semi-annual August 2019 September 2019 26.875 13.4 Common - Quarterly May 2019 July 2019 0.10 58.4 Preferred - Semi-annual February 2019 March 2019 26.875 13.4 Common - Quarterly February 2019 April 2019 0.10 58.4 Common - Annual Variable December 2018 February 2019 2.5140 1,467.9 Preferred - Semi-annual August 2018 September 2018 27.024 13.5 Common - Annual Variable December 2017 February 2018 1.1247 655.1 1 Based on an estimate of shares outstanding as of the record date. See Note 14 – Dividends in our 2018 Annual Report to Shareholders for a discussion of our common share dividend policies in effect during 2019 and 2018 and prior, and a discussion of our Series B Fixed-to-Floating Rate Cumulative Perpetual Serial Preferred Share dividends.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2019
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 June 30, 2019 $ 573.6 $ (120.5 ) $ 453.1 $ 472.9 $ (16.8 ) $ (3.0 ) Other comprehensive income (loss) before reclassifications: Investment securities 134.3 (28.2 ) 106.1 106.1 0 0 Loss attributable to noncontrolling interest (NCI) (1.2 ) 0.3 (0.9 ) 0 0 (0.9 ) Total other comprehensive income (loss) before reclassifications 133.1 (27.9 ) 105.2 106.1 0 (0.9 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 60.7 (12.7 ) 48.0 48.0 0 0 Interest expense (0.3 ) 0.1 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income 60.4 (12.6 ) 47.8 48.0 (0.2 ) 0 Total other comprehensive income (loss) 72.7 (15.3 ) 57.4 58.1 0.2 (0.9 ) Balance at September 30, 2019 $ 646.3 $ (135.8 ) $ 510.5 $ 531.0 $ (16.6 ) $ (3.9 ) Components of Changes in 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 June 30, 2018 $ (280.8 ) $ 58.9 $ (221.9 ) $ (210.9 ) $ (17.6 ) $ 6.6 Reclassification of disproportionate amounts (4.3 ) 0.9 (3.4 ) 0 0 (3.4 ) Adjusted balance at June 30, 2018 (285.1 ) 59.8 (225.3 ) (210.9 ) (17.6 ) 3.2 Other comprehensive income (loss) before reclassifications: Investment securities (58.7 ) 12.3 (46.4 ) (46.4 ) 0 0 Loss attributable to noncontrolling interest (NCI) 0.6 (0.2 ) 0.4 0 0 0.4 Total other comprehensive income (loss) before reclassifications (58.1 ) 12.1 (46.0 ) (46.4 ) 0 0.4 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (9.3 ) 1.9 (7.4 ) (7.4 ) 0 0 Interest expense (0.2 ) 0 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income (9.5 ) 1.9 (7.6 ) (7.4 ) (0.2 ) 0 Total other comprehensive income (loss) (48.6 ) 10.2 (38.4 ) (39.0 ) 0.2 0.4 Balance at September 30, 2018 $ (333.7 ) $ 70.0 $ (263.7 ) $ (249.9 ) $ (17.4 ) $ 3.6 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, 2018 $ (153.0 ) $ 32.1 $ (120.9 ) $ (105.6 ) $ (17.2 ) $ 1.9 Other comprehensive income (loss) before reclassifications: Investment securities 953.5 (200.2 ) 753.3 753.3 0 0 Loss attributable to noncontrolling interest (NCI) (7.4 ) 1.6 (5.8 ) 0 0 (5.8 ) Total other comprehensive income (loss) before reclassifications 946.1 (198.6 ) 747.5 753.3 0 (5.8 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 147.6 (30.9 ) 116.7 116.7 0 0 Interest expense (0.8 ) 0.2 (0.6 ) 0 (0.6 ) 0 Total reclassification adjustment for amounts realized in net income 146.8 (30.7 ) 116.1 116.7 (0.6 ) 0 Total other comprehensive income (loss) 799.3 (167.9 ) 631.4 636.6 0.6 (5.8 ) Balance at September 30, 2019 $ 646.3 $ (135.8 ) $ 510.5 $ 531.0 $ (16.6 ) $ (3.9 ) 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, 2017 $ 1,977.8 $ (695.6 ) $ 1,282.2 $ 1,295.0 $ (14.8 ) $ 2.0 Cumulative effect adjustment (2,006.0 ) 705.8 (1,300.2 ) (1,300.2 ) 0 0 Reclassification of disproportionate amounts (4.3 ) (3.4 ) (7.7 ) (1.1 ) (3.2 ) (3.4 ) Adjusted balance at December 31, 2017 (32.5 ) 6.8 (25.7 ) (6.3 ) (18.0 ) (1.4 ) Other comprehensive income (loss) before reclassifications: Investment securities (352.5 ) 73.9 (278.6 ) (278.6 ) 0 0 Loss attributable to noncontrolling interest (NCI) 6.4 (1.4 ) 5.0 0 0 5.0 Total other comprehensive income (loss) before reclassifications (346.1 ) 72.5 (273.6 ) (278.6 ) 0 5.0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (44.2 ) 9.2 (35.0 ) (35.0 ) 0 0 Interest expense (0.7 ) 0.1 (0.6 ) 0 (0.6 ) 0 Total reclassification adjustment for amounts realized in net income (44.9 ) 9.3 (35.6 ) (35.0 ) (0.6 ) 0 Total other comprehensive income (loss) (301.2 ) 63.2 (238.0 ) (243.6 ) 0.6 5.0 Balance at September 30, 2018 $ (333.7 ) $ 70.0 $ (263.7 ) $ (249.9 ) $ (17.4 ) $ 3.6 In an effort to manage interest rate risk, we often enter into forecasted transactions on Progressive’s debt issuances. 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 2018 Annual Report to Shareholders for further discussion).

Litigation

Litigation	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Litigation	Litigation — The Progressive Corporation and/or its insurance subsidiaries are named as defendants in various lawsuits arising out of claims made under insurance policies written by our insurance subsidiaries in the ordinary course of business. We consider all legal actions relating to such claims in establishing our loss and loss adjustment expense reserves. In addition, The Progressive Corporation and/or its subsidiaries are named as defendants in a number of class action or individual lawsuits that challenge certain of the operations of the subsidiaries. These cases include 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 2018 Annual Report to Shareholders. We plan to contest the pending lawsuits vigorously, but may pursue settlement negotiations in some cases, as we deem appropriate. The outcomes of pending cases are uncertain at this time. We establish accruals for these lawsuits when it is probable that a loss has been or will be incurred and we can reasonably estimate potential loss exposure, which may include a range of loss. As to lawsuits for which the loss is considered neither probable or estimable, or is considered probable but not estimable, we do not establish an accrual. Nevertheless, we continue to evaluate this pending litigation to determine if any losses not deemed probable and estimable become so, at which point we would establish an accrual at our best estimate of the loss or range of loss. With respect to our pending lawsuits that are not related to claims under insurance policies, the accruals that we have established, if any, were not material at September 30, 2019 or 2018 , and there were no material settlements during 2018 or the first nine months of 2019 . 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 2018 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 2018 Annual Report to Shareholders.

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest	9 Months Ended
	Sep. 30, 2019
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 “put” a portion of their ARX shares to Progressive in 2018, and have the right to put all of their remaining shares to Progressive in 2021. During 2018, minority ARX stockholders put 204,527 shares, including 5,483 shares that were issued upon the exercise of outstanding stock options. Progressive acquired these additional shares, in a cash transaction, for a total cost of $295.9 million . If ARX stockholders do not put all of their shares to Progressive in 2021, Progressive has the ability to “call ” all of the outstanding shares shortly thereafter and to bring its ownership stake to 100% in 2021. See Note 15 – Redeemable Noncontrolling Interest in our 2018 Annual Report to Shareholders for a discussion of the purchase price for shares to be purchased by Progressive pursuant to these put or call rights. At September 30, 2019 , Progressive’s share ownership interest in ARX was 87.1% . Since these securities are redeemable upon the occurrence of an event that is not solely within the control of Progressive, we have recorded the redeemable noncontrolling interest (NCI) as mezzanine equity on our consolidated balance sheets, which represents the minority shares at the current estimated purchase price pursuant to the put and call provisions of the stockholders’ agreement. The estimated purchase price is based, in part, on the change in tangible net book value of ARX from December 31, 2014, to the balance sheet dates. In addition to these minority shares, at September 30, 2019 , ARX employees held options to purchase 10,438 ARX shares. These options and any shares issued upon exercise are subject to the stockholders’ agreement, including the “put ” and “call ” rights described above. Until the options are exercised, the underlying obligation of approximately $15.8 million is not recorded as part of redeemable NCI. See Note 9 – Employee Benefit Plans in our 2018 Annual Report to Shareholders for a discussion of ARX employee stock options. The changes in the components of redeemable NCI were: Nine Months Ended September 30, Year Ended (millions) 2019 2018 December 31, 2018 Balance, Beginning of period $ 214.5 $ 503.7 $ 503.7 Net income attributable to NCI 5.9 10.6 5.7 Other comprehensive income (loss) attributable to NCI 1 5.8 (5.0 ) (3.3 ) Exercise of employee stock options 7.7 9.4 9.4 Purchase/change of ARX minority shares (11.2 ) (298.2 ) (298.2 ) Change in redemption value of NCI 0.2 (3.1 ) (2.8 ) Balance, End of period $ 222.9 $ 217.4 $ 214.5 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.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill During the nine months ended September 30, 2019 , there were no changes to the carrying amount of goodwill. No accumulated goodwill impairment losses exist. Intangible Assets The following table is a summary of the net carrying amount of other intangible assets: (millions) September 30, 2019 September 30, 2018 December 31, 2018 Intangible assets subject to amortization $ 230.5 $ 300.2 $ 282.2 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 242.9 $ 312.6 $ 294.6 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for all periods presented. Intangible assets subject to amortization consisted of the following: (millions) September 30, 2019 September 30, 2018 December 31, 2018 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 $ 164.7 $ 91.5 $ 256.2 $ 128.1 $ 128.1 $ 256.2 $ 137.3 $ 118.9 Agency relationships 159.2 51.2 108.0 159.2 39.8 119.4 159.2 42.6 116.6 Software rights 79.1 48.1 31.0 79.1 37.4 41.7 79.1 40.1 39.0 Trade name 34.8 34.8 0 34.8 23.8 11.0 34.8 27.1 7.7 Total $ 529.3 $ 298.8 $ 230.5 $ 529.3 $ 229.1 $ 300.2 $ 529.3 $ 247.1 $ 282.2 Amortization expense was $15.8 million and $51.7 million for the three and nine months ended September 30, 2019 , respectively, compared to $18.0 million and $54.0 million during the same periods last year. As of September 30, 2019 , the average life of the remaining intangible assets was 4.0 years

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	Leases — Included in our consolidated balance sheet for the period ended September 30, 2019 , are certain noncancelable operating leases for office space, computer equipment, and vehicles, all with expected terms greater than one year, that are reported as a component of “other assets” and “accounts payable, accrued expenses, and other liabilities.” The leased assets represent our right to use an underlying asset for the lease term and the lease liabilities represent our obligation to make lease payments arising from the lease. We use an incremental borrowing rate to calculate the present value of the remaining lease payments. At September 30, 2019 , we had operating lease assets of $190.5 million and operating lease liabilities of $204.1 million . At September 30, 2019 , the following table shows our operating lease liabilities, on an undiscounted basis for the periods indicated, along with key inputs used to discount our lease liabilities, in accordance with the new accounting standard adopted on January 1, 2019 (see Note 15 – New Accounting Standards for further discussion): ($ in millions) 2019 (excluding the nine months ended September 30, 2019) $ 21.1 2020 78.1 2021 62.4 2022 29.1 2023 14.3 Thereafter 9.0 Total 214.0 Interest (9.9 ) Present value of lease liabilities $ 204.1 Weighted-average remaining term 3.2 years Weighted-average discount rate 3.3 % We had certain noncancelable operating lease commitments with lease terms greater than one year for property and computer equipment. The minimum commitments under these agreements at December 31, 2018, were as follows: (millions) Commitments 2019 $ 64.1 2020 65.5 2021 52.8 2022 24.3 2023 8.5 Thereafter 3.8 Total $ 219.0 We review each contract at inception to determine if it contains a lease and whether the lease qualifies as an operating or financing lease. Operating leases are expensed on a straight-line basis over the term of the lease. For the nine months ended September 30, 2019 , we incurred operating lease costs of $78.3 million . In determining the lease term, we consider the probability of exercising renewal options. We elected to account for leases with both lease and non-lease components as a single lease component and to apply a portfolio approach to account for our vehicle leases.

New Accounting Standards

New Accounting Standards	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
New Accounting Standards	New Accounting Standards Issued In August 2018, the Financial Accounting Standards Board (FASB) issued an Accounting Standards Update (ASU), which provides additional guidance on the requirements for capitalizing and amortizing implementation costs incurred in a cloud computing arrangement that does not include a software license. This ASU will be effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2019 (2020 for calendar-year companies). We do not expect this standard to have a material impact on our financial condition, cash flows, or results of operations. In August 2018, the FASB issued an 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. The ASU is effective for fiscal years beginning after December 15, 2019 (2020 for calendar-year companies), and should be applied prospectively for the additions to the disclosure requirements and applied retrospectively to all periods presented for all other amendments. As permitted by the ASU, we elected to partially early adopt the removal of current disclosure requirements and will adopt the new disclosure requirements as of the effective date. We do not expect this standard to have an impact on our financial condition, cash flows, or results of operations. In January 2017, the FASB issued an ASU, which eliminates the requirement to determine the implied fair value of goodwill in measuring an impairment loss. Upon adoption, the measurement of a goodwill impairment will represent the excess of the reporting unit’s carrying value over fair value, limited to the carrying value of goodwill. This ASU is effective for goodwill impairment tests in fiscal years beginning after December 15, 2019 (2020 for calendar-year companies), with early adoption permitted. We do not expect this standard to have a material impact on our financial position or results of operations. In June 2016, the FASB issued an ASU intended to improve the timing, and enhance the accounting and disclosure, of credit losses on financial assets. This update will modify the existing accounting guidance related to the impairment evaluation for available-for-sale debt securities and will result in the creation of an allowance for credit losses as a contra asset account. The ASU will require cumulative-effect changes to retained earnings in the period of adoption, if any occur, and will also require prospective changes on previously recorded impairments. This ASU is effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2019 (2020 for calendar-year companies), with early adoption permissible (including interim periods within that fiscal year) beginning after December 15, 2018 (2019 for calendar-year companies). While the ASU creates additional accounting complexities related to the recognition of the impairment losses, and subsequent recoveries, through an allowance for credit losses account, we currently do not expect the ASU to have a material impact on our current method of evaluating securities, premiums receivables, or reinsurance recoverables for credit losses or the timing or recognition of the amounts of impairment losses. Adopted On January 1, 2019, we adopted the ASU that requires lessees to report their operating leases as both an asset and liability on the statement of financial position and to disclose key information about leasing arrangements in the financial statement footnotes. We are reporting our operating leased assets and liabilities as a component of “other assets” and “accounts payable, accrued expenses, and other liabilities,” respectively. We did not restate prior year information. Upon adoption of the ASU, based on our lease portfolio on January 1, 2019, and after applying the practical expedient under which we were not required to reassess any of our existing contracts, classification of our leases, or the initial direct costs for existing leases, we recorded a transition adjustment of $213.0 million for leased assets and $217.6 million for liabilities. The adoption of this ASU had no impact on our results of operations or cash flows. See Note 14 – Leases for further information. On January 1, 2019, we adopted the ASU related to premium amortization on purchased callable debt securities. Under the ASU, the premium is required to be amortized to the earliest call date, which more closely aligns interest income recorded on bonds held at a premium with the economics of the underlying instrument. We applied the ASU on a modified retrospective basis, as required under the standard. Since we have historically used a yield-to-worst scenario for our securities that were purchased at a premium, and the first call on a premium security most often produces the lowest and most conservative yield, the adoption of this standard did not have an impact on our financial condition, cash flows, or results of operations.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2019
Investments Schedule [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. ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value September 30, 2019 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 13,387.6 $ 300.3 $ (9.2 ) $ 0 $ 13,678.7 35.4 % State and local government obligations 1,652.2 32.6 (1.1 ) 0 1,683.7 4.4 Corporate debt securities 7,048.9 231.6 (0.4 ) 1.0 7,281.1 18.9 Residential mortgage-backed securities 677.5 5.5 (1.5 ) 0 681.5 1.8 Commercial mortgage-backed securities 4,547.9 93.0 (1.9 ) 0 4,639.0 12.0 Other asset-backed securities 4,601.0 21.5 (0.6 ) 0 4,621.9 12.0 Redeemable preferred stocks 219.8 4.4 (2.5 ) 5.1 226.8 0.6 Total fixed maturities 32,134.9 688.9 (17.2 ) 6.1 32,812.7 85.1 Short-term investments 1,467.4 0 0 0 1,467.4 3.8 Total available-for-sale securities 33,602.3 688.9 (17.2 ) 6.1 34,280.1 88.9 Equity securities: Nonredeemable preferred stocks 1,054.2 0 0 74.3 1,128.5 2.9 Common equities 1,210.3 0 0 1,954.8 3,165.1 8.2 Total equity securities 2,264.5 0 0 2,029.1 4,293.6 11.1 Total portfolio 1,2 $ 35,866.8 $ 688.9 $ (17.2 ) $ 2,035.2 $ 38,573.7 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value September 30, 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,942.0 $ 0 $ (189.5 ) $ 0 $ 9,752.5 30.2 % State and local government obligations 1,610.1 1.9 (23.2 ) 0 1,588.8 4.9 Corporate debt securities 7,229.1 4.9 (85.2 ) (2.0 ) 7,146.8 22.1 Residential mortgage-backed securities 767.8 7.6 (5.6 ) 0 769.8 2.4 Commercial mortgage-backed securities 2,986.5 3.3 (30.5 ) 0 2,959.3 9.1 Other asset-backed securities 3,205.0 1.4 (13.6 ) 0.1 3,192.9 9.9 Redeemable preferred stocks 222.9 13.2 (1.4 ) (2.1 ) 232.6 0.7 Total fixed maturities 25,963.4 32.3 (349.0 ) (4.0 ) 25,642.7 79.3 Short-term investments 2,809.7 0 0 0 2,809.7 8.7 Total available-for-sale securities 28,773.1 32.3 (349.0 ) (4.0 ) 28,452.4 88.0 Equity securities: Nonredeemable preferred stocks 758.9 0 0 82.0 840.9 2.6 Common equities 1,135.0 0 0 1,922.3 3,057.3 9.4 Total equity securities 1,893.9 0 0 2,004.3 3,898.2 12.0 Total portfolio 1,2 $ 30,667.0 $ 32.3 $ (349.0 ) $ 2,000.3 $ 32,350.6 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) Fair Value % of Value December 31, 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 9,897.4 $ 71.2 $ (52.1 ) $ 0 $ 9,916.5 29.5 % State and local government obligations 1,654.6 7.3 (12.8 ) 0 1,649.1 4.9 Corporate debt securities 8,808.5 13.6 (125.3 ) (2.5 ) 8,694.3 25.9 Residential mortgage-backed securities 733.5 6.0 (5.1 ) 0 734.4 2.2 Commercial mortgage-backed securities 3,332.8 7.8 (39.0 ) 0 3,301.6 9.8 Other asset-backed securities 3,585.4 3.6 (11.8 ) 0.1 3,577.3 10.7 Redeemable preferred stocks 243.7 5.9 (3.5 ) (7.8 ) 238.3 0.7 Total fixed maturities 28,255.9 115.4 (249.6 ) (10.2 ) 28,111.5 83.7 Short-term investments 1,795.9 0 0 0 1,795.9 5.4 Total available-for-sale securities 30,051.8 115.4 (249.6 ) (10.2 ) 29,907.4 89.1 Equity securities: Nonredeemable preferred stocks 1,002.6 0 0 31.3 1,033.9 3.1 Common equities 1,148.9 0 0 1,477.2 2,626.1 7.8 Total equity securities 2,151.5 0 0 1,508.5 3,660.0 10.9 Total portfolio 1,2 $ 32,203.3 $ 115.4 $ (249.6 ) $ 1,498.3 $ 33,567.4 100.0 % 1 Our portfolio reflects the effect of unsettled security transactions; at September 30, 2019 , we had $286.5 million included in “other liabilities,” compared to $5.2 million and $5.9 million at September 30, 2018 and December 31, 2018 , respectively. 2 The total fair value of the portfolio at September 30, 2019 and 2018 , and December 31, 2018 , included $1.5 billion , $1.8 billion , and $2.9 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
Hybrid Instruments Table	Included in our fixed-maturity securities are hybrid securities, which are reported at fair value: September 30, (millions) 2019 2018 December 31, 2018 Fixed maturities: State and local government obligations $ 3.5 $ 3.6 $ 3.6 Corporate debt securities 91.3 159.7 158.9 Other asset-backed securities 3.0 5.0 4.5 Redeemable preferred stocks 90.7 72.0 77.7 Total hybrid securities $ 188.5 $ 240.3 $ 244.7
Investments Classified by Contractual Maturity Date	The composition of fixed maturities by maturity at September 30, 2019 , was: (millions) Cost Fair Value Less than one year $ 5,620.9 $ 5,633.4 One to five years 18,862.6 19,203.2 Five to ten years 7,582.3 7,904.9 Ten years or greater 69.1 71.2 Total $ 32,134.9 $ 32,812.7
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 September 30, 2019 Fixed maturities: U.S. government obligations 14 $ 2,708.0 $ (9.2 ) 7 $ 2,534.4 $ (8.9 ) 7 $ 173.6 $ (0.3 ) State and local government obligations 60 228.3 (1.1 ) 25 100.4 (0.7 ) 35 127.9 (0.4 ) Corporate debt securities 24 245.5 (0.4 ) 5 77.2 (0.1 ) 19 168.3 (0.3 ) Residential mortgage-backed securities 39 301.0 (1.5 ) 5 138.7 (0.1 ) 34 162.3 (1.4 ) Commercial mortgage-backed securities 48 743.3 (1.9 ) 26 361.9 (0.8 ) 22 381.4 (1.1 ) Other asset-backed securities 55 529.4 (0.6 ) 20 359.1 (0.2 ) 35 170.3 (0.4 ) Redeemable preferred stocks 3 57.2 (2.5 ) 2 45.9 (1.3 ) 1 11.3 (1.2 ) Total fixed maturities 243 $ 4,812.7 $ (17.2 ) 90 $ 3,617.6 $ (12.1 ) 153 $ 1,195.1 $ (5.1 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses September 30, 2018 Fixed maturities: U.S. government obligations 91 $ 9,752.5 $ (189.5 ) 39 $ 5,025.0 $ (67.2 ) 52 $ 4,727.5 $ (122.3 ) State and local government obligations 459 1,394.3 (23.2 ) 227 680.5 (6.4 ) 232 713.8 (16.8 ) Corporate debt securities 369 5,959.2 (85.2 ) 221 3,963.9 (45.3 ) 148 1,995.3 (39.9 ) Residential mortgage-backed securities 234 521.7 (5.6 ) 44 325.0 (0.6 ) 190 196.7 (5.0 ) Commercial mortgage-backed securities 151 2,392.7 (30.5 ) 80 1,164.2 (8.3 ) 71 1,228.5 (22.2 ) Other asset-backed securities 219 2,828.6 (13.6 ) 111 1,821.8 (4.0 ) 108 1,006.8 (9.6 ) Redeemable preferred stocks 3 30.8 (1.4 ) 1 4.7 (0.1 ) 2 26.1 (1.3 ) Total fixed maturities 1,526 $ 22,879.8 $ (349.0 ) 723 $ 12,985.1 $ (131.9 ) 803 $ 9,894.7 $ (217.1 ) 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, 2018 Fixed maturities: U.S. government obligations 51 $ 4,438.0 $ (52.1 ) 2 $ 126.6 $ (0.1 ) 49 $ 4,311.4 $ (52.0 ) State and local government obligations 299 972.4 (12.8 ) 49 192.7 (0.3 ) 250 779.7 (12.5 ) Corporate debt securities 368 6,723.3 (125.3 ) 133 2,613.3 (33.4 ) 235 4,110.0 (91.9 ) Residential mortgage-backed securities 228 450.2 (5.1 ) 32 248.8 (0.8 ) 196 201.4 (4.3 ) Commercial mortgage-backed securities 140 2,328.5 (39.0 ) 48 741.2 (8.9 ) 92 1,587.3 (30.1 ) Other asset-backed securities 203 2,691.3 (11.8 ) 84 1,551.7 (3.2 ) 119 1,139.6 (8.6 ) Redeemable preferred stocks 3 48.5 (3.5 ) 1 18.9 (0.6 ) 2 29.6 (2.9 ) Total fixed maturities 1,292 $ 17,652.2 $ (249.6 ) 349 $ 5,493.2 $ (47.3 ) 943 $ 12,159.0 $ (202.3 )
Non Credit Portion Of Other Than Temporary Impairment Recorded In Accumulated Other Comprehensive Income Table	The following table shows the total non-credit portion of the OTTI recorded in accumulated other comprehensive income, reflecting the original non-credit loss at the time the credit impairment was determined (i.e., unadjusted for valuation changes subsequent to the original write-down): September 30, December 31, (millions) 2019 2018 Fixed maturities: Residential mortgage-backed securities $ (19.7 ) $ (19.7 ) $ (19.7 ) Commercial mortgage-backed securities (0.1 ) (0.1 ) (0.1 ) Total fixed maturities $ (19.8 ) $ (19.8 ) $ (19.8 )
Other than Temporary Impairment, Credit Losses Recognized in Earnings	The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended September 30, 2019 and 2018 , for which a portion of the OTTI losses were also recognized in accumulated other comprehensive income at the time the credit impairments were determined and recognized: Three Months Ended September 30, 2019 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2019 $ 0 $ 0.5 $ 0.5 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Balance at September 30, 2019 $ 0 $ 0.5 $ 0.5 Three Months Ended September 30, 2018 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2018 $ 0.3 $ 0.5 $ 0.8 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Balance at September 30, 2018 $ 0.3 $ 0.5 $ 0.8 Nine Months Ended September 30, 2019 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2018 $ 0 $ 0.5 $ 0.5 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Balance at September 30, 2019 $ 0 $ 0.5 $ 0.5 Nine Months Ended September 30, 2018 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2017 $ 0 $ 0.5 $ 0.5 Change in recoveries of future cash flows expected to be collected 1 0.3 0 0.3 Balance at September 30, 2018 $ 0.3 $ 0.5 $ 0.8 1 Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security.
Realized Gain (Loss) on Investments	The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2019 2018 2019 2018 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 41.5 $ 0.1 $ 113.0 $ 1.8 State and local government obligations 1.8 0.2 4.0 9.4 Corporate and other debt securities 21.3 1.7 68.5 2.1 Residential mortgage-backed securities 0 0 0.2 0 Commercial mortgage-backed securities 2.6 0 6.2 2.0 Other asset-backed securities 0.1 0 0.8 0.1 Redeemable preferred stocks 0 0.2 0 4.5 Total available-for-sale securities 67.3 2.2 192.7 19.9 Equity securities: Nonredeemable preferred stocks 3.6 0.1 20.2 3.7 Common equities 4.7 126.8 9.4 265.2 Total equity securities 8.3 126.9 29.6 268.9 Subtotal gross realized gains on security sales 75.6 129.1 222.3 288.8 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (1.5 ) (7.6 ) (13.9 ) (46.4 ) State and local government obligations 0 (0.6 ) (0.7 ) (2.5 ) Corporate and other debt securities (0.2 ) (3.2 ) (7.7 ) (7.3 ) Residential mortgage-backed securities 0 0 (2.3 ) 0 Commercial mortgage-backed securities 0 0 (2.1 ) (6.3 ) Other asset-backed securities 0 (0.1 ) (0.1 ) (1.1 ) Redeemable preferred stocks (0.2 ) 0 (0.3 ) 0 Total available-for-sale securities (1.9 ) (11.5 ) (27.1 ) (63.6 ) Equity securities: Nonredeemable preferred stocks (2.0 ) 0 (2.0 ) (2.3 ) Common equities 0 (9.2 ) (7.9 ) (17.1 ) Total equity securities (2.0 ) (9.2 ) (9.9 ) (19.4 ) Subtotal gross realized losses on security sales (3.9 ) (20.7 ) (37.0 ) (83.0 ) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations 40.0 (7.5 ) 99.1 (44.6 ) State and local government obligations 1.8 (0.4 ) 3.3 6.9 Corporate and other debt securities 21.1 (1.5 ) 60.8 (5.2 ) Residential mortgage-backed securities 0 0 (2.1 ) 0 Commercial mortgage-backed securities 2.6 0 4.1 (4.3 ) Other asset-backed securities 0.1 (0.1 ) 0.7 (1.0 ) Redeemable preferred stocks (0.2 ) 0.2 (0.3 ) 4.5 Total available-for-sale securities 65.4 (9.3 ) 165.6 (43.7 ) Equity securities: Nonredeemable preferred stocks 1.6 0.1 18.2 1.4 Common equities 4.7 117.6 1.5 248.1 Total equity securities 6.3 117.7 19.7 249.5 Subtotal net realized gains (losses) on security sales 71.7 108.4 185.3 205.8 Net holding period gains (losses) Hybrid securities 4.2 1.3 16.3 (4.2 ) Equity securities 27.6 94.5 520.6 (1.7 ) Subtotal net holding period gains (losses) 31.8 95.8 536.9 (5.9 ) Other-than-temporary impairment losses Other asset impairment (38.1 ) (22.1 ) (62.4 ) (33.2 ) Subtotal other-than-temporary impairment losses (38.1 ) (22.1 ) (62.4 ) (33.2 ) Total net realized gains (losses) on securities $ 65.4 $ 182.1 $ 659.8 $ 166.7
Components of Equity Realized Gains (Losses)	The following table reflects our holding period realized gains (losses) on equity securities recognized for the three and nine months ended September 30, 2019 and 2018 , for equity securities held at quarter end: Three Months Nine Months (millions) 2019 2018 2019 2018 Total net gains (losses) recognized during the period on equity securities $ 33.9 $ 212.2 $ 540.3 $ 247.8 Less: Net gains (losses) recognized on equity securities sold during the period 6.3 117.7 19.7 249.5 Net holding period gains (losses) recognized during the period on equity securities held at period end $ 27.6 $ 94.5 $ 520.6 $ (1.7 )
Components of Net Investment Income	The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2019 2018 2019 2018 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 75.8 $ 47.7 $ 198.7 $ 133.4 State and local government obligations 8.7 9.0 26.9 28.1 Corporate debt securities 65.1 62.1 209.8 150.1 Residential mortgage-backed securities 5.4 6.9 16.6 20.4 Commercial mortgage-backed securities 35.6 24.1 100.7 65.5 Other asset-backed securities 31.4 21.2 85.5 50.9 Redeemable preferred stocks 3.9 3.3 16.1 8.8 Total fixed maturities 225.9 174.3 654.3 457.2 Short-term investments 7.1 15.7 34.3 40.7 Total available-for-sale securities 233.0 190.0 688.6 497.9 Equity securities: Nonredeemable preferred stocks 15.9 11.2 47.3 32.5 Common equities 14.1 16.9 41.3 46.1 Total equity securities 30.0 28.1 88.6 78.6 Investment income 263.0 218.1 777.2 576.5 Investment expenses (5.9 ) (5.8 ) (18.3 ) (18.0 ) Net investment income $ 257.1 $ 212.3 $ 758.9 $ 558.5

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Composition of Investment Portfolio by Major Security Type	The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2019 Fixed maturities: U.S. government obligations $ 13,678.7 $ 0 $ 0 $ 13,678.7 $ 13,387.6 State and local government obligations 0 1,683.7 0 1,683.7 1,652.2 Corporate debt securities 0 7,281.1 0 7,281.1 7,048.9 Subtotal 13,678.7 8,964.8 0 22,643.5 22,088.7 Asset-backed securities: Residential mortgage-backed 0 681.5 0 681.5 677.5 Commercial mortgage-backed 0 4,639.0 0 4,639.0 4,547.9 Other asset-backed 0 4,621.9 0 4,621.9 4,601.0 Subtotal asset-backed securities 0 9,942.4 0 9,942.4 9,826.4 Redeemable preferred stocks: Financials 0 51.7 0 51.7 51.7 Utilities 0 10.9 0 10.9 10.0 Industrials 11.2 153.0 0 164.2 158.1 Subtotal redeemable preferred stocks 11.2 215.6 0 226.8 219.8 Total fixed maturities 13,689.9 19,122.8 0 32,812.7 32,134.9 Short-term investments 1,464.9 2.5 0 1,467.4 1,467.4 Total available-for-sale securities 15,154.8 19,125.3 0 34,280.1 33,602.3 Equity securities: Nonredeemable preferred stocks: Financials 82.2 967.1 27.1 1,076.4 1,004.3 Utilities 0 42.1 0 42.1 39.9 Industrials 0 5.0 5.0 10.0 10.0 Subtotal nonredeemable preferred stocks 82.2 1,014.2 32.1 1,128.5 1,054.2 Common equities: Common stocks 3,164.8 0 0 3,164.8 1,210.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,164.8 0 0.3 3,165.1 1,210.3 Total equity securities 3,247.0 1,014.2 32.4 4,293.6 2,264.5 Total portfolio $ 18,401.8 $ 20,139.5 $ 32.4 $ 38,573.7 $ 35,866.8 Debt $ 0 $ 5,113.3 $ 0 $ 5,113.3 $ 4,406.5 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2018 Fixed maturities: U.S. government obligations $ 9,752.5 $ 0 $ 0 $ 9,752.5 $ 9,942.0 State and local government obligations 0 1,588.8 0 1,588.8 1,610.1 Corporate debt securities 0 7,146.8 0 7,146.8 7,229.1 Subtotal 9,752.5 8,735.6 0 18,488.1 18,781.2 Asset-backed securities: Residential mortgage-backed 0 769.8 0 769.8 767.8 Commercial mortgage-backed 0 2,959.3 0 2,959.3 2,986.5 Other asset-backed 0 3,192.9 0 3,192.9 3,205.0 Subtotal asset-backed securities 0 6,922.0 0 6,922.0 6,959.3 Redeemable preferred stocks: Financials 0 67.8 0 67.8 65.2 Utilities 0 4.7 0 4.7 4.8 Industrials 10.1 150.0 0 160.1 152.9 Subtotal redeemable preferred stocks 10.1 222.5 0 232.6 222.9 Total fixed maturities 9,762.6 15,880.1 0 25,642.7 25,963.4 Short-term investments 2,573.4 236.3 0 2,809.7 2,809.7 Total available-for-sale securities 12,336.0 16,116.4 0 28,452.4 28,773.1 Equity securities: Nonredeemable preferred stocks: Financials 76.3 724.0 0 800.3 718.9 Utilities 0 35.6 0 35.6 35.0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 76.3 759.6 5.0 840.9 758.9 Common equities: Common stocks 3,057.0 0 0 3,057.0 1,134.7 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,057.0 0 0.3 3,057.3 1,135.0 Total equity securities 3,133.3 759.6 5.3 3,898.2 1,893.9 Total portfolio $ 15,469.3 $ 16,876.0 $ 5.3 $ 32,350.6 $ 30,667.0 Debt $ 0 $ 3,926.9 $ 0 $ 3,926.9 $ 3,859.9 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2018 Fixed maturities: U.S. government obligations $ 9,916.5 $ 0 $ 0 $ 9,916.5 $ 9,897.4 State and local government obligations 0 1,649.1 0 1,649.1 1,654.6 Corporate debt securities 0 8,694.3 0 8,694.3 8,808.5 Subtotal 9,916.5 10,343.4 0 20,259.9 20,360.5 Asset-backed securities: Residential mortgage-backed 0 734.4 0 734.4 733.5 Commercial mortgage-backed 0 3,301.6 0 3,301.6 3,332.8 Other asset-backed 0 3,577.3 0 3,577.3 3,585.4 Subtotal asset-backed securities 0 7,613.3 0 7,613.3 7,651.7 Redeemable preferred stocks: Financials 0 78.2 0 78.2 79.3 Utilities 0 0 0 0 0 Industrials 9.5 150.6 0 160.1 164.4 Subtotal redeemable preferred stocks 9.5 228.8 0 238.3 243.7 Total fixed maturities 9,926.0 18,185.5 0 28,111.5 28,255.9 Short-term investments 1,722.1 73.8 0 1,795.9 1,795.9 Total available-for-sale securities 11,648.1 18,259.3 0 29,907.4 30,051.8 Equity securities: Nonredeemable preferred stocks: Financials 71.9 887.1 25.1 984.1 951.6 Utilities 0 44.8 0 44.8 46.0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 71.9 931.9 30.1 1,033.9 1,002.6 Common equities: Common stocks 2,625.8 0 0 2,625.8 1,148.6 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,625.8 0 0.3 2,626.1 1,148.9 Total equity securities 2,697.7 931.9 30.4 3,660.0 2,151.5 Total portfolio $ 14,345.8 $ 19,191.2 $ 30.4 $ 33,567.4 $ 32,203.3 Debt $ 0 $ 4,532.3 $ 0 $ 4,532.3 $ 4,404.9
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	The following tables provide a summary of changes in fair value associated with Level 3 assets for the three and nine months ended September 30, 2019 and 2018 : Level 3 Fair Value (millions) Fair Value at June 30, 2019 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 27.1 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 32.4 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 32.4 Level 3 Fair Value (millions) Fair Value at June 30, 2018 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2018 Equity securities: Nonredeemable preferred stocks: Financials $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 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 $ 5.3 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 5.3 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 September 30, 2019 Equity securities: Nonredeemable preferred stocks: Financials $ 25.1 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 27.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 30.4 $ 0 $ 2.0 $ 0 $ 0 $ 0 $ 0 $ 32.4
Fair Value Measurement Inputs and Valuation Techniques	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2019 and 2018 , and December 31, 2018 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2019 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 27.1 internal price unadjusted purchase price per share 9.0 Industrials 2 5.0 internal price price-to-sales ratio 5.5 Subtotal Level 3 securities 32.1 Pricing exemption securities 3 0.3 Total Level 3 securities $ 32.4 1 The security was internally priced since it is a private equity. The security was initially purchased during December 2018 and additional shares were purchased during second quarter 2019. The value at September 30, 2019 reflects the unadjusted purchase price per share (all purchases were at the same price). 2 The security was internally priced since it is a private equity. The price at September 30, 2019 , was calculated using a price-to-sales ratio. 3 The unobservable input is not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2018 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials $ 0 NA NA NA Industrials 1 5.0 internal price unadjusted purchase price per share 3.9 Subtotal Level 3 securities 5.0 Pricing exemption securities 2 0.3 Total Level 3 securities $ 5.3 NA= Not applicable 1 The security was internally priced since it is a private equity. The value at September 30, 2018 reflects the unadjusted purchase price per share. 2 The unobservable input is not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at December 31, 2018 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 2 5.0 internal price price-to-sales ratio 5.5 Subtotal Level 3 securities 30.1 Pricing exemption securities 3 0.3 Total Level 3 securities $ 30.4 1 The security was internally priced since it is a private equity. The security was purchased during December 2018 and the value at December 31, 2018 reflects the unadjusted purchase price per share. 2 The security was internally priced since it is a private equity. The price at December 31, 2018, was calculated using a price-to-sales ratio. 3 The unobservable input is not reasonably available to us.

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Debt Table	Debt at each of the balance sheet periods consisted of: September 30, 2019 September 30, 2018 December 31, 2018 (millions) Carrying Value Fair Value Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 $ 499.3 $ 516.5 $ 499.0 $ 503.9 $ 499.1 $ 506.5 2.45% Senior Notes due 2027 496.8 502.1 496.4 453.3 496.5 455.5 6 5/8% Senior Notes due 2029 296.5 392.2 296.3 360.3 296.4 368.5 4.00% Senior Notes due 2029 544.9 617.0 0 0 544.5 562.4 6.25% Senior Notes due 2032 395.7 547.2 395.4 481.8 395.5 496.6 4.35% Senior Notes due 2044 346.6 414.7 346.6 349.7 346.6 350.2 3.70% Senior Notes due 2045 395.4 431.8 395.3 359.1 395.3 366.7 4.125% Senior Notes due 2047 841.5 987.4 841.3 828.4 841.4 831.9 4.20% Senior Notes due 2048 589.8 704.4 589.6 590.4 589.6 594.0 Total $ 4,406.5 $ 5,113.3 $ 3,859.9 $ 3,926.9 $ 4,404.9 $ 4,532.3

Loss and Loss Adjustment Expe_2

Loss and Loss Adjustment Expense Reserves (Tables)	9 Months Ended
	Sep. 30, 2019
Loss and Loss Adjustment Expenses Reserves [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	Activity in the loss and loss adjustment expense reserves is summarized as follows: September 30, (millions) 2019 2018 Balance, Beginning of period $ 15,400.8 $ 13,086.9 Less reinsurance recoverables on unpaid losses 2,572.7 2,170.1 Net balance, Beginning of period 12,828.1 10,916.8 Incurred related to: Current year 18,108.2 15,722.2 Prior years 215.2 47.0 Total incurred 18,323.4 15,769.2 Paid related to: Current year 10,864.9 9,409.7 Prior years 6,061.7 5,031.9 Total paid 16,926.6 14,441.6 Net balance, End of period 14,224.9 12,244.4 Plus reinsurance recoverables on unpaid losses 3,145.1 2,376.4 Balance, End of period $ 17,370.0 $ 14,620.8

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2019
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Table	We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2019 2018 Income taxes $ 738.7 $ 535.8 Interest 147.3 116.4 Operating lease liabilities 61.2 NA

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Reconciliation of Revenue and operating Income from Segments to Consolidated	Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 3,703.4 $ 380.2 $ 3,318.2 $ 372.2 $ 10,851.5 $ 1,267.9 $ 9,607.7 $ 1,142.2 Direct 3,804.0 291.7 3,337.2 294.4 11,113.7 940.2 9,565.3 880.3 Total Personal Lines 1 7,507.4 671.9 6,655.4 666.6 21,965.2 2,208.1 19,173.0 2,022.5 Commercial Lines 1,106.9 69.7 939.6 112.7 3,190.4 360.7 2,632.5 307.8 Property 2 397.9 (9.1 ) 335.5 (7.8 ) 1,141.1 (35.8 ) 933.2 (31.2 ) Other indemnity 0 0 0 (0.1 ) 0 0 0 0.1 Total underwriting operations 9,012.2 732.5 7,930.5 771.4 26,296.7 2,533.0 22,738.7 2,299.2 Fees and other revenues 3 138.4 NA 122.6 NA 403.4 NA 342.4 NA Service businesses 51.5 2.8 42.5 6.7 144.1 12.0 119.6 17.5 Investments 4 328.4 322.5 400.2 394.4 1,437.0 1,418.7 743.2 725.2 Interest expense NA (47.5 ) NA (42.0 ) NA (142.3 ) NA (120.5 ) Consolidated total $ 9,530.5 $ 1,010.3 $ 8,495.8 $ 1,130.5 $ 28,281.2 $ 3,821.4 $ 23,943.9 $ 2,921.4 NA = Not applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned during the three and nine months ended September 30, 2019 and 2018 ; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 For the three and nine months ended September 30, 2019 , pretax profit (loss) includes $15.8 million and $51.7 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $18.0 million and $54.0 million for the same periods in 2018. 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. 3 Pretax profit (loss) for fees and other revenues is attributable to operating segments. 4 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expense.
Underwriting Margins and Combined Ratios for our Underwriting Operations	Following are the underwriting margins and combined ratios for our underwriting operations for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Under-writing Combined Ratio Under-writing Combined Ratio Under-writing Combined Ratio Under-writing Combined Ratio Personal Lines Agency 10.3 % 89.7 11.2 % 88.8 11.7 % 88.3 11.9 % 88.1 Direct 7.7 92.3 8.8 91.2 8.5 91.5 9.2 90.8 Total Personal Lines 9.0 91.0 10.0 90.0 10.1 89.9 10.5 89.5 Commercial Lines 6.3 93.7 12.0 88.0 11.3 88.7 11.7 88.3 Property 1 (2.3 ) 102.3 (2.3 ) 102.3 (3.1 ) 103.1 (3.3 ) 103.3 Total underwriting operations 8.1 91.9 9.7 90.3 9.6 90.4 10.1 89.9 1 Included in the three and nine months ended September 30, 2019 , is 4.0 points and 4.5 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 5.4 points and 5.8 points, respectively, for the three and nine months ended September 30, 2018 .

Dividends Dividends (Tables)

Dividends Dividends (Tables)	9 Months Ended
	Sep. 30, 2019
Dividends [Abstract]
Dividends	Following is a summary of our common and preferred share dividends that were declared and/or paid during the nine months ended September 30, 2019 and 2018: (millions, except per share amounts) Amount Dividend Type Declared Payable Per Share Accrued 1 Common - Quarterly August 2019 October 2019 $ 0.10 $ 58.5 Preferred - Semi-annual August 2019 September 2019 26.875 13.4 Common - Quarterly May 2019 July 2019 0.10 58.4 Preferred - Semi-annual February 2019 March 2019 26.875 13.4 Common - Quarterly February 2019 April 2019 0.10 58.4 Common - Annual Variable December 2018 February 2019 2.5140 1,467.9 Preferred - Semi-annual August 2018 September 2018 27.024 13.5 Common - Annual Variable December 2017 February 2018 1.1247 655.1 1

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2019
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 June 30, 2019 $ 573.6 $ (120.5 ) $ 453.1 $ 472.9 $ (16.8 ) $ (3.0 ) Other comprehensive income (loss) before reclassifications: Investment securities 134.3 (28.2 ) 106.1 106.1 0 0 Loss attributable to noncontrolling interest (NCI) (1.2 ) 0.3 (0.9 ) 0 0 (0.9 ) Total other comprehensive income (loss) before reclassifications 133.1 (27.9 ) 105.2 106.1 0 (0.9 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 60.7 (12.7 ) 48.0 48.0 0 0 Interest expense (0.3 ) 0.1 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income 60.4 (12.6 ) 47.8 48.0 (0.2 ) 0 Total other comprehensive income (loss) 72.7 (15.3 ) 57.4 58.1 0.2 (0.9 ) Balance at September 30, 2019 $ 646.3 $ (135.8 ) $ 510.5 $ 531.0 $ (16.6 ) $ (3.9 ) Components of Changes in 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 June 30, 2018 $ (280.8 ) $ 58.9 $ (221.9 ) $ (210.9 ) $ (17.6 ) $ 6.6 Reclassification of disproportionate amounts (4.3 ) 0.9 (3.4 ) 0 0 (3.4 ) Adjusted balance at June 30, 2018 (285.1 ) 59.8 (225.3 ) (210.9 ) (17.6 ) 3.2 Other comprehensive income (loss) before reclassifications: Investment securities (58.7 ) 12.3 (46.4 ) (46.4 ) 0 0 Loss attributable to noncontrolling interest (NCI) 0.6 (0.2 ) 0.4 0 0 0.4 Total other comprehensive income (loss) before reclassifications (58.1 ) 12.1 (46.0 ) (46.4 ) 0 0.4 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (9.3 ) 1.9 (7.4 ) (7.4 ) 0 0 Interest expense (0.2 ) 0 (0.2 ) 0 (0.2 ) 0 Total reclassification adjustment for amounts realized in net income (9.5 ) 1.9 (7.6 ) (7.4 ) (0.2 ) 0 Total other comprehensive income (loss) (48.6 ) 10.2 (38.4 ) (39.0 ) 0.2 0.4 Balance at September 30, 2018 $ (333.7 ) $ 70.0 $ (263.7 ) $ (249.9 ) $ (17.4 ) $ 3.6 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, 2018 $ (153.0 ) $ 32.1 $ (120.9 ) $ (105.6 ) $ (17.2 ) $ 1.9 Other comprehensive income (loss) before reclassifications: Investment securities 953.5 (200.2 ) 753.3 753.3 0 0 Loss attributable to noncontrolling interest (NCI) (7.4 ) 1.6 (5.8 ) 0 0 (5.8 ) Total other comprehensive income (loss) before reclassifications 946.1 (198.6 ) 747.5 753.3 0 (5.8 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities 147.6 (30.9 ) 116.7 116.7 0 0 Interest expense (0.8 ) 0.2 (0.6 ) 0 (0.6 ) 0 Total reclassification adjustment for amounts realized in net income 146.8 (30.7 ) 116.1 116.7 (0.6 ) 0 Total other comprehensive income (loss) 799.3 (167.9 ) 631.4 636.6 0.6 (5.8 ) Balance at September 30, 2019 $ 646.3 $ (135.8 ) $ 510.5 $ 531.0 $ (16.6 ) $ (3.9 ) 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, 2017 $ 1,977.8 $ (695.6 ) $ 1,282.2 $ 1,295.0 $ (14.8 ) $ 2.0 Cumulative effect adjustment (2,006.0 ) 705.8 (1,300.2 ) (1,300.2 ) 0 0 Reclassification of disproportionate amounts (4.3 ) (3.4 ) (7.7 ) (1.1 ) (3.2 ) (3.4 ) Adjusted balance at December 31, 2017 (32.5 ) 6.8 (25.7 ) (6.3 ) (18.0 ) (1.4 ) Other comprehensive income (loss) before reclassifications: Investment securities (352.5 ) 73.9 (278.6 ) (278.6 ) 0 0 Loss attributable to noncontrolling interest (NCI) 6.4 (1.4 ) 5.0 0 0 5.0 Total other comprehensive income (loss) before reclassifications (346.1 ) 72.5 (273.6 ) (278.6 ) 0 5.0 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net realized gains (losses) on securities (44.2 ) 9.2 (35.0 ) (35.0 ) 0 0 Interest expense (0.7 ) 0.1 (0.6 ) 0 (0.6 ) 0 Total reclassification adjustment for amounts realized in net income (44.9 ) 9.3 (35.6 ) (35.0 ) (0.6 ) 0 Total other comprehensive income (loss) (301.2 ) 63.2 (238.0 ) (243.6 ) 0.6 5.0 Balance at September 30, 2018 $ (333.7 ) $ 70.0 $ (263.7 ) $ (249.9 ) $ (17.4 ) $ 3.6

Redeemable Noncontrolling Int_2

Redeemable Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2019
Temporary Equity Disclosure [Abstract]
Redeemable Noncontrolling Interest	The changes in the components of redeemable NCI were: Nine Months Ended September 30, Year Ended (millions) 2019 2018 December 31, 2018 Balance, Beginning of period $ 214.5 $ 503.7 $ 503.7 Net income attributable to NCI 5.9 10.6 5.7 Other comprehensive income (loss) attributable to NCI 1 5.8 (5.0 ) (3.3 ) Exercise of employee stock options 7.7 9.4 9.4 Purchase/change of ARX minority shares (11.2 ) (298.2 ) (298.2 ) Change in redemption value of NCI 0.2 (3.1 ) (2.8 ) Balance, End of period $ 222.9 $ 217.4 $ 214.5 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.

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Net Carrying Amount of Other Intangible Assets	The following table is a summary of the net carrying amount of other intangible assets: (millions) September 30, 2019 September 30, 2018 December 31, 2018 Intangible assets subject to amortization $ 230.5 $ 300.2 $ 282.2 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 242.9 $ 312.6 $ 294.6 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) September 30, 2019 September 30, 2018 December 31, 2018 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 $ 164.7 $ 91.5 $ 256.2 $ 128.1 $ 128.1 $ 256.2 $ 137.3 $ 118.9 Agency relationships 159.2 51.2 108.0 159.2 39.8 119.4 159.2 42.6 116.6 Software rights 79.1 48.1 31.0 79.1 37.4 41.7 79.1 40.1 39.0 Trade name 34.8 34.8 0 34.8 23.8 11.0 34.8 27.1 7.7 Total $ 529.3 $ 298.8 $ 230.5 $ 529.3 $ 229.1 $ 300.2 $ 529.3 $ 247.1 $ 282.2

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Schedule Of Operating Lease Obligations	The minimum commitments under these agreements at December 31, 2018, were as follows: (millions) Commitments 2019 $ 64.1 2020 65.5 2021 52.8 2022 24.3 2023 8.5 Thereafter 3.8 Total $ 219.0
Lessee, Operating Lease, Liability, Maturity	At September 30, 2019 , the following table shows our operating lease liabilities, on an undiscounted basis for the periods indicated, along with key inputs used to discount our lease liabilities, in accordance with the new accounting standard adopted on January 1, 2019 (see Note 15 – New Accounting Standards for further discussion): ($ in millions) 2019 (excluding the nine months ended September 30, 2019) $ 21.1 2020 78.1 2021 62.4 2022 29.1 2023 14.3 Thereafter 9.0 Total 214.0 Interest (9.9 ) Present value of lease liabilities $ 204.1 Weighted-average remaining term 3.2 years Weighted-average discount rate 3.3 %

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation-Additional Information (Details) $ in Millions	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)shares	Sep. 30, 2018USD ($)
Business Acquisition [Line Items]
Assets Held-for-sale, Property, Plant and Equipment | $	$ 43.7	$ 39.3	$ 20.5
ARX Holding Corp.
Business Acquisition [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage	87.10%	86.80%	86.80%
Number of Shares Put Pursuant to Stockholders' Agreement | shares		204,527

Investments Investment Portfoli

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 33,602.3	$ 30,051.8	$ 28,773.1
Gross Unrealized Gains	688.9	115.4	32.3
Gross Unrealized Losses	(17.2)	(249.6)	(349)
Net Holding Period Gains (Losses)	6.1	(10.2)	(4)
Total available-for-sale securities	$ 34,280.1	$ 29,907.4	$ 28,452.4
% of Total Fair Value	88.90%	89.10%	88.00%
Equity securities, at Fair Value
Cost	$ 2,264.5	$ 2,151.5	$ 1,893.9
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	2,029.1	1,508.5	2,004.3
Fair Value	$ 4,293.6	$ 3,660	$ 3,898.2
% of Total Fair Value	11.10%	10.90%	12.00%
Debt and Equity Securities, at Fair Value
Cost	$ 35,866.8	$ 32,203.3	$ 30,667
Gross Unrealized Gains	688.9	115.4	32.3
Gross Unrealized Losses	(17.2)	(249.6)	(349)
Net Holding Period Gains (Losses)	2,035.2	1,498.3	2,000.3
Fair Value	$ 38,573.7	$ 33,567.4	$ 32,350.6
% of Total Fair Value	100.00%	100.00%	100.00%
Unsettled security transactions, payable	$ 286.5	$ 5.9	$ 5.2
Total fair value of non-insurance subsidiary portfolio	1,500	2,900	1,800
Nonredeemable preferred stocks
Equity securities, at Fair Value
Cost	1,054.2	1,002.6	758.9
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	74.3	31.3	82
Fair Value	$ 1,128.5	$ 1,033.9	$ 840.9
% of Total Fair Value	2.90%	3.10%	2.60%
Common equities
Equity securities, at Fair Value
Cost	$ 1,210.3	$ 1,148.9	$ 1,135
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Net Holding Period Gains (Losses)	1,954.8	1,477.2	1,922.3
Fair Value	$ 3,165.1	$ 2,626.1	$ 3,057.3
% of Total Fair Value	8.20%	7.80%	9.40%
Total fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 32,134.9	$ 28,255.9	$ 25,963.4
Gross Unrealized Gains	688.9	115.4	32.3
Gross Unrealized Losses	(17.2)	(249.6)	(349)
Net Holding Period Gains (Losses)	6.1	(10.2)	(4)
Total available-for-sale securities	$ 32,812.7	$ 28,111.5	$ 25,642.7
% of Total Fair Value	85.10%	83.70%	79.30%
Total fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 13,387.6	$ 9,897.4	$ 9,942
Gross Unrealized Gains	300.3	71.2	0
Gross Unrealized Losses	(9.2)	(52.1)	(189.5)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 13,678.7	$ 9,916.5	$ 9,752.5
% of Total Fair Value	35.40%	29.50%	30.20%
Total fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 1,652.2	$ 1,654.6	$ 1,610.1
Gross Unrealized Gains	32.6	7.3	1.9
Gross Unrealized Losses	(1.1)	(12.8)	(23.2)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 1,683.7	$ 1,649.1	$ 1,588.8
% of Total Fair Value	4.40%	4.90%	4.90%
Total fixed maturities | Corporate debt securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 7,048.9	$ 8,808.5	$ 7,229.1
Gross Unrealized Gains	231.6	13.6	4.9
Gross Unrealized Losses	(0.4)	(125.3)	(85.2)
Net Holding Period Gains (Losses)	1	(2.5)	(2)
Total available-for-sale securities	$ 7,281.1	$ 8,694.3	$ 7,146.8
% of Total Fair Value	18.90%	25.90%	22.10%
Total fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 677.5	$ 733.5	$ 767.8
Gross Unrealized Gains	5.5	6	7.6
Gross Unrealized Losses	(1.5)	(5.1)	(5.6)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 681.5	$ 734.4	$ 769.8
% of Total Fair Value	1.80%	2.20%	2.40%
Total fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,547.9	$ 3,332.8	$ 2,986.5
Gross Unrealized Gains	93	7.8	3.3
Gross Unrealized Losses	(1.9)	(39)	(30.5)
Net Holding Period Gains (Losses)	0	0	0
Total available-for-sale securities	$ 4,639	$ 3,301.6	$ 2,959.3
% of Total Fair Value	12.00%	9.80%	9.10%
Total fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 4,601	$ 3,585.4	$ 3,205
Gross Unrealized Gains	21.5	3.6	1.4
Gross Unrealized Losses	(0.6)	(11.8)	(13.6)
Net Holding Period Gains (Losses)	0	0.1	0.1
Total available-for-sale securities	$ 4,621.9	$ 3,577.3	$ 3,192.9
% of Total Fair Value	12.00%	10.70%	9.90%
Total fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 219.8	$ 243.7	$ 222.9
Gross Unrealized Gains	4.4	5.9	13.2
Gross Unrealized Losses	(2.5)	(3.5)	(1.4)
Net Holding Period Gains (Losses)	5.1	(7.8)	(2.1)
Total available-for-sale securities	$ 226.8	$ 238.3	$ 232.6
% of Total Fair Value	0.60%	0.70%	0.70%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 1,467.4	$ 1,795.9	$ 2,809.7
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	$ 1,467.4	$ 1,795.9	$ 2,809.7
% of Total Fair Value	3.80%	5.40%	8.70%

Investments Hybrid Securities (

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Hybrid Instruments [Line Items]
Hybrid securities	$ 188.5	$ 244.7	$ 240.3
State and local government obligations
Hybrid Instruments [Line Items]
Hybrid securities	3.5	3.6	3.6
Corporate debt securities
Hybrid Instruments [Line Items]
Hybrid securities	91.3	158.9	159.7
Other asset-backed securities
Hybrid Instruments [Line Items]
Hybrid securities	3	4.5	5
Redeemable preferred stocks
Hybrid Instruments [Line Items]
Hybrid securities	$ 90.7	$ 77.7	$ 72

Investments Composition of Fixe

Investments Composition of Fixed Maturities by Maturity (Detail) - Total fixed maturities $ in Millions	Sep. 30, 2019USD ($)
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Less than one year	$ 5,620.9
One to five years	18,862.6
Five to ten years	7,582.3
Ten years or greater	69.1
Cost	32,134.9
Fair Value
Less than one year	5,633.4
One to five years	19,203.2
Five to ten years	7,904.9
Ten years or greater	71.2
Fair Value	$ 32,812.7

Investments Gross Unrealized lo

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Sep. 30, 2019USD ($)security	Dec. 31, 2018USD ($)security	Sep. 30, 2018USD ($)security
Number of Securities
Total | security	243	1,292	1,526
Less than 12 Months | security	90	349	723
12 Months or Greater | security	153	943	803
Fair Value
Total	$ 4,812.7	$ 17,652.2	$ 22,879.8
Less than 12 Months	3,617.6	5,493.2	12,985.1
12 Months or Greater	1,195.1	12,159	9,894.7
Unrealized Losses
Total	(17.2)	(249.6)	(349)
Less than 12 Months	(12.1)	(47.3)	(131.9)
12 Months or Greater	$ (5.1)	$ (202.3)	$ (217.1)
U.S. government obligations
Number of Securities
Total | security	14	51	91
Less than 12 Months | security	7	2	39
12 Months or Greater | security	7	49	52
Fair Value
Total	$ 2,708	$ 4,438	$ 9,752.5
Less than 12 Months	2,534.4	126.6	5,025
12 Months or Greater	173.6	4,311.4	4,727.5
Unrealized Losses
Total	(9.2)	(52.1)	(189.5)
Less than 12 Months	(8.9)	(0.1)	(67.2)
12 Months or Greater	$ (0.3)	$ (52)	$ (122.3)
State and local government obligations
Number of Securities
Total | security	60	299	459
Less than 12 Months | security	25	49	227
12 Months or Greater | security	35	250	232
Fair Value
Total	$ 228.3	$ 972.4	$ 1,394.3
Less than 12 Months	100.4	192.7	680.5
12 Months or Greater	127.9	779.7	713.8
Unrealized Losses
Total	(1.1)	(12.8)	(23.2)
Less than 12 Months	(0.7)	(0.3)	(6.4)
12 Months or Greater	$ (0.4)	$ (12.5)	$ (16.8)
Corporate debt securities
Number of Securities
Total | security	24	368	369
Less than 12 Months | security	5	133	221
12 Months or Greater | security	19	235	148
Fair Value
Total	$ 245.5	$ 6,723.3	$ 5,959.2
Less than 12 Months	77.2	2,613.3	3,963.9
12 Months or Greater	168.3	4,110	1,995.3
Unrealized Losses
Total	(0.4)	(125.3)	(85.2)
Less than 12 Months	(0.1)	(33.4)	(45.3)
12 Months or Greater	$ (0.3)	$ (91.9)	$ (39.9)
Residential mortgage-backed securities
Number of Securities
Total | security	39	228	234
Less than 12 Months | security	5	32	44
12 Months or Greater | security	34	196	190
Fair Value
Total	$ 301	$ 450.2	$ 521.7
Less than 12 Months	138.7	248.8	325
12 Months or Greater	162.3	201.4	196.7
Unrealized Losses
Total	(1.5)	(5.1)	(5.6)
Less than 12 Months	(0.1)	(0.8)	(0.6)
12 Months or Greater	$ (1.4)	$ (4.3)	$ (5)
Commercial mortgage-backed securities
Number of Securities
Total | security	48	140	151
Less than 12 Months | security	26	48	80
12 Months or Greater | security	22	92	71
Fair Value
Total	$ 743.3	$ 2,328.5	$ 2,392.7
Less than 12 Months	361.9	741.2	1,164.2
12 Months or Greater	381.4	1,587.3	1,228.5
Unrealized Losses
Total	(1.9)	(39)	(30.5)
Less than 12 Months	(0.8)	(8.9)	(8.3)
12 Months or Greater	$ (1.1)	$ (30.1)	$ (22.2)
Other asset-backed securities
Number of Securities
Total | security	55	203	219
Less than 12 Months | security	20	84	111
12 Months or Greater | security	35	119	108
Fair Value
Total	$ 529.4	$ 2,691.3	$ 2,828.6
Less than 12 Months	359.1	1,551.7	1,821.8
12 Months or Greater	170.3	1,139.6	1,006.8
Unrealized Losses
Total	(0.6)	(11.8)	(13.6)
Less than 12 Months	(0.2)	(3.2)	(4)
12 Months or Greater	$ (0.4)	$ (8.6)	$ (9.6)
Redeemable preferred stocks
Number of Securities
Total | security	3	3	3
Less than 12 Months | security	2	1	1
12 Months or Greater | security	1	2	2
Fair Value
Total	$ 57.2	$ 48.5	$ 30.8
Less than 12 Months	45.9	18.9	4.7
12 Months or Greater	11.3	29.6	26.1
Unrealized Losses
Total	(2.5)	(3.5)	(1.4)
Less than 12 Months	(1.3)	(0.6)	(0.1)
12 Months or Greater	$ (1.2)	$ (2.9)	$ (1.3)

Investments Total Non-Credit Po

Investments Total Non-Credit Portion of Other-Than-Temporary Impairment Recorded in Accumulated Other Comprehensive Income, Reflecting Original Non-Credit Loss at Time Credit Impairment (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Non-credit portion of other-than-temporary impairments recognized in accumulated other comprehensive income	$ (19.8)	$ (19.8)	$ (19.8)
Residential mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Non-credit portion of other-than-temporary impairments recognized in accumulated other comprehensive income	(19.7)	(19.7)	(19.7)
Commercial mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Non-credit portion of other-than-temporary impairments recognized in accumulated other comprehensive income	$ (0.1)	$ (0.1)	$ (0.1)

Investments OTTI Credit Losses

Investments OTTI Credit Losses Recognized in Earnings (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 0.5	$ 0.8	$ 0.5	$ 0.5
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0	0	0	0.3
Ending balance	0.5	0.8	0.5	0.8
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0	0.3	0	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0	0	0	0.3
Ending balance	0	0.3	0	0.3
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0.5	0.5	0.5	0.5
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0	0	0	0
Ending balance	$ 0.5	$ 0.5	$ 0.5	$ 0.5

Investments Components of Net R

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	$ 67.3	$ 2.2	$ 192.7	$ 19.9
Equity Securities, FV-NI, Gross Realized Gains on Sales	8.3	126.9	29.6	268.9
Debt and Equity Securities, Gross Realized Gains on Sales	75.6	129.1	222.3	288.8
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(1.9)	(11.5)	(27.1)	(63.6)
Equity Securities, FV-NI, Gross Realized Losses on Sales	(2)	(9.2)	(9.9)	(19.4)
Debt and Equity Securities, Gross Realized Losses on Sales	(3.9)	(20.7)	(37)	(83)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	65.4	(9.3)	165.6	(43.7)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	6.3	117.7	19.7	249.5
Gross Realized Gain (Loss), excluding Holding Period and OTTI	71.7	108.4	185.3	205.8
Unrealized Gain (Loss) on Hybrid Instrument, Net	4.2	1.3	16.3	(4.2)
Net holding period gains (losses), equity securities	27.6	94.5	520.6	(1.7)
Net Holding Period Realized Gain (Loss)	31.8	95.8	536.9	(5.9)
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	(38.1)	(22.1)	(62.4)	(33.2)
Total net realized gains (losses) on securities	65.4	182.1	659.8	166.7
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	41.5	0.1	113	1.8
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(1.5)	(7.6)	(13.9)	(46.4)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	40	(7.5)	99.1	(44.6)
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	1.8	0.2	4	9.4
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(0.6)	(0.7)	(2.5)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	1.8	(0.4)	3.3	6.9
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	21.3	1.7	68.5	2.1
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(0.2)	(3.2)	(7.7)	(7.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	21.1	(1.5)	60.8	(5.2)
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0	0.2	0
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	0	(2.3)	0
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0	0	(2.1)	0
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	2.6	0	6.2	2
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	0	(2.1)	(6.3)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	2.6	0	4.1	(4.3)
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0.1	0	0.8	0.1
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	0	(0.1)	(0.1)	(1.1)
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	0.1	(0.1)	0.7	(1)
Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-Sale, Gross Realized Gains on Sales	0	0.2	0	4.5
Debt Securities, Available-for-Sale, Gross Realized Losses excluding Other-than-Temporary Impairment	(0.2)	0	(0.3)	0
Debt Securities, Available-for-Sale, Realized Gain (Loss) on Sales, Excluding Other-than-Temporary Impairment	(0.2)	0.2	(0.3)	4.5
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	3.6	0.1	20.2	3.7
Equity Securities, FV-NI, Gross Realized Losses on Sales	(2)	0	(2)	(2.3)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	1.6	0.1	18.2	1.4
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Gross Realized Gains on Sales	4.7	126.8	9.4	265.2
Equity Securities, FV-NI, Gross Realized Losses on Sales	0	(9.2)	(7.9)	(17.1)
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	4.7	117.6	1.5	248.1
Other Assets
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	$ (38.1)	$ (22.1)	$ (62.4)	$ (33.2)

Investments Components of Equit

Investments Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Components of Equity Realized Gains (Losses) [Line Items]
Realized Investment Gains (Losses)	$ 33.9	$ 212.2	$ 540.3	$ 247.8
Equity Securities, FV-NI, Net Realized Gain (Loss) on Sales	6.3	117.7	19.7	249.5
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ 27.6	$ 94.5	$ 520.6	$ (1.7)

Investments Components of Net I

Investments Components of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Investment Income [Line Items]
Gross investment income	$ 263	$ 218.1	$ 777.2	$ 576.5
Investment expenses	(5.9)	(5.8)	(18.3)	(18)
Net Investment Income	257.1	212.3	758.9	558.5
Total equity securities
Net Investment Income [Line Items]
Gross investment income	30	28.1	88.6	78.6
Total equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	15.9	11.2	47.3	32.5
Total equity securities | Common equities
Net Investment Income [Line Items]
Gross investment income	14.1	16.9	41.3	46.1
Available-for-sale Securities
Net Investment Income [Line Items]
Gross investment income	233	190	688.6	497.9
Short-term investments
Net Investment Income [Line Items]
Gross investment income	7.1	15.7	34.3	40.7
Total fixed maturities
Net Investment Income [Line Items]
Gross investment income	225.9	174.3	654.3	457.2
Total fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Gross investment income	75.8	47.7	198.7	133.4
Total fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Gross investment income	8.7	9	26.9	28.1
Total fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Gross investment income	65.1	62.1	209.8	150.1
Total fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	5.4	6.9	16.6	20.4
Total fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Gross investment income	35.6	24.1	100.7	65.5
Total fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Gross investment income	31.4	21.2	85.5	50.9
Total fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Gross investment income	$ 3.9	$ 3.3	$ 16.1	$ 8.8

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Deposit Assets	$ 261,000,000		$ 261,000,000
Securities Sold under Agreements to Repurchase	0	$ 0	0	$ 0	$ 0
Open reverse repurchase commitments	400,000,000	0	400,000,000	0	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment			$ 0	$ 0
Investment Portfolio Duration			2 years 10 months 24 days	2 years 7 months 6 days
Trading securities	0	0	$ 0	$ 0	0
Trading Securities, Gain (Loss)	0	0	0	0
Derivative Assets (Liabilities), at Fair Value, Net	$ 0	$ 0	$ 0	$ 0	$ 0

Fair Value Composition of Inves

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	$ 38,573.7	$ 33,567.4	$ 32,350.6
Fair Value	5,113.3	4,532.3	3,926.9
Available-for-sale Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	34,280.1	29,907.4	28,452.4
Available-for-sale Securities | Total fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	32,812.7	28,111.5	25,642.7
Available-for-sale Securities | Total fixed maturities | Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	22,643.5	20,259.9	18,488.1
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	13,678.7	9,916.5	9,752.5
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	1,683.7	1,649.1	1,588.8
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	7,281.1	8,694.3	7,146.8
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,942.4	7,613.3	6,922
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	681.5	734.4	769.8
Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,639	3,301.6	2,959.3
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	4,621.9	3,577.3	3,192.9
Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	226.8	238.3	232.6
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	51.7	78.2	67.8
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	10.9	0	4.7
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	164.2	160.1	160.1
Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,467.4	1,795.9	2,809.7
Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,293.6	3,660	3,898.2
Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,128.5	1,033.9	840.9
Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,076.4	984.1	800.3
Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	42.1	44.8	35.6
Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	10	5	5
Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,165.1	2,626.1	3,057.3
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	3,164.8	2,625.8	3,057
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	18,401.8	14,345.8	15,469.3
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	15,154.8	11,648.1	12,336
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	13,689.9	9,926	9,762.6
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	13,678.7	9,916.5	9,752.5
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	13,678.7	9,916.5	9,752.5
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	11.2	9.5	10.1
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	11.2	9.5	10.1
Fair Value, Inputs, Level 1 | Available-for-sale Securities | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,464.9	1,722.1	2,573.4
Fair Value, Inputs, Level 1 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,247	2,697.7	3,133.3
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	82.2	71.9	76.3
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	82.2	71.9	76.3
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	0	0	0
Fair Value, Inputs, Level 1 | Total equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,164.8	2,625.8	3,057
Fair Value, Inputs, Level 1 | Total equity securities | Common equities | Common Stocks, excluding Other Risk
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	3,164.8	2,625.8	3,057
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	20,139.5	19,191.2	16,876
Fair Value	5,113.3	4,532.3	3,926.9
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	19,125.3	18,259.3	16,116.4
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	19,122.8	18,185.5	15,880.1
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	8,964.8	10,343.4	8,735.6
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	1,683.7	1,649.1	1,588.8
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	7,281.1	8,694.3	7,146.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	9,942.4	7,613.3	6,922
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	681.5	734.4	769.8
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	4,639	3,301.6	2,959.3
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	4,621.9	3,577.3	3,192.9
Fair Value, Inputs, Level 2 | Available-for-sale Securities | Total fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	215.6	228.8	222.5
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	51.7	78.2	67.8
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	10.9	0	4.7
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	153	150.6	150
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	2.5	73.8	236.3
Fair Value, Inputs, Level 2 | Total equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,014.2	931.9	759.6
Fair Value, Inputs, Level 2 | Total equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,014.2	931.9	759.6
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	967.1	887.1	724
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	42.1	44.8	35.6
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	5	0	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	32.4	30.4	5.3
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	32.4	30.4	5.3
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	32.1	30.1	5
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	27.1	25.1	0
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	5	5	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	35,866.8	32,203.3	30,667
Long-term Debt	4,406.5	4,404.9	3,859.9
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	33,602.3	30,051.8	28,773.1
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	32,134.9	28,255.9	25,963.4
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	22,088.7	20,360.5	18,781.2
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	13,387.6	9,897.4	9,942
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	1,652.2	1,654.6	1,610.1
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	7,048.9	8,808.5	7,229.1
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	9,826.4	7,651.7	6,959.3
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	677.5	733.5	767.8
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	4,547.9	3,332.8	2,986.5
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	4,601	3,585.4	3,205
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	219.8	243.7	222.9
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	51.7	79.3	65.2
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	0	4.8
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	158.1	164.4	152.9
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	1,467.4	1,795.9	2,809.7
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	2,264.5	2,151.5	1,893.9
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	1,054.2	1,002.6	758.9
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	1,004.3	951.6	718.9
Carrying (Reported) Amount, Fair Value Disclosure | Total equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, Fair Value	39.9	46	35
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	10	5	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	1,210.3	1,148.9	1,135
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	1,210	1,148.6	1,134.7
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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	$ 32.4	$ 5.3	$ 30.4	$ 5.3
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	2	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	32.4	5.3	32.4	5.3
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	0	25.1	0
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	2	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	27.1	0	27.1	0
Total equity securities | Industrials | Nonredeemable preferred stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	5	5	5	5
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	5	5	5	5
Total equity securities | Other risk investments | Common equities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning balance	0.3	0.3	0.3	0.3
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain)/Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers In (Out)	0	0	0	0
Fair value, ending balance	$ 0.3	$ 0.3	$ 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	9 Months Ended		12 Months Ended
	Sep. 30, 2019USD ($)$ / shares	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)$ / shares
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 38,573.7	$ 32,350.6	$ 33,567.4
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	32.4	5.3	30.4
Fair Value, Inputs, Level 3 | Internal Pricing | Nonredeemable preferred stocks
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	32.1	5	30.1
Fair Value, Inputs, Level 3 | Internal Pricing | Nonredeemable preferred stocks | Financials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 27.1	0	$ 25.1
Fair Value Inputs, Original Issue Price | $ / shares	$ 9		$ 9
Fair Value, Inputs, Level 3 | Internal Pricing | Nonredeemable preferred stocks | Industrials
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 5	$ 5	$ 5
Fair Value Inputs, Price-to-Sales Ratio	5.5	3.9	5.5
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, Fair Value	$ 32.1	$ 5	$ 30.1
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)	Sep. 30, 2019USD ($)security	Dec. 31, 2018USD ($)security	Sep. 30, 2018USD ($)security
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 38,573,700,000	$ 33,567,400,000	$ 32,350,600,000
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	81.00%	79.00%	76.00%
Investments, Fair Value	$ 18,401,800,000	$ 14,345,800,000	$ 15,469,300,000
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	99.00%	99.00%	99.00%
Dealer Quoted Prices, Percent of FV Hierarchy Level	1.00%	1.00%	1.00%
Investments, Fair Value	$ 20,139,500,000	$ 19,191,200,000	$ 16,876,000,000
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	32,400,000	30,400,000	5,300,000
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]
Investments, Fair Value	$ 32,100,000	$ 30,100,000	$ 5,000,000
Number of securities | security	2	2	1
Common equities | Internal Pricing | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Investments, Fair Value	$ 300,000	$ 300,000	$ 300,000
Number of securities | security	1	1	1

Debt (Detail)

Debt (Detail) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Debt Instrument [Line Items]
Fair Value		$ 5,113.3	$ 4,532.3	$ 3,926.9
Debt, Long-term and Short-term, Combined Amount	[1]	4,406.5	4,404.9	3,859.9
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Long-term Debt		499.3	499.1	499
Fair Value		516.5	506.5	503.9
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Long-term Debt		496.8	496.5	496.4
Fair Value		502.1	455.5	453.3
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Long-term Debt		296.5	296.4	296.3
Fair Value		392.2	368.5	360.3
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Long-term Debt		544.9	544.5	0
Fair Value		617	562.4	0
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Long-term Debt		395.7	395.5	395.4
Fair Value		547.2	496.6	481.8
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Long-term Debt		346.6	346.6	346.6
Fair Value		414.7	350.2	349.7
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Long-term Debt		395.4	395.3	395.3
Fair Value		431.8	366.7	359.1
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Long-term Debt		841.5	841.4	841.3
Fair Value		987.4	831.9	828.4
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Long-term Debt		589.8	589.6	589.6
Fair Value		$ 704.4	$ 594	$ 590.4
[1]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	1 Months Ended	9 Months Ended	12 Months Ended
	Oct. 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Discretionary Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 250,000,000
Debt term		30 days
Borrowings outstanding		$ 0	$ 0
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Debt, stated interest rate		3.75%
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Debt, stated interest rate		2.45%
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Debt, stated interest rate		4.20%
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Debt, stated interest rate		6.625%
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Debt, stated interest rate		6.25%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Debt, stated interest rate		4.35%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt, stated interest rate		3.70%
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Debt, stated interest rate		4.125%
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Debt, face amount	$ 550,000,000
Debt, stated interest rate	4.00%	4.00%
Proceeds, net of underwriter's discounts and commissions	$ 544,500,000
Federal Funds Open Rate | Discretionary Line of Credit
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		0.50%

Income Taxes Additional Informa

Income Taxes Additional Information (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2019USD ($)	Mar. 31, 2019USD ($)Investment	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Income Taxes [Line Items]
Document Period End Date				Sep. 30, 2019
Valuation allowance	$ 0		$ 0	$ 0	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Percent	16.50%		17.70%	24.00%	19.20%
Alternative Energy
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount		$ 156,100,000
Number of Sponsors | Investment		3

Loss and Loss Adjustment Expe_3

Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Loss and loss adjustment expense reserves	$ 17,370	$ 14,620.8	$ 15,400.8	$ 13,086.9
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments and Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item	3,145.1	2,376.4	2,572.7	2,170.1
Liability for Unpaid Claims and Claims Adjustment Expense, Net	14,224.9	12,244.4	$ 12,828.1	$ 10,916.8
Current Year Claims and Claims Adjustment Expense	18,108.2	15,722.2
Prior Year Claims and Claims Adjustment Expense	215.2	47
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	18,323.4	15,769.2
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Current Year	10,864.9	9,409.7
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid, Prior Years	6,061.7	5,031.9
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	$ 16,926.6	14,441.6
Short-duration Insurance Contracts, Accident Year 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of Prior Year Claims and Claims Adjustment Expense	50.00%
Short-duration Insurance Contracts, Accident Year 2017 [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of Prior Year Claims and Claims Adjustment Expense	30.00%
Short-duration Insurance Contracts, Accident Year 2016 [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		52
Personal Lines | Personal auto businesses
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ 108	41
Personal Lines | Agency Auto
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		30
Personal Lines | Direct Auto
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense		11
Personal Lines | Special Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	17
Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	71
Property
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior Year Claims and Claims Adjustment Expense	$ 19	$ 5

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Open reverse repurchase commitments	$ 400,000,000	$ 0			$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	43,400,000
Operating Lease, Payments	61,200,000
Income Taxes Paid	738,700,000	535,800,000
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	147,300,000	116,400,000
Cash and Cash Equivalents | ARX Holding Corp.
Open reverse repurchase commitments	62,800,000	$ 152,400,000			$ 117,300,000
Common Stock [Member] | Quarterly dividend [Member]
Dividends payable	$ 58,500,000		$ 58,400,000	$ 58,400,000

Segment Information Operating R

Segment Information Operating Results (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues	$ 9,530.5	$ 8,495.8	$ 28,281.2	$ 23,943.9
Pretax Profit (Loss)	1,010.3	1,130.5	3,821.4	2,921.4
Amortization of intangible assets	15.8	18	51.7	54
Personal Lines | Agency | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	3,703.4	3,318.2	10,851.5	9,607.7
Pretax Profit (Loss)	380.2	372.2	1,267.9	1,142.2
Personal Lines | Direct | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	3,804	3,337.2	11,113.7	9,565.3
Pretax Profit (Loss)	291.7	294.4	940.2	880.3
Operating Segments | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	9,012.2	7,930.5	26,296.7	22,738.7
Pretax Profit (Loss)	732.5	771.4	2,533	2,299.2
Operating Segments | Personal Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	7,507.4	6,655.4	21,965.2	19,173
Pretax Profit (Loss)	$ 671.9	$ 666.6	$ 2,208.1	$ 2,022.5
Personal auto insurance percentage of the total personal lines segment net premiums earned	94.00%	94.00%	94.00%	94.00%
Operating Segments | Commercial Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	$ 1,106.9	$ 939.6	$ 3,190.4	$ 2,632.5
Pretax Profit (Loss)	69.7	112.7	360.7	307.8
Operating Segments | Property | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	397.9	335.5	1,141.1	933.2
Pretax Profit (Loss)	(9.1)	(7.8)	(35.8)	(31.2)
Amortization of intangible assets	15.8	18	51.7	54
Operating Segments | Other Indemnity | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Pretax Profit (Loss)	0	(0.1)	0	0.1
Segment Reconciling Items | Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	138.4	122.6	403.4	342.4
Segment Reconciling Items | Service businesses
Segment Reporting Information [Line Items]
Revenues	51.5	42.5	144.1	119.6
Pretax Profit (Loss)	2.8	6.7	12	17.5
Segment Reconciling Items | Investment income
Segment Reporting Information [Line Items]
Revenues	328.4	400.2	1,437	743.2
Pretax Profit (Loss)	322.5	394.4	1,418.7	725.2
Segment Reconciling Items | Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (47.5)	$ (42)	$ (142.3)	$ (120.5)

Segment Information Underwritin

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Underwriting operations	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Personal Lines | Agency
Segment Reporting Information [Line Items]
Underwriting Margin	10.30%	11.20%	11.70%	11.90%
Combined Ratio	89.70%	88.80%	88.30%	88.10%
Personal Lines | Direct
Segment Reporting Information [Line Items]
Underwriting Margin	7.70%	8.80%	8.50%	9.20%
Combined Ratio	92.30%	91.20%	91.50%	90.80%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	8.10%	9.70%	9.60%	10.10%
Combined Ratio	91.90%	90.30%	90.40%	89.90%
Operating Segments | Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	9.00%	10.00%	10.10%	10.50%
Combined Ratio	91.00%	90.00%	89.90%	89.50%
Operating Segments | Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	6.30%	12.00%	11.30%	11.70%
Combined Ratio	93.70%	88.00%	88.70%	88.30%
Operating Segments | Property
Segment Reporting Information [Line Items]
Underwriting Margin	(2.30%)	(2.30%)	(3.10%)	(3.30%)
Combined Ratio	102.30%	102.30%	103.10%	103.30%
Combined ratio amortization points	0.040	0.054	0.045	0.058

Dividends (Details)

Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended								3 Months Ended		9 Months Ended
	Sep. 30, 2019	Aug. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Feb. 28, 2019	Sep. 30, 2018	Feb. 28, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Aug. 31, 2018	Dec. 31, 2017
Common Stock, Dividends, Per Share, Declared									$ 0.10	$ 0	$ 0.30	$ 0
Dividends paid to common shareholders											$ 1,584.7	$ 654.9
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						$ 2.5140		$ 1.1247
Series B Preferred Stock
Preferred Stock, Dividends, Per Share, Cash Paid	$ 26.875				$ 26.875		$ 27.024
Dividends payable		$ 13.4				$ 13.4									$ 13.5
Common Stock [Member] | Quarterly dividend [Member]
Dividends payable	$ 58.5				$ 58.4				$ 58.5		$ 58.5		$ 58.4
Common Stock [Member] | Annual variable dividend
Dividends payable														$ 1,467.9		$ 655.1

Dividends - Additional Informat

Dividends - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Aug. 31, 2019	Feb. 28, 2019	Aug. 31, 2018
Class of Stock [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.10	$ 0	$ 0.30	$ 0
Series B Preferred Stock
Class of Stock [Line Items]
Dividends payable					$ 13.4	$ 13.4	$ 13.5

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ 573.6	$ (280.8)	$ (153)	$ 1,977.8	$ 1,977.8
Pretax Cumulative Effect of New Accounting Principal in Period of Adoption				(2,006)	(2,006)
Pretax Reclassification of Stranded Amounts in AOCI to Retained Earnings		(4.3)		(4.3)	(4.3)
AOCI before Tax, Attributable to Parent, after Cumulative Effect Adjustment		(285.1)		(32.5)	(32.5)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, before Tax	134.3	(58.7)	953.5	(352.5)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Noncontrolling Interest	(1.2)	0.6	(7.4)	6.4
OCI, before Reclassifications, before Tax, Attributable to Parent	133.1	(58.1)	946.1	(346.1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	60.7	(9.3)	147.6	(44.2)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	(0.3)	(0.2)	(0.8)	(0.7)
Total reclassification adjustment for amounts realized in net income, pre tax	60.4	(9.5)	146.8	(44.9)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	72.7	(48.6)	799.3	(301.2)
AOCI before Tax, Attributable to Parent, ending balance	646.3	(333.7)	646.3	(333.7)	(153)
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	(120.5)	58.9	32.1	(695.6)	(695.6)
Tax, Cumulative Effect of New Accounting Principal in Period of Adoption				705.8	705.8
Tax, Reclassification of Stranded Amounts in AOCI to Retained Earnings		0.9		(3.4)	(3.4)
AOCI Tax, Attributable to Parent, After Cumulative Effect Adjustment		59.8		6.8	6.8
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	(28.2)	12.3	(200.2)	73.9
Other Comprehensive Income (Loss), Tax, Portion Attributable to Noncontrolling Interest	0.3	(0.2)	1.6	(1.4)
Other Comprehensive Income (Loss), Available-for-sale Securities, before Reclassification Adjustments, Tax	(27.9)	12.1	(198.6)	72.5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(12.7)	1.9	(30.9)	9.2
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	0.1	0	0.2	0.1
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	(12.6)	1.9	(30.7)	9.3
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent	(15.3)	10.2	(167.9)	63.2
AOCI Tax, Attributable to Parent, ending balance	(135.8)	70	(135.8)	70	32.1
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	453.1	(221.9)	(120.9)	1,282.2	1,282.2
Cumulative Effect of New Accounting Principle in Period of Adoption							$ (1,300.2)
Reclassification of Stranded Amounts in AOCI to Retained Earnings						$ (3.4)	(7.7)
AOCI, Net of Tax, After Cumulative Effect Adjustment		(225.3)		(25.7)	(25.7)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	106.1	(46.4)	753.3	(278.6)
Other comprehensive (income) loss attributable to NCI	(0.9)	0.4	(5.8)	5	3.3
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	105.2	(46)	747.5	(273.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	48	(7.4)	116.7	(35)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)	(0.2)	(0.6)	(0.6)
Total reclassification adjustment for amounts realized in net income, after tax	47.8	(7.6)	116.1	(35.6)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	57.4	(38.4)	631.4	(238)
After tax total accumulated other comprehensive income, ending balance	510.5	(263.7)	510.5	(263.7)	(120.9)
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	472.9	(210.9)	(105.6)	1,295	1,295
Cumulative Effect of New Accounting Principle in Period of Adoption							(1,300.2)
Reclassification of Stranded Amounts in AOCI to Retained Earnings						0	(1.1)
AOCI, Net of Tax, After Cumulative Effect Adjustment		(210.9)		(6.3)	(6.3)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	106.1	(46.4)	753.3	(278.6)
Other comprehensive (income) loss attributable to NCI	0	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	106.1	(46.4)	753.3	(278.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	48	(7.4)	116.7	(35)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0	0
Total reclassification adjustment for amounts realized in net income, after tax	48	(7.4)	116.7	(35)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	58.1	(39)	636.6	(243.6)
After tax total accumulated other comprehensive income, ending balance	531	(249.9)	531	(249.9)	(105.6)
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	(16.8)	(17.6)	(17.2)	(14.8)	(14.8)
Cumulative Effect of New Accounting Principle in Period of Adoption							0
Reclassification of Stranded Amounts in AOCI to Retained Earnings						0	(3.2)
AOCI, Net of Tax, After Cumulative Effect Adjustment		(17.6)		(18)	(18)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0	0	0	0
Other comprehensive (income) loss attributable to NCI	0	0	0	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.2)	(0.2)	(0.6)	(0.6)
Total reclassification adjustment for amounts realized in net income, after tax	(0.2)	(0.2)	(0.6)	(0.6)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.2	0.2	0.6	0.6
After tax total accumulated other comprehensive income, ending balance	(16.6)	(17.4)	(16.6)	(17.4)	(17.2)
(Income) loss attributable to NCI
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(3)	6.6	1.9	2	2
Cumulative Effect of New Accounting Principle in Period of Adoption							0
Reclassification of Stranded Amounts in AOCI to Retained Earnings						$ (3.4)	$ (3.4)
AOCI, Net of Tax, After Cumulative Effect Adjustment		3.2		(1.4)	(1.4)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax	0	0	0	0
Other comprehensive (income) loss attributable to NCI	(0.9)	0.4	(5.8)	5
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.9)	0.4	(5.8)	5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0	0
Total reclassification adjustment for amounts realized in net income, after tax	0	0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(0.9)	0.4	(5.8)	5
After tax total accumulated other comprehensive income, ending balance	$ (3.9)	$ 3.6	$ (3.9)	$ 3.6	$ 1.9

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement, Additional Information (Detail) $ in Millions	Sep. 30, 2019USD ($)
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) $ in Millions		3 Months Ended		9 Months Ended			12 Months Ended
		Sep. 30, 2019USD ($)shares	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)shares		Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)shares	Apr. 01, 2021
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, Beginning of period				$ 214.5	[1]	$ 503.7	$ 503.7
Net income attributable to NCI		$ 1.9	$ 1.8	5.9		10.6	5.7
Other comprehensive income (loss) attributable to NCI1		0.9	(0.4)	5.8		(5)	(3.3)
Exercise of employee stock options				7.7		9.4	9.4
Purchase/change of ARX minority shares				(11.2)		(298.2)	(298.2)
Change in redemption value of NCI				0.2		(3.1)	(2.8)
Balance, End of period	[1]	$ 222.9	$ 217.4	$ 222.9		$ 217.4	$ 214.5
ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Number of Shares Put Pursuant to Stockholders' Agreement | shares							204,527
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period | shares							5,483
Payments to Acquire Interest in Subsidiaries and Affiliates							$ 295.9
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage		87.10%	86.80%	87.10%		86.80%	86.80%
Shares held in Employee Stock Option Plan, Suspense Shares | shares		10,438		10,438
Employee Stock Ownership Plan (ESOP), Deferred Shares, Fair Value		$ 15.8		$ 15.8
Scenario, Forecast | ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage								100.00%
[1]	See Note 12 – Redeemable Noncontrolling Interest for further discussion .

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets Goodwill (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Goodwill [Line Items]
Goodwill, Acquired During Period			$ 0
Goodwill, Impaired, Accumulated Impairment Loss	$ 0		0
Amortization of intangible assets	$ 15,800,000	$ 18,000,000	$ 51,700,000	$ 54,000,000
Weighted Average
Goodwill [Line Items]
Finite-Lived Intangible Assets, Remaining Amortization Period			4 years

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Schedule of Other Intangible Assets [Line Items]
Indefinite lived intangible assets	$ 12.4	$ 12.4	$ 12.4
Total	242.9	294.6	312.6
Accumulated amortization	299.4	247.7	229.7
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	230.5	282.2	300.2
Accumulated amortization	$ 298.8	$ 247.1	$ 229.1

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 299.4	$ 247.7	$ 229.7
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2	256.2
Accumulated Amortization	164.7	137.3	128.1
Net Carrying Amount	91.5	118.9	128.1
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2	159.2
Accumulated Amortization	51.2	42.6	39.8
Net Carrying Amount	108	116.6	119.4
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	79.1	79.1	79.1
Accumulated Amortization	48.1	40.1	37.4
Net Carrying Amount	31	39	41.7
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.8	34.8	34.8
Accumulated Amortization	34.8	27.1	23.8
Net Carrying Amount	0	7.7	11
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	529.3	529.3	529.3
Accumulated Amortization	298.8	247.1	229.1
Net Carrying Amount	$ 230.5	$ 282.2	$ 300.2

Leases - Additional Information

Leases - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Leases [Abstract]
Operating lease right-of-use asset	$ 190.5
Location of operating lease right-of-use asset in statement of financial position	us-gaap:OtherAssets
Operating lease liabilities	$ 204.1
Location of operating lease liability in statement of financial location	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent
Operating lease costs	$ 78.3

Leases - Schedule of operating

Leases - Schedule of operating lease maturities (Details) $ in Millions	Sep. 30, 2019USD ($)
Leases [Abstract]
2019 (excluding the nine months ended September 30, 2019)	$ 21.1
2020	78.1
2021	62.4
2022	29.1
2023	14.3
Thereafter	9
Total	214
Interest	(9.9)
Present value of lease liabilities	$ 204.1
Weighted-average remaining term	3 years 2 months
Weighted-average discount rate	3.30%

Leases Schedule of Operating Le

Leases Schedule of Operating Lease Obligations (Details) $ in Millions	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019	$ 64.1
2020	65.5
2021	52.8
2022	24.3
2023	8.5
Thereafter	3.8
Total	$ 219

New Accounting Standards Effect

New Accounting Standards Effect of Standard Change (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Sep. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Assets	$ 54,008.1		$ 46,575	$ 45,543.7
Liabilities	$ 39,661.9		$ 35,538.7	$ 33,467.5
Property Subject to Operating Lease | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Assets		$ 213
Liabilities		$ 217.6

Uncategorized Items - pgr-20199

Label	Element	Value
Accounting Standards Update 2018-02 [Member] | Retained Earnings [Member]
Reclassification of Stranded Amounts in AOCI to Equity	pgr_ReclassificationofStrandedAmountsinAOCItoEquity	$ 4,300,000
Accounting Standards Update 2018-02 [Member] | AOCI Attributable to Parent [Member]
Reclassification of Stranded Amounts in AOCI to Equity	pgr_ReclassificationofStrandedAmountsinAOCItoEquity	(4,300,000)
Accounting Standards Update 2016-01 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	1,300,200,000
Accounting Standards Update 2016-01 [Member] | AOCI Attributable to Parent [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (1,300,200,000)