The Progressive Corporation (PGR) 10-K 27 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Jun. 30, 2018
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Entity Small Business	false
Entity Emerging Growth Company	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	PGR
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	80,661
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		583,896,232
Entity Public Float			$ 34,057,145,532

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Net premiums earned	$ 30,933.3	$ 25,729.9	$ 22,474
Investment income	820.5	563.1	478.9
Net realized gains (losses) on securities:
Net realized gains (losses) on security sales	170.7
Net holding period gains (losses) on securities	(507.9)
Net impairment losses recognized in earnings	(68.3)	(64.5)	(86.8)
Total net realized gains (losses) on securities	(405.5)
Net realized gains (losses) on security sales		115.7	155.8
Net holding period gains (losses) on securities		(1.6)	(17.9)
Total net realized gains (losses) on securities		49.6	51.1
Fees and other revenues	472.2	370.6	332.5
Service revenues	158.5	126.8	103.3
Other gains (losses)	0	(1)	1.6
Total revenues	31,979	26,839	23,441.4
Expenses
Losses and loss adjustment expenses	21,721	18,808	16,879.6
Policy acquisition costs	2,573.7	2,124.9	1,863.8
Other underwriting expenses	4,195.8	3,480.7	2,972
Investment expenses	24.3	23.9	22.4
Service expenses	134.1	109.5	92
Interest expense	166.5	153.1	140.9
Total expenses	28,815.4	24,700.1	21,970.7
Net Income
Income before income taxes	3,163.6	2,138.9	1,470.7
Provision for income taxes	542.6	540.8	413.5
Net income	2,621	1,598.1	1,057.2
Net (income) loss attributable to noncontrolling interest (NCI)	(5.7)	(5.9)	(26.2)
Net income attributable to Progressive	2,615.3	1,592.2	1,031
Changes in:
Total net unrealized gains (losses) on securities	(99.3)	355.4	130.6
Net unrealized losses on forecasted transactions	0.8	(5.4)	(1.2)
Foreign currency translation adjustment	0	1.1	0.4
Other comprehensive income (loss)	(98.5)	351.1	129.8
Other comprehensive (income) loss attributable to NCI	3.3	(2.3)	3.2
Comprehensive income attributable to Progressive	2,520.1	1,941	1,164
Computation of Earnings Per Common Share
Net income attributable to Progressive	2,615.3	1,592.2	1,031
Less: Preferred share dividends	21.4	0	0
Net income available to common shareholders	$ 2,593.9	$ 1,592.2	$ 1,031
Average common shares outstanding — Basic	582.4	580.8	581.7
Net effect of dilutive stock-based compensation	4.3	4.9	3.3
Total average equivalent common shares — Diluted	586.7	585.7	585
Basic: Earnings per share (usd per share)	$ 4.45	$ 2.74	$ 1.77
Diluted: Earnings per share (usd per share)	$ 4.42	$ 2.72	$ 1.76

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Assets
Fixed maturities (amortized cost: $28,255.9 and $20,209.9)		$ 28,111.5
Short-term investments (amortized cost: $1,795.9 and $2,869.4)		1,795.9
Fixed maturities (amortized cost: $28,255.9 and $20,209.9)		29,907.4
Nonredeemable preferred stocks (cost: $1,002.6 and $698.6)		1,033.9
Common equities (cost: $1,148.9 and $1,499.0)		2,626.1
Total equity securities		3,660
Total investments		33,567.4
Fixed maturities (amortized cost: $28,255.9 and $20,209.9)			$ 20,201.7
Short-term investments (amortized cost: $1,795.9 and $2,869.4)			2,869.4
Total available-for-sale securities			23,071.1
Nonredeemable preferred stocks (cost: $1,002.6 and $698.6)			803.8
Common equities (cost: $1,148.9 and $1,499.0)			3,399.8
Total equity securities			4,203.6
Total investments			27,274.7
Cash and cash equivalents		69.5	265
Restricted cash		5.5	10.3
Total cash, cash equivalents, and restricted cash		75	275.3
Accrued investment income		190.8	119.7
Premiums receivable, net of allowance for doubtful accounts of $252.1 and $210.9		6,497.1	5,422.5
Reinsurance recoverables		2,696.1	2,273.4
Prepaid reinsurance premiums		309.7	203.3
Deferred acquisition costs		951.6	780.5
Property and equipment, net of accumulated depreciation of $1,033.2 and $940.6		1,131.7	1,119.6
Goodwill		452.7	452.7
Intangible assets, net of accumulated amortization of $247.7 and $175.7		294.6	366.6
Net deferred income taxes		43.2	0
Other assets		365.1	412.9
Total assets		46,575	38,701.2
Liabilities
Unearned premiums		10,686.5	8,903.5
Loss and loss adjustment expense reserves		15,400.8	13,086.9
Net deferred income taxes		0	135
Accounts payable, accrued expenses, and other liabilities	[1]	5,046.5	3,481
Debt	[2]	4,404.9	3,306.3
Total liabilities		35,538.7	28,912.7
Redeemable noncontrolling interest (NCI)	[3]	214.5	503.7
Shareholders’ Equity
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5 and 0)		493.9	0
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 214.3 and 215.8)		583.2	581.7
Paid-in capital		1,479	1,389.2
Retained earnings		8,386.6	6,031.7
Accumulated other comprehensive income:
Net unrealized gains (losses) on securities		(105.6)	1,295
Net unrealized losses on forecasted transactions		(17.2)	(14.8)
Accumulated other comprehensive (income) loss attributable to NCI		1.9	2
Total accumulated other comprehensive income attributable to Progressive		(120.9)	1,282.2
Total shareholders’ equity		10,821.8	9,284.8
Total liabilities, redeemable NCI, and shareholders’ equity		$ 46,575	$ 38,701.2
[1]	See Note 12 – Litigation, Note 13 – Commitments and Contingencies, and Note 14 – Dividends for further discussion.
[2]	Consists of long-term debt. See Note 4 – Debt for further discussion.
[3]	See Note 15 – Redeemable Noncontrolling Interest for further discussion.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fixed maturities, amortized cost	$ 28,255.9
Available-for-Sale Fixed Maturities, Amortized Cost		$ 20,209.9
Nonredeemable preferred stocks, cost	1,002.6
Available-for-Sale Nonredeemable Preferred Stocks, Cost		698.6
Equity Securities Common Equities Cost	1,148.9
Common equities, cost		1,499
Debt Securities, Available-for-Sale Short Term Investments, Amortized Cost	1,795.9
Short Term Investments Amortized Cost		2,869.4
Premiums receivable, allowance for doubtful accounts	252.1	210.9
Property and equipment, accumulated depreciation	1,033.2	940.6
Finite-Lived Intangible Assets, Accumulated Amortization	$ 247.7	$ 175.7
Common Shares, par value (USD per share)	$ 1	$ 1
Common Shares, authorized (shares)	900,000,000	900,000,000
Common Shares, issued (shares)	797,500,000	797,500,000
Common Shares, treasury shares (shares)	214,300,000	215,800,000
Serial Preferred Stock
Preferred Stock, Shares Authorized	20,000,000	20,000,000
Series B Preferred Stock
Preferred Stock, Liquidation Preference Per Share		$ 0
Series B Preferred Stock | Serial Preferred Stock
Preferred Stock, No Par Value	$ 0	$ 0
Preferred Stock, Shares Authorized	500,000	0
Preferred Stock, Shares Issued	500,000	0
Preferred Stock, Shares Outstanding	500,000	0
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 0

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Millions		Total	Preferred Shares, No Par Value	Common Shares, $1.00 Par Value	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss) Attributable to Progressive
Balance, Beginning of year at Dec. 31, 2015			$ 0	$ 583.6	$ 1,218.8	$ 4,686.6	$ 800.4
Stock Issued During Period, Value, New Issues			0
Treasury shares purchased				(6.1)	(13.4)	(173)
Net restricted equity awards issued/vested				2.4	(2.4)
Amortization of equity-based compensation					80.9
Reinvested dividends on restricted stock units					6.1	(6.1)
Adjustment to carrying amount of redeemable noncontrolling interest		$ (4.2)			4.2
Tax benefit from vesting of equity-based compensation					9.2
Net income attributable to Progressive		1,031				1,031
Cash dividends declared on common shares ($2.5140, $1.1247, and $0.6808 per share)						(394.7)
Cash dividends declared on Serial Preferred Shares, Series B ($27.024 per share, $0, and $0)						0
Other, net						(3.4)
Attributable to noncontrolling interest		3.2					3.2
Other comprehensive income (loss)							129.8
Balance, End of year at Dec. 31, 2016		7,957.1	0	579.9	1,303.4	5,140.4	933.4
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	[1]					0	0
Reclassification of Stranded Amounts in AOCI to Equity | Accounting Standards Update 2018-02 [Member]	[1]					0	0
Stock Issued During Period, Value, New Issues			0
Treasury shares purchased				(1.5)	(3.4)	(57.6)
Net restricted equity awards issued/vested				3.3	(3.3)
Amortization of equity-based compensation					92.9
Reinvested dividends on restricted stock units					8	(8)
Adjustment to carrying amount of redeemable noncontrolling interest		8.4			(8.4)
Tax benefit from vesting of equity-based compensation					0
Net income attributable to Progressive		1,592.2				1,592.2
Cash dividends declared on common shares ($2.5140, $1.1247, and $0.6808 per share)						(654.2)
Cash dividends declared on Serial Preferred Shares, Series B ($27.024 per share, $0, and $0)						0
Other, net						18.9
Attributable to noncontrolling interest		(2.3)					(2.3)
Other comprehensive income (loss)							351.1
Balance, End of year at Dec. 31, 2017		9,284.8	0	581.7	1,389.2	6,031.7	1,282.2
Cumulative Effect of New Accounting Principle in Period of Adoption		1,300.2
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	[1]					0	0
Reclassification of Stranded Amounts in AOCI to Equity		7.7
Reclassification of Stranded Amounts in AOCI to Equity | Accounting Standards Update 2018-02 [Member]	[1]					0	0
Stock Issued During Period, Value, New Issues			493.9
Treasury shares purchased				(1.4)	(3.3)	(74.3)
Net restricted equity awards issued/vested				2.9	(2.9)
Amortization of equity-based compensation					76.2
Reinvested dividends on restricted stock units					12.2	(12.2)
Adjustment to carrying amount of redeemable noncontrolling interest		(2.8)			7.6
Tax benefit from vesting of equity-based compensation					0
Net income attributable to Progressive		2,615.3				2,615.3
Cash dividends declared on common shares ($2.5140, $1.1247, and $0.6808 per share)						(1,466)
Cash dividends declared on Serial Preferred Shares, Series B ($27.024 per share, $0, and $0)		(13.5)				(13.5)
Other, net						1.1
Attributable to noncontrolling interest		3.3					(0.1)
Other comprehensive income (loss)							(98.5)
Balance, End of year at Dec. 31, 2018		$ 10,821.8	$ 493.9	$ 583.2	$ 1,479	8,386.6	(120.9)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	[1]					1,300.2	(1,300.2)
Reclassification of Stranded Amounts in AOCI to Equity | Accounting Standards Update 2018-02 [Member]	[1]					$ 4.3	$ (4.3)
[1]	See Note 1 – Accounting and Reporting Policies for further discussion.

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Shareholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash dividends declared on common shares, per share	$ 2.5140	$ 1.1247	$ 0.6808
Common Shares, par value (USD per share)	1	$ 1	$ 1
Series B Preferred Stock
Preferred Stock, Dividends Per Share, Declared	$ 27.024
Voting Preferred Stock
Preference Shares authorized	5,000,000	5,000,000	5,000,000
Preferred Stock, Shares Issued	0	0	0
Serial Preferred Stock
Preference Shares authorized	20,000,000	20,000,000
Serial Preferred Stock | Series B Preferred Stock
Preferred Stock, Dividends Per Share, Declared	$ 27.024	$ 0	$ 0
Preferred Stock, No Par Value	$ 0	$ 0	$ 0
Preference Shares authorized	500,000	0
Preferred Stock, Shares Issued	500,000	0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Cash Flows [Abstract]
Net income	$ 2,621	$ 1,598.1	$ 1,057.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	190.4	169.9	137.4
Amortization of intangible assets	72	66.2	62.1
Net amortization of fixed-income securities	34.3	86.2	77.2
Amortization of equity-based compensation	77.2	95.4	85.2
Net realized (gains) losses on securities	405.5	(49.6)	(51.1)
Net (gains) losses on disposition of property and equipment	32.1	7.2	6.6
Other (gains) losses	0	1	(1.6)
Net loss on exchange transaction	0	0	4.5
Changes in:
Premiums receivable	(1,074.6)	(913.2)	(518.5)
Reinsurance recoverables	(422.7)	(388.6)	(388.2)
Prepaid reinsurance premiums	(106.4)	(32.8)	48.8
Deferred acquisition costs	(171.1)	(129.3)	(103.8)
Income taxes	(158.7)	(172.6)	(55.7)
Unearned premiums	1,783	1,434.9	830.7
Loss and loss adjustment expense reserves	2,313.9	1,718.8	1,323.2
Accounts payable, accrued expenses, and other liabilities	746.6	400	308.9
Other, net	(57.7)	(134.8)	(90.2)
Net cash provided by operating activities	6,284.8	3,756.8	2,732.7
Purchases:
Fixed maturities	(21,153)	(14,587.8)	(11,610.6)
Equity securities	(538.8)	(255.6)	(434.2)
Sales:
Fixed maturities	7,835.6	5,382.5	5,694.9
Equity securities	823.5	252.9	484.6
Maturities, paydowns, calls, and other:
Fixed maturities	5,099.8	5,215.8	4,907.4
Equity securities	26.6	50	0
Net sales (purchases) of short-term investments	1,116.3	727.6	(1,357.2)
Net unsettled security transactions	11.7	(33.6)	50.9
Purchases of property and equipment	(266)	(155.7)	(215)
Sales of property and equipment	9.4	15.3	6.2
Acquisition of additional shares of ARX Holding Corp.	(296.9)	0	0
Acquisition of an insurance company, net of cash acquired	0	(18.1)	0
Net cash disposed in exchange transaction	0	0	(7.7)
Net cash used in investing activities	(7,331.8)	(3,406.7)	(2,480.7)
Cash Flows From Financing Activities
Net proceeds from debt issuance	1,134	841.1	495.6
Net proceeds from issuance of Serial Preferred Shares, Series B	493.9	0	0
Payments of debt	37.1	49	25.5
Dividends paid to common shareholders	654.9	395.4	519
Dividends paid to preferred shareholders	(13.5)	0	0
Proceeds from exercise of equity options	3.3	0.5	0
Acquisition of treasury shares for restricted stock tax liabilities	(78.6)	(57.6)	(25.1)
Acquisition of treasury shares acquired in open market	(0.4)	(4.9)	(167.4)
Redemption/reacquisition of subordinated debt	0	(635.6)	(18.2)
Tax benefit from vesting of equity-based compensation	0	0	9.2
Net cash provided by (used in) financing activities	846.7	(300.9)	(250.4)
Effect of exchange rate changes on cash	0	(0.3)	0.4
Increase (decrease) in cash, cash equivalents, and restricted cash	(200.3)	48.9	2
Cash, cash equivalents, and restricted cash - Beginning of year	275.3	226.4	224.4
Cash, cash equivalents, and restricted cash - End of year	$ 75	$ 275.3	$ 226.4

SCHEDULE I - Summary Of Investm

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2018
Text Block [Abstract]
SCHEDULE I - Summary Of Investments - Other Than Investments In Related Parties	SCHEDULE I — SUMMARY OF INVESTMENTS — OTHER THAN INVESTMENTS IN RELATED PARTIES THE PROGRESSIVE CORPORATION AND SUBSIDIARIES (millions) December 31, 2018 Type of Investment Cost Fair Value Amount At Which Shown In The Balance Sheet Fixed maturities: Bonds: United States Government and government agencies and authorities $ 9,897.4 $ 9,916.5 $ 9,916.5 States, municipalities, and political subdivisions 1,654.6 1,649.1 1,649.1 Public utilities 479.6 473.8 473.8 Corporate and other debt securities 8,328.9 8,220.5 8,220.5 Asset-backed securities 7,651.7 7,613.3 7,613.3 Redeemable preferred stocks 243.7 238.3 238.3 Total fixed maturities 28,255.9 28,111.5 28,111.5 Equity securities: Common stocks: Public utilities 81.4 140.4 140.4 Banks, trusts, and insurance companies 226.4 525.8 525.8 Industrial, miscellaneous, and all other 841.1 1,959.9 1,959.9 Nonredeemable preferred stocks 1,002.6 1,033.9 1,033.9 Total equity securities 2,151.5 3,660.0 3,660.0 Short-term investments $ 1,795.9 $ 1,795.9 $ 1,795.9 Total investments $ 32,203.3 $ 33,567.4 $ 33,567.4 Progressive did not have any securities of any one issuer, excluding U.S. government obligations, with an aggregate cost or fair value exceeding 10% of total shareholders’ equity at December 31, 2018 .

SCHEDULE II - Condensed Financi

SCHEDULE II - Condensed Financial Information Of Registrant	12 Months Ended
	Dec. 31, 2018
Text Block [Abstract]
SCHEDULE II - Condensed Financial Information Of Registrant	SCHEDULE II — CONDENSED FINANCIAL INFORMATION OF REGISTRANT CONDENSED STATEMENTS OF COMPREHENSIVE INCOME THE PROGRESSIVE CORPORATION (PARENT COMPANY) (millions) Years Ended December 31, 2018 2017 2016 Revenues Dividends from subsidiaries $ 939.1 $ 867.3 $ 375.5 Undistributed income (loss) from subsidiaries 1,770.7 866.3 741.9 Equity in net income of subsidiaries 2,709.8 1,733.6 1,117.4 Intercompany investment income 39.4 11.3 5.5 Gains (losses) on extinguishment of debt 0 0.2 1.6 Total revenues 2,749.2 1,745.1 1,124.5 Expenses Interest expense 166.8 151.1 140.4 Deferred compensation 1 7.5 23.2 5.3 Other operating costs and expenses 5.1 4.6 4.2 Total expenses 179.4 178.9 149.9 Income before income taxes 2,569.8 1,566.2 974.6 Benefit for income taxes 45.5 26.0 56.4 Net income attributable to Progressive 2,615.3 1,592.2 1,031.0 Other comprehensive income (loss) (95.2 ) 348.8 133.0 Comprehensive income attributable to Progressive $ 2,520.1 $ 1,941.0 $ 1,164.0 1 See Note 4 – Employee Benefit Plans in these condensed financial statements. See notes to condensed financial statements. CONDENSED BALANCE SHEETS THE PROGRESSIVE CORPORATION (PARENT COMPANY) (millions) December 31, 2018 2017 Assets Investment in affiliate $ 5.0 $ 5.0 Investment in subsidiaries 13,652.2 11,721.3 Receivable from investment subsidiary 2,658.9 1,466.1 Intercompany receivable 651.1 578.6 Net deferred income taxes 68.2 67.1 Other assets 124.2 167.3 Total assets $ 17,159.6 $ 14,005.4 Liabilities Accounts payable, accrued expenses, and other liabilities $ 250.5 $ 292.6 Dividend payable 1,467.9 655.1 Debt 4,404.9 3,269.2 Total liabilities 6,123.3 4,216.9 Redeemable noncontrolling interest (NCI) 214.5 503.7 Shareholders’ Equity Serial Preferred Shares (authorized 20.0) Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5 and 0) 493.9 0 Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 214.3 and 215.8) 583.2 581.7 Paid-in capital 1,479.0 1,389.2 Retained earnings 8,386.6 6,031.7 Total accumulated other comprehensive income attributable to Progressive (120.9 ) 1,282.2 Total shareholders’ equity 10,821.8 9,284.8 Total liabilities, redeemable NCI, and shareholders’ equity $ 17,159.6 $ 14,005.4 See notes to condensed financial statements. CONDENSED STATEMENTS OF CASH FLOWS THE PROGRESSIVE CORPORATION (PARENT COMPANY) (millions) Years Ended December 31, 2018 2017 2016 Cash Flows From Operating Activities: Net income attributable to Progressive $ 2,615.3 $ 1,592.2 $ 1,031.0 Adjustments to reconcile net income attributable to Progressive to net cash provided by operating activities: Undistributed (income) loss from subsidiaries (1,770.7 ) (866.3 ) (741.9 ) Amortization of equity-based compensation 2.4 2.1 2.2 (Gains) losses on extinguishment of debt 0 (0.2 ) (1.6 ) Changes in: Intercompany receivable 77.5 (71.3 ) (37.3 ) Accounts payable, accrued expenses, and other liabilities (29.6 ) 53.6 24.2 Income taxes (14.2 ) 37.3 (5.0 ) Other, net 47.8 (22.6 ) (13.3 ) Net cash provided by operating activities 928.5 724.8 258.3 Cash Flows From Investing Activities: Additional investments in equity securities of consolidated subsidiaries (178.3 ) (86.7 ) (112.0 ) Acquisition of additional shares - ARX (287.9 ) 0 0 Acquisition of an insurance company 0 (18.7 ) 0 (Paid to) received from investment subsidiary (1,192.8 ) (344.2 ) 78.6 Net cash used in investing activities (1,659.0 ) (449.6 ) (33.4 ) Cash Flows From Financing Activities: Net proceeds from debt issuance 1,134.0 841.1 495.6 Net proceeds from preferred stock issuance 493.9 0 0 Reacquisitions of debt 0 (594.4 ) (18.2 ) Dividends paid to common shareholders (654.9 ) (395.4 ) (519.0 ) Dividends paid to preferred shareholders (13.5 ) 0 0 Acquisition of treasury shares for restricted stock tax liabilities (78.6 ) (57.6 ) (25.1 ) Acquisition of treasury shares acquired in open market (0.4 ) (4.9 ) (167.4 ) Loan to ARX Holding Corp. 1 (150.0 ) (64.0 ) 0 Tax benefit from vesting of equity-based compensation 0 0 9.2 Net cash provided by (used in) financing activities 730.5 (275.2 ) (224.9 ) Change in cash, cash equivalents, and restricted cash 0 0 0 Cash, cash equivalents, restricted cash - Beginning of year 0 0 0 Cash, cash equivalents, restricted cash - End of year $ 0 $ 0 $ 0 1 See Note 4 – Debt in our Annual Report. See notes to condensed financial statements. NOTES TO CONDENSED FINANCIAL STATEMENTS The accompanying condensed financial statements of The Progressive Corporation (parent company) should be read in conjunction with the consolidated financial statements and notes thereto in the Annual Report to Shareholders of The Progressive Corporation and its subsidiaries, which is included as Exhibit 13 to this Form 10-K. Note 1. Statements of Cash Flows — For the purpose of the Statements of Cash Flows, cash includes only bank demand deposits. The Progressive Corporation does not hold any cash but has unrestricted access to funds maintained in a non-insurance, investment subsidiary to meet its holding company obligations; at December 31, 2018 and 2017 , $2.9 billion and $1.6 billion , respectively, of marketable securities were available in this subsidiary. Non-cash activity includes declared but unpaid dividends, and the change in redemption value of the redeemable NCI. For the years ended December 31, The Progressive Corporation paid the following: (millions) 2018 2017 2016 Income taxes $ 679.2 $ 669.7 $ 450.2 Interest 153.6 142.2 134.2 Note 2. Income Taxes — The Progressive Corporation files a consolidated federal income tax return with its eligible subsidiaries and acts as an agent for the consolidated tax group when making payments to the Internal Revenue Service. Effective April 2, 2018, The Progressive Corporation acquired additional shares of ARX to increase its ownership above 80% . As a result, ARX and its subsidiaries will be included in The Progressive Corporation consolidated federal income tax return for the period from April 3 to December 31, 2018. The Progressive Corporation consolidated group’s net income taxes currently payable/recoverable are included in other liabilities/assets, respectively, in the accompanying Condensed Balance Sheets based on the balance at the end of the year. The Progressive Corporation and its eligible subsidiaries have adopted, pursuant to a written agreement, a method of allocating consolidated federal income taxes. Amounts allocated to the eligible subsidiaries under the written agreement are included in “Intercompany Receivable” in the accompanying Condensed Balance Sheets. On December 22, 2017, legislation commonly known as the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”) was signed into law. One of the provisions of the 2017 Tax Act reduced the corporate federal income tax rate from 35% to 21% effective January 1, 2018. Pursuant to current accounting guidance, all deferred tax assets and liabilities were revalued at December 31, 2017, to recognize the tax rate that is expected to apply when the tax effects are ultimately recognized in future periods. The impact of revaluing the deferred tax assets and liabilities from 35% to 21% was a net increase to The Progressive Corporation’s income tax expense of $44.7 million in 2017. Note 3. Debt — The information relating to debt is incorporated by reference from Note 4 – Debt in our Annual Report. Note 4. Employee Benefit Plans — The information relating to incentive compensation plans and deferred compensation is incorporated by reference from Note 9 – Employee Benefit Plans in our Annual Report. Note 5. Other Comprehensive Income — On the condensed Statements of Comprehensive Income, other comprehensive income represents activity of the subsidiaries of The Progressive Corporation and includes net unrealized gains (losses) on securities, net unrealized gains on forecasted transactions, and foreign currency translation adjustments. Note 6. Dividends — The information relating to our dividend policy is incorporated by reference from Note 14 – Dividends in our Annual Report.

SCHEDULE III - Supplementary In

SCHEDULE III - Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2018
Text Block [Abstract]
SCHEDULE III - Supplementary Insurance Information	SCHEDULE III — SUPPLEMENTARY INSURANCE INFORMATION THE PROGRESSIVE CORPORATION AND SUBSIDIARIES (millions) Segment Deferred 1 Future 1 Unearned premiums 1 Other 1 Premium revenue Net 1,2 Benefits, Amortization Other Net written Year ended December 31, 2018: Personal Lines $ 26,034.7 $ 18,389.8 $ 1,964.4 $ 3,563.3 $ 27,157.6 Commercial Lines 3,610.9 2,394.0 396.0 396.0 3,996.4 Property 1,287.7 937.0 213.3 237.2 1,455.9 Other indemnity 0 0.2 0 (0.7 ) 0 Total $ 951.6 $ 15,400.8 $ 10,686.5 $ 0 $ 30,933.3 $ 796.2 $ 21,721.0 $ 2,573.7 $ 4,195.8 $ 32,609.9 Year ended December 31, 2017: Personal Lines $ 21,947.2 $ 16,141.4 $ 1,656.4 $ 2,954.8 $ 22,928.4 Commercial Lines 2,793.9 1,966.4 309.3 335.3 3,112.7 Property 988.8 700.2 159.2 190.4 1,091.0 Other indemnity 0 0 0 0.2 0 Total $ 780.5 $ 13,086.9 $ 8,903.5 $ 0 $ 25,729.9 $ 539.2 $ 18,808.0 $ 2,124.9 $ 3,480.7 $ 27,132.1 Year ended December 31, 2016: Personal Lines $ 19,188.2 $ 14,591.1 $ 1,446.6 $ 2,549.2 $ 19,819.5 Commercial Lines 2,421.3 1,741.0 266.7 285.4 2,598.3 Property 864.5 546.1 150.5 137.2 935.7 Other indemnity 0 1.4 0 0.2 0 Total $ 651.2 $ 11,368.0 $ 7,468.3 $ 0 $ 22,474.0 $ 456.5 $ 16,879.6 $ 1,863.8 $ 2,972.0 $ 23,353.5 1 Progressive does not allocate assets, liabilities, or investment income to operating segments. 2 Excludes total net realized gains (losses) on securities.

SCHEDULE IV - Reinsurance

SCHEDULE IV - Reinsurance	12 Months Ended
	Dec. 31, 2018
Text Block [Abstract]
SCHEDULE IV - Reinsurance	SCHEDULE IV — REINSURANCE THE PROGRESSIVE CORPORATION AND SUBSIDIARIES (millions) Year Ended: Gross Amount Ceded to Assumed Net Amount Percentage December 31, 2018 Premiums earned: Property and liability insurance $ 31,970.2 $ 1,036.9 $ 0 $ 30,933.3 0 % December 31, 2017 Premiums earned: Property and liability insurance $ 26,425.7 $ 695.8 $ 0 $ 25,729.9 0 % December 31, 2016 Premiums earned: Property and liability insurance $ 23,111.2 $ 637.2 $ 0 $ 22,474.0 0 %

Reporting and Accounting Polici

Reporting and Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Reporting and Accounting Policies	REPORTING AND ACCOUNTING POLICIES Nature of Operations The Progressive insurance organization began business in 1937. The financial results of The Progressive Corporation include its subsidiaries and affiliates (references to “subsidiaries” in these notes include affiliates as well). Our insurance subsidiaries (collectively the Progressive Group of Insurance Companies) provide personal and commercial auto insurance, residential property insurance, and other specialty property-casualty insurance and related services. Our Personal Lines segment writes insurance for personal autos and recreational vehicles, which we refer to as our special lines products, through both an independent insurance agency channel and a direct channel. 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 through both the independent agency and direct channels. Our Property segment writes residential property insurance for homeowners, other property owners, and renters, through both an independent insurance agency channel and a direct channel. We operate our businesses throughout the United States. Basis of Consolidation and Reporting 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. All intercompany accounts and transactions are eliminated in consolidation. The Progressive Corporation owned 86.8% of the outstanding capital stock of ARX at December 31, 2018 , 69.0% at December 31, 2017 , and 69.2% at December 31, 2016 . The increase in Progressive's ownership of ARX is primarily due to the minority ARX shareholders exercising their rights to "put" a portion of their shares, including exercised stock options, to Progressive pursuant to the ARX stockholders' agreement. See Note 15 – Redeemable Noncontrolling Interest for further discussion. Estimates We are required to make estimates and assumptions when preparing our financial statements and accompanying notes in conformity with accounting principles generally accepted in the United States of America (GAAP). As estimates develop into fact, results may, and will likely, differ from those estimates. Investments Our fixed-maturity securities and short-term investments are accounted for on an available-for-sale basis. Fixed-maturity securities include debt securities and redeemable preferred stocks, which may have fixed or variable principal payment schedules, may be held for indefinite periods of time, and may be used as a part of our asset/liability strategy or sold in response to changes in interest rates, anticipated prepayments, risk/reward characteristics, liquidity needs, or other economic factors. These securities are carried at fair value with the corresponding unrealized gains (losses), net of deferred income taxes, reported in accumulated other comprehensive income. Fair values are obtained from recognized pricing services or are quoted by market makers and dealers, with limited exceptions discussed in Note 3 - Fair Value . Short-term investments may include Eurodollar deposits, commercial paper, repurchase transactions, and other securities expected to mature within one year. From time to time, we may also invest in municipal bonds that have maturity dates that are longer than one year but have either liquidity facilities or mandatory put features within one year. Equity securities include common stocks, nonredeemable preferred stocks, and other risk investments. These securities are carried at fair value, and as of January 1, 2018, with the changes in fair value reported as a component of net holding period gains (losses) on securities reported in net income. See New Accounting Standards - Adopted below for further discussion. Trading securities are securities bought principally for the purpose of sale in the near term. We do not hold any trading securities. To the extent we have trading securities, changes in fair value would be recognized in income in the current period. Derivative instruments, which may be used for trading purposes or classified as trading derivatives due to the characteristics of the transaction, are discussed below. Derivative instruments may include futures, options, forward positions, foreign currency forwards, interest rate swap agreements, and credit default swaps and may be used in the portfolio for general investment purposes or to hedge the exposure to: • Changes in fair value of an asset or liability (fair value hedge), • Foreign currency of an investment in a foreign operation (foreign currency hedge), or • Variable cash flows of a forecasted transaction (cash flow hedge). We did not have any derivatives outstanding at December 31, 2018 and 2017. To the extent we have derivatives held for general investment purposes, these derivative instruments are recognized as either assets or liabilities and measured at fair value, with changes in fair value recognized in income as a component of net holding period gains (losses) on securities during the period of change. Derivatives designated as hedges are required to be evaluated on established criteria to determine the effectiveness of their correlation to, and ability to reduce the designated risk of, specific securities or transactions. Effectiveness is required to be reassessed regularly. Hedges that are deemed to be effective would be accounted for as follows: • Fair value hedge : changes in fair value of the hedge, as well as the hedged item, would be recognized in income in the period of change while the hedge is in effect. • Foreign currency hedge : changes in fair value of the hedge, as well as the hedged item, would be reflected as a change in translation adjustment as part of accumulated other comprehensive income. Gains and losses on the foreign currency hedge would offset the foreign exchange gains and losses on the foreign investment as they are recognized into income. • Cash flow hedge : changes in fair value of the hedge would be reported as a component of accumulated other comprehensive income and subsequently amortized into earnings over the life of the hedged transaction. If a hedge is deemed to become ineffective or discontinued, the following accounting treatment would be applied: • Fair value hedge : the derivative instrument would continue to be adjusted through income, while the adjustment in the change in value of the hedged item would be reflected as a change in unrealized gains (losses) as part of accumulated other comprehensive income. • Foreign currency hedge : changes in the value of the hedged item would continue to be reflected as a change in translation adjustment as part of accumulated other comprehensive income, but the derivative instrument would be adjusted through income for the current period. • Cash flow hedge : changes in fair value of the derivative instrument would be reported in income for the current period. For derivatives settled through a clearinghouse, we will need cash to post initial margin and are subject to increases in margin beyond changes in fair value. For bi-lateral derivative positions, net cash requirements are limited to changes in fair values, which may vary as a result of changes in interest rates, currency exchange rates, and other factors. Exposure to credit risk is limited to the carrying value; collateral may be required to limit credit risk. We have elected not to offset fair value amounts that arise from derivative positions with the same counterparty under a master netting arrangement. Investment securities are exposed to various risks such as interest rate, market, credit, and liquidity risk. Fair values of securities fluctuate based on the nature and magnitude of changing market conditions; significant changes in market conditions could materially affect the portfolio’s value in the near term. We regularly monitor our portfolio for price changes, which might indicate potential impairments, and perform detailed reviews of fixed-maturity securities with unrealized losses. In such cases, changes in fair value are evaluated to determine the extent to which such changes are attributable to: (i) fundamental factors specific to the issuer, such as financial condition, business prospects, or other factors, (ii) market-related factors, such as interest rates, or (iii) credit-related losses, where the present value of cash flows expected to be collected are lower than the amortized cost basis of the security. We analyze our investment in debt securities that are in a loss position to determine if we intend to sell, or if it is more likely than not that we will be required to sell, the security prior to recovery and, if so, we write down the security to its current fair value, with the entire amount of the write-down recorded to earnings. To the extent that it is more likely than not that we will hold the debt security until recovery (which could be maturity), we determine if any of the decline in value is due to a credit loss (i.e., where the present value of future cash flows expected to be collected is lower than the amortized cost basis of the security) and, if so, we recognize that portion of the impairment as a component of net realized gains (losses) in the comprehensive income statement, with the difference (i.e., non-credit related impairment) recognized as part of our net unrealized gains (losses) in accumulated other comprehensive income. Investment income consists of interest, dividends, and accretion net of amortization. Interest is recognized on an accrual basis using the effective yield method, except for asset backed securities, discussed below. Depending on the nature of the equity instruments, dividends are recorded at either the ex-dividend date or on an accrual basis. Asset-backed securities, which are included in our fixed-maturity portfolio, are generally accounted for under the retrospective method. The retrospective method recalculates yield assumptions (based on changes in interest rates or cash flow expectations) historically to the inception of the investment holding period, and applies the required adjustment, if any, to the cost basis, with the offset recorded to investment income. The prospective method is used primarily for interest-only securities, non-investment-grade asset-backed securities, and certain asset-backed securities with sub-prime loan exposure or where there is a greater risk of non-performance and where it is possible the initial investment may not be substantially recovered. The prospective method requires a calculation of expected future repayments and resets the yield to allow for future period adjustments; no current period impact to investment income or the security’s cost is made based on the cash flow update. Prepayment assumptions are updated quarterly. Realized gains (losses) on securities are computed based on the first-in first-out method and include write-downs on available-for-sale securities considered to have other-than-temporary declines in fair value (excluding non-credit related impairments), as well as holding period valuation changes on equity securities, hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument), derivatives, and trading securities. Insurance Premiums and Receivables Insurance premiums written are earned into income on a pro rata basis over the period of risk, based on a daily earnings convention. Accordingly, unearned premiums represent the portion of premiums written that are applicable to the unexpired risk. We provide insurance and related services to individuals and commercial accounts and offer a variety of payment plans. Generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk. For our vehicle businesses, we perform a policy level evaluation to determine the extent to which the premiums receivable balance exceeds the unearned premiums balance. We then age this exposure to establish an allowance for doubtful accounts based on prior experience. For our Property business, we do not establish an allowance for doubtful accounts since the risk of uncollectibility is relatively low. If premiums are unpaid by the policy due date, we provide advance notice of cancellation in accordance with each state’s requirements and, if the premiums remain unpaid after receipt of notice, cancel the policy and write off any remaining balance. Deferred Acquisition Costs Deferred acquisition costs include commissions, premium taxes, and other variable underwriting and direct sales costs incurred in connection with the successful acquisition or renewal of insurance contracts. These acquisition costs, net of ceding allowances, are deferred and amortized over the policy period in which the related premiums are earned. We consider anticipated investment income in determining the recoverability of these costs. Management believes these costs will be fully recoverable in the near term. We do not defer any advertising costs. Total advertising costs, which are expensed as incurred, for the years ended December 31, were: (millions) Advertising Costs 2018 $ 1,422.4 2017 1,005.4 2016 756.2 Loss and Loss Adjustment Expense Reserves Loss reserves represent the estimated liability on claims reported to us, plus reserves for losses incurred but not recorded (IBNR). These estimates are reported net of amounts estimated to be recoverable from salvage and subrogation. Loss adjustment expense reserves represent the estimated expenses required to settle these claims and losses. The methods of making estimates and establishing these reserves are reviewed regularly, and resulting adjustments are reflected in income in the current period. Such loss and loss adjustment expense reserves are susceptible to change in the near term. Reinsurance Our reinsurance transactions include Regulated plans and Non-Regulated plans. The Regulated plans in which we participate are governed by insurance regulations and include state-provided reinsurance facilities (e.g., Michigan Catastrophic Claims Association, Florida Hurricane Catastrophe Fund, North Carolina Reinsurance Facility), as well as state-mandated involuntary plans for commercial vehicles (Commercial Automobile Insurance Procedures/Plans – CAIP) and federally regulated plans for flood (National Flood Insurance Program – NFIP); we act as a servicing agent for CAIP and as a participant in the “Write Your Own” program for the NFIP. The Non-Regulated plans are voluntary contractual arrangements primarily related to the transportation network company business written by our Commercial Lines segment and our Property business. Prepaid reinsurance premiums are earned on a pro rata basis over the period of risk, based on a daily earnings convention, which is consistent with premiums earned. See Note 7 – Reinsurance for further discussion. Income Taxes The income tax provision is calculated under the balance sheet approach. Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. The principal items giving rise to such differences are investment securities (e.g., net unrealized gains (losses), net holding period gains (losses) on securities, write-downs on securities determined to be other-than-temporarily impaired), loss and loss adjustment expense reserves, unearned premiums reserves, deferred acquisition costs, property and equipment, intangible assets, and non-deductible accruals. We review our deferred tax assets regularly for recoverability. The effects of any changes in the tax rate are recorded to our provision for income taxes, including any changes on items initially recognized in accumulated other comprehensive income. See Note 5 – Income Taxes for further discussion. Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation, and include capitalized software developed or acquired for internal use. Depreciation is recognized over the estimated useful lives of the assets using accelerated methods for computer equipment and laptops and the straight-line method for all other fixed assets. We evaluate impairment whenever events or circumstances warrant such a review and write-off the impaired assets if appropriate. The cost and useful lives for property and equipment at December 31, were: ($ in millions) 2018 2017 Useful Lives Buildings, improvements, and integrated components $ 928.8 $ 962.0 7-40 years Capitalized software 327.0 273.1 3-10 years Software licenses (internal use) 259.1 197.0 1-5 years Land 177.0 203.4 NA Computer equipment and laptops 123.2 92.8 3 years All other property and equipment 349.8 331.9 3-15 years Total cost 2,164.9 2,060.2 Accumulated depreciation (1,033.2 ) (940.6 ) Balance at end of year $ 1,131.7 $ 1,119.6 NA = Not applicable At December 31, 2018 and 2017 , included in other assets in the consolidated balance sheets is $39.3 million and $5.3 million , respectively, of “held for sale” property, which represents the fair value of this property less the estimated costs to sell. The increase primarily reflects our decision to transition away from the use of service centers as part of our claims operating model. Total capitalized interest, which primarily relates to capitalized software projects, for the years ended December 31, was: (millions) Capitalized Interest 2018 $ 1.8 2017 2.8 2016 2.9 Goodwill and Intangible Assets Goodwill is the excess of the purchase price over the estimated fair value of the assets and liabilities acquired and represents the future economic benefits arising from other assets acquired that could not be individually identified and separately recognized. Substantially all of the goodwill recorded as of December 31, 2018 and 2017, relates to the April 1, 2015, acquisition of a controlling interest in ARX. Intangible assets primarily arose through the acquisition of ARX and mainly represent the future premiums that will be recognized from the policies and agency relationships that existed at the acquisition date. The majority of the intangible assets have finite lives, which, at December 31, 2018, had a remaining life range from 1 to 10 years. See Note 16 – Goodwill and Intangible Assets for further discussion. We evaluate our goodwill for impairment at least annually using a qualitative approach. If events or changes in circumstances indicate that the carrying value of goodwill or intangible assets may not be recoverable, we will evaluate such items for impairment using a quantitative approach. Guaranty Fund Assessments We are subject to state guaranty fund assessments, which provide for the payment of covered claims or other insurance obligations of insurance companies deemed insolvent. These assessments are accrued after a formal determination of insolvency has occurred, and we have written the premiums on which the assessments will be based. Assessments that are available for recoupment from policyholders are capitalized when incurred; all other assessments are expensed. Fees and Other Revenues Fees and other revenues primarily represent fees collected from policyholders relating to installment charges in accordance with our bill plans, as well as late payment and insufficient funds fees and revenue from ceding commissions. Fees and other revenues are generally earned when invoiced, except for excess ceding commissions, which are earned over the policy period. Service Revenues and Expenses Our service businesses provide insurance-related services. Service revenues and expenses from our commission-based businesses are recorded in the period in which they are earned or incurred. Service revenues generated from processing business for involuntary CAIP plans are earned on a pro rata basis over the term of the related policies. Service expenses related to these CAIP plans are expensed as incurred. Equity-Based Compensation We issue time-based and performance-based restricted stock unit awards to key members of management as our form of equity compensation, and time-based restricted stock awards to non-employee directors. Collectively, we refer to these awards as “restricted equity awards.” Compensation expense for time-based restricted equity awards with installment vesting is recognized over each respective vesting period. For performance-based restricted equity awards, compensation expense is recognized over the respective estimated vesting periods. Dividend equivalent units are credited to outstanding restricted stock unit awards, both time-based and performance-based, at the time a dividend is paid to shareholders and paid upon vesting of the underlying award. We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates. In addition, we shorten the vesting periods of certain time-based restricted equity awards based on the “qualified retirement” provisions in our equity compensation plans, under which (among other provisions) if the participant satisfies certain age and years-of-service requirements, the vesting and distribution of 50% of outstanding time-based restricted equity awards accelerates upon reaching eligibility for a qualified retirement and shortly after the grant date for each subsequent award. ARX also has nonqualified and incentive stock options outstanding that were issued prior to April 2015 as a form of equity compensation to certain of the officers and employees of ARX and its subsidiaries. These outstanding stock options are subject to the put/call features contained in the ARX stockholders’ agreement, pursuant to which The Progressive Corporation has the right, and can be required, to purchase all the shares underlying these awards in 2021. The vested stock options, and the shares issuable upon exercise of the stock options, are also subject to repurchase by ARX if the holder’s employment terminates. See Note 15 – Redeemable Noncontrolling Interest for further discussion. These stock options, which are treated for accounting purposes as liability awards, are expensed over the respective vesting periods based on the Black-Scholes value determined at period end. The total compensation expense recognized for equity-based compensation, including both equity and liability awards, for the years ended December 31, was: (millions) 2018 2017 2016 Pretax expense $ 77.2 $ 95.4 $ 85.2 Tax benefit 1 16.2 33.4 29.8 1 Calculated using the corporate federal tax rate of 21% for 2018 and 35% for 2017 and 2016. Earnings Per Common Share Net income attributable to Progressive is reduced by cumulative preferred share dividends to determine net income available to common shareholders, and is used in our calculation of the per common share amounts. Basic earnings per common share is computed using the weighted average number of common shares outstanding during the reporting period, excluding unvested time-based and performance-based restricted equity awards that are subject to forfeiture. Diluted earnings per common share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents include the incremental shares assumed to be issued for: • earned but unvested time-based restricted equity awards, and • performance-based restricted equity awards that satisfied certain contingency conditions for unvested common stock equivalents during the period; it is highly likely that these awards will continue to satisfy the conditions until the date of vesting. Supplemental Cash Flow Information Cash and cash equivalents include bank demand deposits and daily overnight reverse repurchase commitments of funds held in bank demand deposit accounts by ARX’s subsidiaries. The amount of reverse repurchase commitments held by ARX’s subsidiaries at December 31, 2018 , 2017 , and 2016 , were $117.3 million , $247.2 million , and $150.0 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. Non-cash activity includes declared but unpaid dividends. For the years ended December 31, we paid the following: (millions) 2018 2017 2016 Income taxes $ 702.6 $ 715.6 $ 459.4 Interest 154.0 146.3 139.2 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 also 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, 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 July 2018, the FASB issued an ASU, which provides targeted improvements to the new lease accounting guidance issued by the FASB in February 2016. The ASU, which eliminates the off-balance-sheet accounting for leases, will require 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. Under the ASU, there will be no change to the recognition of lease expense in our results of operations. The ASU will be effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2018 (2019 for calendar-year companies). Under the ASU, companies will have the option to apply the new lease requirements either as of the effective date (i.e., January 1, 2019), with comparative information presented in accordance with the previous standard, or on a modified retrospective basis, which would restate all financial statement information as of the beginning of the earliest period presented. We adopted this standard as of January 1, 2019, and recorded an increase to assets and liabilities of about $215 million , which reflects the present value of future operating lease payments; comparative information is presented in accordance with the previous standard. The ASU had no impact on our results of operations or cash flows. In March 2017, the FASB issued an ASU related to premium amortization on purchased callable debt securities. The intent of the standard is to shorten the amortization period for certain purchased callable debt securities held at a premium. Under the ASU, the premium is required to be amortized to the earliest call date. The ASU more closely aligns interest income recorded on bonds held at a premium with the economics of the underlying instrument. The ASU, which is required to be applied on a modified retrospective basis, is effective for fiscal years beginning after December 15, 2018 (2019 for calendar-year companies), and interim periods within those fiscal years. 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, we do not expect this standard to have a significant 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 condition 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. Additionally, 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 do not expect the ASU to have a material impact on our current method of evaluating investment securities or reinsurance recoverables for credit losses or the timing or recognition of the amounts of the impairment losses. Adopted On January 1, 2018, we adopted the ASU intended to improve the recognition and measurement of financial instruments. Under this update, the changes in fair value of equity securities are recognized as a component of net income. Upon adoption, we recorded a cumulative-effect adjustment of $1.3 billion , which is net of taxes. The cumulative-effect adjustment represents the amount of after-tax net unrealized gains on equity securities that was recorded as part of accumulated other comprehensive income at December 31, 2017. The adoption of this ASU had no impact on comprehensive income. Consistent with our historical presentation, cash flows on equity securities will be reflected as investing activities in the Consolidated Statements of Cash Flows. In the first quarter 2018, we adopted the ASU related to the reclassification of certain tax effects from accumulated other comprehensive income. This update provided companies with the option to reclassify disproportionate tax effects in accumulated other comprehensive income caused by the legislation commonly known as the Tax Cuts and Jobs Act of 2017 to retained earnings. We opted to make the reclassification, which resulted in a decrease to accumulated other comprehensive income and an offsetting increase to retained earnings of $4.3 million . This reclass was solely due to the effect of the change in the U.S. federal tax rate on our available-for-sale fixed-maturity securities and our hedges on forecasted transactions. There were no disproportionate tax effects related to our equity securities subsequent to adopting the ASU related to classification and measurement discussed above.

Investments

Investments	12 Months Ended
	Dec. 31, 2018
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. The changes in the net holding period gains (losses) between periods for the hybrid securities and, beginning in 2018 , equity securities are recorded as a component of net realized gains (losses) on securities in our Consolidated Statements of Comprehensive Income. Prior to 2018, the change in fair value of our equity securities was part of accumulated other comprehensive income (see Note 1 – Reporting and Accounting Policies for further discussion). For comparative purposes, the change in fair value of the hybrid securities that was recognized in 2017 and 2016 was reclassified out of "net realized gains (losses) on security sales" and into "net holding period gains (losses) on securities" to conform to the current year presentation. ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair 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 % ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair Value December 31, 2017 Fixed maturities: U.S. government obligations $ 6,688.8 $ 1.1 $ (44.0 ) $ 0 $ 6,645.9 24.4 % State and local government obligations 2,285.6 20.7 (9.3 ) 0.1 2,297.1 8.4 Corporate debt securities 4,997.2 14.8 (14.4 ) 0.1 4,997.7 18.3 Residential mortgage-backed securities 828.8 11.3 (3.4 ) 0 836.7 3.1 Commercial mortgage-backed securities 2,760.1 11.8 (13.3 ) 0 2,758.6 10.1 Other asset-backed securities 2,454.5 4.5 (4.5 ) 0.2 2,454.7 9.0 Redeemable preferred stocks 194.9 17.8 (1.5 ) (0.2 ) 211.0 0.8 Total fixed maturities 20,209.9 82.0 (90.4 ) 0.2 20,201.7 74.1 Short-term investments 2,869.4 0 0 0 2,869.4 10.5 Total fixed maturities and short-term 23,079.3 82.0 (90.4 ) 0.2 23,071.1 84.6 Equity securities: Nonredeemable preferred stocks 698.6 114.0 (8.8 ) 0 803.8 2.9 Common equities 1,499.0 1,901.0 (0.2 ) 0 3,399.8 12.5 Total equity securities 2,197.6 2,015.0 (9.0 ) 0 4,203.6 15.4 Total available-for-sale portfolio 1,2 $ 25,276.9 $ 2,097.0 $ (99.4 ) $ 0.2 $ 27,274.7 100.0 % 1 Our portfolio reflects the effect of unsettled security transactions; at December 31, 2018 , $5.9 million was included in “other liabilities,” compared to $5.8 million in “other assets” at December 31, 2017 . 2 The total fair value of the portfolio at December 31, 2018 and 2017 included $2.9 billion and $1.6 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. At December 31, 2018 , bonds and certificates of deposit in the principal amount of $250.8 million were on deposit to meet state insurance regulatory and/or rating agency requirements. We did not hold any securities of any one issuer, excluding U.S. government obligations, with an aggregate cost or fair value exceeding 10% of total shareholders’ equity at December 31, 2018 or 2017 . At December 31, 2018 , we did not hold any debt securities that were non-income producing during the preceding 12 months. Short-Term Investments Our short-term investments may include commercial paper and other investments that are expected to mature or are redeemable within one year. We did not have any open repurchase or reverse repurchase transactions in our short-term investment portfolio at December 31, 2018 or 2017 . To the extent we enter into repurchase or reverse repurchase transactions, and 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 maturities are hybrid securities, which are reported at fair value at December 31 : (millions) 2018 2017 Fixed Maturities: State and local government obligations $ 3.6 $ 6.1 Corporate debt securities 158.9 99.8 Other asset-backed securities 4.5 6.7 Redeemable preferred stocks 77.7 30.3 Total hybrid securities $ 244.7 $ 142.9 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 December 31, 2018 , was: (millions) Cost Fair Value Less than one year $ 4,880.1 $ 4,867.0 One to five years 17,719.4 17,652.0 Five to ten years 5,581.3 5,517.5 Ten years or greater 75.1 75.0 Total $ 28,255.9 $ 28,111.5 Asset-backed securities are classified in the maturity distribution table based upon their projected cash flows. All other securities that do not have a single maturity date are reported based upon expected average maturity. Contractual maturities may differ from expected maturities because the issuers of the securities may have the right to call or prepay obligations. Gross Unrealized Losses As of December 31, 2018 , we had $249.6 million of gross unrealized losses in our fixed-maturity securities. A review of these securities indicated that the issuers were current with respect to their interest obligations and that there was no evidence of deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Value Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Value Unrealized Losses No. of Sec. Fair Value 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 ) Total No. of Sec. Total Fair Value Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Value Unrealized Losses No. of Sec. Fair Value Unrealized Losses December 31, 2017 Fixed maturities: U.S. government obligations 58 $ 5,817.0 $ (44.0 ) 41 $ 4,869.3 $ (34.6 ) 17 $ 947.7 $ (9.4 ) State and local government obligations 358 1,200.3 (9.3 ) 230 737.6 (4.4 ) 128 462.7 (4.9 ) Corporate debt securities 222 2,979.4 (14.4 ) 171 2,072.9 (9.1 ) 51 906.5 (5.3 ) Residential mortgage-backed securities 201 300.9 (3.4 ) 30 75.1 (0.2 ) 171 225.8 (3.2 ) Commercial mortgage-backed securities 105 1,682.3 (13.3 ) 63 1,221.2 (5.9 ) 42 461.1 (7.4 ) Other asset-backed securities 197 1,837.3 (4.5 ) 134 1,377.8 (3.3 ) 63 459.5 (1.2 ) Redeemable preferred stocks 2 21.8 (1.5 ) 1 10.8 (0.1 ) 1 11.0 (1.4 ) Total fixed maturities 1,143 13,839.0 (90.4 ) 670 10,364.7 (57.6 ) 473 3,474.3 (32.8 ) Equity securities: Nonredeemable preferred stocks 4 127.8 (8.8 ) 1 56.5 (0.5 ) 3 71.3 (8.3 ) Common equities 19 13.4 (0.2 ) 18 13.4 (0.2 ) 1 0 0 Total equity securities 23 141.2 (9.0 ) 19 69.9 (0.7 ) 4 71.3 (8.3 ) Total portfolio 1,166 $ 13,980.2 $ (99.4 ) 689 $ 10,434.6 $ (58.3 ) 477 $ 3,545.6 $ (41.1 ) During 2018 , the number of securities in our fixed-maturity portfolio with unrealized losses increased slightly as a result of rising interest rates. We had no material decreases in valuation as a result of credit rating downgrades during the year and all of the securities in the table above are current with respect to required principal and interest payments. 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): December 31, (millions) 2018 2017 Fixed maturities: Residential mortgage-backed securities $ (19.7 ) $ (19.7 ) Commercial mortgage-backed securities (0.1 ) (0.3 ) Total fixed maturities $ (19.8 ) $ (20.0 ) The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended December 31, 2018 , 2017 , and 2016 , 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: (millions) Residential Mortgage- Backed Commercial Mortgage- Backed Total Total at December 31, 2017 $ 0 $ 0.5 $ 0.5 Credit losses for which an OTTI was not previously recognized 0 0 0 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Total at December 31, 2018 $ 0 $ 0.5 $ 0.5 (millions) Residential Mortgage- Backed Commercial Mortgage- Backed Total Total at December 31, 2016 $ 11.1 $ 0.4 $ 11.5 Credit losses for which an OTTI was not previously recognized 0 0.4 0.4 Reductions for securities sold/matured (10.9 ) (0.3 ) (11.2 ) Change in recoveries of future cash flows expected to be collected 1 (0.2 ) 0 (0.2 ) Total at December 31, 2017 $ 0 $ 0.5 $ 0.5 (millions) Residential Mortgage- Backed Commercial Mortgage- Backed Total Total at December 31, 2015 $ 12.4 $ 0.4 $ 12.8 Credit losses for which an OTTI was not previously recognized 0 0 0 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 (1.3 ) 0 (1.3 ) Total at December 31, 2016 $ 11.1 $ 0.4 $ 11.5 1 Reflects expected recovery of prior period impairments that will be accreted into income over the remaining life of the security. Although we determined it is more likely that we will not 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 not have any credit impairment write-downs for the year ended December 31, 2018 . Realized Gains (Losses) The components of net realized gains (losses) for the years ended December 31, were: (millions) 2018 2017 2016 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 6.7 $ 6.2 $ 24.6 State and local government obligations 9.5 10.5 16.0 Corporate and other debt securities 2.4 20.3 43.3 Residential mortgage-backed securities 0 23.8 2.5 Commercial mortgage-backed securities 2.0 4.9 13.3 Other asset-backed securities 0.1 0.3 0 Redeemable preferred stocks 4.5 8.5 20.9 Short-term investments 0 0 0.1 Total available-for-sale securities 25.2 74.5 120.7 Equity securities: Nonredeemable preferred stocks 4.1 58.4 11.9 Common equities 286.6 43.0 61.3 Total equity securities 290.7 101.4 73.2 Subtotal gross realized gains on security sales 315.9 175.9 193.9 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (98.7 ) (28.7 ) (2.4 ) State and local government obligations (2.9 ) (0.1 ) (1.6 ) Corporate and other debt securities (10.4 ) (5.1 ) (2.5 ) Residential mortgage-backed securities (0.1 ) (0.4 ) (0.2 ) Commercial mortgage-backed securities (6.3 ) (5.3 ) (5.6 ) Other asset-backed securities (1.1 ) (0.4 ) 0 Redeemable preferred stocks (0.1 ) (6.4 ) (6.6 ) Short-term investments 0 (0.2 ) (0.1 ) Total available-for-sale securities (119.6 ) (46.6 ) (19.0 ) Equity securities: Nonredeemable preferred stocks (3.9 ) (5.9 ) (5.3 ) Common equities (21.7 ) (12.2 ) (15.7 ) Total equity securities (25.6 ) (18.1 ) (21.0 ) Subtotal gross realized losses on security sales (145.2 ) (64.7 ) (40.0 ) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations (92.0 ) (22.5 ) 22.2 State and local government obligations 6.6 10.4 14.4 Corporate and other debt securities (8.0 ) 15.2 40.8 Residential mortgage-backed securities (0.1 ) 23.4 2.3 Commercial mortgage-backed securities (4.3 ) (0.4 ) 7.7 Other asset-backed securities (1.0 ) (0.1 ) 0 Redeemable preferred stocks 4.4 2.1 14.3 Short-term investments 0 (0.2 ) 0 Total available-for-sale securities (94.4 ) 27.9 101.7 Equity securities: Nonredeemable preferred stocks 0.2 52.5 6.6 Common equities 264.9 30.8 45.6 Total equity securities 265.1 83.3 52.2 Litigation settlements and other gains (losses) 0 1.2 0.4 Subtotal net realized gains (losses) on security sales 170.7 112.4 154.3 Net holding period gains (losses) Hybrid securities (10.4 ) (1.6 ) 2.1 Equity securities (497.5 ) 0 0 Derivatives 0 0 (20.0 ) Subtotal net holding period gains (losses) (507.9 ) (1.6 ) (17.9 ) Other-than-temporary impairment losses Fixed maturities: Commercial mortgage-backed securities 0 (0.4 ) 0 Redeemable preferred stocks 0 0 (25.3 ) Total fixed maturities 0 (0.4 ) (25.3 ) Equity securities: Common equities 0 (11.2 ) (0.3 ) Subtotal investment other-than-temporary impairment losses 0 (11.6 ) (25.6 ) Other asset impairment (68.3 ) (49.6 ) (59.7 ) Subtotal other-than-temporary impairment losses (68.3 ) (61.2 ) (85.3 ) Total net realized gains (losses) on securities $ (405.5 ) $ 49.6 $ 51.1 Gross realized gains in 2018 were predominantly in common equities as we sold a portion of our holdings twice during the year in an effort to reduce the portfolio’s overall risk profile. Gross realized losses in 2018 were primarily in treasury securities, within our fixed-maturity portfolio. Treasury securities are used to manage our overall portfolio duration and with the volatility in interest rates during 2018, we were active in managing the portfolio’s duration to limit potentially significant negative impacts to the fixed-maturity portfolio’s overall valuation. Also included are holding period gains and losses, related to valuation changes on equity securities and hybrid securities, recoveries from litigation settlements related to investments, and write-downs for securities determined to be other-than-temporarily impaired. The other asset impairment relates to renewable energy investments, which are reflected in “other assets” on the balance sheet, under which the future pretax cash flows are expected to be less than the carrying value of the assets. See Note 5 - Income Taxes for the tax benefits related to these investments. The following table reflects our holding period realized gains (losses) on equity securities recognized for the year ended December 31, 2018 for equity securities held at year end: (millions) 2018 Total net gains (losses) recognized during the period on equity securities $ (232.4 ) Less: Net gains (losses) recognized on equity securities sold during the period 265.1 Net holding period gains (losses) recognized during the period on equity securities held at period end $ (497.5 ) Note: Comparative disclosure for the prior year period is not meaningful. Net Investment Income The components of net investment income for the years ended December 31, were: (millions) 2018 2017 2016 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 196.8 $ 72.7 $ 18.2 State and local government obligations 37.7 51.5 52.3 Foreign government obligations 0 0.3 0.4 Corporate debt securities 217.9 125.2 110.7 Residential mortgage-backed securities 27.6 34.7 47.3 Commercial mortgage-backed securities 93.9 79.6 81.6 Other asset-backed securities 75.7 47.1 28.0 Redeemable preferred stocks 12.3 11.8 14.9 Total fixed maturities 661.9 422.9 353.4 Short-term investments 52.9 37.8 19.7 Total available-for-sale securities 714.8 460.7 373.1 Equity securities: Nonredeemable preferred stocks 45.9 44.1 48.6 Common equities 59.8 58.3 57.2 Total equity securities 105.7 102.4 105.8 Investment income 820.5 563.1 478.9 Investment expenses (24.3 ) (23.9 ) (22.4 ) Net investment income $ 796.2 $ 539.2 $ 456.5 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 increases in net investment income in 2018 and 2017, were 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 underwriting growth and profitability, as well as the proceeds from debt and preferred stock issuances. The increase in portfolio yields was a result of our decisions to hold a short-duration portfolio, which allowed us to reinvest significant maturities and paydowns of principal at higher yields, and to increase the portfolio duration from 2.2 years at December 31, 2016 to 2.5 years at December 31, 2017 , and finally to 2.8 years at December 31, 2018 , as interest rates generally rose. Trading Securities At December 31, 2018 and 2017 , we did not hold any trading securities and we did not have any net realized gains (losses) on trading securities for the years ended December 31, 2018 , 2017 , and 2016 . Derivative Instruments At December 31, 2018 , 2017 , and 2016 , we had no open derivative positions. During 2018, we reclassified $1.0 million of net unrealized losses from accumulated other comprehensive income to interest expense on our closed debt issuance cash flow hedges, compared to net unrealized gains of $0.3 million and $1.9 million during 2017 and 2016, respectively. During March 2017 , we entered into a forecasted debt issuance hedge, against a possible rise in interest rates, in conjunction with the $850 million of 4.125% Senior Notes due 2047 issued in April 2017 . Upon issuance, we closed the hedge and recognized, as part of accumulated other comprehensive income, a pretax unrealized loss of $8.0 million in April 2017. From time to time, we use interest rate swaps and treasury futures contracts to manage the fixed-income portfolio duration. During 2016 , we closed interest rate swaps and treasury futures contracts with notional values of $750 million and $135 million , respectively. We recorded a net realized loss of $19.0 million on the interest rate swaps and a net realized gain of $0.3 million on the treasury futures.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value	FAIR VALUE We have categorized our financial instruments, based on the degree of subjectivity inherent in the method by which they are valued, into a fair value hierarchy of three levels, as follows: • Level 1 : Inputs are unadjusted, quoted prices in active markets for identical instruments at the measurement date (e.g., U.S. government obligations, which are continually priced on a daily basis, active exchange-traded equity securities, and certain short-term securities). • Level 2 : Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 : Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments). Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations. The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 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 (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2017 Fixed maturities: U.S. government obligations $ 6,645.9 $ 0 $ 0 $ 6,645.9 $ 6,688.8 State and local government obligations 0 2,297.1 0 2,297.1 2,285.6 Corporate debt securities 0 4,997.7 0 4,997.7 4,997.2 Subtotal 6,645.9 7,294.8 0 13,940.7 13,971.6 Asset-backed securities: Residential mortgage-backed 0 836.7 0 836.7 828.8 Commercial mortgage-backed 0 2,758.6 0 2,758.6 2,760.1 Other asset-backed 0 2,454.7 0 2,454.7 2,454.5 Subtotal asset-backed securities 0 6,050.0 0 6,050.0 6,043.4 Redeemable preferred stocks: Financials 0 64.1 0 64.1 61.3 Utilities 0 11.4 0 11.4 10.1 Industrials 0 135.5 0 135.5 123.5 Subtotal redeemable preferred stocks 0 211.0 0 211.0 194.9 Total fixed maturities 6,645.9 13,555.8 0 20,201.7 20,209.9 Short-term investments 1,824.4 1,045.0 0 2,869.4 2,869.4 Total fixed maturities and short-term 8,470.3 14,600.8 0 23,071.1 23,079.3 Equity securities: Nonredeemable preferred stocks: Financials 80.6 718.2 0 798.8 693.6 Utilities 0 0 0 0 0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 80.6 718.2 5.0 803.8 698.6 Common equities: Common stocks 3,399.5 0 0 3,399.5 1,498.7 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,399.5 0 0.3 3,399.8 1,499.0 Total equity securities 3,480.1 718.2 5.3 4,203.6 2,197.6 Total available-for-sale portfolio $ 11,950.4 $ 15,319.0 $ 5.3 $ 27,274.7 $ 25,276.9 Debt $ 0 $ 3,606.5 $ 37.1 $ 3,643.6 $ 3,306.3 Our portfolio valuations, excluding short-term investments, classified as either Level 1 or Level 2 in the above tables are priced exclusively by external sources, including: pricing vendors, dealers/market makers, and exchange-quoted prices. Our short-term security holdings 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 securities are classified as Level 2 and are not priced externally since these securities continually trade at par value. These securities are classified as Level 2 since they are primarily longer-dated securities issued by municipalities that contain either liquidity facilities or mandatory put features within one year. At December 31, 2018 , vendor-quoted prices represented 79% of our Level 1 classifications (excluding short-term investments), compared to 66% at December 31, 2017 . 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 December 31, 2018 , vendor-quoted prices comprised 99% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented 1% , compared to 98% and 2% at December 31, 2017 , respectively. 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, which often leads the source to adjust their pricing input data for future pricing. 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 and fixed-income investments included in the Level 3 category are valued using external pricing supplemented by internal review and analysis. After all the valuations are received and our review is complete, if the inputs used by vendors are determined to not contain sufficient observable market information, we will reclassify the affected security valuations to Level 3. At December 31, 2018 and 2017 , we did not have any securities in our fixed-maturity portfolio listed as Level 3. At December 31, 2018 , we owned two privately held nonredeemable preferred securities with a combined value of $30.1 million that were priced internally, compared to one private nonredeemable preferred security with a value of $5.0 million that was priced internally at December 31, 2017 . At December 31, 2018 , and 2017 , we held one Level 3 other risk investment with a value of $0.3 million . We review the prices from our external sources for reasonableness using internally developed assumptions to derive prices for the Level 3 securities, which are then compared to the prices we received. During 2018 or 2017 , there were no material assets or liabilities measured at fair value on a nonrecurring basis. Based on our review, all prices received from external sources remained unadjusted. Due to the relative size of the Level 3 securities’ fair values compared to the total portfolio’s fair value, any changes in pricing methodology would not have a significant change in valuation that would materially impact net or comprehensive income. The following tables provide a summary of changes in fair value associated with Level 3 assets for the years ended December 31, 2018 and 2017 : Level 3 Fair Value (millions) Fair Value at Dec. 31, 2017 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at Dec. 31, 2018 Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Equity securities: Nonredeemable preferred stocks: Financials 0 0 25.1 0 0 0 0 25.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 5.3 $ 0 $ 25.1 $ 0 $ 0 $ 0 $ 0 $ 30.4 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2016 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at Dec. 31, 2017 Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 0.3 $ (0.3 ) $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Industrials 0 0 5.0 0 0 0 0 5.0 Common equities: Other risk investments 0.4 (0.1 ) 0 0 0 0 0 0.3 Total Level 3 securities $ 0.7 $ (0.4 ) $ 5.0 $ 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 December 31 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2018 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 25.1 Internal price Unadjusted purchase price 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 privately held. 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 privately held. The price at December 31, 2018 , 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 Dec. 31, 2017 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 3.9 Subtotal Level 3 securities 5.0 Pricing exemption securities 2 0.3 Total Level 3 securities $ 5.3 NA= Not Available 1 The security was internally-priced since it is privately held. The security was purchased during third quarter 2017 and the value at December 31, 2017, reflects the unadjusted purchase price per share. 2 The unobservable input is not reasonably available to us.

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	DEBT Debt at December 31, consisted of: 2018 2017 (millions) Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 (issued: $500.0, August 2011) $ 499.1 $ 506.5 $ 498.8 $ 520.7 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) 496.5 455.5 496.1 477.9 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 296.4 368.5 296.1 382.3 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 544.5 562.4 0 0 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 395.5 496.6 395.3 516.9 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.6 350.2 346.5 388.7 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.3 366.7 395.2 402.9 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 841.4 831.9 841.2 917.1 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 589.6 594.0 0 0 Other debt instruments 1 0 0 37.1 37.1 Total $ 4,404.9 $ 4,532.3 $ 3,306.3 $ 3,643.6 1 Consist of term loans issued by ARX prior to The Progressive Corporation acquiring a controlling interest in 2015. The repayment was funded in part with proceeds from fixed-rate loans made to ARX by The Progressive Corporation. These intercompany transactions were eliminated in consolidation. Aggregate required principal payments on debt outstanding at December 31, 2018, are as follows: (millions) Year Payments 2019 $ 0 2020 0 2021 500 2022 0 2023 0 Thereafter 3,950 Total $ 4,450 All of the outstanding debt was issued by The Progressive Corporation and includes amounts that were borrowed and contributed to the capital of its insurance subsidiaries or used, or made available for use, for other business purposes. Fair values for these debt instruments are obtained from external sources. There are no restrictive financial covenants or credit rating triggers on the outstanding debt. Interest on all debt is payable semiannually at the stated rates. All principal is due at the maturity stated in the tables above. Each note is redeemable, in whole or in part, at any time; however, the redemption price will equal the greater of the principal amount of the note or a “make whole” amount calculated by reference to the present values of remaining scheduled principal and interest payments under the note. We issued $550 million of 4.00% Senior Notes due 2029 in October 2018, $600 million of 4.20% Senior Notes due 2048 in March 2018, and $850 million of 4.125% Senior Notes due 2047 in April 2017, in underwritten public offerings. The net proceeds from these issuances, after deducting underwriters’ discounts, commissions, and other issuance costs, were approximately $544.5 million , $589.5 million , and $841.1 million , respectively. Prior to certain issuances of our debt securities, we entered into forecasted transactions to hedge against possible rises in interest rates. When the contracts were closed upon the issuance of the applicable debt securities, we recognized the unrealized gains (losses) on these contracts as part of accumulated other comprehensive income (see Note 1 – Reporting and Accounting Policies for further discussion). These unrealized gains (losses) are being amortized as adjustments to interest expense over the life of the related notes. The following table shows the original gain (loss) recognized at debt issuance and the unamortized balance at December 31, 2018 , on a pretax basis: (millions) Unrealized Gain (Loss) at Debt Issuance Unamortized Balance at December 31, 2018 3.75% Senior Notes $ (5.1 ) $ (1.5 ) 6 5/8% Senior Notes (4.2 ) (2.6 ) 6.25% Senior Notes 5.1 3.5 4.35% Senior Notes (1.6 ) (1.5 ) 3.70% Senior Notes (12.9 ) (11.9 ) 4.125% Senior Notes (8.0 ) (7.8 ) During 2018, The Progressive Corporation entered into a new line of credit with PNC Bank, National Association (PNC) in the maximum principal amount of $250 million . The prior line of credit, entered into in 2017, expired in April 2018. The line of credit has the same terms and conditions of the previous line of credit. Subject to the terms and conditions of the line of credit documents, advances under the line of credit (if any) will bear interest at a variable rate equal to the higher of PNC’s Prime Rate or the sum of the Federal Funds Open Rate plus 50 basis points. Each advance must be repaid on the 30 th day after the advance or, if earlier, on April 30, 2019, the expiration date of the line of credit. Prepayments are permitted without penalty. The line of credit is uncommitted and, as such, all advances are subject to PNC’s discretion. We had no borrowings under either line of credit in 2018 or 2017.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The components of our income tax provision were as follows: (millions) 2018 2017 2016 Current tax provision Federal $ 673.1 $ 680.9 $ 469.6 State 21.5 12.8 12.7 Deferred tax expense (benefit) Federal (145.9 ) (149.4 ) (66.3 ) State (6.1 ) (3.5 ) (2.5 ) Total income tax provision $ 542.6 $ 540.8 $ 413.5 The provision for income taxes in the accompanying consolidated statements of comprehensive income differed from the statutory rate as follows: ($ in millions) 2018 2017 2016 Income before income taxes $ 3,163.6 $ 2,138.9 $ 1,470.7 Tax at statutory federal rate $ 664.4 21 % $ 748.6 35 % $ 514.8 35 % Tax effect of: Tax credits 1 (76.3 ) (2 ) (52.4 ) (2 ) (62.2 ) (4 ) Stock-based compensation 2 (25.1 ) (1 ) (25.1 ) (1 ) 0 0 Tax-deductible dividends (14.6 ) (1 ) (9.7 ) 0 (6.1 ) 0 Dividends received deduction 3, 4 (9.7 ) 0 (20.7 ) (1 ) (22.6 ) (2 ) Exempt interest income 4 (5.9 ) 0 (16.9 ) (1 ) (15.7 ) (1 ) Nondeductible compensation expense 5 (0.2 ) 0 10.1 0 0.5 0 Net deferred tax liability revaluation 6 0 0 (99.5 ) (5 ) 0 0 State income taxes, net of federal taxes 12.2 0 6.0 0 6.6 0 Other items, net (2.2 ) 0 0.4 0 (1.8 ) 0 Total income tax provision $ 542.6 17 % $ 540.8 25 % $ 413.5 28 % 1 Includes $ 71.0 million , $ 48.7 million , and $58.7 million for 2018, 2017, and 2016, respectively, of benefits on investments in federal renewable energy tax credit funds. 2 Represents excess tax benefits associated with share-based payments awards. Prior to 2017, these excess tax benefits were recorded directly to additional paid-in capital under the then existing accounting guidance. 3 2018 amount reflects a dividends received deduction percentage of 50% under the 2017 Tax Act. In 2017 and prior years the deduction percentage was 70% . 4 2018 amounts reflect a proration percentage of 25% for such income attributable to investments held by our insurance companies. In 2017 and prior years the proration percentage was 15% . 5 Decrease in 2018 reflects our updated interpretation regarding compensation that qualifies for deduction under the 2017 Tax Act based on additional guidance issued. Increase in 2017 primarily reflected our initial interpretation regarding the deductibility of such compensation. See further discussion below. 6 Pursuant to the 2017 Tax Act. We understand that the sponsor of three federal renewable energy tax credit funds in which we invested from 2016 through 2018, along with the owners of the sponsor, are under investigation by federal authorities. We have also learned that the sponsor and certain related entities filed for bankruptcy protection in early February 2019 and, since then, federal authorities filed a forfeiture action in federal court against certain real estate and related entities owned, directly or indirectly, by the sponsor’s owners. The forfeiture action alleges that the sponsor and its owners engaged in fraud in connection with its operations and the establishment of certain tax credit funds. Our investment in these transactions generated approximately $150 million of tax benefits. We cannot predict if these matters will lead to an impact on the validity of any portion of these federal tax credits or require an additional write down on the related investments, which were valued at $24.3 million , in the aggregate, as of December 31, 2018. On December 22, 2017, legislation commonly known as the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”) was signed into law. One of the provisions of the 2017 Tax Act reduced the corporate federal income tax rate from 35% to 21% effective January 1, 2018. Pursuant to current accounting guidance, all deferred tax assets and liabilities at December 31, 2017, were revalued to recognize the tax rate that is expected to apply when the tax effects are ultimately recognized in future periods. The impact of revaluing the deferred tax assets and liabilities from 35% to 21% was a net reduction to income tax expense of $99.5 million in 2017, as disclosed in the table above. This revaluation adjustment included a $275.7 million reduction related to the deferred tax liability associated with the net unrealized gains on our investment portfolio, which was originally recorded as a component of other comprehensive income and not through the tax provision. The remaining $176.2 million , which increased the tax provision, was associated with our other deferred tax assets and liabilities identified in the table below. As of December 31, 2018, we updated our accounting for the tax effects of the enactment of the 2017 Tax Act, which we were not able to fully complete at December 31, 2017, with regards to the following: • We reversed $3.9 million of the $4.5 million provisional tax amount that we recorded in 2017 related to deductibility of compensation expense for certain covered executives due to uncertainty surrounding the appropriate tax treatment of outstanding performance-based awards at that time. The IRS issued additional guidance during 2018 that clarified the treatment of these awards. We also recorded a benefit of $0.3 million in 2018 related to compensation expense for time-based awards granted to the chief financial officer that we had treated as nondeductible at December 31, 2017. The benefit of both of these amounts is reflected in the nondeductible compensation expense line item in the table above for the 2018 year. • We recorded an increase to the deferred tax asset for loss and loss adjustment expense reserves of $67.1 million and an offsetting deferred tax liability in the same amount for the transition adjustment, which is recognized over an 8-year period as required by the 2017 Tax Act. At December 31, 2017, we did not record any amounts related to the changes in loss reserve discounting required by the 2017 Tax Act since the IRS had not yet published new discount factors based on loss payment patterns and interest rates determined under the 2017 Tax Act and we were unable to make a reasonable estimate. The IRS published the new discount factors in 2018, which allowed us to compute the adjustments. The impact of these amounts are included in the 2018 deferred tax assets and liabilities and are reflected in the table below. Deferred income taxes reflect the effect for financial statement reporting purposes of temporary differences between the financial statement carrying amounts and the tax bases of assets and liabilities. The following table shows the components of the net deferred tax asset (liability) at December 31, 2018 and 2017 , respectively. As noted above, the federal deferred tax assets (liabilities) at December 31, 2017, have been revalued to reflect the new 21% federal corporate income tax rate under the 2017 Tax Act. (millions) 2018 2017 Federal deferred tax assets: Unearned premiums reserve $ 439.9 $ 368.9 Non-deductible accruals 169.3 166.0 Loss and loss adjustment expense reserves 134.6 48.4 Net unrealized losses on fixed-maturity securities 28.2 0 Hedges on forecasted transactions 4.6 4.8 Other 16.2 7.3 Federal deferred tax liabilities: Net holding period gains on equity securities (316.8 ) 0 Deferred acquisition costs (199.8 ) (163.9 ) Property and equipment (85.7 ) (75.5 ) Loss and loss adjustment expense reserve transition adjustment (58.5 ) 0 Intangible assets (52.2 ) (66.6 ) Investment basis differences (43.3 ) (5.5 ) Prepaid expenses (4.7 ) (7.1 ) Deferred gain on extinguishment of debt 0 (0.4 ) Net unrealized gains on securities 0 (419.5 ) Other (8.9 ) (6.1 ) Net federal deferred tax asset (liability) 22.9 (149.2 ) Net state deferred tax asset 20.3 14.2 Net deferred tax asset (liability) $ 43.2 $ (135.0 ) Although realization of the deferred tax assets is not assured, management believes that it is more likely than not that the deferred tax assets will be realized based on our expectation that we will be able to fully utilize the deductions that are ultimately recognized for tax purposes and, therefore, no valuation allowance was needed at December 31, 2018 or 2017 . At December 31, 2018 and 2017, we had $16.8 million and $23.8 million , respectively, of net taxes payable (included in other liabilities on the balance sheet). The Progressive Corporation and its wholly-owned subsidiaries file a consolidated federal income tax return. Effective April 2, 2018, we acquired additional shares of ARX to increase our ownership above 80% . As a result, ARX and its subsidiaries will be included in The Progressive Corporation consolidated federal income tax return for the period from April 3 to December 31, 2018. ARX will file a final consolidated federal income tax return with its subsidiaries for the period from January 1 to April 2, 2018. The Progressive Corporation and its wholly-owned subsidiaries have been a participant in the Compliance Assurance Program (CAP) since 2007. Under CAP, the IRS begins its examination process for the tax year before the tax return is filed, by examining significant transactions and events as they occur; however, a CAP examination does not include equity investments in pass-through entities in which the taxpayer owns less than 100% (e.g., partnerships, joint ventures, etc.). The goal of the CAP program is to expedite the exam process and to reduce the level of uncertainty regarding a taxpayer’s tax filing positions. All federal income tax years prior to 2015 are closed to examination for both The Progressive Corporation and ARX. The IRS CAP exams for 2015-2017 for The Progressive Corporation have been completed and the returns were accepted as filed. We consider these years to be effectively settled. The 2018 tax year remains open to examination. For 2017 and prior years, ARX and its wholly owned subsidiaries filed their own consolidated federal income tax returns since we owned less than 80% of their outstanding stock. All tax years prior to 2015 are closed and the 2015-2018 tax years remain open to examination. The statute of limitations for state income tax purposes generally remains open for three to four years from the return filing date, depending upon the jurisdiction. There has been no significant state income tax audit activity. We recognize interest and penalties, if any, as a component of income tax expense. For the years ended December 31, 2018, 2017, and 2016, $0 , $0.2 million , and less than $0.1 million , respectively, of interest and penalties expense has been recorded in the tax provision. We have not recorded any unrecognized tax benefits, or any related interest and penalties, as of December 31, 2018 and 2017 .

Loss And Loss Adjustment Expens

Loss And Loss Adjustment Expense Reserves	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Loss And Loss Adjustment Expense Reserves	LOSS AND LOSS ADJUSTMENT EXPENSE RESERVES We write personal and commercial auto insurance, residential property insurance, and other specialty property-casualty insurance and related services throughout the United States. As a property-casualty insurance company, we are exposed to hurricanes or other catastrophes. To help mitigate this risk, we maintain excess of loss and aggregate stop-loss reinsurance coverage on our Property business. Although the occurrence of a major catastrophe could have a significant effect on our monthly or quarterly results, we believe that, based on historical experience, such an event would not be so material as to disrupt the overall normal operations of Progressive. We are unable to predict the frequency or severity of any such events that may occur in the near term or thereafter. As we are primarily an insurer of motor vehicles and residential property, we have limited exposure to environmental, asbestos, and general liability claims. We have established reserves for such exposures, which represent about 0.05% of our total loss and loss adjustment expense reserves. We believe these reserves to be adequate based on information currently known. These claims are not expected to have a material effect on our liquidity, financial condition, cash flows, or results of operations. Loss and Loss Adjustment Expense Reserves Loss and loss adjustment expense (LAE) reserves represent our best estimate of our ultimate liability for losses and LAE relating to events that occurred prior to the end of any given accounting period but have not yet been paid. For our vehicle businesses, which represent about 97% of our total carried reserves, we establish loss and LAE reserves after completing reviews at a disaggregated level of grouping. Progressive’s actuarial staff reviews over 400 subsets of business data, which are at a combined state, product, and line coverage level, to calculate the needed loss and LAE reserves. During a reserve review, ultimate loss amounts are estimated using several industry standard actuarial projection methods. These methods take into account historical comparable loss data at the subset level and estimate the impact of various loss development factors, such as the frequency (number of losses per earned car year), severity (dollars of loss per each claim), and average premium (dollars of premium per earned car year), as well as the frequency and severity of loss adjustment expense costs. We begin our review of a set of data by producing multiple estimates of needed reserves, using both paid and incurred data, to determine if a reserve change is required. In the event of a wide variation among results generated by the different projections, our actuarial group will further analyze the data using additional quantitative analysis. Each review develops a point estimate for a relatively small subset of the business, which allows us to establish meaningful reserve levels for that subset. We believe our comprehensive process of reviewing at a subset level provides us more meaningful estimates of our aggregate loss reserves. The actuarial staff completes separate projections of needed case and incurred but not recorded (IBNR) reserves. Since a large majority of the parties involved in an accident report their claims within a short time period after the occurrence, we do not carry a significant amount of IBNR reserves for older accident years. Based on the methodology we use to estimate case reserves for our vehicle businesses, we do not have expected development on reported claims included in our IBNR reserves. We do, however, include anticipated salvage and subrogation recoveries in our IBNR reserves, which could result in negative carried IBNR reserves, primarily in our physical damage reserves. Changes from historical data may reduce the predictiveness of our projected future loss costs. Internal considerations that are process-related, which generally result from changes in our claims organization’s activities, include claim closure rates, the number of claims that are closed without payment, and the level of the claims representatives’ estimates of the needed case reserve for each claim. These changes and their effect on the historical data are studied at the state level versus on a larger, less indicative, countrywide basis. External items considered include the litigation atmosphere, state-by-state changes in medical costs, and the availability of services to resolve claims. These also are better understood at the state level versus at a more macro, countrywide level. The actuarial staff takes these changes into consideration when making their assumptions to determine needed reserve levels. Similar to our vehicle businesses, our actuarial staff analyzes loss and LAE Property data on an accident period basis. Many of the methodologies and key parameters reviewed are similar. Unlike our vehicle businesses, primarily due to the low levels of reserves, data is reviewed at a macro level and a range of reserves is generated to determine a reasonable range. In addition, for our Property business, since claims adjusters primarily establish the case reserves, the actuarial staff includes expected development on case reserves as a component of the overall IBNR reserves. Activity in the loss and loss adjustment expense reserves is summarized as follows: (millions) 2018 2017 2016 Balance at January 1 $ 13,086.9 $ 11,368.0 $ 10,039.0 Less reinsurance recoverables on unpaid losses 2,170.1 1,801.0 1,442.7 Net balance at January 1 10,916.8 9,567.0 8,596.3 Net loss and loss adjustment reserves disposed 0 0 (2.5 ) Total beginning reserves 10,916.8 9,567.0 8,593.8 Incurred related to: Current year 21,632.5 18,782.1 16,967.1 Prior years 88.5 25.9 (87.5 ) Total incurred 21,721.0 18,808.0 16,879.6 Paid related to: Current year 13,792.1 12,201.5 11,149.0 Prior years 6,017.6 5,256.7 4,757.4 Total paid 19,809.7 17,458.2 15,906.4 Net balance at December 31 12,828.1 10,916.8 9,567.0 Plus reinsurance recoverables on unpaid losses 2,572.7 2,170.1 1,801.0 Balance at December 31 $ 15,400.8 $ 13,086.9 $ 11,368.0 We experienced unfavorable reserve development of $88.5 million and $25.9 million in 2018 and 2017, respectively, and favorable development of $87.5 million in 2016, which is reflected as “Incurred related to prior years” in the table above. 2018 • Approximately $99 million of unfavorable prior year reserve development was attributable to accident years 2017 and 2016. This unfavorable development was offset by about $10 million of favorable development attributable to accident year 2015 and prior accident years. • Our personal auto products incurred almost $85 million of unfavorable loss and LAE reserve development, with approximately 70% attributable to the Agency business and 30% attributable to the Direct business, primarily reflecting unfavorable development from reopened Florida personal injury protection (PIP) claims. • Our special lines and Property businesses experienced about $5 million and $3 million of unfavorable development, respectively, while our commercial auto products had about $4 million of favorable reserve development. 2017 • Approximately $64 million of unfavorable prior year reserve development was attributable to accident years 2016 and 2015. This unfavorable development was offset by $38 million of favorable development attributable to accident year 2014 and prior accident years. • Our personal auto products incurred $70 million of unfavorable loss and LAE reserve development, primarily in the Agency business, in part reflecting an increase in costs related to property damage and higher LAE costs, primarily due to an increase in incentive compensation and defense counsel spend. • Our Property business experienced $37 million in favorable development primarily due to lower severity and frequency than anticipated for accident year 2016 and development of losses eligible to be ceded under our catastrophe bond reinsurance program. • Our commercial auto products had less than $1 million of unfavorable reserve development. 2016 • Approximately $56 million of the favorable prior year reserve development was attributable to accident year 2015, and approximately $51 million of favorable development was attributable to accident years 2013 and prior. This favorable development was partially offset by $19 million of unfavorable development attributable to accident year 2014. • Our Personal Lines and Property businesses incurred $54 million and $52 million , respectively, of favorable loss and LAE reserve development, partially offset by the unfavorable loss and LAE development in Commercial Lines. In our Property business, both the severity and frequency of late reported claims was less than anticipated. • Our personal auto product developed favorably $40 million , almost evenly split between Direct and Agency. • Our personal auto business incurred favorable case development, primarily in bodily injury due to a lower than anticipated severity. • Our personal auto and Commercial Lines businesses incurred unfavorable IBNR loss reserve development, primarily due to a higher severity and frequency of late reported claims than anticipated for accident year 2015, due in part to storms in late December 2015, resulting in a greater number of claims being reported in January 2016 than anticipated. • In addition, our Commercial Lines business experienced unfavorable case reserve development for accident year 2014, primarily due to a higher severity than anticipated on our largest limits, while case reserve development for accident years 2015 and 2013 and prior was favorable. Incurred and Paid Claims Development by Accident Year The tables below present our incurred and paid claims development by accident year for the last five years, which generally represents the maximum development period for claims in any of our segments. The tables below include inception-to-date information for companies acquired and wholly exclude companies disposed of, rather than including information from the date of acquisition, or until the date of disposition. We believe the most meaningful presentation of claims development is through the retrospective approach by presenting all relevant historical information for all periods presented. We have elected to present our incurred and paid claims development consistent with our GAAP reportable segments (see Note 10 – Segment Information for a discussion of our segment reporting), with a further disaggregation of our Personal Lines and Commercial Lines claims development between liability and physical damage, since the loss patterns are significantly different between them. The other business primarily includes reserves for our run-off products, which are not considered material, and, therefore, we are not including separate claims development tables. The following tables show incurred and paid claims development, net of reinsurance, by accident year. Only 2018 is audited; all prior years are considered required supplementary information and, therefore, are unaudited. Expected development on our case reserves is excluded from the IBNR reserves on our vehicle businesses, as discussed above. For the Property business, the IBNR reserves include expected case development based on the methodology used in establishing the case reserves for that segment. The cumulative number of incurred claims are based on accident coverages (e.g., bodily injury, collision, comprehensive, personal injury protection, property damage) related to opened claims. Coverage counts related to claims closed without payment are excluded from the cumulative number of incurred claims. Personal Lines - Agency - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 3,702.1 $ 3,627.7 $ 3,633.2 $ 3,654.4 $ 3,611.2 $ 0 701,788 2015 3,774.9 3,773.8 3,798.8 3,815.6 55.9 704,995 2016 4,082.9 4,130.0 4,152.0 69.5 740,325 2017 4,474.8 4,485.8 188.6 777,415 2018 5,141.8 802.8 839,051 Total $ 21,206.4 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,809.0 $ 2,868.1 $ 3,284.5 $ 3,482.3 $ 3,559.1 2015 1,793.1 2,976.0 3,416.5 3,623.3 2016 1,941.6 3,231.5 3,723.1 2017 2,074.0 3,478.5 2018 2,378.0 Total $ 16,762.0 All outstanding liabilities before 2014, net of reinsurance 1 64.6 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 4,509.0 1 Required supplementary information (unaudited) Personal Lines - Agency - Physical Damage ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 2,107.5 $ 2,090.3 $ 2,089.9 $ 2,088.0 $ 2,091.6 $ 0 1,374,721 2015 2,136.8 2,137.2 2,134.4 2,131.5 (3.8 ) 1,336,486 2016 2,423.4 2,398.9 2,401.8 (2.8 ) 1,398,842 2017 2,635.5 2,638.5 (11.8 ) 1,513,912 2018 2,819.0 (120.8 ) 1,677,878 Total $ 12,082.4 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 2,078.8 $ 2,091.6 $ 2,090.6 $ 2,090.7 $ 2,091.0 2015 2,106.2 2,138.1 2,134.4 2,134.1 2016 2,391.0 2,406.9 2,402.1 2017 2,599.8 2,643.2 2018 2,769.1 Total $ 12,039.5 All outstanding liabilities before 2014, net of reinsurance 1 0.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 43.3 1 Required supplementary information (unaudited) Personal Lines - Direct - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 2,946.8 $ 2,887.4 $ 2,898.1 $ 2,913.6 $ 2,884.1 $ 0 592,145 2015 3,330.5 3,328.3 3,354.2 3,399.3 44.3 659,289 2016 3,819.0 3,843.9 3,871.2 58.9 735,483 2017 4,209.5 4,209.9 167.0 770,740 2018 4,904.8 725.4 856,025 Total $ 19,269.3 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,413.0 $ 2,278.0 $ 2,624.2 $ 2,780.0 $ 2,844.0 2015 1,545.2 2,615.0 3,021.0 3,238.2 2016 1,780.6 2,991.1 3,476.9 2017 1,912.6 3,255.2 2018 2,235.1 Total $ 15,049.4 All outstanding liabilities before 2014, net of reinsurance 1 38.7 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 4,258.6 1 Required supplementary information (unaudited) Personal Lines - Direct - Physical Damage ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,889.3 $ 1,862.2 $ 1,861.7 $ 1,859.2 $ 1,861.7 $ 0 1,471,084 2015 2,110.7 2,097.7 2,093.5 2,090.8 (4.0 ) 1,540,090 2016 2,521.0 2,475.4 2,477.7 (3.8 ) 1,676,008 2017 2,750.6 2,743.7 (16.1 ) 1,790,360 2018 3,202.3 (175.4 ) 2,065,458 Total $ 12,376.2 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,874.6 $ 1,864.1 $ 1,862.7 $ 1,861.8 $ 1,861.4 2015 2,094.7 2,100.1 2,094.7 2,093.7 2016 2,505.0 2,485.8 2,479.3 2017 2,742.1 2,753.5 2018 3,170.0 Total $ 12,357.9 All outstanding liabilities before 2014, net of reinsurance 1 0.1 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 18.4 1 Required supplementary information (unaudited) Commercial Lines - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 822.5 $ 795.4 $ 820.3 $ 823.0 $ 813.5 $ 0 74,682 2015 897.6 911.1 914.8 899.7 14.0 77,839 2016 1,185.8 1,204.8 1,231.1 26.4 92,730 2017 1,374.1 1,366.6 70.9 96,905 2018 1,700.8 292.5 108,792 Total $ 6,011.7 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 234.0 $ 438.7 $ 610.0 $ 715.3 $ 771.0 2015 238.4 501.5 675.0 786.3 2016 298.6 639.9 886.0 2017 325.8 712.9 2018 382.7 Total $ 3,538.9 All outstanding liabilities before 2014, net of reinsurance 1 31.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 2,504.2 1 Required supplementary information (unaudited) Commercial Lines - Physical Damage ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 240.3 $ 239.7 $ 238.6 $ 238.0 $ 238.4 $ 0 59,630 2015 274.4 274.1 273.5 272.4 (0.6 ) 62,599 2016 379.6 379.8 378.2 (0.2 ) 74,180 2017 415.4 412.1 (2.0 ) 77,170 2018 475.0 (10.0 ) 83,350 Total $ 1,776.1 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 224.6 $ 238.3 $ 237.7 $ 237.9 $ 238.2 2015 248.5 271.9 272.0 272.2 2016 336.7 376.9 376.8 2017 369.0 409.4 2018 426.0 Total $ 1,722.6 All outstanding liabilities before 2014, net of reinsurance 1 0.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 53.9 1 Required supplementary information (unaudited) Property Business ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 415.5 $ 389.1 $ 379.7 $ 376.3 $ 375.3 $ 2.5 40,992 2015 460.0 416.5 403.6 398.8 3.8 41,980 2016 568.6 541.2 537.1 9.6 53,582 2017 672.8 680.9 11.5 71,153 2018 839.0 159.8 58,135 Total $ 2,831.1 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 269.2 $ 351.5 $ 365.9 $ 370.3 $ 371.9 2015 280.3 372.8 383.5 390.1 2016 415.2 498.2 516.9 2017 506.7 647.1 2018 595.9 Total $ 2,521.9 All outstanding liabilities before 2014, net of reinsurance 1 5.5 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 314.7 1 Required supplementary information (unaudited) The following table reconciles the net incurred and paid claims development tables to the liability for claims and claim adjustment expenses: (millions) 2018 2017 Net outstanding liabilities Personal Lines Agency, Liability $ 4,509.0 $ 3,955.5 Agency, Physical Damage 43.3 26.2 Direct, Liability 4,258.6 3,685.1 Direct, Physical Damage 18.4 (5.6 ) Commercial Lines Liability 2,504.2 2,027.4 Physical Damage 53.9 51.7 Property 314.7 245.8 Other business 42.9 43.7 Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 11,745.0 10,029.8 Reinsurance recoverable on unpaid claims Personal Lines Agency, Liability 836.8 769.8 Agency, Physical Damage 0 0 Direct, Liability 1,070.4 838.1 Direct, Physical Damage 0 0 Commercial Lines Liability 287.4 105.1 Physical Damage 0 0.1 Property 145.4 243.8 Other business 222.1 200.9 Total reinsurance recoverable on unpaid claims 2,562.1 2,157.8 Unallocated claims adjustment expense related to: Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 1,083.1 887.0 Reinsurance recoverable on unpaid claims 10.6 12.3 Total gross liability for unpaid claims and claim adjustment expense $ 15,400.8 $ 13,086.9 The following table shows the average historical claims duration as of December 31, 2018 : (Required Supplementary Information - Unaudited) Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 Personal Lines Agency, Liability 47.1% 30.7% 11.6% 5.4% 2.1% Agency, Physical Damage 98.9 1.1 (0.1) 0 0 Direct, Liability 46.1 31.2 12.2 5.9 2.2 Direct, Physical Damage 100.1 (0.1) (0.2) 0 0 Commercial Lines Liability 24.6 27.7 20.1 12.6 6.8 Physical Damage 90.4 9.0 (0.1) 0.1 0.1 Property 73.0 20.0 3.3 1.4 0.4

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2018
Reinsurance Disclosures [Abstract]
Reinsurance	REINSURANCE The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows: 2018 2017 2016 (millions) Written Earned Written Earned Written Earned Direct premiums $ 33,753.1 $ 31,970.2 $ 27,860.7 $ 26,425.7 $ 23,941.9 $ 23,111.2 Ceded premiums: Regulated plans (596.4 ) (557.5 ) (505.9 ) (479.6 ) (439.4 ) (425.1 ) Non-Regulated plans (546.8 ) (479.4 ) (222.7 ) (216.2 ) (149.0 ) (212.1 ) Total ceded premiums (1,143.2 ) (1,036.9 ) (728.6 ) (695.8 ) (588.4 ) (637.2 ) Net premiums $ 32,609.9 $ 30,933.3 $ 27,132.1 $ 25,729.9 $ 23,353.5 $ 22,474.0 The Regulated plans are federal or state run plans and primarily include the following: • Federal reinsurance plan • National Flood Insurance Program (NFIP) • State-provided reinsurance facilities • Michigan Catastrophic Claims Association (MCCA) • North Carolina Reinsurance Facility (NCRF) • Florida Hurricane Catastrophe Fund (FHCF) • State-mandated involuntary plans • Commercial Automobile Insurance Procedures/Plans (CAIP) The Non-Regulated plans are comprised of voluntary external reinsurance contracts. These include amounts ceded on our Commercial Lines business primarily related to transportation network company (TNC) business under quota-share reinsurance agreements and amounts ceded on our Property business under catastrophic reinsurance agreements and, effective January 1, 2017, aggregate stop-loss reinsurance agreements. During 2018, we expanded our TNC business from one state in 2016 and 2017 to four states at December 31, 2018. Our prepaid reinsurance premiums and reinsurance recoverables were comprised of the following at December 31: Prepaid Reinsurance Premiums Reinsurance Recoverables ($ in millions) 2018 2017 2018 2017 Regulated plans: MCCA $ 55.3 18 % $ 44.3 22 % $ 1,903.9 71 % $ 1,611.5 71 % CAIP 72.9 24 50.0 25 254.7 9 218.0 10 NCRF 34.0 11 31.5 15 78.1 3 74.2 3 NFIP 55.9 18 53.8 26 27.8 1 148.8 7 Other 0.6 0 0.3 0 21.4 1 8.2 0 Total Regulated plans 218.7 71 179.9 88 2,285.9 85 2,060.7 91 Non-Regulated plans: Commercial Lines 79.2 25 14.3 7 254.2 10 63.4 3 Property 11.8 4 9.1 5 147.7 5 138.6 6 Other 0 0 0 0 8.3 0 10.7 0 Total Non-Regulated plans 91.0 29 23.4 12 410.2 15 212.7 9 Total $ 309.7 100 % $ 203.3 100 % $ 2,696.1 100 % $ 2,273.4 100 % Reinsurance contracts do not relieve us from our obligations to policyholders. Failure of reinsurers to honor their obligations could result in losses to us. Our exposure to losses from the failure of Regulated plans is minimal, since these plans are funded by the federal government or by mechanisms supported by insurance companies in applicable states. We evaluate the financial condition of our other reinsurers and monitor concentrations of credit risk to minimize our exposure to significant losses from reinsurer insolvencies.

Statutory Financial Information

Statutory Financial Information	12 Months Ended
	Dec. 31, 2018
Statutory Financial Information Disclosures [Abstract]
Statutory Financial Information	STATUTORY FINANCIAL INFORMATION Consolidated statutory surplus was $11,731.2 million and $9,664.4 million at December 31, 2018 , and 2017 , respectively. Statutory net income was $2,916.9 million , $1,416.2 million , and $1,022.3 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively. At December 31, 2018 , $955.0 million of consolidated statutory surplus represented net admitted assets of our insurance subsidiaries and affiliates that are required to meet minimum statutory surplus requirements in such entities’ states of domicile. The companies may be licensed in states other than their states of domicile, which may have higher minimum statutory surplus requirements. Generally, the net admitted assets of insurance companies that, subject to other applicable insurance laws and regulations, are available for transfer to the parent company cannot include the net admitted assets required to meet the minimum statutory surplus requirements of the states where the companies are licensed. During 2018 , the insurance subsidiaries paid aggregate cash dividends of $938.9 million to their parent company. Based on the dividend laws in effect at December 31, 2018, the insurance subsidiaries could pay aggregate dividends of $2,887.0 million in 2019 without prior approval from regulatory authorities, provided the dividend payments are not made within 12 months of previous dividends paid by the applicable subsidiary.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Employee Benefit Plans Disclosures [Abstract]
Employee Benefit Plans	EMPLOYEE BENEFIT PLANS Beginning July 1, 2017, employees of ARX and its subsidiaries were included in the benefit plans described below. References in this Note 9 to Progressive refer to The Progressive Corporation and its subsidiaries, including ARX and its subsidiaries. Prior to July 1, 2017, ARX maintained employee benefit plans that were separate from the plans that covered employees of The Progressive Corporation’s other subsidiaries. Retirement Plans Progressive has a defined contribution pension plan (401(k) Plan) that covers employees who have been employed with the company for at least 30 days . Under Progressive’s 401(k) Plan, we match up to a maximum of 6% of an employee’s eligible compensation contributed to the plan. Employee and company matching contributions are invested, at the direction of the employee, in a number of investment options available under the plan, including various mutual funds, a self-directed brokerage option, and a Progressive common stock fund. Progressive’s common stock fund is an employee stock ownership program (ESOP) within the 401(k) Plan. At December 31, 2018, the ESOP held 24.1 million of our common shares, all of which are included in shares outstanding. Dividends on these shares are reinvested in common shares or paid out in cash, at the election of the participant, and the related tax benefit is recorded as part of our tax provision. Matching contributions to these plans for the years ended December 31, 2018, 2017, and 2016 were $106.8 million , $97.3 million , and $86.8 million . Postemployment Benefits Progressive provides various postemployment benefits to former or inactive employees who meet eligibility requirements, and to their beneficiaries and covered dependents. Postemployment benefits include salary continuation and disability-related benefits, including workers’ compensation and, if elected, continuation of health-care benefits for specified limited periods. The liability for these benefits was $20.2 million and $19.5 million at December 31, 2018 and 2017, respectively. Incentive Compensation Plans – Employees Progressive’s incentive compensation programs include both non-equity incentive plans (cash) and equity incentive plans. Progressive’s cash incentive compensation included an annual cash incentive program for a limited number of senior executives and Progressive’s Gainsharing program for other employees; the structures of these programs were similar in nature. Progressive’s equity incentive compensation plans provide for the granting of restricted stock unit awards to key members of management . In addition, ARX provides periodic cash bonuses to its employees and, prior to 2017, annual cash bonuses to its employees. ARX also has an equity compensation plan under which it has granted stock option awards, exercisable for shares of ARX common stock, to certain of its key employees. These stock option awards include both nonqualified and incentive stock options; all such stock options are subject to the put and call provisions of the ARX stockholders’ agreement (see Note 15 – Redeemable Noncontrolling Interest for further discussion). As a result of these provisions, and the determination that the ultimate settlement of these awards would be in cash, the ARX stock options are treated as liability awards for accounting purposes. The amounts charged to income for Progressive and ARX incentive compensation plans for the years ended December 31, were: 2018 2017 2016 (millions) Pretax After Tax Pretax After Tax Pretax After Tax Non-equity incentive plans – cash $ 539.5 $ 426.2 $ 461.3 $ 299.8 $ 386.8 $ 251.4 Equity incentive plans: Equity awards 76.2 60.2 92.9 60.4 80.9 52.6 Liability awards 1.0 0.8 2.5 1.6 4.3 2.8 The increase in 2017 expense for the equity awards, compared to 2018 and 2016, primarily reflected an increase in management’s expectation of the percentage of certain performance-based awards that will ultimately vest (discussed below). The after-tax amounts are determined using the corporate federal tax rate of 21% for 2018 and 35% for 2017 and 2016. Progressive’s 2015 Equity Incentive Plan, which provide for the granting of equity-based compensation to officers and other key employees, currently has authorized awards for up to 17.0 million shares, which includes 4.0 million shares transferred from the 2010 Equity Incentive Plan in accordance with the terms of the 2015 Equity Incentive Plan. No awards have been granted under the 2010 Equity Incentive Plan since January 2016 and none will be granted in the future. The restricted equity awards are issued as either time-based or performance-based awards. All restricted stock units are settled at or after vesting in Progressive common shares from existing treasury shares on a one-to-one basis. The time-based awards vest in equal installments upon the lapse of specified periods of time, typically three , four , and five years. The performance-based awards were granted to approximately 50 Progressive executives and senior managers in 2018 in addition to their time-based awards to provide additional incentive to achieve pre-established profitability and growth targets, relative investment performance, or specific growth measures. Vesting of performance-based awards is contingent upon the achievement of predetermined performance goals within specified time periods. The targets for the performance-based awards, as well as the number of units that ultimately may vest, vary by grant. All performance-based awards include a specified number of units that will vest if performance meets a specified target and minimum performance goals. If at least the minimum performance goals are achieved, the range at which an award can vest is determined by the type of measurement goals included in the award, as follows: Performance Measurement Year(s) of Grant Vesting range (as a percentage of target) Growth of our personal auto and commercial auto businesses and homeowners multi-peril business, each compared to its respective market 2018 0-250% Growth of our personal auto and commercial auto businesses, compared to the combined personal and commercial auto market 2013-2017 0-250% Investment results relative to peer group 2013-2018 0-200% Growth in percentage of auto policies bundled with other specified types of policies 2015 0% or 100-200% Unit growth in a specified customer segment 2016-2017 0% or 85-150% Generally, time-based and performance-based equity awards are expensed pro rata over their respective vesting periods based on the market value of the awards at the time of grant. Performance-based equity awards that contain variable vesting criteria are expensed based on management’s expectation of the percentage of the award, if any, that will ultimately vest. These estimates can change periodically throughout the measurement period. A summary of all employee restricted equity award activity during the years ended December 31, follows: 2018 2017 2016 Restricted Equity Awards Number of Shares 1 Weighted Average Grant Date Fair Value Number of Shares 1 Weighted Average Grant Date Fair Value Number of Shares 1 Weighted Average Grant Date Fair Value Beginning of year 5,858,848 $ 30.47 6,951,373 $ 26.18 7,725,227 $ 23.37 Add (deduct): Granted 2 1,876,109 45.55 2,383,475 32.01 1,870,660 31.54 Vested (2,811,070 ) 26.41 (3,220,671 ) 22.53 (2,422,700 ) 21.50 Forfeited (67,531 ) 36.10 (255,329 ) 28.03 (221,814 ) 24.64 End of year 3,4 4,856,356 $ 38.56 5,858,848 $ 30.47 6,951,373 $ 26.18 1 Includes restricted stock units; Upon vesting, all units will be converted on a one-for-one basis into Progressive common shares funded from existing treasury shares. All performance-based awards are included at their target amounts. 2 We reinvest dividend equivalents on restricted stock units. For 2018 , 2017 , and 2016 , the number of units “granted” shown in the table above includes 144,668 , 157,396 , and 165,045 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0 , since the dividends were factored into the grant date fair value of the original grant. 3 At December 31, 2018 , the number of shares included 1,017,520 performance-based units at their target amounts. We expect 2,447,409 units to vest based upon our current estimates of the likelihood of achieving the pre-determined performance goals applicable to each award. 4 At December 31, 2018 , the total unrecognized compensation cost related to unvested equity awards was $100.6 million , which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the income statement over the weighted average vesting period of 2.2 years. The aggregate fair value of the restricted equity awards that vested during the years ended December 31, 2018 , 2017 , and 2016 , was $162.7 million , $130.5 million , and $77.0 million , respectively, based on the actual stock price on the applicable vesting date. As a result of the put and call rights described in Note 15 – Redeemable Noncontrolling Interest , all outstanding stock options awarded to ARX employees prior to April 1, 2015, are treated as liability awards for accounting purposes; however, the awards maintain the specific features per the original award agreements. The value of each option is based upon our good faith estimate of the fair market value as of the end of the reporting period and the pro rata expense is recognized. A summary of all ARX employee stock option activity during the years ended December 31, follows: 2018 2017 2016 Options Outstanding Number of Shares Weighted Average Number of Shares Weighted Average Number of Shares Weighted Average Beginning of year 22,550 $ 564.60 24,995 $ 526.46 24,995 $ 526.46 Add (deduct): Exercised 1 (6,483 ) 506.26 (2,445 ) 174.65 0 0 End of year 16,067 $ 588.15 22,550 $ 564.60 24,995 $ 526.46 Exercisable, end of year 13,967 $ 562.17 17,950 $ 517.75 16,995 $ 438.77 1 At the time of exercise in 2018 and 2017, the value earned by the option holders was $6.2 million and $2.9 million , respectively. 2018 2017 2016 Non-Vested Options Outstanding Number of Shares Weighted Average Number of Shares Weighted Average Number of Shares Weighted Average Beginning of year 4,600 $ 747.45 8,000 $ 712.74 12,000 $ 677.81 Add (deduct): Vested (2,500 ) 736.12 (3,400 ) 665.79 (4,000 ) 607.95 End of year 1 2,100 $ 760.93 4,600 $ 747.45 8,000 $ 712.74 1 At December 31, 2018, 2017, and 2016, the remaining unrecognized compensation cost related to unvested options was $0.2 million , $0.7 million , and $1.6 million , respectively, and the remaining weighted average vesting period on the unvested awards was 0.53 years, 1.01 years, and 1.36 years, respectively. Incentive Compensation Plans – Directors Progressive’s 2003 Directors Equity Incentive Plan, has expired and no new awards may be made under this plan; in 2017, shareholders approved the Progressive 2017 Directors Equity Incentive Plan and it provides for the granting of equity-based awards, including restricted stock awards, to non-employee directors, and originally authorized awards for up to 0.5 million shares. The Progressive Corporation permits each non-employee director to indicate a preference to receive either 100% of their compensation in the form of a restricted stock award or 60% in the form of a restricted stock award and 40% in the form of cash. If the director does not state a preference, it is presumed that he or she preferred to receive 100% of their compensation in the form of restricted stock. After considering such preferences, the Compensation Committee of the Board of Directors determines the awards (restricted stock, or restricted stock and cash) for each non-employee director. The restricted stock awards are issued as time-based awards. The vesting period (i.e., requisite service period) is typically 11 months from the date of each grant. To the extent a director is newly appointed during the year, or a director’s committee assignments change, the vesting period may be shorter. Both the restricted stock awards and cash, if elected, are expensed pro rata over their respective vesting periods based on the market value of the awards at the time of grant. A summary of all directors’ restricted stock activity during the years ended December 31, follows: 2018 2017 2016 Restricted Stock Number of Shares Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Beginning of year 53,284 $ 40.54 55,839 $ 33.24 89,427 $ 27.23 Add (deduct): Granted 41,706 62.23 53,284 40.54 55,839 33.24 Vested (53,284 ) 40.54 (55,839 ) 33.24 (89,427 ) 27.23 End of year 1 41,706 $ 62.23 53,284 $ 40.54 55,839 $ 33.24 1 At December 31, 2018, the remaining unrecognized compensation cost related to restricted stock awards was $0.9 million . The aggregate fair value of the restricted stock vested, during the years ended December 31, 2018 , 2017 , and 2016 , was $3.2 million , $2.2 million , and $3.0 million , respectively, based on the actual stock price at time of vesting. Deferred Compensation The Progressive Corporation Executive Deferred Compensation Plan (Deferral Plan) permits eligible Progressive executives to defer receipt of some or all of their annual incentive payments and all of their annual equity awards. Deferred cash compensation is deemed invested in one or more investment funds, including Progressive common shares, offered under the Deferral Plan and elected by the participant. All Deferral Plan distributions attributable to deferred cash compensation will be paid in cash. For all equity awards granted in or after March 2005, and deferred pursuant to the Deferral Plan, the deferred amounts are deemed invested in our common shares and are ineligible for transfer to other investment funds in the Deferral Plan; distributions of these deferred awards will be made in Progressive common shares. For all restricted stock awards granted prior to that date, the deferred amounts are eligible to be transferred to any of the investment funds in the Deferral Plan; distributions of these deferred awards will be made in cash. We reserved 11.1 million of our common shares for issuance under the Deferral Plan. An irrevocable grantor trust has been established to provide a source of funds to assist us in meeting our liabilities under the Deferral Plan. The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31: (millions) 2018 2017 Progressive common shares 1 $ 114.7 $ 128.2 Other investment funds 2 124.0 167.0 Total $ 238.7 $ 295.2 1 Included 3.6 million and 4.4 million common shares as of December 31, 2018 and 2017 , respectively, to be distributed in common shares. 2 Amount is included in other assets on the balance sheet.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION We write personal and commercial auto insurance, residential property insurance, and other specialty property-casualty insurance and related services. Our Personal Lines segment writes insurance for personal autos and recreational vehicles (our special lines products). The Personal Lines segment is comprised of both the Agency and Direct businesses. The Agency business includes business written by our network of more than 35,000 independent insurance agencies, including brokerages in New York and California, and strategic alliance business relationships (other insurance companies, financial institutions, and national agencies). The Direct business includes business written directly by us online, by phone, or on mobile devices. We operate our personal auto businesses throughout the United States. 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. This segment operates throughout the United States and is distributed through both the independent agency and direct channels. Our Property segment writes residential property insurance for homeowners, other property owners, and renters through both the independent agency and direct channel, and writes flood insurance, through the “Write Your Own” program for the National Flood Insurance Program, through the agency channel. Our Property segment operates throughout the majority of the United States. Our other indemnity businesses manage our run-off businesses. Our service businesses provide insurance-related services, including processing CAIP business, and serving as an agent for homeowners, general liability, and workers’ compensation insurance, among other products, through our programs with ASI and unaffiliated insurance companies. All segment revenues are generated from external customers and we do not have a reliance on any major customer. We evaluate profitability based on pretax underwriting profit (loss) for the Personal Lines, Commercial Lines, and Property segments and for the other indemnity businesses. Pretax underwriting profit (loss) is calculated as net premiums earned plus fees and other revenues, less: (i) losses and loss adjustment expenses; (ii) policy acquisition costs; and (iii) other underwriting expenses. Service business pretax profit (loss) is the difference between service business revenues and service business expenses. Expense allocations are based on certain assumptions and estimates primarily related to revenue and volume; stated segment operating results would change if different methods were applied. We do not allocate assets or income taxes to operating segments. In addition, we do not separately identify depreciation expense by segment, and such allocation would be impractical. Companywide depreciation expense was $190.4 million in 2018 , $169.9 million in 2017 , and $137.4 million in 2016 . The accounting policies of the operating segments are the same as those described in Note 1 – Reporting and Accounting Policies . Following are the operating results for the years ended December 31: 2018 2017 2016 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 13,017.2 $ 1,435.7 $ 11,177.6 $ 839.6 $ 9,791.7 $ 492.8 Direct 13,017.5 1,088.5 10,769.6 683.7 9,396.5 412.2 Total Personal Lines 1 26,034.7 2,524.2 21,947.2 1,523.3 19,188.2 905.0 Commercial Lines 3,610.9 478.6 2,793.9 214.1 2,421.3 155.2 Property 2 1,287.7 (88.7 ) 988.8 (50.3 ) 864.5 32.5 Other indemnity 0 0.9 0 (0.2 ) 0 (1.6 ) Total underwriting operations 30,933.3 2,915.0 25,729.9 1,686.9 22,474.0 1,091.1 Fees and other revenues 3 472.2 NA 370.6 NA 332.5 NA Service businesses 158.5 24.4 126.8 17.3 103.3 11.3 Investments 4 415.0 390.7 612.7 588.8 530.0 507.6 Other gains (losses) 0 0 (1.0 ) (1.0 ) 1.6 1.6 Interest expense NA (166.5 ) NA (153.1 ) NA (140.9 ) Consolidated total $ 31,979.0 $ 3,163.6 $ 26,839.0 $ 2,138.9 $ 23,441.4 $ 1,470.7 NA = Not Applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned in 2018 , compared to 93% in 2017 and 92% in 2016 ; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 During 2018 , 2017 , and 2016, pretax profit (loss) includes $72.0 million , $66.2 million , and $62.1 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX. Although this expense is included in our Property segment, it is not reported in the consolidated results of ARX and, therefore, does not affect the value of net income attributable to noncontrolling interest. 3 Pretax profit (loss) for fees and other revenues are allocated to operating segments. 4 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses. Our management uses underwriting margin and combined ratio as primary measures of underwriting profitability. 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 years ended December 31: 2018 2017 2016 Underwriting Margin Combined Ratio Underwriting Margin Combined Ratio Underwriting Margin Combined Ratio Personal Lines Agency 11.0 % 89.0 7.5 % 92.5 5.0 % 95.0 Direct 8.4 91.6 6.3 93.7 4.4 95.6 Total Personal Lines 9.7 90.3 6.9 93.1 4.7 95.3 Commercial Lines 13.3 86.7 7.7 92.3 6.4 93.6 Property 1 (6.9 ) 106.9 (5.1 ) 105.1 3.8 96.2 Total underwriting operations 9.4 90.6 6.6 93.4 4.9 95.1 1 Included in 2018 , 2017 , and 2016, are 5.6 points, 6.7 points, and 7.2 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Other Comprehensive Income (Loss)	OTHER COMPREHENSIVE INCOME (LOSS) The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, for the years ended December 31, were as follows: Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income (loss) Total tax (provision) benefit After tax total accumulated other comprehensive income (loss) Total net unrealized gains (losses) on securities Net unrealized gains (losses) on forecasted transactions Foreign currency translation adjustment (Income) loss attributable to NCI Balance at December 31, 2017 $ 1,977.8 $ (695.6 ) $ 1,282.2 $ 1,295.0 $ (14.8 ) $ 0 $ 2.0 Cumulative effect adjustment 1 (2,006.0 ) 705.8 (1,300.2 ) (1,300.2 ) 0 0 0 Reclassification of disproportionate amounts 2 (4.3 ) (3.4 ) (7.7 ) (1.1 ) (3.2 ) 0 (3.4 ) Adjusted balance at December 31, 2017 (32.5 ) 6.8 (25.7 ) (6.3 ) (18.0 ) 0 (1.4 ) Other comprehensive income (loss) before reclassifications: Investment securities (224.1 ) 47.0 (177.1 ) (177.1 ) 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes 0 0 0 0 0 0 0 Forecasted transactions 0 0 0 0 0 0 0 Foreign currency translation adjustment 0 0 0 0 0 0 0 (Income) loss attributable to noncontrolling interest (NCI) 4.3 (1.0 ) 3.3 0 0 0 3.3 Total other comprehensive income (loss) before reclassifications (219.8 ) 46.0 (173.8 ) (177.1 ) 0 0 3.3 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings 0 0 0 0 0 0 0 Net realized gains (losses) on securities (98.3 ) 20.5 (77.8 ) (77.8 ) 0 0 0 Other gains (losses) 0 0 0 0 0 0 0 Interest expense (1.0 ) 0.2 (0.8 ) 0 (0.8 ) 0 0 Total reclassification adjustment for amounts realized in net income (99.3 ) 20.7 (78.6 ) (77.8 ) (0.8 ) 0 0 Total other comprehensive income (loss) (120.5 ) 25.3 (95.2 ) (99.3 ) 0.8 0 3.3 Balance at December 31, 2018 $ (153.0 ) $ 32.1 $ (120.9 ) $ (105.6 ) $ (17.2 ) $ 0 $ 1.9 1 Reflects the fair value changes on equity securities as of December 31, 2017 , which are reported as realized gains (losses) under the new accounting guidance. See Note 1 – Reporting and Accounting Policies for additional information. 2 Reflects the effect of the change in the U.S. federal tax rate on our available-for-sale fixed-maturity securities and our hedges on forecasted transactions as of December 31, 2017 (see Note 1 – Reporting and Accounting Policies for additional information) and the adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the "put" transaction (see Note 15 – Redeemable Noncontrolling Interest for additional information). Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total Total tax After tax total Total net Net Foreign (Income) loss attributable to NCI Balance at December 31, 2016 $ 1,439.5 $ (506.1 ) $ 933.4 $ 939.6 $ (9.4 ) $ (1.1 ) $ 4.3 Other comprehensive income (loss) before reclassifications: Investment securities 636.9 (224.0 ) 412.9 412.9 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes 0 0 0 0 0 0 0 Forecasted transactions (8.0 ) 2.8 (5.2 ) 0 (5.2 ) 0 0 Foreign currency translation adjustment 0.4 (0.1 ) 0.3 0 0 0.3 0 (Income) loss attributable to noncontrolling interest (NCI) (3.5 ) 1.2 (2.3 ) 0 0 0 (2.3 ) Total other comprehensive income (loss) before reclassifications 625.8 (220.1 ) 405.7 412.9 (5.2 ) 0.3 (2.3 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (14.9 ) 5.3 (9.6 ) (9.6 ) 0 0 0 Net realized gains (losses) on securities 103.3 (36.2 ) 67.1 67.1 0 0 0 Other gains (losses) 1 (1.2 ) 0.4 (0.8 ) 0 0 (0.8 ) 0 Interest expense 0.3 (0.1 ) 0.2 0 0.2 0 0 Total reclassification adjustment for amounts realized in net income 87.5 (30.6 ) 56.9 57.5 0.2 (0.8 ) 0 Total other comprehensive income (loss) 538.3 (189.5 ) 348.8 355.4 (5.4 ) 1.1 (2.3 ) Balance at December 31, 2017 $ 1,977.8 $ (695.6 ) $ 1,282.2 $ 1,295.0 $ (14.8 ) $ 0 $ 2.0 1 During 2017, we ceased writing insurance in Australia resulting in a loss of $1.2 million relating to the foreign currency translation adjustment. The loss is netted with other gains (losses) on our consolidated statements of comprehensive income for the year end December 31, 2017. Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total Total tax After tax total Total net Net Foreign (Income) loss attributable to NCI Total at December 31, 2015 $ 1,234.5 $ (434.1 ) $ 800.4 $ 809.0 $ (8.2 ) $ (1.5 ) $ 1.1 Other comprehensive income (loss) before reclassifications: Investment securities 320.5 (112.6 ) 207.9 207.9 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes (0.1 ) 0.1 0 0 0 0 0 Forecasted transactions 0 0 0 0 0 0 0 Foreign currency translation adjustment 0.6 (0.2 ) 0.4 0 0 0.4 0 (Income) loss attributable to noncontrolling interest (NCI) 5.1 (1.9 ) 3.2 0 0 0 3.2 Total other comprehensive income (loss) before reclassifications 326.1 (114.6 ) 211.5 207.9 0 0.4 3.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (27.1 ) 9.5 (17.6 ) (17.6 ) 0 0 0 Net realized gains (losses) on securities 146.3 (51.4 ) 94.9 94.9 0 0 0 Other gains (losses) 0 0 0 0 0 0 0 Interest expense 1.9 (0.7 ) 1.2 0 1.2 0 0 Total reclassification adjustment for amounts realized in net income 121.1 (42.6 ) 78.5 77.3 1.2 0 0 Total other comprehensive income (loss) 205.0 (72.0 ) 133.0 130.6 (1.2 ) 0.4 3.2 Total at December 31, 2016 $ 1,439.5 $ (506.1 ) $ 933.4 $ 939.6 $ (9.4 ) $ (1.1 ) $ 4.3 In an effort to manage interest rate risk, we often enter into forecasted transactions on Progressive’s debt issuances. We expect to reclassify $1.0 million (pretax) into interest expense during the next 12 months, related to net unrealized losses on forecasted transactions (see Note 4 – Debt for further discussion).

Litigation

Litigation	12 Months Ended
	Dec. 31, 2018
Litigation Disclosures [Abstract]
Litigation	LITIGATION The Progressive Corporation and/or its insurance subsidiaries are named as defendants in various lawsuits arising out of claims made under insurance policies written by our insurance subsidiaries in the ordinary course of business. We consider all legal actions relating to such claims in establishing our loss and loss adjustment expense reserves. In addition, The Progressive Corporation and/or its subsidiaries are named as defendants in a number of class action or individual lawsuits that challenge certain of the operations of the subsidiaries. Other insurance companies face many of these same issues. We describe litigation contingencies for which a loss is probable. In addition, we establish accruals for these lawsuits when we can reasonably estimate potential loss exposure, which may include a range of loss, and we will disclose such amount or range of loss if material. As to lawsuits for which the loss is considered probable but not estimable, we do not establish an accrual. Nevertheless, we continue to evaluate this pending litigation to determine if any losses not deemed probable and estimable become so, at which point we would establish an accrual at our best estimate of the loss or range of loss. We also describe litigation contingencies for which a loss is reasonably possible (but not probable). When disclosing reasonably possible litigation contingencies, we will disclose the amount or range of possible loss, if we are able to make that determination and if material. We review all reasonably possible losses on an ongoing basis to determine whether the likelihood of incurring a loss has become probable, or whether the circumstances have changed such that we may now reasonably estimate a range of loss. We may also be exposed to litigation contingencies that are remote. Remote litigation contingencies are those for which the likelihood of a loss is slight at period end. We do not disclose, or establish accruals for, remote litigation contingencies, but we evaluate these contingencies on an ongoing basis to determine whether the likelihood of a loss has increased. Each year, certain of our pending litigation matters are brought to conclusion. For cases that have settled, but for which settlement is not complete, an accrual is established at our best estimate of the loss exposure. We regularly review these and other accruals to ensure they are adequate, and that there is not the possibility of material losses in excess of our accruals. Settlements that are complete are fully reflected in our financial statements. The amounts accrued and/or paid for settlements during the periods presented were not material to our consolidated financial condition, cash flows, or results of operations. The pending lawsuits summarized below are in various stages of development, and the outcomes are uncertain as of December 31, 2018. At period end, except to the extent an immaterial accrual has been established, we do not consider the losses from these pending cases to be both probable and estimable, and we are unable to estimate a range of loss at this time. It is not possible to determine loss exposure for a number of reasons, including, without limitation, one or more of the following: liability appears to be remote; putative class action lawsuits generally pose immaterial exposure until a class is actually certified, which, historically, has not been granted by courts in the vast majority of our cases in which class certification has been sought; class definitions are often indefinite and preclude detailed exposure analysis; and complaints rarely state an amount sought as relief, and when such amount is stated, it often is a function of pleading requirements and may be unrelated to the potential exposure. We plan to contest these suits vigorously, but may pursue settlement negotiations in some cases, as we deem appropriate. In the event that any one or more of these cases results in a substantial judgment against, or settlement by, us or if our accruals (if any) prove to be inadequate, the resulting liability could have a material adverse effect on our consolidated financial condition, cash flows, and/or results of operations. Based on information currently known, we do not believe that the outcome of any pending cases described below will have a material impact on our consolidated financial condition, cash flows, and/or results of operations. At December 31, 2018, pending lawsuits as described above that challenge certain of the operations of our subsidiaries included: Lawsuits seeking class/collective action status : • alleging we sell or charge insureds for illusory coverage or coverage lower than amounts allowed by law for personal injury protection (PIP) coverage and pay related claims at levels lower than allowed by law. • challenging how physical damage claims are handled, adjusted and ultimately paid, including how we value total loss claims, the payment of fees and taxes associated with total losses, and the payment of diminution damages. • challenging our practice in Florida of adjusting PIP payments. • challenging our assessment of fees. • challenging our adjustment of medical bills submitted by insureds or medical providers in medical claims. • challenging our claim settlement practices where the tortfeasor and the injured party are both Progressive insureds. • challenging general claim practices, such as those relating to rental reimbursement. • challenging our payment and reimbursement practices to Medicare Advantage Plans on first party medical, PIP, and bodily injury claims. • alleging we improperly sell secondary PIP coverage to Medicare and Medicaid beneficiaries in New Jersey. • challenging our rating practices. • challenging our acceptance of uninsured motorist (UM) rejection. • alleging we sell illusory underinsured motorist (UIM) coverage. • alleging that the Snapshot ® device causes damage to vehicles. • alleging that we fail to pay overtime to certain employees who we classify as exempt from overtime pay requirements. Lawsuits certified or conditionally certified as class/collective actions : • alleging that we undervalued total loss claims through the use of certain valuation tools. • challenging our practice in Florida of adjusting PIP payments. • challenging the manner in which we grant a discount for anti-theft devices. Individual lawsuits : • challenging the estimation of physical damage and payment practices for physical damage repairs, and allegations of tortious interference with contract and insurance industry antitrust practice asserted by body shops outside our network program. • claiming that we and other shareholders were overpaid for stock as part of a leveraged buy-out that preceded the entity’s bankruptcy. • claiming patent infringement. • alleging that we are vicariously liable for the fraudulent acts of an agent. • challenging, on a representative basis, certain of our pay practices. • challenging various employment practices.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES We have 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 Some of the leases have options to renew at the end of the lease periods. The expense we incurred for the leases disclosed above, as well as other operating leases that may be cancelable or have terms less than one year, was: (millions) Expense 2018 $ 77.3 2017 77.2 2016 72.9 We also have certain noncancelable purchase obligations. The minimum commitment under these agreements at December 31, 2018 , was $697.5 million . The insurance operations of ARX have several multiple-layer property catastrophe reinsurance contracts with various reinsurers with terms ranging from one to three years. The minimum commitment under these contracts was $81.5 million at December 31, 2018.

Dividends

Dividends	12 Months Ended
	Dec. 31, 2018
Dividends [Abstract]
Dividends	DIVIDENDS Common Share Dividends Following is a summary of our common shareholder dividends that were declared in the last three years, under our annual variable dividend policy: (millions, except per share amounts) Amount of Common Share Dividends Dividend Type Declared Paid Per Share Accrued 1 Annual – Variable December 2018 February 2019 $ 2.5140 $ 1,467.9 Annual – Variable December 2017 February 2018 1.1247 655.1 Annual – Variable December 2016 February 2017 0.6808 395.4 1 The accrual is based on an estimate of shares outstanding as of the record date and is recorded as a component of "accounts payable, accrued expenses, and other liabilities" on the Consolidated Balance Sheets; the prior year amount was reclassified into this line item from "dividends payable" to conform to the current year presentation. For the dividends declared in December 2017 and 2016, we paid $654.9 million and $395.4 million , respectively. During 2018, 2017, and 2016, we maintained a policy of paying an annual variable dividend that, when declared, would be payable shortly after the close of the year. This annual variable dividend was based on a target percentage of after-tax underwriting income multiplied by a performance factor (Gainshare factor), which, in 2018, it was determined by reference to the Agency auto, Direct auto, special lines, Commercial Lines, and Property business units, with minor exclusions and adjustments. In December 2017 , the Board determined the target percentage for 2018 to be 33-1/3% of annual after-tax underwriting income, which is unchanged from the target percentage in both 2017 and 2016 . For the dividends declared in 2018, we applied a tax rate of 21% to calculate after-tax underwriting income, and a 35% tax rate for dividends declared for all prior years, since inception of the annual variable dividend. For the dividends declared in 2018 , the Gainshare factor was 1.91 , compared to 1.79 in 2017 and 1.67 in 2016 . In December 2018, the Board of Directors terminated the annual variable dividend policy and replaced it with a policy under which the Board expects to declare regular, quarterly common share dividends and, on at least an annual basis, to consider declaring an additional common share dividend. This policy is effective for 2019. Preferred Share Dividends In March 2018, we issued 500,000 Series B Fixed-to-Floating Rate Cumulative Perpetual Serial Preferred Shares, without par value (the “Series B Preferred Shares”), with a liquidation preference of $1,000 per share (the “stated amount”). Holders of the Series B Preferred Shares will be entitled to receive cumulative cash dividends semi-annually in March and September, if and when declared by the Board of Directors. Until March 15, 2023 (the “fixed-rate period”), the annual dividend rate is fixed at 5.375% of the stated amount per share. Beginning March 15, 2023, the annual dividend rate switches to a floating rate equal to the three-month LIBOR rate plus a spread of 2.539% applied to the stated amount per share. After the fixed-rate period and up until redemption of the Series B Preferred Shares, the dividends would be payable quarterly, if and when declared by the Board of Directors. The Series B Preferred Shares are perpetual and have no stated maturity date. After the fixed-rate period, we may redeem the Series B Preferred Shares at the stated amount plus all accrued and unpaid dividends. In 2018, the Board declared and we paid a dividend of $27.024 per preferred share, or $13.5 million .

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest (Notes)	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Noncontrolling Interest Disclosure [Text Block]	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. As part of the stockholders’ agreement, the minority ARX stockholders had the right to “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. In 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. Progressive's purchase prices for shares, pursuant to these put or call rights, will be determined by adding (A) the price per share paid at the closing on April 1, 2015, to (B) the product of the change in the fully diluted net tangible book value per share of ARX between December 31 , 2014, a nd December 31, 2020, times a multiple of between 1.0 and 2.0 . The multiple will be determined based on the growth and profitability of ARX’s business over the applicable time period, pursuant to criteria included in the stockholders’ agreement. Among other provisions, the stockholders’ agreement also prohibits ARX from taking a number of actions, including the payment of dividends, without the consent of The Progressive Corporation and one other stockholder. 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, calculated as described above, of the stockholders’ agreement. The redeemable noncontrolling interest was initially recorded at a fair value of $411.5 million , representing the minority shares at the net acquisition price adjusted for the fair value of the put and call rights. The value of the put and call rights on the acquisition date was based on an internally developed modified binomial model. Subsequent changes to the redeemable noncontrolling interest are based on the maximum redemption value at the end of the reporting period, as determined in accordance with the stockholders’ agreement. In addition to these minority shares, at December 31, 2018, ARX employees held options to purchase 16,067 ARX shares. These options and any shares issued upon exercise are subject to the stockholders’ agreement, including the right to “put ” these shares to Progressive, as described above. Until the options are exercised, the underlying obligation of approximately $23.1 million is not recorded as part of redeemable NCI. The changes in the components of redeemable NCI during the year ended December 31, were: (millions) 2018 2017 2016 Balance, Beginning of year $ 503.7 $ 483.7 $ 464.9 Net income attributable to NCI 5.7 5.9 26.2 Other comprehensive income (loss) attributable to NCI 1 (3.3 ) 2.3 (3.2 ) Exercise of employee stock options 9.4 3.4 0 Purchase/change of ARX minority shares (298.2 ) 0 0 Change in redemption value of NCI (2.8 ) 8.4 (4.2 ) Balance, End of year $ 214.5 $ 503.7 $ 483.7 1 Amount represents the other comprehensive income (loss) attributable to NCI, as reflected on the the Consolidated Statements of Comprehensive Income; any reclassification to accumulated other comprehensive income (loss) attributable to NCI due to a change in the minority ownership percentage does not impact the amount of redeemable NCI.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	GOODWILL AND INTANGIBLE ASSETS Goodwill Goodwill recorded at December 31, 2018 , and 2017, was $452.7 million . No accumulated goodwill impairment losses exist. Intangible Assets The following table is a summary of the net carrying amount of other intangible assets as of December 31 : (millions) 2018 2017 Intangible assets subject to amortization $ 282.2 $ 354.2 Indefinite-lived intangible assets 1 12.4 12.4 Total $ 294.6 $ 366.6 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 both years presented. Intangible assets subject to amortization for the years ended December 31, consisted of the following: (millions) 2018 2017 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 137.3 $ 118.9 $ 256.2 $ 100.7 $ 155.5 Agency relationships 159.2 42.6 116.6 159.2 31.3 127.9 Software rights 79.1 40.1 39.0 79.1 29.4 49.7 Trade name 34.8 27.1 7.7 34.8 13.7 21.1 Total $ 529.3 $ 247.1 $ 282.2 $ 529.3 $ 175.1 $ 354.2 Amortization expense was $72.0 million , $66.2 million , and $62.1 million for the years ended December 31, 2018 , 2017 , and 2016, respectively. During 2017, we revised our estimate of the economic useful life of our trade name intangible asset from an original life of 10 years to a remaining life of 2 years . The decrease in the useful life represents the estimated length of time that it is expected to take to transition the branding of our Property business from the ASI trade name to the Progressive brand. As of December 31, 2018, the remaining average life of all of our intangible assets was 3.9 years . The estimated aggregate amortization on these intangible assets for each of the next five years as of December 31, 2018, is as follows: (millions) Year Amortization Expense 2019 $ 66.4 2020 56.9 2021 56.6 2022 29.2 2023 13.5

Reporting and Accounting Poli_2

Reporting and Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Nature Of Operations Policy	Nature of Operations The Progressive insurance organization began business in 1937. The financial results of The Progressive Corporation include its subsidiaries and affiliates (references to “subsidiaries” in these notes include affiliates as well). Our insurance subsidiaries (collectively the Progressive Group of Insurance Companies) provide personal and commercial auto insurance, residential property insurance, and other specialty property-casualty insurance and related services. Our Personal Lines segment writes insurance for personal autos and recreational vehicles, which we refer to as our special lines products, through both an independent insurance agency channel and a direct channel. 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 through both the independent agency and direct channels. Our Property segment writes residential property insurance for homeowners, other property owners, and renters, through both an independent insurance agency channel and a direct channel. We operate our businesses throughout the United States.
Basis of Consolidation and Reporting	Basis of Consolidation and Reporting 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. All intercompany accounts and transactions are eliminated in consolidation. The Progressive Corporation owned 86.8% of the outstanding capital stock of ARX at December 31, 2018 , 69.0% at December 31, 2017 , and 69.2% at December 31, 2016 . The increase in Progressive's ownership of ARX is primarily due to the minority ARX shareholders exercising their rights to "put" a portion of their shares, including exercised stock options, to Progressive pursuant to the ARX stockholders' agreement. See Note 15 – Redeemable Noncontrolling Interest for further discussion.
Estimates	Estimates We are required to make estimates and assumptions when preparing our financial statements and accompanying notes in conformity with accounting principles generally accepted in the United States of America (GAAP). As estimates develop into fact, results may, and will likely, differ from those estimates.
Investments	Investments Our fixed-maturity securities and short-term investments are accounted for on an available-for-sale basis. Fixed-maturity securities include debt securities and redeemable preferred stocks, which may have fixed or variable principal payment schedules, may be held for indefinite periods of time, and may be used as a part of our asset/liability strategy or sold in response to changes in interest rates, anticipated prepayments, risk/reward characteristics, liquidity needs, or other economic factors. These securities are carried at fair value with the corresponding unrealized gains (losses), net of deferred income taxes, reported in accumulated other comprehensive income. Fair values are obtained from recognized pricing services or are quoted by market makers and dealers, with limited exceptions discussed in Note 3 - Fair Value . Short-term investments may include Eurodollar deposits, commercial paper, repurchase transactions, and other securities expected to mature within one year. From time to time, we may also invest in municipal bonds that have maturity dates that are longer than one year but have either liquidity facilities or mandatory put features within one year. Equity securities include common stocks, nonredeemable preferred stocks, and other risk investments. These securities are carried at fair value, and as of January 1, 2018, with the changes in fair value reported as a component of net holding period gains (losses) on securities reported in net income. See New Accounting Standards - Adopted below for further discussion. Trading securities are securities bought principally for the purpose of sale in the near term. We do not hold any trading securities. To the extent we have trading securities, changes in fair value would be recognized in income in the current period. Derivative instruments, which may be used for trading purposes or classified as trading derivatives due to the characteristics of the transaction, are discussed below. Derivative instruments may include futures, options, forward positions, foreign currency forwards, interest rate swap agreements, and credit default swaps and may be used in the portfolio for general investment purposes or to hedge the exposure to: • Changes in fair value of an asset or liability (fair value hedge), • Foreign currency of an investment in a foreign operation (foreign currency hedge), or • Variable cash flows of a forecasted transaction (cash flow hedge). We did not have any derivatives outstanding at December 31, 2018 and 2017. To the extent we have derivatives held for general investment purposes, these derivative instruments are recognized as either assets or liabilities and measured at fair value, with changes in fair value recognized in income as a component of net holding period gains (losses) on securities during the period of change. Derivatives designated as hedges are required to be evaluated on established criteria to determine the effectiveness of their correlation to, and ability to reduce the designated risk of, specific securities or transactions. Effectiveness is required to be reassessed regularly. Hedges that are deemed to be effective would be accounted for as follows: • Fair value hedge : changes in fair value of the hedge, as well as the hedged item, would be recognized in income in the period of change while the hedge is in effect. • Foreign currency hedge : changes in fair value of the hedge, as well as the hedged item, would be reflected as a change in translation adjustment as part of accumulated other comprehensive income. Gains and losses on the foreign currency hedge would offset the foreign exchange gains and losses on the foreign investment as they are recognized into income. • Cash flow hedge : changes in fair value of the hedge would be reported as a component of accumulated other comprehensive income and subsequently amortized into earnings over the life of the hedged transaction. If a hedge is deemed to become ineffective or discontinued, the following accounting treatment would be applied: • Fair value hedge : the derivative instrument would continue to be adjusted through income, while the adjustment in the change in value of the hedged item would be reflected as a change in unrealized gains (losses) as part of accumulated other comprehensive income. • Foreign currency hedge : changes in the value of the hedged item would continue to be reflected as a change in translation adjustment as part of accumulated other comprehensive income, but the derivative instrument would be adjusted through income for the current period. • Cash flow hedge : changes in fair value of the derivative instrument would be reported in income for the current period. For derivatives settled through a clearinghouse, we will need cash to post initial margin and are subject to increases in margin beyond changes in fair value. For bi-lateral derivative positions, net cash requirements are limited to changes in fair values, which may vary as a result of changes in interest rates, currency exchange rates, and other factors. Exposure to credit risk is limited to the carrying value; collateral may be required to limit credit risk. We have elected not to offset fair value amounts that arise from derivative positions with the same counterparty under a master netting arrangement. Investment securities are exposed to various risks such as interest rate, market, credit, and liquidity risk. Fair values of securities fluctuate based on the nature and magnitude of changing market conditions; significant changes in market conditions could materially affect the portfolio’s value in the near term. We regularly monitor our portfolio for price changes, which might indicate potential impairments, and perform detailed reviews of fixed-maturity securities with unrealized losses. In such cases, changes in fair value are evaluated to determine the extent to which such changes are attributable to: (i) fundamental factors specific to the issuer, such as financial condition, business prospects, or other factors, (ii) market-related factors, such as interest rates, or (iii) credit-related losses, where the present value of cash flows expected to be collected are lower than the amortized cost basis of the security. We analyze our investment in debt securities that are in a loss position to determine if we intend to sell, or if it is more likely than not that we will be required to sell, the security prior to recovery and, if so, we write down the security to its current fair value, with the entire amount of the write-down recorded to earnings. To the extent that it is more likely than not that we will hold the debt security until recovery (which could be maturity), we determine if any of the decline in value is due to a credit loss (i.e., where the present value of future cash flows expected to be collected is lower than the amortized cost basis of the security) and, if so, we recognize that portion of the impairment as a component of net realized gains (losses) in the comprehensive income statement, with the difference (i.e., non-credit related impairment) recognized as part of our net unrealized gains (losses) in accumulated other comprehensive income. Investment income consists of interest, dividends, and accretion net of amortization. Interest is recognized on an accrual basis using the effective yield method, except for asset backed securities, discussed below. Depending on the nature of the equity instruments, dividends are recorded at either the ex-dividend date or on an accrual basis. Asset-backed securities, which are included in our fixed-maturity portfolio, are generally accounted for under the retrospective method. The retrospective method recalculates yield assumptions (based on changes in interest rates or cash flow expectations) historically to the inception of the investment holding period, and applies the required adjustment, if any, to the cost basis, with the offset recorded to investment income. The prospective method is used primarily for interest-only securities, non-investment-grade asset-backed securities, and certain asset-backed securities with sub-prime loan exposure or where there is a greater risk of non-performance and where it is possible the initial investment may not be substantially recovered. The prospective method requires a calculation of expected future repayments and resets the yield to allow for future period adjustments; no current period impact to investment income or the security’s cost is made based on the cash flow update. Prepayment assumptions are updated quarterly. Realized gains (losses) on securities are computed based on the first-in first-out method and include write-downs on available-for-sale securities considered to have other-than-temporary declines in fair value (excluding non-credit related impairments), as well as holding period valuation changes on equity securities, hybrid instruments (e.g., securities with embedded options, where the option is a feature of the overall change in the value of the instrument), derivatives, and trading securities.
Insurance Premiums and Receivables	Insurance Premiums and Receivables Insurance premiums written are earned into income on a pro rata basis over the period of risk, based on a daily earnings convention. Accordingly, unearned premiums represent the portion of premiums written that are applicable to the unexpired risk. We provide insurance and related services to individuals and commercial accounts and offer a variety of payment plans. Generally, premiums are collected prior to providing risk coverage, minimizing our exposure to credit risk. For our vehicle businesses, we perform a policy level evaluation to determine the extent to which the premiums receivable balance exceeds the unearned premiums balance. We then age this exposure to establish an allowance for doubtful accounts based on prior experience. For our Property business, we do not establish an allowance for doubtful accounts since the risk of uncollectibility is relatively low. If premiums are unpaid by the policy due date, we provide advance notice of cancellation in accordance with each state’s requirements and, if the premiums remain unpaid after receipt of notice, cancel the policy and write off any remaining balance.
Deferred Acquisition Costs	Deferred Acquisition Costs Deferred acquisition costs include commissions, premium taxes, and other variable underwriting and direct sales costs incurred in connection with the successful acquisition or renewal of insurance contracts. These acquisition costs, net of ceding allowances, are deferred and amortized over the policy period in which the related premiums are earned. We consider anticipated investment income in determining the recoverability of these costs. Management believes these costs will be fully recoverable in the near term.
Loss and Loss Adjustment Expense Reserves	Loss and Loss Adjustment Expense Reserves Loss reserves represent the estimated liability on claims reported to us, plus reserves for losses incurred but not recorded (IBNR). These estimates are reported net of amounts estimated to be recoverable from salvage and subrogation. Loss adjustment expense reserves represent the estimated expenses required to settle these claims and losses. The methods of making estimates and establishing these reserves are reviewed regularly, and resulting adjustments are reflected in income in the current period. Such loss and loss adjustment expense reserves are susceptible to change in the near term.
Reinsurance	Reinsurance Our reinsurance transactions include Regulated plans and Non-Regulated plans. The Regulated plans in which we participate are governed by insurance regulations and include state-provided reinsurance facilities (e.g., Michigan Catastrophic Claims Association, Florida Hurricane Catastrophe Fund, North Carolina Reinsurance Facility), as well as state-mandated involuntary plans for commercial vehicles (Commercial Automobile Insurance Procedures/Plans – CAIP) and federally regulated plans for flood (National Flood Insurance Program – NFIP); we act as a servicing agent for CAIP and as a participant in the “Write Your Own” program for the NFIP. The Non-Regulated plans are voluntary contractual arrangements primarily related to the transportation network company business written by our Commercial Lines segment and our Property business. Prepaid reinsurance premiums are earned on a pro rata basis over the period of risk, based on a daily earnings convention, which is consistent with premiums earned. See Note 7 – Reinsurance for further discussion.
Income Taxes	Income Taxes The income tax provision is calculated under the balance sheet approach. Deferred tax assets and liabilities are recorded based on the difference between the financial statement and tax bases of assets and liabilities at the enacted tax rates. The principal items giving rise to such differences are investment securities (e.g., net unrealized gains (losses), net holding period gains (losses) on securities, write-downs on securities determined to be other-than-temporarily impaired), loss and loss adjustment expense reserves, unearned premiums reserves, deferred acquisition costs, property and equipment, intangible assets, and non-deductible accruals. We review our deferred tax assets regularly for recoverability. The effects of any changes in the tax rate are recorded to our provision for income taxes, including any changes on items initially recognized in accumulated other comprehensive income. See Note 5 – Income Taxes for further discussion.
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill is the excess of the purchase price over the estimated fair value of the assets and liabilities acquired and represents the future economic benefits arising from other assets acquired that could not be individually identified and separately recognized. Substantially all of the goodwill recorded as of December 31, 2018 and 2017, relates to the April 1, 2015, acquisition of a controlling interest in ARX. Intangible assets primarily arose through the acquisition of ARX and mainly represent the future premiums that will be recognized from the policies and agency relationships that existed at the acquisition date. The majority of the intangible assets have finite lives, which, at December 31, 2018, had a remaining life range from 1 to 10 years. See Note 16 – Goodwill and Intangible Assets for further discussion. We evaluate our goodwill for impairment at least annually using a qualitative approach. If events or changes in circumstances indicate that the carrying value of goodwill or intangible assets may not be recoverable, we will evaluate such items for impairment using a quantitative approach.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation, and include capitalized software developed or acquired for internal use. Depreciation is recognized over the estimated useful lives of the assets using accelerated methods for computer equipment and laptops and the straight-line method for all other fixed assets. We evaluate impairment whenever events or circumstances warrant such a review and write-off the impaired assets if appropriate. The cost and useful lives for property and equipment at December 31, were: ($ in millions) 2018 2017 Useful Lives Buildings, improvements, and integrated components $ 928.8 $ 962.0 7-40 years Capitalized software 327.0 273.1 3-10 years Software licenses (internal use) 259.1 197.0 1-5 years Land 177.0 203.4 NA Computer equipment and laptops 123.2 92.8 3 years All other property and equipment 349.8 331.9 3-15 years Total cost 2,164.9 2,060.2 Accumulated depreciation (1,033.2 ) (940.6 ) Balance at end of year $ 1,131.7 $ 1,119.6 NA = Not applicable At December 31, 2018 and 2017 , included in other assets in the consolidated balance sheets is $39.3 million and $5.3 million , respectively, of “held for sale” property, which represents the fair value of this property less the estimated costs to sell. The increase primarily reflects our decision to transition away from the use of service centers as part of our claims operating model. Total capitalized interest, which primarily relates to capitalized software projects, for the years ended December 31, was: (millions) Capitalized Interest 2018 $ 1.8 2017 2.8 2016 2.9
Guaranty Fund Assessments	Guaranty Fund Assessments We are subject to state guaranty fund assessments, which provide for the payment of covered claims or other insurance obligations of insurance companies deemed insolvent. These assessments are accrued after a formal determination of insolvency has occurred, and we have written the premiums on which the assessments will be based. Assessments that are available for recoupment from policyholders are capitalized when incurred; all other assessments are expensed.
Fees and Other Revenues	Fees and Other Revenues Fees and other revenues primarily represent fees collected from policyholders relating to installment charges in accordance with our bill plans, as well as late payment and insufficient funds fees and revenue from ceding commissions. Fees and other revenues are generally earned when invoiced, except for excess ceding commissions, which are earned over the policy period.
Service Revenues and Expenses	Service Revenues and Expenses Our service businesses provide insurance-related services. Service revenues and expenses from our commission-based businesses are recorded in the period in which they are earned or incurred. Service revenues generated from processing business for involuntary CAIP plans are earned on a pro rata basis over the term of the related policies. Service expenses related to these CAIP plans are expensed as incurred.
Equity-Based Compensation	Equity-Based Compensation We issue time-based and performance-based restricted stock unit awards to key members of management as our form of equity compensation, and time-based restricted stock awards to non-employee directors. Collectively, we refer to these awards as “restricted equity awards.” Compensation expense for time-based restricted equity awards with installment vesting is recognized over each respective vesting period. For performance-based restricted equity awards, compensation expense is recognized over the respective estimated vesting periods. Dividend equivalent units are credited to outstanding restricted stock unit awards, both time-based and performance-based, at the time a dividend is paid to shareholders and paid upon vesting of the underlying award. We record an estimate for expected forfeitures of restricted equity awards based on our historical forfeiture rates. In addition, we shorten the vesting periods of certain time-based restricted equity awards based on the “qualified retirement” provisions in our equity compensation plans, under which (among other provisions) if the participant satisfies certain age and years-of-service requirements, the vesting and distribution of 50% of outstanding time-based restricted equity awards accelerates upon reaching eligibility for a qualified retirement and shortly after the grant date for each subsequent award. ARX also has nonqualified and incentive stock options outstanding that were issued prior to April 2015 as a form of equity compensation to certain of the officers and employees of ARX and its subsidiaries. These outstanding stock options are subject to the put/call features contained in the ARX stockholders’ agreement, pursuant to which The Progressive Corporation has the right, and can be required, to purchase all the shares underlying these awards in 2021. The vested stock options, and the shares issuable upon exercise of the stock options, are also subject to repurchase by ARX if the holder’s employment terminates. See Note 15 – Redeemable Noncontrolling Interest for further discussion. These stock options, which are treated for accounting purposes as liability awards, are expensed over the respective vesting periods based on the Black-Scholes value determined at period end.
Earnings Per Share	Earnings Per Common Share Net income attributable to Progressive is reduced by cumulative preferred share dividends to determine net income available to common shareholders, and is used in our calculation of the per common share amounts. Basic earnings per common share is computed using the weighted average number of common shares outstanding during the reporting period, excluding unvested time-based and performance-based restricted equity awards that are subject to forfeiture. Diluted earnings per common share includes common stock equivalents assumed outstanding during the period. Our common stock equivalents include the incremental shares assumed to be issued for: • earned but unvested time-based restricted equity awards, and • performance-based restricted equity awards that satisfied certain contingency conditions for unvested common stock equivalents during the period
Cash Flow, Supplemental Disclosures	Supplemental Cash Flow Information Cash and cash equivalents include bank demand deposits and daily overnight reverse repurchase commitments of funds held in bank demand deposit accounts by ARX’s subsidiaries. The amount of reverse repurchase commitments held by ARX’s subsidiaries at December 31, 2018 , 2017 , and 2016 , were $117.3 million , $247.2 million , and $150.0 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. Non-cash activity includes declared but unpaid dividends. For the years ended December 31, we paid the following: (millions) 2018 2017 2016 Income taxes $ 702.6 $ 715.6 $ 459.4 Interest 154.0 146.3 139.2
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 also 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, 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 July 2018, the FASB issued an ASU, which provides targeted improvements to the new lease accounting guidance issued by the FASB in February 2016. The ASU, which eliminates the off-balance-sheet accounting for leases, will require 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. Under the ASU, there will be no change to the recognition of lease expense in our results of operations. The ASU will be effective for fiscal years (including interim periods within those fiscal years) beginning after December 15, 2018 (2019 for calendar-year companies). Under the ASU, companies will have the option to apply the new lease requirements either as of the effective date (i.e., January 1, 2019), with comparative information presented in accordance with the previous standard, or on a modified retrospective basis, which would restate all financial statement information as of the beginning of the earliest period presented. We adopted this standard as of January 1, 2019, and recorded an increase to assets and liabilities of about $215 million , which reflects the present value of future operating lease payments; comparative information is presented in accordance with the previous standard. The ASU had no impact on our results of operations or cash flows. In March 2017, the FASB issued an ASU related to premium amortization on purchased callable debt securities. The intent of the standard is to shorten the amortization period for certain purchased callable debt securities held at a premium. Under the ASU, the premium is required to be amortized to the earliest call date. The ASU more closely aligns interest income recorded on bonds held at a premium with the economics of the underlying instrument. The ASU, which is required to be applied on a modified retrospective basis, is effective for fiscal years beginning after December 15, 2018 (2019 for calendar-year companies), and interim periods within those fiscal years. 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, we do not expect this standard to have a significant 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 condition 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. Additionally, 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 do not expect the ASU to have a material impact on our current method of evaluating investment securities or reinsurance recoverables for credit losses or the timing or recognition of the amounts of the impairment losses. Adopted On January 1, 2018, we adopted the ASU intended to improve the recognition and measurement of financial instruments. Under this update, the changes in fair value of equity securities are recognized as a component of net income. Upon adoption, we recorded a cumulative-effect adjustment of $1.3 billion , which is net of taxes. The cumulative-effect adjustment represents the amount of after-tax net unrealized gains on equity securities that was recorded as part of accumulated other comprehensive income at December 31, 2017. The adoption of this ASU had no impact on comprehensive income. Consistent with our historical presentation, cash flows on equity securities will be reflected as investing activities in the Consolidated Statements of Cash Flows. In the first quarter 2018, we adopted the ASU related to the reclassification of certain tax effects from accumulated other comprehensive income. This update provided companies with the option to reclassify disproportionate tax effects in accumulated other comprehensive income caused by the legislation commonly known as the Tax Cuts and Jobs Act of 2017 to retained earnings. We opted to make the reclassification, which resulted in a decrease to accumulated other comprehensive income and an offsetting increase to retained earnings of $4.3 million . This reclass was solely due to the effect of the change in the U.S. federal tax rate on our available-for-sale fixed-maturity securities and our hedges on forecasted transactions. There were no disproportionate tax effects related to our equity securities subsequent to adopting the ASU related to classification and measurement discussed above.

Reporting and Accounting Poli_3

Reporting and Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Advertising Costs	Total advertising costs, which are expensed as incurred, for the years ended December 31, were: (millions) Advertising Costs 2018 $ 1,422.4 2017 1,005.4 2016 756.2
Property and Equipment	The cost and useful lives for property and equipment at December 31, were: ($ in millions) 2018 2017 Useful Lives Buildings, improvements, and integrated components $ 928.8 $ 962.0 7-40 years Capitalized software 327.0 273.1 3-10 years Software licenses (internal use) 259.1 197.0 1-5 years Land 177.0 203.4 NA Computer equipment and laptops 123.2 92.8 3 years All other property and equipment 349.8 331.9 3-15 years Total cost 2,164.9 2,060.2 Accumulated depreciation (1,033.2 ) (940.6 ) Balance at end of year $ 1,131.7 $ 1,119.6 NA = Not applicable
Interest Capitalized	Total capitalized interest, which primarily relates to capitalized software projects, for the years ended December 31, was: (millions) Capitalized Interest 2018 $ 1.8 2017 2.8 2016 2.9
Equity Based Compensation and Related Tax Benefits	The total compensation expense recognized for equity-based compensation, including both equity and liability awards, for the years ended December 31, was: (millions) 2018 2017 2016 Pretax expense $ 77.2 $ 95.4 $ 85.2 Tax benefit 1 16.2 33.4 29.8 1 Calculated using the corporate federal tax rate of 21% for 2018 and 35% for 2017 and 2016.
Supplemental Cash Flow Information	For the years ended December 31, we paid the following: (millions) 2018 2017 2016 Income taxes $ 702.6 $ 715.6 $ 459.4 Interest 154.0 146.3 139.2

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
Investments Schedule [Abstract]
Investment Portfolio by Major Security Type	The following tables present the composition of our investment portfolio by major security type, consistent with our classification of how we manage, monitor, and measure the portfolio. Our securities are reported in our Consolidated Balance Sheets at fair value. The changes in fair value for our fixed-maturity securities (other than hybrid securities) are reported as a component of accumulated other comprehensive income, net of deferred income taxes, in our Consolidated Balance Sheets. The net holding period gains (losses) reported below represent the inception-to-date changes in fair value. The changes in the net holding period gains (losses) between periods for the hybrid securities and, beginning in 2018 , equity securities are recorded as a component of net realized gains (losses) on securities in our Consolidated Statements of Comprehensive Income. Prior to 2018, the change in fair value of our equity securities was part of accumulated other comprehensive income (see Note 1 – Reporting and Accounting Policies for further discussion). For comparative purposes, the change in fair value of the hybrid securities that was recognized in 2017 and 2016 was reclassified out of "net realized gains (losses) on security sales" and into "net holding period gains (losses) on securities" to conform to the current year presentation. ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair 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 % ($ in millions) Cost Gross Unrealized Gains Gross Unrealized Losses Net Holding Period Gains (Losses) Fair Value % of Total Fair Value December 31, 2017 Fixed maturities: U.S. government obligations $ 6,688.8 $ 1.1 $ (44.0 ) $ 0 $ 6,645.9 24.4 % State and local government obligations 2,285.6 20.7 (9.3 ) 0.1 2,297.1 8.4 Corporate debt securities 4,997.2 14.8 (14.4 ) 0.1 4,997.7 18.3 Residential mortgage-backed securities 828.8 11.3 (3.4 ) 0 836.7 3.1 Commercial mortgage-backed securities 2,760.1 11.8 (13.3 ) 0 2,758.6 10.1 Other asset-backed securities 2,454.5 4.5 (4.5 ) 0.2 2,454.7 9.0 Redeemable preferred stocks 194.9 17.8 (1.5 ) (0.2 ) 211.0 0.8 Total fixed maturities 20,209.9 82.0 (90.4 ) 0.2 20,201.7 74.1 Short-term investments 2,869.4 0 0 0 2,869.4 10.5 Total fixed maturities and short-term 23,079.3 82.0 (90.4 ) 0.2 23,071.1 84.6 Equity securities: Nonredeemable preferred stocks 698.6 114.0 (8.8 ) 0 803.8 2.9 Common equities 1,499.0 1,901.0 (0.2 ) 0 3,399.8 12.5 Total equity securities 2,197.6 2,015.0 (9.0 ) 0 4,203.6 15.4 Total available-for-sale portfolio 1,2 $ 25,276.9 $ 2,097.0 $ (99.4 ) $ 0.2 $ 27,274.7 100.0 % 1 Our portfolio reflects the effect of unsettled security transactions; at December 31, 2018 , $5.9 million was included in “other liabilities,” compared to $5.8 million in “other assets” at December 31, 2017 . 2 The total fair value of the portfolio at December 31, 2018 and 2017 included $2.9 billion and $1.6 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
Hybrid Securities	Included in our fixed maturities are hybrid securities, which are reported at fair value at December 31 : (millions) 2018 2017 Fixed Maturities: State and local government obligations $ 3.6 $ 6.1 Corporate debt securities 158.9 99.8 Other asset-backed securities 4.5 6.7 Redeemable preferred stocks 77.7 30.3 Total hybrid securities $ 244.7 $ 142.9
Composition of Fixed Maturities by Maturity	The composition of fixed maturities by maturity at December 31, 2018 , was: (millions) Cost Fair Value Less than one year $ 4,880.1 $ 4,867.0 One to five years 17,719.4 17,652.0 Five to ten years 5,581.3 5,517.5 Ten years or greater 75.1 75.0 Total $ 28,255.9 $ 28,111.5
Gross Unrealized Losses by Major Security	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Value Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Value Unrealized Losses No. of Sec. Fair Value 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 ) Total No. of Sec. Total Fair Value Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Value Unrealized Losses No. of Sec. Fair Value Unrealized Losses December 31, 2017 Fixed maturities: U.S. government obligations 58 $ 5,817.0 $ (44.0 ) 41 $ 4,869.3 $ (34.6 ) 17 $ 947.7 $ (9.4 ) State and local government obligations 358 1,200.3 (9.3 ) 230 737.6 (4.4 ) 128 462.7 (4.9 ) Corporate debt securities 222 2,979.4 (14.4 ) 171 2,072.9 (9.1 ) 51 906.5 (5.3 ) Residential mortgage-backed securities 201 300.9 (3.4 ) 30 75.1 (0.2 ) 171 225.8 (3.2 ) Commercial mortgage-backed securities 105 1,682.3 (13.3 ) 63 1,221.2 (5.9 ) 42 461.1 (7.4 ) Other asset-backed securities 197 1,837.3 (4.5 ) 134 1,377.8 (3.3 ) 63 459.5 (1.2 ) Redeemable preferred stocks 2 21.8 (1.5 ) 1 10.8 (0.1 ) 1 11.0 (1.4 ) Total fixed maturities 1,143 13,839.0 (90.4 ) 670 10,364.7 (57.6 ) 473 3,474.3 (32.8 ) Equity securities: Nonredeemable preferred stocks 4 127.8 (8.8 ) 1 56.5 (0.5 ) 3 71.3 (8.3 ) Common equities 19 13.4 (0.2 ) 18 13.4 (0.2 ) 1 0 0 Total equity securities 23 141.2 (9.0 ) 19 69.9 (0.7 ) 4 71.3 (8.3 ) Total portfolio 1,166 $ 13,980.2 $ (99.4 ) 689 $ 10,434.6 $ (58.3 ) 477 $ 3,545.6 $ (41.1 )
Total Non-Credit Portion of Other-Than-Temporary Impairment Recorded in Accumulated Other Comprehensive Income, Reflecting Original Non-Credit Loss at the Time Credit Impairment	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): December 31, (millions) 2018 2017 Fixed maturities: Residential mortgage-backed securities $ (19.7 ) $ (19.7 ) Commercial mortgage-backed securities (0.1 ) (0.3 ) Total fixed maturities $ (19.8 ) $ (20.0 )
OTTI Credit Losses Recognized in Earnings	The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended December 31, 2018 , 2017 , and 2016 , 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: (millions) Residential Mortgage- Backed Commercial Mortgage- Backed Total Total at December 31, 2017 $ 0 $ 0.5 $ 0.5 Credit losses for which an OTTI was not previously recognized 0 0 0 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 0 0 0 Total at December 31, 2018 $ 0 $ 0.5 $ 0.5 (millions) Residential Mortgage- Backed Commercial Mortgage- Backed Total Total at December 31, 2016 $ 11.1 $ 0.4 $ 11.5 Credit losses for which an OTTI was not previously recognized 0 0.4 0.4 Reductions for securities sold/matured (10.9 ) (0.3 ) (11.2 ) Change in recoveries of future cash flows expected to be collected 1 (0.2 ) 0 (0.2 ) Total at December 31, 2017 $ 0 $ 0.5 $ 0.5 (millions) Residential Mortgage- Backed Commercial Mortgage- Backed Total Total at December 31, 2015 $ 12.4 $ 0.4 $ 12.8 Credit losses for which an OTTI was not previously recognized 0 0 0 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 (1.3 ) 0 (1.3 ) Total at December 31, 2016 $ 11.1 $ 0.4 $ 11.5 1 Reflects expected recovery of prior period impairments that will be accreted into income over the remaining life of the security.
Components of Net Realized Gains (Losses)	The components of net realized gains (losses) for the years ended December 31, were: (millions) 2018 2017 2016 Gross realized gains on security sales Available-for-sale securities: U.S. government obligations $ 6.7 $ 6.2 $ 24.6 State and local government obligations 9.5 10.5 16.0 Corporate and other debt securities 2.4 20.3 43.3 Residential mortgage-backed securities 0 23.8 2.5 Commercial mortgage-backed securities 2.0 4.9 13.3 Other asset-backed securities 0.1 0.3 0 Redeemable preferred stocks 4.5 8.5 20.9 Short-term investments 0 0 0.1 Total available-for-sale securities 25.2 74.5 120.7 Equity securities: Nonredeemable preferred stocks 4.1 58.4 11.9 Common equities 286.6 43.0 61.3 Total equity securities 290.7 101.4 73.2 Subtotal gross realized gains on security sales 315.9 175.9 193.9 Gross realized losses on security sales Available-for-sale securities: U.S. government obligations (98.7 ) (28.7 ) (2.4 ) State and local government obligations (2.9 ) (0.1 ) (1.6 ) Corporate and other debt securities (10.4 ) (5.1 ) (2.5 ) Residential mortgage-backed securities (0.1 ) (0.4 ) (0.2 ) Commercial mortgage-backed securities (6.3 ) (5.3 ) (5.6 ) Other asset-backed securities (1.1 ) (0.4 ) 0 Redeemable preferred stocks (0.1 ) (6.4 ) (6.6 ) Short-term investments 0 (0.2 ) (0.1 ) Total available-for-sale securities (119.6 ) (46.6 ) (19.0 ) Equity securities: Nonredeemable preferred stocks (3.9 ) (5.9 ) (5.3 ) Common equities (21.7 ) (12.2 ) (15.7 ) Total equity securities (25.6 ) (18.1 ) (21.0 ) Subtotal gross realized losses on security sales (145.2 ) (64.7 ) (40.0 ) Net realized gains (losses) on security sales Available-for-sale securities: U.S. government obligations (92.0 ) (22.5 ) 22.2 State and local government obligations 6.6 10.4 14.4 Corporate and other debt securities (8.0 ) 15.2 40.8 Residential mortgage-backed securities (0.1 ) 23.4 2.3 Commercial mortgage-backed securities (4.3 ) (0.4 ) 7.7 Other asset-backed securities (1.0 ) (0.1 ) 0 Redeemable preferred stocks 4.4 2.1 14.3 Short-term investments 0 (0.2 ) 0 Total available-for-sale securities (94.4 ) 27.9 101.7 Equity securities: Nonredeemable preferred stocks 0.2 52.5 6.6 Common equities 264.9 30.8 45.6 Total equity securities 265.1 83.3 52.2 Litigation settlements and other gains (losses) 0 1.2 0.4 Subtotal net realized gains (losses) on security sales 170.7 112.4 154.3 Net holding period gains (losses) Hybrid securities (10.4 ) (1.6 ) 2.1 Equity securities (497.5 ) 0 0 Derivatives 0 0 (20.0 ) Subtotal net holding period gains (losses) (507.9 ) (1.6 ) (17.9 ) Other-than-temporary impairment losses Fixed maturities: Commercial mortgage-backed securities 0 (0.4 ) 0 Redeemable preferred stocks 0 0 (25.3 ) Total fixed maturities 0 (0.4 ) (25.3 ) Equity securities: Common equities 0 (11.2 ) (0.3 ) Subtotal investment other-than-temporary impairment losses 0 (11.6 ) (25.6 ) Other asset impairment (68.3 ) (49.6 ) (59.7 ) Subtotal other-than-temporary impairment losses (68.3 ) (61.2 ) (85.3 ) Total net realized gains (losses) on securities $ (405.5 ) $ 49.6 $ 51.1
Components of Equity Realized Gains (Losses)	The following table reflects our holding period realized gains (losses) on equity securities recognized for the year ended December 31, 2018 for equity securities held at year end: (millions) 2018 Total net gains (losses) recognized during the period on equity securities $ (232.4 ) Less: Net gains (losses) recognized on equity securities sold during the period 265.1 Net holding period gains (losses) recognized during the period on equity securities held at period end $ (497.5 ) Note: Comparative disclosure for the prior year period is not meaningful.
Components of Net Investment Income	The components of net investment income for the years ended December 31, were: (millions) 2018 2017 2016 Available-for-sale securities: Fixed maturities: U.S. government obligations $ 196.8 $ 72.7 $ 18.2 State and local government obligations 37.7 51.5 52.3 Foreign government obligations 0 0.3 0.4 Corporate debt securities 217.9 125.2 110.7 Residential mortgage-backed securities 27.6 34.7 47.3 Commercial mortgage-backed securities 93.9 79.6 81.6 Other asset-backed securities 75.7 47.1 28.0 Redeemable preferred stocks 12.3 11.8 14.9 Total fixed maturities 661.9 422.9 353.4 Short-term investments 52.9 37.8 19.7 Total available-for-sale securities 714.8 460.7 373.1 Equity securities: Nonredeemable preferred stocks 45.9 44.1 48.6 Common equities 59.8 58.3 57.2 Total equity securities 105.7 102.4 105.8 Investment income 820.5 563.1 478.9 Investment expenses (24.3 ) (23.9 ) (22.4 ) Net investment income $ 796.2 $ 539.2 $ 456.5

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Composition of Investment Portfolio by Major Security Type	The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 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 (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2017 Fixed maturities: U.S. government obligations $ 6,645.9 $ 0 $ 0 $ 6,645.9 $ 6,688.8 State and local government obligations 0 2,297.1 0 2,297.1 2,285.6 Corporate debt securities 0 4,997.7 0 4,997.7 4,997.2 Subtotal 6,645.9 7,294.8 0 13,940.7 13,971.6 Asset-backed securities: Residential mortgage-backed 0 836.7 0 836.7 828.8 Commercial mortgage-backed 0 2,758.6 0 2,758.6 2,760.1 Other asset-backed 0 2,454.7 0 2,454.7 2,454.5 Subtotal asset-backed securities 0 6,050.0 0 6,050.0 6,043.4 Redeemable preferred stocks: Financials 0 64.1 0 64.1 61.3 Utilities 0 11.4 0 11.4 10.1 Industrials 0 135.5 0 135.5 123.5 Subtotal redeemable preferred stocks 0 211.0 0 211.0 194.9 Total fixed maturities 6,645.9 13,555.8 0 20,201.7 20,209.9 Short-term investments 1,824.4 1,045.0 0 2,869.4 2,869.4 Total fixed maturities and short-term 8,470.3 14,600.8 0 23,071.1 23,079.3 Equity securities: Nonredeemable preferred stocks: Financials 80.6 718.2 0 798.8 693.6 Utilities 0 0 0 0 0 Industrials 0 0 5.0 5.0 5.0 Subtotal nonredeemable preferred stocks 80.6 718.2 5.0 803.8 698.6 Common equities: Common stocks 3,399.5 0 0 3,399.5 1,498.7 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 3,399.5 0 0.3 3,399.8 1,499.0 Total equity securities 3,480.1 718.2 5.3 4,203.6 2,197.6 Total available-for-sale portfolio $ 11,950.4 $ 15,319.0 $ 5.3 $ 27,274.7 $ 25,276.9 Debt $ 0 $ 3,606.5 $ 37.1 $ 3,643.6 $ 3,306.3
Summary of Changes in Fair Value Associated With Level 3 Assets	The following tables provide a summary of changes in fair value associated with Level 3 assets for the years ended December 31, 2018 and 2017 : Level 3 Fair Value (millions) Fair Value at Dec. 31, 2017 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at Dec. 31, 2018 Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Equity securities: Nonredeemable preferred stocks: Financials 0 0 25.1 0 0 0 0 25.1 Industrials 5.0 0 0 0 0 0 0 5.0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 5.3 $ 0 $ 25.1 $ 0 $ 0 $ 0 $ 0 $ 30.4 Level 3 Fair Value (millions) Fair Value at Dec. 31, 2016 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain)/Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at Dec. 31, 2017 Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 0.3 $ (0.3 ) $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Industrials 0 0 5.0 0 0 0 0 5.0 Common equities: Other risk investments 0.4 (0.1 ) 0 0 0 0 0 0.3 Total Level 3 securities $ 0.7 $ (0.4 ) $ 5.0 $ 0 $ 0 $ 0 $ 0 $ 5.3
Summary of Quantitative Information about Level 3 Fair Value Measurements	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at December 31 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2018 Valuation Technique Unobservable Input Unobservable Input Assumption Equity securities: Nonredeemable preferred stocks: Financials 1 $ 25.1 Internal price Unadjusted purchase price 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 privately held. 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 privately held. The price at December 31, 2018 , 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 Dec. 31, 2017 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 3.9 Subtotal Level 3 securities 5.0 Pricing exemption securities 2 0.3 Total Level 3 securities $ 5.3 NA= Not Available 1 The security was internally-priced since it is privately held. The security was purchased during third quarter 2017 and the value at December 31, 2017, reflects the unadjusted purchase price per share. 2 The unobservable input is not reasonably available to us.

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Table	Debt at December 31, consisted of: 2018 2017 (millions) Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 (issued: $500.0, August 2011) $ 499.1 $ 506.5 $ 498.8 $ 520.7 2.45% Senior Notes due 2027 (issued: $500.0, August 2016) 496.5 455.5 496.1 477.9 6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999) 296.4 368.5 296.1 382.3 4.00% Senior Notes due 2029 (issued: $550.0, October 2018) 544.5 562.4 0 0 6.25% Senior Notes due 2032 (issued: $400.0, November 2002) 395.5 496.6 395.3 516.9 4.35% Senior Notes due 2044 (issued: $350.0, April 2014) 346.6 350.2 346.5 388.7 3.70% Senior Notes due 2045 (issued: $400.0, January 2015) 395.3 366.7 395.2 402.9 4.125% Senior Notes due 2047 (issued: $850.0, April 2017) 841.4 831.9 841.2 917.1 4.20% Senior Notes due 2048 (issued: $600.0, March 2018) 589.6 594.0 0 0 Other debt instruments 1 0 0 37.1 37.1 Total $ 4,404.9 $ 4,532.3 $ 3,306.3 $ 3,643.6 1 Consist of term loans issued by ARX prior to The Progressive Corporation acquiring a controlling interest in 2015. The repayment was funded in part with proceeds from fixed-rate loans made to ARX by The Progressive Corporation. These intercompany transactions were eliminated in consolidation.
Aggregate Principal Payments on Debt Outstanding	Aggregate required principal payments on debt outstanding at December 31, 2018, are as follows: (millions) Year Payments 2019 $ 0 2020 0 2021 500 2022 0 2023 0 Thereafter 3,950 Total $ 4,450
Cash Flow Hedging [Member]
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges Included in Accumulated Other Comprehensive Income	The following table shows the original gain (loss) recognized at debt issuance and the unamortized balance at December 31, 2018 , on a pretax basis: (millions) Unrealized Gain (Loss) at Debt Issuance Unamortized Balance at December 31, 2018 3.75% Senior Notes $ (5.1 ) $ (1.5 ) 6 5/8% Senior Notes (4.2 ) (2.6 ) 6.25% Senior Notes 5.1 3.5 4.35% Senior Notes (1.6 ) (1.5 ) 3.70% Senior Notes (12.9 ) (11.9 ) 4.125% Senior Notes (8.0 ) (7.8 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Income Tax Provision	The components of our income tax provision were as follows: (millions) 2018 2017 2016 Current tax provision Federal $ 673.1 $ 680.9 $ 469.6 State 21.5 12.8 12.7 Deferred tax expense (benefit) Federal (145.9 ) (149.4 ) (66.3 ) State (6.1 ) (3.5 ) (2.5 ) Total income tax provision $ 542.6 $ 540.8 $ 413.5
Reconciliation of Provision (Benefit) for Income Taxes Reported in Consolidated Statements of Income with Tax at Statutory Rate	The provision for income taxes in the accompanying consolidated statements of comprehensive income differed from the statutory rate as follows: ($ in millions) 2018 2017 2016 Income before income taxes $ 3,163.6 $ 2,138.9 $ 1,470.7 Tax at statutory federal rate $ 664.4 21 % $ 748.6 35 % $ 514.8 35 % Tax effect of: Tax credits 1 (76.3 ) (2 ) (52.4 ) (2 ) (62.2 ) (4 ) Stock-based compensation 2 (25.1 ) (1 ) (25.1 ) (1 ) 0 0 Tax-deductible dividends (14.6 ) (1 ) (9.7 ) 0 (6.1 ) 0 Dividends received deduction 3, 4 (9.7 ) 0 (20.7 ) (1 ) (22.6 ) (2 ) Exempt interest income 4 (5.9 ) 0 (16.9 ) (1 ) (15.7 ) (1 ) Nondeductible compensation expense 5 (0.2 ) 0 10.1 0 0.5 0 Net deferred tax liability revaluation 6 0 0 (99.5 ) (5 ) 0 0 State income taxes, net of federal taxes 12.2 0 6.0 0 6.6 0 Other items, net (2.2 ) 0 0.4 0 (1.8 ) 0 Total income tax provision $ 542.6 17 % $ 540.8 25 % $ 413.5 28 % 1 Includes $ 71.0 million , $ 48.7 million , and $58.7 million for 2018, 2017, and 2016, respectively, of benefits on investments in federal renewable energy tax credit funds. 2 Represents excess tax benefits associated with share-based payments awards. Prior to 2017, these excess tax benefits were recorded directly to additional paid-in capital under the then existing accounting guidance. 3 2018 amount reflects a dividends received deduction percentage of 50% under the 2017 Tax Act. In 2017 and prior years the deduction percentage was 70% . 4 2018 amounts reflect a proration percentage of 25% for such income attributable to investments held by our insurance companies. In 2017 and prior years the proration percentage was 15% . 5 Decrease in 2018 reflects our updated interpretation regarding compensation that qualifies for deduction under the 2017 Tax Act based on additional guidance issued. Increase in 2017 primarily reflected our initial interpretation regarding the deductibility of such compensation. See further discussion below. 6 Pursuant to the 2017 Tax Act.
Components of Net Deferred Tax Assets	The following table shows the components of the net deferred tax asset (liability) at December 31, 2018 and 2017 , respectively. As noted above, the federal deferred tax assets (liabilities) at December 31, 2017, have been revalued to reflect the new 21% federal corporate income tax rate under the 2017 Tax Act. (millions) 2018 2017 Federal deferred tax assets: Unearned premiums reserve $ 439.9 $ 368.9 Non-deductible accruals 169.3 166.0 Loss and loss adjustment expense reserves 134.6 48.4 Net unrealized losses on fixed-maturity securities 28.2 0 Hedges on forecasted transactions 4.6 4.8 Other 16.2 7.3 Federal deferred tax liabilities: Net holding period gains on equity securities (316.8 ) 0 Deferred acquisition costs (199.8 ) (163.9 ) Property and equipment (85.7 ) (75.5 ) Loss and loss adjustment expense reserve transition adjustment (58.5 ) 0 Intangible assets (52.2 ) (66.6 ) Investment basis differences (43.3 ) (5.5 ) Prepaid expenses (4.7 ) (7.1 ) Deferred gain on extinguishment of debt 0 (0.4 ) Net unrealized gains on securities 0 (419.5 ) Other (8.9 ) (6.1 ) Net federal deferred tax asset (liability) 22.9 (149.2 ) Net state deferred tax asset 20.3 14.2 Net deferred tax asset (liability) $ 43.2 $ (135.0 )

Loss And Loss Adjustment Expe_2

Loss And Loss Adjustment Expense Reserves (Tables)	12 Months Ended
	Dec. 31, 2018
Insurance [Abstract]
Activity in Loss and Loss Adjustment Expense Reserves	Activity in the loss and loss adjustment expense reserves is summarized as follows: (millions) 2018 2017 2016 Balance at January 1 $ 13,086.9 $ 11,368.0 $ 10,039.0 Less reinsurance recoverables on unpaid losses 2,170.1 1,801.0 1,442.7 Net balance at January 1 10,916.8 9,567.0 8,596.3 Net loss and loss adjustment reserves disposed 0 0 (2.5 ) Total beginning reserves 10,916.8 9,567.0 8,593.8 Incurred related to: Current year 21,632.5 18,782.1 16,967.1 Prior years 88.5 25.9 (87.5 ) Total incurred 21,721.0 18,808.0 16,879.6 Paid related to: Current year 13,792.1 12,201.5 11,149.0 Prior years 6,017.6 5,256.7 4,757.4 Total paid 19,809.7 17,458.2 15,906.4 Net balance at December 31 12,828.1 10,916.8 9,567.0 Plus reinsurance recoverables on unpaid losses 2,572.7 2,170.1 1,801.0 Balance at December 31 $ 15,400.8 $ 13,086.9 $ 11,368.0
Short-duration Insurance Contracts, Claims Development	The following tables show incurred and paid claims development, net of reinsurance, by accident year. Only 2018 is audited; all prior years are considered required supplementary information and, therefore, are unaudited. Expected development on our case reserves is excluded from the IBNR reserves on our vehicle businesses, as discussed above. For the Property business, the IBNR reserves include expected case development based on the methodology used in establishing the case reserves for that segment. The cumulative number of incurred claims are based on accident coverages (e.g., bodily injury, collision, comprehensive, personal injury protection, property damage) related to opened claims. Coverage counts related to claims closed without payment are excluded from the cumulative number of incurred claims. Personal Lines - Agency - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 3,702.1 $ 3,627.7 $ 3,633.2 $ 3,654.4 $ 3,611.2 $ 0 701,788 2015 3,774.9 3,773.8 3,798.8 3,815.6 55.9 704,995 2016 4,082.9 4,130.0 4,152.0 69.5 740,325 2017 4,474.8 4,485.8 188.6 777,415 2018 5,141.8 802.8 839,051 Total $ 21,206.4 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,809.0 $ 2,868.1 $ 3,284.5 $ 3,482.3 $ 3,559.1 2015 1,793.1 2,976.0 3,416.5 3,623.3 2016 1,941.6 3,231.5 3,723.1 2017 2,074.0 3,478.5 2018 2,378.0 Total $ 16,762.0 All outstanding liabilities before 2014, net of reinsurance 1 64.6 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 4,509.0 1 Required supplementary information (unaudited) Personal Lines - Agency - Physical Damage ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 2,107.5 $ 2,090.3 $ 2,089.9 $ 2,088.0 $ 2,091.6 $ 0 1,374,721 2015 2,136.8 2,137.2 2,134.4 2,131.5 (3.8 ) 1,336,486 2016 2,423.4 2,398.9 2,401.8 (2.8 ) 1,398,842 2017 2,635.5 2,638.5 (11.8 ) 1,513,912 2018 2,819.0 (120.8 ) 1,677,878 Total $ 12,082.4 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 2,078.8 $ 2,091.6 $ 2,090.6 $ 2,090.7 $ 2,091.0 2015 2,106.2 2,138.1 2,134.4 2,134.1 2016 2,391.0 2,406.9 2,402.1 2017 2,599.8 2,643.2 2018 2,769.1 Total $ 12,039.5 All outstanding liabilities before 2014, net of reinsurance 1 0.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 43.3 1 Required supplementary information (unaudited) Personal Lines - Direct - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 2,946.8 $ 2,887.4 $ 2,898.1 $ 2,913.6 $ 2,884.1 $ 0 592,145 2015 3,330.5 3,328.3 3,354.2 3,399.3 44.3 659,289 2016 3,819.0 3,843.9 3,871.2 58.9 735,483 2017 4,209.5 4,209.9 167.0 770,740 2018 4,904.8 725.4 856,025 Total $ 19,269.3 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,413.0 $ 2,278.0 $ 2,624.2 $ 2,780.0 $ 2,844.0 2015 1,545.2 2,615.0 3,021.0 3,238.2 2016 1,780.6 2,991.1 3,476.9 2017 1,912.6 3,255.2 2018 2,235.1 Total $ 15,049.4 All outstanding liabilities before 2014, net of reinsurance 1 38.7 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 4,258.6 1 Required supplementary information (unaudited) Personal Lines - Direct - Physical Damage ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,889.3 $ 1,862.2 $ 1,861.7 $ 1,859.2 $ 1,861.7 $ 0 1,471,084 2015 2,110.7 2,097.7 2,093.5 2,090.8 (4.0 ) 1,540,090 2016 2,521.0 2,475.4 2,477.7 (3.8 ) 1,676,008 2017 2,750.6 2,743.7 (16.1 ) 1,790,360 2018 3,202.3 (175.4 ) 2,065,458 Total $ 12,376.2 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 1,874.6 $ 1,864.1 $ 1,862.7 $ 1,861.8 $ 1,861.4 2015 2,094.7 2,100.1 2,094.7 2,093.7 2016 2,505.0 2,485.8 2,479.3 2017 2,742.1 2,753.5 2018 3,170.0 Total $ 12,357.9 All outstanding liabilities before 2014, net of reinsurance 1 0.1 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 18.4 1 Required supplementary information (unaudited) Commercial Lines - Liability ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 822.5 $ 795.4 $ 820.3 $ 823.0 $ 813.5 $ 0 74,682 2015 897.6 911.1 914.8 899.7 14.0 77,839 2016 1,185.8 1,204.8 1,231.1 26.4 92,730 2017 1,374.1 1,366.6 70.9 96,905 2018 1,700.8 292.5 108,792 Total $ 6,011.7 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 234.0 $ 438.7 $ 610.0 $ 715.3 $ 771.0 2015 238.4 501.5 675.0 786.3 2016 298.6 639.9 886.0 2017 325.8 712.9 2018 382.7 Total $ 3,538.9 All outstanding liabilities before 2014, net of reinsurance 1 31.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 2,504.2 1 Required supplementary information (unaudited) Commercial Lines - Physical Damage ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 240.3 $ 239.7 $ 238.6 $ 238.0 $ 238.4 $ 0 59,630 2015 274.4 274.1 273.5 272.4 (0.6 ) 62,599 2016 379.6 379.8 378.2 (0.2 ) 74,180 2017 415.4 412.1 (2.0 ) 77,170 2018 475.0 (10.0 ) 83,350 Total $ 1,776.1 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 224.6 $ 238.3 $ 237.7 $ 237.9 $ 238.2 2015 248.5 271.9 272.0 272.2 2016 336.7 376.9 376.8 2017 369.0 409.4 2018 426.0 Total $ 1,722.6 All outstanding liabilities before 2014, net of reinsurance 1 0.4 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 53.9 1 Required supplementary information (unaudited) Property Business ($ in millions) As of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance December 31, 2018 For the years ended December 31, Total of IBNR Liabilities Plus Expected Development on Reported Claims Cumulative Number of Incurred Claim Counts Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 415.5 $ 389.1 $ 379.7 $ 376.3 $ 375.3 $ 2.5 40,992 2015 460.0 416.5 403.6 398.8 3.8 41,980 2016 568.6 541.2 537.1 9.6 53,582 2017 672.8 680.9 11.5 71,153 2018 839.0 159.8 58,135 Total $ 2,831.1 Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance For the years ended December 31, Accident Year 2014 1 2015 1 2016 1 2017 1 2018 2014 $ 269.2 $ 351.5 $ 365.9 $ 370.3 $ 371.9 2015 280.3 372.8 383.5 390.1 2016 415.2 498.2 516.9 2017 506.7 647.1 2018 595.9 Total $ 2,521.9 All outstanding liabilities before 2014, net of reinsurance 1 5.5 Liabilities for claims and claim adjustment expenses, net of reinsurance $ 314.7 1 Required supplementary information (unaudited)
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability	The following table reconciles the net incurred and paid claims development tables to the liability for claims and claim adjustment expenses: (millions) 2018 2017 Net outstanding liabilities Personal Lines Agency, Liability $ 4,509.0 $ 3,955.5 Agency, Physical Damage 43.3 26.2 Direct, Liability 4,258.6 3,685.1 Direct, Physical Damage 18.4 (5.6 ) Commercial Lines Liability 2,504.2 2,027.4 Physical Damage 53.9 51.7 Property 314.7 245.8 Other business 42.9 43.7 Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 11,745.0 10,029.8 Reinsurance recoverable on unpaid claims Personal Lines Agency, Liability 836.8 769.8 Agency, Physical Damage 0 0 Direct, Liability 1,070.4 838.1 Direct, Physical Damage 0 0 Commercial Lines Liability 287.4 105.1 Physical Damage 0 0.1 Property 145.4 243.8 Other business 222.1 200.9 Total reinsurance recoverable on unpaid claims 2,562.1 2,157.8 Unallocated claims adjustment expense related to: Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance 1,083.1 887.0 Reinsurance recoverable on unpaid claims 10.6 12.3 Total gross liability for unpaid claims and claim adjustment expense $ 15,400.8 $ 13,086.9
Short-duration Insurance Contracts, Schedule of Historical Claims Duration	The following table shows the average historical claims duration as of December 31, 2018 : (Required Supplementary Information - Unaudited) Average Annual Percentage Payout of Incurred Claims by Age, Net of Reinsurance Years 1 2 3 4 5 Personal Lines Agency, Liability 47.1% 30.7% 11.6% 5.4% 2.1% Agency, Physical Damage 98.9 1.1 (0.1) 0 0 Direct, Liability 46.1 31.2 12.2 5.9 2.2 Direct, Physical Damage 100.1 (0.1) (0.2) 0 0 Commercial Lines Liability 24.6 27.7 20.1 12.6 6.8 Physical Damage 90.4 9.0 (0.1) 0.1 0.1 Property 73.0 20.0 3.3 1.4 0.4

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2018
Reinsurance Disclosures [Abstract]
Effect of Reinsurance on Premiums Written and Earned	The effect of reinsurance on premiums written and earned for the years ended December 31, was as follows: 2018 2017 2016 (millions) Written Earned Written Earned Written Earned Direct premiums $ 33,753.1 $ 31,970.2 $ 27,860.7 $ 26,425.7 $ 23,941.9 $ 23,111.2 Ceded premiums: Regulated plans (596.4 ) (557.5 ) (505.9 ) (479.6 ) (439.4 ) (425.1 ) Non-Regulated plans (546.8 ) (479.4 ) (222.7 ) (216.2 ) (149.0 ) (212.1 ) Total ceded premiums (1,143.2 ) (1,036.9 ) (728.6 ) (695.8 ) (588.4 ) (637.2 ) Net premiums $ 32,609.9 $ 30,933.3 $ 27,132.1 $ 25,729.9 $ 23,353.5 $ 22,474.0
Prepaid Reinsurance Premiums and Reinsurance Recoverables	Our prepaid reinsurance premiums and reinsurance recoverables were comprised of the following at December 31: Prepaid Reinsurance Premiums Reinsurance Recoverables ($ in millions) 2018 2017 2018 2017 Regulated plans: MCCA $ 55.3 18 % $ 44.3 22 % $ 1,903.9 71 % $ 1,611.5 71 % CAIP 72.9 24 50.0 25 254.7 9 218.0 10 NCRF 34.0 11 31.5 15 78.1 3 74.2 3 NFIP 55.9 18 53.8 26 27.8 1 148.8 7 Other 0.6 0 0.3 0 21.4 1 8.2 0 Total Regulated plans 218.7 71 179.9 88 2,285.9 85 2,060.7 91 Non-Regulated plans: Commercial Lines 79.2 25 14.3 7 254.2 10 63.4 3 Property 11.8 4 9.1 5 147.7 5 138.6 6 Other 0 0 0 0 8.3 0 10.7 0 Total Non-Regulated plans 91.0 29 23.4 12 410.2 15 212.7 9 Total $ 309.7 100 % $ 203.3 100 % $ 2,696.1 100 % $ 2,273.4 100 %

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Amounts Charged to Income for Employees Incentive Compensation Plans	The amounts charged to income for Progressive and ARX incentive compensation plans for the years ended December 31, were: 2018 2017 2016 (millions) Pretax After Tax Pretax After Tax Pretax After Tax Non-equity incentive plans – cash $ 539.5 $ 426.2 $ 461.3 $ 299.8 $ 386.8 $ 251.4 Equity incentive plans: Equity awards 76.2 60.2 92.9 60.4 80.9 52.6 Liability awards 1.0 0.8 2.5 1.6 4.3 2.8
Assets Held in Deferral Plan Irrevocable Grantor Trust Account	The Deferral Plan Irrevocable Grantor Trust account held the following assets at December 31: (millions) 2018 2017 Progressive common shares 1 $ 114.7 $ 128.2 Other investment funds 2 124.0 167.0 Total $ 238.7 $ 295.2 1 Included 3.6 million and 4.4 million common shares as of December 31, 2018 and 2017 , respectively, to be distributed in common shares. 2 Amount is included in other assets on the balance sheet.
Employee
Summary of Restricted Stock Activity	A summary of all employee restricted equity award activity during the years ended December 31, follows: 2018 2017 2016 Restricted Equity Awards Number of Shares 1 Weighted Average Grant Date Fair Value Number of Shares 1 Weighted Average Grant Date Fair Value Number of Shares 1 Weighted Average Grant Date Fair Value Beginning of year 5,858,848 $ 30.47 6,951,373 $ 26.18 7,725,227 $ 23.37 Add (deduct): Granted 2 1,876,109 45.55 2,383,475 32.01 1,870,660 31.54 Vested (2,811,070 ) 26.41 (3,220,671 ) 22.53 (2,422,700 ) 21.50 Forfeited (67,531 ) 36.10 (255,329 ) 28.03 (221,814 ) 24.64 End of year 3,4 4,856,356 $ 38.56 5,858,848 $ 30.47 6,951,373 $ 26.18 1 Includes restricted stock units; Upon vesting, all units will be converted on a one-for-one basis into Progressive common shares funded from existing treasury shares. All performance-based awards are included at their target amounts. 2 We reinvest dividend equivalents on restricted stock units. For 2018 , 2017 , and 2016 , the number of units “granted” shown in the table above includes 144,668 , 157,396 , and 165,045 of dividend equivalent units, respectively, at a weighted average grant date fair value of $0 , since the dividends were factored into the grant date fair value of the original grant. 3 At December 31, 2018 , the number of shares included 1,017,520 performance-based units at their target amounts. We expect 2,447,409 units to vest based upon our current estimates of the likelihood of achieving the pre-determined performance goals applicable to each award. 4 At December 31, 2018 , the total unrecognized compensation cost related to unvested equity awards was $100.6 million , which includes performance-based awards at their currently estimated vesting value. This compensation expense will be recognized into the income statement over the weighted average vesting period of 2.2 years.
Director
Summary of Restricted Stock Activity	A summary of all directors’ restricted stock activity during the years ended December 31, follows: 2018 2017 2016 Restricted Stock Number of Shares Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Number of Shares Weighted Average Grant Date Fair Value Beginning of year 53,284 $ 40.54 55,839 $ 33.24 89,427 $ 27.23 Add (deduct): Granted 41,706 62.23 53,284 40.54 55,839 33.24 Vested (53,284 ) 40.54 (55,839 ) 33.24 (89,427 ) 27.23 End of year 1 41,706 $ 62.23 53,284 $ 40.54 55,839 $ 33.24 1 At December 31, 2018, the remaining unrecognized compensation cost related to restricted stock awards was $0.9 million .
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding and Exercisable [Table Text Block]	A summary of all ARX employee stock option activity during the years ended December 31, follows: 2018 2017 2016 Options Outstanding Number of Shares Weighted Average Number of Shares Weighted Average Number of Shares Weighted Average Beginning of year 22,550 $ 564.60 24,995 $ 526.46 24,995 $ 526.46 Add (deduct): Exercised 1 (6,483 ) 506.26 (2,445 ) 174.65 0 0 End of year 16,067 $ 588.15 22,550 $ 564.60 24,995 $ 526.46 Exercisable, end of year 13,967 $ 562.17 17,950 $ 517.75 16,995 $ 438.77 1 At the time of exercise in 2018 and 2017, the value earned by the option holders was $6.2 million and $2.9 million , respectively. 2018 2017 2016 Non-Vested Options Outstanding Number of Shares Weighted Average Number of Shares Weighted Average Number of Shares Weighted Average Beginning of year 4,600 $ 747.45 8,000 $ 712.74 12,000 $ 677.81 Add (deduct): Vested (2,500 ) 736.12 (3,400 ) 665.79 (4,000 ) 607.95 End of year 1 2,100 $ 760.93 4,600 $ 747.45 8,000 $ 712.74 1 At December 31, 2018, 2017, and 2016, the remaining unrecognized compensation cost related to unvested options was $0.2 million , $0.7 million , and $1.6 million , respectively, and the remaining weighted average vesting period on the unvested awards was 0.53 years, 1.01 years, and 1.36 years, respectively.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Reconciliation of Revenue and Operating Income from Segments to Consolidated	Following are the operating results for the years ended December 31: 2018 2017 2016 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 13,017.2 $ 1,435.7 $ 11,177.6 $ 839.6 $ 9,791.7 $ 492.8 Direct 13,017.5 1,088.5 10,769.6 683.7 9,396.5 412.2 Total Personal Lines 1 26,034.7 2,524.2 21,947.2 1,523.3 19,188.2 905.0 Commercial Lines 3,610.9 478.6 2,793.9 214.1 2,421.3 155.2 Property 2 1,287.7 (88.7 ) 988.8 (50.3 ) 864.5 32.5 Other indemnity 0 0.9 0 (0.2 ) 0 (1.6 ) Total underwriting operations 30,933.3 2,915.0 25,729.9 1,686.9 22,474.0 1,091.1 Fees and other revenues 3 472.2 NA 370.6 NA 332.5 NA Service businesses 158.5 24.4 126.8 17.3 103.3 11.3 Investments 4 415.0 390.7 612.7 588.8 530.0 507.6 Other gains (losses) 0 0 (1.0 ) (1.0 ) 1.6 1.6 Interest expense NA (166.5 ) NA (153.1 ) NA (140.9 ) Consolidated total $ 31,979.0 $ 3,163.6 $ 26,839.0 $ 2,138.9 $ 23,441.4 $ 1,470.7 NA = Not Applicable 1 Personal auto insurance accounted for 94% of the total Personal Lines segment net premiums earned in 2018 , compared to 93% in 2017 and 92% in 2016 ; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 During 2018 , 2017 , and 2016, pretax profit (loss) includes $72.0 million , $66.2 million , and $62.1 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX. Although this expense is included in our Property segment, it is not reported in the consolidated results of ARX and, therefore, does not affect the value of net income attributable to noncontrolling interest. 3 Pretax profit (loss) for fees and other revenues are allocated to operating segments. 4 Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.
Underwriting Margins and Combined Ratios for our Underwriting Operations	Following are the underwriting margins and combined ratios for our underwriting operations for the years ended December 31: 2018 2017 2016 Underwriting Margin Combined Ratio Underwriting Margin Combined Ratio Underwriting Margin Combined Ratio Personal Lines Agency 11.0 % 89.0 7.5 % 92.5 5.0 % 95.0 Direct 8.4 91.6 6.3 93.7 4.4 95.6 Total Personal Lines 9.7 90.3 6.9 93.1 4.7 95.3 Commercial Lines 13.3 86.7 7.7 92.3 6.4 93.6 Property 1 (6.9 ) 106.9 (5.1 ) 105.1 3.8 96.2 Total underwriting operations 9.4 90.6 6.6 93.4 4.9 95.1 1 Included in 2018 , 2017 , and 2016, are 5.6 points, 6.7 points, and 7.2 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX.

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Components of Other Comprehensive Income (Loss)	The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, for the years ended December 31, were as follows: Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income (loss) Total tax (provision) benefit After tax total accumulated other comprehensive income (loss) Total net unrealized gains (losses) on securities Net unrealized gains (losses) on forecasted transactions Foreign currency translation adjustment (Income) loss attributable to NCI Balance at December 31, 2017 $ 1,977.8 $ (695.6 ) $ 1,282.2 $ 1,295.0 $ (14.8 ) $ 0 $ 2.0 Cumulative effect adjustment 1 (2,006.0 ) 705.8 (1,300.2 ) (1,300.2 ) 0 0 0 Reclassification of disproportionate amounts 2 (4.3 ) (3.4 ) (7.7 ) (1.1 ) (3.2 ) 0 (3.4 ) Adjusted balance at December 31, 2017 (32.5 ) 6.8 (25.7 ) (6.3 ) (18.0 ) 0 (1.4 ) Other comprehensive income (loss) before reclassifications: Investment securities (224.1 ) 47.0 (177.1 ) (177.1 ) 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes 0 0 0 0 0 0 0 Forecasted transactions 0 0 0 0 0 0 0 Foreign currency translation adjustment 0 0 0 0 0 0 0 (Income) loss attributable to noncontrolling interest (NCI) 4.3 (1.0 ) 3.3 0 0 0 3.3 Total other comprehensive income (loss) before reclassifications (219.8 ) 46.0 (173.8 ) (177.1 ) 0 0 3.3 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings 0 0 0 0 0 0 0 Net realized gains (losses) on securities (98.3 ) 20.5 (77.8 ) (77.8 ) 0 0 0 Other gains (losses) 0 0 0 0 0 0 0 Interest expense (1.0 ) 0.2 (0.8 ) 0 (0.8 ) 0 0 Total reclassification adjustment for amounts realized in net income (99.3 ) 20.7 (78.6 ) (77.8 ) (0.8 ) 0 0 Total other comprehensive income (loss) (120.5 ) 25.3 (95.2 ) (99.3 ) 0.8 0 3.3 Balance at December 31, 2018 $ (153.0 ) $ 32.1 $ (120.9 ) $ (105.6 ) $ (17.2 ) $ 0 $ 1.9 1 Reflects the fair value changes on equity securities as of December 31, 2017 , which are reported as realized gains (losses) under the new accounting guidance. See Note 1 – Reporting and Accounting Policies for additional information. 2 Reflects the effect of the change in the U.S. federal tax rate on our available-for-sale fixed-maturity securities and our hedges on forecasted transactions as of December 31, 2017 (see Note 1 – Reporting and Accounting Policies for additional information) and the adjustment to reflect the change in value on (income) loss attributable to NCI in conjunction with the "put" transaction (see Note 15 – Redeemable Noncontrolling Interest for additional information). Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total Total tax After tax total Total net Net Foreign (Income) loss attributable to NCI Balance at December 31, 2016 $ 1,439.5 $ (506.1 ) $ 933.4 $ 939.6 $ (9.4 ) $ (1.1 ) $ 4.3 Other comprehensive income (loss) before reclassifications: Investment securities 636.9 (224.0 ) 412.9 412.9 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes 0 0 0 0 0 0 0 Forecasted transactions (8.0 ) 2.8 (5.2 ) 0 (5.2 ) 0 0 Foreign currency translation adjustment 0.4 (0.1 ) 0.3 0 0 0.3 0 (Income) loss attributable to noncontrolling interest (NCI) (3.5 ) 1.2 (2.3 ) 0 0 0 (2.3 ) Total other comprehensive income (loss) before reclassifications 625.8 (220.1 ) 405.7 412.9 (5.2 ) 0.3 (2.3 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (14.9 ) 5.3 (9.6 ) (9.6 ) 0 0 0 Net realized gains (losses) on securities 103.3 (36.2 ) 67.1 67.1 0 0 0 Other gains (losses) 1 (1.2 ) 0.4 (0.8 ) 0 0 (0.8 ) 0 Interest expense 0.3 (0.1 ) 0.2 0 0.2 0 0 Total reclassification adjustment for amounts realized in net income 87.5 (30.6 ) 56.9 57.5 0.2 (0.8 ) 0 Total other comprehensive income (loss) 538.3 (189.5 ) 348.8 355.4 (5.4 ) 1.1 (2.3 ) Balance at December 31, 2017 $ 1,977.8 $ (695.6 ) $ 1,282.2 $ 1,295.0 $ (14.8 ) $ 0 $ 2.0 1 During 2017, we ceased writing insurance in Australia resulting in a loss of $1.2 million relating to the foreign currency translation adjustment. The loss is netted with other gains (losses) on our consolidated statements of comprehensive income for the year end December 31, 2017. Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total Total tax After tax total Total net Net Foreign (Income) loss attributable to NCI Total at December 31, 2015 $ 1,234.5 $ (434.1 ) $ 800.4 $ 809.0 $ (8.2 ) $ (1.5 ) $ 1.1 Other comprehensive income (loss) before reclassifications: Investment securities 320.5 (112.6 ) 207.9 207.9 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes (0.1 ) 0.1 0 0 0 0 0 Forecasted transactions 0 0 0 0 0 0 0 Foreign currency translation adjustment 0.6 (0.2 ) 0.4 0 0 0.4 0 (Income) loss attributable to noncontrolling interest (NCI) 5.1 (1.9 ) 3.2 0 0 0 3.2 Total other comprehensive income (loss) before reclassifications 326.1 (114.6 ) 211.5 207.9 0 0.4 3.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (27.1 ) 9.5 (17.6 ) (17.6 ) 0 0 0 Net realized gains (losses) on securities 146.3 (51.4 ) 94.9 94.9 0 0 0 Other gains (losses) 0 0 0 0 0 0 0 Interest expense 1.9 (0.7 ) 1.2 0 1.2 0 0 Total reclassification adjustment for amounts realized in net income 121.1 (42.6 ) 78.5 77.3 1.2 0 0 Total other comprehensive income (loss) 205.0 (72.0 ) 133.0 130.6 (1.2 ) 0.4 3.2 Total at December 31, 2016 $ 1,439.5 $ (506.1 ) $ 933.4 $ 939.6 $ (9.4 ) $ (1.1 ) $ 4.3

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Minimum Commitments under Noncancelable Operating Lease Agreements	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
Expense Incurred for Leases	The expense we incurred for the leases disclosed above, as well as other operating leases that may be cancelable or have terms less than one year, was: (millions) Expense 2018 $ 77.3 2017 77.2 2016 72.9

Dividends (Tables)

Dividends (Tables)	12 Months Ended
	Dec. 31, 2018
Dividends [Abstract]
Dividends	Following is a summary of our common shareholder dividends that were declared in the last three years, under our annual variable dividend policy: (millions, except per share amounts) Amount of Common Share Dividends Dividend Type Declared Paid Per Share Accrued 1 Annual – Variable December 2018 February 2019 $ 2.5140 $ 1,467.9 Annual – Variable December 2017 February 2018 1.1247 655.1 Annual – Variable December 2016 February 2017 0.6808 395.4 1 The accrual is based on an estimate of shares outstanding as of the record date and is recorded as a component of "accounts payable, accrued expenses, and other liabilities" on the Consolidated Balance Sheets; the prior year amount was reclassified into this line item from "dividends payable" to conform to the current year presentation. For the dividends declared in December 2017 and 2016, we paid $654.9 million and $395.4 million , respectively.

Redeemable Noncontrolling Int_2

Redeemable Noncontrolling Interest (Tables)	12 Months Ended
	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Redeemable Noncontrolling Interest [Table Text Block]	The changes in the components of redeemable NCI during the year ended December 31, were: (millions) 2018 2017 2016 Balance, Beginning of year $ 503.7 $ 483.7 $ 464.9 Net income attributable to NCI 5.7 5.9 26.2 Other comprehensive income (loss) attributable to NCI 1 (3.3 ) 2.3 (3.2 ) Exercise of employee stock options 9.4 3.4 0 Purchase/change of ARX minority shares (298.2 ) 0 0 Change in redemption value of NCI (2.8 ) 8.4 (4.2 ) Balance, End of year $ 214.5 $ 503.7 $ 483.7 1 Amount represents the other comprehensive income (loss) attributable to NCI, as reflected on the the Consolidated Statements of Comprehensive Income; any reclassification to accumulated other comprehensive income (loss) attributable to NCI due to a change in the minority ownership percentage does not impact the amount of redeemable NCI.

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Net Carrying Amount of Other Intangible Assets	The following table is a summary of the net carrying amount of other intangible assets as of December 31 : (millions) 2018 2017 Intangible assets subject to amortization $ 282.2 $ 354.2 Indefinite-lived intangible assets 1 12.4 12.4 Total $ 294.6 $ 366.6 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 both years presented.
Intangible Assets Subject to Amortization	Intangible assets subject to amortization for the years ended December 31, consisted of the following: (millions) 2018 2017 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 137.3 $ 118.9 $ 256.2 $ 100.7 $ 155.5 Agency relationships 159.2 42.6 116.6 159.2 31.3 127.9 Software rights 79.1 40.1 39.0 79.1 29.4 49.7 Trade name 34.8 27.1 7.7 34.8 13.7 21.1 Total $ 529.3 $ 247.1 $ 282.2 $ 529.3 $ 175.1 $ 354.2
Amortization on Intangible Assets	The estimated aggregate amortization on these intangible assets for each of the next five years as of December 31, 2018, is as follows: (millions) Year Amortization Expense 2019 $ 66.4 2020 56.9 2021 56.6 2022 29.2 2023 13.5

SCHEDULE I - Summary Of Inves_2

SCHEDULE I - Summary Of Investments - Other Than Investments in Related Parties Summary Of Investments - Other than Investments In Related Parties (Detail) $ in Millions	Dec. 31, 2018USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	$ 32,203.3
Fair Value	33,567.4
Amount At Which Shown In The Balance Sheet	33,567.4
Fixed maturities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	28,255.9
Fair Value	28,111.5
Amount At Which Shown In The Balance Sheet	28,111.5
Fixed maturities | US Government Agencies and Authorities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	9,897.4
Fair Value	9,916.5
Amount At Which Shown In The Balance Sheet	9,916.5
Fixed maturities | State and local government obligations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,654.6
Fair Value	1,649.1
Amount At Which Shown In The Balance Sheet	1,649.1
Fixed maturities | Public Utilities, Bonds
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	479.6
Fair Value	473.8
Amount At Which Shown In The Balance Sheet	473.8
Fixed maturities | Corporate And Other Debt Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	8,328.9
Fair Value	8,220.5
Amount At Which Shown In The Balance Sheet	8,220.5
Fixed maturities | Asset-backed Securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	7,651.7
Fair Value	7,613.3
Amount At Which Shown In The Balance Sheet	7,613.3
Fixed maturities | Redeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	243.7
Fair Value	238.3
Amount At Which Shown In The Balance Sheet	238.3
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,151.5
Fair Value	3,660
Amount At Which Shown In The Balance Sheet	3,660
Equity securities | Utilities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	81.4
Fair Value	140.4
Amount At Which Shown In The Balance Sheet	140.4
Equity securities | Financials
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	226.4
Fair Value	525.8
Amount At Which Shown In The Balance Sheet	525.8
Equity securities | Industrials
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	841.1
Fair Value	1,959.9
Amount At Which Shown In The Balance Sheet	1,959.9
Equity securities | Nonredeemable preferred stocks
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,002.6
Fair Value	1,033.9
Amount At Which Shown In The Balance Sheet	1,033.9
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,795.9
Fair Value	1,795.9
Amount At Which Shown In The Balance Sheet	$ 1,795.9

SCHEDULE II - Condensed Finan_2

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Comprehensive Income (Parent Company) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Total revenues		$ 31,979	$ 26,839	$ 23,441.4
Expenses
Interest expense		166.5	153.1	140.9
Total expenses		28,815.4	24,700.1	21,970.7
Income before income taxes		3,163.6	2,138.9	1,470.7
Benefit for income taxes		542.6	540.8	413.5
Net income attributable to Progressive		2,615.3	1,592.2	1,031
Comprehensive income attributable to Progressive		2,520.1	1,941	1,164
Parent Company
Revenues
Dividends from subsidiaries		939.1	867.3	375.5
Undistributed income (loss) from subsidiaries		1,770.7	866.3	741.9
Equity in net income of subsidiaries		2,709.8	1,733.6	1,117.4
Intercompany investment income		39.4	11.3	5.5
Gains (losses) on extinguishment of debt		0	0.2	1.6
Total revenues		2,749.2	1,745.1	1,124.5
Expenses
Interest expense		166.8	151.1	140.4
Deferred compensation	[1]	7.5	23.2	5.3
Other operating costs and expenses		5.1	4.6	4.2
Total expenses		179.4	178.9	149.9
Income before income taxes		2,569.8	1,566.2	974.6
Benefit for income taxes		45.5	26	56.4
Net income attributable to Progressive		2,615.3	1,592.2	1,031
Other comprehensive income (loss)		(95.2)	348.8	133
Comprehensive income attributable to Progressive		$ 2,520.1	$ 1,941	$ 1,164
[1]	See Note 4 – Employee Benefit Plans in these condensed financial statements.

SCHEDULE II - Condensed Finan_3

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Balance Sheets (Parent Company) (Detail) - USD ($) $ in Millions		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Assets
Net deferred income taxes		$ 43.2		$ 0
Other assets		365.1		412.9
Total assets		46,575		38,701.2
Liabilities and Shareholders' Equity
Accounts payable, accrued expenses, and other liabilities	[1]	5,046.5		3,481
Dividends payable		1,467.9		655.1		$ 395.4
Debt	[2]	4,404.9		3,306.3
Total liabilities		35,538.7		28,912.7
Redeemable noncontrolling interest (NCI)		214.5	[3]	503.7	[3]	483.7	$ 464.9
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5 and 0)		493.9		0
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 214.3 and 215.8)		583.2		581.7
Paid-in capital		1,479		1,389.2
Retained earnings		8,386.6		6,031.7
Total accumulated other comprehensive income attributable to Progressive		(120.9)		1,282.2		933.4	$ 800.4
Total shareholders’ equity		10,821.8		9,284.8		$ 7,957.1
Total liabilities, redeemable NCI, and shareholders’ equity		46,575		38,701.2
Parent Company
Assets
Investment in affiliate		5		5
Investment in subsidiaries		13,652.2		11,721.3
Receivable from investment subsidiary		2,658.9		1,466.1
Intercompany receivable		651.1		578.6
Net deferred income taxes		68.2		67.1
Other assets		124.2		167.3
Total assets		17,159.6		14,005.4
Liabilities and Shareholders' Equity
Accounts payable, accrued expenses, and other liabilities		250.5		292.6
Dividends payable		1,467.9		655.1
Debt		4,404.9		3,269.2
Total liabilities		6,123.3		4,216.9
Redeemable noncontrolling interest (NCI)		214.5		503.7
Serial Preferred Shares, Series B, no par value (cumulative, liquidation preference $1,000 per share) (authorized, issued, and outstanding 0.5 and 0)		493.9		0
Common shares, $1.00 par value (authorized 900.0; issued 797.5, including treasury shares of 214.3 and 215.8)		583.2		581.7
Paid-in capital		1,479		1,389.2
Retained earnings		8,386.6		6,031.7
Total accumulated other comprehensive income attributable to Progressive		(120.9)		1,282.2
Total shareholders’ equity		10,821.8		9,284.8
Total liabilities, redeemable NCI, and shareholders’ equity		$ 17,159.6		$ 14,005.4
[1]	See Note 12 – Litigation, Note 13 – Commitments and Contingencies, and Note 14 – Dividends for further discussion.
[2]	Consists of long-term debt. See Note 4 – Debt for further discussion.
[3]	See Note 15 – Redeemable Noncontrolling Interest for further discussion.

SCHEDULE II - Condensed Finan_4

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Balance Sheets (Parent Company) (Parenthetical) (Detail) - $ / shares	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Common Shares, par value (USD per share)	$ 1		$ 1	$ 1
Common Shares, authorized (shares)	900,000,000		900,000,000
Common Shares, issued (shares)	797,500,000		797,500,000
Common Shares, treasury shares (shares)	214,300,000		215,800,000
Parent Company
Condensed Financial Statements, Captions [Line Items]
Common Shares, par value (USD per share)	$ 1		$ 1
Common Shares, authorized (shares)	900,000,000		900,000,000
Common Shares, issued (shares)	797,500,000		797,500,000
Common Shares, treasury shares (shares)	214,300,000		215,800,000
Series B Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred Stock, Shares Issued		500,000
Preferred Stock, Liquidation Preference Per Share		$ 1,000	$ 0
Serial Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred Stock, Shares Authorized	20,000,000		20,000,000
Serial Preferred Stock | Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred Stock, Shares Authorized	20,000,000		20,000,000
Serial Preferred Stock | Series B Preferred Stock
Condensed Financial Statements, Captions [Line Items]
Preferred Stock, No Par Value	$ 0		$ 0	$ 0
Preferred Stock, Shares Authorized	500,000		0
Preferred Stock, Shares Issued	500,000		0
Preferred Stock, Shares Outstanding	500,000		0
Preferred Stock, Liquidation Preference Per Share	$ 1,000		$ 0
Serial Preferred Stock | Series B Preferred Stock | Parent Company
Condensed Financial Statements, Captions [Line Items]
Preferred Stock, No Par Value	$ 0		$ 0
Preferred Stock, Shares Authorized	500,000		0
Preferred Stock, Shares Issued	500,000		0
Preferred Stock, Shares Outstanding	500,000		0
Preferred Stock, Liquidation Preference Per Share	$ 1,000		$ 0

SCHEDULE II - Condensed Finan_5

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Statements Of Cash Flows (Parent Company) (Detail) - USD ($) $ in Millions		1 Months Ended		12 Months Ended
		Feb. 28, 2018	Feb. 28, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net income attributable to Progressive				$ 2,615.3	$ 1,592.2	$ 1,031
Adjustments to reconcile net income attributable to Progressive to net cash provided by operating activities:
Amortization of equity-based compensation				77.2	95.4	85.2
Changes in:
Accounts payable, accrued expenses, and other liabilities				746.6	400	308.9
Income taxes				(158.7)	(172.6)	(55.7)
Other, net				(57.7)	(134.8)	(90.2)
Net cash provided by operating activities				6,284.8	3,756.8	2,732.7
Cash Flows From Investing Activities:
Payments to Acquire Additional Interest in Subsidiaries				296.9	0	0
Net cash used in investing activities				(7,331.8)	(3,406.7)	(2,480.7)
Cash Flows From Financing Activities:
Net proceeds from debt issuance				1,134	841.1	495.6
Net proceeds from preferred stock issuance				493.9	0	0
Reacquisitions of debt				0	(635.6)	(18.2)
Dividends paid to shareholders		$ (654.9)	$ (395.4)	(654.9)	(395.4)	(519)
Dividends paid to preferred shareholders				(13.5)	0	0
Acquisition of treasury shares for restricted stock tax liabilities				(78.6)	(57.6)	(25.1)
Acquisition of treasury shares acquired in open market				(0.4)	(4.9)	(167.4)
Tax benefit from vesting of equity-based compensation				0	0	9.2
Net cash provided by (used in) financing activities				846.7	(300.9)	(250.4)
Change in cash, cash equivalents, and restricted cash				(200.3)	48.9	2
Cash, cash equivalents, and restricted cash - Beginning of year				275.3	226.4	224.4
Cash, cash equivalents, and restricted cash - End of year				75	275.3	226.4
Parent Company
Cash Flows From Operating Activities:
Net income attributable to Progressive				2,615.3	1,592.2	1,031
Adjustments to reconcile net income attributable to Progressive to net cash provided by operating activities:
Undistributed (income) loss from subsidiaries				(1,770.7)	(866.3)	(741.9)
Amortization of equity-based compensation				2.4	2.1	2.2
(Gains) losses on extinguishment of debt				0	(0.2)	(1.6)
Changes in:
Intercompany receivable				77.5	(71.3)	(37.3)
Accounts payable, accrued expenses, and other liabilities				(29.6)	53.6	24.2
Income taxes				(14.2)	37.3	(5)
Other, net				47.8	(22.6)	(13.3)
Net cash provided by operating activities				928.5	724.8	258.3
Cash Flows From Investing Activities:
Additional investments in equity securities of consolidated subsidiaries				(178.3)	(86.7)	(112)
Payments to Acquire Additional Interest in Subsidiaries				287.9	0	0
Acquisition of business				0	(18.7)	0
(Paid to) received from investment subsidiary				(1,192.8)	(344.2)	78.6
Net cash used in investing activities				(1,659)	(449.6)	(33.4)
Cash Flows From Financing Activities:
Net proceeds from debt issuance				1,134	841.1	495.6
Net proceeds from preferred stock issuance				493.9	0	0
Reacquisitions of debt				0	(594.4)	(18.2)
Dividends paid to shareholders				(654.9)	(395.4)	(519)
Dividends paid to preferred shareholders				(13.5)	0	0
Acquisition of treasury shares for restricted stock tax liabilities				(78.6)	(57.6)	(25.1)
Acquisition of treasury shares acquired in open market				(0.4)	(4.9)	(167.4)
Loan to ARX Holding Corp.	[1]			(150)	(64)	0
Tax benefit from vesting of equity-based compensation				0	0	9.2
Net cash provided by (used in) financing activities				730.5	(275.2)	(224.9)
Change in cash, cash equivalents, and restricted cash				0	0	0
Cash, cash equivalents, and restricted cash - Beginning of year				0	0	0
Cash, cash equivalents, and restricted cash - End of year				$ 0	$ 0	$ 0
[1]	See Note 4 – Debt in our Annual Report.

SCHEDULE II - Condensed Finan_6

SCHEDULE II - Condensed Financial Information Of Registrant Condensed Financial Information Of Registrant - Additional Information (Detail) - USD ($) $ in Billions	Dec. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Securities Held In Consolidated Non-Insurance Subsidiary	$ 2.9	$ 1.6
Parent Company
Significant Accounting Policies [Line Items]
Securities Held In Consolidated Non-Insurance Subsidiary	$ 2.9	$ 1.6

SCHEDULE II - Condensed Finan_7

SCHEDULE II - Condensed Financial Information Of Registrant Progressive Corporation Cash Paid (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income taxes	$ 702.6	$ 715.6	$ 459.4
Interest	154	146.3	139.2
Parent Company
Income taxes	679.2	669.7	450.2
Interest	$ 153.6	$ 142.2	$ 134.2

SCHEDULE II - Condensed Finan_8

SCHEDULE II - Condensed Financial Information Of Registrant Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018
Income Taxes [Line Items]
Benefit for income taxes	$ 44.7
Lower Limit | ARX and subsidiaries
Income Taxes [Line Items]
Noncontrolling interest, ownership percentage (less than)		80.00%

SCHEDULE III - Supplementary _2

SCHEDULE III - Supplementary Insurance Information Supplementary Insurance Information (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	[1]	$ 951.6	$ 780.5	$ 651.2
Future policy benefits, losses, claims, and loss expenses	[1]	15,400.8	13,086.9	11,368
Unearned premiums	[1]	10,686.5	8,903.5	7,468.3
Other policy claims and benefits payable	[1]	0	0	0
Premium revenue		30,933.3	25,729.9	22,474
Net investment income	[1],[2]	796.2	539.2	456.5
Benefits, claims, losses, and settlement expenses		21,721	18,808	16,879.6
Amortization of deferred policy acquisition costs		2,573.7	2,124.9	1,863.8
Other operating expenses		4,195.8	3,480.7	2,972
Net Premiums Written		32,609.9	27,132.1	23,353.5
Personal Lines
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue		26,034.7	21,947.2	19,188.2
Benefits, claims, losses, and settlement expenses		18,389.8	16,141.4	14,591.1
Amortization of deferred policy acquisition costs		1,964.4	1,656.4	1,446.6
Other operating expenses		3,563.3	2,954.8	2,549.2
Net Premiums Written		27,157.6	22,928.4	19,819.5
Commercial Lines
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue		3,610.9	2,793.9	2,421.3
Benefits, claims, losses, and settlement expenses		2,394	1,966.4	1,741
Amortization of deferred policy acquisition costs		396	309.3	266.7
Other operating expenses		396	335.3	285.4
Net Premiums Written		3,996.4	3,112.7	2,598.3
Property, Liability and Casualty Insurance Product Line
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue		1,287.7	988.8	864.5
Benefits, claims, losses, and settlement expenses		937	700.2	546.1
Amortization of deferred policy acquisition costs		213.3	159.2	150.5
Other operating expenses		237.2	190.4	137.2
Net Premiums Written		1,455.9	1,091	935.7
Other Indemnity
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Premium revenue		0	0	0
Benefits, claims, losses, and settlement expenses		0.2	0	1.4
Amortization of deferred policy acquisition costs		0	0	0
Other operating expenses		(0.7)	0.2	0.2
Net Premiums Written		$ 0	$ 0	$ 0
[1]	Progressive does not allocate assets, liabilities, or investment income to operating segments.
[2]	Excludes total net realized gains (losses) on securities.

SCHEDULE IV - Reinsurance Reins

SCHEDULE IV - Reinsurance Reinsurance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	$ 31,970.2	$ 26,425.7	$ 23,111.2
Ceded to Other Companies	1,036.9	695.8	637.2
Property, Liability and Casualty Insurance Product Line
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Gross Amount	31,970.2	26,425.7	23,111.2
Ceded to Other Companies	1,036.9	695.8	637.2
Assumed From Other Companies	0	0	0
Net Amount	$ 30,933.3	$ 25,729.9	$ 22,474
Percentage of Amount Assumed to Net	0.00%	0.00%	0.00%

Reporting and Accounting Poli_4

Reporting and Accounting Policies - Advertising Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Advertising costs	$ 1,422.4	$ 1,005.4	$ 756.2

Reporting and Accounting Poli_5

Reporting and Accounting Policies Property, Plant, and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 2,164.9	$ 2,060.2
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,033.2)	(940.6)
Property and equipment, net of accumulated depreciation of $1,033.2 and $940.6	1,131.7	1,119.6
Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	928.8	962
Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	349.8	331.9
Software Development [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	327	273.1
Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	259.1	197
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	177	203.4
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 123.2	$ 92.8
Property, Plant and Equipment, Useful Life	3 years
Lower Limit | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	7 years
Lower Limit | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Lower Limit | Software Development [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Lower Limit | Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	1 year
Upper Limit | Building and Building Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Upper Limit | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Upper Limit | Software Development [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Upper Limit | Software and Software Development Costs [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years

Reporting and Accounting Poli_6

Reporting and Accounting Policies - Capitalized Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Capitalized interest	$ 1.8	$ 2.8	$ 2.9

Reporting and Accounting Poli_7

Reporting and Accounting Policies - Compensation Expense Recognized for Equity-Based Compensation (Details) - Stock compensation plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax expense	$ 77.2	$ 95.4	$ 85.2
Tax benefit1	$ 16.2	$ 33.4	$ 29.8

Reporting and Accounting Poli_8

Reporting and Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Income taxes	$ 702.6	$ 715.6	$ 459.4
Interest	$ 154	$ 146.3	$ 139.2

Reporting and Accounting Poli_9

Reporting and Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Jan. 31, 2019	Apr. 02, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net	$ 0					$ 0
Held for sale property	$ 39,300,000					5,300,000
Accelerated vesting percentage	50.00%
Open reverse repurchase commitments	$ 0					0
Assets	46,575,000,000					38,701,200,000
Total liabilities	$ 35,538,700,000					28,912,700,000
Cumulative Effect of New Accounting Principle in Period of Adoption						1,300,200,000
Reclassification of Stranded Amounts in AOCI to Equity						$ 7,700,000
ARX Holding Corp.
Property, Plant and Equipment [Line Items]
Equity interest percentage	86.80%					69.00%	69.20%
Accounting Standards Update 2016-01 [Member]
Property, Plant and Equipment [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 1,300,000,000
Accounting Standards Update 2018-02 [Member]
Property, Plant and Equipment [Line Items]
Reclassification of Stranded Amounts in AOCI to Equity				$ 4,300,000
Cash and Cash Equivalents [Member] | ARX Holding Corp.
Property, Plant and Equipment [Line Items]
Open reverse repurchase commitments	$ 117,300,000					$ 247,200,000	$ 150,000,000
Lower Limit | ARX Holding Corp.
Property, Plant and Equipment [Line Items]
Equity interest percentage			80.00%
Intangible assets finite lives	1 year
Upper Limit | ARX Holding Corp.
Property, Plant and Equipment [Line Items]
Equity interest percentage						80.00%
Intangible assets finite lives	10 years
Subsequent Event | Property Subject to Operating Lease [Member] | Adjustments for New Accounting Pronouncement
Property, Plant and Equipment [Line Items]
Assets		$ 215,000,000
Total liabilities		$ 215,000,000

Investments Investment Portfoli

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 30,051.8
Gross Unrealized Gains	115.4
Gross Unrealized Losses	(249.6)
Net Holding Period Gains (Losses)	(10.2)
Fair Value	$ 29,907.4
% of Total Fair Value	89.10%
Equity Securities, at Fair Value
Cost	$ 2,151.5
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Net Holding Period Gains (Losses)	1,508.5
Fair Value	$ 3,660
% of Total Fair Value	10.90%
Debt and Equity securities, at Fair Value
Cost	$ 32,203.3
Gross Unrealized Gains	115.4
Gross Unrealized Losses	(249.6)
Net Holding Periods Gains (Losses)	1,498.3
Fair Value	$ 33,567.4	$ 27,274.7
% of Total Fair Value	100.00%
Available-for-Sale Securities
Cost		25,276.9
Gross Unrealized Gains		2,097
Gross Unrealized Losses		(99.4)
Net Holding Period Gains (Losses)		0.2
Fair Value		$ 27,274.7
% of Total Fair Value		100.00%
Other Receivables from Broker-Dealers and Clearing Organizations		$ 5.8
Other Payables to Broker-Dealers and Clearing Organizations	$ 5.9
Securities Held In Consolidated Non-Insurance Subsidiary	2,900	1,600
Nonredeemable preferred stocks
Equity Securities, at Fair Value
Cost	1,002.6
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Net Holding Period Gains (Losses)	31.3
Fair Value	$ 1,033.9
% of Total Fair Value	3.10%
Common equities
Equity Securities, at Fair Value
Cost	$ 1,148.9
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Net Holding Period Gains (Losses)	1,477.2
Fair Value	$ 2,626.1
% of Total Fair Value	7.80%
Fixed Maturities and Short Term [Member]
Debt and Equity securities, at Fair Value
Fair Value		23,071.1
Available-for-Sale Securities
Cost		23,079.3
Gross Unrealized Gains		82
Gross Unrealized Losses		(90.4)
Net Holding Period Gains (Losses)		0.2
Fair Value		$ 23,071.1
% of Total Fair Value		84.60%
Equity securities
Debt and Equity securities, at Fair Value
Fair Value	$ 3,660	$ 4,203.6
Available-for-Sale Securities
Cost		2,197.6
Gross Unrealized Gains		2,015
Gross Unrealized Losses		(9)
Net Holding Period Gains (Losses)		0
Fair Value		$ 4,203.6
% of Total Fair Value		15.40%
Equity securities | Nonredeemable preferred stocks
Debt and Equity securities, at Fair Value
Fair Value	1,033.9	$ 803.8
Available-for-Sale Securities
Cost		698.6
Gross Unrealized Gains		114
Gross Unrealized Losses		(8.8)
Net Holding Period Gains (Losses)		0
Fair Value		$ 803.8
% of Total Fair Value		2.90%
Equity securities | Common equities
Debt and Equity securities, at Fair Value
Fair Value	2,626.1	$ 3,399.8
Available-for-Sale Securities
Cost		1,499
Gross Unrealized Gains		1,901
Gross Unrealized Losses		(0.2)
Net Holding Period Gains (Losses)		0
Fair Value		$ 3,399.8
% of Total Fair Value		12.50%
Fixed maturities
Available-for-Sale Securities
Cost		$ 20,209.9
Gross Unrealized Gains		82
Gross Unrealized Losses		(90.4)
Net Holding Period Gains (Losses)		0.2
Fair Value		$ 20,201.7
% of Total Fair Value		74.10%
Fixed maturities | U.S. government obligations
Available-for-Sale Securities
Cost		$ 6,688.8
Gross Unrealized Gains		1.1
Gross Unrealized Losses		(44)
Net Holding Period Gains (Losses)		0
Fair Value		$ 6,645.9
% of Total Fair Value		24.40%
Fixed maturities | State and local government obligations
Available-for-Sale Securities
Cost		$ 2,285.6
Gross Unrealized Gains		20.7
Gross Unrealized Losses		(9.3)
Net Holding Period Gains (Losses)		0.1
Fair Value		$ 2,297.1
% of Total Fair Value		8.40%
Fixed maturities | Corporate debt securities
Available-for-Sale Securities
Cost		$ 4,997.2
Gross Unrealized Gains		14.8
Gross Unrealized Losses		(14.4)
Net Holding Period Gains (Losses)		0.1
Fair Value		$ 4,997.7
% of Total Fair Value		18.30%
Fixed maturities | Residential mortgage-backed securities
Available-for-Sale Securities
Cost		$ 828.8
Gross Unrealized Gains		11.3
Gross Unrealized Losses		(3.4)
Net Holding Period Gains (Losses)		0
Fair Value		$ 836.7
% of Total Fair Value		3.10%
Fixed maturities | Commercial mortgage-backed securities
Available-for-Sale Securities
Cost		$ 2,760.1
Gross Unrealized Gains		11.8
Gross Unrealized Losses		(13.3)
Net Holding Period Gains (Losses)		0
Fair Value		$ 2,758.6
% of Total Fair Value		10.10%
Fixed maturities | Other asset-backed securities
Available-for-Sale Securities
Cost		$ 2,454.5
Gross Unrealized Gains		4.5
Gross Unrealized Losses		(4.5)
Net Holding Period Gains (Losses)		0.2
Fair Value		$ 2,454.7
% of Total Fair Value		9.00%
Fixed maturities | Redeemable preferred stocks
Available-for-Sale Securities
Cost		$ 194.9
Gross Unrealized Gains		17.8
Gross Unrealized Losses		(1.5)
Net Holding Period Gains (Losses)		(0.2)
Fair Value		$ 211
% of Total Fair Value		0.80%
Short-term investments
Available-for-Sale Securities
Cost		$ 2,869.4
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Net Holding Period Gains (Losses)		0
Fair Value		$ 2,869.4
% of Total Fair Value		10.50%
Short-term investments
Debt Securities, Available-for-Sale, at Fair Value
Cost	1,795.9
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Net Holding Period Gains (Losses)	0
Fair Value	$ 1,795.9
% of Total Fair Value	5.40%
Fixed maturities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 28,255.9
Gross Unrealized Gains	115.4
Gross Unrealized Losses	(249.6)
Net Holding Period Gains (Losses)	(10.2)
Fair Value	$ 28,111.5
% of Total Fair Value	83.70%
Fixed maturities | U.S. government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 9,897.4
Gross Unrealized Gains	71.2
Gross Unrealized Losses	(52.1)
Net Holding Period Gains (Losses)	0
Fair Value	$ 9,916.5
% of Total Fair Value	29.50%
Fixed maturities | State and local government obligations
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 1,654.6
Gross Unrealized Gains	7.3
Gross Unrealized Losses	(12.8)
Net Holding Period Gains (Losses)	0
Fair Value	$ 1,649.1
% of Total Fair Value	4.90%
Fixed maturities | Corporate debt securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 8,808.5
Gross Unrealized Gains	13.6
Gross Unrealized Losses	(125.3)
Net Holding Period Gains (Losses)	(2.5)
Fair Value	$ 8,694.3
% of Total Fair Value	25.90%
Fixed maturities | Residential mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 733.5
Gross Unrealized Gains	6
Gross Unrealized Losses	(5.1)
Net Holding Period Gains (Losses)	0
Fair Value	$ 734.4
% of Total Fair Value	2.20%
Fixed maturities | Commercial mortgage-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 3,332.8
Gross Unrealized Gains	7.8
Gross Unrealized Losses	(39)
Net Holding Period Gains (Losses)	0
Fair Value	$ 3,301.6
% of Total Fair Value	9.80%
Fixed maturities | Other asset-backed securities
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 3,585.4
Gross Unrealized Gains	3.6
Gross Unrealized Losses	(11.8)
Net Holding Period Gains (Losses)	0.1
Fair Value	$ 3,577.3
% of Total Fair Value	10.70%
Fixed maturities | Redeemable preferred stocks
Debt Securities, Available-for-Sale, at Fair Value
Cost	$ 243.7
Gross Unrealized Gains	5.9
Gross Unrealized Losses	(3.5)
Net Holding Period Gains (Losses)	(7.8)
Fair Value	$ 238.3
% of Total Fair Value	0.70%

Investments Hybrid Securities (

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Hybrid Securities [Line Items]
Hybrid securities	$ 244.7	$ 142.9
State and local government obligations
Hybrid Securities [Line Items]
Hybrid securities	3.6	6.1
Corporate debt securities
Hybrid Securities [Line Items]
Hybrid securities	158.9	99.8
Other asset-backed securities
Hybrid Securities [Line Items]
Hybrid securities	4.5	6.7
Redeemable preferred stocks
Hybrid Securities [Line Items]
Hybrid securities	$ 77.7	$ 30.3

Investments Composition of Fixe

Investments Composition of Fixed Maturities by Maturity (Detail) - Fixed maturities $ in Millions	Dec. 31, 2018USD ($)
Schedule of Debt Securities by Contractual Maturity [Line Items]
Less than one year	$ 4,880.1
One to five years	17,719.4
Five to ten years	5,581.3
Ten years or greater	75.1
Cost	28,255.9
Less than one year	4,867
One to five years	17,652
Five to ten years	5,517.5
Ten years or greater	75
Debt Securities, Available-for-Sale	$ 28,111.5

Investments Gross Unrealized lo

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Dec. 31, 2018USD ($)security	Dec. 31, 2017USD ($)security
Number of Securities
Total | security	1,292
Less than 12 Months | security	349
12 Months or Greater | security	943
Total | security		1,166
Less than 12 Months | security		689
12 Months or Greater | security		477
Fair Value
Total	$ 17,652.2
Less than 12 Months	5,493.2
12 Month or Greater	12,159
Total		$ 13,980.2
Less than 12 Months		10,434.6
12 Months or Greater		3,545.6
Gross Unrealized Losses
Total	249.6
Less than 12 Months	47.3
12 Months or Greater	$ 202.3
Total		99.4
Less than 12 Months		58.3
12 Months or Greater		$ 41.1
U.S. government obligations
Number of Securities
Total | security	51
Less than 12 Months | security	2
12 Months or Greater | security	49
Fair Value
Total	$ 4,438
Less than 12 Months	126.6
12 Month or Greater	4,311.4
Gross Unrealized Losses
Total	52.1
Less than 12 Months	0.1
12 Months or Greater	$ 52
State and local government obligations
Number of Securities
Total | security	299
Less than 12 Months | security	49
12 Months or Greater | security	250
Fair Value
Total	$ 972.4
Less than 12 Months	192.7
12 Month or Greater	779.7
Gross Unrealized Losses
Total	12.8
Less than 12 Months	0.3
12 Months or Greater	$ 12.5
Corporate debt securities
Number of Securities
Total | security	368
Less than 12 Months | security	133
12 Months or Greater | security	235
Fair Value
Total	$ 6,723.3
Less than 12 Months	2,613.3
12 Month or Greater	4,110
Gross Unrealized Losses
Total	125.3
Less than 12 Months	33.4
12 Months or Greater	$ 91.9
Residential mortgage-backed securities
Number of Securities
Total | security	228
Less than 12 Months | security	32
12 Months or Greater | security	196
Fair Value
Total	$ 450.2
Less than 12 Months	248.8
12 Month or Greater	201.4
Gross Unrealized Losses
Total	5.1
Less than 12 Months	0.8
12 Months or Greater	$ 4.3
Commercial mortgage-backed securities
Number of Securities
Total | security	140
Less than 12 Months | security	48
12 Months or Greater | security	92
Fair Value
Total	$ 2,328.5
Less than 12 Months	741.2
12 Month or Greater	1,587.3
Gross Unrealized Losses
Total	39
Less than 12 Months	8.9
12 Months or Greater	$ 30.1
Other asset-backed securities
Number of Securities
Total | security	203
Less than 12 Months | security	84
12 Months or Greater | security	119
Fair Value
Total	$ 2,691.3
Less than 12 Months	1,551.7
12 Month or Greater	1,139.6
Gross Unrealized Losses
Total	11.8
Less than 12 Months	3.2
12 Months or Greater	$ 8.6
Redeemable preferred stocks
Number of Securities
Total | security	3
Less than 12 Months | security	1
12 Months or Greater | security	2
Fair Value
Total	$ 48.5
Less than 12 Months	18.9
12 Month or Greater	29.6
Gross Unrealized Losses
Total	3.5
Less than 12 Months	0.6
12 Months or Greater	$ 2.9
Fixed maturities
Number of Securities
Total | security		1,143
Less than 12 Months | security		670
12 Months or Greater | security		473
Fair Value
Total		$ 13,839
Less than 12 Months		10,364.7
12 Months or Greater		3,474.3
Gross Unrealized Losses
Total		90.4
Less than 12 Months		57.6
12 Months or Greater		$ 32.8
Fixed maturities | U.S. government obligations
Number of Securities
Total | security		58
Less than 12 Months | security		41
12 Months or Greater | security		17
Fair Value
Total		$ 5,817
Less than 12 Months		4,869.3
12 Months or Greater		947.7
Gross Unrealized Losses
Total		44
Less than 12 Months		34.6
12 Months or Greater		$ 9.4
Fixed maturities | State and local government obligations
Number of Securities
Total | security		358
Less than 12 Months | security		230
12 Months or Greater | security		128
Fair Value
Total		$ 1,200.3
Less than 12 Months		737.6
12 Months or Greater		462.7
Gross Unrealized Losses
Total		9.3
Less than 12 Months		4.4
12 Months or Greater		$ 4.9
Fixed maturities | Corporate debt securities
Number of Securities
Total | security		222
Less than 12 Months | security		171
12 Months or Greater | security		51
Fair Value
Total		$ 2,979.4
Less than 12 Months		2,072.9
12 Months or Greater		906.5
Gross Unrealized Losses
Total		14.4
Less than 12 Months		9.1
12 Months or Greater		$ 5.3
Fixed maturities | Residential mortgage-backed securities
Number of Securities
Total | security		201
Less than 12 Months | security		30
12 Months or Greater | security		171
Fair Value
Total		$ 300.9
Less than 12 Months		75.1
12 Months or Greater		225.8
Gross Unrealized Losses
Total		3.4
Less than 12 Months		0.2
12 Months or Greater		$ 3.2
Fixed maturities | Commercial mortgage-backed securities
Number of Securities
Total | security		105
Less than 12 Months | security		63
12 Months or Greater | security		42
Fair Value
Total		$ 1,682.3
Less than 12 Months		1,221.2
12 Months or Greater		461.1
Gross Unrealized Losses
Total		13.3
Less than 12 Months		5.9
12 Months or Greater		$ 7.4
Fixed maturities | Other asset-backed securities
Number of Securities
Total | security		197
Less than 12 Months | security		134
12 Months or Greater | security		63
Fair Value
Total		$ 1,837.3
Less than 12 Months		1,377.8
12 Months or Greater		459.5
Gross Unrealized Losses
Total		4.5
Less than 12 Months		3.3
12 Months or Greater		$ 1.2
Fixed maturities | Redeemable preferred stocks
Number of Securities
Total | security		2
Less than 12 Months | security		1
12 Months or Greater | security		1
Fair Value
Total		$ 21.8
Less than 12 Months		10.8
12 Months or Greater		11
Gross Unrealized Losses
Total		1.5
Less than 12 Months		0.1
12 Months or Greater		$ 1.4
Equity securities
Number of Securities
Total | security		23
Less than 12 Months | security		19
12 Months or Greater | security		4
Fair Value
Total		$ 141.2
Less than 12 Months		69.9
12 Months or Greater		71.3
Gross Unrealized Losses
Total		9
Less than 12 Months		0.7
12 Months or Greater		$ 8.3
Equity securities | Nonredeemable preferred stocks
Number of Securities
Total | security		4
Less than 12 Months | security		1
12 Months or Greater | security		3
Fair Value
Total		$ 127.8
Less than 12 Months		56.5
12 Months or Greater		71.3
Gross Unrealized Losses
Total		8.8
Less than 12 Months		0.5
12 Months or Greater		$ 8.3
Equity securities | Common equities
Number of Securities
Total | security		19
Less than 12 Months | security		18
12 Months or Greater | security		1
Fair Value
Total		$ 13.4
Less than 12 Months		13.4
12 Months or Greater		0
Gross Unrealized Losses
Total		0.2
Less than 12 Months		0.2
12 Months or Greater		$ 0

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) - Fixed maturities - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities	$ (19.8)	$ (20)
Residential mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities	(19.7)	(19.7)
Commercial mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Pre-Tax, Available-for-sale, Debt Securities	$ (0.1)	$ (0.3)

Investments OTTI Credit Losses

Investments OTTI Credit Losses Recognized in Earnings (Detail) - Fixed maturities - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$ 500,000	$ 11,500,000	$ 12,800,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	0	400,000	0
Reductions for securities sold/matured	0	(11,200,000)	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0	(200,000)	(1,300,000)
Ending balance	500,000	500,000	11,500,000
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0	11,100,000	12,400,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	0	0	0
Reductions for securities sold/matured	0	(10,900,000)	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0	(200,000)	(1,300,000)
Ending balance	0	0	11,100,000
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	500,000	400,000	400,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment	0	400,000	0
Reductions for securities sold/matured	0	(300,000)	0
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Changes in Cash Flows	0	0	0
Ending balance	$ 500,000	$ 500,000	$ 400,000

Investments Components of Net R

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	$ 25.2
Equity Securities, FV-NI, Realized Gain	290.7
Debt and Equity Securities, Realized Gains	315.9
Debt Securities, Available-for-sale, Realized Loss	(119.6)
Equity Securities, FV-NI, Realized Loss	(25.6)
Debt and Equity Securities, Realized Losses	(145.2)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	(94.4)
Equity Securities, FV-NI, Realized Gain (Loss)	265.1
Net realized gains (losses) on security sales	170.7
Gross realized gains on securities sales		$ 175.9	$ 193.9
Available-for-sale Securities, Gross Realized Losses		(64.7)	(40)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		115.7	155.8
Available-for-sale Securities, Gross Realized Gain (Loss) and Litigation, Excluding Other than Temporary Impairments		112.4	154.3
Unrealized Gain (Loss) on Hybrid Instrument, Net	(10.4)	(1.6)	2.1
Equity Securities, FV-NI, Unrealized Gain (Loss)	(497.5)
Derivative, Gain (Loss) on Derivative, Net	0	0	(20)
Net holding period gains (losses) on securities	(507.9)
Net holding period gains (losses) on securities		(1.6)	(17.9)
Realized Gain on Litigation Settlements	0	1.2	0.4
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities	0	11.6	25.6
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	(68.3)	(61.2)	(85.3)
Total net realized gains (losses) on securities	(405.5)
Total net realized gains (losses) on securities		49.6	51.1
U.S. government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	6.7
Debt Securities, Available-for-sale, Realized Loss	(98.7)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	(92)
State and local government obligations
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	9.5
Debt Securities, Available-for-sale, Realized Loss	(2.9)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	6.6
Corporate debt securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	2.4
Debt Securities, Available-for-sale, Realized Loss	(10.4)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	(8)
Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	0
Debt Securities, Available-for-sale, Realized Loss	(0.1)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	(0.1)
Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	2
Debt Securities, Available-for-sale, Realized Loss	(6.3)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	(4.3)
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities	0
Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	0.1
Debt Securities, Available-for-sale, Realized Loss	(1.1)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	(1)
Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	4.5
Debt Securities, Available-for-sale, Realized Loss	(0.1)
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	4.4
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities	0
Short-term investments
Gain (Loss) on Securities [Line Items]
Debt Securities, Available-for-sale, Realized Gain	0
Debt Securities, Available-for-sale, Realized Loss	0
Debt Securities, Available-for-sale, Realized Gain (Loss), Excluding Other-than-temporary Impairment	0
Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain	4.1
Equity Securities, FV-NI, Realized Loss	(3.9)
Equity Securities, FV-NI, Realized Gain (Loss)	0.2
Common equities
Gain (Loss) on Securities [Line Items]
Equity Securities, FV-NI, Realized Gain	286.6
Equity Securities, FV-NI, Realized Loss	(21.7)
Equity Securities, FV-NI, Realized Gain (Loss)	264.9
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities	0	11.2	0.3
Fixed Maturities and Short Term [Member]
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		74.5	120.7
Available-for-sale Securities, Gross Realized Losses		(46.6)	(19)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		27.9	101.7
Fixed Maturities and Short Term [Member] | U.S. government obligations
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		6.2	24.6
Available-for-sale Securities, Gross Realized Losses		(28.7)	(2.4)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		(22.5)	22.2
Fixed Maturities and Short Term [Member] | State and local government obligations
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		10.5	16
Available-for-sale Securities, Gross Realized Losses		(0.1)	(1.6)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		10.4	14.4
Fixed Maturities and Short Term [Member] | Corporate debt securities
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		20.3	43.3
Available-for-sale Securities, Gross Realized Losses		(5.1)	(2.5)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		15.2	40.8
Fixed Maturities and Short Term [Member] | Residential mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		23.8	2.5
Available-for-sale Securities, Gross Realized Losses		(0.4)	(0.2)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		23.4	2.3
Fixed Maturities and Short Term [Member] | Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		4.9	13.3
Available-for-sale Securities, Gross Realized Losses		(5.3)	(5.6)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		(0.4)	7.7
Fixed Maturities and Short Term [Member] | Other asset-backed securities
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		0.3	0
Available-for-sale Securities, Gross Realized Losses		(0.4)	0
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		(0.1)	0
Fixed Maturities and Short Term [Member] | Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		8.5	20.9
Available-for-sale Securities, Gross Realized Losses		(6.4)	(6.6)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		2.1	14.3
Fixed Maturities and Short Term [Member] | Short-term investments
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		0	0.1
Available-for-sale Securities, Gross Realized Losses		(0.2)	(0.1)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		(0.2)	0
Fixed maturities
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities	0	0.4	25.3
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities		0.4	0
Fixed maturities | Redeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Debt and Equity Securities		0	25.3
Equity securities
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		101.4	73.2
Available-for-sale Securities, Gross Realized Losses		(18.1)	(21)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		83.3	52.2
Equity securities | Nonredeemable preferred stocks
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		58.4	11.9
Available-for-sale Securities, Gross Realized Losses		(5.9)	(5.3)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		52.5	6.6
Equity securities | Common equities
Gain (Loss) on Securities [Line Items]
Gross realized gains on securities sales		43	61.3
Available-for-sale Securities, Gross Realized Losses		(12.2)	(15.7)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments		30.8	45.6
Other Assets [Member]
Gain (Loss) on Securities [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	$ (68.3)	$ (49.6)	$ (59.7)

Investments Components of Equit

Investments Components of Equity Realized Gains (Losses) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Components of Equity Realized Gains (Losses) [Line Items]
Equity Securities, FV-NI, Gain (Loss)	$ (232.4)
Equity Securities, FV-NI, Realized Gain (Loss)	265.1
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ (497.5)

Investments Components of Net I

Investments Components of Net Investment Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	$ 820.5	$ 563.1	$ 478.9
Investment expenses	(24.3)	(23.9)	(22.4)
Net investment income	796.2	539.2	456.5
Available-for-sale Securities [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	714.8	460.7	373.1
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	105.7	102.4	105.8
Equity securities | Nonredeemable preferred stocks
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	45.9	44.1	48.6
Equity securities | Common equities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	59.8	58.3	57.2
Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	661.9	422.9	353.4
Fixed maturities | U.S. government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	196.8	72.7	18.2
Fixed maturities | State and local government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	37.7	51.5	52.3
Fixed maturities | Foreign government obligations
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	0	0.3	0.4
Fixed maturities | Corporate debt securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	217.9	125.2	110.7
Fixed maturities | Residential mortgage-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	27.6	34.7	47.3
Fixed maturities | Commercial mortgage-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	93.9	79.6	81.6
Fixed maturities | Other asset-backed securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	75.7	47.1	28
Fixed maturities | Redeemable preferred stocks
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	12.3	11.8	14.9
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross Investment Income, Operating	$ 52.9	$ 37.8	$ 19.7

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Apr. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Principal amount of bonds and certificates of deposit on deposit to meet state insurance regulatory and/or rating agency requirements		$ 250,800,000
Securities exceeding 10% of Shareholders' Equity		0	$ 0
Fair value of fixed-maturity securities that were non-income producing during the preceding 12 months		0
Securities Sold under Agreements to Repurchase		0	0
Open reverse repurchase commitments		0	$ 0
Gross Unrealized Losses		$ 249,600,000
Investment Portfolio Duration		2 years 9 months 22 days	2 years 6 months	2 years 2 months 13 days
Trading securities		$ 0	$ 0
Net realized gains (losses) on securities		0	0	$ 0
Derivative Assets (Liabilities), at Fair Value, Net		0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax		(1,000,000)	300,000	1,900,000
Derivative, Gain (Loss) on Derivative, Net		0	0	(20,000,000)
4.125% Senior Notes due 2047
Schedule of Investments [Line Items]
Senior notes, issuance amount	$ 850,000,000	$ 850,000,000	850,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.125%	4.125%
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	$ 8,000,000
Fixed maturities
Schedule of Investments [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment		$ 0	400,000	0
Interest Rate Swaps
Schedule of Investments [Line Items]
Derivative, Notional Amount				750,000,000
Derivative, Gain (Loss) on Derivative, Net				19,000,000
Future [Member]
Schedule of Investments [Line Items]
Derivative, Notional Amount				135,000,000
Derivative, Gain (Loss) on Derivative, Net				300,000
Non-hedging Instruments | Interest Rate Swaps
Schedule of Investments [Line Items]
Derivative Assets (Liabilities), at Fair Value, Net		$ 0	$ 0	$ 0

Fair Value Composition of Inves

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 33,567,400,000	$ 27,274,700,000
Long-term Debt, Fair Value	4,532,300,000	3,643,600,000
Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	29,907,400,000
Fixed Maturities and Short Term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		23,071,100,000
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,660,000,000	4,203,600,000
Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,033,900,000	803,800,000
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	984,100,000	798,800,000
Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	44,800,000	0
Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	5,000,000	5,000,000
Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,626,100,000	3,399,800,000
Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,625,800,000	3,399,500,000
Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	300,000	300,000
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	32,203,300,000	25,276,900,000
Carrying Value	4,404,900,000	3,306,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	30,051,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed Maturities and Short Term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		23,079,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,151,500,000	2,197,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,002,600,000	698,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	951,600,000	693,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	46,000,000	0
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	5,000,000	5,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,148,900,000	1,499,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,148,600,000	1,498,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	300,000	300,000
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	14,345,800,000	11,950,400,000
Long-term Debt, Fair Value	0	0
Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	11,648,100,000
Fair Value, Inputs, Level 1 | Fixed Maturities and Short Term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		8,470,300,000
Fair Value, Inputs, Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,697,700,000	3,480,100,000
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	71,900,000	80,600,000
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	71,900,000	80,600,000
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 1 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,625,800,000	3,399,500,000
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	2,625,800,000	3,399,500,000
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	19,191,200,000	15,319,000,000
Long-term Debt, Fair Value	4,532,300,000	3,606,500,000
Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	18,259,300,000
Fair Value, Inputs, Level 2 | Fixed Maturities and Short Term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		14,600,800,000
Fair Value, Inputs, Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	931,900,000	718,200,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	931,900,000	718,200,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	887,100,000	718,200,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	44,800,000	0
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 2 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	30,400,000	5,300,000
Long-term Debt, Fair Value	0	37,100,000
Fair Value, Inputs, Level 3 | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	300,000	300,000
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0
Fair Value, Inputs, Level 3 | Fixed Maturities and Short Term [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		0
Fair Value, Inputs, Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	30,400,000	5,300,000
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	30,100,000	5,000,000
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	25,100,000	0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	5,000,000	5,000,000
Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	300,000	300,000
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	300,000	300,000
Short-term investments | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,795,900,000	2,869,400,000
Short-term investments | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,795,900,000	2,869,400,000
Short-term investments | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,722,100,000	1,824,400,000
Short-term investments | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	73,800,000	1,045,000,000
Short-term investments | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	28,111,500,000	20,201,700,000
Fixed maturities | Available-for-sale Securities [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	7,613,300,000	6,050,000,000
Fixed maturities | Available-for-sale Securities [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	20,259,900,000	13,940,700,000
Fixed maturities | Available-for-sale Securities [Member] | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,916,500,000	6,645,900,000
Fixed maturities | Available-for-sale Securities [Member] | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,649,100,000	2,297,100,000
Fixed maturities | Available-for-sale Securities [Member] | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,694,300,000	4,997,700,000
Fixed maturities | Available-for-sale Securities [Member] | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	734,400,000	836,700,000
Fixed maturities | Available-for-sale Securities [Member] | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,301,600,000	2,758,600,000
Fixed maturities | Available-for-sale Securities [Member] | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,577,300,000	2,454,700,000
Fixed maturities | Available-for-sale Securities [Member] | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	238,300,000	211,000,000
Fixed maturities | Available-for-sale Securities [Member] | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	78,200,000	64,100,000
Fixed maturities | Available-for-sale Securities [Member] | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	11,400,000
Fixed maturities | Available-for-sale Securities [Member] | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	160,100,000	135,500,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	28,255,900,000	20,209,900,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	7,651,700,000	6,043,400,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	20,360,500,000	13,971,600,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,897,400,000	6,688,800,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,654,600,000	2,285,600,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,808,500,000	4,997,200,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	733,500,000	828,800,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,332,800,000	2,760,100,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,585,400,000	2,454,500,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	243,700,000	194,900,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	79,300,000	61,300,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	10,100,000
Fixed maturities | Carrying (Reported) Amount, Fair Value Disclosure | Available-for-sale Securities [Member] | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	164,400,000	123,500,000
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,926,000,000	6,645,900,000
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,916,500,000	6,645,900,000
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,916,500,000	6,645,900,000
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,500,000	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	9,500,000	0
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	18,185,500,000	13,555,800,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	7,613,300,000	6,050,000,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	10,343,400,000	7,294,800,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,649,100,000	2,297,100,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	8,694,300,000	4,997,700,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	734,400,000	836,700,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,301,600,000	2,758,600,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	3,577,300,000	2,454,700,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	228,800,000	211,000,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	78,200,000	64,100,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	11,400,000
Fixed maturities | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	150,600,000	135,500,000
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	0	0
Fixed maturities | Fair Value, Inputs, Level 3 | Available-for-sale Securities [Member] | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 0	$ 0

Fair Value Summary of Changes i

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	$ 5.3	$ 0.7
Calls/ Maturities/ Paydowns	0	(0.4)
Purchases	25.1	5
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Ending Fair value	30.4	5.3
Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0	0.3
Calls/ Maturities/ Paydowns	0	(0.3)
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Ending Fair value	0	0
Fixed maturities | Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0	0.3
Calls/ Maturities/ Paydowns	0	(0.3)
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Ending Fair value	0	0
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0	0
Calls/ Maturities/ Paydowns	0	0
Purchases	25.1	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Ending Fair value	25.1	0
Equity securities | Nonredeemable preferred stocks | Industrials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	5	0
Calls/ Maturities/ Paydowns	0	0
Purchases	0	5
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Ending Fair value	5	5
Equity securities | Common equities | Other risk investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.3	0.4
Calls/ Maturities/ Paydowns	0	(0.1)
Purchases	0	0
Sales	0	0
Net Realized (Gain)/Loss on Sales	0	0
Change in Valuation	0	0
Net Transfers In (Out)	0	0
Ending Fair value	$ 0.3	$ 0.3

Fair Value Summary of Quantitat

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)$ / shares	Dec. 31, 2017USD ($)$ / shares
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 33,567.4	$ 27,274.7
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	30.4	5.3
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	0.3	0.3
Fair Value, Inputs, Level 3 | Total Quantitative Level Three Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	30.1	5
Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Internal Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	30.1	5
Financials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Internal Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 25.1	0
Fair Value Inputs, Original Issue Price | $ / shares	$ 9
Industrials | Fair Value, Inputs, Level 3 | Nonredeemable preferred stocks | Internal Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 5	$ 5
Fair Value Inputs, Price-to-Sales Ratio	5.5
Fair Value Inputs, Original Issue Price | $ / shares		$ 3.9

Fair Value - Additional Informa

Fair Value - Additional Information (Detail)	Dec. 31, 2018USD ($)security	Dec. 31, 2017USD ($)security
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 33,567,400,000	$ 27,274,700,000
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	79.00%	66.00%
Fair Value	$ 14,345,800,000	$ 11,950,400,000
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Vendor Quoted Prices, Percent of FV Hierarchy Level	99.00%	98.00%
Dealer Quoted Prices, Percent of FV Hierarchy Level	1.00%	2.00%
Fair Value	$ 19,191,200,000	$ 15,319,000,000
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	30,400,000	5,300,000
Fixed maturities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 0	$ 0
Nonredeemable preferred stocks | Internal Pricing | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities | security	2	1
Fair Value	$ 30,100,000	$ 5,000,000
Common equities | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of securities | security	1	1
Fair Value	$ 300,000	$ 300,000

Debt (Detail)

Debt (Detail) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Fair Value		$ 4,532.3	$ 3,643.6
Debt, Long-term and Short-term, Combined Amount	[1]	4,404.9	3,306.3
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Carrying Value		499.1	498.8
Fair Value		506.5	520.7
2.45% Senior Notes Due 2027
Debt Instrument [Line Items]
Carrying Value		496.5	496.1
Fair Value		455.5	477.9
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Carrying Value		296.4	296.1
Fair Value		368.5	382.3
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Carrying Value		544.5	0
Fair Value		562.4	0
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Carrying Value		395.5	395.3
Fair Value		496.6	516.9
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Carrying Value		346.6	346.5
Fair Value		350.2	388.7
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Carrying Value		395.3	395.2
Fair Value		366.7	402.9
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Carrying Value		841.4	841.2
Fair Value		831.9	917.1
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Carrying Value		589.6	0
Fair Value		594	0
Other Debt Instruments [Member]
Debt Instrument [Line Items]
Debt, Long-term and Short-term, Combined Amount		$ 0	$ 37.1
[1]	Consists of long-term debt. See Note 4 – Debt for further discussion.

Debt (Parenthetical) (Detail)

Debt (Parenthetical) (Detail) - USD ($)	Dec. 31, 2018	Oct. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Apr. 30, 2017
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 500,000,000			$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.75%
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 300,000,000			300,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.625%
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 400,000,000			400,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.25%
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 350,000,000			350,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.35%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 400,000,000			400,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.70%
2.45% Senior Notes Due 2027
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 500,000,000			500,000,000
Debt Instrument, Interest Rate, Stated Percentage	2.45%
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 850,000,000			850,000,000	$ 850,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.125%				4.125%
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 600,000,000		$ 600,000,000	0
Debt Instrument, Interest Rate, Stated Percentage	4.20%		4.20%
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Senior notes, issuance amount	$ 550,000,000	$ 550,000,000		$ 0
Debt Instrument, Interest Rate, Stated Percentage	4.00%	4.00%

Debt Aggregate Principal Paymen

Debt Aggregate Principal Payments On Debt Outstanding (Detail) $ in Millions	Dec. 31, 2018USD ($)
Debt Disclosure [Abstract]
Debt Instrument, Periodic Payment, Principal in Next Twelve Months	$ 0
Long-term Debt, Maturities, Repayments of Principal in Year Two	0
Long-Term Debt, Maturities, Repayments of Principal in Year Three	500
Long-Term Debt, Maturities, Repayments of Principal in Year Four	0
Long-Term Debt, Maturities, Repayments of Principal in Year Five	0
Long-Term Debt, Maturities, Repayments of Principal after Year Five	3,950
Total	$ 4,450

Debt Unrealized Gains (Losses)

Debt Unrealized Gains (Losses) From Debt Hedges Included In Accumulated Other (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Apr. 06, 2017	Jan. 26, 2015	Apr. 22, 2014	Aug. 17, 2011	Nov. 21, 2002	Mar. 01, 1999
Debt Instrument [Line Items]
Unrealized Gain (Loss)	$ (17.2)	$ (14.8)
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(1.5)					$ (5.1)
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(2.6)							$ (4.2)
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Unrealized Gain (Loss)	3.5						$ 5.1
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(1.5)				$ (1.6)
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Unrealized Gain (Loss)	(11.9)			$ (12.9)
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Unrealized Gain (Loss)	$ (7.8)		$ (8)

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Oct. 31, 2018	Mar. 31, 2018	Apr. 30, 2017	Dec. 31, 2018	Dec. 31, 2017
Discretionary Line of Credit
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 250,000,000
Debt Instrument, Term				30 days
Proceeds from Lines of Credit				$ 0	$ 0
4.00% Senior Notes due 2029
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 550,000,000			$ 550,000,000	0
Debt Instrument, Interest Rate, Stated Percentage	4.00%			4.00%
Proceeds from Debt, Net of Issuance Costs	$ 544,500,000
4.20% Senior Notes due 2048
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 600,000,000		$ 600,000,000	0
Debt Instrument, Interest Rate, Stated Percentage		4.20%		4.20%
Proceeds from Debt, Net of Issuance Costs		$ 589,500,000
4.125% Senior Notes due 2047
Debt Instrument [Line Items]
Debt Instrument, Face Amount			$ 850,000,000	$ 850,000,000	$ 850,000,000
Debt Instrument, Interest Rate, Stated Percentage			4.125%	4.125%
Proceeds from Debt, Net of Issuance Costs			$ 841,100,000
Federal Funds Rate [Member] | Discretionary Line of Credit
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				0.50%

Income Taxes Components of Inco

Income Taxes Components of Income Tax Provision (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)	$ 673.1	$ 680.9	$ 469.6
Current State and Local Tax Expense (Benefit)	21.5	12.8	12.7
Deferred Federal Income Tax Expense (Benefit)	(145.9)	(149.4)	(66.3)
Deferred State and Local Income Tax Expense (Benefit)	(6.1)	(3.5)	(2.5)
Total income tax provision	$ 542.6	$ 540.8	$ 413.5

Income Taxes Reconciliation of

Income Taxes Reconciliation of Provision (Benefit) for income Taxes Reported in Consolidated Statements Of Income with Tax at Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income before income taxes	$ 3,163.6	$ 2,138.9	$ 1,470.7
Tax at statutory federal rate	664.4	748.6	514.8
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	76.3	52.4	62.2
Stock-based compensation	(25.1)	(25.1)	0
Tax-deductible dividends	(14.6)	(9.7)	(6.1)
Dividends received deduction	(9.7)	(20.7)	(22.6)
Exempt interest income	(5.9)	(16.9)	(15.7)
Nondeductible compensation expense	(0.2)	10.1	0.5
Net deferred tax liability revaluation	0	(99.5)	0
State income taxes, net of federal taxes	12.2	6	6.6
Other items, net	(2.2)	0.4	(1.8)
Total income tax provision	$ 542.6	$ 540.8	$ 413.5
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Tax at statutory federal rate	21.00%	35.00%	35.00%
Tax credits	(2.00%)	(2.00%)	(4.00%)
Stock-based compensation	(1.00%)	(1.00%)	0.00%
Tax-deductible dividends	(1.00%)	(0.00%)	(0.00%)
Dividends received deduction	(0.00%)	(1.00%)	(2.00%)
Exempt interest income	(0.00%)	(1.00%)	(1.00%)
Nondeductible compensation expense	0.00%	0.00%	0.00%
Net deferred tax liability revaluation	0.00%	(5.00%)	0.00%
State income taxes, net of federal taxes	0.00%	0.00%	0.00%
Other items, net	0.00%	0.00%	0.00%
Total income tax provision	17.00%	25.00%	28.00%

Income Taxes Components of Net

Income Taxes Components of Net Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Federal deferred tax assets:
Unearned premiums reserve	$ 439.9	$ 368.9
Non-deductible accruals	169.3	166
Loss and loss adjustment expense reserves	134.6	48.4
Net unrealized losses on fixed-maturity securities	28.2	0
Hedges on forecasted transactions	4.6	4.8
Other	16.2	7.3
Federal deferred tax liabilities:
Net holding period gains on equity securities	(316.8)	0
Deferred acquisition costs	(199.8)	(163.9)
Property and equipment	(85.7)	(75.5)
Loss and loss adjustment expense reserve transition adjustment	(58.5)	0
Intangible assets	(52.2)	(66.6)
Investment basis differences	(43.3)	(5.5)
Prepaid expenses	(4.7)	(7.1)
Deferred gain on extinguishment of debt	0	(0.4)
Net unrealized gains on securities	0	(419.5)
Other	(8.9)	(6.1)
Net federal deferred tax asset (liability)	22.9
Net federal deferred tax asset (liability)		(149.2)
Net state deferred tax asset	20.3	14.2
Net deferred income taxes	43.2	0
Net deferred tax asset (liability)	$ 0	$ (135)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended			36 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Apr. 02, 2018
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	$ 76,300,000	$ 52,400,000	$ 62,200,000
Tax cuts and jobs act, reduction in income tax expense related to revaluing deferred tax assets and liabilities	99,500,000
Tax cuts and jobs act, provisional tax amount related to deductibility of executive compensation expense	(3,900,000)	4,500,000
Stock-based compensation	25,100,000	25,100,000	0
Net deferred income taxes	43,200,000	0		$ 43,200,000
Deferred tax assets valuation allowance	0	0		0
Net taxes payable	16,800,000	23,800,000		16,800,000
Provision for income taxes	542,600,000	540,800,000	413,500,000
Other assets	365,100,000	412,900,000		365,100,000
Net deferred income taxes	0	135,000,000		0
Interest and Penalties [Member]
Income Taxes [Line Items]
Provision for income taxes	0	$ 200,000	$ 100,000
Net unrealized gains (losses) on securities
Income Taxes [Line Items]
Tax cuts and jobs act, reduction in income tax expense related to revaluing deferred tax liability associated with net unrealized gains on investment portfolio	275,700,000
Other Deferred Tax Assets and Liabilities [Member]
Income Taxes [Line Items]
Tax cuts and jobs act, reduction in income tax expense related to other deferred tax assets (liabilities)	176,200,000
Chief Financial Officer [Member]
Income Taxes [Line Items]
Stock-based compensation	300,000
Liability for Claims and Claims Adjustment Expense [Member]
Income Taxes [Line Items]
Net deferred income taxes	67,100,000			67,100,000
Net deferred income taxes	$ 67,100,000			$ 67,100,000
ARX Holding Corp.
Income Taxes [Line Items]
Equity interest percentage	86.80%	69.00%	69.20%	86.80%
ARX Holding Corp. | Lower Limit
Income Taxes [Line Items]
Equity interest percentage					80.00%
ARX Holding Corp. | Upper Limit
Income Taxes [Line Items]
Equity interest percentage		80.00%
Alternative Energy [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount	$ 71,000,000	$ 48,700,000	$ 58,700,000
Provision for income taxes				$ (150,000,000)
Other assets	$ 24,300,000			$ 24,300,000

Loss And Loss Adjustment Expe_3

Loss And Loss Adjustment Expense Reserves Activity in Loss and loss Adjustment Expense Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Balance at beginning of period	$ 13,086.9	$ 11,368	$ 10,039
Less reinsurance recoverables on unpaid losses	2,170.1	1,801	1,442.7
Net balance at beginning of period	10,916.8	9,567	8,596.3
Net loss and loss adjustment reserves acquired	0	0	(2.5)
Total beginning reserves		10,916.8	9,567	$ 8,593.8
Incurred related to:
Current year	21,632.5	18,782.1	16,967.1
Prior years	88.5	25.9	(87.5)
Total incurred	21,721	18,808	16,879.6
Paid related to:
Current year	13,792.1	12,201.5	11,149
Prior years	6,017.6	5,256.7	4,757.4
Total paid	19,809.7	17,458.2	15,906.4
Net balance at ending of period	12,828.1	10,916.8	9,567
Plus reinsurance recoverables on unpaid losses	2,572.7	2,170.1	1,801
Balance at ending of period	$ 15,400.8	$ 13,086.9	$ 11,368

Loss And Loss Adjustment Expe_4

Loss And Loss Adjustment Expense Reserves Loss And Loss Adjustment Expense Reserves - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)data_subset	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Number of subsets of business data reviewed (over) | data_subset	400
Reserve development, prior years	$ 88.5	$ 25.9	$ (87.5)
Short-duration Insurance Contracts, Accident Years 2017 and 2016 [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	99
Short-duration Insurance Contracts, Accident Years 2015 and Prior [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	(10)
Short-duration Insurance Contracts, Accident Year 2016 and 2015 [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years		64
Short-duration Insurance Contracts, Accident Years 2014 and Prior [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years		(38)
2,015
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			(56)
2,013
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			(51)
2,014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			19
Commercial Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	(4)	1
Property Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ 3	(37)
environmental, asbestos, and general liability [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of reserves	0.05%
Auto
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of reserves	97.00%
Personal Auto | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ 85	$ 70	(40)
Special Lines [Member] | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years	$ 5
Personal Lines - Liability | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			(54)
Property | Property Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Reserve development, prior years			$ (52)
Agency Channel | Personal Auto | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percent of personal auto Prior Year Claims and Claims Adjustment Expense	70.00%
Direct Channel | Personal Auto | Personal Lines Segment
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percent of personal auto Prior Year Claims and Claims Adjustment Expense	30.00%

Loss And Loss Adjustment Expe_5

Loss And Loss Adjustment Expense Reserves Incurred and Paid Claims Development with IBNR and Claim Counts (Details) $ in Millions	Dec. 31, 2018USD ($)claim	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Claims Development [Line Items]
Liabilities for claims and claim adjustment expenses, net of reinsurance	$ 11,745	$ 10,029.8
Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,776.1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,722.6
All outstanding liabilities before 2014, net of reinsurance1	0.4
Liabilities for claims and claim adjustment expenses, net of reinsurance	53.9	51.7
Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	6,011.7
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,538.9
All outstanding liabilities before 2014, net of reinsurance1	31.4
Liabilities for claims and claim adjustment expenses, net of reinsurance	2,504.2	2,027.4
Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,831.1
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,521.9
All outstanding liabilities before 2014, net of reinsurance1	5.5
Liabilities for claims and claim adjustment expenses, net of reinsurance	314.7	245.8
2014 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	238.4	238	$ 238.6	$ 239.7	$ 240.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	59,630
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 238.2	237.9	237.7	238.3	224.6
2014 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	813.5	823	820.3	795.4	822.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	74,682
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 771	715.3	610	438.7	234
2014 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	375.3	376.3	379.7	389.1	415.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 2.5
Cumulative Number of Incurred Claim Counts | claim	40,992
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 371.9	370.3	365.9	351.5	269.2
2015 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	272.4	273.5	274.1	274.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (0.6)
Cumulative Number of Incurred Claim Counts | claim	62,599
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 272.2	272	271.9	248.5
2015 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	899.7	914.8	911.1	897.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 14
Cumulative Number of Incurred Claim Counts | claim	77,839
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 786.3	675	501.5	238.4
2015 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	398.8	403.6	416.5	460
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 3.8
Cumulative Number of Incurred Claim Counts | claim	41,980
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 390.1	383.5	372.8	280.3
2016 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	378.2	379.8	379.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (0.2)
Cumulative Number of Incurred Claim Counts | claim	74,180
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 376.8	376.9	336.7
2016 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,231.1	1,204.8	1,185.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 26.4
Cumulative Number of Incurred Claim Counts | claim	92,730
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 886	639.9	298.6
2016 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	537.1	541.2	568.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 9.6
Cumulative Number of Incurred Claim Counts | claim	53,582
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 516.9	498.2	415.2
2017 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	412.1	415.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (2)
Cumulative Number of Incurred Claim Counts | claim	77,170
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 409.4	369
2017 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,366.6	1,374.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 70.9
Cumulative Number of Incurred Claim Counts | claim	96,905
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 712.9	325.8
2017 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	680.9	672.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 11.5
Cumulative Number of Incurred Claim Counts | claim	71,153
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 647.1	506.7
2018 | Commercial Lines - Physical Damage | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	475
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (10)
Cumulative Number of Incurred Claim Counts | claim	83,350
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 426
2018 | Commercial Lines - Liability | Commercial Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,700.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 292.5
Cumulative Number of Incurred Claim Counts | claim	108,792
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 382.7
2018 | Property | Property Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	839
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 159.8
Cumulative Number of Incurred Claim Counts | claim	58,135
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 595.9
Agency Channel | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	21,206.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	16,762
All outstanding liabilities before 2014, net of reinsurance1	64.6
Liabilities for claims and claim adjustment expenses, net of reinsurance	4,509	3,955.5
Agency Channel | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,082.4
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,039.5
All outstanding liabilities before 2014, net of reinsurance1	0.4
Liabilities for claims and claim adjustment expenses, net of reinsurance	43.3	26.2
Agency Channel | 2014 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,611.2	3,654.4	3,633.2	3,627.7	3,702.1
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	701,788
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,559.1	3,482.3	3,284.5	2,868.1	1,809
Agency Channel | 2014 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,091.6	2,088	2,089.9	2,090.3	2,107.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	1,374,721
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,091	2,090.7	2,090.6	2,091.6	2,078.8
Agency Channel | 2015 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,815.6	3,798.8	3,773.8	3,774.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 55.9
Cumulative Number of Incurred Claim Counts | claim	704,995
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,623.3	3,416.5	2,976	1,793.1
Agency Channel | 2015 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,131.5	2,134.4	2,137.2	2,136.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (3.8)
Cumulative Number of Incurred Claim Counts | claim	1,336,486
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,134.1	2,134.4	2,138.1	2,106.2
Agency Channel | 2016 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,152	4,130	4,082.9
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 69.5
Cumulative Number of Incurred Claim Counts | claim	740,325
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,723.1	3,231.5	1,941.6
Agency Channel | 2016 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,401.8	2,398.9	2,423.4
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (2.8)
Cumulative Number of Incurred Claim Counts | claim	1,398,842
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,402.1	2,406.9	2,391
Agency Channel | 2017 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,485.8	4,474.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 188.6
Cumulative Number of Incurred Claim Counts | claim	777,415
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,478.5	2,074
Agency Channel | 2017 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,638.5	2,635.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (11.8)
Cumulative Number of Incurred Claim Counts | claim	1,513,912
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,643.2	2,599.8
Agency Channel | 2018 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	5,141.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 802.8
Cumulative Number of Incurred Claim Counts | claim	839,051
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,378
Agency Channel | 2018 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,819
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (120.8)
Cumulative Number of Incurred Claim Counts | claim	1,677,878
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,769.1
Direct Channel | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	19,269.3
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	15,049.4
All outstanding liabilities before 2014, net of reinsurance1	38.7
Liabilities for claims and claim adjustment expenses, net of reinsurance	4,258.6	3,685.1
Direct Channel | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,376.2
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	12,357.9
All outstanding liabilities before 2014, net of reinsurance1	0.1
Liabilities for claims and claim adjustment expenses, net of reinsurance	18.4	(5.6)
Direct Channel | 2014 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,884.1	2,913.6	2,898.1	2,887.4	2,946.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	592,145
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,844	2,780	2,624.2	2,278	1,413
Direct Channel | 2014 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	1,861.7	1,859.2	1,861.7	1,862.2	1,889.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Incurred Claim Counts | claim	1,471,084
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 1,861.4	1,861.8	1,862.7	1,864.1	$ 1,874.6
Direct Channel | 2015 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,399.3	3,354.2	3,328.3	3,330.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 44.3
Cumulative Number of Incurred Claim Counts | claim	659,289
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,238.2	3,021	2,615	1,545.2
Direct Channel | 2015 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,090.8	2,093.5	2,097.7	2,110.7
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (4)
Cumulative Number of Incurred Claim Counts | claim	1,540,090
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,093.7	2,094.7	2,100.1	$ 2,094.7
Direct Channel | 2016 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,871.2	3,843.9	3,819
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 58.9
Cumulative Number of Incurred Claim Counts | claim	735,483
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,476.9	2,991.1	1,780.6
Direct Channel | 2016 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,477.7	2,475.4	2,521
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (3.8)
Cumulative Number of Incurred Claim Counts | claim	1,676,008
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,479.3	2,485.8	$ 2,505
Direct Channel | 2017 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,209.9	4,209.5
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 167
Cumulative Number of Incurred Claim Counts | claim	770,740
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,255.2	1,912.6
Direct Channel | 2017 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	2,743.7	2,750.6
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (16.1)
Cumulative Number of Incurred Claim Counts | claim	1,790,360
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,753.5	$ 2,742.1
Direct Channel | 2018 | Personal Lines - Liability | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	4,904.8
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ 725.4
Cumulative Number of Incurred Claim Counts | claim	856,025
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 2,235.1
Direct Channel | 2018 | Personal Lines - Physical Damage | Personal Lines Segment
Claims Development [Line Items]
Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	3,202.3
Total of IBNR Liabilities Plus Expected Development on Reported Claims	$ (175.4)
Cumulative Number of Incurred Claim Counts | claim	2,065,458
Cumulative Paid Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance	$ 3,170

Loss And Loss Adjustment Expe_6

Loss And Loss Adjustment Expense Reserves Reconciliation of the Claims Development to the Liability for Claims and Claim Adjustment Expenses (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	$ 11,745	$ 10,029.8
Total reinsurance recoverable on unpaid claims	2,562.1	2,157.8
Unallocated claims adjustment expense related to:	1,083.1	887
Total gross liability for unpaid claims and claim adjustment expense	15,400.8	13,086.9	$ 11,368	$ 10,039
Other business
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	42.9	43.7
Total reinsurance recoverable on unpaid claims	222.1	200.9
Commercial Lines Segment | Commercial Lines - Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	2,504.2	2,027.4
Total reinsurance recoverable on unpaid claims	287.4	105.1
Commercial Lines Segment | Commercial Lines - Physical Damage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	53.9	51.7
Total reinsurance recoverable on unpaid claims	0	0.1
Property Segment | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	314.7	245.8
Total reinsurance recoverable on unpaid claims	145.4	243.8
Short-duration Insurance Contracts, Liability for Unpaid Claims and Claim Adjustment Expense, Other Reconciling Item	10.6	12.3
Agency Channel | Personal Lines Segment | Personal Lines - Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	4,509	3,955.5
Total reinsurance recoverable on unpaid claims	836.8	769.8
Agency Channel | Personal Lines Segment | Personal Lines - Physical Damage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	43.3	26.2
Total reinsurance recoverable on unpaid claims	0	0
Direct Channel | Personal Lines Segment | Personal Lines - Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	4,258.6	3,685.1
Total reinsurance recoverable on unpaid claims	1,070.4	838.1
Direct Channel | Personal Lines Segment | Personal Lines - Physical Damage
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid claims and claim adjustment expenses, net of reinsurance	18.4	(5.6)
Total reinsurance recoverable on unpaid claims	$ 0	$ 0

Loss And Loss Adjustment Expe_7

Loss And Loss Adjustment Expense Reserves Historical Claims Duration (Details)	Dec. 31, 2018
Personal Lines Segment | Agency Channel | Personal Lines - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	47.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	30.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	11.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	5.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.10%
Personal Lines Segment | Agency Channel | Personal Lines - Physical Damage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	98.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	1.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.10%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.00%
Personal Lines Segment | Direct Channel | Personal Lines - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	46.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	31.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	12.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	5.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.20%
Personal Lines Segment | Direct Channel | Personal Lines - Physical Damage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	100.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	(0.10%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.20%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.00%
Commercial Lines Segment | Commercial Lines - Liability
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	24.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	27.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	20.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	12.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.80%
Commercial Lines Segment | Commercial Lines - Physical Damage
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	90.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	9.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	(0.10%)
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	0.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.10%
Property Segment | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Short-duration Insurance Contracts, Historical Claims Duration, Year One	73.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	20.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	3.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	1.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.40%

Reinsurance Effect of Reinsuran

Reinsurance Effect of Reinsurance on Premiums Written and Earned (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Direct premiums written	$ 33,753.1	$ 27,860.7	$ 23,941.9
Ceded written	(1,143.2)	(728.6)	(588.4)
Net premiums written	32,609.9	27,132.1	23,353.5
Direct premiums earned	31,970.2	26,425.7	23,111.2
Ceded earned	(1,036.9)	(695.8)	(637.2)
Net premiums earned	30,933.3	25,729.9	22,474
non regulated reinsurance plan [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded written	(546.8)	(222.7)	(149)
Ceded earned	(479.4)	(216.2)	(212.1)
Regulated reinsurance plan [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Ceded written	(596.4)	(505.9)	(439.4)
Ceded earned	$ (557.5)	$ (479.6)	$ (425.1)

Reinsurance Prepaid Reinsurance

Reinsurance Prepaid Reinsurance Premiums and Reinsurance Recoverables (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 309.7	$ 203.3
Percentage Of Total Prepaid Reinsurance Premiums	100.00%	100.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 2,696.1	$ 2,273.4
Percentage Of Total Reinsurance Recoverables	100.00%	100.00%
State Reinsurance Plans [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 218.7	$ 179.9
Percentage Of Total Prepaid Reinsurance Premiums	71.00%	88.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 2,285.9	$ 2,060.7
Percentage Of Total Reinsurance Recoverables	85.00%	91.00%
State Reinsurance Plans [Member] | Michigan Catastrophic Claims Association [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 55.3	$ 44.3
Percentage Of Total Prepaid Reinsurance Premiums	18.00%	22.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 1,903.9	$ 1,611.5
Percentage Of Total Reinsurance Recoverables	71.00%	71.00%
State Reinsurance Plans [Member] | Commercial Auto Insurance Procedures Plans [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 72.9	$ 50
Percentage Of Total Prepaid Reinsurance Premiums	24.00%	25.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 254.7	$ 218
Percentage Of Total Reinsurance Recoverables	9.00%	10.00%
State Reinsurance Plans [Member] | North Carolina Reinsurance Facility [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 34	$ 31.5
Percentage Of Total Prepaid Reinsurance Premiums	11.00%	15.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 78.1	$ 74.2
Percentage Of Total Reinsurance Recoverables	3.00%	3.00%
State Reinsurance Plans [Member] | other reinsurance program [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 0.6	$ 0.3
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	0.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 21.4	$ 8.2
Percentage Of Total Reinsurance Recoverables	1.00%	0.00%
Federal Reinsurance Plans [Member] | National Flood Insurance Program [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 55.9	$ 53.8
Percentage Of Total Prepaid Reinsurance Premiums	18.00%	26.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 27.8	$ 148.8
Percentage Of Total Reinsurance Recoverables	1.00%	7.00%
Non State Reinsurance Plans [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 91	$ 23.4
Percentage Of Total Prepaid Reinsurance Premiums	29.00%	12.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 410.2	$ 212.7
Percentage Of Total Reinsurance Recoverables	15.00%	9.00%
Property reinsurance program [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 11.8	$ 9.1
Percentage Of Total Prepaid Reinsurance Premiums	4.00%	5.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 147.7	$ 138.6
Percentage Of Total Reinsurance Recoverables	5.00%	6.00%
Commercial Lines reinsurance program [Member] [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 79.2	$ 14.3
Percentage Of Total Prepaid Reinsurance Premiums	25.00%	7.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 254.2	$ 63.4
Percentage Of Total Reinsurance Recoverables	10.00%	3.00%
other reinsurance program [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Prepaid reinsurance premiums	$ 0	$ 0
Percentage Of Total Prepaid Reinsurance Premiums	0.00%	0.00%
Reinsurance Recoverables, Including Reinsurance Premium Paid	$ 8.3	$ 10.7
Percentage Of Total Reinsurance Recoverables	0.00%	0.00%

Reinsurance - Additional Inform

Reinsurance - Additional Information (Detail) - state	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Transportation Network Company [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Number of States in which Entity Operates	4	1	1

Statutory Financial Informati_2

Statutory Financial Information - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statutory Financial Information Disclosures [Abstract]
Consolidated statutory policyholders' surplus	$ 11,731.2	$ 9,664.4
Statutory net income	2,916.9	$ 1,416.2	$ 1,022.3
Consolidated statutory policyholders' surplus, net admitted assets of insurance subsidiaries and affiliate that are required to meet minimum statutory surplus requirements in such entities' states of domicile	955
Aggregate cash dividends paid to the parent company by subsidiaries	938.9
Maximum aggregate dividend amount subsidiaries could pay without prior approval from regulatory authorities	$ 2,887

Employee Benefit Plans Amounts

Employee Benefit Plans Amounts Charged to Income for employees Incentive Compensation Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Incentive Compensation Cash Award
Incentive Compensation Plans Expense [Line Items]
Pretax	$ 539.5	$ 461.3	$ 386.8
After Tax	426.2	299.8	251.4
Employee Stock [Member]
Incentive Compensation Plans Expense [Line Items]
Pretax	76.2	92.9	80.9
After Tax	60.2	60.4	52.6
Employee Stock Option
Incentive Compensation Plans Expense [Line Items]
Pretax	1	2.5	4.3
After Tax	$ 0.8	$ 1.6	$ 2.8

Employee Benefit Plans Summary

Employee Benefit Plans Summary of All Employee Restricted Equity Award Activity (Detail) - Employee Restricted Equity Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning of year	5,858,848	6,951,373	7,725,227
Add (deduct):
Granted	1,876,109	2,383,475	1,870,660
Vested	(2,811,070)	(3,220,671)	(2,422,700)
Forfeited	(67,531)	(255,329)	(221,814)
End of year	4,856,356	5,858,848	6,951,373
Weighted Average Grant Date Fair Value
Beginning of year	$ 30.47	$ 26.18	$ 23.37
Granted	45.55	32.01	31.54
Vested	26.41	22.53	21.50
Forfeited	36.10	28.03	24.64
End of year	$ 38.56	$ 30.47	$ 26.18
Unrecognized compensation cost related to unvested equity awards	$ 100.6
Period of recognition of compensation expense related to unvested equity awards	2 years 2 months
Dividend Equivalent Units
Add (deduct):
Granted	144,668	157,396	165,045
Weighted Average Grant Date Fair Value
Granted	$ 0	$ 0	$ 0
Performance Shares
Weighted Average Grant Date Fair Value
Target shares	1,017,520
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Expected To Vest Number	2,447,409

Employee Benefit Plans Summar_2

Employee Benefit Plans Summary of ARX employee stock option plans (Details) - Employee Stock Option - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Number	16,067	22,550	24,995	24,995
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price	$ 588.15	$ 564.60	$ 526.46	$ 526.46
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(6,483)	(2,445)	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 506.26	$ 174.65	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number	13,967	17,950	16,995
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	$ 562.17	$ 517.75	$ 438.77
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 6.2	$ 2.9
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares	2,100	4,600	8,000	12,000
Share-based Compensation Arrangement by Share-based Payment Award, Option, Nonvested, Weighted Average Exercise Price	$ 760.93	$ 747.45	$ 712.74	$ 677.81
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	(2,500)	(3,400)	(4,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value	$ 736.12	$ 665.79	$ 607.95
Unrecognized compensation cost related to unvested equity awards	$ 0.2	$ 0.7	$ 1.6
Period of recognition of compensation expense related to unvested equity awards	6 months 10 days	1 year 5 days	1 year 4 months 10 days

Employee Benefit Plans Summar_3

Employee Benefit Plans Summary of all Directors' Restricted Stock Activity (Detail) - Non Employee Director Restricted Equity Awards - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning of year	53,284	55,839	89,427
Add (deduct):
Granted	41,706	53,284	55,839
Vested	(53,284)	(55,839)	(89,427)
End of year	41,706	53,284	55,839
Weighted Average Grant Date Fair Value
Beginning of year	$ 40.54	$ 33.24	$ 27.23
Granted	62.23	40.54	33.24
Vested	40.54	33.24	27.23
End of year	$ 62.23	$ 40.54	$ 33.24

Employee Benefit Plans Assets H

Employee Benefit Plans Assets Held in Deferral Plan Irrevocable Grantor Trust Account (Detail) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$ 238.7	$ 295.2
Progressive common shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$ 114.7	$ 128.2
Deferred Compensation Arrangement with Individual, Shares Authorized for Issuance	3.6	4.4
Other Investment Funds
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Assets held in Deferral Plan Irrevocable Grantor Trust account	$ 124	$ 167

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)Personshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Benefits Disclosure [Line Items]
Minimum employment period for benefits	30 days
Employee Stock Ownership Plan Shares held | shares	24,100,000
Postemployment benefits liability | $	$ 20.2	$ 19.5
Compensation, Percentage	100.00%
Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Unrecognized compensation cost related to unvested equity awards | $	$ 100.6
Aggregate fair value of the restricted equity awards that vested during the period | $	162.7	130.5	$ 77
Employee Stock Option
Employee Benefits Disclosure [Line Items]
Unrecognized compensation cost related to unvested equity awards | $	0.2	0.7	1.6
Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Unrecognized compensation cost related to unvested equity awards | $	$ 0.9
Vesting period of grants to date	11 months
Total pretax intrinsic value of options exercised and restricted stock vested | $	$ 3.2	$ 2.2	$ 3
Executive Deferred Compensation Plan
Employee Benefits Disclosure [Line Items]
Common shares reserved for issuance under executive deferred compensation plan | shares	11,100,000
2003 Directors Equity Incentive Plan | Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Shares authorized | shares	0
2017 Directors Equity Incentive Plan | Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Shares authorized | shares	500,000
Equity Incentive Plan Twenty Ten [Member]
Employee Benefits Disclosure [Line Items]
Shares authorized | shares	0
share based compensation arrangement by share based payment award, number of shares transferred | shares	4,000,000
Equity Incentive Plan Twenty Fifteen [Domain]
Employee Benefits Disclosure [Line Items]
Shares authorized | shares	17,000,000
Performance Based Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Estimated Number Of Participants | Person	50
Performance Based Restricted Equity Awards | Insurance Operating Results | Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Performance Based Restricted Equity Awards | Insurance Operating Results | Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	250.00%	250.00%	250.00%	250.00%	250.00%	250.00%
Performance Based Restricted Equity Awards | Investment Results | Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Performance Based Restricted Equity Awards | Investment Results | Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount	200.00%	200.00%	200.00%	200.00%	200.00%	200.00%
Performance Based Restricted Equity Awards | Growth in percentage of auto policies bundled with other specified types of policies [Member] | Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount				100.00%
Performance Based Restricted Equity Awards | Growth in percentage of auto policies bundled with other specified types of policies [Member] | Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount				200.00%
Performance Based Restricted Equity Awards | Growth in percentage of auto policies bundled with other specified types of policies, performance objective not achieved
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount				0.00%
Performance Based Restricted Equity Awards | Unit growth in a particular customer segment [Member] | Lower Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount		85.00%	85.00%
Performance Based Restricted Equity Awards | Unit growth in a particular customer segment [Member] | Upper Limit
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount		150.00%	150.00%
Performance Based Restricted Equity Awards | Unit growth in a particular customer segment, performance objective not achieved
Employee Benefits Disclosure [Line Items]
Performance-based awards granted vesting percentage of the award amount		0.00%	0.00%
Defined Contribution Pension Plan 401k
Employee Benefits Disclosure [Line Items]
Matching contributions | $	$ 106.8	$ 97.3	$ 86.8
Defined Contribution Pension Plan 401k | Upper Limit
Employee Benefits Disclosure [Line Items]
Matching contribution to defined contribution pension plan	6.00%
Cash [Member]
Employee Benefits Disclosure [Line Items]
Compensation, Percentage	40.00%
Non Employee Director Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Compensation, Percentage	60.00%
Vesting tranche one | Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	3 years
Vesting tranche two | Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	4 years
Vesting tranche three | Employee Restricted Equity Awards
Employee Benefits Disclosure [Line Items]
Vesting period of grants to date	5 years

Employee Benefit Plans Summar_4

Employee Benefit Plans Summary of ARX Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Pension Plan 401k
Defined Contribution Plan Disclosure [Line Items]
Matching contributions	$ 106.8	$ 97.3	$ 86.8

Segment Information Operating R

Segment Information Operating Results (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 31,979	$ 26,839	$ 23,441.4
Pretax Profit (Loss)	3,163.6	2,138.9	1,470.7
Personal Lines Segment | Agency Channel | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	13,017.2	11,177.6	9,791.7
Pretax Profit (Loss)	1,435.7	839.6	492.8
Personal Lines Segment | Direct Channel | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	13,017.5	10,769.6	9,396.5
Pretax Profit (Loss)	1,088.5	683.7	412.2
Operating Segments | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	30,933.3	25,729.9	22,474
Pretax Profit (Loss)	2,915	1,686.9	1,091.1
Operating Segments | Personal Lines Segment | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	26,034.7	21,947.2	19,188.2
Pretax Profit (Loss)	2,524.2	1,523.3	905
Operating Segments | Commercial Lines Segment | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	3,610.9	2,793.9	2,421.3
Pretax Profit (Loss)	478.6	214.1	155.2
Operating Segments | Property Segment | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	1,287.7	988.8	864.5
Pretax Profit (Loss)	(88.7)	(50.3)	32.5
Operating Segments | Other Indemnity | Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	0	0	0
Pretax Profit (Loss)	0.9	(0.2)	(1.6)
Segment Reconciling Items | Fees And Other Revenues
Segment Reporting Information [Line Items]
Revenues	472.2	370.6	332.5
Segment Reconciling Items | Service Businesses
Segment Reporting Information [Line Items]
Revenues	158.5	126.8	103.3
Pretax Profit (Loss)	24.4	17.3	11.3
Segment Reconciling Items | Investments
Segment Reporting Information [Line Items]
Revenues	415	612.7	530
Pretax Profit (Loss)	390.7	588.8	507.6
Segment Reconciling Items | Other gains (losses)
Segment Reporting Information [Line Items]
Revenues	0	(1)	1.6
Pretax Profit (Loss)	0	(1)	1.6
Segment Reconciling Items | Interest Expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	$ (166.5)	$ (153.1)	$ (140.9)

Segment Information Operating_2

Segment Information Operating Results (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Amortization of intangible assets	$ 72	$ 66.2	$ 62.1
Personal Lines Segment | Underwriting Operations | Operating Segments
Segment Reporting Information [Line Items]
Personal auto insurance percentage of the total personal lines segment net premiums earned	94.00%	93.00%	92.00%
Property Segment | Underwriting Operations | Operating Segments
Segment Reporting Information [Line Items]
Amortization of intangible assets	$ 72	$ 66.2	$ 62.1

Segment Information Underwritin

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Details) - Underwriting Operations	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Personal Lines Segment | Agency Channel
Segment Reporting Information [Line Items]
Underwriting Margin	11.00%	7.50%	5.00%
Combined Ratio	89.00%	92.50%	95.00%
Personal Lines Segment | Direct Channel
Segment Reporting Information [Line Items]
Underwriting Margin	8.40%	6.30%	4.40%
Combined Ratio	91.60%	93.70%	95.60%
Operating Segments
Segment Reporting Information [Line Items]
Underwriting Margin	9.40%	6.60%	4.90%
Combined Ratio	90.60%	93.40%	95.10%
Operating Segments | Personal Lines Segment
Segment Reporting Information [Line Items]
Underwriting Margin	9.70%	6.90%	4.70%
Combined Ratio	90.30%	93.10%	95.30%
Operating Segments | Commercial Lines Segment
Segment Reporting Information [Line Items]
Underwriting Margin	13.30%	7.70%	6.40%
Combined Ratio	86.70%	92.30%	93.60%
Operating Segments | Property Segment
Segment Reporting Information [Line Items]
Underwriting Margin	(6.90%)	(5.10%)	3.80%
Combined Ratio	106.90%	105.10%	96.20%
Combined ratio amortization points	0.056	0.067	0.072

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)Entity	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Depreciation | $	$ 190.4	$ 169.9	$ 137.4
Operating Segments | Personal Lines Segment | Agency Channel | Lower Limit
Segment Reporting Information [Line Items]
Independent insurance agencies and brokerages | Entity	35,000

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
AOCI before Tax, Attributable to Parent, beginning balance	$ 1,977.8	$ 1,439.5	$ 1,234.5
Pretax Cumulative Effect of New Accounting Principal in Period of Adoption	(2,006)
Pretax Reclassification of Stranded Amounts in AOCI to Equity	(4.3)
AOCI before Tax, Attributable to Parent, after Cumulative Effect Adjustment and Reclassification of Stranded Amounts	(32.5)
Unrealized Holding Gain (Loss) on Securities Arising During the Period, before tax	(224.1)	636.9	320.5
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, before tax	0	0	(0.1)
Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	0	(8)	0
Foreign Currently Translation Adjustment, before tax	0	0.4	0.6
Portion Attributable to Noncontrolling Interest, before tax	4.3	(3.5)	5.1
Total other comprehensive income (loss) before reclassifications, before tax	(219.8)	625.8	326.1
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, before Tax	0	(14.9)	(27.1)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	(98.3)	103.3	146.3
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	0	(1.2)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	(1)	0.3	1.9
Total reclassification adjustment for amounts realized in net income, before tax	(99.3)	87.5	121.1
Total other comprehensive income, before tax	(120.5)	538.3	205
AOCI before Tax, Attributable to Parent, ending balance	(153)	1,977.8	1,439.5
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
AOCI Tax, Attributable to Parent, beginning balance	(695.6)	(506.1)	(434.1)
Tax, Cumulative Effect of New Accounting Principal in Period of Adoption	705.8
Tax, Reclassification of Stranded Amounts in AOCI to Equity	(3.4)
AOCI Tax, Attributable to Parent, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts	6.8
Unrealized Holding Gain (Loss) on Securities Arising During the Period, tax	47	(224)	(112.6)
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, tax	0	0	0.1
Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	0	2.8	0
Foreign currency translation adjustment, tax	0	(0.1)	(0.2)
Portion Attributable to Noncontrolling Interest, tax	(1)	1.2	(1.9)
Total Other Comprehensive Income (Loss), before Reclassification Adjustments, Tax	46	(220.1)	(114.6)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Tax	0	5.3	9.5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	20.5	(36.2)	(51.4)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Tax	0	0.4	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	0.2	(0.1)	(0.7)
Total reclassification adjustment for amounts realized in net income, Total tax (provisions) benefit	(20.7)	30.6	42.6
Total other comprehensive income, Total tax (provision) benefit	25.3	(189.5)	(72)
AOCI Tax, Attributable to Parent, ending balance	32.1	(695.6)	(506.1)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	1,282.2	933.4	800.4
Cumulative Effect of New Accounting Principle in Period of Adoption	(1,300.2)
Reclassification of Stranded Amounts in AOCI to Equity	(7.7)
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts	(25.7)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	(177.1)	412.9	207.9
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, after tax	0	0	0
Unrealized Gain (Loss) on Derivatives Arising During Period, after tax	0	(5.2)	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0.3	0.4
Other comprehensive (income) loss attributable to NCI	3.3	(2.3)	3.2
Total other comprehensive income (loss), before reclassifications, after tax	(173.8)	405.7	211.5
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	(9.6)	(17.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(77.8)	67.1	94.9
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	(0.8)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.8)	0.2	1.2
Total reclassification adjustment for amounts realized in net income, Net of tax	(78.6)	56.9	78.5
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(95.2)	348.8	133
After tax total accumulated other comprehensive income, ending balance	(120.9)	1,282.2	933.4
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	1,295	939.6	809
Cumulative Effect of New Accounting Principle in Period of Adoption	(1,300.2)
Reclassification of Stranded Amounts in AOCI to Equity	(1.1)
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts	(6.3)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	(177.1)	412.9	207.9
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, after tax	0	0	0
Unrealized Gain (Loss) on Derivatives Arising During Period, after tax	0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0	0
Other comprehensive (income) loss attributable to NCI	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	(177.1)	412.9	207.9
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	(9.6)	(17.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	(77.8)	67.1	94.9
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0
Total reclassification adjustment for amounts realized in net income, Net of tax	(77.8)	57.5	77.3
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(99.3)	355.4	130.6
After tax total accumulated other comprehensive income, ending balance	(105.6)	1,295	939.6
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(14.8)	(9.4)	(8.2)
Cumulative Effect of New Accounting Principle in Period of Adoption	0
Reclassification of Stranded Amounts in AOCI to Equity	(3.2)
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts	(18)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0	0	0
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, after tax	0	0	0
Unrealized Gain (Loss) on Derivatives Arising During Period, after tax	0	(5.2)	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0	0
Other comprehensive (income) loss attributable to NCI	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	0	(5.2)	0
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.8)	0.2	1.2
Total reclassification adjustment for amounts realized in net income, Net of tax	(0.8)	0.2	1.2
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0.8	(5.4)	(1.2)
After tax total accumulated other comprehensive income, ending balance	(17.2)	(14.8)	(9.4)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	0	(1.1)	(1.5)
Cumulative Effect of New Accounting Principle in Period of Adoption	0
Reclassification of Stranded Amounts in AOCI to Equity	0
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts	0
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0	0	0
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, after tax	0	0	0
Unrealized Gain (Loss) on Derivatives Arising During Period, after tax	0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0.3	0.4
Other comprehensive (income) loss attributable to NCI	0	0	0
Total other comprehensive income (loss), before reclassifications, after tax	0	0.3	0.4
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	(0.8)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0
Total reclassification adjustment for amounts realized in net income, Net of tax	0	(0.8)	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	0	1.1	0.4
After tax total accumulated other comprehensive income, ending balance	0	0	(1.1)
Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	2	4.3	1.1
Cumulative Effect of New Accounting Principle in Period of Adoption	0
Reclassification of Stranded Amounts in AOCI to Equity	(3.4)
AOCI, Net of Tax, After Cumulative Effect Adjustment and Reclassification of Stranded Amounts	(1.4)
Unrealized Holding Gain (Loss) on Securities Arising During Period, after tax	0	0	0
Net Non-credit Related OTTI Losses, Adjusted for Valuation Changes, after tax	0	0	0
Unrealized Gain (Loss) on Derivatives Arising During Period, after tax	0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax	0	0	0
Other comprehensive (income) loss attributable to NCI	3.3	(2.3)	3.2
Total other comprehensive income (loss), before reclassifications, after tax	3.3	(2.3)	3.2
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, Net of Tax	0	0	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	0	0
Total reclassification adjustment for amounts realized in net income, Net of tax	0	0	0
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	3.3	(2.3)	3.2
After tax total accumulated other comprehensive income, ending balance	$ 1.9	$ 2	$ 4.3

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement Additional Information (Detail) $ in Millions	Dec. 31, 2018USD ($)
Statement of Comprehensive Income [Abstract]
Net unrealized losses on forecasted transactions, expected to reclassify into interest expense within the next 12 months	$ 1

Commitments and Contingencies M

Commitments and Contingencies Minimum Commitments under Noncancelable Operating Lease Agreements (Detail) $ in Millions	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 64.1
Operating Leases, Future Minimum Payments, Due in Two Years	65.5
Operating Leases, Future Minimum Payments, Due in Three Years	52.8
Operating Leases, Future Minimum Payments, Due in Four Years	24.3
Operating Leases, Future Minimum Payments, Due in Five Years	8.5
Operating Leases, Future Minimum Payments, Due Thereafter	3.8
Operating Leases, Future Minimum Payments Due	$ 219

Commitments and Contingencies E

Commitments and Contingencies Expenses Incurred for Leases (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Expense	$ 77.3	$ 77.2	$ 72.9

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
reinsurance contract obligation [Line Items]
Minimum commitment under noncancelable purchase obligations	$ 697.5
unrecorded unconditional purchase obligations reinsurance [Member] | Lower Limit
reinsurance contract obligation [Line Items]
Reinsurance Contract Terms	1 year
Other Commitment	$ 81.5
unrecorded unconditional purchase obligations reinsurance [Member] | Upper Limit
reinsurance contract obligation [Line Items]
Reinsurance Contract Terms	3 years

Dividends Dividends (Details)

Dividends Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Dividends payable				$ 1,467.9	$ 655.1	$ 395.4
Dividends paid to common shareholders		$ 654.9	$ 395.4	$ 654.9	$ 395.4	$ 519
Annual variable dividend
Common Stock, Dividends, Per Share, Cash Paid		$ 1.1247	$ 0.6808
Subsequent Event | Annual variable dividend
Common Stock, Dividends, Per Share, Cash Paid	$ 2.5140

Dividends-Additional Informatio

Dividends-Additional Information (Details) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended	60 Months Ended
	Mar. 31, 2023	Dec. 31, 2018USD ($)$ / shares	Mar. 14, 2023	Mar. 31, 2018$ / sharesshares	Dec. 31, 2017$ / shares	Dec. 31, 2016
Dividends Payable [Line Items]
Target percentage used to determine annual variable dividend		33.33%			33.33%	33.33%
Gainshare factor used to determine annual variable dividend		1.91			1.79	1.67
Dividends, Preferred Stock, Cash | $		$ 13.5
Series B Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Shares Issued | shares				500,000
Preferred Stock, Liquidation Preference Per Share				$ 1,000	$ 0
Preferred Stock, Dividends Per Share, Declared		$ 27.024
Forecast | Series B Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Dividend Rate, Percentage			5.375%
London Interbank Offered Rate (LIBOR) [Member] | Forecast | Series B Preferred Stock
Dividends Payable [Line Items]
Preferred Stock, Basis Spread on Variable Rate	2.539%

Redeemable Noncontrolling Int_3

Redeemable Noncontrolling Interest (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)sharesvote		Dec. 31, 2017USD ($)		Dec. 31, 2016USD ($)	Apr. 01, 2021	Apr. 02, 2018	Dec. 31, 2015USD ($)	Apr. 01, 2015USD ($)
Redeemable Noncontrolling Interest [Line Items]
Number of stockholder votes to approve actions | vote	1
Fair value at date of acquisition									$ 411.5
Redeemable Noncontrolling Interest, Equity, Carrying Amount	$ 214.5	[1]	$ 503.7	[1]	$ 483.7			$ 464.9
Net income attributable to NCI	5.7		5.9		26.2
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	(3.3)		2.3		(3.2)
Stock Issued During Period, Value, Stock Options Exercised Attributable to Redeemable Noncontrolling Interest	9.4		3.4		0
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	(298.2)		0		0
Adjustment to carrying amount of redeemable noncontrolling interest	$ (2.8)		$ 8.4		$ (4.2)
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
Equity interest percentage	86.80%		69.00%		69.20%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number | shares	16,067
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 23.1
ARX Holding Corp. | Forecast
Redeemable Noncontrolling Interest [Line Items]
Equity interest percentage						100.00%
Lower Limit
Redeemable Noncontrolling Interest [Line Items]
Multiple for determining purchase price of shares	1
Lower Limit | ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Equity interest percentage							80.00%
Upper Limit
Redeemable Noncontrolling Interest [Line Items]
Multiple for determining purchase price of shares	2
Upper Limit | ARX Holding Corp.
Redeemable Noncontrolling Interest [Line Items]
Equity interest percentage			80.00%
[1]	See Note 15 – Redeemable Noncontrolling Interest for further discussion.

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets Goodwill (Details) - USD ($)	6 Months Ended	12 Months Ended			18 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Goodwill [Line Items]
Goodwill		$ 452,700,000	$ 452,700,000		$ 452,700,000
Goodwill, Impaired, Accumulated Impairment Loss		0			$ 0
Amortization of intangible assets		$ 72,000,000	$ 66,200,000	$ 62,100,000
Weighted Average [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Remaining Amortization Period		3 years 10 months 27 days
Trade name
Goodwill [Line Items]
Intangible assets finite lives	10 years				2 years

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 247.7	$ 175.7
Indefinite-lived intangible assets	12.4	12.4
Total	294.6	366.6
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	247.1	175.1
Intangible assets subject to amortization	282.2	354.2
Licenses
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 0.6	$ 0.6

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 247.7	$ 175.7
Policies in force
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2
Accumulated Amortization	137.3	100.7
Net Carrying Amount	118.9	155.5
Agency relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2
Accumulated Amortization	42.6	31.3
Net Carrying Amount	116.6	127.9
Software rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	79.1	79.1
Accumulated Amortization	40.1	29.4
Net Carrying Amount	39	49.7
Trade name
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.8	34.8
Accumulated Amortization	27.1	13.7
Net Carrying Amount	7.7	21.1
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	529.3	529.3
Accumulated Amortization	247.1	175.1
Net Carrying Amount	$ 282.2	$ 354.2

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets Goodwill and Intangible Assets - Amortization (Details) $ in Millions	Dec. 31, 2018USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
Finite- Lived Intangible Assets, Amortization Expense, Next Twelve Months	$ 66.4
Finite-Lived Intangible Assets, Amortization Expense, Year Two	56.9
Finite-Lived Intangible Assets, Amortization Expense, Year Three	56.6
Finite-Lived Intangible Assets, Amortization Expense, Year Four	29.2
Finite-Lived Intangible Assets, Amortization Expense, Year Five	$ 13.5