The Progressive Corporation (PGR) 10-Q 3 Nov 16 2016 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2016shares
Document Document And Entity Information [Abstract]
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	80,661
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Amendment Flag	false
Trading Symbol	PGR
Entity Common Stock, Shares Outstanding	580,781,045

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) shares in Millions, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net		$ 61.6	$ 13.6	$ 61.8	$ 23.2
Revenues
Net premiums earned		$ 5,723.4	5,070.6	$ 16,602.6	14,732.7
Period over prior year period percent change in net premiums earned		13.00%		13.00%
Investment income		$ 119.3	117.5	$ 352.7	335.9
Period over prior year period percent change in investment income		2.00%		5.00%
Net realized gains (losses) on securities:
Period over prior year period percent change in net premium losses recognized in earnings		353.00%		166.00%
Net realized gains (losses) on securities		$ 40.9	(2.2)	$ 90.8	116.4
Period over prior year period percent change in net realized gains (losses) on securities				(22.00%)
Total net realized gains (losses) on securities		$ (20.7)	(15.8)	$ 29	93.2
Period over prior year period percent change in total net realized gains (losses) on securities		31.00%		(69.00%)
Fees and other revenues		$ 86.8	79.3	$ 248.2	227.9
Period over prior year period percent change in fees and other revenues		9.00%		9.00%
Service revenues		$ 26.2	23.1	$ 77.7	63.6
Period over prior year period percent change in service revenues		13.00%		22.00%
Gains (losses) on extinguishment of debt		$ 0	(0.9)	$ 1.6	(0.9)
PercentIncrease(Decrease)GainLossonExtingiushmentofDebt		(100.00%)		(278.00%)
Total revenues		$ 5,935	5,273.8	$ 17,311.8	15,452.4
Period over prior year period percent change in total revenues		13.00%		12.00%
Expenses
Losses and loss adjustment expenses		$ 4,398.2	3,654.3	$ 12,554.6	10,640.1
Period over prior year period percent change in losses and loss adjustment expenses		20.00%		18.00%
Policy acquisition costs		$ 475.4	423.2	$ 1,374.6	1,219.9
Period over prior year period percent change in policy acquisition costs		12.00%		13.00%
Other underwriting expenses		$ 739.6	707.5	$ 2,262.2	2,020.3
Period over prior year period percent change in other underwriting expenses		5.00%		12.00%
Investment expenses		$ 4.8	4.9	$ 14.9	15.9
Period over prior year period percent change in investment expenses		(2.00%)		(6.00%)
Service expenses		$ 23.2	20.4	$ 68.5	56.8
Period over prior year period percent change in service expenses		14.00%		21.00%
Interest expense		$ 35.3	34.5	$ 103.8	101.9
Period over prior year period percent change in interest expense		2.00%		2.00%
Total expenses		$ 5,676.5	4,844.8	$ 16,378.6	14,054.9
Period over prior year period percent change in total expenses		17.00%		17.00%
Net Income
Income before income taxes		$ 258.5	429	$ 933.2	1,397.5
Period over prior year period percent change in income before income taxes		(40.00%)		(33.00%)
Provision for income taxes		$ 53	142.5	$ 274.1	446.9
Period over prior year period percent change in provision for income taxes		(63.00%)		(39.00%)
Net income		$ 205.5	286.5	$ 659.1	950.6
Period over prior year period percent change in net income		(28.00%)		(31.00%)
Net income (loss) attributable to noncontrolling interest (NCI), net of tax		$ 6.8	8.2	$ 11.3	13.4
Period over prior year period percent change in net income (loss) attributable to noncontrolling interest, net of tax		(17.00%)		(16.00%)
Net income attributable to Progressive		$ 198.7	278.3	$ 647.8	937.2
Period over prior year period percent change in net income attributable to Progressive		(29.00%)		(31.00%)
Other Comprehensive Income (Loss), Net of Tax
Total net unrealized gains (losses) on securities		$ 87.1	(130.1)	$ 248.2	(244.5)
Period over prior year period percent change in total net unrealized gains (losses) on securities		(167.00%)		(202.00%)
Net unrealized losses on forecasted transactions		$ (0.3)	(0.4)	$ (0.9)	(9.4)
Period over prior year period percent change in net unrealized gains on forecasted transactions		(25.00%)		(90.00%)
Foreign currency translation adjustment		$ 0.3	(0.7)	$ 0.7	(1.2)
Period over prior year period percent change in foreign currency translation adjustment		(143.00%)		(158.00%)
Other comprehensive income (loss)		$ 87.1	(131.2)	$ 248	(255.1)
Period over prior year period percent change in other comprehensive income		(166.00%)		(197.00%)
Other comprehensive (income) loss attributable to NCI		$ 1.2	(1.6)	$ (2.3)	1.2
Period over prior year period changein Comprehensive (income) loss attributable to NCI, net of tax		(175.00%)		(292.00%)
Comprehensive income attributable to Progressive		$ 287	$ 145.5	$ 893.5	$ 683.3
Period over prior year period percent change in comprehensive income		97.00%		31.00%
Computation of Per Share Earnings Attributable to Progressive
Average shares outstanding - Basic		581.5	585.2	582.4	586.1
Period over prior year period percent change in average shares outstanding - basic		(1.00%)		(1.00%)
Net effect of dilutive stock-based compensation		3.1	3.9	3.2	3.7
Period over prior year period percent change in net effect of dilutive stock-based compensation		(21.00%)		(14.00%)
Total equivalent shares - Diluted		584.6	589.1	585.6	589.8
Period over prior year period percent change in total equivalent shares - diluted		(1.00%)		(1.00%)
Basic: Earnings per share		$ 0.34	$ 0.48	$ 1.11	$ 1.60
Period over prior year period percent change in basic: net income per share		(28.00%)		(30.00%)
Diluted: Earnings per share		$ 0.34	0.47	$ 1.11	1.59
Period over prior year period percent change in diluted: net income per share		(28.00%)		(30.00%)
Dividends declared per share1	[1]	$ 0	$ 0	$ 0	$ 0
[1]	Progressive maintains an annual dividend program. See Note 8 - Dividends for further discussion.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Investments - Available-for-sale, at fair value:
Fixed maturities (amortized cost: $13,708.0, $15,539.6, and $15,347.9)		$ 13,916.9	$ 15,332.2	$ 15,622.1
Equity securities:
Nonredeemable preferred stocks (cost: $726.6, $652.4, and $674.2)		860.1	782.6	775.6
Common equities (cost: $1,576.1, $1,487.0, and $1,494.3)		2,868	2,650.5	2,483.9
Short-term investments (amortized cost: $5,876.2, $2,132.0, and $2,172.0)		5,876.2	2,172	2,132
Total investments	[1],[2]	23,521.2	20,937.3	21,013.6
Cash		143.4	224.1	194.5
Restricted cash		22.3	0.3	0
Accrued investment income		97.3	102.2	103.6
Premiums receivable, net of allowance for doubtful accounts of $176.8, $153.3, and $164.8		4,743.6	3,987.7	4,139.8
Reinsurance recoverables, including $67.5, $46.1, and $46.1 on paid losses and loss adjustment expenses		1,901.7	1,488.8	1,415
Prepaid reinsurance premiums		174.4	199.3	221.7
Deferred acquisition costs		675.4	564.1	590.8
Property and equipment, net of accumulated depreciation of $830.1, $758.8, and $778.3		1,115	1,037.2	1,024.1
Goodwill		449.4	447.6	446.4
Intangible assets, net of accumulated amortization of $94.0, $31.8, and $47.4		448.3	494.9	510.5
Other assets		328.8	335.8	275
Total assets		33,620.8	29,819.3	29,935
Liabilities
Unearned premiums		7,792.4	6,621.8	6,971.9
Loss and loss adjustment expense reserves		11,228.2	10,039	9,827.2
Net deferred income taxes		156.9	109.3	85.7
Dividends payable		0	519.2	0
Accounts payable, accrued expenses, and other liabilities		2,722.2	2,067.8	2,431
Debt	[3]	3,153.9	2,707.9	2,714.3
Total liabilities		25,053.6	22,065	22,030.1
Redeemable noncontrolling interest (NCI)2	[4]	472.5	464.9	442.9
Common shares, $1.00 par value (authorized 900.0; issued 797.5, 797.6, and 797.6 including treasury shares of 216.7, 213.0, and 214.0)		580.8	583.6	584.6
Paid-in capital		1,284.7	1,218.8	1,197.3
Retained earnings		5,183.1	4,686.6	4,910.9
Accumulated other comprehensive income, net of tax:
Net unrealized gains (losses) on securities		1,057.2	809	777.4
Net unrealized losses on forecasted transactions		(9.1)	(8.2)	(7.9)
Foreign currency translation adjustment		(0.8)	(1.5)	(1.5)
Accumulated other comprehensive (income) loss attributable to noncontrolling interest		(1.2)	1.1	1.2
Total accumulated other comprehensive income		1,046.1	800.4	769.2
Total shareholders’ equity		8,094.7	7,289.4	7,462
Total liabilities, redeemable NCI, and shareholders’ equity		$ 33,620.8	$ 29,819.3	$ 29,935
[1]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.
[2]	The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[3]	1Consists of both short-term and long-term debt. See Note 4 - Debt for further discussion.
[4]	2See Note 11 – Redeemable Noncontrolling Interest for further discussion.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Fixed maturities, amortized cost	$ 13,708	$ 15,347.9	$ 15,539.6
Nonredeemable preferred stocks, cost	726.6	674.2	652.4
Common equities, cost	1,576.1	1,494.3	1,487
Short-term investments, amortized cost	5,876.2	2,172	2,132
Premiums receivable, allowance for doubtful accounts	176.8	164.8	153.3
Reinsurance recoverables, paid losses and loss adjustment expenses	67.5	46.1	46.1
Finite-Lived Intangible Assets, Accumulated Amortization	94	47.4	31.8
Property and equipment, accumulated depreciation	$ 830.1	$ 778.3	$ 758.8
Common Shares, par value (USD per share)	$ 1	$ 1	$ 1
Common Shares, authorized (shares)	900,000,000	900,000,000	900,000,000
Common Shares, issued (shares)	797,500,000	797,600,000	797,600,000
Common Shares, treasury shares (shares)	216,700,000	214,000,000	213,000,000

Consolidated Statements of Chan

Consolidated Statements of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Common Shares, $1.00 Par Value	Paid-in Capital	Retained Earnings	Accumulated other comprehensive income after tax	Serial Preferred Shares [Member]	Voting Preference Shares [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares authorized (in shares)						20,000,000	5,000,000
Preferred stock, shares issued (in shares)						0	0
Preferred stock, shares outstanding (in shares)						0
Balance, Beginning of period at Dec. 31, 2014		$ 587.8	$ 1,184.3	$ 4,133.4	$ 1,023.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Progressive	$ 937.2			937.2
Tax benefit from vesting of equity-based compensation			15
Treasury shares purchased		(6.3)	(12.9)	(155.7)
Net restricted equity awards (issued)/(vested)/forfeited		3.1	(3.1)
Amortization of equity-based compensation			45.9
Reinvested dividends on restricted stock units			(0.1)	0.1
Adjustment to carrying amount of redeemable noncontrolling interest			(31.8)
Cash dividends declared on common shares				0
Attributable to noncontrolling interest	1.2				1.2
Other comprehensive income	(255.1)				(255.1)
Other, net				(4.1)
Balance, End of period at Sep. 30, 2015	7,462	584.6	1,197.3	4,910.9	769.2
Balance, Beginning of period at Dec. 31, 2014		587.8	1,184.3	4,133.4	1,023.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Tax benefit from vesting of equity-based compensation	16.8
Balance, End of period at Dec. 31, 2015	$ 7,289.4	583.6	1,218.8	4,686.6	800.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares authorized (in shares)						20,000,000	5,000,000
Preferred stock, shares issued (in shares)						0	0
Preferred stock, shares outstanding (in shares)						0
Common Shares, par value (USD per share)	$ 1
Preferred stock, shares authorized (in shares)						20,000,000	5,000,000
Preferred stock, shares issued (in shares)						0	0
Preferred stock, shares outstanding (in shares)						0
Common Shares, par value (USD per share)	$ 1
Net income attributable to Progressive	$ 647.8			647.8
Tax benefit from vesting of equity-based compensation			8
Treasury shares purchased		(5.2)	(11.4)	(147)
Net restricted equity awards (issued)/(vested)/forfeited		2.4	(2.4)
Amortization of equity-based compensation			64.6
Reinvested dividends on restricted stock units			1.1	(1.1)
Adjustment to carrying amount of redeemable noncontrolling interest	(6)		6
Cash dividends declared on common shares				0.2
Attributable to noncontrolling interest	(2.3)				(2.3)
Other comprehensive income	248				248
Other, net				(3.4)
Balance, End of period at Sep. 30, 2016	$ 8,094.7	$ 580.8	$ 1,284.7	$ 5,183.1	$ 1,046.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, shares authorized (in shares)						20,000,000	5,000,000
Preferred stock, shares issued (in shares)						0	0
Preferred stock, shares outstanding (in shares)						0
Common Shares, par value (USD per share)	$ 1

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Statement of Cash Flows [Abstract]
Net income	$ 659.1	$ 950.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	94.6	76.1
Amortization of intangible assets	46.6	31.2
Amortization of fixed-income securities	57.1	71.2
Amortization of equity-based compensation	64.6	45.9
Net realized (gains) losses on securities	(29)	(93.2)
Net (gains) losses on disposition of property and equipment	4.1	0.5
(Gains) losses on extinguishment of debt	(1.6)	0.9
Net loss on exchange transaction	4.5	0
Changes in:
Premiums receivable	(752.8)	(573.2)
Reinsurance recoverables	(405.1)	(128.8)
Prepaid reinsurance premiums	44.9	10.1
Deferred acquisition costs	(128)	(69)
Income taxes	(121.2)	(92.1)
Unearned premiums	1,154.6	982.7
Loss and loss adjustment expense reserves	1,183.2	705.8
Accounts payable, accrued expenses, and other liabilities	464.8	218.7
Increase (Decrease) in Restricted Cash	(22)	0
Other, net	(58.8)	23
Net cash provided by operating activities	2,259.6	2,160.4
Purchases:
Fixed maturities	(7,364.6)	(7,106.7)
Equity securities	(367.1)	(461.3)
Sales:
Fixed maturities	4,746.1	3,639.8
Equity securities	278.2	251.8
Maturities, paydowns, calls, and other:
Fixed maturities	4,189	2,469.4
Equity securities	0	12
Net sales (purchases) of short-term investments	(3,665.2)	60.4
Net unsettled security transactions	208.4	118.6
Sales of property and equipment	4.5	8.7
Purchases of property and equipment	(162.1)	(86.6)
Net cash acquired in exchange transaction	8.5	0
Acquisition of ARX Holding Corp., net of cash acquired	0	(752.7)
Acquisition of additional shares of ARX Holding Corp.	0	(12.6)
Net cash used in investing activities	(2,124.3)	(1,859.2)
Cash Flows From Financing Activities
Tax benefit from vesting of equity-based compensation	8	15
Net proceeds from debt issuance	495.6	382
Payments of debt	(19.2)	(13.6)
Reacquisition of debt	18.2	19.3
Dividends paid to shareholders	(519)	(403.6)
Acquisition of treasury shares	(163.6)	(174.9)
Net cash used in financing activities	(216.4)	(214.4)
Effect of exchange rate changes on cash	0.4	(0.7)
Increase (decrease) in cash	(80.7)	86.1
Cash, January 1	224.1	108.4
Cash, September 30	$ 143.4	$ 194.5

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation — The accompanying consolidated financial statements include the accounts of The Progressive Corporation and ARX Holding Corp. (ARX), and their respective wholly owned insurance and non-insurance subsidiaries and affiliates, in which Progressive or ARX has a controlling financial interest. The Progressive Corporation owned 69.2% of the outstanding capital stock of ARX at September 30, 2016 and December 31, 2015, and 69.1% at September 30, 2015. All intercompany accounts and transactions are eliminated in consolidation. During the second quarter 2016, ARX entered into an exchange transaction with a third party pursuant to which ARX acquired 100% of the equity interest in an insurance subsidiary (and an affiliated company) that writes residential property insurance and disposed of 100% of the equity interest in an insurance subsidiary (and an affiliated company) that writes commercial property insurance. The book values of the entities that were acquired and disposed of were relatively equal at the time of the exchange. The consolidated financial statements reflect all normal recurring adjustments that, in the opinion of management, were necessary for a fair statement of the results for the interim periods presented. The results of operations for the period ended September 30, 2016 , are not necessarily indicative of the results expected for the full year. These consolidated financial statements and the notes thereto should be read in conjunction with Progressive’s audited financial statements and accompanying notes included in Exhibit 13 to our Annual Report on Form 10-K for the year ended December 31, 2015 (" 2015 Annual Report to Shareholders"). Included in other assets on the consolidated balance sheets are properties that are considered "held for sale." The fair value of these properties, less the estimated cost to sell them, was $8.7 million at September 30, 2016 and 2015 , and December 31, 2015 .

Investments

Investments	9 Months Ended
	Sep. 30, 2016
Investments Schedule [Abstract]
Investments	Investments — Our securities are reported at fair value, with the changes in fair value of these securities (other than hybrid securities and derivative instruments) reported as a component of accumulated other comprehensive income, net of deferred income taxes. The changes in fair value of the hybrid securities and derivative instruments are recorded as a component of net realized gains (losses) on securities. 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. The net holding period gains (losses) represent the amounts realized on our hybrid securities only. ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) 1 Fair Value % of Value September 30, 2016 Fixed maturities: U.S. government obligations $ 726.0 $ 8.9 $ (0.3 ) $ 0 $ 734.6 3.1 % State and local government obligations 2,508.9 58.7 (1.6 ) 0 2,566.0 10.9 Foreign government obligations 25.4 0 0 0 25.4 0.1 Corporate debt securities 4,327.5 76.9 (1.8 ) 0.7 4,403.3 18.7 Residential mortgage-backed securities 1,582.6 25.3 (15.5 ) 1.8 1,594.2 6.8 Agency residential pass-through obligations 43.6 0.5 0 0 44.1 0.2 Commercial mortgage-backed securities 2,249.4 35.1 (6.1 ) 0 2,278.4 9.7 Other asset-backed securities 2,037.5 7.9 (0.3 ) 0.3 2,045.4 8.7 Redeemable preferred stocks 207.1 19.6 (1.2 ) 0 225.5 1.0 Total fixed maturities 13,708.0 232.9 (26.8 ) 2.8 13,916.9 59.2 Equity securities: Nonredeemable preferred stocks 726.6 146.2 (13.9 ) 1.2 860.1 3.6 Common equities 1,576.1 1,296.3 (4.4 ) 0 2,868.0 12.2 Short-term investments 5,876.2 0 0 0 5,876.2 25.0 Total portfolio 2,3 $ 21,886.9 $ 1,675.4 $ (45.1 ) $ 4.0 $ 23,521.2 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) 1 Fair Value % of Value September 30, 2015 Fixed maturities: U.S. government obligations $ 2,028.2 $ 10.1 $ 0 $ 0 $ 2,038.3 9.7 % State and local government obligations 3,025.0 47.1 (4.2 ) 0 3,067.9 14.6 Foreign government obligations 19.3 0 0 0 19.3 0.1 Corporate debt securities 3,797.4 23.4 (21.4 ) 0.1 3,799.5 18.1 Residential mortgage-backed securities 1,801.8 26.2 (18.4 ) (0.2 ) 1,809.4 8.6 Agency residential pass-through obligations 112.2 0.1 (0.4 ) 0 111.9 0.5 Commercial mortgage-backed securities 2,641.4 31.1 (9.3 ) 0.4 2,663.6 12.7 Other asset-backed securities 1,859.3 4.1 (1.5 ) 0.5 1,862.4 8.9 Redeemable preferred stocks 255.0 17.6 (22.8 ) 0 249.8 1.2 Total fixed maturities 15,539.6 159.7 (78.0 ) 0.8 15,622.1 74.4 Equity securities: Nonredeemable preferred stocks 652.4 138.3 (14.8 ) (0.3 ) 775.6 3.7 Common equities 1,487.0 1,031.9 (35.0 ) 0 2,483.9 11.8 Short-term investments 2,132.0 0 0 0 2,132.0 10.1 Total portfolio 2,3 $ 19,811.0 $ 1,329.9 $ (127.8 ) $ 0.5 $ 21,013.6 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) 1 Fair Value % of Value December 31, 2015 Fixed maturities: U.S. government obligations $ 2,425.4 $ 4.4 $ (0.6 ) $ 0 $ 2,429.2 11.6 % State and local government obligations 2,677.6 47.5 (3.7 ) 0 2,721.4 13.0 Foreign government obligations 18.6 0 0 0 18.6 0.1 Corporate debt securities 3,713.2 11.3 (33.0 ) 0.1 3,691.6 17.6 Residential mortgage-backed securities 1,726.0 22.1 (20.6 ) (0.8 ) 1,726.7 8.3 Agency residential pass-through obligations 90.3 0.1 (1.1 ) 0 89.3 0.4 Commercial mortgage-backed securities 2,665.7 16.9 (29.4 ) 0 2,653.2 12.7 Other asset-backed securities 1,771.1 1.4 (5.1 ) 0.5 1,767.9 8.4 Redeemable preferred stocks 260.0 17.6 (43.3 ) 0 234.3 1.1 Total fixed maturities 15,347.9 121.3 (136.8 ) (0.2 ) 15,332.2 73.2 Equity securities: Nonredeemable preferred stocks 674.2 122.8 (15.7 ) 1.3 782.6 3.7 Common equities 1,494.3 1,170.4 (14.2 ) 0 2,650.5 12.7 Short-term investments 2,172.0 0 0 0 2,172.0 10.4 Total portfolio 2,3 $ 19,688.4 $ 1,414.5 $ (166.7 ) $ 1.1 $ 20,937.3 100.0 % 1 Represents net holding period gains (losses) realized on certain hybrid securities (discussed below). 2 Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015 , $185.3 million and $149.9 million , respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015 . 3 The total fair value of the portfolio at September 30, 2016 and 2015 , and December 31, 2015 included $1.0 billion , $1.0 billion , and $1.3 billion , respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions. Short-Term Investments Our short-term investments may include commercial paper and other investments that are expected to mature within one year. We did not enter into any repurchase commitment transactions during the first nine months of 2016 or 2015 , and we had no open repurchase commitments at September 30, 2016 , September 30, 2015 , or December 31, 2015 . Also included in short-term investments are reverse repurchase commitment transactions, where we loan cash to approved counterparties and receive U.S. Treasury Notes pledged as collateral against the cash borrowed. Our exposure to credit risk is limited due to the nature of the collateral (i.e., U.S. Treasury Notes) received. We have counterparty exposure on these trades in the event of a counterparty default to the extent the collateral security's value is below the amount of cash we delivered to acquire the collateral. The short-term duration of the transactions (primarily overnight) reduces that exposure. We had $68.0 million in open reverse repurchase commitments at September 30, 2016 ; there were no open reverse repurchase commitments at September 30, 2015 or December 31, 2015 . For the nine months ended September 30, 2016 , our largest outstanding balance of reverse repurchase commitments was $265.0 million , which was open for one day; the average daily balance of reverse repurchase commitments was $122.6 million . To the extent our repurchase and reverse repurchase transactions were with the same counterparty and subject to an enforceable master netting arrangement, we could elect to offset these transactions. Consistent with past practice, we have elected not to offset these transactions and therefore report these transactions on a gross basis on our balance sheets. Hybrid Securities Included in our fixed-maturity and equity securities are hybrid securities, which are reported at fair value: September 30, December 31, (millions) 2016 2015 Fixed maturities: Corporate debt securities $ 31.2 $ 89.4 $ 49.1 Residential mortgage-backed securities 175.3 117.7 144.3 Commercial mortgage-backed securities 0 17.7 17.3 Other asset-backed securities 9.5 11.9 11.3 Total fixed maturities 216.0 236.7 222.0 Equity securities: Nonredeemable preferred stocks 13.6 54.1 50.7 Total hybrid securities $ 229.6 $ 290.8 $ 272.7 Certain corporate debt securities are accounted for as hybrid securities since they were acquired at a premium and contain a change-in-control put option (derivative) that permits the investor, at its sole option if and when a change in control is triggered, to put the security back to the issuer at a 1% premium to par. Due to this change-in-control put option and the substantial market premium paid to acquire these securities, there is the potential that the election to put, upon the change in control, would result in an acceleration of the recognition of the remaining premium paid on these securities in our results of operations. This would result in a loss of $2.1 million as of September 30, 2016 , if all of the bonds experienced a simultaneous change in control and we elected to exercise all of our put options. The put feature limits the potential loss in value that could be experienced in the event a corporate action occurs that results in a change in control that materially diminishes the credit quality of the issuer. We are under no obligation to exercise the put option we hold if a change in control occurs. The residential mortgage-backed securities accounted for as hybrid securities are obligations of the issuer with payments of principal based on the performance of a reference pool of loans. This embedded derivative results in the securities incorporating the risk of default from both the issuer and the related loan pool. During 2016, we sold the commercial mortgage-backed securities referred to in the table above. These securities contained fixed interest rate reset features that would have increased the coupons in the event the securities were not fully paid off on the anticipated repayment date. These reset features had the potential to more than double our initial purchase yield for each security. The other asset-backed security in the table above represents one hybrid security that was acquired at a deep discount to par due to a failing auction, and contains a put option that allows the investor to put that security back to the auction at par if the auction is restored. This embedded derivative had the potential to more than double our initial investment yield at acquisition. The hybrid securities in our nonredeemable preferred stock portfolio are perpetual preferred stocks with fixed-rate coupons that have call features, whereby the change in value of the call features is a component of the overall change in value of the preferred stocks. Fixed Maturities The composition of fixed maturities by maturity at September 30, 2016 , was: (millions) Cost Fair Value Less than one year $ 3,251.2 $ 3,269.8 One to five years 7,471.8 7,552.0 Five to ten years 2,862.2 2,960.3 Ten years or greater 122.8 134.8 Total $ 13,708.0 $ 13,916.9 Asset-backed securities are classified in the maturity distribution table based upon their projected cash flows. All other securities which do not have a single maturity date are reported based upon expected average maturity. Contractual maturities may differ from expected maturities because the issuers of the securities may have the right to call or prepay obligations. Gross Unrealized Losses As of September 30, 2016 , we had $40.7 million of gross unrealized losses in our fixed-income securities (i.e., fixed-maturity securities, nonredeemable preferred stocks, and short-term investments) and $4.4 million in our common equities. We currently do not intend to sell the fixed-income securities and determined that it is more likely that we will not be required to sell these securities for the period of time necessary to recover their cost bases. A review of our fixed-income securities indicated that the issuers were current with respect to their interest obligations and that there was no evidence of any deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. For common equities, 95% of our common stock portfolio was indexed to the Russell 1000; as such, this portfolio may contain securities in a loss position for an extended period of time, subject to possible write-downs, as described below. We may retain these securities as long as the portfolio and index correlation remain similar. To the extent there is issuer-specific deterioration, we may write down the securities of that issuer. The remaining 5% of our common stocks were part of a managed equity strategy selected and administered by an external investment advisor. If our review of loss position securities were to indicate there was a fundamental, or market, impairment on these securities that was determined to be other-than-temporary, we would recognize a write-down in accordance with our stated policy. The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses September 30, 2016 Fixed maturities: U.S. government obligations 4 $ 104.8 $ (0.3 ) 4 $ 104.8 $ (0.3 ) 0 $ 0 $ 0 State and local government obligations 151 512.0 (1.6 ) 117 409.6 (1.0 ) 34 102.4 (0.6 ) Corporate debt securities 52 598.3 (1.8 ) 42 541.5 (0.8 ) 10 56.8 (1.0 ) Residential mortgage-backed securities 138 915.8 (15.5 ) 26 108.8 (0.4 ) 112 807.0 (15.1 ) Agency residential pass-through obligations 15 4.2 0 7 1.9 0 8 2.3 0 Commercial mortgage-backed securities 56 610.6 (6.1 ) 17 194.7 (1.7 ) 39 415.9 (4.4 ) Other asset-backed securities 43 488.7 (0.3 ) 16 219.5 (0.1 ) 27 269.2 (0.2 ) Redeemable preferred stocks 2 31.8 (1.2 ) 0 0 0 2 31.8 (1.2 ) Total fixed maturities 461 3,266.2 (26.8 ) 229 1,580.8 (4.3 ) 232 1,685.4 (22.5 ) Equity securities: Nonredeemable preferred stocks 7 187.5 (13.9 ) 1 9.9 (0.2 ) 6 177.6 (13.7 ) Common equities 86 53.4 (4.4 ) 83 49.5 (4.2 ) 3 3.9 (0.2 ) Total equity securities 93 240.9 (18.3 ) 84 59.4 (4.4 ) 9 181.5 (13.9 ) Total portfolio 554 $ 3,507.1 $ (45.1 ) 313 $ 1,640.2 $ (8.7 ) 241 $ 1,866.9 $ (36.4 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses September 30, 2015 Fixed maturities: U.S. government obligations 0 $ 0 $ 0 0 $ 0 $ 0 0 $ 0 $ 0 State and local government obligations 349 637.1 (4.2 ) 328 551.4 (3.7 ) 21 85.7 (0.5 ) Corporate debt securities 140 1,596.5 (21.4 ) 125 1,292.1 (15.7 ) 15 304.4 (5.7 ) Residential mortgage-backed securities 141 1,205.9 (18.4 ) 76 535.8 (4.1 ) 65 670.1 (14.3 ) Agency residential pass-through obligations 54 67.6 (0.4 ) 54 67.6 (0.4 ) 0 0 0 Commercial mortgage-backed securities 127 1,100.0 (9.3 ) 99 813.8 (7.6 ) 28 286.2 (1.7 ) Other asset-backed securities 60 845.5 (1.5 ) 53 764.0 (0.9 ) 7 81.5 (0.6 ) Redeemable preferred stocks 9 214.8 (22.8 ) 6 121.8 (7.1 ) 3 93.0 (15.7 ) Total fixed maturities 880 5,667.4 (78.0 ) 741 4,146.5 (39.5 ) 139 1,520.9 (38.5 ) Equity securities: Nonredeemable preferred stocks 14 376.9 (14.8 ) 9 197.6 (2.5 ) 5 179.3 (12.3 ) Common equities 136 211.6 (35.0 ) 132 209.1 (34.4 ) 4 2.5 (0.6 ) Total equity securities 150 588.5 (49.8 ) 141 406.7 (36.9 ) 9 181.8 (12.9 ) Total portfolio 1,030 $ 6,255.9 $ (127.8 ) 882 $ 4,553.2 $ (76.4 ) 148 $ 1,702.7 $ (51.4 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses December 31, 2015 Fixed maturities: U.S. government obligations 22 $ 897.1 $ (0.6 ) 22 $ 897.1 $ (0.6 ) 0 $ 0 $ 0 State and local government obligations 290 606.7 (3.7 ) 264 500.7 (2.6 ) 26 106.0 (1.1 ) Corporate debt securities 215 2,580.6 (33.0 ) 197 2,294.6 (25.2 ) 18 286.0 (7.8 ) Residential mortgage-backed securities 188 1,294.7 (20.6 ) 115 493.4 (3.7 ) 73 801.3 (16.9 ) Agency residential pass-through obligations 61 84.9 (1.1 ) 61 84.9 (1.1 ) 0 0 0 Commercial mortgage-backed securities 207 2,046.5 (29.4 ) 171 1,694.6 (25.8 ) 36 351.9 (3.6 ) Other asset-backed securities 101 1,548.6 (5.1 ) 92 1,472.0 (4.5 ) 9 76.6 (0.6 ) Redeemable preferred stocks 9 199.4 (43.3 ) 6 119.4 (14.5 ) 3 80.0 (28.8 ) Total fixed maturities 1,093 9,258.5 (136.8 ) 928 7,556.7 (78.0 ) 165 1,701.8 (58.8 ) Equity securities: Nonredeemable preferred stocks 10 301.8 (15.7 ) 5 124.2 (1.7 ) 5 177.6 (14.0 ) Common equities 64 164.8 (14.2 ) 60 161.4 (14.2 ) 4 3.4 0 Total equity securities 74 466.6 (29.9 ) 65 285.6 (15.9 ) 9 181.0 (14.0 ) Total portfolio 1,167 $ 9,725.1 $ (166.7 ) 993 $ 7,842.3 $ (93.9 ) 174 $ 1,882.8 $ (72.8 ) Since both September 30, 2015 and December 31, 2015 , the number of securities in our fixed-maturity portfolio with unrealized losses decreased, primarily the result of declining interest rates as well as write-downs on certain redeemable preferred stocks during the third quarter 2016. We had no material decreases in valuation as a result of credit rating downgrades on our fixed-maturity securities. All of the fixed-maturity securities in an unrealized loss position at September 30, 2016 in the table above are current with respect to required principal and interest payments. Since December 31, 2015 , our nonredeemable preferred stocks with unrealized losses decreased to seven securities, averaging approximately 7% of their total cost. The decrease in the number of securities is the result of valuation increases in the portfolio. We reviewed these securities and concluded that the unrealized losses are market-related adjustments to the values, which we determined not to be other-than-temporary; we expect to recover our initial investments on these securities. The number of issuers with unrealized losses in our common stock portfolio increased during the first nine months of 2016. A review of the securities in a loss position did not uncover fundamental issues with the issuers that would indicate other-than-temporary impairments existed. Additionally, market expectations for recovery in the next 12 months would put the fair values at or above our current book values. Lastly, we determined, as of the balance sheet date, that it was not likely these securities would be sold prior to that recovery. 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: September 30, December 31, (millions) 2016 2015 Fixed maturities: Residential mortgage-backed securities $ (43.3 ) $ (43.3 ) $ (43.3 ) Commercial mortgage-backed securities (0.6 ) (0.6 ) (0.6 ) Total fixed maturities $ (43.9 ) $ (43.9 ) $ (43.9 ) The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended September 30, 2016 and 2015 , for which a portion of the OTTI losses were also recognized in accumulated other comprehensive income at the time the credit impairments were determined and recognized: Three Months Ended September 30, 2016 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2016 $ 11.8 $ 0.4 $ 12.2 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 (0.3 ) 0 (0.3 ) Balance at September 30, 2016 $ 11.5 $ 0.4 $ 11.9 Nine months ended September 30, 2016 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2015 $ 12.4 $ 0.4 $ 12.8 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 (0.9 ) 0 (0.9 ) Balance at September 30, 2016 $ 11.5 $ 0.4 $ 11.9 Three Months Ended September 30, 2015 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2015 $ 14.0 $ 0.4 $ 14.4 Reductions for securities sold/matured (1.4 ) 0 (1.4 ) Change in recoveries of future cash flows expected to be collected 1 (1.7 ) 0 (1.7 ) Balance at September 30, 2015 $ 10.9 $ 0.4 $ 11.3 Nine Months Ended September 30, 2015 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2014 $ 12.7 $ 0.4 $ 13.1 Reductions for securities sold/matured (1.4 ) 0 (1.4 ) Change in recoveries of future cash flows expected to be collected 1 (0.4 ) 0 (0.4 ) Balance at September 30, 2015 $ 10.9 $ 0.4 $ 11.3 1 Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security. During the third quarter 2016, we recorded $25.4 million in write-downs on securities in our redeemable preferred stock portfolio. These securities had been in an unrealized loss position for greater than 12 months. During the quarter, we determined that we did not intend to hold these securities for the period of time necessary to recover their respective cost bases, given our evaluation of the length of time for such recovery. For the remaining securities in our fixed-income portfolio, 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 nine months ended September 30, 2016 or 2015 . Realized Gains (Losses) The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2016 2015 2016 2015 Gross realized gains on security sales Fixed maturities: U.S. government obligations $ 6.4 $ 2.7 $ 24.1 $ 17.1 State and local government obligations 0.6 0.5 16.0 0.5 Corporate and other debt securities 15.6 3.2 38.1 19.1 Residential mortgage-backed securities 0.2 4.4 1.9 4.6 Agency residential pass-through obligations 0 0 0.1 0 Commercial mortgage-backed securities 5.5 0.9 12.0 15.3 Redeemable preferred stocks 0 0 0 0.1 Total fixed maturities 28.3 11.7 92.2 56.7 Equity securities: Nonredeemable preferred stocks 4.9 3.7 11.9 53.9 Common equities 14.4 13.2 43.3 43.7 Short-term investments 0.1 0 0.1 0 Subtotal gross realized gains on security sales 47.7 28.6 147.5 154.3 Gross realized losses on security sales Fixed maturities: U.S. government obligations (0.8 ) 0 (1.2 ) (0.9 ) State and local government obligations 0 (0.1 ) (1.6 ) (0.1 ) Corporate and other debt securities (0.2 ) (0.9 ) (1.9 ) (2.2 ) Agency residential pass-through obligations 0 0 (0.2 ) 0 Commercial mortgage-backed securities 0 (0.1 ) (4.1 ) (1.1 ) Redeemable preferred stocks (6.5 ) 0 (6.5 ) 0 Total fixed maturities (7.5 ) (1.1 ) (15.5 ) (4.3 ) Equity securities: Nonredeemable preferred stocks (0.4 ) (0.1 ) (3.1 ) (1.5 ) Common equities (0.3 ) (0.8 ) (5.3 ) (1.5 ) Subtotal gross realized losses on security sales (8.2 ) (2.0 ) (23.9 ) (7.3 ) Net realized gains (losses) on security sales Fixed maturities: U.S. government obligations 5.6 2.7 22.9 16.2 State and local government obligations 0.6 0.4 14.4 0.4 Corporate and other debt securities 15.4 2.3 36.2 16.9 Residential mortgage-backed securities 0.2 4.4 1.9 4.6 Agency residential pass-through obligations 0 0 (0.1 ) 0 Commercial mortgage-backed securities 5.5 0.8 7.9 14.2 Redeemable preferred stocks (6.5 ) 0 (6.5 ) 0.1 Total fixed maturities 20.8 10.6 76.7 52.4 Equity securities: Nonredeemable preferred stocks 4.5 3.6 8.8 52.4 Common equities 14.1 12.4 38.0 42.2 Short-term investments 0.1 0 0.1 0 Subtotal net realized gains (losses) on security sales 39.5 26.6 123.6 147.0 Other-than-temporary impairment losses Fixed maturities: Redeemable preferred stocks (25.4 ) 0 (25.4 ) 0 Total fixed maturities (25.4 ) 0 (25.4 ) 0 Equity securities: Common equities (1.4 ) (13.6 ) (1.6 ) (23.0 ) Subtotal investment other-than-temporary impairment losses (26.8 ) (13.6 ) (27.0 ) (23.0 ) Other asset impairment (34.8 ) 0 (34.8 ) 0 Subtotal other-than-temporary impairment losses (61.6 ) (13.6 ) (61.8 ) (23.0 ) Other gains (losses) Hybrid securities 0.6 (1.3 ) 2.9 (1.9 ) Derivative instruments 0.7 (27.7 ) (35.8 ) (29.2 ) Litigation settlements 0.1 0.2 0.1 0.3 Subtotal other gains (losses) 1.4 (28.8 ) (32.8 ) (30.8 ) Total net realized gains (losses) on securities $ (20.7 ) $ (15.8 ) $ 29.0 $ 93.2 Gross realized gains and losses were predominantly the result of sales transactions in our fixed-income portfolio related to movements in credit spreads and interest rates and sales from our equity portfolios. In addition, gains and losses reflect recoveries from litigation settlements related to investments and holding period valuation changes on hybrids and derivatives. Also included are write-downs for securities determined to be other-than-temporarily impaired. The other asset impairment relates to a renewable energy investment, which is 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 asset. Net Investment Income The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2016 2015 2016 2015 Fixed maturities: U.S. government obligations $ 3.3 $ 6.2 $ 12.4 $ 22.5 State and local government obligations 12.6 16.9 39.3 45.0 Foreign government obligations 0.1 0.1 0.3 0.3 Corporate debt securities 27.3 28.0 81.9 75.1 Residential mortgage-backed securities 11.1 13.5 34.9 39.5 Agency residential pass-through obligations 0.3 0.7 0.9 1.4 Commercial mortgage-backed securities 22.4 18.3 62.6 54.0 Other asset-backed securities 6.8 5.7 18.7 16.2 Redeemable preferred stocks 3.8 3.7 11.5 11.3 Total fixed maturities 87.7 93.1 262.5 265.3 Equity securities: Nonredeemable preferred stocks 12.4 11.0 36.8 32.4 Common equities 13.9 12.7 42.0 36.7 Short-term investments 5.3 0.7 11.4 1.5 Investment income 119.3 117.5 352.7 335.9 Investment expenses (4.8 ) (4.9 ) (14.9 ) (15.9 ) Net investment income $ 114.5 $ 112.6 $ 337.8 $ 320.0 The amount of investment income (interest and dividends) we recognize varies from year to year based on the average assets held during the year and the book yields of the securities in our portfolio. Trading Securities At September 30, 2016 and 2015 , and December 31, 2015 , we did not hold any trading securities and did not have any net realized gains (losses) on trading securities for the three and nine months ended September 30, 2016 and 2015 . Derivative Instruments For all derivative positions discussed below, realized holding period gains and losses are netted with any upfront cash that may be exchanged under the contract to determine if the net position should be classified either as an asset or liability. To be reported as a net derivative asset and a component of the available-for-sale portfolio, the inception-to-date realized gain on the derivative position at period end would have to exceed any upfront cash received. On the other hand, a net derivative liability would include any inception-to-date realized loss plus the amount of upfront cash received (or netted, if upfront cash was paid) and would be reported as a component of other liabilities. These net derivative assets/liabilities are not separately disclosed on the balance sheet due to their immaterial effect on our financial condition, cash flows, and results of operations. The following table shows the status of our derivative instruments at September 30, 2016 and 2015 , and December 31, 2015 , and for the three and nine months ended September 30, 2016 and 2015 : (millions) Balance Sheet 2 Comprehensive Income Statement Assets (Liabilities) Pretax Net Realized Gains (Losses) Notional Value 1 Three Months Ended Nine Months Ended September 30, Dec. 31, September 30, Dec. 31, September 30, September 30, Derivatives designated as: 2016 2015 2015 Purpose Classification 2016 2015 2015 2016 2015 2016 2015 Hedging instrument Closed: Ineffective cash flow hedge $ 370 $ 18 $ 18 Manage interest rate risk NA $ 0 $ 0 $ 0 $ (1.4 ) $ 0.2 $ (1.3 ) $ 0.2 Non-hedging instruments Assets: Interest rate swaps 0 0 750 Manage portfolio duration Investments— fixed maturities 0 0 4.4 0 0 0 0 Liabilities: Interest rate swaps 315 750 0 Manage portfolio duration Other liabilities (13.0 ) (6.3 ) 0 1.7 (27.9 ) (17.8 ) (31.2 ) Closed: Interest rate swaps 435 0 0 Manage portfolio duration NA 0 0 0 0.3 0 (17.0 ) 0 U.S. Treasury Note futures 135 505 691 Manage NA 0 0 0 0.1 0 0.3 1.8 Total NA NA NA $ (13.0 ) $ (6.3 ) $ 4.4 $ 0.7 $ (27.7 ) $ (35.8 ) $ (29.2 ) NA= Not applicable 1 The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions. 2 To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation. CASH FLOW HEDGES During the third quarter 2016, we entered into a $350 million forecasted transaction to hedge against a possible rise in interest rates in anticipation of a debt offering under which we issued $500 million of 2.45% Senior Notes due 2027. When the contract was closed, the $1.4 million loss on the derivative was immediately recognized as a realized loss. The remaining portion of our ineffective cash flow hedge, which is reflected in the table above, resulted from the repurchase of a portion of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 during 2015 and the second quarter 2016 , and we reclassified the unrealized gain on forecasted transactions to net realized gains on securities. See Note 4 – Debt for further discussion. INTEREST RATE SWAPS and U.S. TREASURY FUTURES We use interest rate swaps and treasury futures contracts primarily to manage the fixed-income portfolio duration. At September 30, 2016 and 2015 , and December 31, 2015 , we held interest rate swap positions for which we are paying a fixed rate and receiving a variable rate, effectively shortening the duration of our fixed-income portfolio. On the position open at September 30, 2016 , since inception, interest rates have fallen resulting in a fair value loss and a fair value decrease of $14.8 million since December 31, 2015. During 2016 , we closed 10 -year interest rate swap positions (opened in 2013) in which we were paying a fixed rate and receiving a variable rate. The net realized loss during the year was the result of overall falling interest rates during the period the positions were open, while the net realized gain for the third quarter was due to overall rising interest rates during the quarter. As of September 30, 2016 and 2015 , the balance of the cash collateral that we delivered to the applicable counterparties on the interest rate swaps was $15.1 million and $9.6 million , respectively. As of December 31, 2015 , the balance of the cash collateral that we had received from the applicable counterparties on the interest rate swap positions was $4.9 million . During third quarter 2016 and 2015 , we entered into U.S. treasury futures by selling contracts; all positions were closed as of the end of the respective third quarter.

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2016
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, active exchange-traded equity securities, and certain short-term securities). • Level 2 : Inputs (other than quoted prices included within Level 1) that are observable for the instrument either directly or indirectly (e.g., certain corporate and municipal bonds and certain preferred stocks). This includes: (i) quoted prices for similar instruments in active markets, (ii) quoted prices for identical or similar instruments in markets that are not active, (iii) inputs other than quoted prices that are observable for the instruments, and (iv) inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3 : Inputs that are unobservable. Unobservable inputs reflect our subjective evaluation about the assumptions market participants would use in pricing the financial instrument (e.g., certain structured securities and privately held investments). Determining the fair value of the investment portfolio is the responsibility of management. As part of the responsibility, we evaluate whether a market is distressed or inactive in determining the fair value for our portfolio. We review certain market level inputs to evaluate whether sufficient activity, volume, and new issuances exist to create an active market. Based on this evaluation, we concluded that there was sufficient activity related to the sectors and securities for which we obtained valuations. The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2016 Fixed maturities: U.S. government obligations $ 734.6 $ 0 $ 0 $ 734.6 $ 726.0 State and local government obligations 0 2,566.0 0 2,566.0 2,508.9 Foreign government obligations 25.4 0 0 25.4 25.4 Corporate debt securities 0 4,403.3 0 4,403.3 4,327.5 Subtotal 760.0 6,969.3 0 7,729.3 7,587.8 Asset-backed securities: Residential mortgage-backed 0 1,594.2 0 1,594.2 1,582.6 Agency residential pass-through obligations 0 44.1 0 44.1 43.6 Commercial mortgage-backed 0 2,277.8 0.6 2,278.4 2,249.4 Other asset-backed 0 2,045.4 0 2,045.4 2,037.5 Subtotal asset-backed securities 0 5,961.5 0.6 5,962.1 5,913.1 Redeemable preferred stocks: Financials 0 95.7 0 95.7 77.1 Utilities 0 30.4 0 30.4 30.6 Industrials 0 99.4 0 99.4 99.4 Subtotal redeemable preferred stocks 0 225.5 0 225.5 207.1 Total fixed maturities 760.0 13,156.3 0.6 13,916.9 13,708.0 Equity securities: Nonredeemable preferred stocks: Financials 154.6 705.5 0 860.1 726.6 Subtotal nonredeemable preferred stocks 154.6 705.5 0 860.1 726.6 Common equities: Common stocks 2,867.6 0 0 2,867.6 1,575.7 Other risk investments 0 0 0.4 0.4 0.4 Subtotal common equities 2,867.6 0 0.4 2,868.0 1,576.1 Total fixed maturities and equity securities 3,782.2 13,861.8 1.0 17,645.0 16,010.7 Short-term investments 5,051.5 824.7 0 5,876.2 5,876.2 Total portfolio $ 8,833.7 $ 14,686.5 $ 1.0 $ 23,521.2 $ 21,886.9 Debt $ 0 $ 3,371.6 $ 133.6 $ 3,505.2 $ 3,153.9 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2015 Fixed maturities: U.S. government obligations $ 2,038.3 $ 0 $ 0 $ 2,038.3 $ 2,028.2 State and local government obligations 0 3,067.9 0 3,067.9 3,025.0 Foreign government obligations 19.3 0 0 19.3 19.3 Corporate debt securities 0 3,798.5 1.0 3,799.5 3,797.4 Subtotal 2,057.6 6,866.4 1.0 8,925.0 8,869.9 Asset-backed securities: Residential mortgage-backed 0 1,809.4 0 1,809.4 1,801.8 Agency residential pass-through obligations 0 111.9 0 111.9 112.2 Commercial mortgage-backed 0 2,653.3 10.3 2,663.6 2,641.4 Other asset-backed 0 1,862.4 0 1,862.4 1,859.3 Subtotal asset-backed securities 0 6,437.0 10.3 6,447.3 6,414.7 Redeemable preferred stocks: Financials 0 88.1 0 88.1 71.8 Utilities 0 56.0 0 56.0 65.1 Industrials 0 105.7 0 105.7 118.1 Subtotal redeemable preferred stocks 0 249.8 0 249.8 255.0 Total fixed maturities 2,057.6 13,553.2 11.3 15,622.1 15,539.6 Equity securities: Nonredeemable preferred stocks: Financials 158.7 616.9 0 775.6 652.4 Subtotal nonredeemable preferred stocks 158.7 616.9 0 775.6 652.4 Common equities: Common stocks 2,483.6 0 0 2,483.6 1,486.7 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,483.6 0 0.3 2,483.9 1,487.0 Total fixed maturities and equity securities 4,699.9 14,170.1 11.6 18,881.6 17,679.0 Short-term investments 2,007.0 125.0 0 2,132.0 2,132.0 Total portfolio $ 6,706.9 $ 14,295.1 $ 11.6 $ 21,013.6 $ 19,811.0 Debt $ 0 $ 2,727.5 $ 171.7 $ 2,899.2 $ 2,714.3 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2015 Fixed maturities: U.S. government obligations $ 2,429.2 $ 0 $ 0 $ 2,429.2 $ 2,425.4 State and local government obligations 0 2,721.4 0 2,721.4 2,677.6 Foreign government obligations 18.6 0 0 18.6 18.6 Corporate debt securities 0 3,691.6 0 3,691.6 3,713.2 Subtotal 2,447.8 6,413.0 0 8,860.8 8,834.8 Asset-backed securities: Residential mortgage-backed 0 1,726.7 0 1,726.7 1,726.0 Agency residential pass-through obligations 0 89.3 0 89.3 90.3 Commercial mortgage-backed 0 2,643.3 9.9 2,653.2 2,665.7 Other asset-backed 0 1,767.9 0 1,767.9 1,771.1 Subtotal asset-backed securities 0 6,227.2 9.9 6,237.1 6,253.1 Redeemable preferred stocks: Financials 0 92.0 0 92.0 76.8 Utilities 0 51.2 0 51.2 65.1 Industrials 0 91.1 0 91.1 118.1 Subtotal redeemable preferred stocks 0 234.3 0 234.3 260.0 Total fixed maturities 2,447.8 12,874.5 9.9 15,332.2 15,347.9 Equity securities: Nonredeemable preferred stocks: Financials 154.9 627.7 0 782.6 674.2 Subtotal nonredeemable preferred stocks 154.9 627.7 0 782.6 674.2 Common equities: Common stocks 2,650.2 0 0 2,650.2 1,494.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,650.2 0 0.3 2,650.5 1,494.3 Total fixed maturities and equity securities 5,252.9 13,502.2 10.2 18,765.3 17,516.4 Short-term investments 2,056.3 115.7 0 2,172.0 2,172.0 Total portfolio $ 7,309.2 $ 13,617.9 $ 10.2 $ 20,937.3 $ 19,688.4 Debt $ 0 $ 2,722.9 $ 164.9 $ 2,887.8 $ 2,707.9 Our portfolio valuations, excluding short-term investments, classified as either Level 1 or Level 2 in the above tables are priced exclusively by external sources, including: pricing vendors, dealers/market makers, and exchange-quoted prices. We did not have any transfers between Level 1 and Level 2 during 2016 or 2015 . We recognize transfers between levels at the end of the reporting period. Our short-term security holdings classified as Level 1 are highly liquid, actively marketed, and have a very short duration, primarily 30 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 auction securities issued by municipalities that contain a redemption put feature back to the auction pool with a redemption period typically less than seven days. The auction pool is created by a liquidity provider and if the auction is not available at the end of the seven days, we have the right to put the security back to the issuer at par. At September 30, 2016 , vendor-quoted prices represented 24% of our Level 1 classifications (excluding short-term investments), compared to 47% and 49% at September 30, 2015 and December 31, 2015 , respectively. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded, and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. The decline in vendor-quoted Level 1 prices since December 31, 2015 was due to a reduction of U.S. Treasury Notes with the funds deployed primarily to short-term investments. At September 30, 2016 and 2015 , and December 31, 2015 , vendor-quoted prices comprised 99% , 97% , and 97% , respectively, of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented 1% , 3% , and 3% , respectively. In our process for selecting a source (e.g., dealer, 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. We frequently 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 and debentures 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 seven 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 received 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 price to a previous market valuation price. 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 September 30, 2016 and 2015 , and December 31, 2015 , securities in our fixed-maturity portfolio listed as Level 3 were comprised substantially of securities that were either: (i) private placements, (ii) thinly held and/or traded securities, or (iii) non-investment-grade or non-rated securities with little liquidity. Based on these factors, it was difficult to independently verify observable market inputs that were used to generate the external valuations we received. Despite the lack of sufficient observable market information for our Level 3 securities, we believe the valuations received in conjunction with our procedures for evaluating third-party prices support the fair values reported in the financial statements. We did not hold any internally priced securities at September 30, 2016 or December 31, 2015 . At September 30, 2015 , we held two internally priced securities in our corporate portfolio that we priced at cost since we had expected them to be fully redeemed by the end of 2015; these securities were no longer held at December 31, 2015 . We review the prices from our external sources for reasonableness using internally developed assumptions to derive prices for the securities, which are then compared to the prices we received. During 2016 or 2015 , 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. The following tables provide a summary of changes in fair value associated with Level 3 assets for the three and nine months ended September 30, 2016 and 2015 : Level 3 Fair Value Three Months Ended September 30, 2016 (millions) Fair Value at June 30, 2016 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain) Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2016 Fixed maturities: Corporate debt securities $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Asset-backed securities: Commercial mortgage-backed 9.2 (8.7 ) 0 0 0 0.1 0 0.6 Total fixed maturities 9.2 (8.7 ) 0 0 0 0.1 0 0.6 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Common equities: Other risk investments 0.3 0 0 0 0 0.1 0 0.4 Total Level 3 securities $ 9.5 $ (8.7 ) $ 0 $ 0 $ 0 $ 0.2 $ 0 $ 1.0 Level 3 Fair Value Nine Months Ended September 30, 2016 (millions) Fair Value at Dec. 31, 2015 Calls/ Purchases Sales Net Realized (Gain) Loss on Sales Change in Valuation Net Fair Value at September 30, 2016 Fixed maturities: Corporate debt securities $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Asset-backed securities: Commercial mortgage-backed 9.9 (9.3 ) 0 0 0 0 0 0.6 Total fixed maturities 9.9 (9.3 ) 0 0 0 0 0 0.6 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Common equities: Other risk investments 0.3 0 0 0 0 0.1 0 0.4 Total Level 3 securities $ 10.2 $ (9.3 ) $ 0 $ 0 $ 0 $ 0.1 $ 0 $ 1.0 Level 3 Fair Value Three Months Ended September 30, 2015 (millions) Fair Value at June 30, 2015 Calls/ Purchases Sales Net Realized (Gain) Loss on Sales Change in Net Fair Value at September 30, 2015 Fixed maturities: Corporate debt securities $ 1.0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 1.0 Asset-backed securities: Commercial mortgage-backed 10.9 (0.4 ) 0 0 0 (0.2 ) 0 10.3 Total fixed maturities 11.9 (0.4 ) 0 0 0 (0.2 ) 0 11.3 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 12.2 $ (0.4 ) $ 0 $ 0 $ 0 $ (0.2 ) $ 0 $ 11.6 Level 3 Fair Value Nine Months Ended September 30, 2015 (millions) Fair Value at Dec. 31, 2014 Calls/ Purchases Sales Net Realized (Gain) Loss on Sales Change in Net Fair Value at September 30, 2015 Fixed maturities: Corporate debt securities $ 0 $ 0 $ 1.0 $ 0 $ 0 $ 0 $ 0 $ 1.0 Asset-backed securities: Commercial mortgage-backed 11.6 (1.0 ) 0 0 0 (0.3 ) 0 10.3 Total fixed maturities 11.6 (1.0 ) 1.0 0 0 (0.3 ) 0 11.3 Equity securities: Nonredeemable preferred stocks: Financials 1 69.3 0 0 0 (39.4 ) (1.4 ) (28.5 ) 0 Common equities: Other risk investments 0.4 0 0 0 0 (0.1 ) 0 0.3 Total Level 3 securities $ 81.3 $ (1.0 ) $ 1.0 $ 0 $ (39.4 ) $ (1.8 ) $ (28.5 ) $ 11.6 1 The $69.3 million decrease during the year reflects the reclassification of our 5% interest in ARX Holding Corp. upon acquisition of a controlling interest in ARX. The $39.4 million reflects our inception-to-date gain recognized, including a $1.4 million reduction in valuation that occurred during the first nine months of 2015. The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2016 and 2015 , and December 31, 2015 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2016 Valuation Technique Unobservable Input Unobservable Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 0.6 External vendor Prepayment rate 1 0 % Subtotal Level 3 securities 0.6 Pricing exemption securities 2 0.4 Total Level 3 securities $ 1.0 1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year. 2 The fair values for these securities were determined with unobservable inputs not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2015 Valuation Technique Unobservable Input Unobservable Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 10.3 External vendor Prepayment rate 1 0 % Subtotal Level 3 securities 10.3 Pricing exemption securities 2 1.3 Total Level 3 securities $ 11.6 1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year. 2 The fair values for these securities were determined with unobservable inputs not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2015 Valuation Technique Unobservable Input Unobservable Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 9.9 External vendor Prepayment rate 1 0 % Subtotal Level 3 securities 9.9 Pricing exemption securities 2 0.3 Total Level 3 securities $ 10.2 1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year. 2 The fair values for these securities were determined with unobservable inputs not reasonably available to us. 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.

Debt

Debt	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Debt	Debt — Debt consisted of: September 30, 2016 September 30, 2015 December 31, 2015 (millions) Carrying Value Fair Value Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 $ 498.4 $ 544.2 $ 498.1 $ 534.5 $ 498.1 $ 528.7 2.45% Senior Notes due 2027 495.6 497.5 0 0 0 0 6 5/8% Senior Notes due 2029 295.8 402.6 295.6 379.5 295.7 376.0 6.25% Senior Notes due 2032 395.1 533.3 394.9 489.3 395.0 490.6 4.35% Senior Notes due 2044 346.4 403.0 346.4 345.7 346.4 352.8 3.70% Senior Notes due 2045 395.1 418.7 395.0 358.0 395.0 362.0 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 593.9 572.3 612.6 620.5 612.8 612.8 Other debt instruments 133.6 133.6 171.7 171.7 164.9 164.9 Total $ 3,153.9 $ 3,505.2 $ 2,714.3 $ 2,899.2 $ 2,707.9 $ 2,887.8 The other debt instruments reported in the table above represent ARX indebtedness and consist of: September 30, 2016 September 30, 2015 December 31, 2015 Type of debt instrument Number of Instruments Carrying Value Number of Instruments Carrying Number of Instruments Carrying Stated Maturity Date(s) Term loans 2 $ 68.4 2 $ 93.3 2 $ 87.1 December 2018 and 2019 Junior subordinated notes 1 2 41.2 2 41.3 2 41.2 June 2036 and 2037 Senior notes 4 24.0 4 24.0 4 24.0 Various 2 Surplus note 3 0 0 1 13.1 1 12.6 November 2021 Total $ 133.6 $ 171.7 $ 164.9 1 ARX issued junior subordinated floating rate notes to trusts established by ARX in connection with issuances of trust preferred securities by the trusts (discussed below). 2 The senior notes mature in May 2033, April 2034, December 2034, and June 2035. 3 The surplus note was debt of the subsidiary disposed of by ARX in the exchange transaction during the second quarter 2016 (see Note 1 – Basis of Presentation for further discussion). The Progressive Corporation Debt During the third quarter 2016, we issued $500 million of our 2.45% Senior Notes due 2027 (the “2.45% Senior Notes”) in an underwritten public offering. We received proceeds, after deducting underwriter's discounts, commissions, and other issuance costs, of approximately $495.6 million . Interest on these Senior Notes is payable semi-annually and are redeemable in whole or in part at any time. There are no restrictive financial covenants or credit rating triggers on these Senior Notes. During the second quarter 2016 and third quarter 2015, we repurchased, in the open market, $19.8 million and $18.4 million , respectively, in aggregate principal amount of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (the "6.70% Debentures"). Since the carrying value of the debt we repurchased differed from the amount paid to extinguish the debt, we recognized a gain of $1.6 million during 2016 and a loss of $0.9 million during 2015. In addition, for the portion of the 6.70% Debentures we repurchased, we reclassified $0.1 million and $0.2 million during 2016 and 2015, respectively, on a pretax basis, of the unrealized gain on forecasted transactions from accumulated other comprehensive income on the balance sheet to net realized gains on securities on the comprehensive income statement. ARX Debt The other debt instruments were issued by ARX. ARX, not The Progressive Corporation or any of its other subsidiaries, is responsible for the other debt, which includes amounts that were borrowed and contributed to the capital of ARX's insurance subsidiaries or used, or made available for use, for other business purposes. In estimating the fair value of the other debt instruments, it was determined that the fair value of these notes is equal to the carrying value, based on the current rates offered for debt of similar maturities and interest rates. Pursuant to agreements entered into by ARX relating to the trust preferred securities transactions, ARX established trusts that are entirely owned by ARX. The trusts, which are the holders of the junior subordinated notes, issued trust preferred securities to third parties. The shares in the trusts are not transferable. The trusts are considered special purpose variable interest entities for which ARX is not the primary beneficiary and, therefore, they are accounted for under the equity method of accounting and not consolidated with ARX. Our ownership interest of $1.3 million at September 30, 2016 and 2015, and December 31, 2015, in the variable interest entities is reported as a component of "other assets" on our consolidated balance sheets. The Progressive Corporation Line of Credit During the second quarter 2016, we renewed the unsecured, discretionary line of credit (the "Line of Credit") with PNC Bank, National Association (PNC) in the maximum principal amount of $100 million . Subject to the terms and conditions of the Line of Credit documents, advances under the Line of Credit (if any) will bear interest at a variable rate equal to the higher of PNC's Prime Rate and the sum of the Federal Funds Open Rate plus 50 basis points. Each advance would need to be repaid on the 30th day after the advance or, if earlier, on April 30, 2017, the expiration date of the Line of Credit. We had no borrowings under the Line of Credit or the prior line of credit during the first nine months of 2016 or throughout 2015.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes — At September 30, 2016 and 2015 , and December 31, 2015 , we determined that we did not need a valuation allowance on our gross deferred tax assets. Although realization of the deferred tax assets is not assured, management believes that it is more likely than not 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. For the three and nine months ended September 30, 2016 , the effective tax rate was 20.5% and 29.4% , respectively, compared to 33.2% and 32.0% for the same periods last year. The year-over-year decrease in the effective rate for both the three and nine month periods is primarily due to lower underwriting income in 2016, compared to 2015, and recognizing the ratable portion, or $25.8 million , of the total tax benefit for 2016 of $34.4 million earned through a renewable energy investment. For the nine months ended September 30, 2016, there have been no material changes in our uncertain tax positions.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information — Cash includes only bank demand deposits. We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2016 2015 Income taxes $ 380.8 $ 513.1 Interest 98.0 90.3 Restricted cash on our consolidated balance sheets at September 30, 2016, and December 31, 2015, represents cash received from the National Flood Insurance Program, which is restricted to pay flood claims under the "Write Your Own" program, for which American Strategic Insurance and other subsidiaries of ARX (ASI) is an administrator.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Segment Information	Segment Information — Our Personal Lines segment writes insurance for personal autos and recreational vehicles. Our Commercial Lines segment writes primary liability and physical damage insurance for automobiles and trucks owned and/or operated predominantly by small businesses in the business auto, for-hire transportation, contractor, for-hire specialty, tow, and for-hire livery markets. Our Property segment writes personal property insurance for homeowners, other property owners, and renters. Our other indemnity businesses manage our run-off businesses, including the run-off of our professional liability insurance for community banks. Our service businesses provide insurance-related services, including processing Commercial Auto Insurance Procedures/Plans (CAIP) business and serving as an agent for property, general liability and business owners policies, and workers’ compensation insurance through our programs with ASI, and unaffiliated insurance companies. All segment revenues are generated from external customers; all intercompany transactions, including those with ASI, are eliminated in consolidation. Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 2,474.3 $ 98.6 $ 2,284.6 $ 169.4 $ 7,245.5 $ 354.5 $ 6,805.5 $ 535.8 Direct 2,391.2 84.4 2,069.5 100.9 6,946.7 237.5 6,056.7 287.2 Total Personal Lines 1 4,865.5 183.0 4,354.1 270.3 14,192.2 592.0 12,862.2 823.0 Commercial Lines 630.2 4.4 511.3 77.8 1,772.4 96.7 1,467.0 239.5 Property 2 227.7 10.4 205.2 17.2 638.0 (27.7 ) 403.9 18.2 Other indemnity 0 (0.8 ) 0 (0.4 ) 0 (1.6 ) (0.4 ) (0.4 ) Total underwriting operations 5,723.4 197.0 5,070.6 364.9 16,602.6 659.4 14,732.7 1,080.3 Fees and other revenues 3 86.8 NA 79.3 NA 248.2 NA 227.9 NA Service businesses 26.2 3.0 23.1 2.7 77.7 9.2 63.6 6.8 Investments 4 98.6 93.8 101.7 96.8 381.7 366.8 429.1 413.2 Gains on extinguishment of debt 0 0 (0.9 ) (0.9 ) 1.6 1.6 (0.9 ) (0.9 ) Interest expense NA (35.3 ) NA (34.5 ) NA (103.8 ) NA (101.9 ) Consolidated total $ 5,935.0 $ 258.5 $ 5,273.8 $ 429.0 $ 17,311.8 $ 933.2 $ 15,452.4 $ 1,397.5 NA = Not applicable 1 Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in both the third quarters and first nine months of 2016 and 2015; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, manufactured homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 We began reporting our Property business as a segment on April 1, 2015, upon acquisition of a controlling interest in ARX; therefore, the nine months ended September 30, 2015 only include results for six months and are not comparable to results reported for the nine months ended September 30, 2016. For the three and nine months ended September 30, 2016 , pretax loss also includes $15.5 million and $46.6 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $15.5 million and $31.2 million , respectively, for the three and nine months ended September 30, 2015. 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 respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Under-writing Combined Ratio Under-writing Combined Ratio Under-writing Margin Combined Ratio Under-writing Margin Combined Ratio Personal Lines Agency 4.0 % 96.0 7.4 % 92.6 4.9 % 95.1 7.9 % 92.1 Direct 3.5 96.5 4.9 95.1 3.4 96.6 4.7 95.3 Total Personal Lines 3.8 96.2 6.2 93.8 4.2 95.8 6.4 93.6 Commercial Lines 0.7 99.3 15.2 84.8 5.5 94.5 16.3 83.7 Property 1 4.6 95.4 8.4 91.6 (4.3 ) 104.3 4.5 95.5 Other indemnity 2 NM NM NM NM NM NM NM NM Total underwriting operations 3.4 96.6 7.2 92.8 4.0 96.0 7.3 92.7 1 We began reporting our Property business as a segment on April 1, 2015, when we acquired a controlling interest in ARX; therefore, the nine months ended September 30, 2015 only include results for six months and are not comparable to results reported for the nine months ended September 30, 2016. Included in both three and nine months ended September 30, 2016 , is 6.8 points and 7.3 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 7.6 and 7.7 points, respectively, for the three and nine months ended September 30, 2015. In addition, nine months ended September 2016 results include 0.7 points of expense related to the loss on the exchange transaction (See Note 1 - Basis of Presentation for discussion). 2 Underwriting margins and combined ratios are not meaningful (NM) for our other indemnity businesses due to lack of premiums earned by, and the variability of loss costs in, such businesses.

Dividends

Dividends	9 Months Ended
	Sep. 30, 2016
Text Block [Abstract]
Dividends	Dividends — We maintain a policy of paying an annual variable dividend that, if declared, would be payable shortly after the close of the year. This annual variable dividend is based on a target percentage of after-tax underwriting income (using a 35% tax rate) multiplied by a companywide performance factor (Gainshare factor), determined by reference to the Agency auto, Direct auto, special lines, and Commercial Lines business units, subject to the limitations discussed below. The target percentage is determined by our Board of Directors on an annual basis and announced to shareholders and the public. In December 2015 , the Board determined the target percentage for 2016 to be 33-1/3 % of annual after-tax underwriting income, which is unchanged from the 2015 target percentage. The Gainshare factor can range from zero to two and is determined by comparing our operating performance for the Agency auto, Direct auto, special lines, and Commercial Lines business units for the year to certain predetermined profitability and growth objectives approved by the Compensation Committee of the Board. This Gainshare factor is also used in the annual cash bonus program currently in place for our employees (our “Gainsharing program”). Although reviewed every year, the structure of the Gainsharing program generally remains the same. On a year-to-date basis, as of September 30, 2016 , the Gainshare factor was 1.54 . Since the final factor will be determined based on our results for the full year, the final factor may vary from the current factor. Our annual dividend program will result in a variable payment to shareholders each year, subject to certain limitations. If the Gainshare factor is zero or if our comprehensive income is less than after-tax underwriting income, no dividend would be payable under our annual variable dividend policy. For the nine months ended September 30, 2016, our comprehensive income was $893.5 million , which is more than the $428.6 million of after-tax underwriting income for the same period. However, the ultimate decision on whether or not a dividend will be paid, and the amount of any dividend, are in the discretion of the Board of Directors. The Board could decide to alter our policy, or not to pay the annual variable dividend, at any time prior to the declaration of the dividend for the year. Such an action by the Board could result from, among other reasons, changes in the insurance marketplace, changes in our performance or capital needs, changes in federal income tax laws, disruptions of national or international capital markets, or other events affecting our business, liquidity, or financial position. If a dividend for 2016 were to be paid, the Board would likely declare the 2016 annual dividend in December 2016 , with a record date in early 2017 and payment shortly thereafter. Following is a summary of our shareholder dividends that were declared in the last two years: (millions, except per share amounts) Amount Dividend Type Declared Paid Per Share Total 1 Annual – Variable December 2015 February 2016 $ 0.8882 $ 519.0 Annual – Variable December 2014 February 2015 0.6862 404.1 1 Represents the final amount of dividends declared based on shares outstanding as of the record date.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) — The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net Net Foreign (Income)loss attributable to NCI Balance at June 30, 2016 $ 1,477.0 $ (519.2 ) $ 957.8 $ 970.1 $ (8.8 ) $ (1.1 ) $ (2.4 ) Other comprehensive income (loss) before reclassifications: Investment securities 200.4 (70.2 ) 130.2 130.2 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 0.4 (0.1 ) 0.3 0 0 0.3 0 Loss attributable to noncontrolling interest (NCI) 1.8 (0.6 ) 1.2 0 0 0 1.2 Total other comprehensive income (loss) before reclassifications 202.6 (70.9 ) 131.7 130.2 0 0.3 1.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings 26.8 (9.4 ) 17.4 17.4 0 0 0 Net realized gains (losses) on securities 39.6 (13.9 ) 25.7 25.7 0 0 0 Interest expense 0.5 (0.2 ) 0.3 0 0.3 0 0 Total reclassification adjustment for amounts realized in net income 66.9 (23.5 ) 43.4 43.1 0.3 0 0 Total other comprehensive income (loss) 135.7 (47.4 ) 88.3 87.1 (0.3 ) 0.3 1.2 Balance at September 30, 2016 $ 1,612.7 $ (566.6 ) $ 1,046.1 $ 1,057.2 $ (9.1 ) $ (0.8 ) $ (1.2 ) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net Foreign (Income)loss attributable to NCI Balance 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 524.4 (184.2 ) 340.2 340.2 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 1.0 (0.3 ) 0.7 0 0 0.7 0 Loss attributable to noncontrolling interest (NCI) (3.7 ) 1.4 (2.3 ) 0 0 0 (2.3 ) Total other comprehensive income (loss) before reclassifications 521.6 (183.0 ) 338.6 340.2 0 0.7 (2.3 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings 27.0 (9.5 ) 17.5 17.5 0 0 0 Net realized gains (losses) on securities 114.9 (40.4 ) 74.5 74.5 0 0 0 Interest expense 1.5 (0.6 ) 0.9 0 0.9 0 0 Total reclassification adjustment for amounts realized in net income 143.4 (50.5 ) 92.9 92.0 0.9 0 0 Total other comprehensive income (loss) 378.2 (132.5 ) 245.7 248.2 (0.9 ) 0.7 (2.3 ) Balance at September 30, 2016 $ 1,612.7 $ (566.6 ) $ 1,046.1 $ 1,057.2 $ (9.1 ) $ (0.8 ) $ (1.2 ) Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income Total tax (provision) benefit After tax total accumulated other comprehensive income Total net Net unrealized gains on forecasted transactions Foreign currency translation adjustment (Income)loss attributable to NCI Balance at June 30, 2015 $ 1,393.3 $ (491.3 ) $ 902.0 $ 907.5 $ (7.5 ) $ (0.8 ) $ 2.8 Other comprehensive income (loss) before reclassifications: Investment securities (190.6 ) 66.5 (124.1 ) (124.1 ) 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 (1.1 ) 0.4 (0.7 ) 0 0 (0.7 ) 0 Loss attributable to noncontrolling interest (NCI) (2.5 ) 0.9 (1.6 ) 0 0 0 (1.6 ) Total other comprehensive income (loss) before reclassifications (194.2 ) 67.8 (126.4 ) (124.1 ) 0 (0.7 ) (1.6 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (13.6 ) 4.8 (8.8 ) (8.8 ) 0 0 0 Net realized gains (losses) on securities 23.0 (8.1 ) 14.9 14.8 0.1 0 0 Interest expense 0.4 (0.1 ) 0.3 0 0.3 0 0 Total reclassification adjustment for amounts realized in net income 9.8 (3.4 ) 6.4 6.0 0.4 0 0 Total other comprehensive income (loss) (204.0 ) 71.2 (132.8 ) (130.1 ) (0.4 ) (0.7 ) (1.6 ) Balance at September 30, 2015 $ 1,189.3 $ (420.1 ) $ 769.2 $ 777.4 $ (7.9 ) $ (1.5 ) $ 1.2 Components of Changes in (millions) Pretax total Total tax After tax total Total net Net Foreign (Income)loss attributable to NCI Balance at December 31, 2014 $ 1,574.0 $ (550.9 ) $ 1,023.1 $ 1,021.9 $ 1.5 $ (0.3 ) $ 0 Other comprehensive income (loss) before reclassifications: Investment securities (252.8 ) 84.6 (168.2 ) (168.2 ) 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes 0 0 0 0 0 0 0 Forecasted transactions (12.8 ) 4.4 (8.4 ) 0 (8.4 ) 0 0 Foreign currency translation adjustment (2.0 ) 0.8 (1.2 ) 0 0 (1.2 ) 0 Loss attributable to noncontrolling interest (NCI) 1.8 (0.6 ) 1.2 0 0 0 1.2 Total other comprehensive income (loss) before reclassifications (265.8 ) 89.2 (176.6 ) (168.2 ) (8.4 ) (1.2 ) 1.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (23.2 ) 8.2 (15.0 ) (15.0 ) 0 0 0 Net realized gains (losses) on securities 140.7 (49.3 ) 91.4 91.3 0.1 0 0 Interest expense 1.4 (0.5 ) 0.9 0 0.9 0 0 Total reclassification adjustment for amounts realized in net income 118.9 (41.6 ) 77.3 76.3 1.0 0 0 Total other comprehensive income (loss) (384.7 ) 130.8 (253.9 ) (244.5 ) (9.4 ) (1.2 ) 1.2 Balance at September 30, 2015 $ 1,189.3 $ (420.1 ) $ 769.2 $ 777.4 $ (7.9 ) $ (1.5 ) $ 1.2 In an effort to manage interest rate risk, we entered into forecasted transactions on each of Progressive's outstanding debt issuances. Upon issuing the debt, the gains (losses) recognized on these cash flow hedges are recorded as unrealized gains (losses) in accumulated other comprehensive income and amortized into interest expense over the term of the related debt issuance. We expect to reclassify $1.1 million (pretax) into income during the next 12 months, related to net unrealized gains on forecasted transactions.

Litigation

Litigation	9 Months Ended
	Sep. 30, 2016
Commitments and Contingencies Disclosure [Abstract]
Litigation	Litigation — The Progressive Corporation and/or its insurance subsidiaries are named as defendants in various lawsuits arising out of claims made under insurance policies written by our insurance subsidiaries in the ordinary course of business. We consider all legal actions relating to such claims in establishing our loss and loss adjustment expense reserves. In addition, The Progressive Corporation and/or its insurance subsidiaries are named as defendants in a number of class action or individual lawsuits arising out of the operations of the insurance subsidiaries. These cases include those alleging damages as a result of our subsidiaries’ practices in evaluating or paying medical or injury claims or benefits, including, but not limited to, personal injury protection, medical payments, and bodily injury benefits; the utilization, content, or appearance of policy documents; labor rates paid to auto body repair shops; wage and hour issues; and cases challenging other aspects of our subsidiaries’ claims or marketing practices or other business operations. Other insurance companies face many of these same issues. We plan to contest the pending lawsuits vigorously, but may pursue settlement negotiations in some cases, if appropriate. The outcomes of pending cases are uncertain at this time. We establish accruals for these lawsuits when it is probable that a loss has been or will be incurred and we can reasonably estimate its potential exposure, which may include a range of loss. As to lawsuits in which the loss is not considered both probable and estimable, or is considered probable but not estimable, we do not establish an accrual in accordance with current accounting guidance. With respect to our pending lawsuits that are not related to claims under insurance policies, the accruals that we have established were not material at September 30, 2016 . With respect to most of these lawsuits, we do not consider any losses to be both probable and estimable, and we are unable to estimate a meaningful range of loss, if any, at this time, due to the factors discussed in Note 12 - Litigation in our 2015 Annual Report to Shareholders. In the event that any one or more of these lawsuits results in a substantial judgment against, or settlement by, Progressive, or if our accruals prove to be inadequate by a significant amount, the resulting liability could have a material adverse effect on our consolidated financial condition, cash flows, and/or results of operations. For a further discussion on our pending litigation and related reserving policies, see Note 12 - Litigation in our 2015 Annual Report to Shareholders.

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest (Notes)	9 Months Ended
	Sep. 30, 2016
Temporary Equity Disclosure [Abstract]
Redeemable Noncontrolling Interest	Redeemable Noncontrolling Interest — In connection with the acquisition of a controlling interest in ARX, in the second quarter of 2015, The Progressive Corporation entered into a stockholders’ agreement with the other ARX stockholders. As part of the stockholders’ agreement, the minority ARX shareholders have the right to “put” their ARX shares to Progressive in two installments, one in early 2018 and one in early 2021, and Progressive has the ability to "call" a portion of the outstanding shares shortly thereafter. If these rights are exercised in full when available, our ownership stake in ARX capital stock will exceed 80% in 2018 and will reach 100% in 2021. 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 as mezzanine equity on our consolidated balance sheets, which represents the minority shares at the current estimated purchase price pursuant to the put and call provisions of the stockholders' agreement. The estimated purchase price is based, in part, on the change in tangible net book value of ARX from December 31, 2014 to the put and call dates. No redeemable noncontrolling interest (NCI) existed prior to the ARX acquisition on April 1, 2015. The changes in the components of redeemable NCI during the nine months ended September 30, 2016 and 2015, and the year ended December 31, 2015, were: (millions) September 30, 2016 September 30, 2015 December 31, 2015 Balance, Beginning of period $ 464.9 $ 0 $ 0 Fair value at date of acquisition 0 411.5 411.5 Net income attributable to NCI 11.3 13.4 32.9 Other comprehensive income (loss) attributable to NCI 2.3 (1.2 ) (1.1 ) Purchase of shares from NCI 0 (12.6 ) (12.6 ) Change in redemption value of NCI (6.0 ) 31.8 34.2 Balance, End of period $ 472.5 $ 442.9 $ 464.9 The decrease in the redemption value of the noncontrolling interest during 2016 was due in part to a decrease in ARX's tangible net book value as a result of the exchange transaction that occurred during the second quarter 2016 (see Note 1 - Basis for Presentation for further discussion). The entity disposed of in the exchange transaction had more tangible assets than the entity acquired.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	9 Months Ended
	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets Goodwill During the nine months ended September 30, 2016, the carrying amount of goodwill increased $1.8 million as a result of the ARX exchange transaction discussed in Note 1-Basis of Presentation . There were no goodwill impairment charges recognized during the nine months ended September 30, 2016 and 2015, and the year ended December 31, 2015. Additionally, there were no triggering events during 2016 that would have required a change to the carrying amount of goodwill. Goodwill recorded at September 30, 2016 was $449.4 million . Intangible Assets The following table is a summary of the net carrying amount of other intangible assets as of September 30, 2016 and 2015, and December 31, 2015: ($ in millions) September 30, 2016 September 30, 2015 December 31, 2015 Intangible assets subject to amortization $ 435.9 $ 498.1 $ 482.5 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 448.3 $ 510.5 $ 494.9 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for all periods presented. Intangible assets subject to amortization consisted of the following: (millions) September 30, 2016 September 30, 2015 December 31, 2015 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 55.0 $ 201.2 $ 256.2 $ 18.3 $ 237.9 $ 256.2 $ 27.5 $ 228.7 Agency relationships 159.2 17.1 142.1 159.2 5.7 153.5 159.2 8.5 150.7 Software rights 79.1 16.1 63.0 79.1 5.5 73.6 79.1 8.2 70.9 Trade name 34.8 5.2 29.6 34.8 1.7 33.1 34.8 2.6 32.2 Total $ 529.3 $ 93.4 $ 435.9 $ 529.3 $ 31.2 $ 498.1 $ 529.3 $ 46.8 $ 482.5 Amortization expense was $15.5 million and $46.6 million for the three and nine months ended September 30, 2016 and $15.5 million and $31.2 million for the three and nine months ended September 30, 2015; there was no amortization expense incurred in the first quarter 2015.

New Accounting Standards (Notes

New Accounting Standards (Notes)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
New Accounting Standards	New Accounting Standards Issued In March 2016, the Financial Accounting Standards Board (FASB) issued an accounting standard update (ASU) to simplify the accounting for employee share-based payment transactions. This ASU is effective for fiscal years beginning after December 15, 2016 (2017 for calendar-year companies), with early adoption permitted. Several aspects of the ASU include income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. Under provisions of the ASU: • All excess tax benefits and tax deficiencies should be recognized as income tax expense or benefit in the comprehensive income statement (applied prospectively) and classified in the statement of cash flows as an operating activity (applied using either a prospective or retrospective transition method). • Companies are allowed to decide whether or not to record forfeitures of share-based awards when the forfeiture occurs or to record compensation expense over the vesting period net of estimated forfeitures (applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity upon adoption). • Companies are permitted to withhold up to the maximum statutory tax rate and still maintain equity classification of share-based awards (applied using a modified retrospective transition method by means of a cumulative-effect adjustment to equity upon adoption). • Companies are required to classify as a financing activity in the statement of cash flows the payment of cash to a taxing authority when the company withholds shares for such purpose (applied retrospectively). We expect the change in the accounting for the excess tax benefits/deficiencies to impact our results of operations and are currently evaluating the impact of the other provisions of the ASU on our financial condition, cash flows, and results of operations. Over the last three years, the tax benefit, which is currently being recorded in paid in capital, was $16.8 million in 2015, $12.8 million in 2014, and $10.3 million in 2013. We currently record estimated forfeitures over the vesting period and withhold at the minimum statutory tax rate, and we do not anticipate making any changes upon adoption of the ASU. In June 2016, the FASB released 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). We are currently evaluating the impact the guidance will have on our financial statements, including the potential impacts of the new allowance account. Adopted In 2016, we adopted two accounting standard updates that became effective for fiscal years beginning after December 15, 2015. The first was the ASU that clarified guidance around accounting for fees paid in a cloud computing arrangement and amended the accounting treatment for the acquisition of licenses from third-parties for internal use software. Progressive adopted this ASU on a prospective basis and will apply the guidance for future cloud computing arrangements that we enter into. Upon adoption, we began including the costs of our fixed-term licenses as part of the total amount of capitalized software developed or acquired for internal use, rather than recording them as prepaid assets, when applicable. This standard did not have a material impact on our results of operations. The second ASU adopted is related to the accounting for share-based payments when the terms of an employee award can be achieved after the requisite service period. To the extent an equity award contains provisions that permit an employee who leaves the company before the performance targets are reached to receive some or all of the benefits of the award if and as the award later vests, this standard requires companies to recognize the compensation cost during the employee's remaining service period. Since we adopted this ASU prospectively, the requirements only apply to the performance-based restricted stock unit awards granted by Progressive to its executive officers and other select senior managers after January 1, 2016. The amount of expense that was accelerated pursuant to this ASU did not have a material impact on our financial condition, cash flows, or results of operations for the first nine months of 2016.

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2016
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. The net holding period gains (losses) represent the amounts realized on our hybrid securities only. ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) 1 Fair Value % of Value September 30, 2016 Fixed maturities: U.S. government obligations $ 726.0 $ 8.9 $ (0.3 ) $ 0 $ 734.6 3.1 % State and local government obligations 2,508.9 58.7 (1.6 ) 0 2,566.0 10.9 Foreign government obligations 25.4 0 0 0 25.4 0.1 Corporate debt securities 4,327.5 76.9 (1.8 ) 0.7 4,403.3 18.7 Residential mortgage-backed securities 1,582.6 25.3 (15.5 ) 1.8 1,594.2 6.8 Agency residential pass-through obligations 43.6 0.5 0 0 44.1 0.2 Commercial mortgage-backed securities 2,249.4 35.1 (6.1 ) 0 2,278.4 9.7 Other asset-backed securities 2,037.5 7.9 (0.3 ) 0.3 2,045.4 8.7 Redeemable preferred stocks 207.1 19.6 (1.2 ) 0 225.5 1.0 Total fixed maturities 13,708.0 232.9 (26.8 ) 2.8 13,916.9 59.2 Equity securities: Nonredeemable preferred stocks 726.6 146.2 (13.9 ) 1.2 860.1 3.6 Common equities 1,576.1 1,296.3 (4.4 ) 0 2,868.0 12.2 Short-term investments 5,876.2 0 0 0 5,876.2 25.0 Total portfolio 2,3 $ 21,886.9 $ 1,675.4 $ (45.1 ) $ 4.0 $ 23,521.2 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) 1 Fair Value % of Value September 30, 2015 Fixed maturities: U.S. government obligations $ 2,028.2 $ 10.1 $ 0 $ 0 $ 2,038.3 9.7 % State and local government obligations 3,025.0 47.1 (4.2 ) 0 3,067.9 14.6 Foreign government obligations 19.3 0 0 0 19.3 0.1 Corporate debt securities 3,797.4 23.4 (21.4 ) 0.1 3,799.5 18.1 Residential mortgage-backed securities 1,801.8 26.2 (18.4 ) (0.2 ) 1,809.4 8.6 Agency residential pass-through obligations 112.2 0.1 (0.4 ) 0 111.9 0.5 Commercial mortgage-backed securities 2,641.4 31.1 (9.3 ) 0.4 2,663.6 12.7 Other asset-backed securities 1,859.3 4.1 (1.5 ) 0.5 1,862.4 8.9 Redeemable preferred stocks 255.0 17.6 (22.8 ) 0 249.8 1.2 Total fixed maturities 15,539.6 159.7 (78.0 ) 0.8 15,622.1 74.4 Equity securities: Nonredeemable preferred stocks 652.4 138.3 (14.8 ) (0.3 ) 775.6 3.7 Common equities 1,487.0 1,031.9 (35.0 ) 0 2,483.9 11.8 Short-term investments 2,132.0 0 0 0 2,132.0 10.1 Total portfolio 2,3 $ 19,811.0 $ 1,329.9 $ (127.8 ) $ 0.5 $ 21,013.6 100.0 % ($ in millions) Cost Gross Unrealized Gains Gross Losses Net (Losses) 1 Fair Value % of Value December 31, 2015 Fixed maturities: U.S. government obligations $ 2,425.4 $ 4.4 $ (0.6 ) $ 0 $ 2,429.2 11.6 % State and local government obligations 2,677.6 47.5 (3.7 ) 0 2,721.4 13.0 Foreign government obligations 18.6 0 0 0 18.6 0.1 Corporate debt securities 3,713.2 11.3 (33.0 ) 0.1 3,691.6 17.6 Residential mortgage-backed securities 1,726.0 22.1 (20.6 ) (0.8 ) 1,726.7 8.3 Agency residential pass-through obligations 90.3 0.1 (1.1 ) 0 89.3 0.4 Commercial mortgage-backed securities 2,665.7 16.9 (29.4 ) 0 2,653.2 12.7 Other asset-backed securities 1,771.1 1.4 (5.1 ) 0.5 1,767.9 8.4 Redeemable preferred stocks 260.0 17.6 (43.3 ) 0 234.3 1.1 Total fixed maturities 15,347.9 121.3 (136.8 ) (0.2 ) 15,332.2 73.2 Equity securities: Nonredeemable preferred stocks 674.2 122.8 (15.7 ) 1.3 782.6 3.7 Common equities 1,494.3 1,170.4 (14.2 ) 0 2,650.5 12.7 Short-term investments 2,172.0 0 0 0 2,172.0 10.4 Total portfolio 2,3 $ 19,688.4 $ 1,414.5 $ (166.7 ) $ 1.1 $ 20,937.3 100.0 % 1 Represents net holding period gains (losses) realized on certain hybrid securities (discussed below). 2 Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015 , $185.3 million and $149.9 million , respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015 . 3 The total fair value of the portfolio at September 30, 2016 and 2015 , and December 31, 2015 included $1.0 billion , $1.0 billion , and $1.3 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-maturity and equity securities are hybrid securities, which are reported at fair value: September 30, December 31, (millions) 2016 2015 Fixed maturities: Corporate debt securities $ 31.2 $ 89.4 $ 49.1 Residential mortgage-backed securities 175.3 117.7 144.3 Commercial mortgage-backed securities 0 17.7 17.3 Other asset-backed securities 9.5 11.9 11.3 Total fixed maturities 216.0 236.7 222.0 Equity securities: Nonredeemable preferred stocks 13.6 54.1 50.7 Total hybrid securities $ 229.6 $ 290.8 $ 272.7
Composition of Fixed Maturities by Maturity	The composition of fixed maturities by maturity at September 30, 2016 , was: (millions) Cost Fair Value Less than one year $ 3,251.2 $ 3,269.8 One to five years 7,471.8 7,552.0 Five to ten years 2,862.2 2,960.3 Ten years or greater 122.8 134.8 Total $ 13,708.0 $ 13,916.9
Gross Unrealized Losses by Major Security	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position: Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses September 30, 2016 Fixed maturities: U.S. government obligations 4 $ 104.8 $ (0.3 ) 4 $ 104.8 $ (0.3 ) 0 $ 0 $ 0 State and local government obligations 151 512.0 (1.6 ) 117 409.6 (1.0 ) 34 102.4 (0.6 ) Corporate debt securities 52 598.3 (1.8 ) 42 541.5 (0.8 ) 10 56.8 (1.0 ) Residential mortgage-backed securities 138 915.8 (15.5 ) 26 108.8 (0.4 ) 112 807.0 (15.1 ) Agency residential pass-through obligations 15 4.2 0 7 1.9 0 8 2.3 0 Commercial mortgage-backed securities 56 610.6 (6.1 ) 17 194.7 (1.7 ) 39 415.9 (4.4 ) Other asset-backed securities 43 488.7 (0.3 ) 16 219.5 (0.1 ) 27 269.2 (0.2 ) Redeemable preferred stocks 2 31.8 (1.2 ) 0 0 0 2 31.8 (1.2 ) Total fixed maturities 461 3,266.2 (26.8 ) 229 1,580.8 (4.3 ) 232 1,685.4 (22.5 ) Equity securities: Nonredeemable preferred stocks 7 187.5 (13.9 ) 1 9.9 (0.2 ) 6 177.6 (13.7 ) Common equities 86 53.4 (4.4 ) 83 49.5 (4.2 ) 3 3.9 (0.2 ) Total equity securities 93 240.9 (18.3 ) 84 59.4 (4.4 ) 9 181.5 (13.9 ) Total portfolio 554 $ 3,507.1 $ (45.1 ) 313 $ 1,640.2 $ (8.7 ) 241 $ 1,866.9 $ (36.4 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses September 30, 2015 Fixed maturities: U.S. government obligations 0 $ 0 $ 0 0 $ 0 $ 0 0 $ 0 $ 0 State and local government obligations 349 637.1 (4.2 ) 328 551.4 (3.7 ) 21 85.7 (0.5 ) Corporate debt securities 140 1,596.5 (21.4 ) 125 1,292.1 (15.7 ) 15 304.4 (5.7 ) Residential mortgage-backed securities 141 1,205.9 (18.4 ) 76 535.8 (4.1 ) 65 670.1 (14.3 ) Agency residential pass-through obligations 54 67.6 (0.4 ) 54 67.6 (0.4 ) 0 0 0 Commercial mortgage-backed securities 127 1,100.0 (9.3 ) 99 813.8 (7.6 ) 28 286.2 (1.7 ) Other asset-backed securities 60 845.5 (1.5 ) 53 764.0 (0.9 ) 7 81.5 (0.6 ) Redeemable preferred stocks 9 214.8 (22.8 ) 6 121.8 (7.1 ) 3 93.0 (15.7 ) Total fixed maturities 880 5,667.4 (78.0 ) 741 4,146.5 (39.5 ) 139 1,520.9 (38.5 ) Equity securities: Nonredeemable preferred stocks 14 376.9 (14.8 ) 9 197.6 (2.5 ) 5 179.3 (12.3 ) Common equities 136 211.6 (35.0 ) 132 209.1 (34.4 ) 4 2.5 (0.6 ) Total equity securities 150 588.5 (49.8 ) 141 406.7 (36.9 ) 9 181.8 (12.9 ) Total portfolio 1,030 $ 6,255.9 $ (127.8 ) 882 $ 4,553.2 $ (76.4 ) 148 $ 1,702.7 $ (51.4 ) Total No. of Sec. Total Gross Unrealized Losses Less than 12 Months 12 Months or Greater ($ in millions) No. of Sec. Fair Unrealized Losses No. of Sec. Fair Unrealized Losses December 31, 2015 Fixed maturities: U.S. government obligations 22 $ 897.1 $ (0.6 ) 22 $ 897.1 $ (0.6 ) 0 $ 0 $ 0 State and local government obligations 290 606.7 (3.7 ) 264 500.7 (2.6 ) 26 106.0 (1.1 ) Corporate debt securities 215 2,580.6 (33.0 ) 197 2,294.6 (25.2 ) 18 286.0 (7.8 ) Residential mortgage-backed securities 188 1,294.7 (20.6 ) 115 493.4 (3.7 ) 73 801.3 (16.9 ) Agency residential pass-through obligations 61 84.9 (1.1 ) 61 84.9 (1.1 ) 0 0 0 Commercial mortgage-backed securities 207 2,046.5 (29.4 ) 171 1,694.6 (25.8 ) 36 351.9 (3.6 ) Other asset-backed securities 101 1,548.6 (5.1 ) 92 1,472.0 (4.5 ) 9 76.6 (0.6 ) Redeemable preferred stocks 9 199.4 (43.3 ) 6 119.4 (14.5 ) 3 80.0 (28.8 ) Total fixed maturities 1,093 9,258.5 (136.8 ) 928 7,556.7 (78.0 ) 165 1,701.8 (58.8 ) Equity securities: Nonredeemable preferred stocks 10 301.8 (15.7 ) 5 124.2 (1.7 ) 5 177.6 (14.0 ) Common equities 64 164.8 (14.2 ) 60 161.4 (14.2 ) 4 3.4 0 Total equity securities 74 466.6 (29.9 ) 65 285.6 (15.9 ) 9 181.0 (14.0 ) Total portfolio 1,167 $ 9,725.1 $ (166.7 ) 993 $ 7,842.3 $ (93.9 ) 174 $ 1,882.8 $ (72.8 )
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: September 30, December 31, (millions) 2016 2015 Fixed maturities: Residential mortgage-backed securities $ (43.3 ) $ (43.3 ) $ (43.3 ) Commercial mortgage-backed securities (0.6 ) (0.6 ) (0.6 ) Total fixed maturities $ (43.9 ) $ (43.9 ) $ (43.9 )
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 September 30, 2016 and 2015 , for which a portion of the OTTI losses were also recognized in accumulated other comprehensive income at the time the credit impairments were determined and recognized: Three Months Ended September 30, 2016 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2016 $ 11.8 $ 0.4 $ 12.2 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 (0.3 ) 0 (0.3 ) Balance at September 30, 2016 $ 11.5 $ 0.4 $ 11.9 Nine months ended September 30, 2016 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2015 $ 12.4 $ 0.4 $ 12.8 Reductions for securities sold/matured 0 0 0 Change in recoveries of future cash flows expected to be collected 1 (0.9 ) 0 (0.9 ) Balance at September 30, 2016 $ 11.5 $ 0.4 $ 11.9 Three Months Ended September 30, 2015 Mortgage-Backed (millions) Residential Commercial Total Balance at June 30, 2015 $ 14.0 $ 0.4 $ 14.4 Reductions for securities sold/matured (1.4 ) 0 (1.4 ) Change in recoveries of future cash flows expected to be collected 1 (1.7 ) 0 (1.7 ) Balance at September 30, 2015 $ 10.9 $ 0.4 $ 11.3 Nine Months Ended September 30, 2015 Mortgage-Backed (millions) Residential Commercial Total Balance at December 31, 2014 $ 12.7 $ 0.4 $ 13.1 Reductions for securities sold/matured (1.4 ) 0 (1.4 ) Change in recoveries of future cash flows expected to be collected 1 (0.4 ) 0 (0.4 ) Balance at September 30, 2015 $ 10.9 $ 0.4 $ 11.3 1 Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security.
Components of Net Realized Gains (Losses)	The components of net realized gains (losses) for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2016 2015 2016 2015 Gross realized gains on security sales Fixed maturities: U.S. government obligations $ 6.4 $ 2.7 $ 24.1 $ 17.1 State and local government obligations 0.6 0.5 16.0 0.5 Corporate and other debt securities 15.6 3.2 38.1 19.1 Residential mortgage-backed securities 0.2 4.4 1.9 4.6 Agency residential pass-through obligations 0 0 0.1 0 Commercial mortgage-backed securities 5.5 0.9 12.0 15.3 Redeemable preferred stocks 0 0 0 0.1 Total fixed maturities 28.3 11.7 92.2 56.7 Equity securities: Nonredeemable preferred stocks 4.9 3.7 11.9 53.9 Common equities 14.4 13.2 43.3 43.7 Short-term investments 0.1 0 0.1 0 Subtotal gross realized gains on security sales 47.7 28.6 147.5 154.3 Gross realized losses on security sales Fixed maturities: U.S. government obligations (0.8 ) 0 (1.2 ) (0.9 ) State and local government obligations 0 (0.1 ) (1.6 ) (0.1 ) Corporate and other debt securities (0.2 ) (0.9 ) (1.9 ) (2.2 ) Agency residential pass-through obligations 0 0 (0.2 ) 0 Commercial mortgage-backed securities 0 (0.1 ) (4.1 ) (1.1 ) Redeemable preferred stocks (6.5 ) 0 (6.5 ) 0 Total fixed maturities (7.5 ) (1.1 ) (15.5 ) (4.3 ) Equity securities: Nonredeemable preferred stocks (0.4 ) (0.1 ) (3.1 ) (1.5 ) Common equities (0.3 ) (0.8 ) (5.3 ) (1.5 ) Subtotal gross realized losses on security sales (8.2 ) (2.0 ) (23.9 ) (7.3 ) Net realized gains (losses) on security sales Fixed maturities: U.S. government obligations 5.6 2.7 22.9 16.2 State and local government obligations 0.6 0.4 14.4 0.4 Corporate and other debt securities 15.4 2.3 36.2 16.9 Residential mortgage-backed securities 0.2 4.4 1.9 4.6 Agency residential pass-through obligations 0 0 (0.1 ) 0 Commercial mortgage-backed securities 5.5 0.8 7.9 14.2 Redeemable preferred stocks (6.5 ) 0 (6.5 ) 0.1 Total fixed maturities 20.8 10.6 76.7 52.4 Equity securities: Nonredeemable preferred stocks 4.5 3.6 8.8 52.4 Common equities 14.1 12.4 38.0 42.2 Short-term investments 0.1 0 0.1 0 Subtotal net realized gains (losses) on security sales 39.5 26.6 123.6 147.0 Other-than-temporary impairment losses Fixed maturities: Redeemable preferred stocks (25.4 ) 0 (25.4 ) 0 Total fixed maturities (25.4 ) 0 (25.4 ) 0 Equity securities: Common equities (1.4 ) (13.6 ) (1.6 ) (23.0 ) Subtotal investment other-than-temporary impairment losses (26.8 ) (13.6 ) (27.0 ) (23.0 ) Other asset impairment (34.8 ) 0 (34.8 ) 0 Subtotal other-than-temporary impairment losses (61.6 ) (13.6 ) (61.8 ) (23.0 ) Other gains (losses) Hybrid securities 0.6 (1.3 ) 2.9 (1.9 ) Derivative instruments 0.7 (27.7 ) (35.8 ) (29.2 ) Litigation settlements 0.1 0.2 0.1 0.3 Subtotal other gains (losses) 1.4 (28.8 ) (32.8 ) (30.8 ) Total net realized gains (losses) on securities $ (20.7 ) $ (15.8 ) $ 29.0 $ 93.2
Components of Net Investment Income	The components of net investment income for the three and nine months ended September 30, were: Three Months Nine Months (millions) 2016 2015 2016 2015 Fixed maturities: U.S. government obligations $ 3.3 $ 6.2 $ 12.4 $ 22.5 State and local government obligations 12.6 16.9 39.3 45.0 Foreign government obligations 0.1 0.1 0.3 0.3 Corporate debt securities 27.3 28.0 81.9 75.1 Residential mortgage-backed securities 11.1 13.5 34.9 39.5 Agency residential pass-through obligations 0.3 0.7 0.9 1.4 Commercial mortgage-backed securities 22.4 18.3 62.6 54.0 Other asset-backed securities 6.8 5.7 18.7 16.2 Redeemable preferred stocks 3.8 3.7 11.5 11.3 Total fixed maturities 87.7 93.1 262.5 265.3 Equity securities: Nonredeemable preferred stocks 12.4 11.0 36.8 32.4 Common equities 13.9 12.7 42.0 36.7 Short-term investments 5.3 0.7 11.4 1.5 Investment income 119.3 117.5 352.7 335.9 Investment expenses (4.8 ) (4.9 ) (14.9 ) (15.9 ) Net investment income $ 114.5 $ 112.6 $ 337.8 $ 320.0
Derivative Instruments	The following table shows the status of our derivative instruments at September 30, 2016 and 2015 , and December 31, 2015 , and for the three and nine months ended September 30, 2016 and 2015 : (millions) Balance Sheet 2 Comprehensive Income Statement Assets (Liabilities) Pretax Net Realized Gains (Losses) Notional Value 1 Three Months Ended Nine Months Ended September 30, Dec. 31, September 30, Dec. 31, September 30, September 30, Derivatives designated as: 2016 2015 2015 Purpose Classification 2016 2015 2015 2016 2015 2016 2015 Hedging instrument Closed: Ineffective cash flow hedge $ 370 $ 18 $ 18 Manage interest rate risk NA $ 0 $ 0 $ 0 $ (1.4 ) $ 0.2 $ (1.3 ) $ 0.2 Non-hedging instruments Assets: Interest rate swaps 0 0 750 Manage portfolio duration Investments— fixed maturities 0 0 4.4 0 0 0 0 Liabilities: Interest rate swaps 315 750 0 Manage portfolio duration Other liabilities (13.0 ) (6.3 ) 0 1.7 (27.9 ) (17.8 ) (31.2 ) Closed: Interest rate swaps 435 0 0 Manage portfolio duration NA 0 0 0 0.3 0 (17.0 ) 0 U.S. Treasury Note futures 135 505 691 Manage NA 0 0 0 0.1 0 0.3 1.8 Total NA NA NA $ (13.0 ) $ (6.3 ) $ 4.4 $ 0.7 $ (27.7 ) $ (35.8 ) $ (29.2 ) NA= Not applicable 1 The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions. 2 To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Composition of Investment Portfolio by Major Security Type	The composition of the investment portfolio by major security type and our outstanding debt was: Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2016 Fixed maturities: U.S. government obligations $ 734.6 $ 0 $ 0 $ 734.6 $ 726.0 State and local government obligations 0 2,566.0 0 2,566.0 2,508.9 Foreign government obligations 25.4 0 0 25.4 25.4 Corporate debt securities 0 4,403.3 0 4,403.3 4,327.5 Subtotal 760.0 6,969.3 0 7,729.3 7,587.8 Asset-backed securities: Residential mortgage-backed 0 1,594.2 0 1,594.2 1,582.6 Agency residential pass-through obligations 0 44.1 0 44.1 43.6 Commercial mortgage-backed 0 2,277.8 0.6 2,278.4 2,249.4 Other asset-backed 0 2,045.4 0 2,045.4 2,037.5 Subtotal asset-backed securities 0 5,961.5 0.6 5,962.1 5,913.1 Redeemable preferred stocks: Financials 0 95.7 0 95.7 77.1 Utilities 0 30.4 0 30.4 30.6 Industrials 0 99.4 0 99.4 99.4 Subtotal redeemable preferred stocks 0 225.5 0 225.5 207.1 Total fixed maturities 760.0 13,156.3 0.6 13,916.9 13,708.0 Equity securities: Nonredeemable preferred stocks: Financials 154.6 705.5 0 860.1 726.6 Subtotal nonredeemable preferred stocks 154.6 705.5 0 860.1 726.6 Common equities: Common stocks 2,867.6 0 0 2,867.6 1,575.7 Other risk investments 0 0 0.4 0.4 0.4 Subtotal common equities 2,867.6 0 0.4 2,868.0 1,576.1 Total fixed maturities and equity securities 3,782.2 13,861.8 1.0 17,645.0 16,010.7 Short-term investments 5,051.5 824.7 0 5,876.2 5,876.2 Total portfolio $ 8,833.7 $ 14,686.5 $ 1.0 $ 23,521.2 $ 21,886.9 Debt $ 0 $ 3,371.6 $ 133.6 $ 3,505.2 $ 3,153.9 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost September 30, 2015 Fixed maturities: U.S. government obligations $ 2,038.3 $ 0 $ 0 $ 2,038.3 $ 2,028.2 State and local government obligations 0 3,067.9 0 3,067.9 3,025.0 Foreign government obligations 19.3 0 0 19.3 19.3 Corporate debt securities 0 3,798.5 1.0 3,799.5 3,797.4 Subtotal 2,057.6 6,866.4 1.0 8,925.0 8,869.9 Asset-backed securities: Residential mortgage-backed 0 1,809.4 0 1,809.4 1,801.8 Agency residential pass-through obligations 0 111.9 0 111.9 112.2 Commercial mortgage-backed 0 2,653.3 10.3 2,663.6 2,641.4 Other asset-backed 0 1,862.4 0 1,862.4 1,859.3 Subtotal asset-backed securities 0 6,437.0 10.3 6,447.3 6,414.7 Redeemable preferred stocks: Financials 0 88.1 0 88.1 71.8 Utilities 0 56.0 0 56.0 65.1 Industrials 0 105.7 0 105.7 118.1 Subtotal redeemable preferred stocks 0 249.8 0 249.8 255.0 Total fixed maturities 2,057.6 13,553.2 11.3 15,622.1 15,539.6 Equity securities: Nonredeemable preferred stocks: Financials 158.7 616.9 0 775.6 652.4 Subtotal nonredeemable preferred stocks 158.7 616.9 0 775.6 652.4 Common equities: Common stocks 2,483.6 0 0 2,483.6 1,486.7 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,483.6 0 0.3 2,483.9 1,487.0 Total fixed maturities and equity securities 4,699.9 14,170.1 11.6 18,881.6 17,679.0 Short-term investments 2,007.0 125.0 0 2,132.0 2,132.0 Total portfolio $ 6,706.9 $ 14,295.1 $ 11.6 $ 21,013.6 $ 19,811.0 Debt $ 0 $ 2,727.5 $ 171.7 $ 2,899.2 $ 2,714.3 Fair Value (millions) Level 1 Level 2 Level 3 Total Cost December 31, 2015 Fixed maturities: U.S. government obligations $ 2,429.2 $ 0 $ 0 $ 2,429.2 $ 2,425.4 State and local government obligations 0 2,721.4 0 2,721.4 2,677.6 Foreign government obligations 18.6 0 0 18.6 18.6 Corporate debt securities 0 3,691.6 0 3,691.6 3,713.2 Subtotal 2,447.8 6,413.0 0 8,860.8 8,834.8 Asset-backed securities: Residential mortgage-backed 0 1,726.7 0 1,726.7 1,726.0 Agency residential pass-through obligations 0 89.3 0 89.3 90.3 Commercial mortgage-backed 0 2,643.3 9.9 2,653.2 2,665.7 Other asset-backed 0 1,767.9 0 1,767.9 1,771.1 Subtotal asset-backed securities 0 6,227.2 9.9 6,237.1 6,253.1 Redeemable preferred stocks: Financials 0 92.0 0 92.0 76.8 Utilities 0 51.2 0 51.2 65.1 Industrials 0 91.1 0 91.1 118.1 Subtotal redeemable preferred stocks 0 234.3 0 234.3 260.0 Total fixed maturities 2,447.8 12,874.5 9.9 15,332.2 15,347.9 Equity securities: Nonredeemable preferred stocks: Financials 154.9 627.7 0 782.6 674.2 Subtotal nonredeemable preferred stocks 154.9 627.7 0 782.6 674.2 Common equities: Common stocks 2,650.2 0 0 2,650.2 1,494.0 Other risk investments 0 0 0.3 0.3 0.3 Subtotal common equities 2,650.2 0 0.3 2,650.5 1,494.3 Total fixed maturities and equity securities 5,252.9 13,502.2 10.2 18,765.3 17,516.4 Short-term investments 2,056.3 115.7 0 2,172.0 2,172.0 Total portfolio $ 7,309.2 $ 13,617.9 $ 10.2 $ 20,937.3 $ 19,688.4 Debt $ 0 $ 2,722.9 $ 164.9 $ 2,887.8 $ 2,707.9
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 three and nine months ended September 30, 2016 and 2015 : Level 3 Fair Value Three Months Ended September 30, 2016 (millions) Fair Value at June 30, 2016 Calls/ Maturities/ Paydowns Purchases Sales Net Realized (Gain) Loss on Sales Change in Valuation Net Transfers In (Out) Fair Value at September 30, 2016 Fixed maturities: Corporate debt securities $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Asset-backed securities: Commercial mortgage-backed 9.2 (8.7 ) 0 0 0 0.1 0 0.6 Total fixed maturities 9.2 (8.7 ) 0 0 0 0.1 0 0.6 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Common equities: Other risk investments 0.3 0 0 0 0 0.1 0 0.4 Total Level 3 securities $ 9.5 $ (8.7 ) $ 0 $ 0 $ 0 $ 0.2 $ 0 $ 1.0 Level 3 Fair Value Nine Months Ended September 30, 2016 (millions) Fair Value at Dec. 31, 2015 Calls/ Purchases Sales Net Realized (Gain) Loss on Sales Change in Valuation Net Fair Value at September 30, 2016 Fixed maturities: Corporate debt securities $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 Asset-backed securities: Commercial mortgage-backed 9.9 (9.3 ) 0 0 0 0 0 0.6 Total fixed maturities 9.9 (9.3 ) 0 0 0 0 0 0.6 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Common equities: Other risk investments 0.3 0 0 0 0 0.1 0 0.4 Total Level 3 securities $ 10.2 $ (9.3 ) $ 0 $ 0 $ 0 $ 0.1 $ 0 $ 1.0 Level 3 Fair Value Three Months Ended September 30, 2015 (millions) Fair Value at June 30, 2015 Calls/ Purchases Sales Net Realized (Gain) Loss on Sales Change in Net Fair Value at September 30, 2015 Fixed maturities: Corporate debt securities $ 1.0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 0 $ 1.0 Asset-backed securities: Commercial mortgage-backed 10.9 (0.4 ) 0 0 0 (0.2 ) 0 10.3 Total fixed maturities 11.9 (0.4 ) 0 0 0 (0.2 ) 0 11.3 Equity securities: Nonredeemable preferred stocks: Financials 0 0 0 0 0 0 0 0 Common equities: Other risk investments 0.3 0 0 0 0 0 0 0.3 Total Level 3 securities $ 12.2 $ (0.4 ) $ 0 $ 0 $ 0 $ (0.2 ) $ 0 $ 11.6 Level 3 Fair Value Nine Months Ended September 30, 2015 (millions) Fair Value at Dec. 31, 2014 Calls/ Purchases Sales Net Realized (Gain) Loss on Sales Change in Net Fair Value at September 30, 2015 Fixed maturities: Corporate debt securities $ 0 $ 0 $ 1.0 $ 0 $ 0 $ 0 $ 0 $ 1.0 Asset-backed securities: Commercial mortgage-backed 11.6 (1.0 ) 0 0 0 (0.3 ) 0 10.3 Total fixed maturities 11.6 (1.0 ) 1.0 0 0 (0.3 ) 0 11.3 Equity securities: Nonredeemable preferred stocks: Financials 1 69.3 0 0 0 (39.4 ) (1.4 ) (28.5 ) 0 Common equities: Other risk investments 0.4 0 0 0 0 (0.1 ) 0 0.3 Total Level 3 securities $ 81.3 $ (1.0 ) $ 1.0 $ 0 $ (39.4 ) $ (1.8 ) $ (28.5 ) $ 11.6
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 September 30, 2016 and 2015 , and December 31, 2015 : Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2016 Valuation Technique Unobservable Input Unobservable Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 0.6 External vendor Prepayment rate 1 0 % Subtotal Level 3 securities 0.6 Pricing exemption securities 2 0.4 Total Level 3 securities $ 1.0 1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year. 2 The fair values for these securities were determined with unobservable inputs not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at September 30, 2015 Valuation Technique Unobservable Input Unobservable Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 10.3 External vendor Prepayment rate 1 0 % Subtotal Level 3 securities 10.3 Pricing exemption securities 2 1.3 Total Level 3 securities $ 11.6 1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year. 2 The fair values for these securities were determined with unobservable inputs not reasonably available to us. Quantitative Information about Level 3 Fair Value Measurements ($ in millions) Fair Value at Dec. 31, 2015 Valuation Technique Unobservable Input Unobservable Fixed maturities: Asset-backed securities: Commercial mortgage-backed $ 9.9 External vendor Prepayment rate 1 0 % Subtotal Level 3 securities 9.9 Pricing exemption securities 2 0.3 Total Level 3 securities $ 10.2 1 Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year. 2 The fair values for these securities were determined with unobservable inputs not reasonably available to us.

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Debt Table	Debt consisted of: September 30, 2016 September 30, 2015 December 31, 2015 (millions) Carrying Value Fair Value Carrying Value Fair Value Carrying Value Fair Value 3.75% Senior Notes due 2021 $ 498.4 $ 544.2 $ 498.1 $ 534.5 $ 498.1 $ 528.7 2.45% Senior Notes due 2027 495.6 497.5 0 0 0 0 6 5/8% Senior Notes due 2029 295.8 402.6 295.6 379.5 295.7 376.0 6.25% Senior Notes due 2032 395.1 533.3 394.9 489.3 395.0 490.6 4.35% Senior Notes due 2044 346.4 403.0 346.4 345.7 346.4 352.8 3.70% Senior Notes due 2045 395.1 418.7 395.0 358.0 395.0 362.0 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 593.9 572.3 612.6 620.5 612.8 612.8 Other debt instruments 133.6 133.6 171.7 171.7 164.9 164.9 Total $ 3,153.9 $ 3,505.2 $ 2,714.3 $ 2,899.2 $ 2,707.9 $ 2,887.8
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block]	The other debt instruments reported in the table above represent ARX indebtedness and consist of: September 30, 2016 September 30, 2015 December 31, 2015 Type of debt instrument Number of Instruments Carrying Value Number of Instruments Carrying Number of Instruments Carrying Stated Maturity Date(s) Term loans 2 $ 68.4 2 $ 93.3 2 $ 87.1 December 2018 and 2019 Junior subordinated notes 1 2 41.2 2 41.3 2 41.2 June 2036 and 2037 Senior notes 4 24.0 4 24.0 4 24.0 Various 2 Surplus note 3 0 0 1 13.1 1 12.6 November 2021 Total $ 133.6 $ 171.7 $ 164.9 1 ARX issued junior subordinated floating rate notes to trusts established by ARX in connection with issuances of trust preferred securities by the trusts (discussed below). 2 The senior notes mature in May 2033, April 2034, December 2034, and June 2035. 3 The surplus note was debt of the subsidiary disposed of by ARX in the exchange transaction during the second quarter 2016 (see Note 1 – Basis of Presentation for further discussion).

Supplemental Cash Flow Inform23

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2016
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Table	We paid the following in the respective periods: Nine Months Ended September 30, (millions) 2016 2015 Income taxes $ 380.8 $ 513.1 Interest 98.0 90.3

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2016
Segment Reporting [Abstract]
Reconciliation of Revenue and operating Income from Segments to Consolidated	Following are the operating results for the respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 (millions) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Revenues Pretax Profit (Loss) Personal Lines Agency $ 2,474.3 $ 98.6 $ 2,284.6 $ 169.4 $ 7,245.5 $ 354.5 $ 6,805.5 $ 535.8 Direct 2,391.2 84.4 2,069.5 100.9 6,946.7 237.5 6,056.7 287.2 Total Personal Lines 1 4,865.5 183.0 4,354.1 270.3 14,192.2 592.0 12,862.2 823.0 Commercial Lines 630.2 4.4 511.3 77.8 1,772.4 96.7 1,467.0 239.5 Property 2 227.7 10.4 205.2 17.2 638.0 (27.7 ) 403.9 18.2 Other indemnity 0 (0.8 ) 0 (0.4 ) 0 (1.6 ) (0.4 ) (0.4 ) Total underwriting operations 5,723.4 197.0 5,070.6 364.9 16,602.6 659.4 14,732.7 1,080.3 Fees and other revenues 3 86.8 NA 79.3 NA 248.2 NA 227.9 NA Service businesses 26.2 3.0 23.1 2.7 77.7 9.2 63.6 6.8 Investments 4 98.6 93.8 101.7 96.8 381.7 366.8 429.1 413.2 Gains on extinguishment of debt 0 0 (0.9 ) (0.9 ) 1.6 1.6 (0.9 ) (0.9 ) Interest expense NA (35.3 ) NA (34.5 ) NA (103.8 ) NA (101.9 ) Consolidated total $ 5,935.0 $ 258.5 $ 5,273.8 $ 429.0 $ 17,311.8 $ 933.2 $ 15,452.4 $ 1,397.5 NA = Not applicable 1 Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in both the third quarters and first nine months of 2016 and 2015; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, manufactured homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned. 2 We began reporting our Property business as a segment on April 1, 2015, upon acquisition of a controlling interest in ARX; therefore, the nine months ended September 30, 2015 only include results for six months and are not comparable to results reported for the nine months ended September 30, 2016. For the three and nine months ended September 30, 2016 , pretax loss also includes $15.5 million and $46.6 million , respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $15.5 million and $31.2 million , respectively, for the three and nine months ended September 30, 2015. 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 respective periods: Three Months Ended September 30, Nine Months Ended September 30, 2016 2015 2016 2015 Under-writing Combined Ratio Under-writing Combined Ratio Under-writing Margin Combined Ratio Under-writing Margin Combined Ratio Personal Lines Agency 4.0 % 96.0 7.4 % 92.6 4.9 % 95.1 7.9 % 92.1 Direct 3.5 96.5 4.9 95.1 3.4 96.6 4.7 95.3 Total Personal Lines 3.8 96.2 6.2 93.8 4.2 95.8 6.4 93.6 Commercial Lines 0.7 99.3 15.2 84.8 5.5 94.5 16.3 83.7 Property 1 4.6 95.4 8.4 91.6 (4.3 ) 104.3 4.5 95.5 Other indemnity 2 NM NM NM NM NM NM NM NM Total underwriting operations 3.4 96.6 7.2 92.8 4.0 96.0 7.3 92.7 1 We began reporting our Property business as a segment on April 1, 2015, when we acquired a controlling interest in ARX; therefore, the nine months ended September 30, 2015 only include results for six months and are not comparable to results reported for the nine months ended September 30, 2016. Included in both three and nine months ended September 30, 2016 , is 6.8 points and 7.3 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 7.6 and 7.7 points, respectively, for the three and nine months ended September 30, 2015. In addition, nine months ended September 2016 results include 0.7 points of expense related to the loss on the exchange transaction (See Note 1 - Basis of Presentation for discussion). 2 Underwriting margins and combined ratios are not meaningful (NM) for our other indemnity businesses due to lack of premiums earned by, and the variability of loss costs in, such businesses.

Dividends Dividends (Tables)

Dividends Dividends (Tables)	9 Months Ended
	Sep. 30, 2016
Dividends [Abstract]
Dividends	Following is a summary of our shareholder dividends that were declared in the last two years: (millions, except per share amounts) Amount Dividend Type Declared Paid Per Share Total 1 Annual – Variable December 2015 February 2016 $ 0.8882 $ 519.0 Annual – Variable December 2014 February 2015 0.6862 404.1 1 Represents the final amount of dividends declared based on shares outstanding as of the record date.

Other Comprehensive Income (L26

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2016
Equity [Abstract]
Components of Other Comprehensive Income (Loss)	The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows: Components of Changes in (millions) Pretax total Total tax After tax total Total net Net Foreign (Income)loss attributable to NCI Balance at June 30, 2016 $ 1,477.0 $ (519.2 ) $ 957.8 $ 970.1 $ (8.8 ) $ (1.1 ) $ (2.4 ) Other comprehensive income (loss) before reclassifications: Investment securities 200.4 (70.2 ) 130.2 130.2 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 0.4 (0.1 ) 0.3 0 0 0.3 0 Loss attributable to noncontrolling interest (NCI) 1.8 (0.6 ) 1.2 0 0 0 1.2 Total other comprehensive income (loss) before reclassifications 202.6 (70.9 ) 131.7 130.2 0 0.3 1.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings 26.8 (9.4 ) 17.4 17.4 0 0 0 Net realized gains (losses) on securities 39.6 (13.9 ) 25.7 25.7 0 0 0 Interest expense 0.5 (0.2 ) 0.3 0 0.3 0 0 Total reclassification adjustment for amounts realized in net income 66.9 (23.5 ) 43.4 43.1 0.3 0 0 Total other comprehensive income (loss) 135.7 (47.4 ) 88.3 87.1 (0.3 ) 0.3 1.2 Balance at September 30, 2016 $ 1,612.7 $ (566.6 ) $ 1,046.1 $ 1,057.2 $ (9.1 ) $ (0.8 ) $ (1.2 ) Components of Changes in (millions) Pretax total Total tax After tax total Total net Net Foreign (Income)loss attributable to NCI Balance 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 524.4 (184.2 ) 340.2 340.2 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 1.0 (0.3 ) 0.7 0 0 0.7 0 Loss attributable to noncontrolling interest (NCI) (3.7 ) 1.4 (2.3 ) 0 0 0 (2.3 ) Total other comprehensive income (loss) before reclassifications 521.6 (183.0 ) 338.6 340.2 0 0.7 (2.3 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings 27.0 (9.5 ) 17.5 17.5 0 0 0 Net realized gains (losses) on securities 114.9 (40.4 ) 74.5 74.5 0 0 0 Interest expense 1.5 (0.6 ) 0.9 0 0.9 0 0 Total reclassification adjustment for amounts realized in net income 143.4 (50.5 ) 92.9 92.0 0.9 0 0 Total other comprehensive income (loss) 378.2 (132.5 ) 245.7 248.2 (0.9 ) 0.7 (2.3 ) Balance at September 30, 2016 $ 1,612.7 $ (566.6 ) $ 1,046.1 $ 1,057.2 $ (9.1 ) $ (0.8 ) $ (1.2 ) Components of Changes in Accumulated Other Comprehensive Income (after tax) (millions) Pretax total accumulated other comprehensive income Total tax (provision) benefit After tax total accumulated other comprehensive income Total net Net unrealized gains on forecasted transactions Foreign currency translation adjustment (Income)loss attributable to NCI Balance at June 30, 2015 $ 1,393.3 $ (491.3 ) $ 902.0 $ 907.5 $ (7.5 ) $ (0.8 ) $ 2.8 Other comprehensive income (loss) before reclassifications: Investment securities (190.6 ) 66.5 (124.1 ) (124.1 ) 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 (1.1 ) 0.4 (0.7 ) 0 0 (0.7 ) 0 Loss attributable to noncontrolling interest (NCI) (2.5 ) 0.9 (1.6 ) 0 0 0 (1.6 ) Total other comprehensive income (loss) before reclassifications (194.2 ) 67.8 (126.4 ) (124.1 ) 0 (0.7 ) (1.6 ) Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (13.6 ) 4.8 (8.8 ) (8.8 ) 0 0 0 Net realized gains (losses) on securities 23.0 (8.1 ) 14.9 14.8 0.1 0 0 Interest expense 0.4 (0.1 ) 0.3 0 0.3 0 0 Total reclassification adjustment for amounts realized in net income 9.8 (3.4 ) 6.4 6.0 0.4 0 0 Total other comprehensive income (loss) (204.0 ) 71.2 (132.8 ) (130.1 ) (0.4 ) (0.7 ) (1.6 ) Balance at September 30, 2015 $ 1,189.3 $ (420.1 ) $ 769.2 $ 777.4 $ (7.9 ) $ (1.5 ) $ 1.2 Components of Changes in (millions) Pretax total Total tax After tax total Total net Net Foreign (Income)loss attributable to NCI Balance at December 31, 2014 $ 1,574.0 $ (550.9 ) $ 1,023.1 $ 1,021.9 $ 1.5 $ (0.3 ) $ 0 Other comprehensive income (loss) before reclassifications: Investment securities (252.8 ) 84.6 (168.2 ) (168.2 ) 0 0 0 Net non-credit related OTTI losses, adjusted for valuation changes 0 0 0 0 0 0 0 Forecasted transactions (12.8 ) 4.4 (8.4 ) 0 (8.4 ) 0 0 Foreign currency translation adjustment (2.0 ) 0.8 (1.2 ) 0 0 (1.2 ) 0 Loss attributable to noncontrolling interest (NCI) 1.8 (0.6 ) 1.2 0 0 0 1.2 Total other comprehensive income (loss) before reclassifications (265.8 ) 89.2 (176.6 ) (168.2 ) (8.4 ) (1.2 ) 1.2 Less: Reclassification adjustment for amounts realized in net income by income statement line item: Net impairment losses recognized in earnings (23.2 ) 8.2 (15.0 ) (15.0 ) 0 0 0 Net realized gains (losses) on securities 140.7 (49.3 ) 91.4 91.3 0.1 0 0 Interest expense 1.4 (0.5 ) 0.9 0 0.9 0 0 Total reclassification adjustment for amounts realized in net income 118.9 (41.6 ) 77.3 76.3 1.0 0 0 Total other comprehensive income (loss) (384.7 ) 130.8 (253.9 ) (244.5 ) (9.4 ) (1.2 ) 1.2 Balance at September 30, 2015 $ 1,189.3 $ (420.1 ) $ 769.2 $ 777.4 $ (7.9 ) $ (1.5 ) $ 1.2

Redeemable Noncontrolling Int27

Redeemable Noncontrolling Interest (Tables)	9 Months Ended
	Sep. 30, 2016
Temporary Equity Disclosure [Abstract]
Redeemable Noncontrolling Interest	The changes in the components of redeemable NCI during the nine months ended September 30, 2016 and 2015, and the year ended December 31, 2015, were: (millions) September 30, 2016 September 30, 2015 December 31, 2015 Balance, Beginning of period $ 464.9 $ 0 $ 0 Fair value at date of acquisition 0 411.5 411.5 Net income attributable to NCI 11.3 13.4 32.9 Other comprehensive income (loss) attributable to NCI 2.3 (1.2 ) (1.1 ) Purchase of shares from NCI 0 (12.6 ) (12.6 ) Change in redemption value of NCI (6.0 ) 31.8 34.2 Balance, End of period $ 472.5 $ 442.9 $ 464.9

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Sep. 30, 2016
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 September 30, 2016 and 2015, and December 31, 2015: ($ in millions) September 30, 2016 September 30, 2015 December 31, 2015 Intangible assets subject to amortization $ 435.9 $ 498.1 $ 482.5 Indefinite-lived intangible assets 1 12.4 12.4 12.4 Total $ 448.3 $ 510.5 $ 494.9 1 Indefinite-lived intangible assets are comprised of state insurance and agent licenses. State insurance licenses were previously subject to amortization under superseded accounting guidance and have $0.6 million of accumulated amortization for all periods presented.
Intangible Assets Subject to Amortization	Intangible assets subject to amortization consisted of the following: (millions) September 30, 2016 September 30, 2015 December 31, 2015 Category Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Policies in force $ 256.2 $ 55.0 $ 201.2 $ 256.2 $ 18.3 $ 237.9 $ 256.2 $ 27.5 $ 228.7 Agency relationships 159.2 17.1 142.1 159.2 5.7 153.5 159.2 8.5 150.7 Software rights 79.1 16.1 63.0 79.1 5.5 73.6 79.1 8.2 70.9 Trade name 34.8 5.2 29.6 34.8 1.7 33.1 34.8 2.6 32.2 Total $ 529.3 $ 93.4 $ 435.9 $ 529.3 $ 31.2 $ 498.1 $ 529.3 $ 46.8 $ 482.5 Amortization expense was $15.5 million and $46.6 million for the three and nine months ended September 30, 2016 and $15.5 million and $31.2 million for the three and nine months ended September 30, 2015; there was no amortization expense incurred in the first quarter 2015.

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation-Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Assets Held-for-sale, Property, Plant and Equipment	$ 8.7	$ 8.7	$ 8.7

Basis of Presentation Business

Basis of Presentation Business Acquisition (Details)	3 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Business Acquisition [Line Items]
Business Combination, Control Obtained Description	1	2
Disposal Group, Including Discontinued Operation, Description and Timing of Disposal	1
ARX Holding Corp. [Member]
Business Acquisition [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage			69.20%	69.20%	69.10%

Investments Investment Portfoli

Investments Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost	[1],[2]	$ 21,886.9	$ 19,688.4	$ 19,811
Gross Unrealized Gains	[1],[2]	1,675.4	1,414.5	1,329.9
Gross Unrealized Losses	[1],[2]	(45.1)	(166.7)	(127.8)
Net Realized Gains (Losses)	[1],[2],[3]	4	1.1	0.5
Fair Value	[1],[2]	$ 23,521.2	$ 20,937.3	$ 21,013.6
% of Total Fair Value	[1],[2]	100.00%	100.00%	100.00%
Net unsettled security transactions offset in other liabilities		$ 185.3		$ 149.9
Other Receivables from Broker-Dealers and Clearing Organizations			$ 23.1
Securities in the portfolio of a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions		1,000	1,300	1,000
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Cost		13,708	15,347.9	15,539.6
Gross Unrealized Gains		232.9	121.3	159.7
Gross Unrealized Losses		(26.8)	(136.8)	(78)
Net Realized Gains (Losses)	[3]	2.8	(0.2)	0.8
Fair Value		$ 13,916.9	$ 15,332.2	$ 15,622.1
% of Total Fair Value		59.20%	73.20%	74.40%
Fixed maturities | U.S. government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 726	$ 2,425.4	$ 2,028.2
Gross Unrealized Gains		8.9	4.4	10.1
Gross Unrealized Losses		(0.3)	(0.6)	0
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 734.6	$ 2,429.2	$ 2,038.3
% of Total Fair Value		3.10%	11.60%	9.70%
Fixed maturities | State and local government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 2,508.9	$ 2,677.6	$ 3,025
Gross Unrealized Gains		58.7	47.5	47.1
Gross Unrealized Losses		(1.6)	(3.7)	(4.2)
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 2,566	$ 2,721.4	$ 3,067.9
% of Total Fair Value		10.90%	13.00%	14.60%
Fixed maturities | Foreign government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 25.4	$ 18.6	$ 19.3
Gross Unrealized Gains		0	0	0
Gross Unrealized Losses		0	0	0
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 25.4	$ 18.6	$ 19.3
% of Total Fair Value		0.10%	0.10%	0.10%
Fixed maturities | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 4,327.5	$ 3,713.2	$ 3,797.4
Gross Unrealized Gains		76.9	11.3	23.4
Gross Unrealized Losses		(1.8)	(33)	(21.4)
Net Realized Gains (Losses)	[3]	0.7	0.1	0.1
Fair Value		$ 4,403.3	$ 3,691.6	$ 3,799.5
% of Total Fair Value		18.70%	17.60%	18.10%
Fixed maturities | Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 1,582.6	$ 1,726	$ 1,801.8
Gross Unrealized Gains		25.3	22.1	26.2
Gross Unrealized Losses		(15.5)	(20.6)	(18.4)
Net Realized Gains (Losses)	[3]	1.8	(0.8)	(0.2)
Fair Value		$ 1,594.2	$ 1,726.7	$ 1,809.4
% of Total Fair Value		6.80%	8.30%	8.60%
Fixed maturities | Agency residential pass-through obligations
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 43.6	$ 90.3	$ 112.2
Gross Unrealized Gains		0.5	0.1	0.1
Gross Unrealized Losses		0	(1.1)	(0.4)
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 44.1	$ 89.3	$ 111.9
% of Total Fair Value		0.20%	0.40%	0.50%
Fixed maturities | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 2,249.4	$ 2,665.7	$ 2,641.4
Gross Unrealized Gains		35.1	16.9	31.1
Gross Unrealized Losses		(6.1)	(29.4)	(9.3)
Net Realized Gains (Losses)	[3]	0	0	0.4
Fair Value		$ 2,278.4	$ 2,653.2	$ 2,663.6
% of Total Fair Value		9.70%	12.70%	12.70%
Fixed maturities | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 2,037.5	$ 1,771.1	$ 1,859.3
Gross Unrealized Gains		7.9	1.4	4.1
Gross Unrealized Losses		(0.3)	(5.1)	(1.5)
Net Realized Gains (Losses)	[3]	0.3	0.5	0.5
Fair Value		$ 2,045.4	$ 1,767.9	$ 1,862.4
% of Total Fair Value		8.70%	8.40%	8.90%
Fixed maturities | Redeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 207.1	$ 260	$ 255
Gross Unrealized Gains		19.6	17.6	17.6
Gross Unrealized Losses		(1.2)	(43.3)	(22.8)
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 225.5	$ 234.3	$ 249.8
% of Total Fair Value		1.00%	1.10%	1.20%
Equity securities | Nonredeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 726.6	$ 674.2	$ 652.4
Gross Unrealized Gains		146.2	122.8	138.3
Gross Unrealized Losses		(13.9)	(15.7)	(14.8)
Net Realized Gains (Losses)	[3]	1.2	1.3	(0.3)
Fair Value		$ 860.1	$ 782.6	$ 775.6
% of Total Fair Value		3.60%	3.70%	3.70%
Equity securities | Common equities
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 1,576.1	$ 1,494.3	$ 1,487
Gross Unrealized Gains		1,296.3	1,170.4	1,031.9
Gross Unrealized Losses		(4.4)	(14.2)	(35)
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 2,868	$ 2,650.5	$ 2,483.9
% of Total Fair Value		12.20%	12.70%	11.80%
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost		$ 5,876.2	$ 2,172	$ 2,132
Gross Unrealized Gains		0	0	0
Gross Unrealized Losses		0	0	0
Net Realized Gains (Losses)	[3]	0	0	0
Fair Value		$ 5,876.2	$ 2,172	$ 2,132
% of Total Fair Value		25.00%	10.40%	10.10%
[1]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.
[2]	The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[3]	Represents net holding period gains (losses) realized on certain hybrid securities (discussed below).

Investments Hybrid Securities (

Investments Hybrid Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Hybrid Securities [Line Items]
Hybrid securities	$ 229.6	$ 272.7	$ 290.8
Fixed maturities
Hybrid Securities [Line Items]
Hybrid securities	216	222	236.7
Fixed maturities | Corporate debt securities
Hybrid Securities [Line Items]
Hybrid securities	31.2	49.1	89.4
Fixed maturities | Residential mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	175.3	144.3	117.7
Fixed maturities | Commercial mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	0	17.3	17.7
Fixed maturities | Other asset-backed securities
Hybrid Securities [Line Items]
Hybrid securities	9.5	11.3	11.9
Equity securities | Nonredeemable preferred stocks
Hybrid Securities [Line Items]
Hybrid securities	$ 13.6	$ 50.7	$ 54.1

Investments Composition of Fixe

Investments Composition of Fixed Maturities by Maturity (Detail) $ in Millions	Sep. 30, 2016USD ($)
Available for sale, cost
Less than one year	$ 3,251.2
One to five years	7,471.8
Five to ten years	2,862.2
Ten years or greater	122.8
Total	13,708
Available for sale, Fair value
Less than one year	3,269.8
One to five years	7,552
Five to ten years	2,960.3
Ten years or greater	134.8
Total	$ 13,916.9

Investments Gross Unrealized lo

Investments Gross Unrealized losses by Major Security (Detail) $ in Millions	Sep. 30, 2016USD ($)	Dec. 31, 2015USD ($)	Sep. 30, 2015USD ($)
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	554	1,167	1,030
Total Fair Value	$ 3,507.1	$ 9,725.1	$ 6,255.9
Gross Unrealized Losses	$ (45.1)	$ (166.7)	$ (127.8)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	313	993	882
Less than 12 Months Fair Value	$ 1,640.2	$ 7,842.3	$ 4,553.2
Less than 12 Months Unrealized Losses	$ (8.7)	$ (93.9)	$ (76.4)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	241	174	148
12 Months or Greater Fair Value	$ 1,866.9	$ 1,882.8	$ 1,702.7
12 Months or Greater Unrealized Losses	$ (36.4)	$ (72.8)	$ (51.4)
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	461	1,093	880
Total Fair Value	$ 3,266.2	$ 9,258.5	$ 5,667.4
Gross Unrealized Losses	$ (26.8)	$ (136.8)	$ (78)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	229	928	741
Less than 12 Months Fair Value	$ 1,580.8	$ 7,556.7	$ 4,146.5
Less than 12 Months Unrealized Losses	$ (4.3)	$ (78)	$ (39.5)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	232	165	139
12 Months or Greater Fair Value	$ 1,685.4	$ 1,701.8	$ 1,520.9
12 Months or Greater Unrealized Losses	$ (22.5)	$ (58.8)	$ (38.5)
Fixed maturities | U.S. government obligations
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	4	22	0
Total Fair Value	$ 104.8	$ 897.1	$ 0
Gross Unrealized Losses	$ (0.3)	$ (0.6)	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	4	22	0
Less than 12 Months Fair Value	$ 104.8	$ 897.1	$ 0
Less than 12 Months Unrealized Losses	$ (0.3)	$ (0.6)	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	0	0	0
12 Months or Greater Fair Value	$ 0	$ 0	$ 0
12 Months or Greater Unrealized Losses	$ 0	$ 0	$ 0
Fixed maturities | State and local government obligations
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	151	290	349
Total Fair Value	$ 512	$ 606.7	$ 637.1
Gross Unrealized Losses	$ (1.6)	$ (3.7)	$ (4.2)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	117	264	328
Less than 12 Months Fair Value	$ 409.6	$ 500.7	$ 551.4
Less than 12 Months Unrealized Losses	$ (1)	$ (2.6)	$ (3.7)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	34	26	21
12 Months or Greater Fair Value	$ 102.4	$ 106	$ 85.7
12 Months or Greater Unrealized Losses	$ (0.6)	$ (1.1)	$ (0.5)
Fixed maturities | Corporate debt securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	52	215	140
Total Fair Value	$ 598.3	$ 2,580.6	$ 1,596.5
Gross Unrealized Losses	$ (1.8)	$ (33)	$ (21.4)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	42	197	125
Less than 12 Months Fair Value	$ 541.5	$ 2,294.6	$ 1,292.1
Less than 12 Months Unrealized Losses	$ (0.8)	$ (25.2)	$ (15.7)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	10	18	15
12 Months or Greater Fair Value	$ 56.8	$ 286	$ 304.4
12 Months or Greater Unrealized Losses	$ (1)	$ (7.8)	$ (5.7)
Fixed maturities | Residential mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	138	188	141
Total Fair Value	$ 915.8	$ 1,294.7	$ 1,205.9
Gross Unrealized Losses	$ (15.5)	$ (20.6)	$ (18.4)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	26	115	76
Less than 12 Months Fair Value	$ 108.8	$ 493.4	$ 535.8
Less than 12 Months Unrealized Losses	$ (0.4)	$ (3.7)	$ (4.1)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	112	73	65
12 Months or Greater Fair Value	$ 807	$ 801.3	$ 670.1
12 Months or Greater Unrealized Losses	$ (15.1)	$ (16.9)	$ (14.3)
Fixed maturities | Agency residential pass-through obligations
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	15	61	54
Total Fair Value	$ 4.2	$ 84.9	$ 67.6
Gross Unrealized Losses	$ 0	$ (1.1)	$ (0.4)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	7	61	54
Less than 12 Months Fair Value	$ 1.9	$ 84.9	$ 67.6
Less than 12 Months Unrealized Losses	$ 0	$ (1.1)	$ (0.4)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	8	0	0
12 Months or Greater Fair Value	$ 2.3	$ 0	$ 0
12 Months or Greater Unrealized Losses	$ 0	$ 0	$ 0
Fixed maturities | Commercial mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	56	207	127
Total Fair Value	$ 610.6	$ 2,046.5	$ 1,100
Gross Unrealized Losses	$ (6.1)	$ (29.4)	$ (9.3)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	17	171	99
Less than 12 Months Fair Value	$ 194.7	$ 1,694.6	$ 813.8
Less than 12 Months Unrealized Losses	$ (1.7)	$ (25.8)	$ (7.6)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	39	36	28
12 Months or Greater Fair Value	$ 415.9	$ 351.9	$ 286.2
12 Months or Greater Unrealized Losses	$ (4.4)	$ (3.6)	$ (1.7)
Fixed maturities | Other asset-backed securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	43	101	60
Total Fair Value	$ 488.7	$ 1,548.6	$ 845.5
Gross Unrealized Losses	$ (0.3)	$ (5.1)	$ (1.5)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	16	92	53
Less than 12 Months Fair Value	$ 219.5	$ 1,472	$ 764
Less than 12 Months Unrealized Losses	$ (0.1)	$ (4.5)	$ (0.9)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	27	9	7
12 Months or Greater Fair Value	$ 269.2	$ 76.6	$ 81.5
12 Months or Greater Unrealized Losses	$ (0.2)	$ (0.6)	$ (0.6)
Fixed maturities | Redeemable preferred stocks
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	2	9	9
Total Fair Value	$ 31.8	$ 199.4	$ 214.8
Gross Unrealized Losses	$ (1.2)	$ (43.3)	$ (22.8)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	0	6	6
Less than 12 Months Fair Value	$ 0	$ 119.4	$ 121.8
Less than 12 Months Unrealized Losses	$ 0	$ (14.5)	$ (7.1)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	3	3
12 Months or Greater Fair Value	$ 31.8	$ 80	$ 93
12 Months or Greater Unrealized Losses	$ (1.2)	$ (28.8)	$ (15.7)
Equity securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	93	74	150
Total Fair Value	$ 240.9	$ 466.6	$ 588.5
Gross Unrealized Losses	$ (18.3)	$ (29.9)	$ (49.8)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	84	65	141
Less than 12 Months Fair Value	$ 59.4	$ 285.6	$ 406.7
Less than 12 Months Unrealized Losses	$ (4.4)	$ (15.9)	$ (36.9)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	9	9	9
12 Months or Greater Fair Value	$ 181.5	$ 181	$ 181.8
12 Months or Greater Unrealized Losses	$ (13.9)	$ (14)	$ (12.9)
Equity securities | Nonredeemable preferred stocks
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	7	10	14
Total Fair Value	$ 187.5	$ 301.8	$ 376.9
Gross Unrealized Losses	$ (13.9)	$ (15.7)	$ (14.8)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	5	9
Less than 12 Months Fair Value	$ 9.9	$ 124.2	$ 197.6
Less than 12 Months Unrealized Losses	$ (0.2)	$ (1.7)	$ (2.5)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	6	5	5
12 Months or Greater Fair Value	$ 177.6	$ 177.6	$ 179.3
12 Months or Greater Unrealized Losses	$ (13.7)	$ (14)	$ (12.3)
Equity securities | Common equities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	86	64	136
Total Fair Value	$ 53.4	$ 164.8	$ 211.6
Gross Unrealized Losses	$ (4.4)	$ (14.2)	$ (35)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	83	60	132
Less than 12 Months Fair Value	$ 49.5	$ 161.4	$ 209.1
Less than 12 Months Unrealized Losses	$ (4.2)	$ (14.2)	$ (34.4)
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	3	4	4
12 Months or Greater Fair Value	$ 3.9	$ 3.4	$ 2.5
12 Months or Greater Unrealized Losses	$ (0.2)	$ 0	$ (0.6)

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	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Non-credit portion of other-than-temporary impairments recognized in accumulated other comprehensive income	$ (43.9)	$ (43.9)	$ (43.9)
Residential mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Non-credit portion of other-than-temporary impairments recognized in accumulated other comprehensive income	(43.3)	(43.3)	(43.3)
Commercial mortgage-backed securities
Other Than Temporary Impairment Non Credit Losses Recognized In Accumulated Other Comprehensive Income [Line Items]
Non-credit portion of other-than-temporary impairments recognized in accumulated other comprehensive income	$ (0.6)	$ (0.6)	$ (0.6)

Investments OTTI Credit Losses

Investments OTTI Credit Losses Recognized in Earnings (Detail) - Fixed maturities - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance		$ 12.2	$ 14.4	$ 12.8	$ 13.1
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		0	(1.4)	0	(1.4)
Change in recoveries of future cash flows expected to be collected	[1]	(0.3)	(1.7)	(0.9)	(0.4)
Ending balance		11.9	11.3	11.9	11.3
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance		11.8	14	12.4	12.7
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		0	(1.4)	0	(1.4)
Change in recoveries of future cash flows expected to be collected	[1]	(0.3)	(1.7)	(0.9)	(0.4)
Ending balance		11.5	10.9	11.5	10.9
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance		0.4	0.4	0.4	0.4
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold		0	0	0	0
Change in recoveries of future cash flows expected to be collected	[1]	0	0	0	0
Ending balance		$ 0.4	$ 0.4	$ 0.4	$ 0.4
[1]	Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security.

Investments Components of Net R

Investments Components of Net Realized Gains (Losses) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	$ 47.7	$ 28.6	$ 147.5	$ 154.3
Gross realized losses on securities sales	(8.2)	(2)	(23.9)	(7.3)
Net realized gains (losses) on securities sales	39.5	26.6	123.6	147
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Available for Sale Securities	26.8	13.6	27	23
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	61.6	13.6	61.8	23
Other gains (losses)	1.4	(28.8)	(32.8)	(30.8)
Total net realized gains (losses) on securities	(20.7)	(15.8)	29	93.2
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	28.3	11.7	92.2	56.7
Gross realized losses on securities sales	(7.5)	(1.1)	(15.5)	(4.3)
Net realized gains (losses) on securities sales	20.8	10.6	76.7	52.4
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Available for Sale Securities	25.4	0	25.4	0
Fixed maturities | U.S. government obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	6.4	2.7	24.1	17.1
Gross realized losses on securities sales	(0.8)	0	(1.2)	(0.9)
Net realized gains (losses) on securities sales	5.6	2.7	22.9	16.2
Fixed maturities | State and local government obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0.6	0.5	16	0.5
Gross realized losses on securities sales	0	(0.1)	(1.6)	(0.1)
Net realized gains (losses) on securities sales	0.6	0.4	14.4	0.4
Fixed maturities | Corporate and other debt securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	15.6	3.2	38.1	19.1
Gross realized losses on securities sales	(0.2)	(0.9)	(1.9)	(2.2)
Net realized gains (losses) on securities sales	15.4	2.3	36.2	16.9
Fixed maturities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0.2	4.4	1.9	4.6
Net realized gains (losses) on securities sales	0.2	4.4	1.9	4.6
Fixed maturities | Agency residential pass-through obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0	0	0.1	0
Gross realized losses on securities sales	0	0	(0.2)	0
Net realized gains (losses) on securities sales	0	0	(0.1)	0
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	5.5	0.9	12	15.3
Gross realized losses on securities sales	0	(0.1)	(4.1)	(1.1)
Net realized gains (losses) on securities sales	5.5	0.8	7.9	14.2
Fixed maturities | Redeemable preferred stocks
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0	0	0	0.1
Gross realized losses on securities sales	(6.5)	0	(6.5)	0
Net realized gains (losses) on securities sales	(6.5)	0	(6.5)	0.1
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Available for Sale Securities	25.4	0	25.4	0
Equity securities | Nonredeemable preferred stocks
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	4.9	3.7	11.9	53.9
Gross realized losses on securities sales	(0.4)	(0.1)	(3.1)	(1.5)
Net realized gains (losses) on securities sales	4.5	3.6	8.8	52.4
Equity securities | Common equities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	14.4	13.2	43.3	43.7
Gross realized losses on securities sales	(0.3)	(0.8)	(5.3)	(1.5)
Net realized gains (losses) on securities sales	14.1	12.4	38	42.2
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales, Available for Sale Securities	1.4	13.6	1.6	23
Other Assets [Member]
Gain (Loss) on Investments [Line Items]
Other than Temporary Impairment Losses, Portion Recognized in Earnings, Net of Sales	34.8	0	34.8	0
Short-term investments
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0.1	0	0.1	0
Net realized gains (losses) on securities sales	0.1	0	0.1	0
Hybrid and Derivative Instruments and Litigation Settlements | Litigation Settlements
Gain (Loss) on Investments [Line Items]
Other gains (losses)	0.1	0.2	0.1	0.3
Hybrid and Derivative Instruments and Litigation Settlements | Hybrid Preferred Stock
Gain (Loss) on Investments [Line Items]
Other gains (losses)	0.6	(1.3)	2.9	(1.9)
Hybrid and Derivative Instruments and Litigation Settlements | Derivative Instruments
Gain (Loss) on Investments [Line Items]
Other gains (losses)	$ 0.7	$ (27.7)	$ (35.8)	$ (29.2)

Investments Components of Net I

Investments Components of Net Investment Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net Investment Income [Line Items]
Investment income	$ 119.3	$ 117.5	$ 352.7	$ 335.9
Investment expenses	(4.8)	(4.9)	(14.9)	(15.9)
Net Investment Income	114.5	112.6	337.8	320
Fixed maturities
Net Investment Income [Line Items]
Investment income	87.7	93.1	262.5	265.3
Fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Investment income	3.3	6.2	12.4	22.5
Fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Investment income	12.6	16.9	39.3	45
Fixed maturities | Foreign government obligations
Net Investment Income [Line Items]
Investment income	0.1	0.1	0.3	0.3
Fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Investment income	27.3	28	81.9	75.1
Fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Investment income	11.1	13.5	34.9	39.5
Fixed maturities | Agency residential pass-through obligations
Net Investment Income [Line Items]
Investment income	0.3	0.7	0.9	1.4
Fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Investment income	22.4	18.3	62.6	54
Fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Investment income	6.8	5.7	18.7	16.2
Fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Investment income	3.8	3.7	11.5	11.3
Equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Investment income	12.4	11	36.8	32.4
Equity securities | Common equities
Net Investment Income [Line Items]
Investment income	13.9	12.7	42	36.7
Short-term investments
Net Investment Income [Line Items]
Investment income	$ 5.3	$ 0.7	$ 11.4	$ 1.5

Investments Derivative Instrume

Investments Derivative Instruments (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended				12 Months Ended
		Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2016		Sep. 30, 2015		Dec. 31, 2015		Aug. 25, 2016
Derivative [Line Items]
Balance Sheet - Fair Value	[1]	$ (13)		$ (6.3)		$ (13)		$ (6.3)		$ 4.4
Income Statement - Net Realized Gain (Loss) on Securities		0.7		(27.7)		(35.8)		(29.2)
Designated as Hedging Instruments | Ineffective Cash Flow Hedge [Member]
Derivative [Line Items]
Derivative, Notional Amount		370	[2]	18	[2]	$ 370	[2]	18	[2]	$ 18	[2]	$ 350
Purpose						Manage  interest  rate risk				Manage interest rate risk
Balance Sheet - Fair Value	[1]	0		0		$ 0		0		$ 0
Income Statement - Net Realized Gain (Loss) on Securities		(1.4)		0.2		(1.3)		0.2
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Fixed maturities
Derivative [Line Items]
Derivative, Notional Amount	[2]	0		0		0		$ 0		$ 750
Purpose								Manage  portfolio duration		Manage portfolio duration
Balance Sheet - Fair Value	[1]	0		0		0		$ 0		$ 4.4
Income Statement - Net Realized Gain (Loss) on Securities		0		0		0		0
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Other Liabilities [Member]
Derivative [Line Items]
Derivative, Notional Amount	[2]	315		750		$ 315		750		0
Purpose						Manage  portfolio duration
Balance Sheet - Fair Value	[1]	(13)		(6.3)		$ (13)		(6.3)		0
Income Statement - Net Realized Gain (Loss) on Securities		1.7		(27.9)		(17.8)		(31.2)
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Closed Positions [Member]
Derivative [Line Items]
Derivative, Notional Amount	[2]	435		0		$ 435		0		0
Purpose						Manage  portfolio duration
Balance Sheet - Fair Value	[1]	0		0		$ 0		0		0
Income Statement - Net Realized Gain (Loss) on Securities		0.3		0		(17)		0
Not Designated as Hedging Instrument [Member] | Future [Member] | Closed Positions [Member]
Derivative [Line Items]
Derivative, Notional Amount	[2]	135		505		$ 135		505		$ 691
Purpose						Manage  portfolio duration				Manage portfolio duration
Balance Sheet - Fair Value	[1]	0		0		$ 0		0		$ 0
Income Statement - Net Realized Gain (Loss) on Securities		$ 0.1		$ 0		$ 0.3		$ 1.8
[1]	To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
[2]	The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions.

Investments Investments - Addit

Investments Investments - Additional Information (Detail)		3 Months Ended				9 Months Ended
		Sep. 30, 2016USD ($)		Sep. 30, 2015USD ($)		Sep. 30, 2016USD ($)		Sep. 30, 2015USD ($)		Aug. 25, 2016USD ($)	Dec. 31, 2015USD ($)		Jun. 18, 2007
Schedule of Investments [Line Items]
Proceeds from (Payments for) in Securities Sold under Agreements to Repurchase						$ 0		$ 0
Securities Sold under Agreements to Repurchase		$ 0		$ 0		0		0			$ 0
Open reverse repurchase commitments		68,000,000		0		68,000,000		0			0
Largest Outstanding Balance of Reverse Repurchase Agreements						$ 265,000,000
RRP Largest Outstanding Balance Number of Days Open						1 day
Reverse Repurchase Agreement Average Daily Balance						$ 122,600,000
Gross unrealized losses		$ 45,100,000		$ 127,800,000		$ 45,100,000		$ 127,800,000			$ 166,700,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		554		1,030		554		1,030			1,167
Trading securities		$ 0		$ 0		$ 0		$ 0			$ 0
Net realized gains (losses) on securities		40,900,000		(2,200,000)		90,800,000		116,400,000
Income Statement - Net Realized Gain (Loss) on Securities		700,000		(27,700,000)		(35,800,000)		(29,200,000)
2.45% Senior Notes due 2027
Schedule of Investments [Line Items]
Debt Instrument, Face Amount		$ 500,000,000				$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage		2.45%				2.45%
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Schedule of Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.70%				6.70%							6.70%
Fixed Income Securities
Schedule of Investments [Line Items]
Gross unrealized losses		$ 40,700,000				$ 40,700,000
Equity securities
Schedule of Investments [Line Items]
Gross unrealized losses		$ 18,300,000		$ 49,800,000		$ 18,300,000		$ 49,800,000			$ 29,900,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		93		150		93		150			74
Equity securities | Common equities
Schedule of Investments [Line Items]
Gross unrealized losses		$ 4,400,000		$ 35,000,000		$ 4,400,000		$ 35,000,000			$ 14,200,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		86		136		86		136			64
Equity securities | Nonredeemable preferred stocks
Schedule of Investments [Line Items]
Gross unrealized losses		$ 13,900,000		$ 14,800,000		$ 13,900,000		$ 14,800,000			$ 15,700,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		7		14		7		14			10
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage Decline		7.00%				7.00%
Fixed maturities
Schedule of Investments [Line Items]
Gross unrealized losses		$ 26,800,000		$ 78,000,000		$ 26,800,000		$ 78,000,000			$ 136,800,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		461		880		461		880			1,093
Fixed maturities | Corporate debt securities
Schedule of Investments [Line Items]
Percentage which the issuer receives the security back at once the change of control is triggered		1.00%				1.00%
Realized investment losses						$ 2,100,000
Gross unrealized losses		$ 1,800,000		$ 21,400,000		$ 1,800,000		$ 21,400,000			$ 33,000,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		52		140		52		140			215
Fixed maturities | Redeemable preferred stocks
Schedule of Investments [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities		$ 25,400,000
Gross unrealized losses		$ 1,200,000		$ 22,800,000		$ 1,200,000		$ 22,800,000			$ 43,300,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions		2		9		2		9			9
Interest Rate Swap [Member]
Schedule of Investments [Line Items]
Collateral Delivered to Counterparties on Derivative Instruments		$ 15,100,000		$ 9,600,000		$ 15,100,000		$ 9,600,000
Cash collateral received from counterparties											$ 4,900,000
Categories of Investments, Marketable Securities, Trading Securities
Schedule of Investments [Line Items]
Net realized gains (losses) on securities		$ 0		0		$ 0		0
Russell One Thousand | Equity securities | Common equities
Schedule of Investments [Line Items]
Percentage of common stock portfolio		95.00%				95.00%
Managed Equity Strategy | Equity securities | Common equities
Schedule of Investments [Line Items]
Percentage of common stock portfolio		5.00%				5.00%
Designated as Hedging Instruments | Ineffective Cash Flow Hedge [Member]
Schedule of Investments [Line Items]
Income Statement - Net Realized Gain (Loss) on Securities		$ (1,400,000)		200,000		$ (1,300,000)		200,000
Derivative, Notional Amount		370,000,000	[1]	18,000,000	[1]	370,000,000	[1]	18,000,000	[1]	$ 350,000,000	18,000,000	[1]
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Schedule of Investments [Line Items]
Derivative, Gain (Loss) on Derivative, Net						14,800,000
Not Designated as Hedging Instrument [Member] | Fixed maturities | Interest Rate Swap [Member]
Schedule of Investments [Line Items]
Income Statement - Net Realized Gain (Loss) on Securities		0		0		0		0
Derivative, Notional Amount	[1]	0		0		0		0			750,000,000
Closed Positions [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Schedule of Investments [Line Items]
Income Statement - Net Realized Gain (Loss) on Securities		300,000		0		(17,000,000)		0
Derivative, Notional Amount	[1]	$ 435,000,000		$ 0		$ 435,000,000		$ 0			$ 0
Derivative, Term of Contract		10 years
[1]	The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions.

Fair Value Composition of Inves

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) - USD ($) $ in Millions		Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	[1],[2]	$ 23,521.2	$ 20,937.3	$ 21,013.6
Long-Term Debt, Fair Value		3,505.2	2,887.8	2,899.2
Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,916.9	15,332.2	15,622.1
Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		7,729.3	8,860.8	8,925
Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,962.1	6,237.1	6,447.3
Fixed maturities | U.S. government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		734.6	2,429.2	2,038.3
Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		734.6	2,429.2	2,038.3
Fixed maturities | State and local government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,566	2,721.4	3,067.9
Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,566	2,721.4	3,067.9
Fixed maturities | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Fixed maturities | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,403.3	3,691.6	3,799.5
Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,403.3	3,691.6	3,799.5
Fixed maturities | Residential mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,594.2	1,726.7	1,809.4
Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,594.2	1,726.7	1,809.4
Fixed maturities | Agency residential pass-through obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		44.1	89.3	111.9
Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		44.1	89.3	111.9
Fixed maturities | Commercial mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,278.4	2,653.2	2,663.6
Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,278.4	2,653.2	2,663.6
Fixed maturities | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,045.4	1,767.9	1,862.4
Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,045.4	1,767.9	1,862.4
Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		225.5	234.3	249.8
Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		95.7	92	88.1
Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		30.4	51.2	56
Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		99.4	91.1	105.7
Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		860.1	782.6	775.6
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		860.1	782.6	775.6
Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,868	2,650.5	2,483.9
Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,867.6	2,650.2	2,483.6
Equity securities | Common equities | Other risk investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.4	0.3	0.3
Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		17,645	18,765.3	18,881.6
Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,876.2	2,172	2,132
Carrying (Reported) Amount, Fair Value Disclosure
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		21,886.9	19,688.4	19,811
Debt		3,153.9	2,707.9	2,714.3
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,708	15,347.9	15,539.6
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		7,587.8	8,834.8	8,869.9
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,913.1	6,253.1	6,414.7
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		726	2,425.4	2,028.2
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,508.9	2,677.6	3,025
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,327.5	3,713.2	3,797.4
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,582.6	1,726	1,801.8
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		43.6	90.3	112.2
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,249.4	2,665.7	2,641.4
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,037.5	1,771.1	1,859.3
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		207.1	260	255
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		77.1	76.8	71.8
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		30.6	65.1	65.1
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		99.4	118.1	118.1
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		726.6	674.2	652.4
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]
Available-for-sale Securities		726.6	674.2	652.4
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,576.1	1,494.3	1,487
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]
Available-for-sale Securities		1,575.7	1,494	1,486.7
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]
Available-for-sale Securities		0.4	0.3	0.3
Carrying (Reported) Amount, Fair Value Disclosure | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		16,010.7	17,516.4	17,679
Carrying (Reported) Amount, Fair Value Disclosure | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,876.2	2,172	2,132
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		8,833.7	7,309.2	6,706.9
Long-Term Debt, Fair Value		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		760	2,447.8	2,057.6
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		760	2,447.8	2,057.6
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		734.6	2,429.2	2,038.3
Fair Value, Inputs, Level 1 | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		25.4	18.6	19.3
Fair Value, Inputs, Level 1 | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		154.6	154.9	158.7
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		154.6	154.9	158.7
Fair Value, Inputs, Level 1 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,867.6	2,650.2	2,483.6
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,867.6	2,650.2	2,483.6
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]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 1 | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		3,782.2	5,252.9	4,699.9
Fair Value, Inputs, Level 1 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,051.5	2,056.3	2,007
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		14,686.5	13,617.9	14,295.1
Long-Term Debt, Fair Value		3,371.6	2,722.9	2,727.5
Fair Value, Inputs, Level 2 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,156.3	12,874.5	13,553.2
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		6,969.3	6,413	6,866.4
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		5,961.5	6,227.2	6,437
Fair Value, Inputs, Level 2 | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 2 | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,566	2,721.4	3,067.9
Fair Value, Inputs, Level 2 | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 2 | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		4,403.3	3,691.6	3,798.5
Fair Value, Inputs, Level 2 | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1,594.2	1,726.7	1,809.4
Fair Value, Inputs, Level 2 | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		44.1	89.3	111.9
Fair Value, Inputs, Level 2 | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,277.8	2,643.3	2,653.3
Fair Value, Inputs, Level 2 | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		2,045.4	1,767.9	1,862.4
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		225.5	234.3	249.8
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		95.7	92	88.1
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		30.4	51.2	56
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		99.4	91.1	105.7
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		705.5	627.7	616.9
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		705.5	627.7	616.9
Fair Value, Inputs, Level 2 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	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]
Available-for-sale Securities		0	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]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 2 | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		13,861.8	13,502.2	14,170.1
Fair Value, Inputs, Level 2 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		824.7	115.7	125
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1	10.2	11.6
Long-Term Debt, Fair Value		133.6	164.9	171.7
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.6	9.9	11.3
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	1
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.6	9.9	10.3
Fair Value, Inputs, Level 3 | Fixed maturities | U.S. government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | State and local government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Foreign government obligations | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Corporate debt securities | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	1
Fair Value, Inputs, Level 3 | Fixed maturities | Residential mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Agency residential pass-through obligations | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Commercial mortgage-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.6	9.9	10.3
Fair Value, Inputs, Level 3 | Fixed maturities | Other asset-backed securities | Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	0	0
Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0.4	0.3	0.3
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Common equities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		0	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]
Available-for-sale Securities		0.4	0.3	0.3
Fair Value, Inputs, Level 3 | Total Fixed Maturities and Equity Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		1	10.2	11.6
Fair Value, Inputs, Level 3 | Short-term investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		$ 0	$ 0	$ 0
[1]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.
[2]	The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.

Fair Value Summary of Changes i

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Apr. 01, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	$ 9.5	$ 12.2	$ 10.2	$ 81.3
Calls/ Maturities/ Paydowns	(8.7)	(0.4)	(9.3)	(1)
Purchases	0	0	0	1
Sales	0	0	0	0
Net Realized (Gain) Loss on Sales	0	0	0	(39.4)
Change in Valuation	0.2	(0.2)	0.1	(1.8)
Net Transfers in (out)	0	0	0	(28.5)
Ending Fair value	1	11.6	1	11.6
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0	0	0	69.3
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain) Loss on Sales	0	0	0	(39.4)
Change in Valuation	0	0	0	(1.4)
Net Transfers in (out)	0	0	0	(28.5)
Ending Fair value	0	0	0	0
Equity securities | Common equities | Other risk investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.3	0.3	0.3	0.4
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain) Loss on Sales	0	0	0	0
Change in Valuation	0.1	0	0.1	(0.1)
Net Transfers in (out)	0	0	0	0
Ending Fair value	0.4	0.3	0.4	0.3
Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	9.2	11.9	9.9	11.6
Calls/ Maturities/ Paydowns	(8.7)	(0.4)	(9.3)	(1)
Purchases	0	0	0	1
Sales	0	0	0	0
Net Realized (Gain) Loss on Sales	0	0	0	0
Change in Valuation	0.1	(0.2)	0	(0.3)
Net Transfers in (out)	0	0	0	0
Ending Fair value	0.6	11.3	0.6	11.3
Asset-backed Securities | Fixed maturities | Commercial mortgage-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	9.2	10.9	9.9	11.6
Calls/ Maturities/ Paydowns	(8.7)	(0.4)	(9.3)	(1)
Purchases	0	0	0	0
Sales	0	0	0	0
Net Realized (Gain) Loss on Sales	0	0	0	0
Change in Valuation	0.1	(0.2)	0	(0.3)
Net Transfers in (out)	0	0	0	0
Ending Fair value	0.6	10.3	0.6	10.3
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Realized (Gain) Loss on Sales				(39.4)
Change in Valuation				(1.4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)				69.3
Fixed maturities | Debt Securities [Member] | Corporate debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0	1	0	0
Calls/ Maturities/ Paydowns	0	0	0	0
Purchases	0	0	0	1
Sales	0	0	0	0
Net Realized (Gain) Loss on Sales	0	0	0	0
Change in Valuation	0	0	0	0
Net Transfers in (out)	0	0	0	0
Ending Fair value	$ 0	$ 1	$ 0	$ 1
ARX Holding Corp. [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage					5.00%

Fair Value Summary of Quantitat

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) $ in Millions		9 Months Ended				12 Months Ended
		Sep. 30, 2016USD ($)Investment		Sep. 30, 2015USD ($)Investment		Dec. 31, 2015USD ($)Investment
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities	[1],[2]	$ 23,521.2		$ 21,013.6		$ 20,937.3
Equity securities | Nonredeemable preferred stocks
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		860.1		775.6		782.6
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		860.1		775.6		782.6
Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		13,916.9		15,622.1		15,332.2
Fixed maturities | Residential mortgage-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		1,594.2		1,809.4		1,726.7
Fixed maturities | Commercial mortgage-backed securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		2,278.4		2,663.6		2,653.2
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		1		11.6		10.2
Fair Value, Inputs, Level 3 | Third Party Pricing Exemption Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		0.4	[3]	1.3	[4]	0.3	[5]
Fair Value, Inputs, Level 3 | Subtotal Level 3 Securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 0.6		$ 10.3		$ 9.9
Fair Value, Inputs, Level 3 | Internal Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities | Investment		0		2		0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 0		$ 0		$ 0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Available-for-sale Securities		$ 0.6		$ 11.3		$ 9.9
Fair Value, Inputs, Level 3 | Fixed maturities | Commercial mortgage-backed securities | External Pricing
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities | Investment		1		1		1
Available-for-sale Securities		$ 0.6		$ 10.3		$ 9.9
Valuation Technique		External vendor		External vendor		External vendor
Unobservable Input, prepayment rate		0.00%		0.00%		0.00%
[1]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.
[2]	The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[3]	The fair values for these securities were determined with unobservable inputs not reasonably available to us.
[4]	The fair values for these securities were determined with unobservable inputs not reasonably available to us.
[5]	The fair values for these securities were determined with unobservable inputs not reasonably available to us.

Fair Value Fair Value - Additio

Fair Value Fair Value - Additional Information (Detail)		Sep. 30, 2016USD ($)Investment	Dec. 31, 2015USD ($)Investment	Sep. 30, 2015USD ($)Investment
Fair Value Measurements [Line Items]
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount | $		$ 0	$ 0	$ 0
Quoted prices percentage of fair value assets	[1],[2]	100.00%	100.00%	100.00%
Internal Pricing | Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Number of securities | Investment		0	0	2
Dealer Quoted Pricing | Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets		1.00%	3.00%	3.00%
Vendor Quoted Pricing | Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets		24.00%	49.00%	47.00%
Vendor Quoted Pricing | Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets		99.00%	97.00%	97.00%
[1]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2016 and 2015, $185.3 million and $149.9 million, respectively, were included in "other liabilities" and $23.1 million was in "other assets" at December 31, 2015.
[2]	The total fair value of the portfolio at September 30, 2016 and 2015, and December 31, 2015 included $1.0 billion, $1.0 billion, and $1.3 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.

Debt (Detail)

Debt (Detail)		3 Months Ended				6 Months Ended	9 Months Ended
		Sep. 30, 2016USD ($)instrument		Jun. 30, 2016USD ($)	Sep. 30, 2015USD ($)instrument	Jun. 30, 2015USD ($)	Sep. 30, 2016USD ($)instrument		Sep. 30, 2015USD ($)instrument	Dec. 31, 2015USD ($)instrument	Jun. 18, 2007
Debt Instrument [Line Items]
Gains (losses) on extinguishment of debt		$ 0			$ (900,000)		$ 1,600,000		$ (900,000)
Fair Value		3,505,200,000			2,899,200,000		3,505,200,000		2,899,200,000	$ 2,887,800,000
Debt, Long-term and Short-term, Combined Amount	[1]	$ 3,153,900,000			2,714,300,000		$ 3,153,900,000		2,714,300,000	2,707,900,000
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.75%					3.75%
Carrying Value		$ 498,400,000			498,100,000		$ 498,400,000		498,100,000	498,100,000
Fair Value		$ 544,200,000			534,500,000		$ 544,200,000		534,500,000	528,700,000
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		2.45%					2.45%
Carrying Value		$ 495,600,000			0		$ 495,600,000		0	0
Fair Value		$ 497,500,000			0		$ 497,500,000		0	0
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.25%					6.25%
Carrying Value		$ 395,100,000			394,900,000		$ 395,100,000		394,900,000	395,000,000
Fair Value		$ 533,300,000			489,300,000		$ 533,300,000		489,300,000	490,600,000
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.625%					6.625%
Carrying Value		$ 295,800,000			295,600,000		$ 295,800,000		295,600,000	295,700,000
Fair Value		$ 402,600,000			379,500,000		$ 402,600,000		379,500,000	376,000,000
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.35%					4.35%
Carrying Value		$ 346,400,000			346,400,000		$ 346,400,000		346,400,000	346,400,000
Fair Value		$ 403,000,000			345,700,000		$ 403,000,000		345,700,000	352,800,000
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		3.70%					3.70%
Carrying Value		$ 395,100,000			395,000,000		$ 395,100,000		395,000,000	395,000,000
Fair Value		$ 418,700,000			358,000,000		$ 418,700,000		358,000,000	362,000,000
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Repurchase of debt, face amount				$ 19,800,000	18,400,000	$ 0
Debt Instrument, Interest Rate, Stated Percentage		6.70%					6.70%				6.70%
Gains (losses) on extinguishment of debt				1,600,000					(900,000)
Carrying Value		$ 593,900,000			612,600,000		$ 593,900,000		612,600,000	612,800,000
Fair Value		572,300,000			620,500,000		572,300,000		620,500,000	612,800,000
Other debt instruments
Debt Instrument [Line Items]
Debt, Long-term and Short-term, Combined Amount		$ 133,600,000			$ 171,700,000		$ 133,600,000		$ 171,700,000	$ 164,900,000
Notes Payable, Other Payables [Member] | Other debt instruments
Debt Instrument [Line Items]
Number of debt instruments | instrument		2			2		2		2	2
Debt, Long-term and Short-term, Combined Amount		$ 68,400,000			$ 93,300,000		$ 68,400,000		$ 93,300,000	$ 87,100,000
Trust Preferred Debt Securities [Member] | Other debt instruments
Debt Instrument [Line Items]
Carrying Value	[2]	$ 41,200,000			$ 41,300,000		$ 41,200,000		$ 41,300,000	$ 41,200,000
Number of debt instruments | instrument		2			2		2		2	2
Senior Notes [Member] | Other debt instruments
Debt Instrument [Line Items]
Carrying Value	[3]	$ 24,000,000			$ 24,000,000		$ 24,000,000		$ 24,000,000	$ 24,000,000
Number of debt instruments | instrument		4			4		4		4	4
Surplus Note [Member] | Other debt instruments
Debt Instrument [Line Items]
Number of debt instruments | instrument		0	[4]		1		0	[4]	1	1
Debt, Long-term and Short-term, Combined Amount		$ 0			$ 13,100,000		$ 0		$ 13,100,000	$ 12,600,000
Net unrealized gains on forecasted transactions | 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)				$ 100,000					$ 200,000
[1]	1Consists of both short-term and long-term debt. See Note 4 - Debt for further discussion.
[2]	1 ARX issued junior subordinated floating rate notes to trusts established by ARX in connection with issuances of trust preferred securities by the trusts (discussed below).
[3]	2 The senior notes mature in May 2033, April 2034, December 2034, and June 2035.
[4]	3 The surplus note was debt of the subsidiary disposed of by ARX in the exchange transaction during the second quarter 2016 (see Note 1 – Basis of Presentation for further discussion).

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Jun. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Jun. 18, 2007
Debt Instrument [Line Items]
Gains (losses) on extinguishment of debt	$ 0		$ 900,000			$ (1,600,000)	$ 900,000
Line of Credit Facility, Description				Each advance would need to be repaid on the 30th day after the advance or, if earlier, on April 30, 2017, the expiration date of the Line of Credit.				Each advance would need to be repaid on the 30th day after the advance or, if earlier, on April 30, 2016, the expiration date of the Line of Credit.
Discretionary Line of Credit
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 100,000,000
Line of Credit Facility, Interest Rate Description				advances under the Line of Credit (if any) will bear interest at a variable rate equal to the higher of PNC's Prime Rate and the sum of the Federal Funds Open Rate plus 50 basis points.				advances under the Line of Credit (if any) will bear interest at a variable rate equal to the higher of PNC's Prime Rate and the sum of the Federal Funds Open Rate plus 50 basis points.
Line of Credit Facility, Amount Outstanding						0			$ 0
Debt Instrument, Basis Spread on Variable Rate				0.50%				0.50%
2.45% Senior Notes due 2027
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000,000			$ 500,000,000		$ 500,000,000
Debt Instrument, Interest Rate, Stated Percentage	2.45%			2.45%		2.45%
Carrying Value	$ 495,600,000		0	$ 495,600,000		$ 495,600,000	0		0
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Repurchase of debt, face amount		19,800,000	18,400,000		$ 0
Debt Instrument, Interest Rate, Stated Percentage	6.70%			6.70%		6.70%				6.70%
Carrying Value	$ 593,900,000		612,600,000	$ 593,900,000		$ 593,900,000	612,600,000		612,800,000
Gains (losses) on extinguishment of debt		(1,600,000)					900,000
Other Assets [Member]
Debt Instrument [Line Items]
Ownership interest in the variable interest entities	$ 1,300,000		$ 1,300,000	$ 1,300,000		$ 1,300,000	1,300,000		$ 1,300,000
Net unrealized gains on forecasted transactions | 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)		$ 100,000					$ 200,000

Income Taxes Effective Tax Rate

Income Taxes Effective Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount	$ 25.8
Effective tax rate	20.50%	33.20%	29.40%	32.00%
Scenario, Forecast [Member]
Tax Credit Carryforward [Line Items]
Tax Credit Carryforward, Amount					$ 34.4

Supplemental Cash Flow Inform48

Supplemental Cash Flow Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Supplemental Cash Flow Elements [Abstract]
Income taxes	$ 380.8	$ 513.1
Interest	$ 98	$ 90.3

Segment Information Operating R

Segment Information Operating Results (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues		$ 5,935	$ 5,273.8		$ 17,311.8	$ 15,452.4
Pretax Profit (Loss)		258.5	429		933.2	1,397.5
Amortization of intangible assets		15.5	15.5	$ 0	46.6	31.2
Personal Lines | Agency | Underwriting operations
Segment Reporting Information [Line Items]
Revenues		2,474.3	2,284.6		7,245.5	6,805.5
Pretax Profit (Loss)		98.6	169.4		354.5	535.8
Personal Lines | Direct | Underwriting operations
Segment Reporting Information [Line Items]
Revenues		2,391.2	2,069.5		6,946.7	6,056.7
Pretax Profit (Loss)		84.4	100.9		237.5	287.2
Operating Segments | Underwriting operations
Segment Reporting Information [Line Items]
Revenues		5,723.4	5,070.6		16,602.6	14,732.7
Pretax Profit (Loss)		197	364.9		659.4	1,080.3
Operating Segments | Personal Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	[1]	4,865.5	4,354.1		14,192.2	12,862.2
Pretax Profit (Loss)		$ 183	$ 270.3		$ 592	$ 823
Personal auto insurance percentage of the total personal lines segment net premiums earned		92.00%	92.00%		92.00%	92.00%
Operating Segments | Commercial Lines | Underwriting operations
Segment Reporting Information [Line Items]
Revenues		$ 630.2	$ 511.3		$ 1,772.4	$ 1,467
Pretax Profit (Loss)		4.4	77.8		96.7	239.5
Operating Segments | Property | Underwriting operations
Segment Reporting Information [Line Items]
Revenues	[2]	227.7	205.2		638	403.9
Pretax Profit (Loss)	[2]	10.4	17.2		(27.7)	18.2
Amortization of intangible assets		15.5	15.5		46.6	31.2
Operating Segments | Other Indemnity | Underwriting operations
Segment Reporting Information [Line Items]
Revenues		0	0		0	(0.4)
Pretax Profit (Loss)		(0.8)	(0.4)		(1.6)	(0.4)
Segment Reconciling Items | Fees and other revenues
Segment Reporting Information [Line Items]
Revenues	[3]	86.8	79.3		248.2	227.9
Segment Reconciling Items | Service businesses
Segment Reporting Information [Line Items]
Revenues		26.2	23.1		77.7	63.6
Pretax Profit (Loss)		3	2.7		9.2	6.8
Segment Reconciling Items | Investment income
Segment Reporting Information [Line Items]
Revenues	[4]	98.6	101.7		381.7	429.1
Pretax Profit (Loss)	[4]	93.8	96.8		366.8	413.2
Segment Reconciling Items | Gains on extinguishment of debt
Segment Reporting Information [Line Items]
Revenues		0	(0.9)		1.6	(0.9)
Pretax Profit (Loss)		0	(0.9)		1.6	(0.9)
Segment Reconciling Items | Interest expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)		$ (35.3)	$ (34.5)		$ (103.8)	$ (101.9)
[1]	1Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in both the third quarters and first nine months of 2016 and 2015; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, manufactured homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
[2]	2We began reporting our Property business as a segment on April 1, 2015, upon acquisition of a controlling interest in ARX; therefore, the nine months ended September 30, 2015 only include results for six months and are not comparable to results reported for the nine months ended September 30, 2016. For the three and nine months ended September 30, 2016, pretax loss also includes $15.5 million and $46.6 million, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and $15.5 million and $31.2 million, respectively, for the three and nine months ended September 30, 2015.
[3]	3Pretax profit (loss) for fees and other revenues are allocated to operating segments.
[4]	4Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.

Segment Information Underwritin

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Operating Segments - Underwriting operations		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Underwriting Margin		3.40%	7.20%	4.00%	7.30%
Combined Ratio		96.60%	92.80%	96.00%	92.70%
Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin		3.80%	6.20%	4.20%	6.40%
Combined Ratio		96.20%	93.80%	95.80%	93.60%
Personal Lines | Agency
Segment Reporting Information [Line Items]
Underwriting Margin		4.00%	7.40%	4.90%	7.90%
Combined Ratio		96.00%	92.60%	95.10%	92.10%
Personal Lines | Direct
Segment Reporting Information [Line Items]
Underwriting Margin		3.50%	4.90%	3.40%	4.70%
Combined Ratio		96.50%	95.10%	96.60%	95.30%
Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin		0.70%	15.20%	5.50%	16.30%
Combined Ratio		99.30%	84.80%	94.50%	83.70%
Property
Segment Reporting Information [Line Items]
Underwriting Margin	[1]	4.60%	8.40%	(4.30%)	4.50%
Combined Ratio	[1]	95.40%	91.60%	104.30%	95.50%
Combined ratio amortization points		0.068	0.076	0.073	0.077
Combined ratio exchange loss				0.007
[1]	1We began reporting our Property business as a segment on April 1, 2015, when we acquired a controlling interest in ARX; therefore, the nine months ended September 30, 2015 only include results for six months and are not comparable to results reported for the nine months ended September 30, 2016. Included in both three and nine months ended September 30, 2016, is 6.8 points and 7.3 points, respectively, of amortization expense predominately associated with the acquisition of a controlling interest in ARX and 7.6 and 7.7 points, respectively, for the three and nine months ended September 30, 2015. In addition, nine months ended September 2016 results include 0.7 points of expense related to the loss on the exchange transaction (See Note 1 - Basis of Presentation for discussion).

Dividends Dividends (Details)

Dividends Dividends (Details) - USD ($) $ / shares in Units, $ in Millions		Feb. 12, 2016	Feb. 13, 2015
Dividends [Abstract]
Dividend paid per share (USD per share)		$ 0.8882	$ 0.6862
Payments of Ordinary Dividends, Common Stock	[1]	$ 519	$ 404.1
[1]	1Represents the final amount of dividends declared based on shares outstanding as of the record date.

Dividends - Additional Informat

Dividends - Additional Information (Detail)		3 Months Ended		9 Months Ended
		Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2015USD ($)
Dividends [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent				35.00%
Target percentage used to determine annual variable dividend		33.30%		33.30%
Gainshare factor used to determine annual variable dividend range, minimum		0		0
Minimum Payments of Ordinary Dividends, Common Stock	[1]			$ 0
Gainshare factor used to determine annual variable dividend range, maximum		2		2
Gainshare factor used to determine annual variable dividend		1.54		1.54
Comprehensive income		$ 287,000,000	$ 145,500,000	$ 893,500,000	$ 683,300,000
After-tax underwriting income				$ 428,600,000
[1]	1Represents the final amount of dividends declared based on shares outstanding as of the record date.

Other Comprehensive Income (L53

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Pre tax total accumulated other comprehensive income, beginning balance	$ 1,477	$ 1,393.3		$ 1,234.5		$ 1,574
Investment securities, pre tax	200.4	(190.6)		524.4		(252.8)
Net non-credit related OTTI losses, adjusted for valuation changes, pre tax	0	0		(0.1)		0
Forecasted transactions, pre tax	0	0		0		(12.8)
Foreign currency translation adjustment, pre tax	0.4	(1.1)		1		(2)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Noncontrolling Interest	1.8	(2.5)		(3.7)		1.8
Total other comprehensive income (loss) before reclassifications, pre tax	202.6	(194.2)		521.6		(265.8)
Total reclassification adjustment for amounts realized in net income, pre tax	66.9	9.8		143.4		118.9
Total other comprehensive income (loss), pre tax	135.7	(204)		378.2		(384.7)
Pre tax total accumulated other comprehensive income, ending balance	1,612.7	1,189.3	$ 1,189.3	1,612.7	$ 1,234.5	1,189.3
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
Accumulated other comprehensive income loss tax (Provision) benefit, beginning balance	(519.2)	(491.3)		(434.1)		(550.9)
Investment securities, Total tax (provision) benefit	(70.2)	66.5		(184.2)		84.6
Net non-credit related OTTI losses, adjusted for valuation changes, Total tax (provision) benefit	0	0		0.1		0
Forecasted transactions, Total tax (provision) benefit	0	0		0		4.4
Foreign currency translation adjustment, Total tax (provision) benefit	(0.1)	0.4		(0.3)		0.8
Other Comprehensive Income (Loss), Tax, Portion Attributable to Noncontrolling Interest	(0.6)	0.9		1.4		(0.6)
Total other comprehensive income (loss) before reclassifications, Total tax (provision) benefit	(70.9)	67.8		(183)		89.2
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	(23.5)	(3.4)		(50.5)		(41.6)
Total other comprehensive income (loss), Total tax (provision) benefit	(47.4)	71.2		(132.5)		130.8
Accumulated other comprehensive income loss tax (Provision) benefit, ending balance	(566.6)	(420.1)	(420.1)	(566.6)	(434.1)	(420.1)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	957.8	902		800.4		1,023.1
Investment securities, after tax	130.2	(124.1)		340.2		(168.2)
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0		0		0
Forecasted transactions, after tax	0	0		0		(8.4)
Foreign currency translation adjustment, after tax	0.3	(0.7)		0.7		(1.2)
Other comprehensive (income) loss attributable to NCI	1.2	(1.6)	1.2	(2.3)	1.1	1.2
Total other comprehensive income (loss) before reclassifications, after tax	131.7	(126.4)		338.6		(176.6)
Total reclassification adjustment for amounts realized in net income, after tax	43.4	6.4		92.9		77.3
Other comprehensive income (loss)	88.3	(132.8)		245.7		(253.9)
After tax total accumulated other comprehensive income, ending balance	1,046.1	769.2	769.2	1,046.1	800.4	769.2
Net realized gains (losses) on securities	40.9	(2.2)		90.8		116.4
Interest expense	35.3	34.5		103.8		101.9
Accumulated other comprehensive income after tax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Other comprehensive (income) loss attributable to NCI				(2.3)		1.2
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	970.1	907.5		809		1,021.9
Investment securities, after tax	130.2	(124.1)		340.2		(168.2)
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0		0		0
Forecasted transactions, after tax	0	0		0		0
Foreign currency translation adjustment, after tax	0	0		0		0
Other comprehensive (income) loss attributable to NCI	0	0		0		0
Total other comprehensive income (loss) before reclassifications, after tax	130.2	(124.1)		340.2		(168.2)
Total reclassification adjustment for amounts realized in net income, after tax	43.1	6		92		76.3
Other comprehensive income (loss)	87.1	(130.1)		248.2		(244.5)
After tax total accumulated other comprehensive income, ending balance	1,057.2	777.4	777.4	1,057.2	809	777.4
Net unrealized gains on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(8.8)	(7.5)		(8.2)		1.5
Investment securities, after tax	0	0		0		0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0		0		0
Forecasted transactions, after tax	0	0		0		(8.4)
Foreign currency translation adjustment, after tax	0	0		0		0
Other comprehensive (income) loss attributable to NCI	0	0		0		0
Total other comprehensive income (loss) before reclassifications, after tax	0	0		0		(8.4)
Total reclassification adjustment for amounts realized in net income, after tax	0.3	0.4		0.9		1
Other comprehensive income (loss)	(0.3)	(0.4)		(0.9)		(9.4)
After tax total accumulated other comprehensive income, ending balance	(9.1)	(7.9)	(7.9)	(9.1)	(8.2)	(7.9)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(1.1)	(0.8)		(1.5)		(0.3)
Investment securities, after tax	0	0		0		0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0		0		0
Forecasted transactions, after tax	0	0		0		0
Foreign currency translation adjustment, after tax	0.3	(0.7)		0.7		(1.2)
Other comprehensive (income) loss attributable to NCI	0	0		0		0
Total other comprehensive income (loss) before reclassifications, after tax	0.3	(0.7)		0.7		(1.2)
Total reclassification adjustment for amounts realized in net income, after tax	0	0		0		0
Other comprehensive income (loss)	0.3	(0.7)		0.7		(1.2)
After tax total accumulated other comprehensive income, ending balance	(0.8)	(1.5)	(1.5)	(0.8)	(1.5)	(1.5)
Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	(2.4)	2.8		1.1		0
Investment securities, after tax	0	0		0		0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0		0		0
Forecasted transactions, after tax	0	0		0		0
Foreign currency translation adjustment, after tax	0	0		0		0
Other comprehensive (income) loss attributable to NCI	1.2	(1.6)		(2.3)		1.2
Total other comprehensive income (loss) before reclassifications, after tax	1.2	(1.6)		(2.3)		1.2
Total reclassification adjustment for amounts realized in net income, after tax	0	0		0		0
Other comprehensive income (loss)	1.2	(1.6)		(2.3)		1.2
After tax total accumulated other comprehensive income, ending balance	(1.2)	1.2	$ 1.2	(1.2)	$ 1.1	1.2
Reclassification out of Accumulated Other Comprehensive Income | Accumulated other comprehensive income pretax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	26.8	(13.6)		27		(23.2)
Net realized gains (losses) on securities	39.6	23		114.9		140.7
Interest expense	0.5	0.4		1.5		1.4
Reclassification out of Accumulated Other Comprehensive Income | Accumulated other comprehensive income tax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	(9.4)	4.8		(9.5)		8.2
Net realized gains (losses) on securities	(13.9)	(8.1)		(40.4)		(49.3)
Interest expense	(0.2)	(0.1)		(0.6)		(0.5)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated other comprehensive income after tax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	17.4	(8.8)		17.5		(15)
Net realized gains (losses) on securities	25.7	14.9		74.5		91.4
Interest expense	0.3	0.3		0.9		0.9
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains (losses) on securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	17.4	(8.8)		17.5		(15)
Net realized gains (losses) on securities	25.7	14.8		74.5		91.3
Interest expense	0	0		0		0
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	0	0		0		0
Net realized gains (losses) on securities	0	0.1		0		0.1
Interest expense	0.3	0.3		0.9		0.9
Reclassification out of Accumulated Other Comprehensive Income | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	0	0		0		0
Net realized gains (losses) on securities	0	0		0		0
Interest expense	0	0		0		0
Reclassification out of Accumulated Other Comprehensive Income | Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	0	0		0		0
Net realized gains (losses) on securities	0	0		0		0
Interest expense	$ 0	$ 0		$ 0		$ 0

Other Comprehensive Income (L54

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement, Additional Information (Detail) $ in Millions	Sep. 30, 2016USD ($)
Pre Tax
Components Of Other Comprehensive Income Loss [Line Items]
Net unrealized gains on forecasted transactions, expected to reclassify into income within the next 12 months	$ 1.1

Redeemable Noncontrolling Int55

Redeemable Noncontrolling Interest (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended	9 Months Ended
		Jun. 30, 2021	Jun. 30, 2018	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2016		Dec. 31, 2015	Sep. 30, 2015	Apr. 01, 2021	Apr. 01, 2018	Apr. 01, 2015
Redeemable Noncontrolling Interest [Line Items]
Business Combination, Control Obtained Description					1		2
Increase (Decrease) in Temporary Equity [Roll Forward]
Balance, Beginning of period							$ 0	$ 0	$ 464.9	[1]	$ 0
Fair value at date of acquisition															$ 411.5
Net income (loss) attributable to noncontrolling interest (NCI), net of tax				$ 6.8		$ 8.2		13.4	11.3		32.9	$ 13.4
Other comprehensive income (loss) attributable to NCI				(1.2)		1.6		(1.2)	2.3		(1.1)	(1.2)
Purchase of shares from NCI								(12.6)	0		(12.6)
Change in redemption value of NCI								31.8	(6)		34.2
Balance, End of period	[1]			$ 472.5		$ 442.9		$ 442.9	$ 472.5		$ 464.9	$ 442.9
ARX Holding Corp. [Member]
Redeemable Noncontrolling Interest [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage				69.20%		69.10%		69.10%	69.20%		69.20%	69.10%
Scenario, Forecast [Member]
Redeemable Noncontrolling Interest [Line Items]
Business Combination, Control Obtained Description		1	1
Scenario, Forecast [Member] | ARX Holding Corp. [Member]
Redeemable Noncontrolling Interest [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage													100.00%	80.00%
[1]	2See Note 11 – Redeemable Noncontrolling Interest for further discussion.

Goodwill and Intangible Asset56

Goodwill and Intangible Assets Goodwill (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Acquired During Period	$ 1,800,000
Goodwill, Impairment Loss	0	$ 0	$ 0
Goodwill	$ 449,400,000	$ 446,400,000	$ 447,600,000

Goodwill and Intangible Asset57

Goodwill and Intangible Assets - Net Carrying Amount of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Schedule of Other Intangible Assets [Line Items]
Intangible assets subject to amortization	$ 435.9	$ 482.5	$ 498.1
Indefinite lived intangible assets	12.4	12.4	12.4
Total	448.3	494.9	510.5
Accumulated amortization	94	47.4	31.8
Licensing Agreements [Member]
Schedule of Other Intangible Assets [Line Items]
Accumulated amortization	$ 0.6	$ 0.6	$ 0.6

Goodwill and Intangible Asset58

Goodwill and Intangible Assets - Finite-lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ 94	$ 31.8		$ 94	$ 31.8	$ 47.4
Net Carrying Amount	435.9	498.1		435.9	498.1	482.5
Amortization of intangible assets	15.5	15.5	$ 0	46.6	31.2
Finite-Lived Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	529.3	529.3		529.3	529.3	529.3
Accumulated Amortization	93.4	31.2		93.4	31.2	46.8
Net Carrying Amount	435.9	498.1		435.9	498.1	482.5
Finite-Lived Intangible Assets [Member] | Policies in force [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	256.2	256.2		256.2	256.2	256.2
Accumulated Amortization	55	18.3		55	18.3	27.5
Net Carrying Amount	201.2	237.9		201.2	237.9	228.7
Finite-Lived Intangible Assets [Member] | Agency relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	159.2	159.2		159.2	159.2	159.2
Accumulated Amortization	17.1	5.7		17.1	5.7	8.5
Net Carrying Amount	142.1	153.5		142.1	153.5	150.7
Finite-Lived Intangible Assets [Member] | Software rights [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	79.1	79.1		79.1	79.1	79.1
Accumulated Amortization	16.1	5.5		16.1	5.5	8.2
Net Carrying Amount	63	73.6		63	73.6	70.9
Finite-Lived Intangible Assets [Member] | Trade name [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	34.8	34.8		34.8	34.8	34.8
Accumulated Amortization	5.2	1.7		5.2	1.7	2.6
Net Carrying Amount	$ 29.6	$ 33.1		$ 29.6	$ 33.1	$ 32.2

New Accounting Standards Effect

New Accounting Standards Effect of Standard Change (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Tax benefit from vesting of equity-based compensation	$ 16.8	$ 12.8	$ 10.3