The Progressive Corporation (PGR) 10-Q 29 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014
Document Document And Entity Information [Abstract]	'
Entity Registrant Name	'PROGRESSIVE CORP/OH/
Entity Central Index Key	'0000080661
Current Fiscal Year End Date	'--12-31
Entity Filer Category	'Large Accelerated Filer
Document Type	'10-Q
Document Period End Date	30-Sep-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3
Amendment Flag	'false
Trading Symbol	'PGR
Entity Common Stock, Shares Outstanding	589,206,958

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended				9 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Revenues	'		'		'		'
Net premiums earned	$4,540.10		$4,303		$13,455.90		$12,759.30
Period over prior year period percent change in net premiums earned	6.00%		'		5.00%		'
Investment income	101.7		107.4		304.2		310.1
Period over prior year period percent change in investment income	-5.00%		'		-2.00%		'
Other-than-temporary impairment (OTTI) losses:	'		'		'		'
Total OTTI losses	-0.1		-1.9		-0.1		-3.6
Period over prior year period percent change in total OTTI losses	-95.00%		'		-97.00%		'
Non-credit losses, net of credit losses recognized on previously recorded non-credit OTTI losses	0		0		0		-0.1
Period over prior year period percent change in non-credit losses, net of credit losses recognized on previously recorded non-credit other than temporary impairment losses	'		'		-100.00%		'
Net impairment losses recognized in earnings	-0.1		-1.9		-0.1		-3.7
Period over prior year period percent change in net impairment losses recognized in earnings	-95.00%		'		-97.00%		'
Net realized gains (losses) on securities	38.3		29.8		198.1		245.1
Period over prior year period percent change in net realized gains (losses) on securities	29.00%		'		-19.00%		'
Total net realized gains (losses) on securities	38.2		27.9		198		241.4
Period over prior year period percent change in total net realized gains (losses) on securities	37.00%		'		-18.00%		'
Fees and other revenues	75.9		76		223.1		215.3
Period over prior year period percent change in fees and other revenues	0.00%		'		4.00%		'
Service revenues	15		11.3		38.8		30.3
Period over prior year period percent change in service revenues	33.00%		'		28.00%		'
Gains (losses) on extinguishment of debt	-4.8		-4.3		-4.8		-4.3
Period over prior year period percent change in gains (losses) on extinguishment of debt	12.00%		'		12.00%		'
Total revenues	4,766.10		4,521.30		14,215.20		13,552.10
Period over prior year period percent change in total revenues	5.00%		'		5.00%		'
Expenses	'		'		'		'
Losses and loss adjustment expenses	3,291.80		3,164.20		9,766.80		9,266.70
Period over prior year period percent change in losses and loss adjustment expenses	4.00%		'		5.00%		'
Policy acquisition costs	375.2		363.1		1,119		1,086
Period over prior year period percent change in policy acquisition costs	3.00%		'		3.00%		'
Other underwriting expenses	609.2		602.3		1,831.30		1,769
Period over prior year period percent change in other underwriting expenses	1.00%		'		4.00%		'
Investment expenses	3.9		5.2		14		14.5
Period over prior year period percent change in investment expenses	-25.00%		'		-3.00%		'
Service expenses	13.5		11.1		36.1		30.1
Period over prior year period percent change in service expenses	22.00%		'		20.00%		'
Interest expense	30.7		30.4		87		91.4
Period over prior year period percent change in interest expense	1.00%		'		-5.00%		'
Total expenses	4,324.30		4,176.30		12,854.20		12,257.70
Period over prior year period percent change in total expenses	4.00%		'		5.00%		'
Net Income	'		'		'		'
Income before income taxes	441.8		345		1,361		1,294.40
Period over prior year period percent change in income before income taxes	28.00%		'		5.00%		'
Provision for income taxes	145.7		112.6		450.2		428.8
Period over prior year period percent change in provision for income taxes	29.00%		'		5.00%		'
Net income	296.1		232.4		910.8		865.6
Period over prior year period percent change in net income	27.00%		'		5.00%		'
Net unrealized gains (losses) on securities:	'		'		'		'
Net non-credit related OTTI losses, adjusted for valuation changes	0		0		0		0.3
Period over prior year period percent change in net non-credit related OTTI losses, adjusted for valuation changes	'		'		-100.00%		'
Other net unrealized gains (losses) on securities	-65.1		57.8		23.2		2.4
Period over prior year period percent change in other net unrealized gains (losses) on securities	-213.00%		'		867.00%		'
Total net unrealized gains (losses) on securities	-65.1		57.8		23.2		2.7
Period over prior year period percent change in total net unrealized gains (losses) on securities	-213.00%		'		759.00%		'
Net unrealized gains on forecasted transactions	-0.7		-0.9		-2.3		-1.6
Period over prior year period percent change in net unrealized gains on forecasted transactions	-22.00%		'		44.00%		'
Foreign currency translation adjustment	-0.4		-0.2		0.1		-1.2
Period over prior year period percent change in foreign currency translation adjustment	100.00%		'		-108.00%		'
Other comprehensive income (loss)	-66.2		56.7		21		-0.1
Period over prior year period percent change in other comprehensive income (loss)	-217.00%		'		'		'
Comprehensive income	$229.90		$289.10		$931.80		$865.50
Period over prior year period percent change in comprehensive income	-20.00%		'		8.00%		'
Computation of Net Income Per Share	'		'		'		'
Average shares outstanding - Basic (shares)	589.8		598.9		591.6		599.7
Period over prior year period percent change in average shares outstanding - basic	-2.00%		'		-1.00%		'
Net effect of dilutive stock-based compensation (shares)	3.9		4.6		4.1		4.2
Period over prior year period percent change in net effect of dilutive stock-based compensation	-15.00%		'		-2.00%		'
Total equivalent shares - Diluted (shares)	593.7		603.5		595.7		603.9
Period over prior year period percent change in total equivalent shares - diluted	-2.00%		'		-1.00%		'
Basic: Net income per share (USD per share)	$0.50		$0.39		$1.54		$1.44
Period over prior year period percent change in basic: net income per share	30.00%		'		7.00%		'
Diluted: Net income per share (USD per share)	$0.50		$0.39		$1.53		$1.43
Period over prior year period percent change in diluted: net income per share	30.00%		'		7.00%		'
Dividends declared per share (USD per share)	$0	[1]	$0	[1]	$0	[1]	$0	[1]
[1]	Progressive maintains an annual dividend program. See Note 8 - Dividends for further discussion.

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
In Millions, unless otherwise specified
Investments - Available-for-sale, at fair value:	'		'		'
Fixed maturities (amortized cost: $13,090.0, $13,644.9, and $13,415.3)	$13,269.40		$13,540.40		$13,797.70
Equity securities:	'		'		'
Nonredeemable preferred stocks (cost: $532.8, $442.1, and $445.7)	763.3		711.2		726
Common equities (cost: $1,278.4, $1,422.3, and $1,451.1)	2,379.40		2,530.50		2,326.10
Short-term investments (amortized cost: $2,671.1, $1,146.1, and $1,272.6)	2,671.10		1,272.60		1,146.10
Total investments at fair value	19,083.20	[1],[2]	18,054.70	[1],[2]	17,995.90	[1],[2]
Cash	90.6		75.1		100.9
Accrued investment income	81.9		89.8		91.5
Premiums receivable, net of allowance for doubtful accounts of $143.6, $133.7, and $142.4	3,705.60		3,310.70		3,500.80
Reinsurance recoverables, including $39.4, $36.4, and $44.3 on paid losses and loss adjustment expenses	1,165.90		1,090.20		1,031.90
Prepaid reinsurance premiums	92.3		74.9		82.6
Deferred acquisition costs	488.3		447.6		474.7
Property and equipment, net of accumulated depreciation of $715.9, $665.8, and $680.4	954		960.9		955.3
Net deferred income taxes	0		0		27.4
Other assets	264.2		304.3		247.9
Total assets	25,926		24,408.20		24,508.90
Liabilities and Shareholders’ Equity	'		'		'
Unearned premiums	5,777		5,174.50		5,477.90
Loss and loss adjustment expense reserves	8,728.40		8,479.70		8,310.30
Net deferred income taxes	57.4		28.4		0
Dividends payable	0		890.2		0
Accounts payable, accrued expenses, and other liabilities	2,263.60		1,785		1,917.50
Debt	2,164.30	[3]	1,860.90	[3]	2,010.60	[3]
Total liabilities	18,990.70		18,218.70		17,716.30
Common Shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 208.4, 197.6, and 201.8)	589.2		595.8		600
Paid-in capital	1,169.90		1,142		1,123
Retained earnings	4,203.50		3,500		4,198.70
Accumulated other comprehensive income, net of tax:	'		'		'
Net non-credit related OTTI losses, adjusted for valuation changes	0		0		0
Other net unrealized gains (losses) on securities	970.2		947		865.4
Total net unrealized gains (losses) on securities	970.2		947		865.4
Net unrealized gains on forecasted transactions	1.8		4.1		4.5
Foreign currency translation adjustment	0.7		0.6		1
Total accumulated other comprehensive income	972.7		951.7		870.9
Total shareholders’ equity	6,935.30		6,189.50		6,792.60
Total liabilities and shareholders’ equity	$25,926		$24,408.20		$24,508.90
[1]	The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.
[3]	Consists of both short- and long-term debt. See Note 4 - Debt.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Millions, except Per Share data, unless otherwise specified
Fixed maturities, amortized cost	$13,090	$13,415.30	$13,644.90
Nonredeemable preferred stocks, cost	532.8	445.7	442.1
Common equities, cost	1,278.40	1,451.10	1,422.30
Short-term investments, amortized cost	2,671.10	1,272.60	1,146.10
Premiums receivable, allowance for doubtful accounts	143.6	142.4	133.7
Reinsurance recoverables, paid losses and loss adjustment expenses	39.4	44.3	36.4
Property and equipment, accumulated depreciation	$715.90	$680.40	$665.80
Common Shares, par value (USD per share)	$1	$1	$1
Common Shares, authorized (shares)	900	900	900
Common Shares, issued (shares)	797.6	797.6	797.6
Common Shares, treasury shares (shares)	208.4	201.8	197.6

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Cash Flows From Operating Activities	'		'
Net income	$910.80		$865.60
Adjustments to reconcile net income to net cash provided by operating activities:	'		'
Depreciation	71.8		74.9
Amortization of fixed-income securities	59.5		111.4
Amortization of equity-based compensation	38.4		49.8
Net realized (gains) losses on securities	-198		-241.4
Net (gains) losses on disposition of property and equipment	4.2		4.1
(Gains) losses on extinguishment of debt	4.8		4.3
Changes in:	'		'
Premiums receivable	-394.9		-317.4
Reinsurance recoverables	-75.7		-130.9
Prepaid reinsurance premiums	-17.4		-16.3
Deferred acquisition costs	-40.7		-40.2
Income taxes	82.1		77.3
Unearned premiums	602.4		548
Loss and loss adjustment expense reserves	248.7		472
Accounts payable, accrued expenses, and other liabilities	333.1		277.4
Other, net	28.4		9.4
Net cash provided by operating activities	1,657.50		1,748
Purchases:	'		'
Fixed maturities	-5,774.50		-6,070.80
Equity securities	-250.7		-260.2
Sales:	'		'
Fixed maturities	4,342		2,352.80
Equity securities	500.2		308
Maturities, paydowns, calls, and other:	'		'
Fixed maturities	1,714.50		1,338.70
Equity securities	14.2		0
Net sales (purchases) of short-term investments	-1,397.90		843
Net unsettled security transactions	96.7		154.6
Purchases of property and equipment	-73.6		-105.6
Sales of property and equipment	4.5		2.4
Net cash used in investing activities	-824.6		-1,437.10
Cash Flows From Financing Activities	'		'
Tax benefit from vesting of equity-based compensation	12.8		10.3
Proceeds from debt issuance	344.7		0
Reacquisition of debt	-48.9		-58.1
Dividends paid to shareholders	-892.6	[1]	-175.6	[1]
Acquisition of treasury shares	-234.7		-164.8
Net cash used in financing activities	-818.7		-388.2
Effect of exchange rate changes on cash	1.3		-0.9
Increase (decrease) in cash	15.5		-78.2
Cash, Beginning of year	75.1		179.1
Cash, End of period	$90.60		$100.90
[1]	Progressive maintains an annual dividend program. See Note 8 - Dividends for further discussion.

Basis_of_Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Basis of Presentation	'
	Basis of Presentation — The consolidated financial statements include the accounts of The Progressive Corporation, its subsidiaries, a mutual insurance company affiliate, and a limited partnership investment affiliate. All of the subsidiaries and affiliates are wholly owned or controlled. 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, 2014, 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 our Annual Report on Form 10-K for the year ended December 31, 2013.
	During the first half of 2014, decisions were made to sell two properties originally purchased for future Service Center sites. At September 30, 2014, included in other assets in the consolidated balance sheets is $13.4 million of "held for sale" property, which represents the fair value of these properties less the estimated costs to sell.

Investments

Investments	9 Months Ended
	Sep. 30, 2014
Investments Schedule [Abstract]	'
Investments	'
	Investments — The following tables present the composition of our investment portfolio by major security type, consistent with our classification of how we manage, monitor, and measure the portfolio:
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	30-Sep-14
	Fixed maturities:
	U.S. government obligations	$	3,033.20			$	33.6			$	(3.9	)		$	0			$	3,062.90		16	%
	State and local government obligations	2,124.20				49.5				(.9		)		0				2,172.80			11.4
	Foreign government obligations	20.2				0				0				0				20.2			0.1
	Corporate debt securities	2,501.80				30.7				(13.1		)		(.3		)		2,519.10			13.2
	Residential mortgage-backed securities	1,460.60				36.9				(10.1		)		(.9		)		1,486.50			7.8
	Commercial mortgage-backed securities	2,143.80				33.8				(5.1		)		0				2,172.50			11.4
	Other asset-backed securities	1,546.00				5				(.6		)		0.2				1,550.60			8.1
	Redeemable preferred stocks	260.2				28.8				(4.2		)		0				284.8			1.5
	Total fixed maturities	13,090.00				218.3				(37.9		)		(1.0		)		13,269.40			69.5
	Equity securities:
	Nonredeemable preferred stocks	532.8				218.4				(7.2		)		19.3				763.3			4
	Common equities	1,278.40				1,107.70				(6.7		)		0				2,379.40			12.5
	Short-term investments:
	Other short-term investments	2,671.10				0				0				0				2,671.10			14
	Total portfolio2,3	$	17,572.30			$	1,544.40			$	(51.8	)		$	18.3			$	19,083.20		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	30-Sep-13
	Fixed maturities:
	U.S. government obligations	$	3,691.20			$	61.8			$	(11.3	)		$	0			$	3,741.70		20.8	%
	State and local government obligations	2,125.70				29.9				(17.0		)		0				2,138.60			11.9
	Foreign government obligations	15.9				0				0				0				15.9			0.1
	Corporate debt securities	3,118.80				67				(28.9		)		0.7				3,157.60			17.6
	Residential mortgage-backed securities	994.9				31.5				(16.5		)		0				1,009.90			5.6
	Commercial mortgage-backed securities	2,224.10				49				(33.1		)		0				2,240.00			12.4
	Other asset-backed securities	1,143.30				7.4				(2.0		)		0.2				1,148.90			6.4
	Redeemable preferred stocks	331				24.5				(10.4		)		0				345.1			1.9
	Total fixed maturities	13,644.90				271.1				(119.2		)		0.9				13,797.70			76.7
	Equity securities:
	Nonredeemable preferred stocks	442.1				280.5				(4.8		)		8.2				726			4
	Common equities	1,422.30				908.8				(5.0		)		0				2,326.10			12.9
	Short-term investments:
	Other short-term investments	1,146.10				0				0				0				1,146.10			6.4
	Total portfolio2,3	$	16,655.40			$	1,460.40			$	(129.0	)		$	9.1			$	17,995.90		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	$	3,630.40			$	48.4			$	(16.6	)		$	0			$	3,662.20		20.3	%
	State and local government obligations	2,247.30				27.1				(18.4		)		0				2,256.00			12.5
	Foreign government obligations	15.6				0				0				0				15.6			0.1
	Corporate debt securities	2,885.00				60.4				(20.4		)		1.6				2,926.60			16.2
	Residential mortgage-backed securities	1,110.10				31.9				(14.1		)		0				1,127.90			6.2
	Commercial mortgage-backed securities	2,154.40				43.9				(37.8		)		0				2,160.50			12
	Other asset-backed securities	1,073.00				6.6				(2.1		)		0.2				1,077.70			6
	Redeemable preferred stocks	299.5				24.1				(9.7		)		0				313.9			1.7
	Total fixed maturities	13,415.30				242.4				(119.1		)		1.8				13,540.40			75
	Equity securities:
	Nonredeemable preferred stocks	445.7				258.7				(4.5		)		11.3				711.2			3.9
	Common equities	1,451.10				1,081.80				(2.4		)		0				2,530.50			14
	Short-term investments:
	Other short-term investments	1,272.60				0				0				0				1,272.60			7.1
Total portfolio2,3	$	16,584.70			$	1,582.90			$	(126.0	)		$	13.1			$	18,054.70		100	%
1Represents net holding period gains (losses) on certain hybrid securities (discussed below).
2Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.
3The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
Our other short-term investments may include commercial paper, reverse repurchase transactions, and other investments that are expected to mature, or be redeemed, within one year. We had no open reverse repurchase commitments at September 30, 2014, compared to $278.1 million, and $200.0 million at September 30, 2013 and December 31, 2013, respectively. At these dates, we had no repurchase transactions where we lent collateral. To the extent our 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 report these transactions on a gross basis on our balance sheets.
Included in our fixed-maturity and equity securities are hybrid securities, which are reported at fair value:
	September 30,								December 31,
(millions)	2014				2013				2013
Fixed maturities:
Corporate debt securities	$	138.5			$	171.8			$	164.2
Residential mortgage-backed securities	116.8				0				0
Other asset-backed securities	13.5				15.3				14.8
Total fixed maturities	268.8				187.1				179
Equity securities:
Nonredeemable preferred stocks	93.4				57.3				60.3
Total hybrid securities	$	362.2			$	244.4			$	239.3
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 $10.0 million as of September 30, 2014, 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.
The other asset-backed security in the table above represents a 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 has the potential to more than double our initial investment yield.
The hybrid securities in our nonredeemable preferred stock portfolio are perpetual preferred stocks that have call features with fixed-rate coupons, whereby the change in value of the call features is a component of the overall change in value of the preferred stocks. One security in our preferred portfolio contains a convertible derivative feature that could provide for a conversion from an equity instrument to a debt instrument at the discretion of the issuer.
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.
Fixed Maturities The composition of fixed maturities by maturity at September 30, 2014, was:
(millions)	Cost				Fair Value
Less than one year	$	2,472.70			$	2,506.70
One to five years	7,571.80				7,672.20
Five to ten years	2,938.80				2,976.10
Ten years or greater	69.7				77.4
Total1	$	13,053.00			$	13,232.40
1Excludes $37.0 million related to our open interest rate swap positions.
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, 2014, we had $45.1 million of gross unrealized losses in our fixed-income securities (i.e., fixed-maturity securities, nonredeemable preferred stocks, and short-term investments) and $6.7 million in our common equities. We currently do not intend to sell the fixed-income securities and determined that it is more likely than not that we will not be required to sell these securities for the period of time necessary to recover their cost bases. A review of our fixed-income securities indicated that the issuers were current with respect to their interest obligations and that there was no evidence of any deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. For common equities, 87% of our common stock portfolio was indexed to the Russell 1000; as such, this portfolio may contain securities in a loss position for an extended period of time, subject to possible write-downs, as described below. We may retain these securities as long as the portfolio and index correlation remain similar. The remaining 13% of our common stocks are part of a managed equity strategy selected and administered by external investment advisors. If our review of loss position securities indicates there is a fundamental, or market, impairment on these securities that is determined to be other-than-temporary, we would recognize a write-down in accordance with our stated policy.
The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position:
	Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
			Fair
($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
											Value								Value
30-Sep-14
Fixed maturities:
U.S. government obligations	19		$	627		$	(3.9	)	9		$	211		$	(.7	)		10	$	416		$	(3.2	)
State and local government obligations	31		181.8			(.9		)	11		89.7			(.1		)		20	92.1			(.8		)
Corporate debt securities	50		891.4			(13.1		)	42		744.5			(9.7		)		8	146.9			(3.4		)
Residential mortgage-backed securities	62		725.8			(10.1		)	24		290.5			(1.8		)		38	435.3			(8.3		)
Commercial mortgage-backed securities	72		894.5			(5.1		)	61		787.3			(2.9		)		11	107.2			(2.2		)
Other asset-backed securities	38		650.8			(.6		)	36		624.7			(.4		)		2	26.1			(.2		)
Redeemable preferred stocks	2		70.5			(4.2		)	0		0			0				2	70.5			(4.2		)
Total fixed maturities	274		4,041.80			(37.9		)	183		2,747.70			(15.6		)		91	1,294.10			(22.3		)
Equity securities:
Nonredeemable preferred stocks	7		206.3			(7.2		)	4		118.6			(4.0		)		3	87.7			(3.2		)
Common equities	39		57.5			(6.7		)	37		45.7			(5.4		)		2	11.8			(1.3		)
Total equity securities	46		263.8			(13.9		)	41		164.3			(9.4		)		5	99.5			(4.5		)
Total portfolio	320		$	4,305.60		$	(51.8	)	224		$	2,912.00		$	(25.0	)		96	$	1,393.60		$	(26.8	)
	Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
			Fair
($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
											Value								Value
30-Sep-13
Fixed maturities:
U.S. government obligations	18		$	969.1		$	(11.3	)	18		$	969.1		$	(11.3	)		0	$	0		$	0
State and local government obligations	126		728.3			(17.0		)	108		666.7			(16.2		)		18	61.6			(.8		)
Corporate debt securities	63		1,174.20			(28.9		)	61		1,113.40			(28.5		)		2	60.8			(.4		)
Residential mortgage-backed securities	63		663			(16.5		)	49		585.5			(12.4		)		14	77.5			(4.1		)
Commercial mortgage-backed securities	67		993.3			(33.1		)	64		993.2			(33.0		)		3	0.1			(.1		)
Other asset-backed securities	22		282.8			(2.0		)	22		282.8			(2.0		)		0	0			0
Redeemable preferred stocks	6		158.4			(10.4		)	2		36.2			(.2		)		4	122.2			(10.2		)
Total fixed maturities	365		4,969.10			(119.2		)	324		4,646.90			(103.6		)		41	322.2			(15.6		)
Equity securities:
Nonredeemable preferred stocks	7		123.6			(4.8		)	7		123.6			(4.8		)		0	0			0
Common equities	26		47.3			(5.0		)	21		43			(4.7		)		5	4.3			(.3		)
Total equity securities	33		170.9			(9.8		)	28		166.6			(9.5		)		5	4.3			(.3		)
Total portfolio	398		$	5,140.00		$	(129.0	)	352		$	4,813.50		$	(113.1	)		46	$	326.5		$	(15.9	)
	Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
			Fair
($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
											Value								Value
31-Dec-13
Fixed maturities:
U.S. government obligations	29		$	1,444.30		$	(16.6	)	28		$	1,434.60		$	(16.3	)		1	$	9.7		$	(.3	)
State and local government obligations	141		844.2			(18.4		)	119		759.3			(17.1		)		22	84.9			(1.3		)
Corporate debt securities	51		997.6			(20.4		)	45		831.1			(17.8		)		6	166.5			(2.6		)
Residential mortgage-backed securities	66		763.5			(14.1		)	45		597.6			(7.9		)		21	165.9			(6.2		)
Commercial mortgage-backed securities	76		1,061.90			(37.8		)	60		809.2			(19.7		)		16	252.7			(18.1		)
Other asset-backed securities	25		287.2			(2.1		)	22		233.3			(1.8		)		3	53.9			(.3		)
Redeemable preferred stocks	4		122.7			(9.7		)	0		0			0				4	122.7			(9.7		)
Total fixed maturities	392		5,521.40			(119.1		)	319		4,665.10			(80.6		)		73	856.3			(38.5		)
Equity securities:
Nonredeemable preferred stocks	7		142.3			(4.5		)	7		142.3			(4.5		)		0	0			0
Common equities	24		59.7			(2.4		)	20		58.5			(2.4		)		4	1.2			0
Total equity securities	31		202			(6.9		)	27		200.8			(6.9		)		4	1.2			0
Total portfolio	423		$	5,723.40		$	(126.0	)	346		$	4,865.90		$	(87.5	)		77	$	857.5		$	(38.5	)
Since December 31, 2013, the number of securities in our fixed-maturity portfolio with unrealized losses decreased, reflecting a combination of an increase in prices associated with a general decline in interest rates at certain maturities, as well as sales of securities for portfolio management reasons. We had no material decreases in valuation as a result of credit rating downgrades on our fixed-maturity securities during the third quarter or first nine months of 2014. All of the fixed-maturity securities in an unrealized loss position at September 30, 2014 in the table above are current with respect to required principal and interest payments. The number of common equity securities in an unrealized loss position increased by 15 since December 31, 2013, which was predominantly the result of the recent equity market decline during the last month of the third quarter. The increase in the number of securities was mainly in the less than one year category and the overall change in the unrealized loss for that category was approximately $3.0 million for the additional securities since year end. None of the losses are a significant dollar decline and none represent any fundamental issuer impairments based on our review. Unrealized losses on our nonredeemable preferred stocks remained at seven issuers with unrealized losses, averaging approximately 3% of our total cost of those securities. A review of these securities concluded that the unrealized losses are market-related adjustments to the values, which were determined not to be other-than-temporary, and we expect to recover our initial investments on these securities.
Other-Than-Temporary Impairment (OTTI) The following table shows the total non-credit portion of the OTTI losses 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)	2014				2013				2013
Fixed maturities:
Residential mortgage-backed securities	$	(44.1	)		$	(44.1	)		$	(44.1	)
Commercial mortgage-backed securities	(.6		)		(.9		)		(.9		)
Total fixed maturities	$	(44.7	)		$	(45.0	)		$	(45.0	)
The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended September 30, 2014 and 2013, 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, 2014
	Mortgage-Backed
(millions)	Residential				Commercial				Total
Balance at June 30, 2014	$	13			$	0.4			$	13.4
Reductions for securities sold/matured	(.1		)		0				(.1		)
Change in recoveries of future cash flows expected to be collected1	0.1				0				0.1
Reductions for previously recognized credit impairments written-down to fair value2	0				0				0
Balance at September 30, 2014	$	13			$	0.4			$	13.4
	Nine Months Ended September 30, 2014
	Mortgage-Backed
(millions)	Residential				Commercial				Total
Balance at December 31, 2013	$	19.2			$	0.4			$	19.6
Reductions for securities sold/matured	(.1		)		0				(.1		)
Change in recoveries of future cash flows expected to be collected1	(6.1		)		0				(6.1		)
Reductions for previously recognized credit impairments written-down to fair value2	0				0				0
Balance at September 30, 2014	$	13			$	0.4			$	13.4
	Three Months Ended September 30, 2013
	Mortgage-Backed
(millions)	Residential				Commercial				Total
Balance at June 30, 2013	$	26.9			$	0.5			$	27.4
Reductions for securities sold/matured	0				0				0
Change in recoveries of future cash flows expected to be collected1	(2.4		)		(.1		)		(2.5		)
Reductions for previously recognized credit impairments written-down to fair value2	0				0				0
Balance at September 30, 2013	$	24.5			$	0.4			$	24.9
	Nine Months Ended September 30, 2013
	Mortgage-Backed
(millions)	Residential				Commercial				Total
Balance at December 31, 2012	$	27.1			$	0.6			$	27.7
Reductions for securities sold/matured	0				0				0
Change in recoveries of future cash flows expected to be collected1	(2.4		)		(.2		)		(2.6		)
Reductions for previously recognized credit impairments written-down to fair value2	(.2		)		0				(.2		)
Balance at September 30, 2013	$	24.5			$	0.4			$	24.9
1Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security.
2Reflects reductions of prior credit impairments where the current credit impairment requires writing securities down to fair value (i.e., no remaining non-credit loss).
Although it is more likely than not 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 and report the amount of credit losses on the securities that were determined to be other-than-temporarily impaired. 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 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 was deemed to exist, and the security was written down.
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)	2014				2013				2014				2013
Gross realized gains on security sales
Fixed maturities:
U.S. government obligations	$	2.5			$	3.1			$	13.2			$	6.8
State and local government obligations	3.8				0				8.2				6.8
Corporate and other debt securities	0.9				1.7				33.8				38.4
Residential mortgage-backed securities	0.2				0.3				2.2				2.4
Commercial mortgage-backed securities	5.2				0.1				14.8				8.4
Redeemable preferred stocks	2.3				0				2.7				0
Total fixed maturities	14.9				5.2				74.9				62.8
Equity securities:
Nonredeemable preferred stocks	20.9				11.9				80				113.1
Common equities	4.6				11.1				97				26.1
Subtotal gross realized gains on security sales	40.4				28.2				251.9				202
Gross realized losses on security sales
Fixed maturities:
U.S. government obligations	(1.3		)		(.8		)		(6.4		)		(2.2		)
State and local government obligations	(.3		)		0				(.5		)		0
Corporate and other debt securities	0				(2.1		)		(2.3		)		(3.1		)
Residential mortgage-backed securities	0				0				(.2		)		0
Commercial mortgage-backed securities	(1.4		)		0				(8.2		)		(.7		)
Redeemable preferred stocks	0				0				(3.2		)		(.1		)
Total fixed maturities	(3.0		)		(2.9		)		(20.8		)		(6.1		)
Equity securities:
Common equities	0				(.1		)		(3.4		)		(.4		)
Subtotal gross realized losses on security sales	(3.0		)		(3.0		)		(24.2		)		(6.5		)
Net realized gains (losses) on security sales
Fixed maturities:
U.S. government obligations	1.2				2.3				6.8				4.6
State and local government obligations	3.5				0				7.7				6.8
Corporate and other debt securities	0.9				(.4		)		31.5				35.3
Residential mortgage-backed securities	0.2				0.3				2				2.4
Commercial mortgage-backed securities	3.8				0.1				6.6				7.7
Redeemable preferred stocks	2.3				0				(.5		)		(.1		)
Total fixed maturities	11.9				2.3				54.1				56.7
Equity securities:
Nonredeemable preferred stocks	20.9				11.9				80				113.1
Common equities	4.6				11				93.6				25.7
Subtotal net realized gains (losses) on security sales	37.4				25.2				227.7				195.5
Other-than-temporary impairment losses
Fixed maturities:
Residential mortgage-backed securities	0				(.1		)		0				(.5		)
Total fixed maturities	0				(.1		)		0				(.5		)
Equity securities:
Common equities	(.1		)		(1.8		)		(.1		)		(3.2		)
Subtotal other-than-temporary impairment losses	(.1		)		(1.9		)		(.1		)		(3.7		)
Other gains (losses)
Hybrid securities	(1.8		)		3.5				5.7				2.3
Derivative instruments	(.7		)		(1.2		)		(39.9		)		45
Litigation settlements	3.4				2.3				4.6				2.3
Subtotal other gains (losses)	0.9				4.6				(29.6		)		49.6
Total net realized gains (losses) on securities	$	38.2			$	27.9			$	198			$	241.4
Gross realized gains and losses were predominately the result of sales transactions in our fixed-income portfolio related to movements in credit spreads and interest rates and sales from our equity-indexed portfolio primarily during the first quarter 2014. In addition, gains and losses reflect recoveries from litigation settlements and holding period valuation changes on hybrids and derivatives. Also included are write-downs for securities determined to be other-than-temporarily impaired in our fixed-maturity and/or equity portfolios.
Net Investment Income  The components of net investment income for the three and nine months ended September 30, were:
	Three Months							Nine Months
(millions)	2014			2013				2014			2013
Fixed maturities:
U.S. government obligations	$	11.3		$	12.9			$	36.3		$	36.8
State and local government obligations	12.8			12.3				38.2			34.8
Foreign government obligations	0.1			0.1				0.3			0.1
Corporate debt securities	19.5			24.3				60.3			74.1
Residential mortgage-backed securities	11.3			7.9				32.5			18.1
Commercial mortgage-backed securities	16.5			19.1				49.2			55.9
Other asset-backed securities	4.2			4.5				12.1			12.2
Redeemable preferred stocks	3.7			5.5				11.7			16.3
Total fixed maturities	79.4			86.6				240.6			248.3
Equity securities:
Nonredeemable preferred stocks	9.4			9.2				28.6			27.3
Common equities	12.5			11.3				34.1			32.8
Short-term investments:
Other short-term investments	0.4			0.3				0.9			1.7
Investment income	101.7			107.4				304.2			310.1
Investment expenses	(3.9		)	(5.2		)		(14.0		)	(14.5		)
Net investment income	$	97.8		$	102.2			$	290.2		$	295.6
The decrease in our investment income year over year for both periods was due in part to an increase in short-term investments held and lower yields on securities purchased during the last 12 months.
The decrease in investment expenses primarily reflects a lower estimated bonus accrual for our internal investment managers in 2014. Included in investment expenses for the nine months ended September 30, 2014, were $0.7 million of costs related to the issuance of our 4.35% Senior Notes due 2044.
Trading Securities At September 30, 2014 and 2013, and December 31, 2013, 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, 2014 and 2013.
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, 2014 and 2013, and December 31, 2013, and for the three and nine months ended September 30, 2014 and 2013; amounts are on a pretax basis:
(millions)															Balance Sheet2											Comprehensive Income Statement
																	Assets (Liabilities)									Net Realized
																	Fair Value									Gains (Losses) on Securities
	Notional Value1																									Three Months Ended						Nine Months Ended
	September 30,								Dec. 31,								September 30,							Dec. 31,		September 30,						September 30,
Derivatives designated as:	2014				2013				2013				Purpose		Classification		2014			2013				2013		2014			2013			2014			2013
Hedging instruments
Closed:
Ineffective cash flow hedge	$	44			$	54			$	54			Manage interest		NA		$	0		$	0			$	0	$	0.5		$	0.8		$	0.5		$	0.8
													rate risk
Non-hedging instruments
Assets:
Interest rate swaps	750				750				750				Manage portfolio		Investments—		37			53.5				68.1		(1.2		)	(2.0		)	(40.4		)	48.2
													duration		fixed maturities
Closed:
Interest rate swaps	0				1,263				1,263				Manage portfolio		NA		0			0				0		0			0			0			(4.0		)
													duration
Total	NA				NA				NA								$	37		$	53.5			$	68.1	$	(.7	)	$	(1.2	)	$	(39.9	)	$	45
1The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions.
2To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we report them on a gross basis on our balance sheets, consistent with our historical presentation.
NA=ot Applicable
CASH FLOW HEDGES
In April 2014, we issued $350 million of 4.35% Senior Notes due 2044 (the “4.35% Senior Notes”). Upon issuance of the 4.35% Senior Notes, we closed a forecasted debt issuance hedge, which was entered into to hedge against a possible rise in interest rates, and recognized a $1.6 million pretax loss as part of accumulated other comprehensive income (loss); the loss will be recognized as an adjustment to interest expense and amortized over the life of the 4.35% Senior Notes.
During the third quarter 2014 and 2013, we repurchased, in the open market, $44.3 million and $54.1 million, respectively, in aggregate principal amount of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (the “6.70% Debentures”). For the portion of the 6.70% Debentures we repurchased during 2014 and 2013, we reclassified $0.5 million and $0.8 million, 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.
INTEREST RATE SWAPS
We use interest rate swap contracts primarily to manage the fixed-income portfolio duration. At September 30, 2014 and 2013, and December 31, 2013, we held three 10-year interest rate swap positions (opened in the second quarter of 2013) with a total notional value of $750 million. In each case, we are paying a fixed rate and receiving a variable rate, effectively shortening the duration of our fixed-income portfolio. As of September 30, 2014 and 2013 and December 31, 2013, we recognized inception-to-date fair value gains of $37.0 million, $53.5 million, and $68.1 million, respectively, on the balance sheet, reflecting rising interest rates since the positions were opened. The decrease in the fair value gain during the first nine months of 2014 reflected a decline in the benchmark interest rates.
During the second quarter 2013, we closed three interest rate swap positions with a total notional value of $1,263 million. These positions included one 9-year interest rate swap position (opened in 2009) and two 5-year interest rate swap positions (opened in 2011); in each case, we were paying a fixed rate and receiving a variable rate, effectively shortening the duration of our fixed-income portfolio.
As of September 30, 2014 and 2013, and December 31, 2013, the balance of the cash collateral that we had received from the applicable counterparties on the open positions was $31.8 million, $49.3 million, and $62.7 million, respectively.

Fair_Value

Fair Value	9 Months Ended
	Sep. 30, 2014
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
	30-Sep-14
	Fixed maturities:
	U.S. government obligations	$	3,062.90	$	0		$	0	$	3,062.90		$	3,033.20
	State and local government obligations	0		2,172.80			0		2,172.80			2,124.20
	Foreign government obligations	20.2		0			0		20.2			20.2
	Corporate debt securities	0		2,519.10			0		2,519.10			2,501.80
	Subtotal	3,083.10		4,691.90			0		7,775.00			7,679.40
	Asset-backed securities:
	Residential mortgage-backed	0		1,486.50			0		1,486.50			1,460.60
	Commercial mortgage-backed	0		2,160.00			12.5		2,172.50			2,143.80
	Other asset-backed	0		1,550.60			0		1,550.60			1,546.00
	Subtotal asset-backed securities	0		5,197.10			12.5		5,209.60			5,150.40
	Redeemable preferred stocks:
	Financials	0		100.3			0		100.3			77.3
	Utilities	0		65.3			0		65.3			65
	Industrials	0		119.2			0		119.2			117.9
	Subtotal redeemable preferred stocks	0		284.8			0		284.8			260.2
	Total fixed maturities	3,083.10		10,173.80			12.5		13,269.40			13,090.00
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	220		496.6			46.7		763.3			532.8
	Utilities	0		0			0		0			0
	Subtotal nonredeemable preferred stocks	220		496.6			46.7		763.3			532.8
	Common equities:
	Common stocks	2,379.00		0			0		2,379.00			1,278.00
	Other risk investments	0		0			0.4		0.4			0.4
	Subtotal common equities	2,379.00		0			0.4		2,379.40			1,278.40
	Total fixed maturities and equity securities	5,682.10		10,670.40			59.6		16,412.10			14,901.20
	Short-term investments:
	Other short-term investments	2,393.70		277.4			0		2,671.10			2,671.10
	Total portfolio	$	8,075.80	$	10,947.80		$	59.6	$	19,083.20		$	17,572.30
	Debt	$	0	$	2,475.10		$	0	$	2,475.10		$	2,164.30
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total			Cost
	30-Sep-13
	Fixed maturities:
	U.S. government obligations	$	3,741.70	$	0		$	0	$	3,741.70		$	3,691.20
	State and local government obligations	0		2,138.60			0		2,138.60			2,125.70
	Foreign government obligations	15.9		0			0		15.9			15.9
	Corporate debt securities	0		3,157.60			0		3,157.60			3,118.80
	Subtotal	3,757.60		5,296.20			0		9,053.80			8,951.60
	Asset-backed securities:
	Residential mortgage-backed	0		1,009.70			0.2		1,009.90			994.9
	Commercial mortgage-backed	0		2,208.70			31.3		2,240.00			2,224.10
	Other asset-backed	0		1,148.90			0		1,148.90			1,143.30
	Subtotal asset-backed securities	0		4,367.30			31.5		4,398.80			4,362.30
	Redeemable preferred stocks:
	Financials	0		134.2			0		134.2			115.7
	Utilities	0		65.3			0		65.3			64.9
	Industrials	0		145.6			0		145.6			150.4
	Subtotal redeemable preferred stocks	0		345.1			0		345.1			331
	Total fixed maturities	3,757.60		10,008.60			31.5		13,797.70			13,644.90
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	244		429.1			36.1		709.2			427.9
Utilities	0		16.8			0		16.8			14.2
Subtotal nonredeemable preferred stocks	244		445.9			36.1		726			442.1
Common equities:
Common stocks	2,287.40		0			0		2,287.40			1,419.20
Other risk investments	0		0			38.7		38.7			3.1
Subtotal common equities	2,287.40		0			38.7		2,326.10			1,422.30
Total fixed maturities and equity securities	6,289.00		10,454.50			106.3		16,849.80			15,509.30
Short-term investments:
Other short-term investments	751.5		394.6			0		1,146.10			1,146.10
Total portfolio	$	7,040.50	$	10,849.10		$	106.3	$	17,995.90		$	16,655.40
Debt	$	0	$	2,231.40		$	0	$	2,231.40		$	2,010.60
	Fair Value
(millions)	Level 1		Level 2			Level 3		Total			Cost
31-Dec-13
Fixed maturities:
U.S. government obligations	$	3,662.20	$	0		$	0	$	3,662.20		$	3,630.40
State and local government obligations	0		2,256.00			0		2,256.00			2,247.30
Foreign government obligations	15.6		0			0		15.6			15.6
Corporate debt securities	0		2,926.60			0		2,926.60			2,885.00
Subtotal	3,677.80		5,182.60			0		8,860.40			8,778.30
Asset-backed securities:
Residential mortgage-backed	0		1,127.70			0.2		1,127.90			1,110.10
Commercial mortgage-backed	0		2,131.50			29		2,160.50			2,154.40
Other asset-backed	0		1,077.70			0		1,077.70			1,073.00
Subtotal asset-backed securities	0		4,336.90			29.2		4,366.10			4,337.50
Redeemable preferred stocks:
Financials	0		102.8			0		102.8			84.2
Utilities	0		65.6			0		65.6			64.9
Industrials	0		145.5			0		145.5			150.4
Subtotal redeemable preferred stocks	0		313.9			0		313.9			299.5
Total fixed maturities	3,677.80		9,833.40			29.2		13,540.40			13,415.30
Equity securities:
Nonredeemable preferred stocks:
Financials	240.8		414.6			39		694.4			431.5
Utilities	0		16.8			0		16.8			14.2
Subtotal nonredeemable preferred stocks	240.8		431.4			39		711.2			445.7
Common equities:
Common stocks	2,530.00		0			0		2,530.00			1,450.60
Other risk investments	0		0			0.5		0.5			0.5
Subtotal common equities	2,530.00		0			0.5		2,530.50			1,451.10
Total fixed maturities and equity securities	6,448.60		10,264.80			68.7		16,782.10			15,312.10
Short-term investments:
Other short-term investments	987.8		284.8			0		1,272.60			1,272.60
Total portfolio	$	7,436.40	$	10,549.60		$	68.7	$	18,054.70		$	16,584.70
Debt	$	0	$	2,073.70		$	0	$	2,073.70		$	1,860.90
Our portfolio valuations, excluding the other 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. During the first quarter 2014, we had two nonredeemable preferred stocks with a value of $41.7 million that were transferred from Level 2 to Level 1 due to the availability of a consistent exchange price; no securities were transferred during the second or third quarter 2014. We did not have any transfers between Level 1 and Level 2 during the year ended December 31, 2013. 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, 2014, vendor-quoted prices represented 54% of our Level 1 classifications (excluding short-term investments), compared to 59% at September 30, 2013 and 56% at December 31, 2013. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges.
At September 30, 2014, vendor-quoted prices comprised 96% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented 4%, compared to 97% and 3% and 98% and 2% at September 30, 2013 and December 31, 2013, 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 global 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 the appropriate fair value.
For our corporate debt and preferred stock (redeemable and nonredeemable) portfolios, 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, 2014 and 2013, and December 31, 2013, 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 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.
At both September 30, 2014 and December 31, 2013, we did not have any private common equity securities that were priced internally. At September 30, 2013, we had one private common equity security with a value of $38.0 million that was priced internally; the security was sold prior to the end of 2013 at that price. At September 30, 2014, we held one private preferred equity security, with a value of $46.7 million, that was priced internally. The same security had a value of $36.1 million at September 30, 2013 and $39.0 million at December 31, 2013. At September 30, 2014 and 2013, and December 31, 2013, we did not hold any securities in our fixed-maturity portfolio that were priced internally.
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. 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, 2014 and 2013:
	Level 3 Fair Value
	Three Months Ended September 30, 2014
(millions)	Fair Value at June 30, 2014		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in Valuation			Net			Fair Value at Sept. 30, 2014
			Maturities/														Transfers
			Paydowns														In (Out)1
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0	$	0		$	0	$	0		$	0		$	0		$	0		$	0
Commercial mortgage-backed	27.6		(1.2		)	0		0			0			(.3		)	(13.6		)	12.5
Total fixed maturities	27.6		(1.2		)	0		0			0			(.3		)	(13.6		)	12.5
Equity securities:
Nonredeemable preferred stocks:
Financials2	43.8		0			0		0			0			2.9			0			46.7
Common equities:
Other risk investments	0.5		(.1		)	0		0			0			0			0			0.4
Total Level 3 securities	$	71.9	$	(1.3	)	$	0	$	0		$	0		$	2.6		$	(13.6	)	$	59.6
1The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
2The $2.9 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
	Level 3 Fair Value
	Nine Months Ended September 30, 2014
(millions)	Fair Value at Dec. 31, 2013		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in Valuation			Net			Fair Value at Sept. 30, 2014
			Maturities/														Transfers
			Paydowns														In (Out)1
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0.2	$	0		$	0	$	(.1	)	$	0.1		$	(.2	)	$	0		$	0
Commercial mortgage-backed	29		(3.0		)	0		0			0			0.1			(13.6		)	12.5
Total fixed maturities	29.2		(3.0		)	0		(.1		)	0.1			(.1		)	(13.6		)	12.5
Equity securities:
Nonredeemable preferred stocks:
Financials2	39		0			0		0			0			7.7			0			46.7
Common equities:
Other risk investments	0.5		(.1		)	0		0			0			0			0			0.4
Total Level 3 securities	$	68.7	$	(3.1	)	$	0	$	(.1	)	$	0.1		$	7.6		$	(13.6	)	$	59.6
1The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
2The $7.7 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
	Level 3 Fair Value
	Three Months Ended September 30, 2013
(millions)	Fair Value at June 30, 2013		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in			Net			Fair Value at Sept. 30, 2013
			Maturities/											Valuation			Transfers
			Paydowns														In (Out)1
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	157.1	$	(17.0	)	$	0	$	0		$	0		$	1.5		$	(141.4	)	$	0.2
Commercial mortgage-backed	27.6		(.3		)	0		0			0			4			0			31.3
Total fixed maturities	184.7		(17.3		)	0		0			0			5.5			(141.4		)	31.5
Equity securities:
Nonredeemable preferred stocks:
Financials2	34.8		0			0		0			0			1.3			0			36.1
Common equities:
Other risk investments	38.7		0			0		0			0			0			0			38.7
Total Level 3 securities	$	258.2	$	(17.3	)	$	0	$	0		$	0		$	6.8		$	(141.4	)	$	106.3
1The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
2The $1.3 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
	Level 3 Fair Value
	Nine Months Ended September 30, 2013
(millions)	Fair Value at Dec. 31, 2012		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in			Net			Fair Value at Sept. 30, 2013
			Maturities/											Valuation			Transfers
			Paydowns														In (Out)1
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	45.5	$	(28.6	)	$	125.1	$	0		$	0		$	(.4	)	$	(141.4	)	$	0.2
Commercial mortgage-backed	25.3		(1.1		)	0		0			0			7.1			0			31.3
Total fixed maturities	70.8		(29.7		)	125.1		0			0			6.7			(141.4		)	31.5
Equity securities:
Nonredeemable preferred stocks:
Financials2	31.9		0			0		0			0			4.2			0			36.1
Common equities:
Other risk investments	12		(.1		)	0.3		0			(.5		)	27			0			38.7
Total Level 3 securities	$	114.7	$	(29.8	)	$	125.4	$	0		$	(.5	)	$	37.9		$	(141.4	)	$	106.3
1The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
2The $4.2 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2014 and 2013, and December 31, 2013:
	Quantitative Information about Level 3 Fair Value Measurements
($ in millions)	Fair Value at Sept. 30, 2014		Valuation Technique		Unobservable Input	Unobservable
						Input Assumption
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0
Commercial mortgage-backed	12.5		External vendor		Prepayment rate1	0
Total fixed maturities	12.5
Equity securities:
Nonredeemable preferred stocks:
Financials	46.7		Multiple of tangible net book value		Price to book ratio multiple	1.9
Subtotal Level 3 securities	59.2
Pricing exemption securities2	0.4
Total Level 3 securities	$	59.6
1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
	Quantitative Information about Level 3 Fair Value Measurements
($ in millions)	Fair Value at Sept. 30, 2013		Valuation Technique		Unobservable Input	Unobservable
						Input Assumption
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0.2	External vendor		Prepayment rate1	0
Commercial mortgage-backed	31.3		External vendor		Prepayment rate2	0
Total fixed maturities	31.5
Equity securities:
Nonredeemable preferred stocks:
Financials	36.1		Multiple of tangible net book value		Price to book ratio multiple	1.9
Subtotal Level 3 securities	67.6
Pricing exemption securities3	38.7
Total Level 3 securities	$	106.3
1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
3The fair values for $0.7 million of these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us. The remaining $38.0 million reflects a negotiated sale on a private common equity security that was completed by the end of 2013.
	Quantitative Information about Level 3 Fair Value Measurements
($ in millions)	Fair Value at Dec. 31, 2013		Valuation Technique		Unobservable Input	Unobservable
						Input Assumption
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0.2	External vendor		Prepayment rate1	0
Commercial mortgage-backed	29		External vendor		Prepayment rate2	0
Total fixed maturities	29.2
Equity securities:
Nonredeemable preferred stocks:
Financials	39		Multiple of tangible net book value		Price to book ratio multiple	1.9
Subtotal Level 3 securities	68.2
Pricing exemption securities3	0.5
Total Level 3 securities	$	68.7
1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
3The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
Due to the relative size of the 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 and comprehensive income. During 2014 or 2013, there were no material assets or liabilities measured at fair value on a nonrecurring basis.

Debt

Debt	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Debt	'
	Debt — Debt consisted of:
		30-Sep-14				30-Sep-13				31-Dec-13
	(millions)	Carrying		Fair		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value		Value		Value
	7% Notes due 2013	$	0	$	0	$	150	$	150	$	0	$	0
	3.75% Senior Notes due 2021	497.8		527.9		497.5		516.7		497.6		509.1
	6 5/8% Senior Notes due 2029	295.4		390.9		295.3		362		295.3		359.6
	6.25% Senior Notes due 2032	394.8		510.3		394.6		478.2		394.6		473.7
	4.35% Senior Notes due 2044	346.3		352.7		0		0		0		0
	6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	630		693.3		673.2		724.5		673.4		731.3
	Total	$	2,164.30	$	2,475.10	$	2,010.60	$	2,231.40	$	1,860.90	$	2,073.70
	During the third quarter 2014 and 2013, we repurchased, in the open market, $44.3 million and $54.1 million, respectively, in aggregate principal amount of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (the "6.70% Debentures"); no other debt repurchases occurred during either year. Since the amount paid exceeded the carrying value of the debt we repurchased, we recognized losses on these extinguishments of $4.8 million in 2014 and $4.3 million last year. In addition, for the portion of the 6.70% Debentures we repurchased, we reclassified $0.5 million 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 during 2014, and $0.8 million during 2013.
	In April 2014, we issued $350 million of 4.35% Senior Notes due 2044 (the “4.35% Senior Notes”).  We received proceeds of $346.3 million, after deducting underwriter’s discounts and commissions. In addition, we incurred expenses of approximately $0.7 million related to the issuance.  Upon issuance of the 4.35% Senior Notes, we closed a forecasted debt issuance hedge, which was entered into to hedge against a possible rise in interest rates, and recognized a $1.6 million pretax loss as part of accumulated other comprehensive income (loss); the loss will be recognized as an adjustment to interest expense and amortized over the life of the 4.35% Senior Notes.
	In October 2013, we retired the entire $150 million of our 7% Notes at maturity.
	During the first quarter 2014, 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. The prior line of credit, entered into in the first quarter 2013, has expired. The Line of Credit is on substantially the same terms and conditions as the prior line of credit. Subject to the terms and conditions of the Line of Credit documents, advances under the Line of Credit (if any) will bear interest at a variable rate equal to the higher of PNC's Prime Rate and the sum of the Federal Funds Open Rate plus 50 basis points. Each advance must be repaid on the 30th date after the advance or, if earlier, on March 25, 2015, the expiration date of the Line of Credit. Prepayments are permitted without penalty. All advances under the Line of Credit are subject to PNC's discretion. We had no borrowings under the Line of Credit or the prior line of credit during the first nine months of 2014 or throughout 2013.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes — At September 30, 2014 and 2013, and December 31, 2013, 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 nine months ended September 30, 2014, there have been no material changes in our uncertain tax positions or effective tax rate.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2014
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)	2014		2013
	Income taxes	$	355	$	340
	Interest	74.7		81.9

Segment_Information

Segment Information	9 Months Ended
	Sep. 30, 2014
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 predominately by small businesses in the business auto, for-hire transportation, contractor, for-hire specialty, and tow markets. 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 homeowners, general liability, and workers’ compensation insurance through our programs with unaffiliated insurance companies. All segment revenues are generated from external customers.
	Following are the operating results for the respective periods:
		Three Months Ended September 30,															Nine Months Ended September 30,
		2014							2013								2014						2013
	(millions)	Revenues				Pretax			Revenues				Pretax				Revenues			Pretax			Revenues			Pretax
						Profit							Profit							Profit						Profit
						(Loss)							(Loss)							(Loss)						(Loss)
	Personal Lines
	Agency	$	2,235.20			$	147		$	2,162.70			$	122			$	6,680.70		$	468.5		$	6,421.40		$	428.4
	Direct	1,848.90				107.6			1,693.40				107.3				5,435.10			294.3			5,020.40			360.5
	Total Personal Lines1	4,084.10				254.6			3,856.10				229.3				12,115.80			762.8			11,441.80			788.9
	Commercial Lines	456				85.1			446.8				26.3				1,340.10			204.4			1,317.30			73.7
	Other indemnity	0				0.1			0.1				(6.2		)		0			(5.3		)	0.2			(9.7		)
	Total underwriting operations	4,540.10				339.8			4,303.00				249.4				13,455.90			961.9			12,759.30			852.9
	Fees and other revenues2	75.9				NA			76				NA				223.1			NA			215.3			NA
	Service businesses	15				1.5			11.3				0.2				38.8			2.7			30.3			0.2
	Investments3	139.9				136			135.3				130.1				502.2			488.2			551.5			537
	Gains (losses) on extinguishment of debt	(4.8		)		(4.8		)	(4.3		)		(4.3		)		(4.8		)	(4.8		)	(4.3		)	(4.3		)
	Interest expense	NA				(30.7		)	NA				(30.4		)		NA			(87.0		)	NA			(91.4		)
	Consolidated total	$	4,766.10			$	441.8		$	4,521.30			$	345			$	14,215.20		$	1,361.00		$	13,552.10		$	1,294.40
	1Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in the first nine months of 2014, compared to 91% in all other periods presented; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, mobile homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
	2Pretax profit (loss) for fees and other revenues is allocated to operating segments.
	3Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.
	NA =ot Applicable
	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/combined ratios for our underwriting operations for the respective periods:
		Three Months Ended September 30,									Nine Months Ended September 30,
		2014					2013				2014					2013
		Under-writing			Combined		Under-writing		Combined		Under-writing			Combined		Under-writing			Combined
		Margin			Ratio		Margin		Ratio		Margin			Ratio		Margin			Ratio
	Personal Lines
	Agency	6.6	%		93.4		5.6	%	94.4		7	%		93		6.7	%		93.3
	Direct	5.8			94.2		6.3		93.7		5.4			94.6		7.2			92.8
	Total Personal Lines	6.2			93.8		5.9		94.1		6.3			93.7		6.9			93.1
	Commercial Lines	18.6			81.4		5.9		94.1		15.2			84.8		5.6			94.4
	Other indemnity1	NM			NM		NM		NM		NM			NM		NM			NM
	Total underwriting operations	7.5			92.5		5.8		94.2		7.1			92.9		6.7			93.3
	1Underwriting margins and combined ratios are not meaningful (NM) for our other indemnity businesses due to the low level of premiums earned by, and the variability of loss costs in, such businesses.

Dividends

Dividends	9 Months Ended
	Sep. 30, 2014
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 multiplied by a performance factor (“Gainshare factor”), 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 2013, the Board determined the target percentage for 2014 to be 33-1/3% of annual after-tax underwriting income, which is unchanged from the 2013 target percentage.
	The Gainshare factor can range from zero to two and is determined by comparing our core insurance operating performance 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 recalibrated every year, the structure of the Gainsharing program generally remains the same. On a year-to-date basis, as of September 30, 2014, the Gainshare factor was 1.38. 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. However, the ultimate decision on whether or not a dividend will be paid is in the discretion of the Board of Directors. If a dividend for 2014 were to be paid, the Board would likely declare the 2014 annual dividend in December 2014, with a record date in January 2015 and payment shortly thereafter. For the nine months ended September 30, 2014, our comprehensive income was $931.8 million, which is higher than the $625.2 million of after-tax underwriting income for the same period.
	We paid dividends per common share of $.4929 and $.2845 in February 2014 and 2013, respectively, under our annual variable dividend policy. These dividends were paid pursuant to declarations made by the Board of Directors in December 2013 and 2012, respectively. In addition to the annual variable dividend, the Board of Directors declared a $1.00 per common share special dividend in December 2013, which was paid in February 2014.

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Other Comprehensive Income (Loss)	'
	Other Comprehensive Income (Loss) — The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows:
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions1,3
	Balance at June 30, 2014	$	1,598.20		$	(559.3	)	$	1,038.90		$	1,035.30		$	2.5		$	1.1
	Other comprehensive income (loss) before reclassifications:
	Investment securities	(62.5		)	21.9			(40.6		)	(40.6		)	0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	(.5		)	0.1			(.4		)	0			0			(.4		)
	Total other comprehensive income (loss) before reclassifications	(63.0		)	22			(41.0		)	(40.6		)	0			(.4		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(.1		)	0			(.1		)	(.1		)	0			0
	Net realized gains (losses) on securities2	38.3			(13.4		)	24.9			24.6			0.3			0
	Interest expense3	0.5			(.1		)	0.4			0			0.4			0
	Total reclassification adjustment for amounts realized in net income	38.7			(13.5		)	25.2			24.5			0.7			0
	Total other comprehensive income (loss)	(101.7		)	35.5			(66.2		)	(65.1		)	(.7		)	(.4		)
	Balance at September 30, 2014	$	1,496.50		$	(523.8	)	$	972.7		$	970.2		$	1.8		$	0.7
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions1,3
	Balance at December 31, 2013	$	1,464.10		$	(512.4	)	$	951.7		$	947		$	4.1		$	0.6
	Other comprehensive income (loss) before reclassifications:
	Investment securities	258.2			(90.3		)	167.9			167.9			0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	(1.6		)	0.6			(1.0		)	0			(1.0		)	0
	Foreign currency translation adjustment	0.3			(.2		)	0.1			0			0			0.1
	Total other comprehensive income (loss) before reclassifications	256.9			(89.9		)	167			167.9			(1.0		)	0.1
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(.1		)	0			(.1		)	(.1		)	0			0
	Net realized gains (losses) on securities2	223.1			(78.0		)	145.1			144.8			0.3			0
	Interest expense3	1.5			(.5		)	1			0			1			0
	Total reclassification adjustment for amounts realized in net income	224.5			(78.5		)	146			144.7			1.3			0
	Total other comprehensive income (loss)	32.4			(11.4		)	21			23.2			(2.3		)	0.1
	Balance at September 30, 2014	$	1,496.50		$	(523.8	)	$	972.7		$	970.2		$	1.8		$	0.7
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions1
	Balance at June 30, 2013	$	1,252.60		$	(438.4	)	$	814.2		$	807.6		$	5.4		$	1.2
	Other comprehensive income (loss) before reclassifications:
	Investment securities	111.9			(39.2		)	72.7			72.7			0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	(.4		)	0.2			(.2		)	0			0			(.2		)
	Total other comprehensive income (loss) before reclassifications	111.5			(39.0		)	72.5			72.7			0			(.2		)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net impairment losses recognized in earnings	(1.9		)	0.7			(1.2		)	(1.2		)	0			0
Net realized gains (losses) on securities2	25.6			(9.0		)	16.6			16.1			0.5			0
Interest expense	0.6			(.2		)	0.4			0			0.4			0
Total reclassification adjustment for amounts realized in net income	24.3			(8.5		)	15.8			14.9			0.9			0
Total other comprehensive income (loss)	87.2			(30.5		)	56.7			57.8			(.9		)	(.2		)
Balance at September 30, 2013	$	1,339.80		$	(468.9	)	$	870.9		$	865.4		$	4.5		$	1
										Components of Changes in
										Accumulated Other
										Comprehensive Income (after tax)
(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
	accumulated			(provision)			accumulated			unrealized			unrealized			currency
	other			benefit			other			gains (losses)			gains on			translation
	comprehensive						comprehensive			on securities			forecasted			adjustment
	income						income						transactions1
Balance at December 31, 2012	$	1,340.00		$	(469.0	)	$	871		$	862.7		$	6.1		$	2.2
Other comprehensive income (loss) before reclassifications:
Investment securities	192.6			(67.4		)	125.2			125.2			0			0
Net non-credit related OTTI losses, adjusted for	0.4			(.1		)	0.3			0.3			0			0
valuation changes
Forecasted transactions	0			0			0			0			0			0
Foreign currency translation adjustment	(1.9		)	0.7			(1.2		)	0			0			(1.2		)
Total other comprehensive income (loss) before reclassifications	191.1			(66.8		)	124.3			125.5			0			(1.2		)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net impairment losses recognized in earnings	(3.5		)	1.3			(2.2		)	(2.2		)	0			0
Net realized gains (losses) on securities2	193.2			(67.7		)	125.5			125			0.5			0
Interest expense	1.6			(.5		)	1.1			0			1.1			0
Total reclassification adjustment for amounts realized in net income	191.3			(66.9		)	124.4			122.8			1.6			0
Total other comprehensive income (loss)	(.2		)	0.1			(.1		)	2.7			(1.6		)	(1.2		)
Balance at September 30, 2013	$	1,339.80		$	(468.9	)	$	870.9		$	865.4		$	4.5		$	1
1Entered into for the purpose of managing interest rate risk associated with our debt issuances.
2During both the third quarter and first nine months of 2014, we reclassified $0.5 million, on a pretax basis, from accumulated other comprehensive income on the balance sheet to net realized gains on securities on the comprehensive income statement, reflecting the portion of the unrealized gain on forecasted transactions that was related to the portion of the 6.70% Debentures repurchased during the period, compared to $0.8 million during the third quarter and first nine months of 2013 (see Note 4 - Debt for further discussion).
3We expect to reclassify $2.0 million (pretax) into income during the next 12 months, related to the net unrealized gains on forecasted transactions.

Litigation

Litigation	9 Months Ended
	Sep. 30, 2014
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, 2014. 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 range of loss, if any, at this time, due to the factors discussed in Note 12 - Litigation in our Annual Report to Shareholders for the year ended December 31, 2013, which is included as Exhibit 13 to our Annual Report on Form 10-K ( the "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 to our consolidated financial statements in our Annual Report to Shareholders.

New_Accounting_Standard

New Accounting Standard	9 Months Ended
	Sep. 30, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
New Accounting Standard	'
	New Accounting Standards — In May 2014, the Financial Accounting Standards Board (FASB) issued an accounting standard update (ASU) related to the accounting for revenue from contracts with customers. This standard is intended to help reduce diversity in practice and enhance comparability between entities related to revenue recognition and is effective for fiscal years beginning after December 15, 2016 (2017 for calendar-year companies). Since the accounting for insurance contracts is outside of the scope of this ASU, we do not expect this standard to have a significant impact on our financial condition, cash flows, and results of operations.
	In June 2014, the FASB issued an ASU 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 the equity awards contain provisions that permit employees who leave the company before the performance targets are reached and the awards later vest,  to receive some or all of the benefits of the award, this standard requires companies to recognize the compensation cost during the employees' remaining service period. This standard is effective for fiscal years beginning after December 15, 2015 (2016 for calendar-year companies). We plan to adopt this standard prospectively.  Although this standard may require an acceleration of the expense recognition of our share-based payment awards, we do not expect it to have a significant impact on our financial condition, cash flows, and results of operations.
	In June 2014, the FASB also issued an ASU related to repurchase-to-maturity transactions, repurchase financings, and related disclosures. The intent is to clarify that repurchase-to-maturity transactions should be accounted for and disclosed as secured borrowings, rather than potentially accounted for as sales, as permissible under certain circumstances in the previous guidance. This guidance is effective for annual and interim periods after December 15, 2014 (2015 for calendar-year companies). We do not typically engage in these type of transactions; therefore, we do not expect this standard to have a significant impact on our financial condition, cash flows, and results of operations.

Investments_Tables

Investments (Tables)	9 Months Ended
	Sep. 30, 2014
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:
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	30-Sep-14
	Fixed maturities:
	U.S. government obligations	$	3,033.20			$	33.6			$	(3.9	)		$	0			$	3,062.90		16	%
	State and local government obligations	2,124.20				49.5				(.9		)		0				2,172.80			11.4
	Foreign government obligations	20.2				0				0				0				20.2			0.1
	Corporate debt securities	2,501.80				30.7				(13.1		)		(.3		)		2,519.10			13.2
	Residential mortgage-backed securities	1,460.60				36.9				(10.1		)		(.9		)		1,486.50			7.8
	Commercial mortgage-backed securities	2,143.80				33.8				(5.1		)		0				2,172.50			11.4
	Other asset-backed securities	1,546.00				5				(.6		)		0.2				1,550.60			8.1
	Redeemable preferred stocks	260.2				28.8				(4.2		)		0				284.8			1.5
	Total fixed maturities	13,090.00				218.3				(37.9		)		(1.0		)		13,269.40			69.5
	Equity securities:
	Nonredeemable preferred stocks	532.8				218.4				(7.2		)		19.3				763.3			4
	Common equities	1,278.40				1,107.70				(6.7		)		0				2,379.40			12.5
	Short-term investments:
	Other short-term investments	2,671.10				0				0				0				2,671.10			14
	Total portfolio2,3	$	17,572.30			$	1,544.40			$	(51.8	)		$	18.3			$	19,083.20		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	30-Sep-13
	Fixed maturities:
	U.S. government obligations	$	3,691.20			$	61.8			$	(11.3	)		$	0			$	3,741.70		20.8	%
	State and local government obligations	2,125.70				29.9				(17.0		)		0				2,138.60			11.9
	Foreign government obligations	15.9				0				0				0				15.9			0.1
	Corporate debt securities	3,118.80				67				(28.9		)		0.7				3,157.60			17.6
	Residential mortgage-backed securities	994.9				31.5				(16.5		)		0				1,009.90			5.6
	Commercial mortgage-backed securities	2,224.10				49				(33.1		)		0				2,240.00			12.4
	Other asset-backed securities	1,143.30				7.4				(2.0		)		0.2				1,148.90			6.4
	Redeemable preferred stocks	331				24.5				(10.4		)		0				345.1			1.9
	Total fixed maturities	13,644.90				271.1				(119.2		)		0.9				13,797.70			76.7
	Equity securities:
	Nonredeemable preferred stocks	442.1				280.5				(4.8		)		8.2				726			4
	Common equities	1,422.30				908.8				(5.0		)		0				2,326.10			12.9
	Short-term investments:
	Other short-term investments	1,146.10				0				0				0				1,146.10			6.4
	Total portfolio2,3	$	16,655.40			$	1,460.40			$	(129.0	)		$	9.1			$	17,995.90		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	$	3,630.40			$	48.4			$	(16.6	)		$	0			$	3,662.20		20.3	%
	State and local government obligations	2,247.30				27.1				(18.4		)		0				2,256.00			12.5
	Foreign government obligations	15.6				0				0				0				15.6			0.1
	Corporate debt securities	2,885.00				60.4				(20.4		)		1.6				2,926.60			16.2
	Residential mortgage-backed securities	1,110.10				31.9				(14.1		)		0				1,127.90			6.2
	Commercial mortgage-backed securities	2,154.40				43.9				(37.8		)		0				2,160.50			12
	Other asset-backed securities	1,073.00				6.6				(2.1		)		0.2				1,077.70			6
	Redeemable preferred stocks	299.5				24.1				(9.7		)		0				313.9			1.7
	Total fixed maturities	13,415.30				242.4				(119.1		)		1.8				13,540.40			75
	Equity securities:
	Nonredeemable preferred stocks	445.7				258.7				(4.5		)		11.3				711.2			3.9
	Common equities	1,451.10				1,081.80				(2.4		)		0				2,530.50			14
	Short-term investments:
	Other short-term investments	1,272.60				0				0				0				1,272.60			7.1
Total portfolio2,3	$	16,584.70			$	1,582.90			$	(126.0	)		$	13.1			$	18,054.70		100	%
1Represents net holding period gains (losses) on certain hybrid securities (discussed below).
2Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.
3The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 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)	2014				2013				2013
	Fixed maturities:
	Corporate debt securities	$	138.5			$	171.8			$	164.2
	Residential mortgage-backed securities	116.8				0				0
	Other asset-backed securities	13.5				15.3				14.8
	Total fixed maturities	268.8				187.1				179
	Equity securities:
	Nonredeemable preferred stocks	93.4				57.3				60.3
	Total hybrid securities	$	362.2			$	244.4			$	239.3
Composition of Fixed Maturities by Maturity	'
	The composition of fixed maturities by maturity at September 30, 2014, was:
	(millions)	Cost				Fair Value
	Less than one year	$	2,472.70			$	2,506.70
	One to five years	7,571.80				7,672.20
	Five to ten years	2,938.80				2,976.10
	Ten years or greater	69.7				77.4
	Total1	$	13,053.00			$	13,232.40
	1Excludes $37.0 million related to our open interest rate swap positions.
Gross Unrealized Losses by Major Security	'
	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position:
		Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
				Fair
	($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
												Value								Value
	30-Sep-14
	Fixed maturities:
	U.S. government obligations	19		$	627		$	(3.9	)	9		$	211		$	(.7	)		10	$	416		$	(3.2	)
	State and local government obligations	31		181.8			(.9		)	11		89.7			(.1		)		20	92.1			(.8		)
	Corporate debt securities	50		891.4			(13.1		)	42		744.5			(9.7		)		8	146.9			(3.4		)
	Residential mortgage-backed securities	62		725.8			(10.1		)	24		290.5			(1.8		)		38	435.3			(8.3		)
	Commercial mortgage-backed securities	72		894.5			(5.1		)	61		787.3			(2.9		)		11	107.2			(2.2		)
	Other asset-backed securities	38		650.8			(.6		)	36		624.7			(.4		)		2	26.1			(.2		)
	Redeemable preferred stocks	2		70.5			(4.2		)	0		0			0				2	70.5			(4.2		)
	Total fixed maturities	274		4,041.80			(37.9		)	183		2,747.70			(15.6		)		91	1,294.10			(22.3		)
	Equity securities:
	Nonredeemable preferred stocks	7		206.3			(7.2		)	4		118.6			(4.0		)		3	87.7			(3.2		)
	Common equities	39		57.5			(6.7		)	37		45.7			(5.4		)		2	11.8			(1.3		)
	Total equity securities	46		263.8			(13.9		)	41		164.3			(9.4		)		5	99.5			(4.5		)
	Total portfolio	320		$	4,305.60		$	(51.8	)	224		$	2,912.00		$	(25.0	)		96	$	1,393.60		$	(26.8	)
		Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
				Fair
	($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
												Value								Value
	30-Sep-13
	Fixed maturities:
	U.S. government obligations	18		$	969.1		$	(11.3	)	18		$	969.1		$	(11.3	)		0	$	0		$	0
	State and local government obligations	126		728.3			(17.0		)	108		666.7			(16.2		)		18	61.6			(.8		)
	Corporate debt securities	63		1,174.20			(28.9		)	61		1,113.40			(28.5		)		2	60.8			(.4		)
	Residential mortgage-backed securities	63		663			(16.5		)	49		585.5			(12.4		)		14	77.5			(4.1		)
	Commercial mortgage-backed securities	67		993.3			(33.1		)	64		993.2			(33.0		)		3	0.1			(.1		)
	Other asset-backed securities	22		282.8			(2.0		)	22		282.8			(2.0		)		0	0			0
	Redeemable preferred stocks	6		158.4			(10.4		)	2		36.2			(.2		)		4	122.2			(10.2		)
	Total fixed maturities	365		4,969.10			(119.2		)	324		4,646.90			(103.6		)		41	322.2			(15.6		)
	Equity securities:
	Nonredeemable preferred stocks	7		123.6			(4.8		)	7		123.6			(4.8		)		0	0			0
	Common equities	26		47.3			(5.0		)	21		43			(4.7		)		5	4.3			(.3		)
	Total equity securities	33		170.9			(9.8		)	28		166.6			(9.5		)		5	4.3			(.3		)
	Total portfolio	398		$	5,140.00		$	(129.0	)	352		$	4,813.50		$	(113.1	)		46	$	326.5		$	(15.9	)
		Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
				Fair
	($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
												Value								Value
	31-Dec-13
	Fixed maturities:
	U.S. government obligations	29		$	1,444.30		$	(16.6	)	28		$	1,434.60		$	(16.3	)		1	$	9.7		$	(.3	)
	State and local government obligations	141		844.2			(18.4		)	119		759.3			(17.1		)		22	84.9			(1.3		)
	Corporate debt securities	51		997.6			(20.4		)	45		831.1			(17.8		)		6	166.5			(2.6		)
	Residential mortgage-backed securities	66		763.5			(14.1		)	45		597.6			(7.9		)		21	165.9			(6.2		)
	Commercial mortgage-backed securities	76		1,061.90			(37.8		)	60		809.2			(19.7		)		16	252.7			(18.1		)
	Other asset-backed securities	25		287.2			(2.1		)	22		233.3			(1.8		)		3	53.9			(.3		)
	Redeemable preferred stocks	4		122.7			(9.7		)	0		0			0				4	122.7			(9.7		)
	Total fixed maturities	392		5,521.40			(119.1		)	319		4,665.10			(80.6		)		73	856.3			(38.5		)
	Equity securities:
	Nonredeemable preferred stocks	7		142.3			(4.5		)	7		142.3			(4.5		)		0	0			0
	Common equities	24		59.7			(2.4		)	20		58.5			(2.4		)		4	1.2			0
	Total equity securities	31		202			(6.9		)	27		200.8			(6.9		)		4	1.2			0
	Total portfolio	423		$	5,723.40		$	(126.0	)	346		$	4,865.90		$	(87.5	)		77	$	857.5		$	(38.5	)
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 losses 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)	2014				2013				2013
	Fixed maturities:
	Residential mortgage-backed securities	$	(44.1	)		$	(44.1	)		$	(44.1	)
	Commercial mortgage-backed securities	(.6		)		(.9		)		(.9		)
	Total fixed maturities	$	(44.7	)		$	(45.0	)		$	(45.0	)
OTTI Credit Losses Recognized in Earnings	'
	The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended September 30, 2014 and 2013, 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, 2014
		Mortgage-Backed
	(millions)	Residential				Commercial				Total
	Balance at June 30, 2014	$	13			$	0.4			$	13.4
	Reductions for securities sold/matured	(.1		)		0				(.1		)
	Change in recoveries of future cash flows expected to be collected1	0.1				0				0.1
	Reductions for previously recognized credit impairments written-down to fair value2	0				0				0
	Balance at September 30, 2014	$	13			$	0.4			$	13.4
		Nine Months Ended September 30, 2014
		Mortgage-Backed
	(millions)	Residential				Commercial				Total
	Balance at December 31, 2013	$	19.2			$	0.4			$	19.6
	Reductions for securities sold/matured	(.1		)		0				(.1		)
	Change in recoveries of future cash flows expected to be collected1	(6.1		)		0				(6.1		)
	Reductions for previously recognized credit impairments written-down to fair value2	0				0				0
	Balance at September 30, 2014	$	13			$	0.4			$	13.4
		Three Months Ended September 30, 2013
		Mortgage-Backed
	(millions)	Residential				Commercial				Total
	Balance at June 30, 2013	$	26.9			$	0.5			$	27.4
	Reductions for securities sold/matured	0				0				0
	Change in recoveries of future cash flows expected to be collected1	(2.4		)		(.1		)		(2.5		)
	Reductions for previously recognized credit impairments written-down to fair value2	0				0				0
	Balance at September 30, 2013	$	24.5			$	0.4			$	24.9
		Nine Months Ended September 30, 2013
		Mortgage-Backed
	(millions)	Residential				Commercial				Total
	Balance at December 31, 2012	$	27.1			$	0.6			$	27.7
	Reductions for securities sold/matured	0				0				0
	Change in recoveries of future cash flows expected to be collected1	(2.4		)		(.2		)		(2.6		)
	Reductions for previously recognized credit impairments written-down to fair value2	(.2		)		0				(.2		)
	Balance at September 30, 2013	$	24.5			$	0.4			$	24.9
	1Reflects the current period change in the expected recovery of prior impairments that will be accreted into income over the remaining life of the security.
	2Reflects reductions of prior credit impairments where the current credit impairment requires writing securities down to fair value (i.e., no remaining non-credit loss).
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)	2014				2013				2014				2013
	Gross realized gains on security sales
	Fixed maturities:
	U.S. government obligations	$	2.5			$	3.1			$	13.2			$	6.8
	State and local government obligations	3.8				0				8.2				6.8
	Corporate and other debt securities	0.9				1.7				33.8				38.4
	Residential mortgage-backed securities	0.2				0.3				2.2				2.4
	Commercial mortgage-backed securities	5.2				0.1				14.8				8.4
	Redeemable preferred stocks	2.3				0				2.7				0
	Total fixed maturities	14.9				5.2				74.9				62.8
	Equity securities:
	Nonredeemable preferred stocks	20.9				11.9				80				113.1
	Common equities	4.6				11.1				97				26.1
	Subtotal gross realized gains on security sales	40.4				28.2				251.9				202
	Gross realized losses on security sales
	Fixed maturities:
	U.S. government obligations	(1.3		)		(.8		)		(6.4		)		(2.2		)
	State and local government obligations	(.3		)		0				(.5		)		0
	Corporate and other debt securities	0				(2.1		)		(2.3		)		(3.1		)
	Residential mortgage-backed securities	0				0				(.2		)		0
	Commercial mortgage-backed securities	(1.4		)		0				(8.2		)		(.7		)
	Redeemable preferred stocks	0				0				(3.2		)		(.1		)
	Total fixed maturities	(3.0		)		(2.9		)		(20.8		)		(6.1		)
	Equity securities:
	Common equities	0				(.1		)		(3.4		)		(.4		)
	Subtotal gross realized losses on security sales	(3.0		)		(3.0		)		(24.2		)		(6.5		)
	Net realized gains (losses) on security sales
	Fixed maturities:
	U.S. government obligations	1.2				2.3				6.8				4.6
	State and local government obligations	3.5				0				7.7				6.8
	Corporate and other debt securities	0.9				(.4		)		31.5				35.3
	Residential mortgage-backed securities	0.2				0.3				2				2.4
	Commercial mortgage-backed securities	3.8				0.1				6.6				7.7
	Redeemable preferred stocks	2.3				0				(.5		)		(.1		)
	Total fixed maturities	11.9				2.3				54.1				56.7
	Equity securities:
	Nonredeemable preferred stocks	20.9				11.9				80				113.1
	Common equities	4.6				11				93.6				25.7
	Subtotal net realized gains (losses) on security sales	37.4				25.2				227.7				195.5
	Other-than-temporary impairment losses
	Fixed maturities:
	Residential mortgage-backed securities	0				(.1		)		0				(.5		)
	Total fixed maturities	0				(.1		)		0				(.5		)
	Equity securities:
	Common equities	(.1		)		(1.8		)		(.1		)		(3.2		)
	Subtotal other-than-temporary impairment losses	(.1		)		(1.9		)		(.1		)		(3.7		)
	Other gains (losses)
	Hybrid securities	(1.8		)		3.5				5.7				2.3
	Derivative instruments	(.7		)		(1.2		)		(39.9		)		45
	Litigation settlements	3.4				2.3				4.6				2.3
	Subtotal other gains (losses)	0.9				4.6				(29.6		)		49.6
	Total net realized gains (losses) on securities	$	38.2			$	27.9			$	198			$	241.4
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)	2014			2013				2014			2013
	Fixed maturities:
	U.S. government obligations	$	11.3		$	12.9			$	36.3		$	36.8
	State and local government obligations	12.8			12.3				38.2			34.8
	Foreign government obligations	0.1			0.1				0.3			0.1
	Corporate debt securities	19.5			24.3				60.3			74.1
	Residential mortgage-backed securities	11.3			7.9				32.5			18.1
	Commercial mortgage-backed securities	16.5			19.1				49.2			55.9
	Other asset-backed securities	4.2			4.5				12.1			12.2
	Redeemable preferred stocks	3.7			5.5				11.7			16.3
	Total fixed maturities	79.4			86.6				240.6			248.3
	Equity securities:
	Nonredeemable preferred stocks	9.4			9.2				28.6			27.3
	Common equities	12.5			11.3				34.1			32.8
	Short-term investments:
	Other short-term investments	0.4			0.3				0.9			1.7
	Investment income	101.7			107.4				304.2			310.1
	Investment expenses	(3.9		)	(5.2		)		(14.0		)	(14.5		)
	Net investment income	$	97.8		$	102.2			$	290.2		$	295.6
Derivative Instruments	'
	The following table shows the status of our derivative instruments at September 30, 2014 and 2013, and December 31, 2013, and for the three and nine months ended September 30, 2014 and 2013; amounts are on a pretax basis:
	(millions)															Balance Sheet2											Comprehensive Income Statement
																		Assets (Liabilities)									Net Realized
																		Fair Value									Gains (Losses) on Securities
		Notional Value1																									Three Months Ended						Nine Months Ended
		September 30,								Dec. 31,								September 30,							Dec. 31,		September 30,						September 30,
	Derivatives designated as:	2014				2013				2013				Purpose		Classification		2014			2013				2013		2014			2013			2014			2013
	Hedging instruments
	Closed:
	Ineffective cash flow hedge	$	44			$	54			$	54			Manage interest		NA		$	0		$	0			$	0	$	0.5		$	0.8		$	0.5		$	0.8
														rate risk
	Non-hedging instruments
	Assets:
	Interest rate swaps	750				750				750				Manage portfolio		Investments—		37			53.5				68.1		(1.2		)	(2.0		)	(40.4		)	48.2
														duration		fixed maturities
	Closed:
	Interest rate swaps	0				1,263				1,263				Manage portfolio		NA		0			0				0		0			0			0			(4.0		)
														duration
	Total	NA				NA				NA								$	37		$	53.5			$	68.1	$	(.7	)	$	(1.2	)	$	(39.9	)	$	45
	1The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions.
	2To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we report them on a gross basis on our balance sheets, consistent with our historical presentation.
	NA=ot Applicable

Fair_Value_Tables

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2014
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
	30-Sep-14
	Fixed maturities:
	U.S. government obligations	$	3,062.90	$	0		$	0	$	3,062.90		$	3,033.20
	State and local government obligations	0		2,172.80			0		2,172.80			2,124.20
	Foreign government obligations	20.2		0			0		20.2			20.2
	Corporate debt securities	0		2,519.10			0		2,519.10			2,501.80
	Subtotal	3,083.10		4,691.90			0		7,775.00			7,679.40
	Asset-backed securities:
	Residential mortgage-backed	0		1,486.50			0		1,486.50			1,460.60
	Commercial mortgage-backed	0		2,160.00			12.5		2,172.50			2,143.80
	Other asset-backed	0		1,550.60			0		1,550.60			1,546.00
	Subtotal asset-backed securities	0		5,197.10			12.5		5,209.60			5,150.40
	Redeemable preferred stocks:
	Financials	0		100.3			0		100.3			77.3
	Utilities	0		65.3			0		65.3			65
	Industrials	0		119.2			0		119.2			117.9
	Subtotal redeemable preferred stocks	0		284.8			0		284.8			260.2
	Total fixed maturities	3,083.10		10,173.80			12.5		13,269.40			13,090.00
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	220		496.6			46.7		763.3			532.8
	Utilities	0		0			0		0			0
	Subtotal nonredeemable preferred stocks	220		496.6			46.7		763.3			532.8
	Common equities:
	Common stocks	2,379.00		0			0		2,379.00			1,278.00
	Other risk investments	0		0			0.4		0.4			0.4
	Subtotal common equities	2,379.00		0			0.4		2,379.40			1,278.40
	Total fixed maturities and equity securities	5,682.10		10,670.40			59.6		16,412.10			14,901.20
	Short-term investments:
	Other short-term investments	2,393.70		277.4			0		2,671.10			2,671.10
	Total portfolio	$	8,075.80	$	10,947.80		$	59.6	$	19,083.20		$	17,572.30
	Debt	$	0	$	2,475.10		$	0	$	2,475.10		$	2,164.30
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total			Cost
	30-Sep-13
	Fixed maturities:
	U.S. government obligations	$	3,741.70	$	0		$	0	$	3,741.70		$	3,691.20
	State and local government obligations	0		2,138.60			0		2,138.60			2,125.70
	Foreign government obligations	15.9		0			0		15.9			15.9
	Corporate debt securities	0		3,157.60			0		3,157.60			3,118.80
	Subtotal	3,757.60		5,296.20			0		9,053.80			8,951.60
	Asset-backed securities:
	Residential mortgage-backed	0		1,009.70			0.2		1,009.90			994.9
	Commercial mortgage-backed	0		2,208.70			31.3		2,240.00			2,224.10
	Other asset-backed	0		1,148.90			0		1,148.90			1,143.30
	Subtotal asset-backed securities	0		4,367.30			31.5		4,398.80			4,362.30
	Redeemable preferred stocks:
	Financials	0		134.2			0		134.2			115.7
	Utilities	0		65.3			0		65.3			64.9
	Industrials	0		145.6			0		145.6			150.4
	Subtotal redeemable preferred stocks	0		345.1			0		345.1			331
	Total fixed maturities	3,757.60		10,008.60			31.5		13,797.70			13,644.90
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	244		429.1			36.1		709.2			427.9
	Utilities	0		16.8			0		16.8			14.2
	Subtotal nonredeemable preferred stocks	244		445.9			36.1		726			442.1
	Common equities:
	Common stocks	2,287.40		0			0		2,287.40			1,419.20
	Other risk investments	0		0			38.7		38.7			3.1
Subtotal common equities	2,287.40		0			38.7		2,326.10			1,422.30
Total fixed maturities and equity securities	6,289.00		10,454.50			106.3		16,849.80			15,509.30
Short-term investments:
Other short-term investments	751.5		394.6			0		1,146.10			1,146.10
Total portfolio	$	7,040.50	$	10,849.10		$	106.3	$	17,995.90		$	16,655.40
Debt	$	0	$	2,231.40		$	0	$	2,231.40		$	2,010.60
	Fair Value
(millions)	Level 1		Level 2			Level 3		Total			Cost
31-Dec-13
Fixed maturities:
U.S. government obligations	$	3,662.20	$	0		$	0	$	3,662.20		$	3,630.40
State and local government obligations	0		2,256.00			0		2,256.00			2,247.30
Foreign government obligations	15.6		0			0		15.6			15.6
Corporate debt securities	0		2,926.60			0		2,926.60			2,885.00
Subtotal	3,677.80		5,182.60			0		8,860.40			8,778.30
Asset-backed securities:
Residential mortgage-backed	0		1,127.70			0.2		1,127.90			1,110.10
Commercial mortgage-backed	0		2,131.50			29		2,160.50			2,154.40
Other asset-backed	0		1,077.70			0		1,077.70			1,073.00
Subtotal asset-backed securities	0		4,336.90			29.2		4,366.10			4,337.50
Redeemable preferred stocks:
Financials	0		102.8			0		102.8			84.2
Utilities	0		65.6			0		65.6			64.9
Industrials	0		145.5			0		145.5			150.4
Subtotal redeemable preferred stocks	0		313.9			0		313.9			299.5
Total fixed maturities	3,677.80		9,833.40			29.2		13,540.40			13,415.30
Equity securities:
Nonredeemable preferred stocks:
Financials	240.8		414.6			39		694.4			431.5
Utilities	0		16.8			0		16.8			14.2
Subtotal nonredeemable preferred stocks	240.8		431.4			39		711.2			445.7
Common equities:
Common stocks	2,530.00		0			0		2,530.00			1,450.60
Other risk investments	0		0			0.5		0.5			0.5
Subtotal common equities	2,530.00		0			0.5		2,530.50			1,451.10
Total fixed maturities and equity securities	6,448.60		10,264.80			68.7		16,782.10			15,312.10
Short-term investments:
Other short-term investments	987.8		284.8			0		1,272.60			1,272.60
Total portfolio	$	7,436.40	$	10,549.60		$	68.7	$	18,054.70		$	16,584.70
Debt	$	0	$	2,073.70		$	0	$	2,073.70		$	1,860.90
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, 2014 and 2013:
		Level 3 Fair Value
		Three Months Ended September 30, 2014
	(millions)	Fair Value at June 30, 2014		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in Valuation			Net			Fair Value at Sept. 30, 2014
				Maturities/														Transfers
				Paydowns														In (Out)1
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0	$	0		$	0	$	0		$	0		$	0		$	0		$	0
	Commercial mortgage-backed	27.6		(1.2		)	0		0			0			(.3		)	(13.6		)	12.5
	Total fixed maturities	27.6		(1.2		)	0		0			0			(.3		)	(13.6		)	12.5
	Equity securities:
	Nonredeemable preferred stocks:
	Financials2	43.8		0			0		0			0			2.9			0			46.7
	Common equities:
	Other risk investments	0.5		(.1		)	0		0			0			0			0			0.4
	Total Level 3 securities	$	71.9	$	(1.3	)	$	0	$	0		$	0		$	2.6		$	(13.6	)	$	59.6
	1The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
	2The $2.9 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
		Level 3 Fair Value
		Nine Months Ended September 30, 2014
	(millions)	Fair Value at Dec. 31, 2013		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in Valuation			Net			Fair Value at Sept. 30, 2014
				Maturities/														Transfers
				Paydowns														In (Out)1
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0.2	$	0		$	0	$	(.1	)	$	0.1		$	(.2	)	$	0		$	0
	Commercial mortgage-backed	29		(3.0		)	0		0			0			0.1			(13.6		)	12.5
	Total fixed maturities	29.2		(3.0		)	0		(.1		)	0.1			(.1		)	(13.6		)	12.5
	Equity securities:
	Nonredeemable preferred stocks:
	Financials2	39		0			0		0			0			7.7			0			46.7
	Common equities:
	Other risk investments	0.5		(.1		)	0		0			0			0			0			0.4
	Total Level 3 securities	$	68.7	$	(3.1	)	$	0	$	(.1	)	$	0.1		$	7.6		$	(13.6	)	$	59.6
	1The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
	2The $7.7 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
		Level 3 Fair Value
		Three Months Ended September 30, 2013
	(millions)	Fair Value at June 30, 2013		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in			Net			Fair Value at Sept. 30, 2013
				Maturities/											Valuation			Transfers
				Paydowns														In (Out)1
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	157.1	$	(17.0	)	$	0	$	0		$	0		$	1.5		$	(141.4	)	$	0.2
	Commercial mortgage-backed	27.6		(.3		)	0		0			0			4			0			31.3
	Total fixed maturities	184.7		(17.3		)	0		0			0			5.5			(141.4		)	31.5
	Equity securities:
	Nonredeemable preferred stocks:
	Financials2	34.8		0			0		0			0			1.3			0			36.1
	Common equities:
	Other risk investments	38.7		0			0		0			0			0			0			38.7
	Total Level 3 securities	$	258.2	$	(17.3	)	$	0	$	0		$	0		$	6.8		$	(141.4	)	$	106.3
	1The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
	2The $1.3 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
		Level 3 Fair Value
		Nine Months Ended September 30, 2013
	(millions)	Fair Value at Dec. 31, 2012		Calls/			Purchases		Sales			Net Realized (Gain) Loss on Sales			Change in			Net			Fair Value at Sept. 30, 2013
				Maturities/											Valuation			Transfers
				Paydowns														In (Out)1
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	45.5	$	(28.6	)	$	125.1	$	0		$	0		$	(.4	)	$	(141.4	)	$	0.2
Commercial mortgage-backed	25.3		(1.1		)	0		0			0			7.1			0			31.3
Total fixed maturities	70.8		(29.7		)	125.1		0			0			6.7			(141.4		)	31.5
Equity securities:
Nonredeemable preferred stocks:
Financials2	31.9		0			0		0			0			4.2			0			36.1
Common equities:
Other risk investments	12		(.1		)	0.3		0			(.5		)	27			0			38.7
Total Level 3 securities	$	114.7	$	(29.8	)	$	125.4	$	0		$	(.5	)	$	37.9		$	(141.4	)	$	106.3
1The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
2The $4.2 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
Summary of Quantitative Information about Level 3 Fair Value Measurements	'
	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at September 30, 2014 and 2013, and December 31, 2013:
		Quantitative Information about Level 3 Fair Value Measurements
	($ in millions)	Fair Value at Sept. 30, 2014		Valuation Technique		Unobservable Input	Unobservable
							Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0
	Commercial mortgage-backed	12.5		External vendor		Prepayment rate1	0
	Total fixed maturities	12.5
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	46.7		Multiple of tangible net book value		Price to book ratio multiple	1.9
	Subtotal Level 3 securities	59.2
	Pricing exemption securities2	0.4
	Total Level 3 securities	$	59.6
	1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
		Quantitative Information about Level 3 Fair Value Measurements
	($ in millions)	Fair Value at Sept. 30, 2013		Valuation Technique		Unobservable Input	Unobservable
							Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0.2	External vendor		Prepayment rate1	0
	Commercial mortgage-backed	31.3		External vendor		Prepayment rate2	0
	Total fixed maturities	31.5
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	36.1		Multiple of tangible net book value		Price to book ratio multiple	1.9
	Subtotal Level 3 securities	67.6
	Pricing exemption securities3	38.7
	Total Level 3 securities	$	106.3
	1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	3The fair values for $0.7 million of these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us. The remaining $38.0 million reflects a negotiated sale on a private common equity security that was completed by the end of 2013.
		Quantitative Information about Level 3 Fair Value Measurements
	($ in millions)	Fair Value at Dec. 31, 2013		Valuation Technique		Unobservable Input	Unobservable
							Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0.2	External vendor		Prepayment rate1	0
	Commercial mortgage-backed	29		External vendor		Prepayment rate2	0
	Total fixed maturities	29.2
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	39		Multiple of tangible net book value		Price to book ratio multiple	1.9
	Subtotal Level 3 securities	68.2
	Pricing exemption securities3	0.5
	Total Level 3 securities	$	68.7
	1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	3The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2014
Debt Disclosure [Abstract]	'
Debt Table	'
	Debt consisted of:
		30-Sep-14				30-Sep-13				31-Dec-13
	(millions)	Carrying		Fair		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value		Value		Value
	7% Notes due 2013	$	0	$	0	$	150	$	150	$	0	$	0
	3.75% Senior Notes due 2021	497.8		527.9		497.5		516.7		497.6		509.1
	6 5/8% Senior Notes due 2029	295.4		390.9		295.3		362		295.3		359.6
	6.25% Senior Notes due 2032	394.8		510.3		394.6		478.2		394.6		473.7
	4.35% Senior Notes due 2044	346.3		352.7		0		0		0		0
	6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	630		693.3		673.2		724.5		673.4		731.3
	Total	$	2,164.30	$	2,475.10	$	2,010.60	$	2,231.40	$	1,860.90	$	2,073.70

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2014
Supplemental Cash Flow Elements [Abstract]	'
Supplemental Cash Flow Information Table	'
	We paid the following in the respective periods:
		Nine Months Ended September 30,
	(millions)	2014		2013
	Income taxes	$	355	$	340
	Interest	74.7		81.9

Segment_Information_Tables

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2014
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,
		2014							2013								2014						2013
	(millions)	Revenues				Pretax			Revenues				Pretax				Revenues			Pretax			Revenues			Pretax
						Profit							Profit							Profit						Profit
						(Loss)							(Loss)							(Loss)						(Loss)
	Personal Lines
	Agency	$	2,235.20			$	147		$	2,162.70			$	122			$	6,680.70		$	468.5		$	6,421.40		$	428.4
	Direct	1,848.90				107.6			1,693.40				107.3				5,435.10			294.3			5,020.40			360.5
	Total Personal Lines1	4,084.10				254.6			3,856.10				229.3				12,115.80			762.8			11,441.80			788.9
	Commercial Lines	456				85.1			446.8				26.3				1,340.10			204.4			1,317.30			73.7
	Other indemnity	0				0.1			0.1				(6.2		)		0			(5.3		)	0.2			(9.7		)
	Total underwriting operations	4,540.10				339.8			4,303.00				249.4				13,455.90			961.9			12,759.30			852.9
	Fees and other revenues2	75.9				NA			76				NA				223.1			NA			215.3			NA
	Service businesses	15				1.5			11.3				0.2				38.8			2.7			30.3			0.2
	Investments3	139.9				136			135.3				130.1				502.2			488.2			551.5			537
	Gains (losses) on extinguishment of debt	(4.8		)		(4.8		)	(4.3		)		(4.3		)		(4.8		)	(4.8		)	(4.3		)	(4.3		)
	Interest expense	NA				(30.7		)	NA				(30.4		)		NA			(87.0		)	NA			(91.4		)
	Consolidated total	$	4,766.10			$	441.8		$	4,521.30			$	345			$	14,215.20		$	1,361.00		$	13,552.10		$	1,294.40
	1Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in the first nine months of 2014, compared to 91% in all other periods presented; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, mobile homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
	2Pretax profit (loss) for fees and other revenues is allocated to operating segments.
	3Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.
	NA =ot Applicable
Underwriting Margins and Combined Ratios for our Underwriting Operations	'
	Following are the underwriting margins/combined ratios for our underwriting operations for the respective periods:
		Three Months Ended September 30,									Nine Months Ended September 30,
		2014					2013				2014					2013
		Under-writing			Combined		Under-writing		Combined		Under-writing			Combined		Under-writing			Combined
		Margin			Ratio		Margin		Ratio		Margin			Ratio		Margin			Ratio
	Personal Lines
	Agency	6.6	%		93.4		5.6	%	94.4		7	%		93		6.7	%		93.3
	Direct	5.8			94.2		6.3		93.7		5.4			94.6		7.2			92.8
	Total Personal Lines	6.2			93.8		5.9		94.1		6.3			93.7		6.9			93.1
	Commercial Lines	18.6			81.4		5.9		94.1		15.2			84.8		5.6			94.4
	Other indemnity1	NM			NM		NM		NM		NM			NM		NM			NM
	Total underwriting operations	7.5			92.5		5.8		94.2		7.1			92.9		6.7			93.3
	1Underwriting margins and combined ratios are not meaningful (NM) for our other indemnity businesses due to the low level of premiums earned by, and the variability of loss costs in, such businesses.

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2014
Equity [Abstract]	'
Components of Other Comprehensive Income (Loss)	'
	The components of other comprehensive income (loss), including reclassification adjustments by income statement line item, were as follows:
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions1,3
	Balance at June 30, 2014	$	1,598.20		$	(559.3	)	$	1,038.90		$	1,035.30		$	2.5		$	1.1
	Other comprehensive income (loss) before reclassifications:
	Investment securities	(62.5		)	21.9			(40.6		)	(40.6		)	0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	(.5		)	0.1			(.4		)	0			0			(.4		)
	Total other comprehensive income (loss) before reclassifications	(63.0		)	22			(41.0		)	(40.6		)	0			(.4		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(.1		)	0			(.1		)	(.1		)	0			0
	Net realized gains (losses) on securities2	38.3			(13.4		)	24.9			24.6			0.3			0
	Interest expense3	0.5			(.1		)	0.4			0			0.4			0
	Total reclassification adjustment for amounts realized in net income	38.7			(13.5		)	25.2			24.5			0.7			0
	Total other comprehensive income (loss)	(101.7		)	35.5			(66.2		)	(65.1		)	(.7		)	(.4		)
	Balance at September 30, 2014	$	1,496.50		$	(523.8	)	$	972.7		$	970.2		$	1.8		$	0.7
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions1,3
	Balance at December 31, 2013	$	1,464.10		$	(512.4	)	$	951.7		$	947		$	4.1		$	0.6
	Other comprehensive income (loss) before reclassifications:
	Investment securities	258.2			(90.3		)	167.9			167.9			0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	(1.6		)	0.6			(1.0		)	0			(1.0		)	0
	Foreign currency translation adjustment	0.3			(.2		)	0.1			0			0			0.1
	Total other comprehensive income (loss) before reclassifications	256.9			(89.9		)	167			167.9			(1.0		)	0.1
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(.1		)	0			(.1		)	(.1		)	0			0
	Net realized gains (losses) on securities2	223.1			(78.0		)	145.1			144.8			0.3			0
	Interest expense3	1.5			(.5		)	1			0			1			0
	Total reclassification adjustment for amounts realized in net income	224.5			(78.5		)	146			144.7			1.3			0
	Total other comprehensive income (loss)	32.4			(11.4		)	21			23.2			(2.3		)	0.1
	Balance at September 30, 2014	$	1,496.50		$	(523.8	)	$	972.7		$	970.2		$	1.8		$	0.7
											Components of Changes in
											Accumulated Other
											Comprehensive Income (after tax)
	(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
		accumulated			(provision)			accumulated			unrealized			unrealized			currency
		other			benefit			other			gains (losses)			gains on			translation
		comprehensive						comprehensive			on securities			forecasted			adjustment
		income						income						transactions1
	Balance at June 30, 2013	$	1,252.60		$	(438.4	)	$	814.2		$	807.6		$	5.4		$	1.2
	Other comprehensive income (loss) before reclassifications:
	Investment securities	111.9			(39.2		)	72.7			72.7			0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	0			0			0			0			0			0
	Foreign currency translation adjustment	(.4		)	0.2			(.2		)	0			0			(.2		)
	Total other comprehensive income (loss) before reclassifications	111.5			(39.0		)	72.5			72.7			0			(.2		)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net impairment losses recognized in earnings	(1.9		)	0.7			(1.2		)	(1.2		)	0			0
Net realized gains (losses) on securities2	25.6			(9.0		)	16.6			16.1			0.5			0
Interest expense	0.6			(.2		)	0.4			0			0.4			0
Total reclassification adjustment for amounts realized in net income	24.3			(8.5		)	15.8			14.9			0.9			0
Total other comprehensive income (loss)	87.2			(30.5		)	56.7			57.8			(.9		)	(.2		)
Balance at September 30, 2013	$	1,339.80		$	(468.9	)	$	870.9		$	865.4		$	4.5		$	1
										Components of Changes in
										Accumulated Other
										Comprehensive Income (after tax)
(millions)	Pretax total			Total tax			After tax total			Total net			Net			Foreign
	accumulated			(provision)			accumulated			unrealized			unrealized			currency
	other			benefit			other			gains (losses)			gains on			translation
	comprehensive						comprehensive			on securities			forecasted			adjustment
	income						income						transactions1
Balance at December 31, 2012	$	1,340.00		$	(469.0	)	$	871		$	862.7		$	6.1		$	2.2
Other comprehensive income (loss) before reclassifications:
Investment securities	192.6			(67.4		)	125.2			125.2			0			0
Net non-credit related OTTI losses, adjusted for	0.4			(.1		)	0.3			0.3			0			0
valuation changes
Forecasted transactions	0			0			0			0			0			0
Foreign currency translation adjustment	(1.9		)	0.7			(1.2		)	0			0			(1.2		)
Total other comprehensive income (loss) before reclassifications	191.1			(66.8		)	124.3			125.5			0			(1.2		)
Less: Reclassification adjustment for amounts realized in net income by income statement line item:
Net impairment losses recognized in earnings	(3.5		)	1.3			(2.2		)	(2.2		)	0			0
Net realized gains (losses) on securities2	193.2			(67.7		)	125.5			125			0.5			0
Interest expense	1.6			(.5		)	1.1			0			1.1			0
Total reclassification adjustment for amounts realized in net income	191.3			(66.9		)	124.4			122.8			1.6			0
Total other comprehensive income (loss)	(.2		)	0.1			(.1		)	2.7			(1.6		)	(1.2		)
Balance at September 30, 2013	$	1,339.80		$	(468.9	)	$	870.9		$	865.4		$	4.5		$	1
1Entered into for the purpose of managing interest rate risk associated with our debt issuances.
2During both the third quarter and first nine months of 2014, we reclassified $0.5 million, on a pretax basis, from accumulated other comprehensive income on the balance sheet to net realized gains on securities on the comprehensive income statement, reflecting the portion of the unrealized gain on forecasted transactions that was related to the portion of the 6.70% Debentures repurchased during the period, compared to $0.8 million during the third quarter and first nine months of 2013 (see Note 4 - Debt for further discussion).
3We expect to reclassify $2.0 million (pretax) into income during the next 12 months, related to the net unrealized gains on forecasted transactions.

Basis_of_Presentation_Basis_of

Basis of Presentation Basis of Presentation-Additional Information (Details) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Disposal Group, Including Discontinued Operation, Long Lived Assets, Current [Abstract]	'
Number of Properties Held for Sale	2
Assets Held-for-sale, Property, Plant and Equipment	$13.40

Investments_Investment_Portfol

Investments Investment Portfolio by Major Security Type (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	$17,572.30	[1],[2]	$16,584.70	[1],[2]	$16,655.40	[1],[2]
Gross Unrealized Gains	1,544.40	[1],[2]	1,582.90	[1],[2]	1,460.40	[1],[2]
Gross Unrealized Losses	-51.8	[1],[2]	-126	[1],[2]	-129	[1],[2]
Net Realized Gains (Losses)	18.3	[1],[2],[3]	13.1	[1],[2],[3]	9.1	[1],[2],[3]
Total investments at fair value	19,083.20	[1],[2]	18,054.70	[1],[2]	17,995.90	[1],[2]
% of Total Fair Value	100.00%	[1],[2]	100.00%	[1],[2]	100.00%	[1],[2]
Fixed maturities	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	13,090		13,415.30		13,644.90
Gross Unrealized Gains	218.3		242.4		271.1
Gross Unrealized Losses	-37.9		-119.1		-119.2
Net Realized Gains (Losses)	-1	[3]	1.8	[3]	0.9	[3]
Total investments at fair value	13,269.40		13,540.40		13,797.70
% of Total Fair Value	69.50%		75.00%		76.70%
Fixed maturities | U.S. government obligations	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	3,033.20		3,630.40		3,691.20
Gross Unrealized Gains	33.6		48.4		61.8
Gross Unrealized Losses	-3.9		-16.6		-11.3
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	3,062.90		3,662.20		3,741.70
% of Total Fair Value	16.00%		20.30%		20.80%
Fixed maturities | State and local government obligations	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	2,124.20		2,247.30		2,125.70
Gross Unrealized Gains	49.5		27.1		29.9
Gross Unrealized Losses	-0.9		-18.4		-17
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	2,172.80		2,256		2,138.60
% of Total Fair Value	11.40%		12.50%		11.90%
Fixed maturities | Foreign government obligations	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	20.2		15.6		15.9
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	20.2		15.6		15.9
% of Total Fair Value	0.10%		0.10%		0.10%
Fixed maturities | Corporate debt securities	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	2,501.80		2,885		3,118.80
Gross Unrealized Gains	30.7		60.4		67
Gross Unrealized Losses	-13.1		-20.4		-28.9
Net Realized Gains (Losses)	-0.3	[3]	1.6	[3]	0.7	[3]
Total investments at fair value	2,519.10		2,926.60		3,157.60
% of Total Fair Value	13.20%		16.20%		17.60%
Fixed maturities | Residential mortgage-backed securities	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	1,460.60		1,110.10		994.9
Gross Unrealized Gains	36.9		31.9		31.5
Gross Unrealized Losses	-10.1		-14.1		-16.5
Net Realized Gains (Losses)	-0.9	[3]	0	[3]	0	[3]
Total investments at fair value	1,486.50		1,127.90		1,009.90
% of Total Fair Value	7.80%		6.20%		5.60%
Fixed maturities | Commercial mortgage-backed securities	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	2,143.80		2,154.40		2,224.10
Gross Unrealized Gains	33.8		43.9		49
Gross Unrealized Losses	-5.1		-37.8		-33.1
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	2,172.50		2,160.50		2,240
% of Total Fair Value	11.40%		12.00%		12.40%
Fixed maturities | Other asset-backed securities	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	1,546		1,073		1,143.30
Gross Unrealized Gains	5		6.6		7.4
Gross Unrealized Losses	-0.6		-2.1		-2
Net Realized Gains (Losses)	0.2	[3]	0.2	[3]	0.2	[3]
Total investments at fair value	1,550.60		1,077.70		1,148.90
% of Total Fair Value	8.10%		6.00%		6.40%
Fixed maturities | Redeemable preferred stocks	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	260.2		299.5		331
Gross Unrealized Gains	28.8		24.1		24.5
Gross Unrealized Losses	-4.2		-9.7		-10.4
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	284.8		313.9		345.1
% of Total Fair Value	1.50%		1.70%		1.90%
Equity securities | Nonredeemable preferred stocks	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	532.8		445.7		442.1
Gross Unrealized Gains	218.4		258.7		280.5
Gross Unrealized Losses	-7.2		-4.5		-4.8
Net Realized Gains (Losses)	19.3	[3]	11.3	[3]	8.2	[3]
Total investments at fair value	763.3		711.2		726
% of Total Fair Value	4.00%		3.90%		4.00%
Equity securities | Common equities	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	1,278.40		1,451.10		1,422.30
Gross Unrealized Gains	1,107.70		1,081.80		908.8
Gross Unrealized Losses	-6.7		-2.4		-5
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	2,379.40		2,530.50		2,326.10
% of Total Fair Value	12.50%		14.00%		12.90%
Short-term investments | Other short-term investments	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Cost	2,671.10		1,272.60		1,146.10
Gross Unrealized Gains	0		0		0
Gross Unrealized Losses	0		0		0
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	$2,671.10		$1,272.60		$1,146.10
% of Total Fair Value	14.00%		7.10%		6.40%
[1]	The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.
[3]	Represents net holding period gains (losses) on certain hybrid securities (discussed below).

Investments_Investment_Portfol1

Investments Investment Portfolio by Major Security Type (Parenthetical) (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Investments, Debt and Equity Securities [Abstract]	'	'	'
Net unsettled security transactions offset in other liabilities	$158,000,000	$61,300,000	$63,700,000
Securities in the portfolio of a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions	$1,300,000,000	$1,800,000,000	$1,300,000,000

Investments_Hybrid_Securities_

Investments Hybrid Securities (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Millions, unless otherwise specified
Hybrid Securities [Line Items]	'	'	'
Hybrid securities	$362.20	$239.30	$244.40
Fixed maturities	'	'	'
Hybrid Securities [Line Items]	'	'	'
Hybrid securities	268.8	179	187.1
Fixed maturities | Corporate debt securities	'	'	'
Hybrid Securities [Line Items]	'	'	'
Hybrid securities	138.5	164.2	171.8
Fixed maturities | Residential mortgage-backed securities	'	'	'
Hybrid Securities [Line Items]	'	'	'
Hybrid securities	116.8	0	0
Fixed maturities | Other asset-backed securities	'	'	'
Hybrid Securities [Line Items]	'	'	'
Hybrid securities	13.5	14.8	15.3
Equity securities | Nonredeemable preferred stocks	'	'	'
Hybrid Securities [Line Items]	'	'	'
Hybrid securities	$93.40	$60.30	$57.30

Investments_Composition_of_Fix

Investments Composition of Fixed Maturities by Maturity (Detail) (USD $)	Sep. 30, 2014
In Millions, unless otherwise specified
Available for sale, cost	'
Less than one year	$2,472.70
One to five years	7,571.80
Five to ten years	2,938.80
Ten years or greater	69.7
Total	13,053	[1]
Available for sale, Fair value	'
Less than one year	2,506.70
One to five years	7,672.20
Five to ten years	2,976.10
Ten years or greater	77.4
Total	$13,232.40	[1]
[1]	Excludes $37.0 million related to our open interest rate swap positions.

Investments_Composition_of_Fix1

Investments Composition of Fixed Maturities by Maturity (Parenthetical) (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Open interest rate swap positions	$37	[1]	$68.10	[1]	$53.50	[1]
Interest rate swaps	'		'		'
Schedule of Available-for-sale Securities [Line Items]	'		'		'
Open interest rate swap positions	$37		'		'
[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 report them on a gross basis on our balance sheets, consistent with our historical presentation.

Investments_Gross_Unrealized_l

Investments Gross Unrealized losses by Major Security (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Millions, unless otherwise specified
Investments, Unrealized Loss Position [Line Items]	'	'	'
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	320	423	398
Total Fair Value	$4,305.60	$5,723.40	$5,140
Gross Unrealized Losses	-51.8	-126	-129
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	224	346	352
Less than 12 Months Fair Value	2,912	4,865.90	4,813.50
Less than 12 Months Unrealized Losses	-25	-87.5	-113.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	96	77	46
12 Months or Greater Fair Value	1,393.60	857.5	326.5
12 Months or Greater Unrealized Losses	-26.8	-38.5	-15.9
Fixed maturities	'	'	'
Investments, Unrealized Loss Position [Line Items]	'	'	'
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	274	392	365
Total Fair Value	4,041.80	5,521.40	4,969.10
Gross Unrealized Losses	-37.9	-119.1	-119.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	183	319	324
Less than 12 Months Fair Value	2,747.70	4,665.10	4,646.90
Less than 12 Months Unrealized Losses	-15.6	-80.6	-103.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	91	73	41
12 Months or Greater Fair Value	1,294.10	856.3	322.2
12 Months or Greater Unrealized Losses	-22.3	-38.5	-15.6
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	19	29	18
Total Fair Value	627	1,444.30	969.1
Gross Unrealized Losses	-3.9	-16.6	-11.3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	9	28	18
Less than 12 Months Fair Value	211	1,434.60	969.1
Less than 12 Months Unrealized Losses	-0.7	-16.3	-11.3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	10	1	0
12 Months or Greater Fair Value	416	9.7	0
12 Months or Greater Unrealized Losses	-3.2	-0.3	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	31	141	126
Total Fair Value	181.8	844.2	728.3
Gross Unrealized Losses	-0.9	-18.4	-17
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	11	119	108
Less than 12 Months Fair Value	89.7	759.3	666.7
Less than 12 Months Unrealized Losses	-0.1	-17.1	-16.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	20	22	18
12 Months or Greater Fair Value	92.1	84.9	61.6
12 Months or Greater Unrealized Losses	-0.8	-1.3	-0.8
Fixed maturities | Corporate debt securities	'	'	'
Investments, Unrealized Loss Position [Line Items]	'	'	'
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	50	51	63
Total Fair Value	891.4	997.6	1,174.20
Gross Unrealized Losses	-13.1	-20.4	-28.9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	42	45	61
Less than 12 Months Fair Value	744.5	831.1	1,113.40
Less than 12 Months Unrealized Losses	-9.7	-17.8	-28.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	8	6	2
12 Months or Greater Fair Value	146.9	166.5	60.8
12 Months or Greater Unrealized Losses	-3.4	-2.6	-0.4
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	62	66	63
Total Fair Value	725.8	763.5	663
Gross Unrealized Losses	-10.1	-14.1	-16.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	24	45	49
Less than 12 Months Fair Value	290.5	597.6	585.5
Less than 12 Months Unrealized Losses	-1.8	-7.9	-12.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	38	21	14
12 Months or Greater Fair Value	435.3	165.9	77.5
12 Months or Greater Unrealized Losses	-8.3	-6.2	-4.1
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	72	76	67
Total Fair Value	894.5	1,061.90	993.3
Gross Unrealized Losses	-5.1	-37.8	-33.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	61	60	64
Less than 12 Months Fair Value	787.3	809.2	993.2
Less than 12 Months Unrealized Losses	-2.9	-19.7	-33
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	11	16	3
12 Months or Greater Fair Value	107.2	252.7	0.1
12 Months or Greater Unrealized Losses	-2.2	-18.1	-0.1
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	38	25	22
Total Fair Value	650.8	287.2	282.8
Gross Unrealized Losses	-0.6	-2.1	-2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	36	22	22
Less than 12 Months Fair Value	624.7	233.3	282.8
Less than 12 Months Unrealized Losses	-0.4	-1.8	-2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	3	0
12 Months or Greater Fair Value	26.1	53.9	0
12 Months or Greater Unrealized Losses	-0.2	-0.3	0
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	4	6
Total Fair Value	70.5	122.7	158.4
Gross Unrealized Losses	-4.2	-9.7	-10.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	0	0	2
Less than 12 Months Fair Value	0	0	36.2
Less than 12 Months Unrealized Losses	0	0	-0.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	4	4
12 Months or Greater Fair Value	70.5	122.7	122.2
12 Months or Greater Unrealized Losses	-4.2	-9.7	-10.2
Equity securities	'	'	'
Investments, Unrealized Loss Position [Line Items]	'	'	'
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	46	31	33
Total Fair Value	263.8	202	170.9
Gross Unrealized Losses	-13.9	-6.9	-9.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	41	27	28
Less than 12 Months Fair Value	164.3	200.8	166.6
Less than 12 Months Unrealized Losses	-9.4	-6.9	-9.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	5	4	5
12 Months or Greater Fair Value	99.5	1.2	4.3
12 Months or Greater Unrealized Losses	-4.5	0	-0.3
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	7	7
Total Fair Value	206.3	142.3	123.6
Gross Unrealized Losses	-7.2	-4.5	-4.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	4	7	7
Less than 12 Months Fair Value	118.6	142.3	123.6
Less than 12 Months Unrealized Losses	-4	-4.5	-4.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	3	0	0
12 Months or Greater Fair Value	87.7	0	0
12 Months or Greater Unrealized Losses	-3.2	0	0
Equity securities | Common equities	'	'	'
Investments, Unrealized Loss Position [Line Items]	'	'	'
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	39	24	26
Total Fair Value	57.5	59.7	47.3
Gross Unrealized Losses	-6.7	-2.4	-5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	37	20	21
Less than 12 Months Fair Value	45.7	58.5	43
Less than 12 Months Unrealized Losses	-5.4	-2.4	-4.7
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	4	5
12 Months or Greater Fair Value	11.8	1.2	4.3
12 Months or Greater Unrealized Losses	($1.30)	$0	($0.30)

Investments_Total_NonCredit_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 $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
In Millions, unless otherwise specified
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	($44.70)	($45)	($45)
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	-44.1	-44.1	-44.1
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	($0.60)	($0.90)	($0.90)

Investments_OTTI_Credit_Losses

Investments OTTI Credit Losses Recognized in Earnings (Detail) (Fixed maturities, USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]	'		'		'		'
Beginning balance	$13.40		$27.40		$19.60		$27.70
Reductions for securities sold/matured	-0.1		0		-0.1		0
Change in recoveries of future cash flows expected to be collected	0.1	[1]	-2.5	[1]	-6.1	[1]	-2.6	[1]
Reductions for previously recognized credit impairments written-down to fair value	0	[2]	0	[2]	0	[2]	-0.2	[2]
Ending balance	13.4		24.9		13.4		24.9
Residential mortgage-backed securities	'		'		'		'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]	'		'		'		'
Beginning balance	13		26.9		19.2		27.1
Reductions for securities sold/matured	-0.1		0		-0.1		0
Change in recoveries of future cash flows expected to be collected	0.1	[1]	-2.4	[1]	-6.1	[1]	-2.4	[1]
Reductions for previously recognized credit impairments written-down to fair value	0	[2]	0	[2]	0	[2]	-0.2	[2]
Ending balance	13		24.5		13		24.5
Commercial mortgage-backed securities	'		'		'		'
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]	'		'		'		'
Beginning balance	0.4		0.5		0.4		0.6
Reductions for securities sold/matured	0		0		0		0
Change in recoveries of future cash flows expected to be collected	0	[1]	-0.1	[1]	0	[1]	-0.2	[1]
Reductions for previously recognized credit impairments written-down to fair value	0	[2]	0	[2]	0	[2]	0	[2]
Ending balance	$0.40		$0.40		$0.40		$0.40
[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.
[2]	Reflects reductions of prior credit impairments where the current credit impairment requires writing securities down to fair value (i.e., no remaining non-credit loss).

Investments_Components_of_Net_

Investments Components of Net Realized Gains (Losses) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	$40.40	$28.20	$251.90	$202
Gross realized losses on securities sales	-3	-3	-24.2	-6.5
Net realized gains (losses) on securities sales	37.4	25.2	227.7	195.5
Other-than-temporary impairment losses	-0.1	-1.9	-0.1	-3.7
Total net realized gains (losses) on securities	38.2	27.9	198	241.4
Fixed maturities	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	14.9	5.2	74.9	62.8
Gross realized losses on securities sales	-3	-2.9	-20.8	-6.1
Net realized gains (losses) on securities sales	11.9	2.3	54.1	56.7
Other-than-temporary impairment losses	0	-0.1	0	-0.5
Fixed maturities | U.S. government obligations	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	2.5	3.1	13.2	6.8
Gross realized losses on securities sales	-1.3	-0.8	-6.4	-2.2
Net realized gains (losses) on securities sales	1.2	2.3	6.8	4.6
Fixed maturities | State and local government obligations	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	3.8	0	8.2	6.8
Gross realized losses on securities sales	-0.3	0	-0.5	0
Net realized gains (losses) on securities sales	3.5	0	7.7	6.8
Fixed maturities | Corporate And Other Debt Securities	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	0.9	1.7	33.8	38.4
Gross realized losses on securities sales	0	-2.1	-2.3	-3.1
Net realized gains (losses) on securities sales	0.9	-0.4	31.5	35.3
Fixed maturities | Residential mortgage-backed securities	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	0.2	0.3	2.2	2.4
Gross realized losses on securities sales	0	0	-0.2	0
Net realized gains (losses) on securities sales	0.2	0.3	2	2.4
Other-than-temporary impairment losses	0	-0.1	0	-0.5
Fixed maturities | Commercial mortgage-backed securities	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	5.2	0.1	14.8	8.4
Gross realized losses on securities sales	-1.4	0	-8.2	-0.7
Net realized gains (losses) on securities sales	3.8	0.1	6.6	7.7
Fixed maturities | Redeemable preferred stocks	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	2.3	0	2.7	0
Gross realized losses on securities sales	0	0	-3.2	-0.1
Net realized gains (losses) on securities sales	2.3	0	-0.5	-0.1
Equity securities | Nonredeemable preferred stocks	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	20.9	11.9	80	113.1
Net realized gains (losses) on securities sales	20.9	11.9	80	113.1
Equity securities | Common equities	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Gross realized gains on securities sales	4.6	11.1	97	26.1
Gross realized losses on securities sales	0	-0.1	-3.4	-0.4
Net realized gains (losses) on securities sales	4.6	11	93.6	25.7
Other-than-temporary impairment losses	-0.1	-1.8	-0.1	-3.2
Hybrid and Derivative Instruments and Litigation Settlements	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Other gains (losses)	0.9	4.6	-29.6	49.6
Hybrid and Derivative Instruments and Litigation Settlements | Hybrid Preferred Stock	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Other gains (losses)	-1.8	3.5	5.7	2.3
Hybrid and Derivative Instruments and Litigation Settlements | Derivative Instruments	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Other gains (losses)	-0.7	-1.2	-39.9	45
Hybrid and Derivative Instruments and Litigation Settlements | Litigation Settlements	'	'	'	'
Gain (Loss) on Investments [Line Items]	'	'	'	'
Other gains (losses)	$3.40	$2.30	$4.60	$2.30

Investments_Components_of_Net_1

Investments Components of Net Investment Income (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Investment Income [Line Items]	'	'	'	'
Investment income	$101.70	$107.40	$304.20	$310.10
Investment expenses	-3.9	-5.2	-14	-14.5
Net Investment Income	97.8	102.2	290.2	295.6
Fixed maturities	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	79.4	86.6	240.6	248.3
Fixed maturities | U.S. government obligations	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	11.3	12.9	36.3	36.8
Fixed maturities | State and local government obligations	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	12.8	12.3	38.2	34.8
Fixed maturities | Foreign government obligations	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	0.1	0.1	0.3	0.1
Fixed maturities | Corporate debt securities	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	19.5	24.3	60.3	74.1
Fixed maturities | Residential mortgage-backed securities	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	11.3	7.9	32.5	18.1
Fixed maturities | Commercial mortgage-backed securities	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	16.5	19.1	49.2	55.9
Fixed maturities | Other asset-backed securities	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	4.2	4.5	12.1	12.2
Fixed maturities | Redeemable preferred stocks	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	3.7	5.5	11.7	16.3
Equity securities | Nonredeemable preferred stocks	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	9.4	9.2	28.6	27.3
Equity securities | Common equities	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	12.5	11.3	34.1	32.8
Short-term investments | Other short-term investments	'	'	'	'
Net Investment Income [Line Items]	'	'	'	'
Investment income	$0.40	$0.30	$0.90	$1.70

Investments_Derivative_Instrum

Investments Derivative Instruments (Detail) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Derivative [Line Items]

'

'

'

'

'

'

Balance Sheet - Fair Value

$37

[1]

$53.50

[1]

$37

[1]

$53.50

[1]

$68.10

[1]

'

Income Statement - Net Realized Gain (Loss) on Securities

-0.7

-1.2

-39.9

45

'

'

Designated as Hedging Instruments | Closed Positions | Ineffective Cash Flow Hedge

'

'

'

'

'

'

Derivative [Line Items]

'

'

'

'

'

'

Notional Value

44

[2]

54

[2]

44

[2]

54

[2]

54

[2]

'

Purpose

'Manage interest  rate risk

'Manage interest rate risk

'

'

'Manage interest rate risk

'

Balance Sheet - Fair Value

0

[1]

0

[1]

0

[1]

0

[1]

0

[1]

'

Income Statement - Net Realized Gain (Loss) on Securities

0.5

0.8

0.5

0.8

'

'

Non-hedging Instruments | Closed Positions | Interest rate swaps

'

'

'

'

'

'

Derivative [Line Items]

'

'

'

'

'

'

Notional Value

0

[2]

1,263

[2]

0

[2]

1,263

[2]

1,263

[2]

1,263

[2]

Purpose

'

'

'

'Manage portfolio duration

'Manage portfolio duration

'

Balance Sheet - Fair Value

0

[1]

0

[1]

0

[1]

0

[1]

0

[1]

'

Income Statement - Net Realized Gain (Loss) on Securities

0

0

0

-4

'

'

Non-hedging Instruments | Assets | Interest rate swaps | Fixed maturities

'

'

'

'

'

'

Derivative [Line Items]

'

'

'

'

'

'

Notional Value

750

[2]

750

[2]

750

[2]

750

[2]

750

[2]

'

Purpose

'

'

'Manage portfolio duration

'Manage portfolio duration

'Manage portfolio duration

'

Balance Sheet - Fair Value

37

[1]

53.5

[1]

37

[1]

53.5

[1]

68.1

[1]

'

Income Statement - Net Realized Gain (Loss) on Securities

($1.20)

($2)

($40.40)

$48.20

'

'

[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 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_Additi

Investments Investments - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

1 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

6 Months Ended

3 Months Ended

9 Months Ended

9 Months Ended

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Apr. 25, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Jun. 30, 2013

Jun. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

4.35% Senior Notes due 2044

4.35% Senior Notes due 2044

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Categories of Investments, Marketable Securities, Trading Securities

Categories of Investments, Marketable Securities, Trading Securities

Categories of Investments, Marketable Securities, Trading Securities

Categories of Investments, Marketable Securities, Trading Securities

Fixed Income Securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Fixed maturities

Fixed maturities

Fixed maturities

Fixed maturities

Fixed maturities

Fixed maturities

Fixed maturities

Fixed maturities

Fixed maturities

Ineffective Cash Flow Hedge

Ineffective Cash Flow Hedge

Ineffective Cash Flow Hedge

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Interest rate swaps

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Opened in 2013

Opened in 2013

Opened in 2013

Opened in 2009

Opened in 2011

Common equities

Common equities

Common equities

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Russell One Thousand

Managed Equity Strategy

State and local government obligations

State and local government obligations

State and local government obligations

Corporate debt securities

Corporate debt securities

Corporate debt securities

Designated as Hedging Instruments

Designated as Hedging Instruments

Designated as Hedging Instruments

Non-hedging Instruments

Non-hedging Instruments

Non-hedging Instruments

Non-hedging Instruments

Non-hedging Instruments

Non-hedging Instruments

Non-hedging Instruments

Ten Year Time Horizon

Ten Year Time Horizon

Ten Year Time Horizon

Nine Year Time Horizon

Five Year Time Horizon

Common equities

Common equities

Closed Positions

Closed Positions

Closed Positions

Closed Positions

Closed Positions

Closed Positions

Closed Positions

Fixed maturities

Fixed maturities

Fixed maturities

Assets

Assets

Assets

Schedule of Investments [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Open reverse repurchase commitments

$0

$278,100,000

$0

$278,100,000

$200,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage which the issuer receives the security back at once the change of control is triggered

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.00%

'

'

'

'

'

'

'

'

'

'

'

'

Realized investment losses

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,000,000

'

'

'

'

'

'

'

'

'

'

'

'

Gross unrealized losses

51,800,000

129,000,000

51,800,000

129,000,000

126,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

45,100,000

13,900,000

6,900,000

9,800,000

6,700,000

2,400,000

5,000,000

7,200,000

4,500,000

4,800,000

'

'

37,900,000

119,100,000

119,200,000

900,000

18,400,000

17,000,000

13,100,000

20,400,000

28,900,000

'

'

'

'

'

'

'

'

'

'

Percentage of common stock portfolio

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

87.00%

13.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions

320

398

320

398

423

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

46

31

33

39

24

26

7

7

7

'

'

274

392

365

31

141

126

50

51

63

'

'

'

'

'

'

'

'

'

'

Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage Decline

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional Expenses Related to the Issuance

'

'

'

'

'

700,000

700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Trading securities

0

0

0

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net realized gains (losses) on securities

38,300,000

29,800,000

198,100,000

245,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

0

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Issuance Date

'

'

'

'

'

25-Apr-14

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Face Amount

'

'

'

'

'

350,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument, Interest Rate, Stated Percentage

'

'

'

'

'

4.35%

4.35%

6.70%

'

6.70%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)

'

'

'

'

'

1,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repurchase of debt, face amount

'

'

'

'

'

'

'

44,300,000

54,100,000

44,300,000

54,100,000

54,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities

'

'

'

'

'

'

'

'

'

'

'

'

500,000

800,000

500,000

800,000

800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of derivative positions held during the period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3

3

3

3

1

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Derivative Maturity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'10 years

'10 years

'9 years

'5 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Notional Value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

44,000,000

[1]

54,000,000

[1]

54,000,000

[1]

0

[1]

1,263,000,000

[1]

1,263,000,000

[1]

1,263,000,000

[1]

750,000,000

[1]

750,000,000

[1]

750,000,000

[1]

Balance Sheet - Fair Value

37,000,000

[2]

53,500,000

[2]

37,000,000

[2]

53,500,000

[2]

68,100,000

[2]

'

'

'

'

'

'

'

'

'

'

'

'

37,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

[2]

0

[2]

0

[2]

0

[2]

0

[2]

0

[2]

'

37,000,000

[2]

68,100,000

[2]

53,500,000

[2]

Cash collateral received from counterparties

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$31,800,000

$62,700,000

$49,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[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 report them on a gross basis on our balance sheets, consistent with our historical presentation.

Fair_Value_Composition_of_Inve

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
Fair Value Measurements [Line Items]	'		'		'
Portfolio	$19,083,200,000	[1],[2]	$18,054,700,000	[1],[2]	$17,995,900,000	[1],[2]
Debt, Fair Value	2,475,100,000		2,073,700,000		2,231,400,000
Debt	2,164,300,000	[3]	1,860,900,000	[3]	2,010,600,000	[3]
Fixed maturities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	13,269,400,000		13,540,400,000		13,797,700,000
Fixed maturities | Redeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	284,800,000		313,900,000		345,100,000
Fixed maturities | Redeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	100,300,000		102,800,000		134,200,000
Fixed maturities | Redeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	65,300,000		65,600,000		65,300,000
Fixed maturities | Redeemable preferred stocks | Industrials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	119,200,000		145,500,000		145,600,000
Fixed maturities | Debt Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	7,775,000,000		8,860,400,000		9,053,800,000
Fixed maturities | Debt Securities | U.S. government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	3,062,900,000		3,662,200,000		3,741,700,000
Fixed maturities | Debt Securities | State and local government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,172,800,000		2,256,000,000		2,138,600,000
Fixed maturities | Debt Securities | Foreign government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	20,200,000		15,600,000		15,900,000
Fixed maturities | Debt Securities | Corporate debt securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,519,100,000		2,926,600,000		3,157,600,000
Fixed maturities | Asset-backed Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	5,209,600,000		4,366,100,000		4,398,800,000
Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,486,500,000		1,127,900,000		1,009,900,000
Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,172,500,000		2,160,500,000		2,240,000,000
Fixed maturities | Asset-backed Securities | Other asset-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,550,600,000		1,077,700,000		1,148,900,000
Equity securities | Nonredeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	763,300,000		711,200,000		726,000,000
Equity securities | Nonredeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	763,300,000		694,400,000		709,200,000
Equity securities | Nonredeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		16,800,000		16,800,000
Equity securities | Common equities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,379,400,000		2,530,500,000		2,326,100,000
Equity securities | Common equities | Common Stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,379,000,000		2,530,000,000		2,287,400,000
Equity securities | Common equities | Other risk investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	400,000		500,000		38,700,000
Total Fixed Maturities and Equity Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	16,412,100,000		16,782,100,000		16,849,800,000
Short-term investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,671,100,000		1,272,600,000		1,146,100,000
Fair Value, Inputs, Level 1	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	8,075,800,000		7,436,400,000		7,040,500,000
Debt, Fair Value	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	3,083,100,000		3,677,800,000		3,757,600,000
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Redeemable preferred stocks | Industrials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	3,083,100,000		3,677,800,000		3,757,600,000
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | U.S. government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	3,062,900,000		3,662,200,000		3,741,700,000
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | State and local government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | Foreign government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	20,200,000		15,600,000		15,900,000
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | Corporate debt securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities | Asset-backed Securities | Other asset-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	220,000,000		240,800,000		244,000,000
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	220,000,000		240,800,000		244,000,000
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Equity securities | Common equities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,379,000,000		2,530,000,000		2,287,400,000
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Common Stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,379,000,000		2,530,000,000		2,287,400,000
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Other risk investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 1 | Total Fixed Maturities and Equity Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	5,682,100,000		6,448,600,000		6,289,000,000
Fair Value, Inputs, Level 1 | Short-term investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,393,700,000		987,800,000		751,500,000
Fair Value, Inputs, Level 2	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	10,947,800,000		10,549,600,000		10,849,100,000
Debt, Fair Value	2,475,100,000		2,073,700,000		2,231,400,000
Fair Value, Inputs, Level 2 | Fixed maturities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	10,173,800,000		9,833,400,000		10,008,600,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	284,800,000		313,900,000		345,100,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	100,300,000		102,800,000		134,200,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	65,300,000		65,600,000		65,300,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Industrials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	119,200,000		145,500,000		145,600,000
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	4,691,900,000		5,182,600,000		5,296,200,000
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | U.S. government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | State and local government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,172,800,000		2,256,000,000		2,138,600,000
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | Foreign government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities | Corporate debt securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,519,100,000		2,926,600,000		3,157,600,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	5,197,100,000		4,336,900,000		4,367,300,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,486,500,000		1,127,700,000		1,009,700,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,160,000,000		2,131,500,000		2,208,700,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Other asset-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,550,600,000		1,077,700,000		1,148,900,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	496,600,000		431,400,000		445,900,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	496,600,000		414,600,000		429,100,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		16,800,000		16,800,000
Fair Value, Inputs, Level 2 | Equity securities | Common equities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Common Stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 2 | Equity securities | Common equities | Other risk investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 2 | Total Fixed Maturities and Equity Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	10,670,400,000		10,264,800,000		10,454,500,000
Fair Value, Inputs, Level 2 | Short-term investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	277,400,000		284,800,000		394,600,000
Fair Value, Inputs, Level 3	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	59,600,000		68,700,000		106,300,000
Debt, Fair Value	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	12,500,000		29,200,000		31,500,000
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Redeemable preferred stocks | Industrials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | U.S. government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | State and local government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | Foreign government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Debt Securities | Corporate debt securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	12,500,000		29,200,000		31,500,000
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		200,000		200,000
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	12,500,000		29,000,000		31,300,000
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Other asset-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	46,700,000		39,000,000		36,100,000
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	46,700,000		39,000,000		36,100,000
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Equity securities | Common equities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	400,000		500,000		38,700,000
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Common Stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Other risk investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	400,000		500,000		38,700,000
Fair Value, Inputs, Level 3 | Total Fixed Maturities and Equity Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	59,600,000		68,700,000		106,300,000
Fair Value, Inputs, Level 3 | Short-term investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		0		0
Carrying (Reported) Amount, Fair Value Disclosure	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	17,572,300,000		16,584,700,000		16,655,400,000
Debt	2,164,300,000		1,860,900,000		2,010,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	13,090,000,000		13,415,300,000		13,644,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	260,200,000		299,500,000		331,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	77,300,000		84,200,000		115,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	65,000,000		64,900,000		64,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Industrials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	117,900,000		150,400,000		150,400,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	7,679,400,000		8,778,300,000		8,951,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | U.S. government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	3,033,200,000		3,630,400,000		3,691,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | State and local government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,124,200,000		2,247,300,000		2,125,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | Foreign government obligations	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	20,200,000		15,600,000		15,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | Corporate debt securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,501,800,000		2,885,000,000		3,118,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	5,150,400,000		4,337,500,000		4,362,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,460,600,000		1,110,100,000		994,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	2,143,800,000		2,154,400,000		2,224,100,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Other asset-backed securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,546,000,000		1,073,000,000		1,143,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	532,800,000		445,700,000		442,100,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Financials	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	532,800,000		431,500,000		427,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Utilities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	0		14,200,000		14,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,278,400,000		1,451,100,000		1,422,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Common Stocks	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	1,278,000,000		1,450,600,000		1,419,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Other risk investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	400,000		500,000		3,100,000
Carrying (Reported) Amount, Fair Value Disclosure | Total Fixed Maturities and Equity Securities	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	14,901,200,000		15,312,100,000		15,509,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Short-term investments	'		'		'
Fair Value Measurements [Line Items]	'		'		'
Portfolio	$2,671,100,000		$1,272,600,000		$1,146,100,000
[1]	The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.
[3]	Consists of both short- and long-term debt. See Note 4 - Debt.

Fair_Value_Summary_of_Changes_

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning Fair Value	$71.90		$258.20		$68.70		$114.70
Calls/ Maturities/ Paydowns	-1.3		-17.3		-3.1		-29.8
Purchases	0		0		0		125.4
Sales	0		0		-0.1		0
Net Realized (Gain) Loss on Sales	0		0		0.1		-0.5
Change in Valuation	2.6		6.8		7.6		37.9
Net Transfers in (out)	-13.6	[1]	-141.4	[2]	-13.6	[1]	-141.4	[2]
Ending Fair value	59.6		106.3		59.6		106.3
Fixed maturities	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning Fair Value	27.6		184.7		29.2		70.8
Calls/ Maturities/ Paydowns	-1.2		-17.3		-3		-29.7
Purchases	0		0		0		125.1
Sales	0		0		-0.1		0
Net Realized (Gain) Loss on Sales	0		0		0.1		0
Change in Valuation	-0.3		5.5		-0.1		6.7
Net Transfers in (out)	-13.6	[1]	-141.4	[2]	-13.6	[1]	-141.4	[2]
Ending Fair value	12.5		31.5		12.5		31.5
Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning Fair Value	0		157.1		0.2		45.5
Calls/ Maturities/ Paydowns	0		-17		0		-28.6
Purchases	0		0		0		125.1
Sales	0		0		-0.1		0
Net Realized (Gain) Loss on Sales	0		0		0.1		0
Change in Valuation	0		1.5		-0.2		-0.4
Net Transfers in (out)	0	[1]	-141.4	[2]	0	[1]	-141.4	[2]
Ending Fair value	0		0.2		0		0.2
Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning Fair Value	27.6		27.6		29		25.3
Calls/ Maturities/ Paydowns	-1.2		-0.3		-3		-1.1
Purchases	0		0		0		0
Sales	0		0		0		0
Net Realized (Gain) Loss on Sales	0		0		0		0
Change in Valuation	-0.3		4		0.1		7.1
Net Transfers in (out)	-13.6	[1]	0	[2]	-13.6	[1]	0	[2]
Ending Fair value	12.5		31.3		12.5		31.3
Equity securities | Nonredeemable preferred stocks | Financials	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning Fair Value	43.8	[3]	34.8	[4]	39	[5]	31.9	[6]
Calls/ Maturities/ Paydowns	0	[3]	0	[4]	0	[5]	0	[6]
Purchases	0	[3]	0	[4]	0	[5]	0	[6]
Sales	0	[3]	0	[4]	0	[5]	0	[6]
Net Realized (Gain) Loss on Sales	0	[3]	0	[4]	0	[5]	0	[6]
Change in Valuation	2.9	[3]	1.3	[4]	7.7	[5]	4.2	[6]
Net Transfers in (out)	0	[1],[3]	0	[2],[4]	0	[1],[5]	0	[2],[6]
Ending Fair value	46.7	[3],[5]	36.1	[4],[6]	46.7	[3],[5]	36.1	[4],[6]
Equity securities | Common equities | Other risk investments	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'		'
Beginning Fair Value	0.5		38.7		0.5		12
Calls/ Maturities/ Paydowns	-0.1		0		-0.1		-0.1
Purchases	0		0		0		0.3
Sales	0		0		0		0
Net Realized (Gain) Loss on Sales	0		0		0		-0.5
Change in Valuation	0		0		0		27
Net Transfers in (out)	0	[1]	0	[2]	0	[1]	0	[2]
Ending Fair value	$0.40		$38.70		$0.40		$38.70
[1]	The $13.6 million was transferred out of Level 3 and into Level 2 due to an improvement in the security's underlying collateral and an increase in liquidity and market activity in comparable securities.
[2]	The $141.4 million was transferred out of Level 3 and into Level 2 due to an increase in liquidity and trading volume in the market.
[3]	The $2.9 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
[4]	The $1.3 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
[5]	The $7.7 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
[6]	The $4.2 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.

Fair_Value_Summary_of_Changes_1

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Net realized gains (losses) on securities	$38,300,000	$29,800,000	$198,100,000	$245,100,000
Equity securities | Nonredeemable preferred stocks | Hybrid Securities | Financials	'	'	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Net realized gains (losses) on securities	2,900,000	1,300,000	7,700,000	4,200,000
Asset-backed Securities | Fixed maturities | Residential mortgage-backed securities	'	'	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Transfer out of Level 3 into Level 2	'	-141,400,000	'	-141,400,000
Asset-backed Securities | Fixed maturities | Commercial mortgage-backed securities	'	'	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'	'
Transfer out of Level 3 into Level 2	($13,600,000)	'	($13,600,000)	'

Fair_Value_Summary_of_Quantita

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $)	9 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
	Investment		Investment		Investment
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	$19,083.20	[1],[2]	$17,995.90	[1],[2]	$18,054.70	[1],[2]
Fair Value, Inputs, Level 3	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	59.6		106.3		68.7
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	12.5		31.5		29.2
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	0		'		'
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities | Prepayment Rate Zero Percent	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Number of securities	'		1		1
Fair Value	'		0.2		0.2
Valuation Technique	'		'External vendor		'External vendor
Unobservable Input, prepayment rate	'		0.00%		0.00%
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities | Prepayment Rate Zero Percent	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Number of securities	1		2		2
Fair Value	12.5		31.3		29
Valuation Technique	'External vendor		'External vendor		'External vendor
Unobservable Input, prepayment rate	0.00%		0.00%		0.00%
Internal Pricing | Fair Value, Inputs, Level 3 | Fixed maturities	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Number of securities	0		0		0
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Number of securities	1		1		1
Fair Value	46.7		36.1		39
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	46.7		36.1		39
Valuation Technique	'Multiple of tangible net book value		'Multiple of tangible net book value		'Multiple of tangible net book value
Unobservable Input, price to book ratio multiple	1.9		1.9		1.9
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Common equities	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Number of securities	0		1		0
Fair Value	'		38		'
Subtotal Level 3 Securities | Fair Value, Inputs, Level 3	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	59.2		67.6		68.2
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	0.4	[3]	38.7	[4]	0.5	[3]
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3 | Other Non Binding Externally Priced Securities	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	'		0.7		'
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3 | Equity securities	'		'		'
Fair Value Inputs, Assets, Quantitative Information [Line Items]	'		'		'
Fair Value	'		$38		'
[1]	The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
[2]	Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.
[3]	The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
[4]	The fair values for $0.7 million of these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us. The remaining $38.0 million reflects a negotiated sale on a private common equity security that was completed by the end of 2013.

Fair_Value_Fair_Value_Addition

Fair Value Fair Value - Additional Information (Detail) (USD $)

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Jun. 30, 2014

Mar. 31, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2013

In Millions, unless otherwise specified

Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 1

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 2

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Investment Portfolio

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Nonredeemable preferred stocks

Common equities

Common equities

Common equities

Vendor Quoted Pricing

Vendor Quoted Pricing

Vendor Quoted Pricing

Vendor Quoted Pricing

Vendor Quoted Pricing

Vendor Quoted Pricing

Dealer Quoted Pricing

Dealer Quoted Pricing

Dealer Quoted Pricing

Fixed maturities

Fixed maturities

Fixed maturities

Investment

Equity securities

Equity securities

Equity securities

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Fair Value, Inputs, Level 3

Internal Pricing

Internal Pricing

Internal Pricing

Investment

Investment

Investment

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Equity securities

Investment

Investment

Investment

Internal Pricing

Internal Pricing

Internal Pricing

Internal Pricing

Internal Pricing

Internal Pricing

Investment

Investment

Investment

Investment

Investment

Investment

Fair Value Measurements [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of securities transferred out of Level 2 into Level 1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

2

'

'

'

'

'

'

Fair Value, Assets, Level 2 to Level 1 Transfers, Amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$41.70

'

'

'

'

'

'

Number of securities transferred out of Level 1 into Level 2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

Quoted prices percentage of fair value assets

100.00%

[1],[2]

100.00%

[1],[2]

100.00%

[1],[2]

'

'

'

54.00%

56.00%

59.00%

'

'

'

96.00%

98.00%

97.00%

4.00%

2.00%

3.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of securities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

0

'

'

'

'

1

1

1

0

0

1

Portfolio

$19,083.20

[1],[2]

$18,054.70

[1],[2]

$17,995.90

[1],[2]

$8,075.80

$7,436.40

$7,040.50

'

'

'

$10,947.80

$10,549.60

$10,849.10

'

'

'

'

'

'

$59.60

$68.70

$106.30

'

'

'

'

'

'

'

$46.70

$39

$36.10

'

'

$38

[1]

The total fair value of the portfolio at September 30, 2014 and 2013, and December 31, 2013 included $1.3 billion, $1.3 billion, and $1.8 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.

[2]

Our portfolio reflects the effect of unsettled security transactions and collateral on open derivative positions; at September 30, 2014, $158.0 million was included in "other liabilities," compared to $63.7 million and $61.3 million at September 30, 2013 and December 31, 2013, respectively.

Debt_Detail

Debt (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013
Debt Instrument [Line Items]	'		'		'
Carrying Value	$2,164,300,000	[1]	$1,860,900,000	[1]	$2,010,600,000	[1]
Fair Value	2,475,100,000		2,073,700,000		2,231,400,000
7% Notes due 2013	'		'		'
Debt Instrument [Line Items]	'		'		'
Carrying Value	0		0		150,000,000
Fair Value	0		0		150,000,000
3.75% Senior Notes due 2021	'		'		'
Debt Instrument [Line Items]	'		'		'
Carrying Value	497,800,000		497,600,000		497,500,000
Fair Value	527,900,000		509,100,000		516,700,000
6 5/8% Senior Notes due 2029	'		'		'
Debt Instrument [Line Items]	'		'		'
Carrying Value	295,400,000		295,300,000		295,300,000
Fair Value	390,900,000		359,600,000		362,000,000
6.25% Senior Notes due 2032	'		'		'
Debt Instrument [Line Items]	'		'		'
Carrying Value	394,800,000		394,600,000		394,600,000
Fair Value	510,300,000		473,700,000		478,200,000
4.35% Senior Notes due 2044	'		'		'
Debt Instrument [Line Items]	'		'		'
Carrying Value	346,300,000		0		0
Fair Value	352,700,000		0		0
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	'		'		'
Debt Instrument [Line Items]	'		'		'
Carrying Value	630,000,000		673,400,000		673,200,000
Fair Value	$693,300,000		$731,300,000		$724,500,000
[1]	Consists of both short- and long-term debt. See Note 4 - Debt.

Debt_Parenthetical_Details

Debt (Parenthetical) (Details)	Sep. 30, 2014	Apr. 25, 2014
7% Notes due 2013	'	'
Debt Instrument [Line Items]	'	'
Debt Instrument, Interest Rate, Stated Percentage	7.00%	'
3.75% Senior Notes due 2021	'	'
Debt Instrument [Line Items]	'	'
Debt Instrument, Interest Rate, Stated Percentage	3.75%	'
6 5/8% Senior Notes due 2029	'	'
Debt Instrument [Line Items]	'	'
Debt Instrument, Interest Rate, Stated Percentage	6.63%	'
6.25% Senior Notes due 2032	'	'
Debt Instrument [Line Items]	'	'
Debt Instrument, Interest Rate, Stated Percentage	6.25%	'
4.35% Senior Notes due 2044	'	'
Debt Instrument [Line Items]	'	'
Debt Instrument, Interest Rate, Stated Percentage	4.35%	4.35%
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	'	'
Debt Instrument [Line Items]	'	'
Debt Instrument, Interest Rate, Stated Percentage	6.70%	'

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

9 Months Ended

1 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Apr. 25, 2014

Sep. 30, 2014

Oct. 31, 2013

Sep. 30, 2014

Discretionary Line of Credit

Discretionary Line of Credit

Discretionary Line of Credit

Discretionary Line of Credit

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067

4.35% Senior Notes due 2044

4.35% Senior Notes due 2044

7% Notes due 2013

7% Notes due 2013

Federal Funds Rate

Federal Funds Rate

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Net unrealized gains on forecasted transactions

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repurchase of debt, face amount

'

'

'

'

'

'

'

'

$44,300,000

$54,100,000

$44,300,000

$54,100,000

$54,100,000

'

'

'

'

'

'

'

'

'

(Gains) losses on extinguishment of debt

4,800,000

4,300,000

4,800,000

4,300,000

'

'

'

'

4,800,000

4,300,000

4,800,000

4,300,000

4,300,000

'

'

'

'

'

'

'

'

'

Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities

'

'

'

'

'

'

'

'

'

'

'

'

'

500,000

800,000

500,000

800,000

800,000

'

'

'

'

Debt Instrument, Issuance Date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25-Apr-14

'

'

'

Debt Instrument, Face Amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

350,000,000

'

'

'

Debt Instrument, Interest Rate, Stated Percentage

'

'

'

'

'

'

'

'

6.70%

'

6.70%

'

'

'

'

'

'

'

4.35%

4.35%

'

7.00%

Proceeds from Debt, Net of Issuance Costs

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

346,300,000

'

'

'

Additional Expenses Related to the Issuance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

700,000

700,000

'

'

Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,600,000

'

'

'

Payment of debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

150,000,000

'

Line of Credit Facility, Maximum Borrowing Capacity

'

'

'

'

100,000,000

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Basis points

'

'

'

'

'

'

0.50%

0.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Detail) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Supplemental Cash Flow Elements [Abstract]	'	'
Income taxes	$355	$340
Interest	$74.70	$81.90

Segment_Information_Operating_

Segment Information Operating Results (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	$4,766.10		$4,521.30		$14,215.20		$13,552.10
Pretax Profit (Loss)	441.8		345		1,361		1,294.40
Underwriting Operations	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	4,540.10		4,303		13,455.90		12,759.30
Pretax Profit (Loss)	339.8		249.4		961.9		852.9
Underwriting Operations | Personal Lines	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	4,084.10	[1]	3,856.10	[1]	12,115.80	[1]	11,441.80	[1]
Pretax Profit (Loss)	254.6	[1]	229.3	[1]	762.8	[1]	788.9	[1]
Underwriting Operations | Personal Lines | Agency Channel	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	2,235.20		2,162.70		6,680.70		6,421.40
Pretax Profit (Loss)	147		122		468.5		428.4
Underwriting Operations | Personal Lines | Direct Channel	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	1,848.90		1,693.40		5,435.10		5,020.40
Pretax Profit (Loss)	107.6		107.3		294.3		360.5
Underwriting Operations | Commercial Lines	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	456		446.8		1,340.10		1,317.30
Pretax Profit (Loss)	85.1		26.3		204.4		73.7
Underwriting Operations | Other Indemnity	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	0		0.1		0		0.2
Pretax Profit (Loss)	0.1		-6.2		-5.3		-9.7
Fees and Other Revenues	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	75.9	[2]	76	[2]	223.1	[2]	215.3	[2]
Service Businesses	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	15		11.3		38.8		30.3
Pretax Profit (Loss)	1.5		0.2		2.7		0.2
Investments	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	139.9	[3]	135.3	[3]	502.2	[3]	551.5	[3]
Pretax Profit (Loss)	136	[3]	130.1	[3]	488.2	[3]	537	[3]
Gains (losses) on extinguishment of debt	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Revenues	-4.8		-4.3		-4.8		-4.3
Pretax Profit (Loss)	-4.8		-4.3		-4.8		-4.3
Interest Expense	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Pretax Profit (Loss)	($30.70)		($30.40)		($87)		($91.40)
[1]	Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in the first nine months of 2014, compared to 91% in all other periods presented; insurance for our special lines products (e.g., motorcycles, ATVs, RVs, mobile homes, watercraft, and snowmobiles) accounted for the balance of the Personal Lines net premiums earned.
[2]	Pretax profit (loss) for fees and other revenues is allocated to operating segments.
[3]	Revenues represent recurring investment income and total net realized gains (losses) on securities; pretax profit is net of investment expenses.

Segment_Information_Operating_1

Segment Information Operating Results (Parenthetical) (Detail) (Underwriting Operations, Personal Lines, Personal Auto)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Underwriting Operations | Personal Lines | Personal Auto	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Personal auto insurance percentage of the total personal lines segment net premiums earned	91.00%	91.00%	92.00%	91.00%

Segment_Information_Underwriti

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) (Underwriting Operations)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]	'	'	'	'
Underwriting Margin	7.50%	5.80%	7.10%	6.70%
Combined Ratio	92.50%	94.20%	92.90%	93.30%
Personal Lines	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Underwriting Margin	6.20%	5.90%	6.30%	6.90%
Combined Ratio	93.80%	94.10%	93.70%	93.10%
Personal Lines | Agency Channel	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Underwriting Margin	6.60%	5.60%	7.00%	6.70%
Combined Ratio	93.40%	94.40%	93.00%	93.30%
Personal Lines | Direct Channel	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Underwriting Margin	5.80%	6.30%	5.40%	7.20%
Combined Ratio	94.20%	93.70%	94.60%	92.80%
Commercial Lines	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Underwriting Margin	18.60%	5.90%	15.20%	5.60%
Combined Ratio	81.40%	94.10%	84.80%	94.40%

Dividends_Additional_Informati

Dividends - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended
In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014
					Annual variable dividend	Annual variable dividend	Special dividend
Dividends Payable [Line Items]	'	'	'	'	'	'	'
Target percentage used to determine annual variable dividend	33.33%	'	33.33%	'	'	'	'
Gainshare factor used to determine annual variable dividend range, minimum	0	'	0	'	'	'	'
Gainshare factor used to determine annual variable dividend range, maximum	2	'	2	'	'	'	'
Gainshare factor used to determine annual variable dividend	1.38	'	1.38	'	'	'	'
Comprehensive income	$229.90	$289.10	$931.80	$865.50	'	'	'
After-tax underwriting income	'	'	$625.20	'	'	'	'
Dividend paid per share (USD per share)	'	'	'	'	$0.49	$0.28	$1

Other_Comprehensive_Income_Los2

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]	'		'		'		'
Pre tax total accumulated other comprehensive income, beginning balance	$1,598,200,000		$1,252,600,000		$1,464,100,000		$1,340,000,000
Investment securities, pre tax	-62,500,000		111,900,000		258,200,000		192,600,000
Net non-credit related OTTI losses, adjusted for valuation changes, pre tax	0		0		0		400,000
Forecasted transactions, pre tax	0		0		-1,600,000		0
Foreign currency translation adjustment, pre tax	-500,000		-400,000		300,000		-1,900,000
Total other comprehensive income (loss) before reclassifications, pre tax	-63,000,000		111,500,000		256,900,000		191,100,000
Total reclassification adjustment for amounts realized in net income, pre tax	38,700,000		24,300,000		224,500,000		191,300,000
Total other comprehensive income (loss), pre tax	-101,700,000		87,200,000		32,400,000		-200,000
Pre tax total accumulated other comprehensive income, ending balance	1,496,500,000		1,339,800,000		1,496,500,000		1,339,800,000
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]	'		'		'		'
Accumulated other comprehensive income loss tax (Provision) benefit, beginning balance	-559,300,000		-438,400,000		-512,400,000		-469,000,000
Investment securities, Total tax (provision) benefit	21,900,000		-39,200,000		-90,300,000		-67,400,000
Net non-credit related OTTI losses, adjusted for valuation changes, Total tax (provision) benefit	0		0		0		-100,000
Forecasted transactions, Total tax (provision) benefit	0		0		600,000		0
Foreign currency translation adjustment, Total tax (provision) benefit	100,000		200,000		-200,000		700,000
Total other comprehensive income (loss) before reclassifications, Total tax (provision) benefit	22,000,000		-39,000,000		-89,900,000		-66,800,000
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	-13,500,000		-8,500,000		-78,500,000		-66,900,000
Total other comprehensive income (loss), Total tax (provision) benefit	35,500,000		-30,500,000		-11,400,000		100,000
Accumulated other comprehensive income loss tax (Provision) benefit, ending balance	-523,800,000		-468,900,000		-523,800,000		-468,900,000
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]	'		'		'		'
After tax total accumulated other comprehensive income, beginning balance	1,038,900,000		814,200,000		951,700,000		871,000,000
Investment securities, after tax	-40,600,000		72,700,000		167,900,000		125,200,000
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0		0		0		300,000
Forecasted transactions, after tax	0		0		-1,000,000		0
Foreign currency translation adjustment, after tax	-400,000		-200,000		100,000		-1,200,000
Total other comprehensive income (loss) before reclassifications, after tax	-41,000,000		72,500,000		167,000,000		124,300,000
Total reclassification adjustment for amounts realized in net income, after tax	25,200,000		15,800,000		146,000,000		124,400,000
Other comprehensive income (loss)	-66,200,000		56,700,000		21,000,000		-100,000
After tax total accumulated other comprehensive income, ending balance	972,700,000		870,900,000		972,700,000		870,900,000
Net impairment losses recognized in earnings	-100,000		-1,900,000		-100,000		-3,700,000
Net realized gains (losses) on securities	38,300,000		29,800,000		198,100,000		245,100,000
Interest expense	30,700,000		30,400,000		87,000,000		91,400,000
Net unrealized gains (losses) on securities	'		'		'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]	'		'		'		'
After tax total accumulated other comprehensive income, beginning balance	1,035,300,000		807,600,000		947,000,000		862,700,000
Investment securities, after tax	-40,600,000		72,700,000		167,900,000		125,200,000
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0		0		0		300,000
Forecasted transactions, after tax	0		0		0		0
Foreign currency translation adjustment, after tax	0		0		0		0
Total other comprehensive income (loss) before reclassifications, after tax	-40,600,000		72,700,000		167,900,000		125,500,000
Total reclassification adjustment for amounts realized in net income, after tax	24,500,000		14,900,000		144,700,000		122,800,000
Other comprehensive income (loss)	-65,100,000		57,800,000		23,200,000		2,700,000
After tax total accumulated other comprehensive income, ending balance	970,200,000		865,400,000		970,200,000		865,400,000
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	2,500,000	[1],[2]	5,400,000	[1]	4,100,000	[1],[2]	6,100,000	[1]
Investment securities, after tax	0	[1],[2]	0	[1]	0	[1],[2]	0	[1]
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	[1],[2]	0	[1]	0	[1],[2]	0	[1]
Forecasted transactions, after tax	0	[1],[2]	0	[1]	-1,000,000	[1],[2]	0	[1]
Foreign currency translation adjustment, after tax	0	[1],[2]	0	[1]	0	[1],[2]	0	[1]
Total other comprehensive income (loss) before reclassifications, after tax	0	[1],[2]	0	[1]	-1,000,000	[1],[2]	0	[1]
Total reclassification adjustment for amounts realized in net income, after tax	700,000	[1],[2]	900,000	[1]	1,300,000	[1],[2]	1,600,000	[1]
Other comprehensive income (loss)	-700,000	[1],[2]	-900,000	[1]	-2,300,000	[1],[2]	-1,600,000	[1]
After tax total accumulated other comprehensive income, ending balance	1,800,000	[1],[2]	4,500,000	[1]	1,800,000	[1],[2]	4,500,000	[1]
Foreign Currency Translation Adjustments	'		'		'		'
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]	'		'		'		'
After tax total accumulated other comprehensive income, beginning balance	1,100,000		1,200,000		600,000		2,200,000
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	-400,000		-200,000		100,000		-1,200,000
Total other comprehensive income (loss) before reclassifications, after tax	-400,000		-200,000		100,000		-1,200,000
Total reclassification adjustment for amounts realized in net income, after tax	0		0		0		0
Other comprehensive income (loss)	-400,000		-200,000		100,000		-1,200,000
After tax total accumulated other comprehensive income, ending balance	700,000		1,000,000		700,000		1,000,000
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	-100,000		-1,900,000		-100,000		-3,500,000
Net realized gains (losses) on securities	38,300,000	[3]	25,600,000	[3]	223,100,000	[3]	193,200,000	[3]
Interest expense	500,000	[2]	600,000		1,500,000	[2]	1,600,000
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	0		700,000		0		1,300,000
Net realized gains (losses) on securities	-13,400,000	[3]	-9,000,000	[3]	-78,000,000	[3]	-67,700,000	[3]
Interest expense	-100,000	[2]	-200,000		-500,000	[2]	-500,000
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	-100,000		-1,200,000		-100,000		-2,200,000
Net realized gains (losses) on securities	24,900,000	[3]	16,600,000	[3]	145,100,000	[3]	125,500,000	[3]
Interest expense	400,000	[2]	400,000		1,000,000	[2]	1,100,000
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	-100,000		-1,200,000		-100,000		-2,200,000
Net realized gains (losses) on securities	24,600,000	[3]	16,100,000	[3]	144,800,000	[3]	125,000,000	[3]
Interest expense	0	[2]	0		0	[2]	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	[1],[2]	0	[1]	0	[1],[2]	0	[1]
Net realized gains (losses) on securities	300,000	[1],[2],[3]	500,000	[1],[3]	300,000	[1],[2],[3]	500,000	[1],[3]
Interest expense	400,000	[1],[2]	400,000	[1]	1,000,000	[1],[2]	1,100,000	[1]
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	[3]	0	[3]	0	[3]	0	[3]
Interest expense	$0	[2]	$0		$0	[2]	$0
[1]	Entered into for the purpose of managing interest rate risk associated with our debt issuances.
[2]	We expect to reclassify $2.0 million (pretax) into income during the next 12 months, related to the net unrealized gains on forecasted transactions.
[3]	During both the third quarter and first nine months of 2014, we reclassified $0.5 million, on a pretax basis, from accumulated other comprehensive income on the balance sheet to net realized gains on securities on the comprehensive income statement, reflecting the portion of the unrealized gain on forecasted transactions that was related to the portion of the 6.70% Debentures repurchased during the period, compared to $0.8 million during the third quarter and first nine months of 2013 (see Note 4 - Debt for further discussion).

Other_Comprehensive_Income_Los3

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
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	$2	'	$2	'	'
Net unrealized gains on forecasted transactions | 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	'	'	'	'	'
Components Of Other Comprehensive Income Loss [Line Items]	'	'	'	'	'
Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities	$0.50	$0.80	$0.50	$0.80	$0.80