The Progressive Corporation (PGR) 10-Q 11 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document Document And Entity Information [Abstract]
Entity Registrant Name	PROGRESSIVE CORP/OH/
Entity Central Index Key	80661
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	FALSE
Trading Symbol	PGR
Entity Common Stock, Shares Outstanding		586,722,794

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Revenues
Net premiums earned	$4,666.30		$4,402.30
Period over prior year period percent change in net premiums earned	6.00%
Investment income	105.1		103.3
Period over prior year period percent change in investment income	2.00%
Other-than-temporary impairment (OTTI) losses:
Total OTTI losses	-7.9		0
Non-credit losses, net of credit losses recognized on previously recorded non-credit OTTI losses	0		0
Net impairment losses recognized in earnings	-7.9		0
Net realized gains (losses) on securities	40.9		119.4
Period over prior year period percent change in net realized gains (losses) on securities	-66.00%
Total net realized gains (losses) on securities	33		119.4
Period over prior year period percent change in total net realized gains (losses) on securities	-72.00%
Fees and other revenues	73.7		72.8
Period over prior year period percent change in fees and other revenues	1.00%
Service revenues	17.2		9.8
Period over prior year period percent change in service revenues	76.00%
Total revenues	4,895.30		4,707.60
Period over prior year period percent change in total revenues	4.00%
Expenses
Losses and loss adjustment expenses	3,368.60		3,205.90
Period over prior year period percent change in losses and loss adjustment expenses	5.00%
Policy acquisition costs	379.4		369
Period over prior year period percent change in policy acquisition costs	3.00%
Other underwriting expenses	650.4		610.4
Period over prior year period percent change in other underwriting expenses	7.00%
Investment expenses	5.3		4.1
Period over prior year period percent change in investment expenses	29.00%
Service expenses	15.9		9.7
Period over prior year period percent change in service expenses	64.00%
Interest expense	32.5		26.7
Period over prior year period percent change in interest expense	22.00%
Total expenses	4,452.10		4,225.80
Period over prior year period percent change in total expenses	5.00%
Net Income
Income before income taxes	443.2		481.8
Period over prior year period percent change in income before income taxes	-8.00%
Provision for income taxes	147.6		160.5
Period over prior year period percent change in provision for income taxes	-8.00%
Net income	295.6		321.3
Period over prior year period percent change in net income	-8.00%
Net unrealized gains (losses) on securities:
Net non-credit related OTTI losses, adjusted for valuation changes	0		0
Other net unrealized gains (losses) on securities	35.4		-0.1
Total net unrealized gains (losses) on securities	35.4		-0.1
Net unrealized gains (losses) on forecasted transactions	-8.7		-0.3
Foreign currency translation adjustment	-0.5		0
Other comprehensive income (loss)	26.2		-0.4
Comprehensive income	$321.80		$320.90
Period over prior year period percent change in comprehensive income	0.00%
Computation of Net Income Per Share
Average shares outstanding - Basic (shares)	587.6		593.9
Period over prior year period percent change in average shares outstanding - basic	-1.00%
Net effect of dilutive stock-based compensation (shares)	3.4		3.8
Period over prior year period percent change in net effect of dilutive stock-based compensation	-11.00%
Total equivalent shares - Diluted (shares)	591		597.7
Period over prior year period percent change in total equivalent shares - diluted	-1.00%
Basic: Net income per share (USD per share)	$0.50		$0.54
Period over prior year period percent change in basic: net income per share	-7.00%
Diluted: Net income per share (USD per share)	$0.50		$0.54
Period over prior year period percent change in diluted: net income per share	-7.00%
Dividends declared per share (USD per share)	$0	[1]	$0	[1]
[1]	Progressive maintains an annual dividend program. See Note 8 - Dividends for further discussion.See notes to consolidated financial statements.

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
In Millions, unless otherwise specified
Investments - Available-for-sale, at fair value:
Fixed maturities (amortized cost: $13,997.5, $12,335.8, and $13,374.2)	$14,219.80		$13,549.20		$12,506.20
Equity securities:
Nonredeemable preferred stocks (cost: $598.3, $460.7, and $590.4)	828.1		827.5		737.9
Common equities (cost: $1,295.0, $1,252.7, and $1,289.2)	2,515.70		2,492.30		2,278.70
Short-term investments (amortized cost: $2,267.0, $1,872.9, and $2,149.0)	2,267		2,149		1,872.90
Total investments at fair value	19,830.60	[1],[2]	19,018	[1],[2]	17,395.70	[1],[2]
Cash	101.5		108.4		96.7
Accrued investment income	84.7		87.3		82.3
Premiums receivable, net of allowance for doubtful accounts of $138.7, $131.9, and $152.2	3,777		3,537.50		3,515.90
Reinsurance recoverables, including $50.8, $34.5, and $46.0 on paid losses and loss adjustment expenses	1,257.20		1,231.90		1,111.50
Prepaid reinsurance premiums	99.3		85.3		81.8
Deferred acquisition costs	484		457.2		466.9
Property and equipment, net of accumulated depreciation of $742.7, $687.1, and $731.0	957.5		960.6		950
Other assets	288.9		301.4		614.6
Total assets	26,880.70		25,787.60		24,315.40
Liabilities and Shareholders’ Equity
Unearned premiums	5,854		5,440.10		5,460.10
Loss and loss adjustment expense reserves	9,001.60		8,857.40		8,592.60
Net deferred income taxes	97.2		98.9		51.1
Dividends payable	0		404.1		0
Accounts payable, accrued expenses, and other liabilities	2,165.90		1,893.80		1,911.70
Debt	2,560.10	[3]	2,164.70	[3]	1,861.30	[3]
Total liabilities	19,678.80		18,859		17,876.80
Common Shares, $1.00 par value (authorized 900.0; issued 797.6, including treasury shares of 210.3, 204.5, and 209.8)	587.3		587.8		593.1
Paid-in capital	1,196.70		1,184.30		1,159
Retained earnings	4,368.60		4,133.40		3,735.20
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	1,057.30		1,021.90		946.9
Total net unrealized gains (losses) on securities	1,057.30		1,021.90		946.9
Net unrealized gains (losses) on forecasted transactions	-7.2		1.5		3.8
Foreign currency translation adjustment	-0.8		-0.3		0.6
Total accumulated other comprehensive income	1,049.30		1,023.10		951.3
Total shareholders’ equity	7,201.90		6,928.60		6,438.60
Total liabilities and shareholders’ equity	$26,880.70		$25,787.60		$24,315.40
[1]	The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
[3]	1Consists of long-term debt. See Note 4 - Debt.See notes to consolidated financial statements.

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Millions, except Per Share data, unless otherwise specified
Fixed maturities, amortized cost	$13,997.50	$13,374.20	$12,335.80
Nonredeemable preferred stocks, cost	598.3	590.4	460.7
Common equities, cost	1,295	1,289.20	1,252.70
Short-term investments, amortized cost	2,267	2,149	1,872.90
Premiums receivable, allowance for doubtful accounts	138.7	152.2	131.9
Reinsurance recoverables, paid losses and loss adjustment expenses	50.8	46	34.5
Property and equipment, accumulated depreciation	$742.70	$731	$687.10
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)	210.3	209.8	204.5

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Shareholders' Equity Statement (USD $)	Total	Common Shares, $1.00 Par Value	Paid-in Capital	Retained Earnings	Accumulated other comprehensive income after tax
In Millions
Balance, Beginning of period at Dec. 31, 2013		$595.80	$1,142	$3,500	$951.70
Net income	321.3			321.3
Other comprehensive income (loss)	-0.4				-0.4
Tax benefit from exercise/vesting of equity-based compensation			10.7
Treasury shares purchased		-3.9	-7.5	-83.3
Net restricted equity awards (issued) (vested) forfeited		1.2	-1.2
Cash dividends declared on common shares				1.1
Amortization of equity-based compensation			15.2
Reinvested dividends on restricted stock units			-0.2
Other				-3.9
Balance, End of period at Mar. 31, 2014	6,438.60	593.1	1,159	3,735.20	951.3
Balance, Beginning of period at Dec. 31, 2014	6,928.60	587.8	1,184.30	4,133.40	1,023.10
Net income	295.6			295.6
Other comprehensive income (loss)	26.2				26.2
Tax benefit from exercise/vesting of equity-based compensation			6.3
Treasury shares purchased		-2.5	-5	-58.4
Net restricted equity awards (issued) (vested) forfeited		2	-2
Cash dividends declared on common shares				0
Amortization of equity-based compensation			13.1
Reinvested dividends on restricted stock units			0
Other				-2
Balance, End of period at Mar. 31, 2015	$7,201.90	$587.30	$1,196.70	$4,368.60	$1,049.30

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Cash Flows From Operating Activities
Net income	$295.60		$321.30
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	23.8		22.8
Amortization of fixed-income securities	17.3		19
Amortization of equity-based compensation	13.1		15.2
Net realized (gains) losses on securities	-33		-119.4
Net (gains) losses on disposition of property and equipment	0.1		2.1
Changes in:
Premiums receivable	-239.6		-205.2
Reinsurance recoverables	-25.3		-21.3
Prepaid reinsurance premiums	-14		-6.9
Deferred acquisition costs	-26.8		-19.3
Income taxes	80.6		149.6
Unearned premiums	414.4		285.6
Loss and loss adjustment expense reserves	144.4		112.9
Accounts payable, accrued expenses, and other liabilities	106.9		77
Other, net	13.6		27.2
Net cash provided by operating activities	771.1		660.6
Purchases:
Fixed maturities	-3,023.80		-1,731.60
Equity securities	-77.2		-86.6
Sales:
Fixed maturities	1,534.60		2,107.10
Equity securities	88.9		362.5
Maturities, paydowns, calls, and other:
Fixed maturities	855.1		697
Equity securities	0		14.3
Net sales (purchases) of short-term investments	-117.7		-600.4
Net unsettled security transactions	64.5		-411.3
Purchases of property and equipment	-22.2		-16.2
Sales of property and equipment	1.4		2.2
Net cash provided by (used in) investing activities	-696.4		337
Cash Flows From Financing Activities
Tax benefit from vesting of equity-based compensation	6.3		10.7
Proceeds from debt issuance	382		0
Dividends paid to shareholders	-403.6	[1]	-892.6	[1]
Acquisition of treasury shares	-65.9		-94.7
Net cash used in financing activities	-81.2		-976.6
Effect of exchange rate changes on cash	-0.4		0.6
Increase (decrease) in cash	-6.9		21.6
Cash, Beginning of year	108.4		75.1
Cash, End of period	$101.50		$96.70
[1]	Progressive maintains an annual dividend program. See Note 8 - Dividends for further discussion.See notes to consolidated financial statements.

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015, 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, 2014.
	Included in other assets in the consolidated balance sheets for March 31, 2015 and 2014 and December 31, 2014, is $8.7 million of "held for sale" property, which represents the fair value of this property less the estimated costs to sell.

Investments

Investments	3 Months Ended
	Mar. 31, 2015
Investments Schedule [Abstract]
Investments	Investments — Our securities are reported at fair value, with the changes in fair value of these securities (other than hybrid securities and derivative instruments) reported as a component of accumulated other comprehensive income, net of deferred income taxes. The changes in fair value of the hybrid securities and derivative instruments are recorded as a component of net realized gains (losses) on securities.
	The following tables present the composition of our investment portfolio by major security type, consistent with our classification of how we manage, monitor, and measure the portfolio:
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Mar-15
	Fixed maturities:
	U.S. government obligations	$	2,678.10			$	30.1			$	0			$	0			$	2,708.20		13.7	%
	State and local government obligations	2,224.80				50				(1.0		)		0				2,273.80			11.5
	Foreign government obligations	20				0				0				0				20			0.1
	Corporate debt securities	2,851.60				54.4				(3.8		)		1.8				2,904.00			14.6
	Residential mortgage-backed securities	1,629.20				32.4				(13.1		)		(0.3		)		1,648.20			8.3
	Commercial mortgage-backed securities	2,437.40				50.1				(1.1		)		0.7				2,487.10			12.5
	Other asset-backed securities	1,896.10				4.9				(0.3		)		0.8				1,901.50			9.6
	Redeemable preferred stocks	260.3				23.3				(6.6		)		0				277			1.4
	Total fixed maturities	13,997.50				245.2				(25.9		)		3				14,219.80			71.7
	Equity securities:
	Nonredeemable preferred stocks	598.3				192.5				(5.9		)		43.2				828.1			4.2
	Common equities	1,295.00				1,226.70				(6.0		)		0				2,515.70			12.7
	Short-term investments	2,267.00				0				0				0				2,267.00			11.4
	Total portfolio2,3	$	18,157.80			$	1,664.40			$	(37.8	)		$	46.2			$	19,830.60		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Mar-14
	Fixed maturities:
	U.S. government obligations	$	3,197.80			$	39			$	(6.8	)		$	0			$	3,230.00		18.5	%
	State and local government obligations	2,131.00				33.1				(9.2		)		0				2,154.90			12.4
	Foreign government obligations	17.9				0				0				0				17.9			0.1
	Corporate debt securities	2,461.60				45.4				(7.2		)		1.8				2,501.60			14.4
	Residential mortgage-backed securities	1,286.70				32.6				(11.9		)		0				1,307.40			7.5
	Commercial mortgage-backed securities	2,037.70				41.5				(17.6		)		0				2,061.60			11.9
	Other asset-backed securities	936.2				6.6				(0.6		)		0.3				942.5			5.4
	Redeemable preferred stocks	266.9				29.6				(6.2		)		0				290.3			1.7
	Total fixed maturities	12,335.80				227.8				(59.5		)		2.1				12,506.20			71.9
	Equity securities:
	Nonredeemable preferred stocks	460.7				263.7				(1.2		)		14.7				737.9			4.2
	Common equities	1,252.70				1,028.80				(2.8		)		0				2,278.70			13.1
	Short-term investments	1,872.90				0				0				0				1,872.90			10.8
	Total portfolio2,3	$	15,922.10			$	1,520.30			$	(63.5	)		$	16.8			$	17,395.70		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	$	2,641.10			$	27.3			$	(1.3	)		$	0			$	2,667.10		14	%
	State and local government obligations	2,095.70				44.6				(1.1		)		0				2,139.20			11.2
	Foreign government obligations	14.2				0				0				0				14.2			0.1
	Corporate debt securities	2,813.90				32.9				(10.4		)		0.3				2,836.70			14.9
	Residential mortgage-backed securities	1,635.50				34.5				(10.8		)		(0.7		)		1,658.50			8.7
	Commercial mortgage-backed securities	2,278.70				39.3				(2.6		)		0.2				2,315.60			12.2
	Other asset-backed securities	1,634.90				3.8				(0.8		)		0.8				1,638.70			8.6
	Redeemable preferred stocks	260.2				24.7				(5.7		)		0				279.2			1.5
	Total fixed maturities	13,374.20				207.1				(32.7		)		0.6				13,549.20			71.2
	Equity securities:
	Nonredeemable preferred stocks	590.4				201.1				(6.4		)		42.4				827.5			4.4
	Common equities	1,289.20				1,213.20				(10.1		)		0				2,492.30			13.1
	Short-term investments	2,149.00				0				0				0				2,149.00			11.3
	Total portfolio2,3	$	17,402.80			$	1,621.40			$	(49.2	)		$	43			$	19,018.00		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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
3The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 billion, respectively, of securities held in a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions.
Short-Term Investments Our short-term investments may include commercial paper and other investments that are expected to mature within one year. We did not hold any repurchase transactions where we lent collateral at March 31, 2015, March 31, 2014, or December 31, 2014. 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 have elected not to offset these transactions and therefore report these transactions on a gross basis on our balance sheets.
Also included in short-term investments are reverse repurchase commitment transactions, where we loan cash to internally approved counterparties and receive U.S. Treasury Notes pledged as collateral against the cash borrowed. Our exposure to credit risk is limited due to the nature of the collateral (i.e., U.S. Treasury Notes) received. We have counterparty exposure on these trades in the event of a counterparty default to the extent the general collateral security's value is below the amount of cash we delivered to acquire the collateral. The short-term duration of the transactions (primarily overnight) reduces that exposure.
We had no open reverse repurchase commitments at March 31, 2015 or December 31, 2014, compared to $140.0 million with one counterparty at March 31, 2014. For the three months ended March 31, 2015, our largest outstanding balance of reverse repurchase commitments was $215.0 million, which was open for one day; the average daily balance of reverse repurchase commitments was $137.7 million.
Hybrid Securities Included in our fixed-maturity and equity securities are hybrid securities, which are reported at fair value:
	March 31,								December 31,
(millions)	2015				2014				2014
Fixed maturities:
Corporate debt securities	$	132.9			$	145.7			$	139.8
Residential mortgage-backed securities	111.7				0				120.7
Commercial mortgage-backed securities	18				0				31.2
Other asset-backed securities	13.1				13.9				13.7
Total fixed maturities	275.7				159.6				305.4
Equity securities:
Nonredeemable preferred stocks	137.2				63.8				122.3
Total hybrid securities	$	412.9			$	223.4			$	427.7
Certain corporate debt securities are accounted for as hybrid securities since they were acquired at a premium and contain a change-in-control put option (derivative) that permits the investor, at its sole option if and when a change in control is triggered, to put the security back to the issuer at a 1% premium to par. Due to this change-in-control put option and the substantial market premium paid to acquire these securities, there is the potential that the election to put, upon the change in control, would result in an acceleration of the recognition of the remaining premium paid on these securities in our results of operations. This would result in a loss of $8.2 million as of March 31, 2015, 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 commercial mortgage-backed securities in the table above contain fixed interest rate reset features that will increase the coupons in the event the securities are not fully paid off on the anticipated repayment date. These reset features have the potential to more than double our initial purchase yield for each security.
The other asset-backed security in the table above represents one hybrid security that was acquired at a deep discount to par due to a failing auction, and contains a put option that allows the investor to put that security back to the auction at par if the auction is restored. This embedded derivative has the potential to more than double our initial investment yield at acquisition.
The hybrid securities in our nonredeemable preferred stock portfolio are perpetual preferred stocks 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.
Fixed Maturities The composition of fixed maturities by maturity at March 31, 2015, was:
(millions)	Cost				Fair Value
Less than one year	$	3,839.10			$	3,878.20
One to five years	6,771.60				6,848.90
Five to ten years	3,318.80				3,413.50
Ten years or greater	67.9				79.1
Total1	$	13,997.40			$	14,219.70
1Excludes $0.1 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 March 31, 2015, we had $31.8 million of gross unrealized losses in our fixed-income securities (i.e., fixed-maturity securities, nonredeemable preferred stocks, and short-term investments) and $6.0 million in our common equities. We currently do not intend to sell the fixed-income securities and determined that it is more likely than not that we will not be required to sell these securities for the period of time necessary to recover their cost bases. A review of our fixed-income securities indicated that the issuers were current with respect to their interest obligations and that there was no evidence of any deterioration of the current cash flow projections that would indicate we would not receive the remaining principal at maturity. For common equities, 89% of our common stock portfolio was indexed to the Russell 1000; as such, this portfolio may contain securities in a loss position for an extended period of time, subject to possible write-downs, as described below. We may retain these securities as long as the portfolio and index correlation remain similar. To the extent there is issuer-specific deterioration, we may write-down the securities of that issuer. The remaining 11% of our common stocks were part of a managed equity strategy selected and administered by external investment advisors. If our review of loss position securities indicates there was a fundamental, or market, impairment on these securities that was determined to be other-than-temporary, we would recognize a write-down in accordance with our stated policy.
The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position:
	Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
			Fair
($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
											Value								Value
31-Mar-15
Fixed maturities:
U.S. government obligations	1		$	7.2		$	0		1		$	7.2		$	0			0	$	0		$	0
State and local government obligations	57		270.3			(1.0		)	42		231.8			(0.5		)		15	38.5			(0.5		)
Corporate debt securities	25		390.3			(3.8		)	17		242.4			(2.3		)		8	147.9			(1.5		)
Residential mortgage-backed securities	80		1,013.90			(13.1		)	34		540.6			(3.1		)		46	473.3			(10.0		)
Commercial mortgage-backed securities	59		564.2			(1.1		)	53		560.8			(1.0		)		6	3.4			(0.1		)
Other asset-backed securities	30		490.9			(0.3		)	29		472.4			(0.1		)		1	18.5			(0.2		)
Redeemable preferred stocks	3		102.1			(6.6		)	1		33			(1.0		)		2	69.1			(5.6		)
Total fixed maturities	255		2,838.90			(25.9		)	177		2,088.20			(8.0		)		78	750.7			(17.9		)
Equity securities:
Nonredeemable preferred stocks	5		183.1			(5.9		)	2		74.5			(2.2		)		3	108.6			(3.7		)
Common equities	40		58.3			(6.0		)	40		58.3			(6.0		)		0	0			0
Total equity securities	45		241.4			(11.9		)	42		132.8			(8.2		)		3	108.6			(3.7		)
Total portfolio	300		$	3,080.30		$	(37.8	)	219		$	2,221.00		$	(16.2	)		81	$	859.3		$	(21.6	)
	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-Mar-14
Fixed maturities:
U.S. government obligations	18		$	930.4		$	(6.8	)	5		$	163.1		$	(0.3	)		13	$	767.3		$	(6.5	)
State and local government obligations	106		603			(9.2		)	28		76.8			(0.6		)		78	526.2			(8.6		)
Corporate debt securities	31		594.3			(7.2		)	7		101.6			(0.4		)		24	492.7			(6.8		)
Residential mortgage-backed securities	66		812.6			(11.9		)	24		359.7			(1.9		)		42	452.9			(10.0		)
Commercial mortgage-backed securities	59		783.7			(17.6		)	19		116.7			(0.2		)		40	667			(17.4		)
Other asset-backed securities	8		112.7			(0.6		)	4		36.8			(0.1		)		4	75.9			(0.5		)
Redeemable preferred stocks	3		93.5			(6.2		)	0		0			0				3	93.5			(6.2		)
Total fixed maturities	291		3,930.20			(59.5		)	87		854.7			(3.5		)		204	3,075.50			(56.0		)
Equity securities:
Nonredeemable preferred stocks	3		84.3			(1.2		)	0		0			0				3	84.3			(1.2		)
Common equities	9		34			(2.8		)	7		23.1			(1.6		)		2	10.9			(1.2		)
Total equity securities	12		118.3			(4.0		)	7		23.1			(1.6		)		5	95.2			(2.4		)
Total portfolio	303		$	4,048.50		$	(63.5	)	94		$	877.8		$	(5.1	)		209	$	3,170.70		$	(58.4	)
	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-14
Fixed maturities:
U.S. government obligations	11		$	428.2		$	(1.3	)	5		$	150.7		$	(0.3	)		6	$	277.5		$	(1.0	)
State and local government obligations	46		234.2			(1.1		)	28		177.9			(0.4		)		18	56.3			(0.7		)
Corporate debt securities	53		843.2			(10.4		)	43		647.5			(6.1		)		10	195.7			(4.3		)
Residential mortgage-backed securities	70		844.2			(10.8		)	33		465.2			(3.1		)		37	379			(7.7		)
Commercial mortgage-backed securities	63		723.4			(2.6		)	54		667.5			(1.4		)		9	55.9			(1.2		)
Other asset-backed securities	44		741.8			(0.8		)	42		715.7			(0.7		)		2	26.1			(0.1		)
Redeemable preferred stocks	3		103			(5.7		)	1		33			(1.0		)		2	70			(4.7		)
Total fixed maturities	290		3,918.00			(32.7		)	206		2,857.50			(13.0		)		84	1,060.50			(19.7		)
Equity securities:
Nonredeemable preferred stocks	8		231.4			(6.4		)	5		143.2			(3.6		)		3	88.2			(2.8		)
Common equities	20		68.4			(10.1		)	19		61.8			(9.6		)		1	6.6			(0.5		)
Total equity securities	28		299.8			(16.5		)	24		205			(13.2		)		4	94.8			(3.3		)
Total portfolio	318		$	4,217.80		$	(49.2	)	230		$	3,062.50		$	(26.2	)		88	$	1,155.30		$	(23.0	)
Since both March 31, 2014 and December 31, 2014, 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. All of the fixed-maturity securities in an unrealized loss position at March 31, 2015 in the table above are current with respect to required principal and interest payments. Since December 31, 2014, our nonredeemable preferred stocks decreased to five securities with unrealized losses, averaging approximately 3% of their total cost. We reviewed these securities and concluded that the unrealized losses are market-related adjustments to the values, which we determined not to be other-than-temporary; we expect to recover our initial investments on these securities. The number of issuers with unrealized losses in our common stock portfolio increased during the first quarter 2015, though the total gross unrealized loss for the portfolio decreased during the period. A review of the securities in a loss position did not uncover fundamental issues with the issuers that would indicate other-than-temporary impairments existed. Additionally, expectations for recovery in the next 12 months would put the fair values at or above our current book values. Lastly, we determined, as of the balance sheet date, that it was not likely these securities would be sold prior to that recovery.
Other-Than-Temporary Impairment (OTTI) The following table shows the total non-credit portion of the OTTI recorded in accumulated other comprehensive income, reflecting the original non-credit loss at the time the credit impairment was determined:
	March 31,								December 31,
(millions)	2015				2014				2014
Fixed maturities:
Residential mortgage-backed securities	$	(44.1	)		$	(44.1	)		$	(44.1	)
Commercial mortgage-backed securities	(0.6		)		(0.9		)		(0.6		)
Total fixed maturities	$	(44.7	)		$	(45.0	)		$	(44.7	)
The following tables provide rollforwards of the amounts related to credit losses recognized in earnings for the periods ended March 31, 2015 and 2014, 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 March 31, 2015
	Mortgage-Backed
(millions)	Residential				Commercial				Total
Balance at December 31, 2014	$	12.7			$	0.4			$	13.1
Change in recoveries of future cash flows expected to be collected1	(0.5		)		0				(0.5		)
Balance at March 31, 2015	$	12.2			$	0.4			$	12.6
	Three Months Ended March 31, 2014
	Mortgage-Backed
(millions)	Residential				Commercial				Total
Balance at December 31, 2013	$	19.2			$	0.4			$	19.6
Change in recoveries of future cash flows expected to be collected1	(0.1		)		0				(0.1		)
Balance at March 31, 2014	$	19.1			$	0.4			$	19.5
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.
Although we determined 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 the amount of potential credit losses on the securities that were in an unrealized loss position. In that process, we considered a number of factors and inputs related to the individual securities. The methodology and significant inputs used to measure the amount of credit losses in our portfolio included: current performance indicators on the 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. We did not have any credit impairment write-downs as of March 31, 2015 or 2014.
Realized Gains (Losses) The components of net realized gains (losses) for the three months ended March 31, were:
(millions)	2015				2014
Gross realized gains on security sales
Fixed maturities:
U.S. government obligations	$	4.9			$	6.5
State and local government obligations	0				4.4
Corporate and other debt securities	9.1				23.1
Residential mortgage-backed securities	0.1				1
Commercial mortgage-backed securities	10.8				6.1
Total fixed maturities	24.9				41.1
Equity securities:
Nonredeemable preferred stocks	15.8				25.9
Common equities	17.8				83
Subtotal gross realized gains on security sales	58.5				150
Gross realized losses on security sales
Fixed maturities:
U.S. government obligations	(0.8		)		(4.7		)
State and local government obligations	0				(0.1		)
Corporate and other debt securities	(0.8		)		(2.2		)
Commercial mortgage-backed securities	(0.2		)		(2.7		)
Redeemable preferred stocks	0				(3.2		)
Total fixed maturities	(1.8		)		(12.9		)
Equity securities:
Common equities	(0.4		)		(3.4		)
Subtotal gross realized losses on security sales	(2.2		)		(16.3		)
Net realized gains (losses) on security sales
Fixed maturities:
U.S. government obligations	4.1				1.8
State and local government obligations	0				4.3
Corporate and other debt securities	8.3				20.9
Residential mortgage-backed securities	0.1				1
Commercial mortgage-backed securities	10.6				3.4
Redeemable preferred stocks	0				(3.2		)
Total fixed maturities	23.1				28.2
Equity securities:
Nonredeemable preferred stocks	15.8				25.9
Common equities	17.4				79.6
Subtotal net realized gains (losses) on security sales	56.3				133.7
Other-than-temporary impairment losses
Equity securities:
Common equities	(7.9		)		0
Subtotal other-than-temporary impairment losses	(7.9		)		0
Other gains (losses)
Hybrid securities	3.3				3.8
Derivative instruments	(18.8		)		(19.3		)
Litigation settlements	0.1				1.2
Subtotal other gains (losses)	(15.4		)		(14.3		)
Total net realized gains (losses) on securities	$	33			$	119.4
Gross realized gains and losses were predominantly the result of sales transactions in our fixed-income portfolio related to movements in credit spreads and interest rates and sales from our equity portfolios. In addition, gains and losses reflect recoveries from litigation settlements 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 equity portfolio.
Net Investment Income  The components of net investment income for the three months ended March 31, were:
(millions)	2015			2014
Fixed maturities:
U.S. government obligations	$	9.1		$	13
State and local government obligations	11.9			12.8
Foreign government obligations	0.1			0.1
Corporate debt securities	22.9			22
Residential mortgage-backed securities	12.8			9.9
Commercial mortgage-backed securities	16.9			16.7
Other asset-backed securities	5			4.2
Redeemable preferred stocks	3.8			4.1
Total fixed maturities	82.5			82.8
Equity securities:
Nonredeemable preferred stocks	10.5			9.9
Common equities	11.7			10.4
Short-term investments	0.4			0.2
Investment income	105.1			103.3
Investment expenses	(5.3		)	(4.1		)
Net investment income	$	99.8		$	99.2
Trading Securities At March 31, 2015 and 2014, and December 31, 2014, we did not hold any trading securities and did not have any net realized gains (losses) on trading securities for the three months ended March 31, 2015 and 2014.
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 March 31, 2015 and 2014, and December 31, 2014, and for the three months ended March 31, 2015 and 2014:
(millions)															Balance Sheet2											Comprehensive Income Statement
																	Assets (Liabilities)									Pretax Net Realized
																	Fair Value									Gains (Losses)
	Notional Value1																									Three Months Ended
	March 31,								Dec. 31,								March 31,							Dec. 31,		March 31,
Derivatives designated as:	2015				2014				2014				Purpose		Classification		2015			2014				2014		2015			2014
Hedging instruments
Closed:
Ineffective cash flow hedge	$	0			$	0			$	44			Manage interest		NA		$	0		$	0			$	0	$	0		$	0
													rate risk
Non-hedging instruments
Assets:
Interest rate swaps	750				750				750				Manage portfolio		Investments—		0.1			51.9				15.8		(18.8		)	(19.3		)
													duration		fixed maturities
Total	NA				NA				NA								$	0.1		$	51.9			$	15.8	$	(18.8	)	$	(19.3	)
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 expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
NA=ot Applicable
CASH FLOW HEDGES
In January 2015, upon issuance of $400 million of 3.70% Senior Notes due 2045 (the "3.70% 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 $12.9 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 3.70% Senior Notes.
Our ineffective cash flow hedge, which is reflected in the table above, resulted from the repurchase of a portion of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 during 2014, and we reclassified the unrealized gain on forecasted transactions to net realized gains on securities. There was no repurchase activity during the first quarter of 2015 or 2014.
See Note 4 – Debt for further discussion.
INTEREST RATE SWAPS
We use interest rate swap contracts primarily to manage the fixed-income portfolio duration. At March 31, 2015 and 2014, and December 31, 2014, we held interest rate swap positions for which we are paying a fixed rate and receiving a variable rate, effectively shortening the duration of our fixed-income portfolio. Since inception, interest rates have increased slightly; however, as interest rates fell during 2015, our fair value gain decreased by $15.7 million.
As of March 31, 2015, the balance of the cash collateral that we delivered to the applicable counterparties on the positions was $4.7 million. As of March 31, 2014 and December 31, 2014, the balance of the cash collateral that we had received from the applicable counterparties on the positions was $43.3 million and $16.1 million, respectively.

Fair_Value

Fair Value	3 Months Ended
	Mar. 31, 2015
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
	31-Mar-15
	Fixed maturities:
	U.S. government obligations	$	2,708.20	$	0		$	0	$	2,708.20	$	2,678.10
	State and local government obligations	0		2,273.80			0		2,273.80		2,224.80
	Foreign government obligations	20		0			0		20		20
	Corporate debt securities	0		2,904.00			0		2,904.00		2,851.60
	Subtotal	2,728.20		5,177.80			0		7,906.00		7,774.50
	Asset-backed securities:
	Residential mortgage-backed	0		1,648.20			0		1,648.20		1,629.20
	Commercial mortgage-backed	0		2,475.70			11.4		2,487.10		2,437.40
	Other asset-backed	0		1,901.50			0		1,901.50		1,896.10
	Subtotal asset-backed securities	0		6,025.40			11.4		6,036.80		5,962.70
	Redeemable preferred stocks:
	Financials	0		98.2			0		98.2		77.3
	Utilities	0		64.4			0		64.4		65
	Industrials	0		114.4			0		114.4		118
	Subtotal redeemable preferred stocks	0		277			0		277		260.3
	Total fixed maturities	2,728.20		11,480.20			11.4		14,219.80		13,997.50
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	181.7		576.5			69.9		828.1		598.3
	Subtotal nonredeemable preferred stocks	181.7		576.5			69.9		828.1		598.3
	Common equities:
	Common stocks	2,515.40		0			0		2,515.40		1,294.70
	Other risk investments	0		0			0.3		0.3		0.3
	Subtotal common equities	2,515.40		0			0.3		2,515.70		1,295.00
	Total fixed maturities and equity securities	5,425.30		12,056.70			81.6		17,563.60		15,890.80
	Short-term investments	2,267.00		0			0		2,267.00		2,267.00
	Total portfolio	$	7,692.30	$	12,056.70		$	81.6	$	19,830.60	$	18,157.80
	Debt	$	0	$	2,910.90		$	0	$	2,910.90	$	2,560.10
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total		Cost
	31-Mar-14
	Fixed maturities:
	U.S. government obligations	$	3,230.00	$	0		$	0	$	3,230.00	$	3,197.80
	State and local government obligations	0		2,154.90			0		2,154.90		2,131.00
	Foreign government obligations	17.9		0			0		17.9		17.9
	Corporate debt securities	0		2,501.60			0		2,501.60		2,461.60
	Subtotal	3,247.90		4,656.50			0		7,904.40		7,808.30
	Asset-backed securities:
	Residential mortgage-backed	0		1,307.40			0		1,307.40		1,286.70
	Commercial mortgage-backed	0		2,033.00			28.6		2,061.60		2,037.70
	Other asset-backed	0		942.5			0		942.5		936.2
	Subtotal asset-backed securities	0		4,282.90			28.6		4,311.50		4,260.60
	Redeemable preferred stocks:
	Financials	0		107.4			0		107.4		84.2
	Utilities	0		65.2			0		65.2		64.9
	Industrials	0		117.7			0		117.7		117.8
	Subtotal redeemable preferred stocks	0		290.3			0		290.3		266.9
	Total fixed maturities	3,247.90		9,229.70			28.6		12,506.20		12,335.80
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	284		411.8			42.1		737.9		460.7
	Subtotal nonredeemable preferred stocks	284		411.8			42.1		737.9		460.7
	Common equities:
	Common stocks	2,278.30		0			0		2,278.30		1,252.30
Other risk investments	0		0			0.4		0.4		0.4
Subtotal common equities	2,278.30		0			0.4		2,278.70		1,252.70
Total fixed maturities and equity securities	5,810.20		9,641.50			71.1		15,522.80		14,049.20
Short-term investments	1,611.70		261.2			0		1,872.90		1,872.90
Total portfolio	$	7,421.90	$	9,902.70		$	71.1	$	17,395.70	$	15,922.10
Debt	$	0	$	2,152.50		$	0	$	2,152.50	$	1,861.30
	Fair Value
(millions)	Level 1		Level 2			Level 3		Total		Cost
31-Dec-14
Fixed maturities:
U.S. government obligations	$	2,667.10	$	0		$	0	$	2,667.10	$	2,641.10
State and local government obligations	0		2,139.20			0		2,139.20		2,095.70
Foreign government obligations	14.2		0			0		14.2		14.2
Corporate debt securities	0		2,836.70			0		2,836.70		2,813.90
Subtotal	2,681.30		4,975.90			0		7,657.20		7,564.90
Asset-backed securities:
Residential mortgage-backed	0		1,658.50			0		1,658.50		1,635.50
Commercial mortgage-backed	0		2,304.00			11.6		2,315.60		2,278.70
Other asset-backed	0		1,638.70			0		1,638.70		1,634.90
Subtotal asset-backed securities	0		5,601.20			11.6		5,612.80		5,549.10
Redeemable preferred stocks:
Financials	0		97.9			0		97.9		77.3
Utilities	0		65.3			0		65.3		65
Industrials	0		116			0		116		117.9
Subtotal redeemable preferred stocks	0		279.2			0		279.2		260.2
Total fixed maturities	2,681.30		10,856.30			11.6		13,549.20		13,374.20
Equity securities:
Nonredeemable preferred stocks:
Financials	204.1		554.1			69.3		827.5		590.4
Subtotal nonredeemable preferred stocks	204.1		554.1			69.3		827.5		590.4
Common equities:
Common stocks	2,491.90		0			0		2,491.90		1,288.80
Other risk investments	0		0			0.4		0.4		0.4
Subtotal common equities	2,491.90		0			0.4		2,492.30		1,289.20
Total fixed maturities and equity securities	5,377.30		11,410.40			81.3		16,869.00		15,253.80
Short-term investments	1,937.00		212			0		2,149.00		2,149.00
Total portfolio	$	7,314.30	$	11,622.40		$	81.3	$	19,018.00	$	17,402.80
Debt	$	0	$	2,527.50		$	0	$	2,527.50	$	2,164.70
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. We did not have any transfers between Level 1 and Level 2 during the first quarter of 2015. During the first quarter of 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; this was the only transfer during 2014. 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 both March 31, 2015 and December 31, 2014, vendor-quoted prices represented 50% of our Level 1 classifications (excluding short-term investments), compared to 55% at March 31, 2014. The securities quoted by vendors in Level 1 primarily represent our holdings in U.S. Treasury Notes, which are frequently traded and the quotes are considered similar to exchange-traded quotes. The balance of our Level 1 pricing comes from quotes obtained directly from trades made on active exchanges. The decline in vendor-quoted Level 1 prices since March 31, 2014 was due to a reduction of U.S. Treasury Notes with the funds deployed primarily to short-term investments.
At both March 31, 2015 and December 31, 2014, vendor-quoted prices comprised 97% of our Level 2 classifications (excluding short-term investments), while dealer-quoted prices represented 3%, compared to 96% and 4% at March 31, 2014. In our process for selecting a source (e.g., dealer, pricing service) to provide pricing for securities in our portfolio, we reviewed documentation from the sources that detailed the pricing techniques and methodologies used by these sources and determined if their policies adequately considered market activity, either based on specific transactions for the particular security type or based on modeling of securities with similar credit quality, duration, yield, and structure that were recently transacted. Once a source is chosen, we continue to monitor any changes or modifications to their processes by reviewing their documentation on internal controls for pricing and market reviews. We review quality control measures of our sources as they become available to determine if any significant changes have occurred from period to period that might indicate issues or concerns regarding their evaluation or market coverage.
As part of our pricing procedures, we obtain quotes from more than one source to help us fully evaluate the market price of securities. However, our internal pricing policy is to use a consistent source for individual securities in order to maintain the integrity of our valuation process. Quotes obtained from the sources are not considered binding offers to transact. Under our policy, when a review of the valuation received from our selected source appears to be outside of what is considered market level activity (which is defined as trading at spreads or yields significantly different than those of comparable securities or outside the general sector level movement without a reasonable explanation), we may use an alternate source’s price. To the extent we determine that it may be prudent to substitute one source’s price for another, we will contact the initial source to obtain an understanding of the factors that may be contributing to the significant price variance, which often leads the source to adjust their pricing input data for future pricing.
To allow us to determine if our initial source is providing a price that is outside of a reasonable range, we review our portfolio pricing on a weekly basis. We frequently challenge prices from our sources when a price provided does not match our expectations based on our evaluation of market trends and activity. Initially, we perform a review of our portfolio by sector to identify securities whose prices appear outside of a reasonable range. We then perform a more detailed review of fair values for securities disclosed as Level 2. We review dealer bids and quotes for these and/or similar securities to determine the market level context for our valuations. We then evaluate inputs relevant for each class of securities disclosed in the preceding hierarchy tables.
For our structured debt securities, including commercial, residential, and asset-backed securities, we evaluate available market-related data for these and similar securities related to collateral, delinquencies, and defaults for historical trends and reasonably estimable projections, as well as historical prepayment rates and current prepayment assumptions and cash flow estimates. We further stratify each class of our structured debt securities into more finite sectors (e.g., planned amortization class, first pay, second pay, senior, subordinated, etc.) and use duration, credit quality, and coupon to determine if the fair value is appropriate.
For our corporate debt and preferred stock (redeemable and nonredeemable) portfolios, 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 March 31, 2015 and 2014, and December 31, 2014, 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 March 31, 2015, we held one private preferred equity security (in ARX Holding Corp.) with a value of $69.9 million, that was priced internally. The same security had a value of $42.1 million at March 31, 2014 and $69.3 million at December 31, 2014. The increase in value is due primarily to a higher price to book ratio multiple included in the terms of the stock purchase agreement we entered into during December 2014 to purchase a majority interest in ARX Holding Corp. This was the only internally-priced security in the portfolio at March 31, 2015 and 2014, and December 31, 2014.
We review the prices from our external sources for reasonableness using internally developed assumptions to derive prices for the securities, which are then compared to the prices we received. During 2015 or 2014, there were no material assets or liabilities measured at fair value on a nonrecurring basis. Based on our review, all prices received from external sources remained unadjusted.
The following tables provide a summary of changes in fair value associated with Level 3 assets for the three months ended March 31, 2015 and 2014:
	Level 3 Fair Value
	Three Months Ended March 31, 2015
(millions)	Fair Value at December 31, 2014		Calls/			Purchases		Sales		Net Realized (Gain) Loss on Sales		Change in Valuation			Net		Fair Value at March 31, 2015
			Maturities/												Transfers
			Paydowns												In (Out)
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0	$	0		$	0	$	0	$	0	$	0		$	0	$	0
Commercial mortgage-backed	11.6		(0.2		)	0		0		0		0			0		11.4
Total fixed maturities	11.6		(0.2		)	0		0		0		0			0		11.4
Equity securities:
Nonredeemable preferred stocks:
Financials1	69.3		0			0		0		0		0.6			0		69.9
Common equities:
Other risk investments	0.4		0			0		0		0		(0.1		)	0		0.3
Total Level 3 securities	$	81.3	$	(0.2	)	$	0	$	0	$	0	$	0.5		$	0	$	81.6
1The $0.6 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 March 31, 2014
(millions)	Fair Value at December 31, 2013		Calls/			Purchases		Sales		Net Realized (Gain) Loss on Sales		Change in			Net		Fair Value at March 31, 2014
			Maturities/									Valuation			Transfers
			Paydowns												In (Out)
Fixed maturities:
Asset-backed securities:
Residential mortgage-backed	$	0.2	$	0		$	0	$	0	$	0	$	(0.2	)	$	0	$	0
Commercial mortgage-backed	29		(0.5		)	0		0		0		0.1			0		28.6
Total fixed maturities	29.2		(0.5		)	0		0		0		(0.1		)	0		28.6
Equity securities:
Nonredeemable preferred stocks:
Financials1	39		0			0		0		0		3.1			0		42.1
Common equities:
Other risk investments	0.5		(0.1		)	0		0		0		0			0		0.4
Total Level 3 securities	$	68.7	$	(0.6	)	$	0	$	0	$	0	$	3		$	0	$	71.1
1The $3.1 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at March 31, 2015 and 2014, and December 31, 2014:
	Quantitative Information about Level 3 Fair Value Measurements
($ in millions)	Fair Value at March 31, 2015		Valuation Technique		Unobservable Input	Unobservable
						Input Assumption
Fixed maturities:
Asset-backed securities:
Commercial mortgage-backed	$	11.4	External vendor		Prepayment rate1	0
Total fixed maturities	11.4
Equity securities:
Nonredeemable preferred stocks:
Financials	69.9		Multiple of tangible net book value		Price to book ratio multiple	2.6
Subtotal Level 3 securities	81.3
Pricing exemption securities2	0.3
Total Level 3 securities	$	81.6
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 March 31, 2014		Valuation Technique		Unobservable Input	Unobservable
						Input Assumption
Fixed maturities:
Asset-backed securities:
Commercial mortgage-backed	$	28.6	External vendor		Prepayment rate1	0
Total fixed maturities	28.6
Equity securities:
Nonredeemable preferred stocks:
Financials	42.1		Multiple of tangible net book value		Price to book ratio multiple	1.9
Subtotal Level 3 securities	70.7
Pricing exemption securities2	0.4
Total Level 3 securities	$	71.1
1Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2 The fair values for these securities were 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 Dec. 31, 2014		Valuation Technique		Unobservable Input	Unobservable
						Input Assumption
Fixed maturities:
Asset-backed securities:
Commercial mortgage-backed	$	11.6	External vendor		Prepayment rate1	0
Total fixed maturities	11.6
Equity securities:
Nonredeemable preferred stocks:
Financials	69.3		Multiple of tangible net book value		Price to book ratio multiple	2.6
Subtotal Level 3 securities	80.9
Pricing exemption securities2	0.4
Total Level 3 securities	$	81.3
1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
2 The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.
Due to the relative size of the Level 3 securities’ fair values compared to the total portfolio’s fair value, any changes in pricing methodology would not have a significant change in valuation that would materially impact net or comprehensive income.

Debt

Debt	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt	Debt — Debt consisted of:
		31-Mar-15				31-Mar-14				31-Dec-14
	(millions)	Carrying		Fair		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value		Value		Value
	3.75% Senior Notes due 2021	$	497.9	$	542.6	$	497.6	$	524.5	$	497.8	$	535.6
	6 5/8% Senior Notes due 2029	295.6		393.6		295.4		381.8		295.5		400.6
	6.25% Senior Notes due 2032	394.9		525.6		394.7		501.4		394.8		527.9
	4.35% Senior Notes due 2044	346.3		387.1		0		0		346.3		378.9
	3.70% Senior Notes due 2045	394.9		394.8		0		0		0		0
	6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	630.5		667.2		673.6		744.8		630.3		684.5
	Total	$	2,560.10	$	2,910.90	$	1,861.30	$	2,152.50	$	2,164.70	$	2,527.50
	In January 2015, we issued $400 million of our 3.70% Senior Notes due 2045 (the “3.70% Senior Notes”) and, in April 2014, $350 million of our 4.35% Senior Notes due 2044 (the “4.35% Senior Notes”) in underwritten public offerings. We
	received proceeds, after deducting underwriter's discounts and commissions of approximately $394.9 million and $346.3 million, respectively. In addition, we incurred expenses of approximately $0.8 million and $0.7 million, respectively, related to the issuances. Upon issuance of the 3.70% Senior Notes and 4.35% Senior Notes, we also closed forecasted debt issuance hedges, which were entered into to hedge against a possible rise in interest rates, and recognized a $12.9 million and a $1.6 million pretax loss, respectively, as part of accumulated other comprehensive income (loss); the losses will be recognized as an
	adjustment to interest expense and amortized over the applicable life of the 3.70% and 4.35% Senior Notes.
	We did not repurchase any debt securities in the first quarter of 2015 or 2014. During the year ended December 31, 2014, we repurchased, in the open market, $44.3 million in aggregate principal amount of our 6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 (the "6.70% Debentures"). Since the amount paid exceeded the carrying value of the debt we repurchased, we recognized losses on these extinguishments of $4.8 million. 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 the first quarter 2015, 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 2014, 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 or the sum of the Federal Funds Open Rate plus 50 basis points. Each advance would need to be repaid on the 30th day after the advance or, if earlier, on April 30, 2016, 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 three months of 2015 or throughout 2014.

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes — At March 31, 2015 and 2014, and December 31, 2014, we determined that we did not need a valuation allowance on our gross deferred tax assets. Although realization of the deferred tax assets is not assured, management believes that it is more likely than not that the deferred tax assets will be realized based on our expectation that we will be able to fully utilize the deductions that are ultimately recognized for tax purposes. For the three months ended March 31, 2015, there have been no material changes in our uncertain tax positions or effective tax rate.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2015
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:
		Three Months Ended March 31,
	(millions)	2015		2014
	Income taxes	$	60	$	0
	Interest	19.3		19.3

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	Segment Information — Our Personal Lines segment writes insurance for personal autos and recreational vehicles. Our Commercial Lines segment writes primary liability and physical damage insurance for automobiles and trucks owned and/or operated predominantly by small businesses in the business auto, for-hire transportation, contractor, for-hire specialty, tow, and for-hire livery markets. Our 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 March 31,
		2015						2014
	(millions)	Revenues			Pretax			Revenues		Pretax
					Profit					Profit
					(Loss)					(Loss)
	Personal Lines
	Agency	$	2,244.50		$	194.5		$	2,203.20	$	178.6
	Direct	1,955.40			68.2			1,762.20		71
	Total Personal Lines1	4,199.90			262.7			3,965.40		249.6
	Commercial Lines	466.4			78.5			436.9		40.9
	Other indemnity	0			0.4			0		(0.7		)
	Total underwriting operations	4,666.30			341.6			4,402.30		289.8
	Fees and other revenues2	73.7			NA			72.8		NA
	Service businesses	17.2			1.3			9.8		0.1
	Investments3	138.1			132.8			222.7		218.6
	Interest expense	NA			(32.5		)	NA		(26.7		)
	Consolidated total	$	4,895.30		$	443.2		$	4,707.60	$	481.8
	NA =ot Applicable
	1Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in both the first quarters of 2015 and 2014; 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.
	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 March 31,
		2015				2014
		Under-writing		Combined		Under-writing		Combined
		Margin		Ratio		Margin		Ratio
	Personal Lines
	Agency	8.7	%	91.3		8.1	%	91.9
	Direct	3.5		96.5		4		96
	Total Personal Lines	6.3		93.7		6.3		93.7
	Commercial Lines	16.8		83.2		9.4		90.6
	Other indemnity1	NM		NM		NM		NM
	Total underwriting operations	7.3		92.7		6.6		93.4
	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	3 Months Ended
	Mar. 31, 2015
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 companywide 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 2014, the Board determined the target percentage for 2015 to be 33-1/3% of annual after-tax underwriting income, which is unchanged from the 2014 target percentage.
	The Gainshare factor can range from zero to two and is determined by comparing our 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 March 31, 2015, the Gainshare factor was 0.95. 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. In addition, 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 2015 were to be paid, the Board would likely declare the 2015 annual dividend in December 2015, with a record date in early 2016 and payment shortly thereafter. For the three months ended March 31, 2015, our comprehensive income was $321.8 million, which is higher than the $222.0 million of after-tax underwriting income for the same period.
	Following is a summary of our shareholder dividends, both variable and special, that were paid in the last two years:
	(millions, except per share amounts)			Amount
	Dividend Type	Declared	Paid	Per Share		Total
	Annual – Variable	Dec-14	Feb-15	$	0.6862	$	404.1
	Annual – Variable	Dec-13	Feb-14	0.4929		293.9
	Special	Dec-13	Feb-14	1		596.3

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2015
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						transactions
	Balance at December 31, 2014	$	1,574.00		$	(550.9	)	$	1,023.10		$	1,021.90		$	1.5		$	(0.3	)
	Other comprehensive income (loss) before reclassifications:
	Investment securities	99.3			(34.7		)	64.6			64.6			0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	(12.8		)	4.4			(8.4		)	0			(8.4		)	0
	Foreign currency translation adjustment	(0.9		)	0.4			(0.5		)	0			0			(0.5		)
	Total other comprehensive income (loss) before reclassifications	85.6			(29.9		)	55.7			64.6			(8.4		)	(0.5		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(7.9		)	2.8			(5.1		)	(5.1		)	0			0
	Net realized gains (losses) on securities	52.8			(18.5		)	34.3			34.3			0			0
	Interest expense	0.5			(0.2		)	0.3			0			0.3			0
	Total reclassification adjustment for amounts realized in net income	45.4			(15.9		)	29.5			29.2			0.3			0
	Total other comprehensive income (loss)	40.2			(14.0		)	26.2			35.4			(8.7		)	(0.5		)
	Balance at March 31, 2015	$	1,614.20		$	(564.9	)	$	1,049.30		$	1,057.30		$	(7.2	)	$	(0.8	)
											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						transactions
	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	131.8			(46.1		)	85.7			85.7			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	0			0			0			0			0			0
	Total other comprehensive income (loss) before reclassifications	131.8			(46.1		)	85.7			85.7			0			0
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	0			0			0			0			0			0
	Net realized gains (losses) on securities	131.9			(46.1		)	85.8			85.8			0			0
	Interest expense	0.5			(0.2		)	0.3			0			0.3			0
	Total reclassification adjustment for amounts realized in net income	132.4			(46.3		)	86.1			85.8			0.3			0
	Total other comprehensive income (loss)	(0.6		)	0.2			(0.4		)	(0.1		)	(0.3		)	0
	Balance at March 31, 2014	$	1,463.50		$	(512.2	)	$	951.3		$	946.9		$	3.8		$	0.6
	In an effort to manage interest rate risk, we entered into forecasted transactions on each of our outstanding debt issuances. Upon issuing the debt, the gains (losses) recognized on these cash flow hedges are recorded as unrealized gains (losses) in accumulated other comprehensive income and amortized into interest expense over the term of the related debt issuance. We expect to reclassify $1.9 million (pretax) into income during the next 12 months, related to net unrealized gains on forecasted transactions.

Litigation

Litigation	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015. 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, 2014, 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	3 Months Ended
	Mar. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Standard	New Accounting Standard — In April 2015, the Financial Accounting Standards Board issued an accounting standard update related to the presentation of the cost of issuing debt on balance sheets. This standard requires that all costs incurred to issue debt be presented in the balance sheet as a direct deduction from the carrying value of the debt. This standard, which is required to be applied on a retrospective basis, is effective for fiscal years beginning after December 15, 2015 (2016 for calendar-year companies), with early adoption permitted. We have historically deducted the majority of our debt issuance costs from the carrying value of the debt, therefore, we do not expect this standard to have a significant impact on our financial condition, cash flows, or results of operations.

Subsequent_Event

Subsequent Event	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	Subsequent Event — On April 1, 2015, we acquired approximately 63.5% of the outstanding capital stock of ARX Holding Corp. (ARX), the parent company of American Strategic Insurance (ASI), primarily from non-management shareholders. ASI is one of the 20 largest homeowners insurance carriers in the United States. The total cost of this acquisition was approximately $877 million and was funded with available cash on hand. As of March 31, 2015, ARX, on a consolidated basis, had assets of $1.8 billion, which consists primarily of investments, and liabilities of $1.3 billion, including unearned premiums of $0.6 billion, loss and loss adjustment expense reserves of $0.3 billion, and debt of $0.2 billion. We are currently evaluating the initial accounting for the acquisition, including purchase price allocation.
	Prior to this additional acquisition, we held a 5% interest in ARX that had a value of $69.9 million at March 31, 2015. During the first quarter 2015, we recognized a $0.6 million holding period gain on this position that was reflected in net realized gains (losses) on securities in our statement of comprehensive income (See Note 3 - Fair Value, for a discussion on the method used for valuing this security). Through the April 2015 acquisition, which brought our total ownership interest to 68.5%, we are able to build on the pre-existing relationship we had with ASI to further our bundling strategy in the Agency channel.

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2015
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
	31-Mar-15
	Fixed maturities:
	U.S. government obligations	$	2,678.10			$	30.1			$	0			$	0			$	2,708.20		13.7	%
	State and local government obligations	2,224.80				50				(1.0		)		0				2,273.80			11.5
	Foreign government obligations	20				0				0				0				20			0.1
	Corporate debt securities	2,851.60				54.4				(3.8		)		1.8				2,904.00			14.6
	Residential mortgage-backed securities	1,629.20				32.4				(13.1		)		(0.3		)		1,648.20			8.3
	Commercial mortgage-backed securities	2,437.40				50.1				(1.1		)		0.7				2,487.10			12.5
	Other asset-backed securities	1,896.10				4.9				(0.3		)		0.8				1,901.50			9.6
	Redeemable preferred stocks	260.3				23.3				(6.6		)		0				277			1.4
	Total fixed maturities	13,997.50				245.2				(25.9		)		3				14,219.80			71.7
	Equity securities:
	Nonredeemable preferred stocks	598.3				192.5				(5.9		)		43.2				828.1			4.2
	Common equities	1,295.00				1,226.70				(6.0		)		0				2,515.70			12.7
	Short-term investments	2,267.00				0				0				0				2,267.00			11.4
	Total portfolio2,3	$	18,157.80			$	1,664.40			$	(37.8	)		$	46.2			$	19,830.60		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Mar-14
	Fixed maturities:
	U.S. government obligations	$	3,197.80			$	39			$	(6.8	)		$	0			$	3,230.00		18.5	%
	State and local government obligations	2,131.00				33.1				(9.2		)		0				2,154.90			12.4
	Foreign government obligations	17.9				0				0				0				17.9			0.1
	Corporate debt securities	2,461.60				45.4				(7.2		)		1.8				2,501.60			14.4
	Residential mortgage-backed securities	1,286.70				32.6				(11.9		)		0				1,307.40			7.5
	Commercial mortgage-backed securities	2,037.70				41.5				(17.6		)		0				2,061.60			11.9
	Other asset-backed securities	936.2				6.6				(0.6		)		0.3				942.5			5.4
	Redeemable preferred stocks	266.9				29.6				(6.2		)		0				290.3			1.7
	Total fixed maturities	12,335.80				227.8				(59.5		)		2.1				12,506.20			71.9
	Equity securities:
	Nonredeemable preferred stocks	460.7				263.7				(1.2		)		14.7				737.9			4.2
	Common equities	1,252.70				1,028.80				(2.8		)		0				2,278.70			13.1
	Short-term investments	1,872.90				0				0				0				1,872.90			10.8
	Total portfolio2,3	$	15,922.10			$	1,520.30			$	(63.5	)		$	16.8			$	17,395.70		100	%
	($ in millions)	Cost				Gross				Gross				Net				Fair			% of
						Unrealized Gains				Unrealized				Realized				Value			Total
										Losses				Gains							Fair
														(Losses)1							Value
	31-Dec-14
	Fixed maturities:
	U.S. government obligations	$	2,641.10			$	27.3			$	(1.3	)		$	0			$	2,667.10		14	%
	State and local government obligations	2,095.70				44.6				(1.1		)		0				2,139.20			11.2
	Foreign government obligations	14.2				0				0				0				14.2			0.1
	Corporate debt securities	2,813.90				32.9				(10.4		)		0.3				2,836.70			14.9
	Residential mortgage-backed securities	1,635.50				34.5				(10.8		)		(0.7		)		1,658.50			8.7
	Commercial mortgage-backed securities	2,278.70				39.3				(2.6		)		0.2				2,315.60			12.2
	Other asset-backed securities	1,634.90				3.8				(0.8		)		0.8				1,638.70			8.6
	Redeemable preferred stocks	260.2				24.7				(5.7		)		0				279.2			1.5
	Total fixed maturities	13,374.20				207.1				(32.7		)		0.6				13,549.20			71.2
	Equity securities:
	Nonredeemable preferred stocks	590.4				201.1				(6.4		)		42.4				827.5			4.4
	Common equities	1,289.20				1,213.20				(10.1		)		0				2,492.30			13.1
	Short-term investments	2,149.00				0				0				0				2,149.00			11.3
	Total portfolio2,3	$	17,402.80			$	1,621.40			$	(49.2	)		$	43			$	19,018.00		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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
	3The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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:
		March 31,								December 31,
	(millions)	2015				2014				2014
	Fixed maturities:
	Corporate debt securities	$	132.9			$	145.7			$	139.8
	Residential mortgage-backed securities	111.7				0				120.7
	Commercial mortgage-backed securities	18				0				31.2
	Other asset-backed securities	13.1				13.9				13.7
	Total fixed maturities	275.7				159.6				305.4
	Equity securities:
	Nonredeemable preferred stocks	137.2				63.8				122.3
	Total hybrid securities	$	412.9			$	223.4			$	427.7
Composition of Fixed Maturities by Maturity	The composition of fixed maturities by maturity at March 31, 2015, was:
	(millions)	Cost				Fair Value
	Less than one year	$	3,839.10			$	3,878.20
	One to five years	6,771.60				6,848.90
	Five to ten years	3,318.80				3,413.50
	Ten years or greater	67.9				79.1
	Total1	$	13,997.40			$	14,219.70
	1Excludes $0.1 million related to our open interest rate swap positions.
Gross Unrealized Losses by Major Security	The following tables show the composition of gross unrealized losses by major security type and by the length of time that individual securities have been in a continuous unrealized loss position:
		Total No. of Sec.		Total			Gross Unrealized Losses			Less than 12 Months									12 Months or Greater
				Fair
	($ in millions)			Value						No. of Sec.		Fair			Unrealized Losses				No. of Sec.	Fair			Unrealized Losses
												Value								Value
	31-Mar-15
	Fixed maturities:
	U.S. government obligations	1		$	7.2		$	0		1		$	7.2		$	0			0	$	0		$	0
	State and local government obligations	57		270.3			(1.0		)	42		231.8			(0.5		)		15	38.5			(0.5		)
	Corporate debt securities	25		390.3			(3.8		)	17		242.4			(2.3		)		8	147.9			(1.5		)
	Residential mortgage-backed securities	80		1,013.90			(13.1		)	34		540.6			(3.1		)		46	473.3			(10.0		)
	Commercial mortgage-backed securities	59		564.2			(1.1		)	53		560.8			(1.0		)		6	3.4			(0.1		)
	Other asset-backed securities	30		490.9			(0.3		)	29		472.4			(0.1		)		1	18.5			(0.2		)
	Redeemable preferred stocks	3		102.1			(6.6		)	1		33			(1.0		)		2	69.1			(5.6		)
	Total fixed maturities	255		2,838.90			(25.9		)	177		2,088.20			(8.0		)		78	750.7			(17.9		)
	Equity securities:
	Nonredeemable preferred stocks	5		183.1			(5.9		)	2		74.5			(2.2		)		3	108.6			(3.7		)
	Common equities	40		58.3			(6.0		)	40		58.3			(6.0		)		0	0			0
	Total equity securities	45		241.4			(11.9		)	42		132.8			(8.2		)		3	108.6			(3.7		)
	Total portfolio	300		$	3,080.30		$	(37.8	)	219		$	2,221.00		$	(16.2	)		81	$	859.3		$	(21.6	)
		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-Mar-14
	Fixed maturities:
	U.S. government obligations	18		$	930.4		$	(6.8	)	5		$	163.1		$	(0.3	)		13	$	767.3		$	(6.5	)
	State and local government obligations	106		603			(9.2		)	28		76.8			(0.6		)		78	526.2			(8.6		)
	Corporate debt securities	31		594.3			(7.2		)	7		101.6			(0.4		)		24	492.7			(6.8		)
	Residential mortgage-backed securities	66		812.6			(11.9		)	24		359.7			(1.9		)		42	452.9			(10.0		)
	Commercial mortgage-backed securities	59		783.7			(17.6		)	19		116.7			(0.2		)		40	667			(17.4		)
	Other asset-backed securities	8		112.7			(0.6		)	4		36.8			(0.1		)		4	75.9			(0.5		)
	Redeemable preferred stocks	3		93.5			(6.2		)	0		0			0				3	93.5			(6.2		)
	Total fixed maturities	291		3,930.20			(59.5		)	87		854.7			(3.5		)		204	3,075.50			(56.0		)
	Equity securities:
	Nonredeemable preferred stocks	3		84.3			(1.2		)	0		0			0				3	84.3			(1.2		)
	Common equities	9		34			(2.8		)	7		23.1			(1.6		)		2	10.9			(1.2		)
	Total equity securities	12		118.3			(4.0		)	7		23.1			(1.6		)		5	95.2			(2.4		)
	Total portfolio	303		$	4,048.50		$	(63.5	)	94		$	877.8		$	(5.1	)		209	$	3,170.70		$	(58.4	)
		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-14
	Fixed maturities:
	U.S. government obligations	11		$	428.2		$	(1.3	)	5		$	150.7		$	(0.3	)		6	$	277.5		$	(1.0	)
	State and local government obligations	46		234.2			(1.1		)	28		177.9			(0.4		)		18	56.3			(0.7		)
	Corporate debt securities	53		843.2			(10.4		)	43		647.5			(6.1		)		10	195.7			(4.3		)
	Residential mortgage-backed securities	70		844.2			(10.8		)	33		465.2			(3.1		)		37	379			(7.7		)
	Commercial mortgage-backed securities	63		723.4			(2.6		)	54		667.5			(1.4		)		9	55.9			(1.2		)
	Other asset-backed securities	44		741.8			(0.8		)	42		715.7			(0.7		)		2	26.1			(0.1		)
	Redeemable preferred stocks	3		103			(5.7		)	1		33			(1.0		)		2	70			(4.7		)
	Total fixed maturities	290		3,918.00			(32.7		)	206		2,857.50			(13.0		)		84	1,060.50			(19.7		)
	Equity securities:
	Nonredeemable preferred stocks	8		231.4			(6.4		)	5		143.2			(3.6		)		3	88.2			(2.8		)
	Common equities	20		68.4			(10.1		)	19		61.8			(9.6		)		1	6.6			(0.5		)
	Total equity securities	28		299.8			(16.5		)	24		205			(13.2		)		4	94.8			(3.3		)
	Total portfolio	318		$	4,217.80		$	(49.2	)	230		$	3,062.50		$	(26.2	)		88	$	1,155.30		$	(23.0	)
Total Non-Credit Portion of Other-Than-Temporary Impairment Recorded in Accumulated Other Comprehensive Income, Reflecting Original Non-Credit Loss at the Time Credit Impairment	The following table shows the total non-credit portion of the OTTI recorded in accumulated other comprehensive income, reflecting the original non-credit loss at the time the credit impairment was determined:
		March 31,								December 31,
	(millions)	2015				2014				2014
	Fixed maturities:
	Residential mortgage-backed securities	$	(44.1	)		$	(44.1	)		$	(44.1	)
	Commercial mortgage-backed securities	(0.6		)		(0.9		)		(0.6		)
	Total fixed maturities	$	(44.7	)		$	(45.0	)		$	(44.7	)
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 March 31, 2015 and 2014, 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 March 31, 2015
		Mortgage-Backed
	(millions)	Residential				Commercial				Total
	Balance at December 31, 2014	$	12.7			$	0.4			$	13.1
	Change in recoveries of future cash flows expected to be collected1	(0.5		)		0				(0.5		)
	Balance at March 31, 2015	$	12.2			$	0.4			$	12.6
		Three Months Ended March 31, 2014
		Mortgage-Backed
	(millions)	Residential				Commercial				Total
	Balance at December 31, 2013	$	19.2			$	0.4			$	19.6
	Change in recoveries of future cash flows expected to be collected1	(0.1		)		0				(0.1		)
	Balance at March 31, 2014	$	19.1			$	0.4			$	19.5
	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.
Components of Net Realized Gains (Losses)	The components of net realized gains (losses) for the three months ended March 31, were:
	(millions)	2015				2014
	Gross realized gains on security sales
	Fixed maturities:
	U.S. government obligations	$	4.9			$	6.5
	State and local government obligations	0				4.4
	Corporate and other debt securities	9.1				23.1
	Residential mortgage-backed securities	0.1				1
	Commercial mortgage-backed securities	10.8				6.1
	Total fixed maturities	24.9				41.1
	Equity securities:
	Nonredeemable preferred stocks	15.8				25.9
	Common equities	17.8				83
	Subtotal gross realized gains on security sales	58.5				150
	Gross realized losses on security sales
	Fixed maturities:
	U.S. government obligations	(0.8		)		(4.7		)
	State and local government obligations	0				(0.1		)
	Corporate and other debt securities	(0.8		)		(2.2		)
	Commercial mortgage-backed securities	(0.2		)		(2.7		)
	Redeemable preferred stocks	0				(3.2		)
	Total fixed maturities	(1.8		)		(12.9		)
	Equity securities:
	Common equities	(0.4		)		(3.4		)
	Subtotal gross realized losses on security sales	(2.2		)		(16.3		)
	Net realized gains (losses) on security sales
	Fixed maturities:
	U.S. government obligations	4.1				1.8
	State and local government obligations	0				4.3
	Corporate and other debt securities	8.3				20.9
	Residential mortgage-backed securities	0.1				1
	Commercial mortgage-backed securities	10.6				3.4
	Redeemable preferred stocks	0				(3.2		)
	Total fixed maturities	23.1				28.2
	Equity securities:
	Nonredeemable preferred stocks	15.8				25.9
	Common equities	17.4				79.6
	Subtotal net realized gains (losses) on security sales	56.3				133.7
	Other-than-temporary impairment losses
	Equity securities:
	Common equities	(7.9		)		0
	Subtotal other-than-temporary impairment losses	(7.9		)		0
	Other gains (losses)
	Hybrid securities	3.3				3.8
	Derivative instruments	(18.8		)		(19.3		)
	Litigation settlements	0.1				1.2
	Subtotal other gains (losses)	(15.4		)		(14.3		)
	Total net realized gains (losses) on securities	$	33			$	119.4
Components of Net Investment Income	The components of net investment income for the three months ended March 31, were:
	(millions)	2015			2014
	Fixed maturities:
	U.S. government obligations	$	9.1		$	13
	State and local government obligations	11.9			12.8
	Foreign government obligations	0.1			0.1
	Corporate debt securities	22.9			22
	Residential mortgage-backed securities	12.8			9.9
	Commercial mortgage-backed securities	16.9			16.7
	Other asset-backed securities	5			4.2
	Redeemable preferred stocks	3.8			4.1
	Total fixed maturities	82.5			82.8
	Equity securities:
	Nonredeemable preferred stocks	10.5			9.9
	Common equities	11.7			10.4
	Short-term investments	0.4			0.2
	Investment income	105.1			103.3
	Investment expenses	(5.3		)	(4.1		)
	Net investment income	$	99.8		$	99.2
Derivative Instruments	The following table shows the status of our derivative instruments at March 31, 2015 and 2014, and December 31, 2014, and for the three months ended March 31, 2015 and 2014:
	(millions)															Balance Sheet2											Comprehensive Income Statement
																		Assets (Liabilities)									Pretax Net Realized
																		Fair Value									Gains (Losses)
		Notional Value1																									Three Months Ended
		March 31,								Dec. 31,								March 31,							Dec. 31,		March 31,
	Derivatives designated as:	2015				2014				2014				Purpose		Classification		2015			2014				2014		2015			2014
	Hedging instruments
	Closed:
	Ineffective cash flow hedge	$	0			$	0			$	44			Manage interest		NA		$	0		$	0			$	0	$	0		$	0
														rate risk
	Non-hedging instruments
	Assets:
	Interest rate swaps	750				750				750				Manage portfolio		Investments—		0.1			51.9				15.8		(18.8		)	(19.3		)
														duration		fixed maturities
	Total	NA				NA				NA								$	0.1		$	51.9			$	15.8	$	(18.8	)	$	(19.3	)
	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 expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
	NA=ot Applicable

Fair_Value_Tables

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2015
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
	31-Mar-15
	Fixed maturities:
	U.S. government obligations	$	2,708.20	$	0		$	0	$	2,708.20	$	2,678.10
	State and local government obligations	0		2,273.80			0		2,273.80		2,224.80
	Foreign government obligations	20		0			0		20		20
	Corporate debt securities	0		2,904.00			0		2,904.00		2,851.60
	Subtotal	2,728.20		5,177.80			0		7,906.00		7,774.50
	Asset-backed securities:
	Residential mortgage-backed	0		1,648.20			0		1,648.20		1,629.20
	Commercial mortgage-backed	0		2,475.70			11.4		2,487.10		2,437.40
	Other asset-backed	0		1,901.50			0		1,901.50		1,896.10
	Subtotal asset-backed securities	0		6,025.40			11.4		6,036.80		5,962.70
	Redeemable preferred stocks:
	Financials	0		98.2			0		98.2		77.3
	Utilities	0		64.4			0		64.4		65
	Industrials	0		114.4			0		114.4		118
	Subtotal redeemable preferred stocks	0		277			0		277		260.3
	Total fixed maturities	2,728.20		11,480.20			11.4		14,219.80		13,997.50
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	181.7		576.5			69.9		828.1		598.3
	Subtotal nonredeemable preferred stocks	181.7		576.5			69.9		828.1		598.3
	Common equities:
	Common stocks	2,515.40		0			0		2,515.40		1,294.70
	Other risk investments	0		0			0.3		0.3		0.3
	Subtotal common equities	2,515.40		0			0.3		2,515.70		1,295.00
	Total fixed maturities and equity securities	5,425.30		12,056.70			81.6		17,563.60		15,890.80
	Short-term investments	2,267.00		0			0		2,267.00		2,267.00
	Total portfolio	$	7,692.30	$	12,056.70		$	81.6	$	19,830.60	$	18,157.80
	Debt	$	0	$	2,910.90		$	0	$	2,910.90	$	2,560.10
		Fair Value
	(millions)	Level 1		Level 2			Level 3		Total		Cost
	31-Mar-14
	Fixed maturities:
	U.S. government obligations	$	3,230.00	$	0		$	0	$	3,230.00	$	3,197.80
	State and local government obligations	0		2,154.90			0		2,154.90		2,131.00
	Foreign government obligations	17.9		0			0		17.9		17.9
	Corporate debt securities	0		2,501.60			0		2,501.60		2,461.60
	Subtotal	3,247.90		4,656.50			0		7,904.40		7,808.30
	Asset-backed securities:
	Residential mortgage-backed	0		1,307.40			0		1,307.40		1,286.70
	Commercial mortgage-backed	0		2,033.00			28.6		2,061.60		2,037.70
	Other asset-backed	0		942.5			0		942.5		936.2
	Subtotal asset-backed securities	0		4,282.90			28.6		4,311.50		4,260.60
	Redeemable preferred stocks:
	Financials	0		107.4			0		107.4		84.2
	Utilities	0		65.2			0		65.2		64.9
	Industrials	0		117.7			0		117.7		117.8
	Subtotal redeemable preferred stocks	0		290.3			0		290.3		266.9
	Total fixed maturities	3,247.90		9,229.70			28.6		12,506.20		12,335.80
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	284		411.8			42.1		737.9		460.7
	Subtotal nonredeemable preferred stocks	284		411.8			42.1		737.9		460.7
	Common equities:
	Common stocks	2,278.30		0			0		2,278.30		1,252.30
	Other risk investments	0		0			0.4		0.4		0.4
	Subtotal common equities	2,278.30		0			0.4		2,278.70		1,252.70
	Total fixed maturities and equity securities	5,810.20		9,641.50			71.1		15,522.80		14,049.20
	Short-term investments	1,611.70		261.2			0		1,872.90		1,872.90
	Total portfolio	$	7,421.90	$	9,902.70		$	71.1	$	17,395.70	$	15,922.10
Debt	$	0	$	2,152.50		$	0	$	2,152.50	$	1,861.30
	Fair Value
(millions)	Level 1		Level 2			Level 3		Total		Cost
31-Dec-14
Fixed maturities:
U.S. government obligations	$	2,667.10	$	0		$	0	$	2,667.10	$	2,641.10
State and local government obligations	0		2,139.20			0		2,139.20		2,095.70
Foreign government obligations	14.2		0			0		14.2		14.2
Corporate debt securities	0		2,836.70			0		2,836.70		2,813.90
Subtotal	2,681.30		4,975.90			0		7,657.20		7,564.90
Asset-backed securities:
Residential mortgage-backed	0		1,658.50			0		1,658.50		1,635.50
Commercial mortgage-backed	0		2,304.00			11.6		2,315.60		2,278.70
Other asset-backed	0		1,638.70			0		1,638.70		1,634.90
Subtotal asset-backed securities	0		5,601.20			11.6		5,612.80		5,549.10
Redeemable preferred stocks:
Financials	0		97.9			0		97.9		77.3
Utilities	0		65.3			0		65.3		65
Industrials	0		116			0		116		117.9
Subtotal redeemable preferred stocks	0		279.2			0		279.2		260.2
Total fixed maturities	2,681.30		10,856.30			11.6		13,549.20		13,374.20
Equity securities:
Nonredeemable preferred stocks:
Financials	204.1		554.1			69.3		827.5		590.4
Subtotal nonredeemable preferred stocks	204.1		554.1			69.3		827.5		590.4
Common equities:
Common stocks	2,491.90		0			0		2,491.90		1,288.80
Other risk investments	0		0			0.4		0.4		0.4
Subtotal common equities	2,491.90		0			0.4		2,492.30		1,289.20
Total fixed maturities and equity securities	5,377.30		11,410.40			81.3		16,869.00		15,253.80
Short-term investments	1,937.00		212			0		2,149.00		2,149.00
Total portfolio	$	7,314.30	$	11,622.40		$	81.3	$	19,018.00	$	17,402.80
Debt	$	0	$	2,527.50		$	0	$	2,527.50	$	2,164.70
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 months ended March 31, 2015 and 2014:
		Level 3 Fair Value
		Three Months Ended March 31, 2015
	(millions)	Fair Value at December 31, 2014		Calls/			Purchases		Sales		Net Realized (Gain) Loss on Sales		Change in Valuation			Net		Fair Value at March 31, 2015
				Maturities/												Transfers
				Paydowns												In (Out)
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0	$	0		$	0	$	0	$	0	$	0		$	0	$	0
	Commercial mortgage-backed	11.6		(0.2		)	0		0		0		0			0		11.4
	Total fixed maturities	11.6		(0.2		)	0		0		0		0			0		11.4
	Equity securities:
	Nonredeemable preferred stocks:
	Financials1	69.3		0			0		0		0		0.6			0		69.9
	Common equities:
	Other risk investments	0.4		0			0		0		0		(0.1		)	0		0.3
	Total Level 3 securities	$	81.3	$	(0.2	)	$	0	$	0	$	0	$	0.5		$	0	$	81.6
	1The $0.6 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 March 31, 2014
	(millions)	Fair Value at December 31, 2013		Calls/			Purchases		Sales		Net Realized (Gain) Loss on Sales		Change in			Net		Fair Value at March 31, 2014
				Maturities/									Valuation			Transfers
				Paydowns												In (Out)
	Fixed maturities:
	Asset-backed securities:
	Residential mortgage-backed	$	0.2	$	0		$	0	$	0	$	0	$	(0.2	)	$	0	$	0
	Commercial mortgage-backed	29		(0.5		)	0		0		0		0.1			0		28.6
	Total fixed maturities	29.2		(0.5		)	0		0		0		(0.1		)	0		28.6
	Equity securities:
	Nonredeemable preferred stocks:
	Financials1	39		0			0		0		0		3.1			0		42.1
	Common equities:
	Other risk investments	0.5		(0.1		)	0		0		0		0			0		0.4
	Total Level 3 securities	$	68.7	$	(0.6	)	$	0	$	0	$	0	$	3		$	0	$	71.1
	1The $3.1 million represents net holding period gains on a hybrid security, which is reflected in net realized gains (losses) on securities in the comprehensive income statement.
Summary of Quantitative Information about Level 3 Fair Value Measurements	The following tables provide a summary of the quantitative information about Level 3 fair value measurements for our applicable securities at March 31, 2015 and 2014, and December 31, 2014:
		Quantitative Information about Level 3 Fair Value Measurements
	($ in millions)	Fair Value at March 31, 2015		Valuation Technique		Unobservable Input	Unobservable
							Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Commercial mortgage-backed	$	11.4	External vendor		Prepayment rate1	0
	Total fixed maturities	11.4
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	69.9		Multiple of tangible net book value		Price to book ratio multiple	2.6
	Subtotal Level 3 securities	81.3
	Pricing exemption securities2	0.3
	Total Level 3 securities	$	81.6
	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 March 31, 2014		Valuation Technique		Unobservable Input	Unobservable
							Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Commercial mortgage-backed	$	28.6	External vendor		Prepayment rate1	0
	Total fixed maturities	28.6
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	42.1		Multiple of tangible net book value		Price to book ratio multiple	1.9
	Subtotal Level 3 securities	70.7
	Pricing exemption securities2	0.4
	Total Level 3 securities	$	71.1
	1Assumes that two securities have 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2 The fair values for these securities were 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 Dec. 31, 2014		Valuation Technique		Unobservable Input	Unobservable
							Input Assumption
	Fixed maturities:
	Asset-backed securities:
	Commercial mortgage-backed	$	11.6	External vendor		Prepayment rate1	0
	Total fixed maturities	11.6
	Equity securities:
	Nonredeemable preferred stocks:
	Financials	69.3		Multiple of tangible net book value		Price to book ratio multiple	2.6
	Subtotal Level 3 securities	80.9
	Pricing exemption securities2	0.4
	Total Level 3 securities	$	81.3
	1Assumes that one security has 0% of the principal amount of the underlying loans that will be paid off prematurely in each year.
	2 The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt Table	Debt consisted of:
		31-Mar-15				31-Mar-14				31-Dec-14
	(millions)	Carrying		Fair		Carrying		Fair		Carrying		Fair
		Value		Value		Value		Value		Value		Value
	3.75% Senior Notes due 2021	$	497.9	$	542.6	$	497.6	$	524.5	$	497.8	$	535.6
	6 5/8% Senior Notes due 2029	295.6		393.6		295.4		381.8		295.5		400.6
	6.25% Senior Notes due 2032	394.9		525.6		394.7		501.4		394.8		527.9
	4.35% Senior Notes due 2044	346.3		387.1		0		0		346.3		378.9
	3.70% Senior Notes due 2045	394.9		394.8		0		0		0		0
	6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067	630.5		667.2		673.6		744.8		630.3		684.5
	Total	$	2,560.10	$	2,910.90	$	1,861.30	$	2,152.50	$	2,164.70	$	2,527.50

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information Table	Cash includes only bank demand deposits. We paid the following in the respective periods:
		Three Months Ended March 31,
	(millions)	2015		2014
	Income taxes	$	60	$	0
	Interest	19.3		19.3

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Reconciliation of Revenue and operating Income from Segments to Consolidated	Following are the operating results for the respective periods:
		Three Months Ended March 31,
		2015						2014
	(millions)	Revenues			Pretax			Revenues		Pretax
					Profit					Profit
					(Loss)					(Loss)
	Personal Lines
	Agency	$	2,244.50		$	194.5		$	2,203.20	$	178.6
	Direct	1,955.40			68.2			1,762.20		71
	Total Personal Lines1	4,199.90			262.7			3,965.40		249.6
	Commercial Lines	466.4			78.5			436.9		40.9
	Other indemnity	0			0.4			0		(0.7		)
	Total underwriting operations	4,666.30			341.6			4,402.30		289.8
	Fees and other revenues2	73.7			NA			72.8		NA
	Service businesses	17.2			1.3			9.8		0.1
	Investments3	138.1			132.8			222.7		218.6
	Interest expense	NA			(32.5		)	NA		(26.7		)
	Consolidated total	$	4,895.30		$	443.2		$	4,707.60	$	481.8
	NA =ot Applicable
	1Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in both the first quarters of 2015 and 2014; 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.
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 March 31,
		2015				2014
		Under-writing		Combined		Under-writing		Combined
		Margin		Ratio		Margin		Ratio
	Personal Lines
	Agency	8.7	%	91.3		8.1	%	91.9
	Direct	3.5		96.5		4		96
	Total Personal Lines	6.3		93.7		6.3		93.7
	Commercial Lines	16.8		83.2		9.4		90.6
	Other indemnity1	NM		NM		NM		NM
	Total underwriting operations	7.3		92.7		6.6		93.4
	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_Tables

Dividends Dividends (Tables)	3 Months Ended
	Mar. 31, 2015
Dividends [Abstract]
Dividends	Following is a summary of our shareholder dividends, both variable and special, that were paid in the last two years:
	(millions, except per share amounts)			Amount
	Dividend Type	Declared	Paid	Per Share		Total
	Annual – Variable	Dec-14	Feb-15	$	0.6862	$	404.1
	Annual – Variable	Dec-13	Feb-14	0.4929		293.9
	Special	Dec-13	Feb-14	1		596.3

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2015
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						transactions
	Balance at December 31, 2014	$	1,574.00		$	(550.9	)	$	1,023.10		$	1,021.90		$	1.5		$	(0.3	)
	Other comprehensive income (loss) before reclassifications:
	Investment securities	99.3			(34.7		)	64.6			64.6			0			0
	Net non-credit related OTTI losses, adjusted for	0			0			0			0			0			0
	valuation changes
	Forecasted transactions	(12.8		)	4.4			(8.4		)	0			(8.4		)	0
	Foreign currency translation adjustment	(0.9		)	0.4			(0.5		)	0			0			(0.5		)
	Total other comprehensive income (loss) before reclassifications	85.6			(29.9		)	55.7			64.6			(8.4		)	(0.5		)
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	(7.9		)	2.8			(5.1		)	(5.1		)	0			0
	Net realized gains (losses) on securities	52.8			(18.5		)	34.3			34.3			0			0
	Interest expense	0.5			(0.2		)	0.3			0			0.3			0
	Total reclassification adjustment for amounts realized in net income	45.4			(15.9		)	29.5			29.2			0.3			0
	Total other comprehensive income (loss)	40.2			(14.0		)	26.2			35.4			(8.7		)	(0.5		)
	Balance at March 31, 2015	$	1,614.20		$	(564.9	)	$	1,049.30		$	1,057.30		$	(7.2	)	$	(0.8	)
											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						transactions
	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	131.8			(46.1		)	85.7			85.7			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	0			0			0			0			0			0
	Total other comprehensive income (loss) before reclassifications	131.8			(46.1		)	85.7			85.7			0			0
	Less: Reclassification adjustment for amounts realized in net income by income statement line item:
	Net impairment losses recognized in earnings	0			0			0			0			0			0
	Net realized gains (losses) on securities	131.9			(46.1		)	85.8			85.8			0			0
	Interest expense	0.5			(0.2		)	0.3			0			0.3			0
	Total reclassification adjustment for amounts realized in net income	132.4			(46.3		)	86.1			85.8			0.3			0
	Total other comprehensive income (loss)	(0.6		)	0.2			(0.4		)	(0.1		)	(0.3		)	0
	Balance at March 31, 2014	$	1,463.50		$	(512.2	)	$	951.3		$	946.9		$	3.8		$	0.6

Basis_of_Presentation_Basis_of

Basis of Presentation Basis of Presentation-Additional Information (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Disposal Group, Including Discontinued Operation, Assets, Current [Abstract]
Assets Held-for-sale, Property, Plant and Equipment	$8.70	$8.70	$8.70

Investments_Investment_Portfol

Investments Investment Portfolio by Major Security Type (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Cost	$18,157.80	[1],[2]	$17,402.80	[1],[2]	$15,922.10	[1],[2]
Gross Unrealized Gains	1,664.40	[1],[2]	1,621.40	[1],[2]	1,520.30	[1],[2]
Gross Unrealized Losses	-37.8	[1],[2]	-49.2	[1],[2]	-63.5	[1],[2]
Net Realized Gains (Losses)	46.2	[1],[2],[3]	43	[1],[2],[3]	16.8	[1],[2],[3]
Total investments at fair value	19,830.60	[1],[2]	19,018	[1],[2]	17,395.70	[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	13,997.50		13,374.20		12,335.80
Gross Unrealized Gains	245.2		207.1		227.8
Gross Unrealized Losses	-25.9		-32.7		-59.5
Net Realized Gains (Losses)	3	[3]	0.6	[3]	2.1	[3]
Total investments at fair value	14,219.80		13,549.20		12,506.20
% of Total Fair Value	71.70%		71.20%		71.90%
Fixed maturities | U.S. government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost	2,678.10		2,641.10		3,197.80
Gross Unrealized Gains	30.1		27.3		39
Gross Unrealized Losses	0		-1.3		-6.8
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	2,708.20		2,667.10		3,230
% of Total Fair Value	13.70%		14.00%		18.50%
Fixed maturities | State and local government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost	2,224.80		2,095.70		2,131
Gross Unrealized Gains	50		44.6		33.1
Gross Unrealized Losses	-1		-1.1		-9.2
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	2,273.80		2,139.20		2,154.90
% of Total Fair Value	11.50%		11.20%		12.40%
Fixed maturities | Foreign government obligations
Schedule of Available-for-sale Securities [Line Items]
Cost	20		14.2		17.9
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		14.2		17.9
% of Total Fair Value	0.10%		0.10%		0.10%
Fixed maturities | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Cost	2,851.60		2,813.90		2,461.60
Gross Unrealized Gains	54.4		32.9		45.4
Gross Unrealized Losses	-3.8		-10.4		-7.2
Net Realized Gains (Losses)	1.8	[3]	0.3	[3]	1.8	[3]
Total investments at fair value	2,904		2,836.70		2,501.60
% of Total Fair Value	14.60%		14.90%		14.40%
Fixed maturities | Residential mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,629.20		1,635.50		1,286.70
Gross Unrealized Gains	32.4		34.5		32.6
Gross Unrealized Losses	-13.1		-10.8		-11.9
Net Realized Gains (Losses)	-0.3	[3]	-0.7	[3]	0	[3]
Total investments at fair value	1,648.20		1,658.50		1,307.40
% of Total Fair Value	8.30%		8.70%		7.50%
Fixed maturities | Commercial mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	2,437.40		2,278.70		2,037.70
Gross Unrealized Gains	50.1		39.3		41.5
Gross Unrealized Losses	-1.1		-2.6		-17.6
Net Realized Gains (Losses)	0.7	[3]	0.2	[3]	0	[3]
Total investments at fair value	2,487.10		2,315.60		2,061.60
% of Total Fair Value	12.50%		12.20%		11.90%
Fixed maturities | Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,896.10		1,634.90		936.2
Gross Unrealized Gains	4.9		3.8		6.6
Gross Unrealized Losses	-0.3		-0.8		-0.6
Net Realized Gains (Losses)	0.8	[3]	0.8	[3]	0.3	[3]
Total investments at fair value	1,901.50		1,638.70		942.5
% of Total Fair Value	9.60%		8.60%		5.40%
Fixed maturities | Redeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	260.3		260.2		266.9
Gross Unrealized Gains	23.3		24.7		29.6
Gross Unrealized Losses	-6.6		-5.7		-6.2
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	277		279.2		290.3
% of Total Fair Value	1.40%		1.50%		1.70%
Equity securities | Nonredeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Cost	598.3		590.4		460.7
Gross Unrealized Gains	192.5		201.1		263.7
Gross Unrealized Losses	-5.9		-6.4		-1.2
Net Realized Gains (Losses)	43.2	[3]	42.4	[3]	14.7	[3]
Total investments at fair value	828.1		827.5		737.9
% of Total Fair Value	4.20%		4.40%		4.20%
Equity securities | Common equities
Schedule of Available-for-sale Securities [Line Items]
Cost	1,295		1,289.20		1,252.70
Gross Unrealized Gains	1,226.70		1,213.20		1,028.80
Gross Unrealized Losses	-6		-10.1		-2.8
Net Realized Gains (Losses)	0	[3]	0	[3]	0	[3]
Total investments at fair value	2,515.70		2,492.30		2,278.70
% of Total Fair Value	12.70%		13.10%		13.10%
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Cost	2,267		2,149		1,872.90
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	$2,267		$2,149		$1,872.90
% of Total Fair Value	11.40%		11.30%		10.80%
[1]	The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
[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 $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Net unsettled security transactions offset in other liabilities	$95,800,000	$31,300,000
Other Receivables from Broker-Dealers and Clearing Organizations			350,000,000
Securities in the portfolio of a consolidated, non-insurance subsidiary of the holding company, net of any unsettled security transactions	$1,700,000,000	$1,900,000,000	$800,000,000

Investments_Hybrid_Securities_

Investments Hybrid Securities (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Hybrid Securities [Line Items]
Hybrid securities	$412.90	$427.70	$223.40
Fixed maturities
Hybrid Securities [Line Items]
Hybrid securities	275.7	305.4	159.6
Fixed maturities | Corporate debt securities
Hybrid Securities [Line Items]
Hybrid securities	132.9	139.8	145.7
Fixed maturities | Residential mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	111.7	120.7	0
Fixed maturities | Commercial mortgage-backed securities
Hybrid Securities [Line Items]
Hybrid securities	18	31.2	0
Fixed maturities | Other asset-backed securities
Hybrid Securities [Line Items]
Hybrid securities	13.1	13.7	13.9
Equity securities | Nonredeemable preferred stocks
Hybrid Securities [Line Items]
Hybrid securities	$137.20	$122.30	$63.80

Investments_Composition_of_Fix

Investments Composition of Fixed Maturities by Maturity (Detail) (USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Available for sale, cost
Less than one year	$3,839.10
One to five years	6,771.60
Five to ten years	3,318.80
Ten years or greater	67.9
Total	13,997.40	[1]
Available for sale, Fair value
Less than one year	3,878.20
One to five years	6,848.90
Five to ten years	3,413.50
Ten years or greater	79.1
Total	$14,219.70	[1]
[1]	Excludes $0.1 million related to our open interest rate swap positions.

Investments_Composition_of_Fix1

Investments Composition of Fixed Maturities by Maturity (Parenthetical) (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Open interest rate swap positions	$0.10	[1]	$15.80	[1]	$51.90	[1]
Interest rate swaps
Schedule of Available-for-sale Securities [Line Items]
Open interest rate swap positions	$0.10
[1]	To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.

Investments_Gross_Unrealized_l

Investments Gross Unrealized losses by Major Security (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
In Millions, unless otherwise specified
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	300	318	303
Total Fair Value	$3,080.30	$4,217.80	$4,048.50
Gross Unrealized Losses	-37.8	-49.2	-63.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	219	230	94
Less than 12 Months Fair Value	2,221	3,062.50	877.8
Less than 12 Months Unrealized Losses	-16.2	-26.2	-5.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	81	88	209
12 Months or Greater Fair Value	859.3	1,155.30	3,170.70
12 Months or Greater Unrealized Losses	-21.6	-23	-58.4
Fixed maturities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	255	290	291
Total Fair Value	2,838.90	3,918	3,930.20
Gross Unrealized Losses	-25.9	-32.7	-59.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	177	206	87
Less than 12 Months Fair Value	2,088.20	2,857.50	854.7
Less than 12 Months Unrealized Losses	-8	-13	-3.5
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	78	84	204
12 Months or Greater Fair Value	750.7	1,060.50	3,075.50
12 Months or Greater Unrealized Losses	-17.9	-19.7	-56
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	1	11	18
Total Fair Value	7.2	428.2	930.4
Gross Unrealized Losses	0	-1.3	-6.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	5	5
Less than 12 Months Fair Value	7.2	150.7	163.1
Less than 12 Months Unrealized Losses	0	-0.3	-0.3
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	0	6	13
12 Months or Greater Fair Value	0	277.5	767.3
12 Months or Greater Unrealized Losses	0	-1	-6.5
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	57	46	106
Total Fair Value	270.3	234.2	603
Gross Unrealized Losses	-1	-1.1	-9.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	42	28	28
Less than 12 Months Fair Value	231.8	177.9	76.8
Less than 12 Months Unrealized Losses	-0.5	-0.4	-0.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	15	18	78
12 Months or Greater Fair Value	38.5	56.3	526.2
12 Months or Greater Unrealized Losses	-0.5	-0.7	-8.6
Fixed maturities | Corporate debt securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	25	53	31
Total Fair Value	390.3	843.2	594.3
Gross Unrealized Losses	-3.8	-10.4	-7.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	17	43	7
Less than 12 Months Fair Value	242.4	647.5	101.6
Less than 12 Months Unrealized Losses	-2.3	-6.1	-0.4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	8	10	24
12 Months or Greater Fair Value	147.9	195.7	492.7
12 Months or Greater Unrealized Losses	-1.5	-4.3	-6.8
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	80	70	66
Total Fair Value	1,013.90	844.2	812.6
Gross Unrealized Losses	-13.1	-10.8	-11.9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	34	33	24
Less than 12 Months Fair Value	540.6	465.2	359.7
Less than 12 Months Unrealized Losses	-3.1	-3.1	-1.9
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	46	37	42
12 Months or Greater Fair Value	473.3	379	452.9
12 Months or Greater Unrealized Losses	-10	-7.7	-10
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	59	63	59
Total Fair Value	564.2	723.4	783.7
Gross Unrealized Losses	-1.1	-2.6	-17.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	53	54	19
Less than 12 Months Fair Value	560.8	667.5	116.7
Less than 12 Months Unrealized Losses	-1	-1.4	-0.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	6	9	40
12 Months or Greater Fair Value	3.4	55.9	667
12 Months or Greater Unrealized Losses	-0.1	-1.2	-17.4
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	30	44	8
Total Fair Value	490.9	741.8	112.7
Gross Unrealized Losses	-0.3	-0.8	-0.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	29	42	4
Less than 12 Months Fair Value	472.4	715.7	36.8
Less than 12 Months Unrealized Losses	-0.1	-0.7	-0.1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	1	2	4
12 Months or Greater Fair Value	18.5	26.1	75.9
12 Months or Greater Unrealized Losses	-0.2	-0.1	-0.5
Fixed maturities | Redeemable preferred stocks
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	3	3	3
Total Fair Value	102.1	103	93.5
Gross Unrealized Losses	-6.6	-5.7	-6.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1	1	0
Less than 12 Months Fair Value	33	33	0
Less than 12 Months Unrealized Losses	-1	-1	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	2	2	3
12 Months or Greater Fair Value	69.1	70	93.5
12 Months or Greater Unrealized Losses	-5.6	-4.7	-6.2
Equity securities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	45	28	12
Total Fair Value	241.4	299.8	118.3
Gross Unrealized Losses	-11.9	-16.5	-4
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	42	24	7
Less than 12 Months Fair Value	132.8	205	23.1
Less than 12 Months Unrealized Losses	-8.2	-13.2	-1.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	3	4	5
12 Months or Greater Fair Value	108.6	94.8	95.2
12 Months or Greater Unrealized Losses	-3.7	-3.3	-2.4
Equity securities | Nonredeemable preferred stocks
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	5	8	3
Total Fair Value	183.1	231.4	84.3
Gross Unrealized Losses	-5.9	-6.4	-1.2
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	2	5	0
Less than 12 Months Fair Value	74.5	143.2	0
Less than 12 Months Unrealized Losses	-2.2	-3.6	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	3	3	3
12 Months or Greater Fair Value	108.6	88.2	84.3
12 Months or Greater Unrealized Losses	-3.7	-2.8	-1.2
Equity securities | Common equities
Investments, Unrealized Loss Position [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	40	20	9
Total Fair Value	58.3	68.4	34
Gross Unrealized Losses	-6	-10.1	-2.8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	40	19	7
Less than 12 Months Fair Value	58.3	61.8	23.1
Less than 12 Months Unrealized Losses	-6	-9.6	-1.6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	0	1	2
12 Months or Greater Fair Value	0	6.6	10.9
12 Months or Greater Unrealized Losses	$0	($0.50)	($1.20)

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 $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
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)	($44.70)	($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)	($0.60)	($0.90)

Investments_OTTI_Credit_Losses

Investments OTTI Credit Losses Recognized in Earnings (Detail) (Fixed maturities, USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	$13.10		$19.60
Change in recoveries of future cash flows expected to be collected	-0.5	[1]	-0.1	[1]
Ending balance	12.6		19.5
Residential mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	12.7		19.2
Change in recoveries of future cash flows expected to be collected	-0.5	[1]	-0.1	[1]
Ending balance	12.2		19.1
Commercial mortgage-backed securities
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning balance	0.4		0.4
Change in recoveries of future cash flows expected to be collected	0	[1]	0	[1]
Ending balance	$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.

Investments_Components_of_Net_

Investments Components of Net Realized Gains (Losses) (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	$58.50	$150
Gross realized losses on securities sales	-2.2	-16.3
Net realized gains (losses) on securities sales	56.3	133.7
Other-than-temporary impairment losses	-7.9	0
Total net realized gains (losses) on securities	33	119.4
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	24.9	41.1
Gross realized losses on securities sales	-1.8	-12.9
Net realized gains (losses) on securities sales	23.1	28.2
Fixed maturities | U.S. government obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	4.9	6.5
Gross realized losses on securities sales	-0.8	-4.7
Net realized gains (losses) on securities sales	4.1	1.8
Fixed maturities | State and local government obligations
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0	4.4
Gross realized losses on securities sales	0	-0.1
Net realized gains (losses) on securities sales	0	4.3
Fixed maturities | Corporate And Other Debt Securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	9.1	23.1
Gross realized losses on securities sales	-0.8	-2.2
Net realized gains (losses) on securities sales	8.3	20.9
Fixed maturities | Residential mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	0.1	1
Net realized gains (losses) on securities sales	0.1	1
Fixed maturities | Commercial mortgage-backed securities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	10.8	6.1
Gross realized losses on securities sales	-0.2	-2.7
Net realized gains (losses) on securities sales	10.6	3.4
Fixed maturities | Redeemable preferred stocks
Gain (Loss) on Investments [Line Items]
Gross realized losses on securities sales	0	-3.2
Net realized gains (losses) on securities sales	0	-3.2
Equity securities | Nonredeemable preferred stocks
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	15.8	25.9
Net realized gains (losses) on securities sales	15.8	25.9
Equity securities | Common equities
Gain (Loss) on Investments [Line Items]
Gross realized gains on securities sales	17.8	83
Gross realized losses on securities sales	-0.4	-3.4
Net realized gains (losses) on securities sales	17.4	79.6
Other-than-temporary impairment losses	-7.9	0
Hybrid and Derivative Instruments and Litigation Settlements
Gain (Loss) on Investments [Line Items]
Other gains (losses)	-15.4	-14.3
Hybrid and Derivative Instruments and Litigation Settlements | Litigation Settlements
Gain (Loss) on Investments [Line Items]
Other gains (losses)	0.1	1.2
Hybrid and Derivative Instruments and Litigation Settlements | Hybrid Preferred Stock
Gain (Loss) on Investments [Line Items]
Other gains (losses)	3.3	3.8
Hybrid and Derivative Instruments and Litigation Settlements | Derivative Instruments
Gain (Loss) on Investments [Line Items]
Other gains (losses)	($18.80)	($19.30)

Investments_Components_of_Net_1

Investments Components of Net Investment Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net Investment Income [Line Items]
Investment income	$105.10	$103.30
Investment expenses	-5.3	-4.1
Net Investment Income	99.8	99.2
Fixed maturities
Net Investment Income [Line Items]
Investment income	82.5	82.8
Fixed maturities | U.S. government obligations
Net Investment Income [Line Items]
Investment income	9.1	13
Fixed maturities | State and local government obligations
Net Investment Income [Line Items]
Investment income	11.9	12.8
Fixed maturities | Foreign government obligations
Net Investment Income [Line Items]
Investment income	0.1	0.1
Fixed maturities | Corporate debt securities
Net Investment Income [Line Items]
Investment income	22.9	22
Fixed maturities | Residential mortgage-backed securities
Net Investment Income [Line Items]
Investment income	12.8	9.9
Fixed maturities | Commercial mortgage-backed securities
Net Investment Income [Line Items]
Investment income	16.9	16.7
Fixed maturities | Other asset-backed securities
Net Investment Income [Line Items]
Investment income	5	4.2
Fixed maturities | Redeemable preferred stocks
Net Investment Income [Line Items]
Investment income	3.8	4.1
Equity securities | Nonredeemable preferred stocks
Net Investment Income [Line Items]
Investment income	10.5	9.9
Equity securities | Common equities
Net Investment Income [Line Items]
Investment income	11.7	10.4
Short-term investments
Net Investment Income [Line Items]
Investment income	$0.40	$0.20

Investments_Derivative_Instrum

Investments Derivative Instruments (Detail) (USD $)	3 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Derivative [Line Items]
Balance Sheet - Fair Value	$0.10	[1]	$51.90	[1]	$15.80	[1]
Income Statement - Net Realized Gain (Loss) on Securities	-18.8		-19.3
Designated as Hedging Instruments | Closed Positions | Ineffective Cash Flow Hedge
Derivative [Line Items]
Notional Value	0	[2]	0	[2]	44	[2]
Purpose					Manage interest  rate risk
Balance Sheet - Fair Value	0	[1]	0	[1]	0	[1]
Income Statement - Net Realized Gain (Loss) on Securities	0		0
Non-hedging Instruments | Assets | Interest rate swaps | Fixed maturities
Derivative [Line Items]
Notional Value	750	[2]	750	[2]	750	[2]
Purpose	Manage portfolio duration		Manage portfolio duration		Manage portfolio duration
Balance Sheet - Fair Value	0.1	[1]	51.9	[1]	15.8	[1]
Income Statement - Net Realized Gain (Loss) on Securities	-18.8		-19.3
Interest rate swaps
Derivative [Line Items]
Balance Sheet - Fair Value	$0.10
[1]	To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
[2]	The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions.

Investments_Investments_Additi

Investments Investments - Additional Information (Detail) (USD $)	3 Months Ended				1 Months Ended		12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Jan. 26, 2015	Apr. 25, 2014	Dec. 31, 2014
Schedule of Investments [Line Items]
Open reverse repurchase commitments	$0		$140,000,000				$0
Gross unrealized losses	37,800,000		63,500,000				49,200,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	300		303				318
Trading securities	0		0				0
Net realized gains (losses) on securities	40,900,000		119,400,000
Balance Sheet - Fair Value	100,000	[1]	51,900,000	[1]			15,800,000	[1]
Largest Outstanding Balance of Reverse Repurchase Agreements	215,000,000
RRP Largest Outstanding Balance Number of Days Open	1 day
Reverse Repurchase Agreement Average Daily Balance	137,700,000
3.70% Senior Notes due 2045
Schedule of Investments [Line Items]
Additional Expenses Related to the Issuance					800,000
Debt Instrument, Issuance Date					26-Jan-15
Debt Instrument, Face Amount					400,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.70%				3.70%
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)					12,900,000
4.35% Senior Notes due 2044
Schedule of Investments [Line Items]
Additional Expenses Related to the Issuance						700,000
Debt Instrument, Issuance Date						25-Apr-14
Debt Instrument, Face Amount						350,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.35%					4.35%
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)						1,600,000
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Schedule of Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.70%
Repurchase of debt, face amount	0		0				44,300,000
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 | Net unrealized gains on forecasted transactions
Schedule of Investments [Line Items]
Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities	0		0				500,000
Fixed Income Securities
Schedule of Investments [Line Items]
Gross unrealized losses	31,800,000
Equity securities
Schedule of Investments [Line Items]
Gross unrealized losses	11,900,000		4,000,000				16,500,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	45		12				28
Equity securities | Common equities
Schedule of Investments [Line Items]
Gross unrealized losses	6,000,000		2,800,000				10,100,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	40		9				20
Equity securities | Nonredeemable preferred stocks
Schedule of Investments [Line Items]
Gross unrealized losses	5,900,000		1,200,000				6,400,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	5		3				8
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Percentage Decline	3.00%
Fixed maturities
Schedule of Investments [Line Items]
Gross unrealized losses	25,900,000		59,500,000				32,700,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	255		291				290
Fixed maturities | State and local government obligations
Schedule of Investments [Line Items]
Gross unrealized losses	1,000,000		9,200,000				1,100,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	57		106				46
Fixed maturities | Corporate debt securities
Schedule of Investments [Line Items]
Percentage which the issuer receives the security back at once the change of control is triggered	1.00%
Realized investment losses	8,200,000
Gross unrealized losses	3,800,000		7,200,000				10,400,000
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	25		31				53
Interest rate swaps
Schedule of Investments [Line Items]
Collateral Delivered to Counterparties on Derivative Instruments	4,700,000
Derivative, Gain (Loss) on Derivative, Net	15,700,000
Balance Sheet - Fair Value	100,000
Cash collateral received from counterparties			43,300,000				16,100,000
Categories of Investments, Marketable Securities, Trading Securities
Schedule of Investments [Line Items]
Net realized gains (losses) on securities	0		0
Russell One Thousand | Equity securities | Common equities
Schedule of Investments [Line Items]
Percentage of common stock portfolio	89.00%
Managed Equity Strategy | Equity securities | Common equities
Schedule of Investments [Line Items]
Percentage of common stock portfolio	11.00%
Non-hedging Instruments | Interest rate swaps | Fixed maturities | Assets
Schedule of Investments [Line Items]
Notional Value	750,000,000	[2]	750,000,000	[2]			750,000,000	[2]
Balance Sheet - Fair Value	100,000	[1]	51,900,000	[1]			15,800,000	[1]
Designated as Hedging Instruments | Ineffective Cash Flow Hedge | Closed Positions
Schedule of Investments [Line Items]
Notional Value	0	[2]	0	[2]			44,000,000	[2]
Balance Sheet - Fair Value	$0	[1]	$0	[1]			$0	[1]
[1]	To the extent we hold both derivative assets and liabilities with the same counterparty that are subject to an enforceable master netting arrangement, we expect that we will report them on a gross basis on our balance sheets, consistent with our historical presentation.
[2]	The amounts represent the value held at quarter and year end for open positions and the maximum amount held during the period for closed positions.

Fair_Value_Composition_of_Inve

Fair Value Composition of Investment Portfolio by Major Security Type (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Fair Value Measurements [Line Items]
Portfolio	$19,830,600,000	[1],[2]	$19,018,000,000	[1],[2]	$17,395,700,000	[1],[2]
Long-Term Debt, Fair Value	2,910,900,000		2,527,500,000		2,152,500,000
Debt	2,560,100,000	[3]	2,164,700,000	[3]	1,861,300,000	[3]
Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	14,219,800,000		13,549,200,000		12,506,200,000
Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	277,000,000		279,200,000		290,300,000
Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	98,200,000		97,900,000		107,400,000
Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	64,400,000		65,300,000		65,200,000
Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	114,400,000		116,000,000		117,700,000
Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	7,906,000,000		7,657,200,000		7,904,400,000
Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	2,708,200,000		2,667,100,000		3,230,000,000
Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	2,273,800,000		2,139,200,000		2,154,900,000
Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	20,000,000		14,200,000		17,900,000
Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	2,904,000,000		2,836,700,000		2,501,600,000
Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	6,036,800,000		5,612,800,000		4,311,500,000
Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,648,200,000		1,658,500,000		1,307,400,000
Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	2,487,100,000		2,315,600,000		2,061,600,000
Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,901,500,000		1,638,700,000		942,500,000
Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	828,100,000		827,500,000		737,900,000
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	828,100,000		827,500,000		737,900,000
Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,515,700,000		2,492,300,000		2,278,700,000
Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,515,400,000		2,491,900,000		2,278,300,000
Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	300,000		400,000		400,000
Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	17,563,600,000		16,869,000,000		15,522,800,000
Short-term investments
Fair Value Measurements [Line Items]
Portfolio	2,267,000,000		2,149,000,000		1,872,900,000
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Portfolio	7,692,300,000		7,314,300,000		7,421,900,000
Long-Term Debt, Fair Value	0		0		0
Fair Value, Inputs, Level 1 | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	2,728,200,000		2,681,300,000		3,247,900,000
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	2,728,200,000		2,681,300,000		3,247,900,000
Fair Value, Inputs, Level 1 | Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	2,708,200,000		2,667,100,000		3,230,000,000
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	20,000,000		14,200,000		17,900,000
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	181,700,000		204,100,000		284,000,000
Fair Value, Inputs, Level 1 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	181,700,000		204,100,000		284,000,000
Fair Value, Inputs, Level 1 | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,515,400,000		2,491,900,000		2,278,300,000
Fair Value, Inputs, Level 1 | Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	2,515,400,000		2,491,900,000		2,278,300,000
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	5,425,300,000		5,377,300,000		5,810,200,000
Fair Value, Inputs, Level 1 | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	2,267,000,000		1,937,000,000		1,611,700,000
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Portfolio	12,056,700,000		11,622,400,000		9,902,700,000
Long-Term Debt, Fair Value	2,910,900,000		2,527,500,000		2,152,500,000
Fair Value, Inputs, Level 2 | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	11,480,200,000		10,856,300,000		9,229,700,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	277,000,000		279,200,000		290,300,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	98,200,000		97,900,000		107,400,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	64,400,000		65,300,000		65,200,000
Fair Value, Inputs, Level 2 | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	114,400,000		116,000,000		117,700,000
Fair Value, Inputs, Level 2 | Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	5,177,800,000		4,975,900,000		4,656,500,000
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	2,273,800,000		2,139,200,000		2,154,900,000
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	2,904,000,000		2,836,700,000		2,501,600,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	6,025,400,000		5,601,200,000		4,282,900,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,648,200,000		1,658,500,000		1,307,400,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	2,475,700,000		2,304,000,000		2,033,000,000
Fair Value, Inputs, Level 2 | Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,901,500,000		1,638,700,000		942,500,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	576,500,000		554,100,000		411,800,000
Fair Value, Inputs, Level 2 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	576,500,000		554,100,000		411,800,000
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 equities
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	12,056,700,000		11,410,400,000		9,641,500,000
Fair Value, Inputs, Level 2 | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	0		212,000,000		261,200,000
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Portfolio	81,600,000		81,300,000		71,100,000
Long-Term Debt, Fair Value	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	11,400,000		11,600,000		28,600,000
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	11,400,000		11,600,000		28,600,000
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	0		0		0
Fair Value, Inputs, Level 3 | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	11,400,000		11,600,000		28,600,000
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	69,900,000		69,300,000		42,100,000
Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	69,900,000		69,300,000		42,100,000
Fair Value, Inputs, Level 3 | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	300,000		400,000		400,000
Fair Value, Inputs, Level 3 | Equity securities | Common equities | Common equities
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	300,000		400,000		400,000
Fair Value, Inputs, Level 3 | Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	81,600,000		81,300,000		71,100,000
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	18,157,800,000		17,402,800,000		15,922,100,000
Debt	2,560,100,000		2,164,700,000		1,861,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities
Fair Value Measurements [Line Items]
Portfolio	13,997,500,000		13,374,200,000		12,335,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	260,300,000		260,200,000		266,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	77,300,000		77,300,000		84,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Utilities
Fair Value Measurements [Line Items]
Portfolio	65,000,000		65,000,000		64,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Redeemable preferred stocks | Industrials
Fair Value Measurements [Line Items]
Portfolio	118,000,000		117,900,000		117,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities
Fair Value Measurements [Line Items]
Portfolio	7,774,500,000		7,564,900,000		7,808,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | U.S. government obligations
Fair Value Measurements [Line Items]
Portfolio	2,678,100,000		2,641,100,000		3,197,800,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | State and local government obligations
Fair Value Measurements [Line Items]
Portfolio	2,224,800,000		2,095,700,000		2,131,000,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | Foreign government obligations
Fair Value Measurements [Line Items]
Portfolio	20,000,000		14,200,000		17,900,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Debt Securities | Corporate debt securities
Fair Value Measurements [Line Items]
Portfolio	2,851,600,000		2,813,900,000		2,461,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities
Fair Value Measurements [Line Items]
Portfolio	5,962,700,000		5,549,100,000		4,260,600,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Residential mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,629,200,000		1,635,500,000		1,286,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Commercial mortgage-backed securities
Fair Value Measurements [Line Items]
Portfolio	2,437,400,000		2,278,700,000		2,037,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Fixed maturities | Asset-backed Securities | Other asset-backed securities
Fair Value Measurements [Line Items]
Portfolio	1,896,100,000		1,634,900,000		936,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks
Fair Value Measurements [Line Items]
Portfolio	598,300,000		590,400,000		460,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Measurements [Line Items]
Portfolio	598,300,000		590,400,000		460,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities
Fair Value Measurements [Line Items]
Portfolio	1,295,000,000		1,289,200,000		1,252,700,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Common equities
Fair Value Measurements [Line Items]
Portfolio	1,294,700,000		1,288,800,000		1,252,300,000
Carrying (Reported) Amount, Fair Value Disclosure | Equity securities | Common equities | Other risk investments
Fair Value Measurements [Line Items]
Portfolio	300,000		400,000		400,000
Carrying (Reported) Amount, Fair Value Disclosure | Total Fixed Maturities and Equity Securities
Fair Value Measurements [Line Items]
Portfolio	15,890,800,000		15,253,800,000		14,049,200,000
Carrying (Reported) Amount, Fair Value Disclosure | Short-term investments
Fair Value Measurements [Line Items]
Portfolio	$2,267,000,000		$2,149,000,000		$1,872,900,000
[1]	The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
[3]	1Consists of long-term debt. See Note 4 - Debt.See notes to consolidated financial statements.

Fair_Value_Summary_of_Changes_

Fair Value Summary of Changes in Fair Value Associated With Level 3 Assets (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	$81.30		$68.70
Calls/ Maturities/ Paydowns	-0.2		-0.6
Purchases	0		0
Sales	0		0
Net Realized (Gain) Loss on Sales	0		0
Change in Valuation	0.5		3
Net Transfers in (out)	0		0
Ending Fair value	81.6		71.1
Fixed maturities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	11.6		29.2
Calls/ Maturities/ Paydowns	-0.2		-0.5
Purchases	0		0
Sales	0		0
Net Realized (Gain) Loss on Sales	0		0
Change in Valuation	0		-0.1
Net Transfers in (out)	0		0
Ending Fair value	11.4		28.6
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		0.2
Calls/ Maturities/ Paydowns	0		0
Purchases	0		0
Sales	0		0
Net Realized (Gain) Loss on Sales	0		0
Change in Valuation	0		-0.2
Net Transfers in (out)	0		0
Ending Fair value	0		0
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	11.6		29
Calls/ Maturities/ Paydowns	-0.2		-0.5
Purchases	0		0
Sales	0		0
Net Realized (Gain) Loss on Sales	0		0
Change in Valuation	0		0.1
Net Transfers in (out)	0		0
Ending Fair value	11.4		28.6
Equity securities | Nonredeemable preferred stocks | Financials
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	69.3	[1]	39	[2]
Calls/ Maturities/ Paydowns	0	[1]	0	[2]
Purchases	0	[1]	0	[2]
Sales	0	[1]	0	[2]
Net Realized (Gain) Loss on Sales	0	[1]	0	[2]
Change in Valuation	0.6	[1]	3.1	[2]
Net Transfers in (out)	0	[1]	0	[2]
Ending Fair value	69.9	[1]	42.1	[2]
Equity securities | Common equities | Other risk investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Fair Value	0.4		0.5
Calls/ Maturities/ Paydowns	0		-0.1
Purchases	0		0
Sales	0		0
Net Realized (Gain) Loss on Sales	0		0
Change in Valuation	-0.1		0
Net Transfers in (out)	0		0
Ending Fair value	$0.30		$0.40
[1]	The $0.6 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.
[2]	The $3.1 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
	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net realized gains (losses) on securities	$40,900,000	$119,400,000
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	$600,000	$3,100,000

Fair_Value_Summary_of_Quantita

Fair Value Summary of Quantitative Information about Level 3 Fair Value Measurements (Detail) (USD $)	3 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
	Investment		Investment		Investment
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$19,830.60	[1],[2]	$17,395.70	[1],[2]	$19,018	[1],[2]
Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	81.6		71.1		81.3
External Pricing | Fair Value, Inputs, Level 3 | Fixed maturities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	11.4		28.6		11.6
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		1
Fair Value	11.4		28.6		11.6
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 | Equity securities | Nonredeemable preferred stocks
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Number of securities	1		1		1
Fair Value	69.9		42.1		69.3
Internal Pricing | Fair Value, Inputs, Level 3 | Equity securities | Nonredeemable preferred stocks | Financials
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	69.9		42.1		69.3
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	2.6		1.9		2.6
Subtotal Level 3 Securities | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	81.3		70.7		80.9
Third Party Pricing Exemption Securities | Fair Value, Inputs, Level 3
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$0.30	[3]	$0.40	[3]	$0.40	[3]
[1]	The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
[3]	The fair values for these securities were obtained from non-binding external sources where unobservable inputs are not reasonably available to us.

Fair_Value_Fair_Value_Addition

Fair Value Fair Value - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
	Investment		Investment
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	100.00%	[1],[2]	100.00%	[1],[2]	100.00%	[1],[2]
Portfolio	19,830.60	[1],[2]	$17,395.70	[1],[2]	$19,018	[1],[2]
Fair Value, Inputs, Level 1
Fair Value Measurements [Line Items]
Portfolio	7,692.30		7,421.90		7,314.30
Fair Value, Inputs, Level 1 | Vendor Quoted Pricing
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	50.00%		55.00%		50.00%
Fair Value, Inputs, Level 2
Fair Value Measurements [Line Items]
Portfolio	12,056.70		9,902.70		11,622.40
Fair Value, Inputs, Level 2 | Vendor Quoted Pricing
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	97.00%		96.00%		97.00%
Fair Value, Inputs, Level 2 | Dealer Quoted Pricing
Fair Value Measurements [Line Items]
Quoted prices percentage of fair value assets	3.00%		4.00%		3.00%
Fair Value, Inputs, Level 3
Fair Value Measurements [Line Items]
Portfolio	81.6		71.1		81.3
Nonredeemable preferred stocks | Equity securities
Fair Value Measurements [Line Items]
Number of securities transferred out of Level 2 into Level 1	0		2
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount			41.7
Nonredeemable preferred stocks | Fair Value, Inputs, Level 3 | Equity securities | Internal Pricing
Fair Value Measurements [Line Items]
Number of securities	1		1		1
Portfolio	69.9		$42.10		$69.30
[1]	The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.

Debt_Detail

Debt (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Debt Instrument [Line Items]
Carrying Value	$2,560,100,000	[1]	$2,164,700,000	[1]	$1,861,300,000	[1]
Fair Value	2,910,900,000		2,527,500,000		2,152,500,000
3.75% Senior Notes due 2021
Debt Instrument [Line Items]
Carrying Value	497,900,000		497,800,000		497,600,000
Fair Value	542,600,000		535,600,000		524,500,000
6 5/8% Senior Notes due 2029
Debt Instrument [Line Items]
Carrying Value	295,600,000		295,500,000		295,400,000
Fair Value	393,600,000		400,600,000		381,800,000
6.25% Senior Notes due 2032
Debt Instrument [Line Items]
Carrying Value	394,900,000		394,800,000		394,700,000
Fair Value	525,600,000		527,900,000		501,400,000
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Carrying Value	346,300,000		346,300,000		0
Fair Value	387,100,000		378,900,000		0
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Carrying Value	394,900,000		0		0
Fair Value	394,800,000		0		0
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Carrying Value	630,500,000		630,300,000		673,600,000
Fair Value	$667,200,000		$684,500,000		$744,800,000
[1]	1Consists of long-term debt. See Note 4 - Debt.See notes to consolidated financial statements.

Debt_Parenthetical_Details

Debt (Parenthetical) (Details)	Mar. 31, 2015	Apr. 25, 2014	Jan. 26, 2015
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%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.70%		3.70%
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	12 Months Ended	1 Months Ended		3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Jan. 26, 2015	Apr. 25, 2014	Mar. 31, 2014
Discretionary Line of Credit
Debt Instrument [Line Items]
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 or 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
Discretionary Line of Credit | Federal Funds Rate
Debt Instrument [Line Items]
Basis points	0.50%	0.50%
3.70% Senior Notes due 2045
Debt Instrument [Line Items]
Debt Instrument, Issuance Date			26-Jan-15
Debt Instrument, Face Amount			400,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.70%		3.70%
Proceeds from Debt, Net of Issuance Costs			394,900,000
Additional Expenses Related to the Issuance			800,000
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)			-12,900,000
4.35% Senior Notes due 2044
Debt Instrument [Line Items]
Debt Instrument, Issuance Date				25-Apr-14
Debt Instrument, Face Amount				350,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.35%			4.35%
Proceeds from Debt, Net of Issuance Costs				346,300,000
Additional Expenses Related to the Issuance				700,000
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)				-1,600,000
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.70%
Repurchase of debt, face amount	0	44,300,000			0
(Gains) losses on extinguishment of debt	0	4,800,000			0
6.70% Fixed-to-Floating Rate Junior Subordinated Debentures due 2067 | Net unrealized gains on forecasted transactions
Debt Instrument [Line Items]
Cash flow hedge gain reclassification from accumulated other comprehensive income to net realized gains/losses on securities	$0	$500,000			$0

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Income taxes	$60	$0
Interest	$19.30	$19.30

Segment_Information_Operating_

Segment Information Operating Results (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$4,895.30		$4,707.60
Pretax Profit (Loss)	443.2		481.8
Underwriting Operations
Segment Reporting Information [Line Items]
Revenues	4,666.30		4,402.30
Pretax Profit (Loss)	341.6		289.8
Underwriting Operations | Personal Lines
Segment Reporting Information [Line Items]
Revenues	4,199.90	[1]	3,965.40	[1]
Pretax Profit (Loss)	262.7	[1]	249.6	[1]
Underwriting Operations | Personal Lines | Agency Channel
Segment Reporting Information [Line Items]
Revenues	2,244.50		2,203.20
Pretax Profit (Loss)	194.5		178.6
Underwriting Operations | Personal Lines | Direct Channel
Segment Reporting Information [Line Items]
Revenues	1,955.40		1,762.20
Pretax Profit (Loss)	68.2		71
Underwriting Operations | Commercial Lines
Segment Reporting Information [Line Items]
Revenues	466.4		436.9
Pretax Profit (Loss)	78.5		40.9
Underwriting Operations | Other Indemnity
Segment Reporting Information [Line Items]
Revenues	0		0
Pretax Profit (Loss)	0.4		-0.7
Fees and Other Revenues
Segment Reporting Information [Line Items]
Revenues	73.7	[2]	72.8	[2]
Service Businesses
Segment Reporting Information [Line Items]
Revenues	17.2		9.8
Pretax Profit (Loss)	1.3		0.1
Investments
Segment Reporting Information [Line Items]
Revenues	138.1	[3]	222.7	[3]
Pretax Profit (Loss)	132.8	[3]	218.6	[3]
Interest Expense
Segment Reporting Information [Line Items]
Pretax Profit (Loss)	($32.50)		($26.70)
[1]	Personal auto insurance accounted for 92% of the total Personal Lines segment net premiums earned in both the first quarters of 2015 and 2014; 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
	Mar. 31, 2015	Mar. 31, 2014
Underwriting Operations | Personal Lines | Personal Auto
Segment Reporting Information [Line Items]
Personal auto insurance percentage of the total personal lines segment net premiums earned	92.00%	92.00%

Segment_Information_Underwriti

Segment Information Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) (Underwriting Operations)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Underwriting Margin	7.30%	6.60%
Combined Ratio	92.70%	93.40%
Personal Lines
Segment Reporting Information [Line Items]
Underwriting Margin	6.30%	6.30%
Combined Ratio	93.70%	93.70%
Personal Lines | Agency Channel
Segment Reporting Information [Line Items]
Underwriting Margin	8.70%	8.10%
Combined Ratio	91.30%	91.90%
Personal Lines | Direct Channel
Segment Reporting Information [Line Items]
Underwriting Margin	3.50%	4.00%
Combined Ratio	96.50%	96.00%
Commercial Lines
Segment Reporting Information [Line Items]
Underwriting Margin	16.80%	9.40%
Combined Ratio	83.20%	90.60%

Dividends_Dividends_Details

Dividends Dividends (Details) (USD $)	0 Months Ended	1 Months Ended
	Feb. 13, 2015	Feb. 28, 2014
Annual variable dividend
Dividends [Line Items]
Dividend paid per share (USD per share)	$0.69	$0.49
Payments of Ordinary Dividends, Common Stock	$404.10	$293.90
Special dividend
Dividends [Line Items]
Dividend paid per share (USD per share)		$1
Payments of Ordinary Dividends, Common Stock		$596.30

Dividends_Additional_Informati

Dividends - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Dividends [Abstract]
Target percentage used to determine annual variable dividend	33.33%
Gainshare factor used to determine annual variable dividend range, minimum	0
Gainshare factor used to determine annual variable dividend range, maximum	2
Gainshare factor used to determine annual variable dividend	0.95
Comprehensive income	$321.80	$320.90
After-tax underwriting income	$222

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
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Pre tax total accumulated other comprehensive income, beginning balance	$1,574,000,000	$1,464,100,000
Investment securities, pre tax	99,300,000	131,800,000
Net non-credit related OTTI losses, adjusted for valuation changes, pre tax	0	0
Forecasted transactions, pre tax	-12,800,000	0
Foreign currency translation adjustment, pre tax	-900,000	0
Total other comprehensive income (loss) before reclassifications, pre tax	85,600,000	131,800,000
Total reclassification adjustment for amounts realized in net income, pre tax	45,400,000	132,400,000
Total other comprehensive income (loss), pre tax	40,200,000	-600,000
Pre tax total accumulated other comprehensive income, ending balance	1,614,200,000	1,463,500,000
Accumulated Other Comprehensive Income (Loss), Tax [Roll Forward]
Accumulated other comprehensive income loss tax (Provision) benefit, beginning balance	-550,900,000	-512,400,000
Investment securities, Total tax (provision) benefit	-34,700,000	-46,100,000
Net non-credit related OTTI losses, adjusted for valuation changes, Total tax (provision) benefit	0	0
Forecasted transactions, Total tax (provision) benefit	4,400,000	0
Foreign currency translation adjustment, Total tax (provision) benefit	400,000	0
Total other comprehensive income (loss) before reclassifications, Total tax (provision) benefit	-29,900,000	-46,100,000
Total reclassification adjustment for amounts realized in net income, Total tax (provision) benefit	-15,900,000	-46,300,000
Total other comprehensive income (loss), Total tax (provision) benefit	-14,000,000	200,000
Accumulated other comprehensive income loss tax (Provision) benefit, ending balance	-564,900,000	-512,200,000
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	1,023,100,000	951,700,000
Investment securities, after tax	64,600,000	85,700,000
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0
Forecasted transactions, after tax	-8,400,000	0
Foreign currency translation adjustment, after tax	-500,000	0
Total other comprehensive income (loss) before reclassifications, after tax	55,700,000	85,700,000
Total reclassification adjustment for amounts realized in net income, after tax	29,500,000	86,100,000
Other comprehensive income (loss)	26,200,000	-400,000
After tax total accumulated other comprehensive income, ending balance	1,049,300,000	951,300,000
Net impairment losses recognized in earnings	-7,900,000	0
Net realized gains (losses) on securities	40,900,000	119,400,000
Interest expense	32,500,000	26,700,000
Accumulated other comprehensive income after tax
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Other comprehensive income (loss)	26,200,000	-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	1,021,900,000	947,000,000
Investment securities, after tax	64,600,000	85,700,000
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0
Forecasted transactions, after tax	0	0
Foreign currency translation adjustment, after tax	0	0
Total other comprehensive income (loss) before reclassifications, after tax	64,600,000	85,700,000
Total reclassification adjustment for amounts realized in net income, after tax	29,200,000	85,800,000
Other comprehensive income (loss)	35,400,000	-100,000
After tax total accumulated other comprehensive income, ending balance	1,057,300,000	946,900,000
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	1,500,000	4,100,000
Investment securities, after tax	0	0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0
Forecasted transactions, after tax	-8,400,000	0
Foreign currency translation adjustment, after tax	0	0
Total other comprehensive income (loss) before reclassifications, after tax	-8,400,000	0
Total reclassification adjustment for amounts realized in net income, after tax	300,000	300,000
Other comprehensive income (loss)	-8,700,000	-300,000
After tax total accumulated other comprehensive income, ending balance	-7,200,000	3,800,000
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
After tax total accumulated other comprehensive income, beginning balance	-300,000	600,000
Investment securities, after tax	0	0
Net non-credit related OTTI losses, adjusted for valuation changes, after tax	0	0
Forecasted transactions, after tax	0	0
Foreign currency translation adjustment, after tax	-500,000	0
Total other comprehensive income (loss) before reclassifications, after tax	-500,000	0
Total reclassification adjustment for amounts realized in net income, after tax	0	0
Other comprehensive income (loss)	-500,000	0
After tax total accumulated other comprehensive income, ending balance	-800,000	600,000
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	-7,900,000	0
Net realized gains (losses) on securities	52,800,000	131,900,000
Interest expense	500,000	500,000
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	2,800,000	0
Net realized gains (losses) on securities	-18,500,000	-46,100,000
Interest expense	-200,000	-200,000
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	-5,100,000	0
Net realized gains (losses) on securities	34,300,000	85,800,000
Interest expense	300,000	300,000
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	-5,100,000	0
Net realized gains (losses) on securities	34,300,000	85,800,000
Interest expense	0	0
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains on forecasted transactions
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Net impairment losses recognized in earnings	0	0
Net realized gains (losses) on securities	0	0
Interest expense	300,000	300,000
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
Net realized gains (losses) on securities	0	0
Interest expense	$0	$0

Other_Comprehensive_Income_Los3

Other Comprehensive Income (Loss) Components of Other Comprehensive Income (Loss) Including Reclassification Adjustments by Income Statement (Parenthetical) (Detail) (Pre Tax, USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Pre Tax
Components Of Other Comprehensive Income Loss [Line Items]
Net unrealized gains on forecasted transactions, expected to reclassify into income within the next 12 months	$1.90

Subsequent_Event_Subsequent_Ev

Subsequent Event Subsequent Event - Additional Information(Details) (USD $)	0 Months Ended
	Apr. 01, 2015	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Subsequent Event [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$1,800,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	1,300,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deferred Revenue	600,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	300,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	200,000,000
Portfolio		19,830,600,000	[1],[2]	19,018,000,000	[1],[2]	17,395,700,000	[1],[2]
Net Realized Gain Loss On Hybrid Instrument		-46,200,000	[1],[2],[3]	-43,000,000	[1],[2],[3]	-16,800,000	[1],[2],[3]
ARX Holding Corp.
Subsequent Event [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		5.00%
Portfolio		69,900,000
Net Realized Gain Loss On Hybrid Instrument		600,000
Subsequent Event | ARX Holding Corp.
Subsequent Event [Line Items]
Business Acquisition, Effective Date of Acquisition	1-Apr-15
Business Acquisition, Percentage of Voting Interests Acquired	63.50%
Business Acquisition, Transaction Costs	$877,000,000
Noncontrolling Interest, Ownership Percentage by Parent	68.50%
[1]	The total fair value of the portfolio at March 31, 2015 and 2014, and December 31, 2014 included $1.7 billion, $0.8 billion, and $1.9 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 March 31, 2015, $95.8 million was included in "other liabilities," compared to $350.0 million included in "other assets" at March 31, 2014 and $31.3 million included in "other liabilities" at December 31, 2014.
[3]	Represents net holding period gains (losses) on certain hybrid securities (discussed below).