Unum (UNM) 10-Q 8 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	6-May-14
Document Document and Entity Information [Abstract]	'	'
Entity Registrant Name	'Unum Group	'
Trading Symbol	'UNM	'
Entity Central Index Key	'0000005513	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	257,410,153

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Investments	'	'
Fixed Maturity Securities - at fair value (amortized cost: $38,516.0; $38,289.6)	$43,666.80	$42,344.40
Mortgage Loans	1,843.30	1,815.10
Policy Loans	3,268.30	3,276
Other Long-term Investments	565	566
Short-term Investments	1,189.50	913.4
Total Investments	50,532.90	48,914.90
Other Assets	'	'
Cash and Bank Deposits	76.2	94.1
Accounts and Premiums Receivable	1,664.40	1,647.80
Reinsurance Recoverable	4,837.60	4,806.50
Accrued Investment Income	756.3	700.2
Deferred Acquisition Costs	1,832.30	1,829.20
Goodwill	201	200.9
Property and Equipment	519.4	511.9
Income Tax Receivable	0	50.3
Other Assets	658.5	647.8
Total Assets	61,078.60	59,403.60
Liabilities	'	'
Policy and Contract Benefits	1,569.20	1,511
Reserves for Future Policy and Contract Benefits	43,932.50	43,099.10
Unearned Premiums	472.2	413.8
Other Policyholders' Funds	1,672.20	1,658.40
Income Tax Payable	17.3	0
Deferred Income Tax	312.6	144.3
Short-term Debt	61.6	76.5
Long-term Debt	2,948.20	2,612
Other Liabilities	1,137.10	1,229.40
Total Liabilities	52,122.90	50,744.50
Commitments and Contingent Liabilities - Note 10	'	'
Stockholders' Equity	'	'
Common Stock, $0.10 par; authorized: 725,000,000 shares; issued: 361,265,467 and 360,802,426 shares	36.1	36.1
Additional Paid-in Capital	2,640.80	2,634.10
Accumulated Other Comprehensive Income	454.4	255
Retained Earnings	8,273.80	8,083.20
Treasury Stock - at cost: 103,703,671 and 100,785,012 shares	-2,449.40	-2,349.30
Total Stockholders' Equity	8,955.70	8,659.10
Total Liabilities and Stockholders' Equity	$61,078.60	$59,403.60

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Investments	'	'
Fixed Maturity Securities, Amortized Cost	$38,516	$38,289.60
Stockholders' Equity	'	'
Common Stock, Par	$0.10	$0.10
Common Stock, Authorized	725,000,000	725,000,000
Common Stock, Issued	361,265,467	360,802,426
Treasury Stock, Shares at Cost	103,703,671	100,785,012

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenue	'	'
Premium Income	$1,938.50	$1,930.90
Net Investment Income	612.5	621.1
Realized Investment Gain (Loss)	'	'
Other-Than-Temporary Impairment Loss on Fixed Maturity Securities	0	-0.8
Net Realized Investment Gain, Excluding Other-Than-Temporary Impairment Loss on Fixed Maturity Securities	6.3	11.1
Net Realized Investment Gain	6.3	10.3
Other Income	53.8	62.5
Total Revenue	2,611.10	2,624.80
Benefits and Expenses	'	'
Benefits and Change in Reserves for Future Benefits	1,631.30	1,648.50
Commissions	236	238.2
Interest and Debt Expense	37.9	37.1
Deferral of Acquisition Costs	-129	-118.2
Amortization of Deferred Acquisition Costs	118.6	123.8
Compensation Expense	201	197.6
Other Expenses	188.8	194
Total Benefits and Expenses	2,284.60	2,321
Income Before Income Tax	326.5	303.8
Income Tax	'	'
Current	29.7	81.8
Deferred	67.9	9.4
Total Income Tax	97.6	91.2
Net Income	$228.90	$212.60
Net Income Per Common Share	'	'
Basic	$0.88	$0.79
Assuming Dilution	$0.88	$0.79

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]	'	'
Net Income	$228.90	$212.60
Other Comprehensive Income (Loss)	'	'
Change in Net Unrealized Gain on Securities Before Adjustment (net of tax expense (benefit) of $371.1; $(159.4)	710	-278.5
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance (net of tax expense (benefit) of $(272.0); $108.6	-520.4	197.4
Change in Net Gain on Cash Flow Hedges (net of tax expense (benefit) of $1.0; $(0.2)	1.7	-2
Change in Foreign Currency Translation Adjustment	7.6	-69.9
Change in Unrecognized Pension and Postretirement Benefit Costs (net of tax expense of $0.3; $5.5)	0.5	10.7
Total Other Comprehensive Income (Loss)	199.4	-142.3
Comprehensive Income	$428.30	$70.30

CONSOLIDATED_STATEMENTS_OF_COM1

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]	'	'
Change in Net Unrealized Gain on Securities Before Adjustment, Tax Expense (Benefit)	$371.10	($159.40)
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense (Benefit)	-272	108.6
Change in Net Gain on Cash Flow Hedges, Tax Expense (Benefit)	1	-0.2
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense	$0.30	$5.50

CONSOLIDATED_STATEMENTS_OF_STO

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $)	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock
In Millions
Balance at Beginning of Year at Dec. 31, 2012	'	$36	$2,607.70	$628	$7,371.60	($2,030.70)
Common Stock Activity	'	'	5.7	'	'	'
Other Comprehensive Income (Loss)	-142.3	'	'	-142.3	'	'
Net Income	212.6	'	'	'	212.6	'
Dividends to Stockholders (per common share: $0.145; $0.130)	'	'	'	'	-35.7	'
Purchases of Treasury Stock	-95.1	'	'	'	'	-95.1
Balance at End of Period at Mar. 31, 2013	8,557.80	36	2,613.40	485.7	7,548.50	-2,125.80
Balance at Beginning of Year at Dec. 31, 2013	8,659.10	36.1	2,634.10	255	8,083.20	-2,349.30
Common Stock Activity	'	'	6.7	'	'	'
Other Comprehensive Income (Loss)	199.4	'	'	199.4	'	'
Net Income	228.9	'	'	'	228.9	'
Dividends to Stockholders (per common share: $0.145; $0.130)	'	'	'	'	-38.3	'
Purchases of Treasury Stock	-100.1	'	'	'	'	-100.1
Balance at End of Period at Mar. 31, 2014	$8,955.70	$36.10	$2,640.80	$454.40	$8,273.80	($2,449.40)

CONSOLIDATED_STATEMENTS_OF_STO1

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Stockholders' Equity Attributable to Parent	$8,955.70	$8,557.80
Retained Earnings	'	'
Dividends to Stockholders, per common share	$0.14	$0.13
Stockholders' Equity Attributable to Parent	8,273.80	7,548.50
Common Stock	'	'
Stockholders' Equity Attributable to Parent	$36.10	$36

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Cash Flows from Operating Activities	'	'
Net Income	$228.90	$212.60
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities	'	'
Change in Receivables	14	-130.1
Change in Deferred Acquisition Costs	-10.4	5.6
Change in Insurance Reserves and Liabilities	120.6	197.6
Change in Income Taxes	136.5	40.1
Change in Other Accrued Liabilities	-62.6	23.4
Non-cash Adjustments to Net Investment Income	-96.7	-96.1
Net Realized Investment Gain	-6.3	-10.3
Depreciation	20.8	21.2
Other, Net	1.9	1.1
Net Cash Provided by Operating Activities	346.7	265.1
Cash Flows from Investing Activities	'	'
Proceeds from Sales of Fixed Maturity Securities	193.4	158.4
Proceeds from Maturities of Fixed Maturity Securities	510	518.5
Proceeds from Sales and Maturities of Other Investments	57.4	42.3
Purchase of Fixed Maturity Securities	-904.4	-721.9
Purchase of Other Investments	-95.6	-43.4
Net Sales (Purchases) of Short-term Investments	-273.3	256.3
Other, Net	-28.1	-26.1
Net Cash Provided (Used) by Investing Activities	-540.6	184.1
Cash Flows from Financing Activities	'	'
Net Short-term Debt Repayments	-14.9	-219.5
Issuance of Long-term Debt	347.2	0
Long-term Debt Repayments	-15	-71.2
Issuance of Common Stock	1.6	0.7
Repurchase of Common Stock	-100.5	-99
Dividends Paid to Stockholders	-38.3	-35.7
Other, Net	-4.1	0.2
Net Cash Provided (Used) by Financing Activities	176	-424.5
Net Increase (Decrease) in Cash and Bank Deposits	-17.9	24.7
Cash and Bank Deposits at Beginning of Year	94.1	77.3
Cash and Bank Deposits at End of Period	$76.20	$102

Basis_of_Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2014
Accounting Policies [Abstract]	'
Basis of Presentation	'
	The accompanying consolidated financial statements of Unum Group and its subsidiaries (the Company) have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes included in our annual report on Form 10-K for the year ended December 31, 2013.
	In our opinion, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Interim results are not necessarily indicative of full year performance.

Accounting_Developments

Accounting Developments	3 Months Ended
	Mar. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
Accounting Changes Disclosure	'
	Accounting Updates Outstanding:
	ASC 323 "Investments - Equity Method and Joint Ventures"
	In January 2014, the FASB issued an update to provide guidance on the accounting and reporting for investments in affordable housing projects that qualify for low-income housing tax credits. The amendments in the update permit entities to make an accounting policy election to account for their investments in qualified affordable housing projects using the proportional amortization method if certain conditions are met. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the income statement as a component of income tax expense (benefit). Additional disclosures concerning investments in qualified affordable housing projects will also be required by the update. The amendments in the update are effective for interim and annual periods beginning on or after December 15, 2014, with early adoption permitted, and are to be applied retrospectively. We have not yet finalized the expected impact on our financial position or results of operations. We expect to adopt this update effective January 1, 2015.

Fair_Values_of_Financial_Instr

Fair Values of Financial Instruments	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Fair Values of Financial Instruments	'
	Presented as follows are the carrying amounts and fair values of financial instruments. The carrying values of financial instruments such as short-term investments, cash and bank deposits, accounts and premiums receivable, accrued investment income, and short-term debt approximate fair value due to the short-term nature of the instruments. As such, these financial instruments are not included in the following chart.
		31-Mar-14						31-Dec-13
		Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value
		(in millions of dollars)
	Assets
	Fixed Maturity Securities	$	43,666.80		$	43,666.80		$	42,344.40		$	42,344.40
	Mortgage Loans	1,843.30			2,009.80			1,815.10			1,980.20
	Policy Loans	3,268.30			3,336.30			3,276.00			3,339.60
	Other Long-term Investments
	Derivatives	10.9			10.9			10.8			10.8
	Equity Securities	15.1			15.1			16.4			16.4
	Miscellaneous Long-term Investments	477.4			477.4			475.2			475.2
	Liabilities
	Policyholders' Funds
	Deferred Annuity Products	$	629.7		$	629.7		$	631.5		$	631.5
	Supplementary Contracts without Life Contingencies	585.7			585.7			563.1			563.1
	Long-term Debt	2,948.20			3,194.50			2,612.00			2,824.40
	Other Liabilities
	Derivatives	117.7			117.7			135.6			135.6
	Embedded Derivative in Modified Coinsurance Arrangement	44.7			44.7			53.2			53.2
	Unfunded Commitments to Investment Partnerships	17.9			17.9			27.2			27.2
	The methods and assumptions used to estimate fair values of financial instruments are discussed as follows.
	Fair Value Measurements for Financial Instruments Not Carried at Fair Value
	Mortgage Loans: Fair values are estimated using discounted cash flow analyses and interest rates currently being offered for similar loans to borrowers with similar credit ratings and maturities. Loans with similar characteristics are aggregated for purposes of the calculations. These financial instruments are assigned a Level 2 within the fair value hierarchy.
	Policy Loans: Fair values for policy loans, net of reinsurance ceded, are estimated using discounted cash flow analyses and interest rates currently being offered to policyholders with similar policies. Carrying amounts for ceded policy loans, which equal $3,034.4 million and $3,043.7 million as of March 31, 2014 and December 31, 2013, respectively, approximate fair value and are reported on a gross basis in our consolidated balance sheets. A change in interest rates for ceded policy loans will not impact our financial position because the benefits and risks are fully ceded to reinsuring counterparties. These financial instruments are assigned a Level 3 within the fair value hierarchy.
	Miscellaneous Long-term Investments: Carrying amounts for tax credit partnerships equal the unamortized balance of our contractual commitments and approximate fair value. Fair values for private equity partnerships are primarily derived from net asset values provided by the general partner in the partnerships' financial statements. Our private equity partnerships represent funds that are primarily invested in power, energy, railcar leasing, infrastructure development, and mezzanine debt. Distributions received from the funds arise from income generated by the underlying investments as well as the liquidation of the underlying investments. As of March 31, 2014, we estimate that the underlying assets of the funds will be liquidated over the next one to ten years. These financial instruments are assigned a Level 3 within the fair value hierarchy.
	Policyholders' Funds: Policyholders' funds are comprised primarily of deferred annuity products and supplementary contracts without life contingencies and represent customer deposits plus interest credited at contract rates. Carrying amounts approximate fair value. These financial instruments are assigned a Level 3 within the fair value hierarchy.
	Fair values for insurance contracts other than investment contracts are not required to be disclosed. However, the fair values of liabilities under all insurance contracts are taken into consideration in our overall management of interest rate risk, which seeks to minimize exposure to changing interest rates through the matching of investment maturities with amounts due under insurance contracts.
	Long-term Debt: Fair values for long-term debt are obtained from independent pricing services or discounted cash flow analyses based on current incremental borrowing rates for similar types of borrowing arrangements. Debt instruments which are valued using active trades from independent pricing services for which there was current market activity in that specific debt instrument have fair values of $1,429.8 million and $1,329.2 million as of March 31, 2014 and December 31, 2013, respectively, and are assigned a Level 1 within the fair value hierarchy. Debt instruments which are valued based on prices from pricing services that generally use observable inputs for securities or comparable securities in active markets in their valuation techniques have fair values of $1,764.7 million and $1,495.2 million as of March 31, 2014 and December 31, 2013, respectively, and are assigned a Level 2.
	Unfunded Commitments to Investment Partnerships: Unfunded equity commitments represent legally binding amounts that we have committed to certain investment partnerships subject to the partnerships meeting specified conditions. When these conditions are met, we are obligated to invest these amounts in the partnerships. Carrying amounts approximate fair value. These financial instruments are assigned a Level 2 within the fair value hierarchy.
	Fair Value Measurements for Financial Instruments Carried at Fair Value
	We report fixed maturity securities, derivative financial instruments, and equity securities at fair value in our consolidated balance sheets. The degree of judgment utilized in measuring the fair value of financial instruments generally correlates to the level of pricing observability. Financial instruments with readily available active quoted prices or for which fair value can be measured from actively quoted prices in active markets generally have more pricing observability and less judgment utilized in measuring fair value. An active market for a financial instrument is a market in which transactions for an asset or a similar asset occur with sufficient frequency and volume to provide pricing information on an ongoing basis. A quoted price in an active market provides the most reliable evidence of fair value and should be used to measure fair value whenever available. Conversely, financial instruments rarely traded or not quoted have less observability and are measured at fair value using valuation techniques that require more judgment. Pricing observability is generally impacted by a number of factors, including the type of financial instrument, whether the financial instrument is new to the market and not yet established, the characteristics specific to the transaction, and overall market conditions.
	Valuation techniques used for assets and liabilities accounted for at fair value are generally categorized into three types. The market approach uses prices and other relevant information from market transactions involving identical or comparable assets or liabilities. The income approach converts future amounts, such as cash flows or earnings, to a single present amount, or a discounted amount. The cost approach is based upon the amount that currently would be required to replace the service capacity of an asset, or the current replacement cost.
	We use valuation techniques that are appropriate in the circumstances and for which sufficient data are available that can be obtained without undue cost and effort. In some cases, a single valuation technique will be appropriate (for example, when valuing an asset or liability using quoted prices in an active market for identical assets or liabilities). In other cases, multiple valuation techniques will be appropriate. If we use multiple valuation techniques to measure fair value, we evaluate and weigh the results, as appropriate, considering the reasonableness of the range indicated by those results. A fair value measurement is the point within that range that is most representative of fair value in the circumstances.
	The selection of the valuation method(s) to apply considers the definition of an exit price and depends on the nature of the asset or liability being valued. For assets and liabilities accounted for at fair value, we generally use valuation techniques consistent with the market approach, and to a lesser extent, the income approach. We believe the market approach valuation technique provides more observable data than the income approach, considering the type of investments we hold. Our fair value measurements could differ significantly based on the valuation technique and available inputs. When using a pricing service, we obtain the vendor's pricing documentation to ensure we understand their methodologies. We periodically review and approve the selection of our pricing vendors to ensure we are in agreement with their current methodologies. When markets are less active, brokers may rely more on models with inputs based on the information available only to the broker. Our internal investment management professionals, which include portfolio managers and analysts, monitor securities priced by brokers and evaluate their prices for reasonableness based on benchmarking to available primary and secondary market information. In weighing a broker quote as an input to fair value, we place less reliance on quotes that do not reflect the result of market transactions. We also consider the nature of the quote, particularly whether the quote is a binding offer. If prices in an inactive market do not reflect current prices for the same or similar assets, adjustments may be necessary to arrive at fair value. When relevant market data is unavailable, which may be the case during periods of market uncertainty, the income approach can, in suitable circumstances, provide a more appropriate fair value. During 2014, we have applied valuation techniques on a consistent basis to similar assets and liabilities and consistent with those techniques used at year end 2013.
	We use observable and unobservable inputs in measuring the fair value of our financial instruments. Inputs that may be used include the following:
	•	Broker market maker prices and price levels
	•	Trade Reporting and Compliance Engine (TRACE) pricing
	•	Prices obtained from external pricing services
	•	Benchmark yields (Treasury and interest rate swap curves)
	•	Transactional data for new issuance and secondary trades
	•	Security cash flows and structures
	•	Recent issuance/supply
	•	Sector and issuer level spreads
	•	Security credit ratings/maturity/capital structure/optionality
	•	Corporate actions
	•	Underlying collateral
	•	Prepayment speeds/loan performance/delinquencies/weighted average life/seasoning
	•	Public covenants
	•	Comparative bond analysis
	•	Derivative spreads
	•	Relevant reports issued by analysts and rating agencies
	•	Audited financial statements
	The management of our investment portfolio includes establishing pricing policy and reviewing the reasonableness of sources and inputs used in developing pricing. We review all prices obtained to ensure they are consistent with a variety of observable market inputs and to verify the validity of a security's price.  In the event we receive a vendor's market price that does not appear reasonable based on our market analysis, we may challenge the price and request further information about the assumptions and methodologies used by the vendor to price the security. We may change the vendor price based on a better data source such as an actual trade. We also review all price changes from the prior month which fall outside a predetermined corridor. The overall valuation process for determining fair values may include adjustments to valuations obtained from our pricing sources when they do not represent a valid exit price. These adjustments may be made when, in our judgment and considering our knowledge of the financial conditions and industry in which the issuer operates, certain features of the financial instrument require that an adjustment be made to the value originally obtained from our pricing sources. These features may include the complexity of the financial instrument, the market in which the financial instrument is traded, counterparty credit risk, credit structure, concentration, or liquidity. Additionally, an adjustment to the price derived from a model typically reflects our judgment of the inputs that other participants in the market for the financial instrument being measured at fair value would consider in pricing that same financial instrument. In the event an asset is sold, we test the validity of the fair value determined by our valuation techniques by comparing the selling price to the fair value determined for the asset in the immediately preceding month end reporting period.
	The parameters and inputs used to validate a price on a security may be adjusted for assumptions about risk and current market conditions on a quarter to quarter basis, as certain features may be more significant drivers of valuation at the time of pricing. Changes to inputs in valuations are not changes to valuation methodologies; rather, the inputs are modified to reflect direct or indirect impacts on asset classes from changes in market conditions.
	Fair values for derivatives other than embedded derivatives in modified coinsurance arrangements are based on market quotes or pricing models and represent the net amount of cash we would have paid or received if the contracts had been settled or closed as of the last day of the period. We analyze credit default swap spreads relative to the average credit spread embedded within the LIBOR-setting syndicate in determining the effect of credit risk on our derivatives' fair values.  If net counterparty credit risk for a derivative asset is determined to be material and is not adequately reflected in the LIBOR-based fair value obtained from our pricing sources, we adjust the valuations obtained from our pricing sources. For purposes of valuing net counterparty risk, we measure the fair value of a group of financial assets and financial liabilities on the basis of the price that would be received to sell a net long position or transfer a net short position for a particular risk exposure in an orderly transaction between market participants at the measurement date under current market conditions. In regard to our own credit risk component, we adjust the valuation of derivative liabilities wherein the counterparty is exposed to our credit risk when the LIBOR-based valuation of our derivatives obtained from pricing sources does not effectively include an adequate credit component for our own credit risk.
	Fair values for our embedded derivative in a modified coinsurance arrangement are estimated using internal pricing models and represent the hypothetical value of the duration mismatch of assets and liabilities, interest rate risk, and third party credit risk embedded in the modified coinsurance arrangement.
	Certain of our investments do not have readily determinable market prices and/or observable inputs or may at times be affected by the lack of market liquidity. For these securities, we use internally prepared valuations combining matrix pricing with vendor purchased software programs, including valuations based on estimates of future profitability, to estimate the fair value. Additionally, we may obtain prices from independent third-party brokers to aid in establishing valuations for certain of these securities. Key assumptions used by us to determine fair value for these securities include risk free interest rates, risk premiums, performance of underlying collateral (if any), and other factors involving significant assumptions which may or may not reflect those of an active market.
	At March 31, 2014, approximately 11.0 percent of our fixed maturity securities were valued using active trades from TRACE pricing or broker market maker prices for which there was current market activity in that specific security (comparable to receiving one binding quote).  The prices obtained were not adjusted, and the assets were classified as Level 1, the highest category of the three-level fair value hierarchy classification wherein inputs are unadjusted and represent quoted prices in active markets for identical assets or liabilities.
	The remaining 89.0 percent of our fixed maturity securities were valued based on non-binding quotes or other observable and unobservable inputs, as discussed below.
	•	Approximately 72.4 percent of our fixed maturity securities were valued based on prices from pricing services that generally use observable inputs such as prices for securities or comparable securities in active markets in their valuation techniques. These assets were classified as Level 2.  Level 2 assets or liabilities are those valued using inputs (other than prices included in Level 1) that are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument's anticipated life.
	•	Approximately 3.6 percent of our fixed maturity securities were valued based on one or more non-binding broker price levels, if validated by observable market data, or on TRACE prices for identical or similar assets absent current market activity. When only one price is available, it is used if observable inputs and analysis confirms that it is appropriate. These assets, for which we were able to validate the price using other observable market data, were classified as Level 2.
•	Approximately 13.0 percent of our fixed maturity securities were valued based on prices of comparable securities, matrix pricing, market models, and/or internal models or were valued based on non-binding quotes with no other observable market data. These assets were classified as either Level 2 or Level 3, with the categorization dependent on whether there was other observable market data.  Level 3 is the lowest category of the fair value hierarchy and reflects the judgment of management regarding what market participants would use in pricing assets or liabilities at the measurement date. Financial assets and liabilities categorized as Level 3 are generally those that are valued using unobservable inputs to extrapolate an estimated fair value.
We consider transactions in inactive or disorderly markets to be less representative of fair value. We use all available observable inputs when measuring fair value, but when significant other unobservable inputs and adjustments are necessary, we classify these assets or liabilities as Level 3.
Fair value measurements by input level for financial instruments carried at fair value are as follows:
	March 31, 2014
	Quoted Prices			Significant Other			Significant			Total
	in Active Markets			Observable			Unobservable
	for Identical Assets			Inputs			Inputs
	or Liabilities			(Level 2)			(Level 3)
	(Level 1)
	(in millions of dollars)
Assets
Fixed Maturity Securities
United States Government and Government Agencies and Authorities	$	189.2		$	967.5		$	—		$	1,156.70
States, Municipalities, and Political Subdivisions	—			1,770.70			156.1			1,926.80
Foreign Governments	—			1,290.60			80.4			1,371.00
Public Utilities	709.4			9,783.70			310			10,803.10
Mortgage/Asset-Backed Securities	—			2,286.30			0.4			2,286.70
All Other Corporate Bonds	3,912.30			20,698.20			1,473.60			26,084.10
Redeemable Preferred Stocks	—			14			24.4			38.4
Total Fixed Maturity Securities	4,810.90			36,811.00			2,044.90			43,666.80
Other Long-term Investments
Derivatives
Interest Rate Swaps	—			8.1			—			8.1
Foreign Exchange Contracts	—			2.8			—			2.8
Total Derivatives	—			10.9			—			10.9
Equity Securities	—			12			3.1			15.1
Liabilities
Other Liabilities
Derivatives
Interest Rate Swaps	$	—		$	30.9		$	—		$	30.9
Foreign Exchange Contracts	—			84.8			—			84.8
Credit Default Swaps	—			2			—			2
Embedded Derivative in Modified Coinsurance Arrangement	—			—			44.7			44.7
Total Derivatives	—			117.7			44.7			162.4
	December 31, 2013
	Quoted Prices			Significant Other			Significant			Total
	in Active Markets			Observable			Unobservable
	for Identical Assets			Inputs			Inputs
	or Liabilities			(Level 2)			(Level 3)
	(Level 1)
	(in millions of dollars)
Assets
Fixed Maturity Securities
United States Government and Government Agencies and Authorities	$	144.5		$	1,051.60		$	—		$	1,196.10
States, Municipalities, and Political Subdivisions	—			1,608.10			175.1			1,783.20
Foreign Governments	—			1,294.70			78.5			1,373.20
Public Utilities	396.8			9,802.70			203.5			10,403.00
Mortgage/Asset-Backed Securities	—			2,038.80			0.5			2,039.30
All Other Corporate Bonds	1,982.00			21,670.80			1,859.10			25,511.90
Redeemable Preferred Stocks	—			13.9			23.8			37.7
Total Fixed Maturity Securities	2,523.30			37,480.60			2,340.50			42,344.40
Other Long-term Investments
Derivatives
Interest Rate Swaps	—			9.2			—			9.2
Foreign Exchange Contracts	—			1.6			—			1.6
Total Derivatives	—			10.8			—			10.8
Equity Securities	—			11.8			4.6			16.4
Liabilities
Other Liabilities
Derivatives
Interest Rate Swaps	$	—		$	35		$	—		$	35
Foreign Exchange Contracts	—			98.7			—			98.7
Credit Default Swaps	—			1.9			—			1.9
Embedded Derivative in Modified Coinsurance Arrangement	—			—			53.2			53.2
Total Derivatives	—			135.6			53.2			188.8
Transfers of assets between Level 1 and Level 2 are as follows:
	Three Months Ended March 31
	2014						2013
	Transfers into
	Level 1 from			Level 2 from			Level 1 from			Level 2 from
	Level 2			Level 1			Level 2			Level 1
	(in millions of dollars)
Fixed Maturity Securities
United States Government and Government Agencies and Authorities	$	163.2		$	121.5		$	256.9		$	—
States, Municipalities, and Political Subdivisions	—			—			—			19.4
Public Utilities	452.1			192.8			502.1			53.5
All Other Corporate Bonds	2,391.50			652.8			2,266.30			1,140.80
Total Fixed Maturity Securities	$	3,006.80		$	967.1		$	3,025.30		$	1,213.70
Transfers between Level 1 and Level 2 occurred due to the change in availability of either a TRACE or broker market maker price. Depending on current market conditions, the availability of these Level 1 prices can vary from period to period. For fair value measurements of financial instruments that were transferred either into or out of Level 1 or 2, we reflect the transfers using the fair value at the beginning of the period.
Changes in assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) are as follows:
	Three Months Ended March 31, 2014
				Total Realized and
				Unrealized Investment
				Gains (Losses) Included in
	Beginning			Earnings			Other			Purchases		Sales			Level 3 Transfers					End of
	of Year						Comprehensive													Period
							Income or Loss								Into		Out of
	(in millions of dollars)
Fixed Maturity Securities
States, Municipalities, and Political Subdivisions	$	175.1		$	—		$	6.5		$	—	$	—		$	—	$	(25.5	)	$	156.1
Foreign Governments	78.5			—			1.9			—		—			—		—			80.4
Public Utilities	203.5			—			5.6			6.6		—			124.5		(30.2		)	310
Mortgage/Asset-Backed Securities	0.5			—			—			—		(0.1		)	—		—			0.4
All Other Corporate Bonds	1,859.10			—			24.2			73		(29.6		)	362.9		(816.0		)	1,473.60
Redeemable Preferred Stocks	23.8			—			0.6			—		—			—		—			24.4
Total Fixed Maturity Securities	2,340.50			—			38.8			79.6		(29.7		)	487.4		(871.7		)	2,044.90
Equity Securities	4.6			2.1			(0.1		)	—		(3.5		)	—		—			3.1
Embedded Derivative in Modified Coinsurance Arrangement	(53.2		)	8.5			—			—		—			—		—			(44.7		)
	Three Months Ended March 31, 2013
				Total Realized and
				Unrealized Investment
				Gains (Losses) Included in
	Beginning			Earnings			Other			Purchases		Sales			Level 3 Transfers					End of
	of Year						Comprehensive													Period
							Income or Loss								Into		Out of
	(in millions of dollars)
Fixed Maturity Securities
States, Municipalities, and Political Subdivisions	$	128.7		$	—		$	2.7		$	—	$	—		$	43.4	$	—		$	174.8
Foreign Governments	82.1			—			0.5			—		—			—		—			82.6
Public Utilities	574.4			—			1.1			—		(0.1		)	252.3		(425.2		)	402.5
Mortgage/Asset-Backed Securities	0.5			—			—			—		—			—		—			0.5
All Other Corporate Bonds	1,177.80			0.8			(8.8		)	30.3		(18.1		)	382.4		(572.1		)	992.3
Redeemable Preferred Stocks	24.8			—			—			—		—			—		—			24.8
Total Fixed Maturity Securities	1,988.30			0.8			(4.5		)	30.3		(18.2		)	678.1		(997.3		)	1,677.50
Equity Securities	4.3			—			—			—		—			—		—			4.3
Embedded Derivative in Modified Coinsurance Arrangement	(83.9		)	6.4			—			—		—			—		—			(77.5		)
Realized and unrealized investment gains and losses presented in the preceding tables represent gains and losses only for the time during which the applicable financial instruments were classified as Level 3. The transfers between levels resulted primarily from a change in observability of three inputs used to determine fair values of the securities transferred: (1) transactional data for new issuance and secondary trades, (2) broker/dealer quotes and pricing, primarily related to changes in the level of activity in the market and whether the market was considered orderly, and (3) comparable bond metrics from which to perform an analysis. For fair value measurements of financial instruments that were transferred either into or out of Level 3, we reflect the transfers using the fair value at the beginning of the period. We believe this allows for greater transparency, as all changes in fair value that arise during the reporting period of the transfer are disclosed as a component of our Level 3 reconciliation. Gains for the three months ended March 31, 2014 and 2013 which are included in earnings and are attributable to the change in unrealized gains or losses relating to assets or liabilities valued using significant unobservable inputs and still held at period end were $8.5 million and $6.4 million, respectively. These amounts relate entirely to the changes in fair value of an embedded derivative in a modified coinsurance arrangement which are reported as realized investment gains and losses.
The table below provides quantitative information regarding the significant unobservable inputs used in Level 3 fair value measurements derived from internal models. Certain securities classified as Level 3 are excluded from the table below due to limitations in our ability to obtain the underlying inputs used by external pricing sources.
	31-Mar-14
	Fair Value			Unobservable Input		Range/Weighted Average
	(in millions of dollars)
Fixed Maturity Securities
States, Municipalities, and Political Subdivisions - Private	$	122.1		- Comparability Adjustment	(b)	0.25% - 1.25% / 0.74%
Public Utilities	72.4			- Volatility of Credit	(e)	0.75% - 1.50% / 1.05%
Mortgage/Asset-Backed Securities - Private	0.4			- Discount for Size	(c)	5.60% - 5.71% / 5.68%
All Other Corporate Bonds - Private	296.1			- Change in Benchmark Reference	(a)	0.54% - 0.75% / 0.67%
				- Comparability Adjustment	(b)	(0.70)% - (0.40)% / (0.60)%
				- Discount for Size	(c)	0.50% - 0.50% / 0.50%
				- Lack of Marketability	(d)	0.20% - 2.96% / 1.01%
				- Volatility of Credit	(e)	0.40% - 4.00% / 0.85%
				- Market Convention	(f)	Priced at Par
All Other Corporate Bonds - Public	344.7			- Change in Benchmark Reference	(a)	(0.85%) - (0.85%) / (0.85)%
				- Comparability Adjustment	(b)	0.20% - 1.43% / 0.60%
				- Lack of Marketability	(d)	0.10% - 0.25% / 0.23%
				- Volatility of Credit	(e)	(0.86)% - 1.34% / (0.03)%
Equity Securities - Private	2.8			- Market Convention	(f)	Priced at Cost or Owner's Equity
Embedded Derivative in Modified Coinsurance Arrangement	(44.7		)	- Projected Liability Cash Flows	(g)	Actuarial Assumptions
	31-Dec-13
	Fair Value			Unobservable Input		Range/Weighted Average
	(in millions of dollars)
Fixed Maturity Securities
States, Municipalities, and Political Subdivisions - Private	$	142.7		- Comparability Adjustment	(b)	0.25% - 1.25% / 0.65%
Public Utilities	64.3			- Volatility of Credit	(e)	0.75% - 1.25% / 0.92%
Mortgage/Asset-Backed Securities - Private	0.5			- Discount for Size	(c)	4.93% - 5.03% / 5.01%
All Other Corporate Bonds - Private	307			- Change in Benchmark Reference	(a)	3.36% - 3.36% / 3.36%
				- Comparability Adjustment	(b)	(0.70)% - (0.40)% / (0.60)%
				- Discount for Size	(c)	0.50% - 0.50% / 0.50%
				- Lack of Marketability	(d)	0.20% - 1.00% / 0.55%
				- Volatility of Credit	(e)	0.07% - 4.00% / 0.84%
				- Market Convention	(f)	Priced at Par
All Other Corporate Bonds - Public	514.4			- Change in Benchmark Reference	(a)	(0.32)% - 0.25% / 0.04%
				- Comparability Adjustment	(b)	(0.23)% - 1.00% / 0.41%
				- Lack of Marketability	(d)	0.20% - 0.20% / 0.20%
				- Volatility of Credit	(e)	(0.88)% - 0.46% / (0.26)%
Equity Securities - Private	4.2			- Market Convention	(f)	Priced at Cost or Owner's Equity
Embedded Derivative in Modified Coinsurance Arrangement	(53.2		)	- Projected Liability Cash Flows	(g)	Actuarial Assumptions
(a)	Represents basis point adjustments for changes in benchmark spreads associated with various ratings categories
(b)	Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors
(c)	Represents basis point adjustments based on issue/issuer size relative to the benchmark
(d)	Represents basis point adjustments to apply a discount due to the illiquidity of an investment
(e)	Represents basis point adjustments for credit-specific factors
(f)	Represents a decision to price based on par value, cost, or owner's equity when limited data is available
(g)	Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates
Isolated increases in unobservable inputs other than market convention will result in a lower fair value measurement, whereas isolated decreases will result in a higher fair value measurement. The unobservable input for market convention is not sensitive to input movements. The projected liability cash flows used in the fair value measurement of our Level 3 embedded derivative are based on expected claim payments. If claim payments increase, the projected liability cash flows will increase, resulting in a decrease in the fair value of the embedded derivative. Decreases in projected liability cash flows will result in an increase in the fair value of the embedded derivative.

Investments

Investments	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Investments	'
	Fixed Maturity Securities
	At March 31, 2014 and December 31, 2013, all fixed maturity securities were classified as available-for-sale. The amortized cost and fair values of securities by security type are shown as follows.
		March 31, 2014
		Amortized			Gross				Gross				Fair
		Cost			Unrealized				Unrealized				Value
					Gain				Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	959.1		$	200.1			$	2.5			$	1,156.70
	States, Municipalities, and Political Subdivisions	1,732.30			212.2				17.7				1,926.80
	Foreign Governments	1,205.70			166.3				1				1,371.00
	Public Utilities	9,436.80			1,394.30				28				10,803.10
	Mortgage/Asset-Backed Securities	2,102.50			186.8				2.6				2,286.70
	All Other Corporate Bonds	23,046.60			3,125.50				88				26,084.10
	Redeemable Preferred Stocks	33			5.4				—				38.4
	Total Fixed Maturity Securities	$	38,516.00		$	5,290.60			$	139.8			$	43,666.80
		December 31, 2013
		Amortized			Gross				Gross				Fair
		Cost			Unrealized				Unrealized				Value
					Gain				Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	1,028.60		$	173.1			$	5.6			$	1,196.10
	States, Municipalities, and Political Subdivisions	1,706.00			117.2				40				1,783.20
	Foreign Governments	1,226.40			149.6				2.8				1,373.20
	Public Utilities	9,328.90			1,126.90				52.8				10,403.00
	Mortgage/Asset-Backed Securities	1,858.70			184.6				4				2,039.30
	All Other Corporate Bonds	23,108.00			2,602.60				198.7				25,511.90
	Redeemable Preferred Stocks	33			4.7				—				37.7
	Total Fixed Maturity Securities	$	38,289.60		$	4,358.70			$	303.9			$	42,344.40
	The following charts indicate the length of time our fixed maturity securities have been in a gross unrealized loss position.
		March 31, 2014
		Less Than 12 Months							12 Months or Greater
		Fair			Gross				Fair				Gross
		Value			Unrealized				Value				Unrealized
					Loss								Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	9.2		$	0.5			$	5.8			$	2
	States, Municipalities, and Political Subdivisions	186.3			9.8				55.9				7.9
	Foreign Governments	34.8			1				—				—
	Public Utilities	628			24.2				49.2				3.8
	Mortgage/Asset-Backed Securities	261.4			2.2				2.4				0.4
	All Other Corporate Bonds	1,908.60			66.6				257.1				21.4
	Total Fixed Maturity Securities	$	3,028.30		$	104.3			$	370.4			$	35.5
		December 31, 2013
		Less Than 12 Months							12 Months or Greater
		Fair			Gross				Fair				Gross
		Value			Unrealized				Value				Unrealized
					Loss								Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	41.1		$	3.1			$	5.2			$	2.5
	States, Municipalities, and Political Subdivisions	412.5			33.5				37.2				6.5
	Foreign Governments	87.2			2.8				—				—
	Public Utilities	870.6			47.1				58.7				5.7
	Mortgage/Asset-Backed Securities	341			3.6				2.5				0.4
	All Other Corporate Bonds	3,412.30			174				207.4				24.7
	Total Fixed Maturity Securities	$	5,164.70		$	264.1			$	311			$	39.8
	The following is a distribution of the maturity dates for fixed maturity securities. The maturity dates have not been adjusted for possible calls or prepayments.
		March 31, 2014
		Total			Unrealized Gain Position								Unrealized Loss Position
		Amortized Cost			Gross Gain				Fair Value				Gross Loss				Fair Value
		(in millions of dollars)
	1 year or less	$	841.9		$	21.5			$	854.4			$	—			$	9
	Over 1 year through 5 years	7,186.20			769.6				7,908.90				0.3				46.6
	Over 5 years through 10 years	9,640.00			1,030.00				9,239.50				41.2				1,389.30
Over 10 years	18,745.40			3,282.70				20,242.40				95.7				1,690.00
	36,413.50			5,103.80				38,245.20				137.2				3,134.90
Mortgage/Asset-Backed Securities	2,102.50			186.8				2,022.90				2.6				263.8
Total Fixed Maturity Securities	$	38,516.00		$	5,290.60			$	40,268.10			$	139.8			$	3,398.70
	December 31, 2013
	Total			Unrealized Gain Position								Unrealized Loss Position
	Amortized Cost			Gross Gain				Fair Value				Gross Loss				Fair Value
	(in millions of dollars)
1 year or less	$	903.9		$	20.6			$	915.5			$	—			$	9
Over 1 year through 5 years	7,098.20			727.1				7,678.50				0.6				146.2
Over 5 years through 10 years	9,492.60			940.2				8,137.40				95.8				2,199.60
Over 10 years	18,936.20			2,486.20				18,441.50				203.5				2,777.40
	36,430.90			4,174.10				35,172.90				299.9				5,132.20
Mortgage/Asset-Backed Securities	1,858.70			184.6				1,695.80				4				343.5
Total Fixed Maturity Securities	$	38,289.60		$	4,358.70			$	36,868.70			$	303.9			$	5,475.70
At March 31, 2014, the fair value of investment-grade fixed maturity securities was $40,372.3 million, with a gross unrealized gain of $5,104.7 million and a gross unrealized loss of $113.5 million. The gross unrealized loss on investment-grade fixed maturity securities was 81.2 percent of the total gross unrealized loss on fixed maturity securities. Unrealized losses on investment-grade fixed maturity securities principally relate to changes in interest rates or changes in market or sector credit spreads which occurred subsequent to the acquisition of the securities.
At March 31, 2014, the fair value of below-investment-grade fixed maturity securities was $3,294.5 million, with a gross unrealized gain of $185.9 million and a gross unrealized loss of $26.3 million. The gross unrealized loss on below-investment-grade fixed maturity securities was 18.8 percent of the total gross unrealized loss on fixed maturity securities. Generally, below-investment-grade fixed maturity securities are more likely to develop credit concerns than investment-grade securities. At March 31, 2014, the unrealized losses in our below-investment-grade fixed maturity securities were generally due to credit spreads in certain industries or sectors and, to a lesser extent, credit concerns related to specific securities. For each specific security in an unrealized loss position, we believe there are positive factors which mitigate credit concerns and the securities for which we have not recorded an other-than-temporary impairment will recover in value.
As of March 31, 2014, we held 148 individual investment-grade fixed maturity securities and 38 individual below-investment-grade fixed maturity securities that were in an unrealized loss position, of which 16 investment-grade fixed maturity securities and 10 below-investment-grade fixed maturity securities had been in an unrealized loss position continuously for over one year.
In determining when a decline in fair value below amortized cost of a fixed maturity security is other than temporary, we evaluate the following factors:
•	Whether we expect to recover the entire amortized cost basis of the security
•	Whether we intend to sell the security or will be required to sell the security before the recovery of its amortized cost basis
•	Whether the security is current as to principal and interest payments
•	The significance of the decline in value
•	The time period during which there has been a significant decline in value
•	Current and future business prospects and trends of earnings
•	The valuation of the security's underlying collateral
•	Relevant industry conditions and trends relative to their historical cycles
•	Market conditions
•	Rating agency and governmental actions
•	Bid and offering prices and the level of trading activity
•	Adverse changes in estimated cash flows for securitized investments
•	Changes in fair value subsequent to the balance sheet date
•	Any other key measures for the related security
We evaluate available information, including the factors noted above, both positive and negative, in reaching our conclusions. In particular, we also consider the strength of the issuer's balance sheet, its debt obligations and near term funding requirements, cash flow and liquidity, the profitability of its core businesses, the availability of marketable assets which could be sold to increase liquidity, its industry fundamentals and regulatory environment, and its access to capital markets. Although available and applicable factors are considered in our analysis, our expectation of recovering the entire amortized cost basis of the security, whether we intend to sell the security, whether it is more likely than not we will be required to sell the security before recovery of its amortized cost, and whether the security is current on principal and interest payments are the most critical factors in determining whether impairments are other than temporary. The significance of the decline in value and the length of time during which there has been a significant decline are also important factors, but we generally do not record an impairment loss based solely on these two factors, since often other more relevant factors will impact our evaluation of a security.
While determining other-than-temporary impairments is a judgmental area, we utilize a formal, well-defined, and disciplined process to monitor and evaluate our fixed income investment portfolio, supported by issuer specific research and documentation as of the end of each period. The process results in a thorough evaluation of problem investments and the recording of losses on a timely basis for investments determined to have an other-than-temporary impairment.
If we determine that the decline in value of an investment is other than temporary, the investment is written down to fair value, and an impairment loss is recognized in the current period, either in earnings or in both earnings and other comprehensive income, as applicable. For those fixed maturity securities with an unrealized loss for which we have not recognized an other-than-temporary impairment, we believe we will recover the entire amortized cost, we do not intend to sell the security, and we do not believe it is more likely than not we will be required to sell the security before recovery of its amortized cost. There have been no defaults in the repayment obligations of any securities for which we have not recorded an other-than-temporary impairment.
We held no fixed maturity securities as of March 31, 2014 or December 31, 2013 for which a portion of an other-than-temporary impairment was recognized in accumulated other comprehensive income.
At March 31, 2014, we had non-binding commitments of $60.0 million to fund private placement fixed maturity securities.
Variable Interest Entities
We invest in variable interests issued by variable interest entities. These investments include tax credit partnerships, private equity partnerships, and special purpose entities. For those variable interests that are not consolidated in our financial statements, we are not the primary beneficiary because we have neither the power to direct the activities that are most significant to economic performance nor the responsibility to absorb a majority of the expected losses. The determination of whether we are the primary beneficiary is performed at the time of our initial investment and at the date of each subsequent reporting period.
As of March 31, 2014, the carrying amount of our variable interest entity investments that are not consolidated in our financial statements was $473.0 million, comprised of $304.8 million of tax credit partnerships and $168.2 million of private equity partnerships. These variable interest entity investments are reported as other long-term investments in our consolidated balance sheets.
Additionally, we recognize a liability for all legally binding unfunded commitments to these partnerships, with a corresponding recognition of an invested asset.  Our liability for legally binding unfunded commitments to the tax credit partnerships was $17.9 million at March 31, 2014. Contractually, we are a limited partner in these investments, and our maximum exposure to loss is limited to the carrying value of our investment. We also had non-binding commitments of $144.7 million to fund certain private equity partnerships at March 31, 2014, the amount of which may or may not be funded.
We are the sole beneficiary of a special purpose entity which is consolidated in our financial statements.  This entity is a securitized asset trust containing a highly rated bond for principal protection and a private equity partnership investment.  We contributed the bond and several partnership investments into the trust at the time it was established.  The trust supports our investment objectives and allows us to maintain our investment in the remaining partnership while at the same time protecting the principal of the investment.  There are no restrictions on the assets held in this trust, and the trust is free to dispose of the assets at any time.  The fair values of the bond and partnership were $138.1 million and $4.4 million, respectively, as of March 31, 2014.  The bond is reported as a component of fixed maturity securities, and the partnership is reported as a component of other long-term investments in our consolidated balance sheets. At March 31, 2014, we had no commitments to fund the underlying partnership, nor did we fund any amounts to the partnerships during the three months ended March 31, 2014 and 2013.
Mortgage Loans
Our mortgage loan portfolio is well diversified by both geographic region and property type to reduce risk of concentration. All of our mortgage loans are collateralized by commercial real estate. When issuing a new loan, our general policy is not to exceed a loan-to-value ratio, or the ratio of the loan balance to the estimated fair value of the underlying collateral, of 75 percent. We update the loan-to-value ratios at least every three years for each loan, and properties undergo a general inspection at least every two years. Our general policy for newly issued loans is to have a debt service coverage ratio greater than 1.25 times on a normalized 25 year amortization period. We update our debt service coverage ratios annually.
Mortgage loans by property type and geographic region are presented below.
	31-Mar-14						31-Dec-13
	(in millions of dollars)
	Carrying			Percent of			Carrying				Percent of
	Amount			Total			Amount				Total
Property Type
Apartment	$	74.5		4	%		$	61.1			3.3	%
Industrial	538			29.2			567.8				31.3
Office	809.6			43.9			776.5				42.8
Retail	421.2			22.9			409.7				22.6
Total	$	1,843.30		100	%		$	1,815.10			100	%
Region
New England	$	122.5		6.7	%		$	100.9			5.6	%
Mid-Atlantic	186.2			10.1			191.5				10.5
East North Central	227.4			12.3			244.3				13.5
West North Central	172.8			9.4			162.3				8.9
South Atlantic	441.1			23.9			447.7				24.7
East South Central	66.5			3.6			67.7				3.7
West South Central	206.5			11.2			190.9				10.5
Mountain	114.7			6.2			101.9				5.6
Pacific	305.6			16.6			307.9				17
Total	$	1,843.30		100	%		$	1,815.10			100	%
We evaluate each of our mortgage loans individually for impairment and assign an internal credit quality rating based on a comprehensive rating system used to evaluate the credit risk of the loan. The factors we use to derive our internal credit ratings may include the following:
•	Loan-to-value ratio
•	Debt service coverage ratio based on current operating income
•	Property location, including regional economics, trends and demographics
•	Age, condition, and construction quality of property
•	Current and historical occupancy of property
•	Lease terms relative to market
•	Tenant size and financial strength
•	Borrower's financial strength
•	Borrower's equity in transaction
•	Additional collateral, if any
Although all available and applicable factors are considered in our analysis, loan-to-value and debt service coverage ratios are the most critical factors in determining whether we will initially issue the loan and also in assigning values and determining impairment. If we determine that it is probable we will be unable to collect all amounts due under the contractual terms of a
mortgage loan, we establish an allowance for credit loss. If we expect to foreclose on the property, the amount of the allowance typically equals the excess carrying value of the mortgage loan over the fair value of the underlying collateral. If we expect to retain the mortgage loan until payoff, the allowance equals the excess carrying value of the mortgage loan over the expected future cash flows of the loan. We assign an overall rating to each loan using an internal rating scale of Aa (highest quality) to B (lowest quality). We review and adjust, as needed, our internal credit quality ratings on an annual basis. This review process is performed more frequently for mortgage loans deemed to have a higher risk of delinquency.
Mortgage loans, sorted by the applicable credit quality indicators, are as follows:
	March 31 2014			December 31 2013
	(in millions of dollars)
Internal Rating
Aa	$	10.6		$	10.8
A	666.8			683.1
Baa	1,121.30			1,094.60
Ba	13.4			13.5
B	31.2			13.1
Total	$	1,843.30		$	1,815.10
Loan-to-Value Ratio
<=5%	$	815.3		$	777.4
> 65% <=5%	888.4			867.5
> 75% <=5%	95.1			107.6
> 85%	44.5			62.6
Total	$	1,843.30		$	1,815.10
There have been no changes to our accounting policies or methodology from the prior period regarding estimating the allowance for credit losses on our mortgage loans. We hold one mortgage loan which was modified in a troubled debt restructuring during the three months ended March 31, 2014. The loan had a principal balance of $21.1 million prior to the restructuring, wherein the terms of the loan were modified to reduce monthly payments to interest-only at the current note rate and to permit a discounted payoff by the end of 2014. We increased our allowance for credit losses on mortgage loans for this restructuring and recognized an impairment loss of $3.0 million. We had no troubled debt restructurings during the three months ended March 31, 2013.
For mortgage loans on which collection of interest income is uncertain, we discontinue the accrual of interest and recognize it in the period when an interest payment is received. We typically do not resume the accrual of interest on mortgage loans on nonaccrual status until there are significant improvements in the underlying financial condition of the borrower. We consider a loan to be delinquent if full payment is not received in accordance with the contractual terms of the loan. At March 31, 2014 and December 31, 2013, we held no mortgage loans that were greater than 90 days past due regarding principal and/or interest payments.
The activity in the allowance for credit losses is as follows:
	Three Months Ended March 31
	2014			2013
	(in millions of dollars)
Balance at Beginning of Year	$	1.5		$	1.5
Provision	3			—
Balance at End of Period	$	4.5		$	1.5
Impaired mortgage loans are as follows:
	March 31, 2014
	(in millions of dollars)
				Unpaid
	Recorded			Principal				Related
	Investment			Balance				Allowance
With an Allowance Recorded	$	31.2		$	35.7			$	4.5
	December 31, 2013
	(in millions of dollars)
				Unpaid
	Recorded			Principal				Related
	Investment			Balance				Allowance
With an Allowance Recorded	$	13.1		$	14.6			$	1.5
Our average investment in impaired mortgage loans was $19.1 million and $17.4 million for the three months ended March 31, 2014 and 2013, respectively, and we recognized $0.3 million and $0.2 million, respectively, of interest income on those loans.
At March 31, 2014, we had non-binding commitments of $21.7 million to fund certain commercial mortgage loans, the amount of which may or may not be funded.
Transfers of Financial Assets
To manage our cash position more efficiently, we may enter into repurchase agreements with unaffiliated financial institutions. We generally use repurchase agreements as a means to finance the purchase of invested assets or for short-term general business purposes until projected cash flows become available from our operations or existing investments. Our repurchase agreements are typically outstanding for less than 30 days. We post collateral through our repurchase agreement transactions whereby the counterparty commits to purchase securities with the agreement to resell them to us at a later, specified date. The fair value of collateral posted is generally 102 percent of the cash received.
Our investment policy also permits us to lend fixed maturity securities to unaffiliated financial institutions in short-term securities lending agreements. These agreements increase our investment income with minimal risk. Our securities lending policy requires that a minimum of 102 percent of the fair value of the securities loaned be maintained as collateral. Generally, cash is received as collateral under these agreements and is typically reinvested in short-term investments. In the event that securities are received as collateral, we are not permitted to sell or re-post them.
We account for all of our securities lending agreements and repurchase agreements as collateralized financings. As of March 31, 2014, the carrying amount of fixed maturity securities loaned to third parties under our securities lending program was $187.4 million, for which we received collateral in the form of cash and securities of $61.6 million and $132.5 million, respectively. As of December 31, 2013, the carrying amount of fixed maturity securities loaned to third parties under our securities lending program was $201.6 million, for which we received collateral in the form of cash and securities of $76.5 million and $132.9 million, respectively. We had no outstanding repurchase agreements at March 31, 2014 or December 31, 2013.
Offsetting of Financial Instruments
We enter into master netting agreements with each of our derivatives counterparties. These agreements provide for conditional rights of set-off upon the occurrence of an early termination event. An early termination event is considered a default, and it allows the non-defaulting party to offset its contracts in a loss position against any gain positions or payments due to the defaulting party. Under our agreements, default type events are defined as failure to pay or deliver as contractually agreed, misrepresentation, bankruptcy, or merger without assumption. See Note 5 for further discussion of collateral related to our derivative contracts.
We have securities lending agreements with unaffiliated financial institutions that post collateral to us in return for the use of our fixed maturity securities. A right of set-off exists that allows us to keep and apply collateral received in the event of default by the counterparty. Default within a securities lending agreement would typically occur if the counterparty failed to return the securities borrowed from us as contractually agreed. In addition, if we default by not returning collateral received, the counterparty has a right of set-off against our securities or any other amounts due to us.
Shown below are our financial instruments that either meet the accounting requirements that allow them to be offset in our balance sheets or that are subject to an enforceable master netting arrangement or similar agreement. Our accounting policy is to not offset these financial instruments in our balance sheets. Net amounts disclosed below have been reduced by the amount of collateral pledged to or received from our counterparties.
		March 31, 2014
		Gross Amount											Gross Amount Not
		of Recognized			Gross Amount				Net Amount				Offset in Balance Sheet
		Financial			Offset in				Presented in				Financial				Cash			Net
		Instruments			Balance Sheet				Balance Sheet				Instruments				Collateral			Amount
		(in millions of dollars)
Financial Assets:
Derivatives		$	10.9		$	—			$	10.9			$	(7.9	)		$	(2.8	)	$	0.2
Securities Lending		187.4			—				187.4				(125.8		)		(61.6		)	—
Total		$	198.3		$	—			$	198.3			$	(133.7	)		$	(64.4	)	$	0.2
Financial Liabilities:
Derivatives		$	117.7		$	—			$	117.7			$	(84.1	)		$	—		$	33.6
Securities Lending		61.6			—				61.6				(61.6		)		—			—
Total		$	179.3		$	—			$	179.3			$	(145.7	)		$	—		$	33.6
		December 31, 2013
		Gross Amount											Gross Amount Not
		of Recognized			Gross Amount				Net Amount				Offset in Balance Sheet
		Financial			Offset in				Presented in				Financial				Cash			Net
		Instruments			Balance Sheet				Balance Sheet				Instruments				Collateral			Amount
		(in millions of dollars)
Financial Assets:
Derivatives		$	10.8		$	—			$	10.8			$	(9.5	)		$	(1.1	)	$	0.2
Securities Lending		201.6			—				201.6				(125.1		)		(76.5		)	—
Total		$	212.4		$	—			$	212.4			$	(134.6	)		$	(77.6	)	$	0.2
Financial Liabilities:
Derivatives		$	135.6		$	—			$	135.6			$	(98.6	)		$	—		$	37
Securities Lending		76.5			—				76.5				(76.5		)		—			—
Total		$	212.1		$	—			$	212.1			$	(175.1	)		$	—		$	37
Net Investment Income
Net investment income reported in our consolidated statements of income is as follows:
	Three Months Ended March 31
	2014			2013
	(in millions of dollars)
Fixed Maturity Securities	$	581.1		$	589.9
Derivative Financial Instruments	9.9			7.7
Mortgage Loans	28.4			26
Policy Loans	3.9			3.7
Other Long-term Investments	3.8			7.7
Short-term Investments	0.5			0.8
Gross Investment Income	627.6			635.8
Less Investment Expenses	8			7.1
Less Investment Income on Participation Fund Account Assets	3.8			4
Less Amortization of Tax Credit Partnerships	3.3			3.6
Net Investment Income	$	612.5		$	621.1
Realized Investment Gain and Loss
Realized investment gains and losses, which for sales are based upon specific identification of the investments sold, are as follows:
	Three Months Ended March 31
	2014			2013
	(in millions of dollars)
Fixed Maturity Securities
Gross Gains on Sales	$	0.9		$	6.6
Gross Losses on Sales	(5.4		)	(5.5		)
Other-Than-Temporary Impairment Loss	—			(0.8		)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales	7.4			7.6
Gross Losses on Sales	(0.6		)	—
Impairment Loss	(3.0		)	(1.0		)
Embedded Derivative in Modified Coinsurance Arrangement	8.5			6.4
Credit Default Swaps	(0.4		)	(0.3		)
Foreign Currency Transactions	(1.1		)	(2.7		)
Net Realized Investment Gain	$	6.3		$	10.3

Derivative_Financial_Instrumen

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Derivative Financial Instruments	'
	Purpose of Derivatives
	We are exposed to certain risks relating to our ongoing business operations. The primary risks managed by using derivative instruments are interest rate risk, risk related to matching duration for our assets and liabilities, foreign currency risk, and credit risk. Historically, we have utilized current and forward interest rate swaps and options on forward interest rate swaps and U.S. Treasury rates, current and forward currency swaps, forward treasury locks, currency forward contracts, forward contracts on specific fixed income securities, and credit default swaps. Transactions hedging interest rate risk are primarily associated with our individual and group long-term care and individual and group disability products. All other product portfolios are periodically reviewed to determine if hedging strategies would be appropriate for risk management purposes. We do not use derivative financial instruments for speculative purposes.
	Derivatives designated as cash flow hedges and used to reduce our exposure to interest rate and duration risk are as follows:
	•	Interest rate swaps are used to hedge interest rate risks and to improve the matching of assets and liabilities. An interest rate swap is an agreement in which we agree with other parties to exchange, at specified intervals, the difference between fixed rate and variable rate interest amounts. We use interest rate swaps to hedge the anticipated purchase of fixed maturity securities thereby protecting us from the potential adverse impact of declining interest rates on the associated policy reserves. We also use interest rate swaps to hedge the potential adverse impact of rising interest rates in anticipation of issuing fixed rate long-term debt.
	•	Forward treasury locks are used to minimize interest rate risk associated with the anticipated purchase or disposal of fixed maturity securities. A forward treasury lock is a derivative contract without an initial investment where we and the counterparty agree to purchase or sell a specific U.S. Treasury bond at a future date at a pre-determined price.
	•	Options on U.S. Treasury rates are used to hedge the interest rate risk associated with the anticipated purchase of fixed maturity securities. These options give us the right, but not the obligation, to receive a specific interest rate for a specified period of time. These options enable us to lock in a minimum investment yield to hedge the potential adverse impact of declining interest rates.
	Derivatives designated as fair value hedges and used to reduce our exposure to interest rate and duration risk are as follows:
	•	Interest rate swaps are used to effectively convert certain of our fixed rate securities into floating rate securities which are used to fund our floating rate long-term debt. Under these swap agreements, we receive a variable rate of interest and pay a fixed rate of interest. Additionally, we use interest rate swaps to effectively convert certain fixed rate, long-term debt into floating rate long-term debt. Under these swap agreements, we receive a fixed rate of interest and pay a variable rate of interest.
	Derivatives designated as cash flow hedges and used to reduce our exposure to foreign currency risk are as follows:
	•	Foreign currency interest rate swaps have historically been used to hedge the currency risk of certain foreign currency-denominated fixed maturity securities owned for portfolio diversification and to hedge the currency risk associated with certain of the principal and interest payments of the U.S. dollar-denominated debt issued by one of our U.K. subsidiaries. For hedges of fixed maturity securities, we agree to pay, at specified intervals, fixed rate foreign currency-denominated principal and interest payments in exchange for fixed rate payments in the functional currency of the operating segment. For hedges of debt issued, we agree to pay, at specified intervals, fixed rate foreign currency-denominated principal and interest payments to the counterparty in exchange for fixed rate U.S. dollar-denominated principal and interest payments.
	•	Foreign currency forward contracts are used to minimize foreign currency risks. A foreign currency forward is a derivative without an initial investment where we and the counterparty agree to exchange a specific amount of currencies, at a specific exchange rate, on a specific date. We have used these forward contracts to hedge the foreign currency risk associated with certain of the principal repayments of the U.S. dollar-denominated debt issued by one of our U.K. subsidiaries and to hedge the currency risk of certain foreign currency-denominated fixed maturity securities owned for diversification purposes.
	Derivatives not designated as hedging instruments and used to reduce our exposure to credit losses on securities owned are as follows:
	•	Credit default swaps are used as economic hedges against credit risk but do not qualify for hedge accounting. A credit default swap is an agreement in which we agree with another party to pay, at specified intervals, a fixed-rate fee in exchange for insurance against a credit event on a specific investment. If a defined credit event occurs, our counterparty may either pay us a net cash settlement or we may surrender the specific investment to them in exchange for cash equal to the full notional amount of the swap. Credit events typically include events such as bankruptcy, failure to pay, or certain types of debt restructuring.
	Derivative Risks
	The basic types of risks associated with derivatives are market risk (that the value of the derivative will be adversely impacted by changes in the market, primarily the change in interest and exchange rates) and credit risk (that the counterparty will not perform according to the terms of the contract). The market risk of the derivatives should generally offset the market risk associated with the hedged financial instrument or liability. To help limit the credit exposure of the derivatives, we enter into master netting agreements with our counterparties whereby contracts in a gain position can be offset against contracts in a loss position. We also typically enter into bilateral, cross-collateralization agreements with our counterparties to help limit the credit exposure of the derivatives. These agreements require the counterparty in a loss position to submit acceptable collateral with the other counterparty in the event the net loss position meets or exceeds an agreed upon amount. Our current credit exposure on derivatives, which is limited to the value of those contracts in a net gain position, including accrued interest receivable less collateral held, was $0.2 million at March 31, 2014. We held $2.8 million and $1.1 million cash collateral from our counterparties at March 31, 2014 and December 31, 2013, respectively. We post either fixed maturity securities or cash as collateral to our counterparties. The carrying value of fixed maturity securities posted as collateral to our counterparties was $80.4 million and $95.6 million at March 31, 2014 and December 31, 2013, respectively. We had no cash posted as collateral to our counterparties at March 31, 2014 and December 31, 2013. See Note 4 for further discussion of our master netting agreements.
	The majority of our derivative instruments contain provisions that require us to maintain specified issuer credit ratings and financial strength ratings. Should our ratings fall below these specified levels, we would be in violation of the provisions, and our derivatives counterparties could terminate our contracts and request immediate payment. The aggregate fair value of all derivative instruments with credit risk-related contingent features that were in a liability position was $117.7 million and $135.6 million at March 31, 2014 and December 31, 2013, respectively.
	Derivative Transactions
	The table below summarizes, by notional amounts, the activity for each category of derivatives. The notional amounts represent the basis upon which our counterparty pay and receive amounts are calculated.
		Swaps
		Receive				Receive				Receive		Credit Default		Forwards		Total
		Variable/Pay				Fixed/Pay				Fixed/Pay
		Fixed				Fixed				Variable
		(in millions of dollars)
	Balance at December 31, 2012	$	174			$	508.8			$	750	$	—	$	—	$	1,432.80
	Additions	—				—				—		70		24		94
	Terminations	—				18				40		—		24		82
	Balance at March 31, 2013	174				490.8				710		70		—		1,444.80
	Balance at December 31, 2013	150				630.4				600		97		—		1,477.40
	Additions	—				—				—		—		10		10
	Terminations	—				7.9				—		—		10		17.9
	Balance at March 31, 2014	$	150			$	622.5			$	600	$	97	$	—	$	1,469.50
	Cash Flow Hedges
	As of March 31, 2014 and December 31, 2013, we had $622.5 million and $630.4 million, respectively, notional amount of receive fixed, pay fixed, open current and forward foreign currency swaps to hedge fixed income foreign currency-denominated securities and U.S. dollar-denominated debt issued by one of our U.K. subsidiaries.
	For the three months ended March 31, 2014 and 2013, there was no material ineffectiveness related to our cash flow hedges, and no component of the derivative instruments' gain or loss was excluded from the assessment of hedge effectiveness.
	As of March 31, 2014, we expect to amortize approximately $47.3 million of net deferred gains on derivative instruments during the next twelve months. This amount will be reclassified from accumulated other comprehensive income into earnings and reported on the same income statement line item as the hedged item. The income statement line items that will be affected by this amortization are net investment income and interest and debt expense. Amounts that will be reclassified from accumulated other comprehensive income into earnings to offset the earnings impact of foreign currency translation of hedged items are not estimable.
	Subsequent to March 31, 2014, we gave notice of our election to redeem on May 15, 2014 a portion of the outstanding principal of the U.S. dollar-denominated debt issued by one of our U.K. subsidiaries. In conjunction with this redemption, we will reclassify approximately $13 million of the deferred gain on cash flow hedges from accumulated other comprehensive income to realized investment gain in our consolidated statements of income. This amount represents the applicable portion of the deferred gain from previously terminated derivatives associated with the hedge of this debt. See Note 11 for further information.
	As of March 31, 2014, we are hedging the variability of future cash flows associated with forecasted transactions through the year 2038.
	Fair Value Hedges
	As of March 31, 2014 and December 31, 2013, we had $150.0 million notional amount of receive variable, pay fixed interest rate swaps to hedge the changes in fair value of certain fixed rate securities held. These swaps effectively convert the associated fixed rate securities into floating rate securities, which are used to fund our floating rate long-term debt. The change in fair value of the hedged fixed maturity securities attributable to the hedged benchmark interest rate resulted in a loss of $1.4 million and $2.4 million for the three months ended March 31, 2014 and 2013, respectively, with an offsetting gain on the related interest rate swaps.
	As of March 31, 2014 and December 31, 2013, we had $600.0 million notional amount of receive fixed, pay variable interest rate swaps to hedge the changes in the fair value of certain fixed rate long-term debt. These swaps effectively convert the associated fixed rate long-term debt into floating rate debt and provide for a better matching of interest rates with our short-term investments, which have frequent interest rate resets similar to a floating rate security. The change in fair value of the hedged debt attributable to the hedged benchmark interest rate resulted in a gain (loss) of $(1.6) million and $4.1 million for the three months ended March 31, 2014 and 2013, respectively, with an offsetting gain or loss on the related interest rate swaps.
	For the three months ended March 31, 2014, and 2013, there was no material ineffectiveness related to our fair value hedges, and no component of the derivative instruments' gain or loss was excluded from the assessment of hedge effectiveness. There were no instances wherein we discontinued fair value hedge accounting due to a hedged firm commitment no longer qualifying as a fair value hedge.
	Derivatives not Designated as Hedging Instruments
	As of March 31, 2014 and December 31, 2013, we held $97.0 million notional amount of single name credit default swaps. We entered into these swaps in order to mitigate the credit risk associated with specific securities owned.
	We have an embedded derivative in a modified coinsurance arrangement for which we include in our realized investment gains and losses a calculation intended to estimate the value of the option of our reinsurance counterparty to cancel the reinsurance contract with us. However, neither party can unilaterally terminate the reinsurance agreement except in extreme circumstances resulting from regulatory supervision, delinquency proceedings, or other direct regulatory action. Cash settlements or collateral related to this embedded derivative are not required at any time during the reinsurance contract or at termination of the reinsurance contract. There are no credit-related counterparty triggers, and any accumulated embedded derivative gain or loss reduces to zero over time as the reinsured business winds down.
	Locations and Amounts of Derivative Financial Instruments
	The following tables summarize the location and fair values of derivative financial instruments, as reported in our consolidated balance sheets.
		March 31, 2014
		Asset Derivatives						Liability Derivatives
		Balance Sheet		Fair				Balance Sheet		Fair
		Location		Value				Location		Value
		(in millions of dollars)
	Designated as Hedging Instruments
	Interest Rate Swaps	Other L-T Investments		$	8.1			Other Liabilities		$	30.9
	Foreign Exchange Contracts	Other L-T Investments		2.8				Other Liabilities		84.8
	Total			$	10.9					$	115.7
	Not Designated as Hedging Instruments
	Credit Default Swaps							Other Liabilities		$	2
	Embedded Derivative in Modified Coinsurance Arrangement							Other Liabilities		44.7
	Total									$	46.7
		December 31, 2013
		Asset Derivatives						Liability Derivatives
		Balance Sheet		Fair				Balance Sheet		Fair
		Location		Value				Location		Value
	(in millions of dollars)
Designated as Hedging Instruments
Interest Rate Swaps	Other L-T Investments		$	9.2			Other Liabilities		$	35
Foreign Exchange Contracts	Other L-T Investments		1.6				Other Liabilities		98.7
Total			$	10.8					$	133.7
Not Designated as Hedging Instruments
Credit Default Swaps							Other Liabilities		$	1.9
Embedded Derivative in Modified Coinsurance Arrangement							Other Liabilities		53.2
Total									$	55.1
The following table summarizes the location of gains and losses on the effective portion of derivative financial instruments designated as cash flow hedging instruments, as reported in our consolidated statements of income and consolidated statements of comprehensive income.
		Three Months Ended March 31
		2014				2013
		(in millions of dollars)
Gain (Loss) Recognized in Other Comprehensive Income (Loss) on Derivatives
Interest Rate Swaps and Forwards		$	—			$	(2.2	)
Foreign Exchange Contracts		12.9				4.1
	Total	$	12.9			$	1.9
Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income
Net Investment Income
	Interest Rate Swaps and Forwards	$	11.7			$	10
	Foreign Exchange Contracts	(1.1		)		(1.7		)
Net Realized Investment Gain (Loss)
	Interest Rate Swaps	2.5				—
	Foreign Exchange Contracts	(2.1		)		(6.7		)
Interest and Debt Expense
	Interest Rate Swaps	(0.4		)		(0.4		)
	Total	$	10.6			$	1.2
The following table summarizes the location of gains and losses on our derivatives not designated as hedging instruments, as reported in our consolidated statements of income.
		Three Months Ended March 31
		2014				2013
		(in millions of dollars)
Net Realized Investment Gain (Loss)
	Credit Default Swaps	$	(0.4	)		$	(0.3	)
	Embedded Derivative in Modified Coinsurance Arrangement	8.5				6.4
	Total	$	8.1			$	6.1

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income	3 Months Ended
	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Comprehensive Income (Loss) Disclosure	'
	Components of our accumulated other comprehensive income, after tax, and related changes are as follows:
				Net Unrealized Gain on Securities				Net Gain on Cash Flow Hedges				Foreign Currency Translation Adjustment			Unrecognized Pension and Postretirement Benefit Costs			Total
				(in millions of dollars)
	Balance at December 31, 2013			$	135.7			$	396.3			$	(47.1	)	$	(229.9	)	$	255
		Other Comprehensive Income (Loss) Before Reclassifications		187.2				8.5				7.6			(0.2		)	203.1
		Amounts Reclassified from Accumulated Other Comprehensive Income or Loss		2.4				(6.8		)		—			0.7			(3.7		)
		Net Other Comprehensive Income		189.6				1.7				7.6			0.5			199.4
	Balance at March 31, 2014			$	325.3			$	398			$	(39.5	)	$	(229.4	)	$	454.4
	Balance at December 31, 2012			$	873.5			$	401.6			$	(72.6	)	$	(574.5	)	$	628
		Other Comprehensive Income (Loss) Before Reclassifications		(73.3		)		(1.2		)		(69.9		)	1.7			(142.7		)
		Amounts Reclassified from Accumulated Other Comprehensive Income or Loss		(7.8		)		(0.8		)		—			9			0.4
		Net Other Comprehensive Income (Loss)		(81.1		)		(2.0		)		(69.9		)	10.7			(142.3		)
	Balance at March 31, 2013			$	792.4			$	399.6			$	(142.5	)	$	(563.8	)	$	485.7
	The net unrealized gain on securities consists of the following components:
			31-Mar				31-Dec
			2014				2013				Change
			(in millions of dollars)
	Fixed Maturity Securities		$	5,150.80			$	4,054.80			$	1,096.00
	Other Investments		40.6				55.5				(14.9		)
	Deferred Acquisition Costs		(48.9		)		(41.6		)		(7.3		)
	Reserves for Future Policy and Contract Benefits		(4,939.7		)		(4,108.5		)		(831.2		)
	Reinsurance Recoverable		309.9				263.8				46.1
	Deferred Income Tax		(187.4		)		(88.3		)		(99.1		)
	Total		$	325.3			$	135.7			$	189.6
			31-Mar				31-Dec
			2013				2012				Change
			(in millions of dollars)
	Fixed Maturity Securities		$	6,803.90			$	7,221.50			$	(417.6	)
	Other Investments		72.5				92.8				(20.3		)
	Deferred Acquisition Costs		(61.2		)		(67.0		)		5.8
	Reserves for Future Policy and Contract Benefits		(5,979.7		)		(6,277.5		)		297.8
	Reinsurance Recoverable		353.9				351.5				2.4
	Deferred Income Tax		(397.0		)		(447.8		)		50.8
	Total		$	792.4			$	873.5			$	(81.1	)
	Amounts reclassified from accumulated other comprehensive income or loss were recognized in our consolidated statements of income as follows:
				Three Months Ended March 31
				2014				2013
				(in millions of dollars)
	Net Unrealized Gain on Securities
		Net Realized Investment Gain (Loss)
			Gain (Loss) on Sales of Securities and Other Invested Assets	$	(3.7	)		$	12.7
			Other-Than-Temporary Impairment Loss	—				(0.8		)
				(3.7		)		11.9
		Income Tax Expense (Benefit)		(1.3		)		4.1
		Total		$	(2.4	)		$	7.8
	Net Gain on Cash Flow Hedges
		Net Investment Income
			Gain on Interest Rate Swaps and Forwards	$	11.7			$	10
			Loss on Foreign Exchange Contracts	(1.1		)		(1.7		)
		Net Realized Investment Gain (Loss)
			Gain on Interest Rate Swaps	2.5				—
			Loss on Foreign Exchange Contracts	(2.1		)		(6.7		)
		Interest and Debt Expense
			Loss on Interest Rate Swaps	(0.4		)		(0.4		)
				10.6				1.2
		Income Tax Expense		3.8				0.4
		Total		$	6.8			$	0.8
	Unrecognized Pension and Postretirement Benefit Costs
		Other Expenses
			Amortization of Net Actuarial Loss	$	(1.4	)		$	(14.9	)
			Amortization of Prior Service Credit	0.4				1.2
				(1.0		)		(13.7		)
		Income Tax Benefit		(0.3		)		(4.7		)
	Total		$	(0.7	)		$	(9.0	)

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Segment Information	'
	We have three principal operating business segments: Unum US, Unum UK, and Colonial Life. Our other segments are the Closed Block and the Corporate segments.
	Premium income by major line of business within each of our segments is presented as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Unum US
	Group Disability
	Group Long-term Disability	$	383.5		$	392.7
	Group Short-term Disability	137.3			131
	Group Life and Accidental Death & Dismemberment
	Group Life	309.9			302.2
	Accidental Death & Dismemberment	30.6			30.9
	Supplemental and Voluntary
	Individual Disability - Recently Issued	115.9			120.1
	Voluntary Benefits	175.3			162.8
		1,152.50			1,139.70
	Unum UK
	Group Long-term Disability	103			97.9
	Group Life	34.8			31
	Supplemental	13.9			14.9
		151.7			143.8
	Colonial Life
	Accident, Sickness, and Disability	189.1			184.8
	Life	57.4			54.8
	Cancer and Critical Illness	69.9			67.5
		316.4			307.1
	Closed Block
	Individual Disability	161.1			181.8
	Long-term Care	156.5			158.8
	All Other	0.3			(0.3		)
		317.9			340.3
	Total	$	1,938.50		$	1,930.90
	Selected operating statement data by segment is presented as follows:
		Unum US			Unum UK			Colonial Life			Closed Block		Corporate			Total
		(in millions of dollars)
	Three Months Ended March 31, 2014
	Premium Income	$	1,152.50		$	151.7		$	316.4		$	317.9	$	—		$	1,938.50
	Net Investment Income	226.4			33.6			36.9			316.3		(0.7		)	612.5
	Other Income	30.9			(0.1		)	(0.1		)	21.6		1.5			53.8
	Operating Revenue	$	1,409.80		$	185.2		$	353.2		$	655.8	$	0.8		$	2,604.80
	Operating Income (Loss)	$	210.8		$	36.5		$	79.4		$	29.1	$	(34.2	)	$	321.6
	Three Months Ended March 31, 2013
	Premium Income	$	1,139.70		$	143.8		$	307.1		$	340.3	$	—		$	1,930.90
	Net Investment Income	235.7			30.8			39.7			313.1		1.8			621.1
	Other Income	36.7			0.1			—			24.1		1.6			62.5
	Operating Revenue	$	1,412.10		$	174.7		$	346.8		$	677.5	$	3.4		$	2,614.50
	Operating Income (Loss)	$	208.1		$	31.3		$	75.4		$	27.3	$	(33.7	)	$	308.4
	A reconciliation of "operating revenue" to total revenue and "operating income" to income before income tax is as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Operating Revenue	$	2,604.80		$	2,614.50
	Net Realized Investment Gain	6.3			10.3
	Total Revenue	$	2,611.10		$	2,624.80
	Operating Income	$	321.6		$	308.4
	Net Realized Investment Gain	6.3			10.3
	Non-operating Retirement-related Loss	(1.4		)	(14.9		)
	Income Before Income Tax	$	326.5		$	303.8
	Assets by segment are as follows:
		31-Mar			31-Dec
		2014			2013
		(in millions of dollars)
	Unum US	$	18,517.90		$	18,384.30
Unum UK	3,793.40			3,654.10
Colonial Life	3,542.50			3,482.90
Closed Block	32,397.30			31,564.20
Corporate	2,827.50			2,318.10
Total	$	61,078.60		$	59,403.60

Employee_Benefit_Plans

Employee Benefit Plans	3 Months Ended
	Mar. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Pension and Other Postretirement Benefits Disclosure	'
	Defined Benefit Pension and Other Postretirement Benefit Plans
	We sponsor several defined benefit pension and other postretirement benefit (OPEB) plans for our employees, including non-qualified pension plans. We maintain a separate defined benefit plan for eligible employees in our U.K. operation (the U.K. plan). The U.S. defined benefit pension plans were closed to new entrants and amended to freeze participation and benefit accruals for existing participants effective December 31, 2013. The U.K. plan was closed to new entrants effective December 31, 2002 and was amended to freeze participation for existing participants effective June 30, 2014.
	The following table provides the components of the net periodic benefit cost for the defined benefit pension and OPEB plans.
		Three Months Ended March 31
		Pension Benefits
		U.S. Plans						Non U.S. Plans						OPEB
		2014			2013			2014			2013			2014			2013
		(in millions of dollars)
	Service Cost	$	0.9		$	14.9		$	1.1		$	1.1		$	0.1		$	0.2
	Interest Cost	22.5			21.9			2.3			2.1			2			2
	Expected Return on Plan Assets	(29.5		)	(25.5		)	(3.4		)	(3.0		)	(0.2		)	(0.2		)
	Amortization of:
	Net Actuarial Loss	1.3			14.6			0.1			0.3			—			—
	Prior Service Credit	—			—			—			—			(0.4		)	(1.2		)
	Total	$	(4.8	)	$	25.9		$	0.1		$	0.5		$	1.5		$	0.8

Stockholders_Equity_and_Earnin

Stockholders' Equity and Earnings Per Common Share	3 Months Ended
	Mar. 31, 2014
Stockholders' Equity Note [Abstract]	'
Stockholders Equity and Earnings Per Common Share	'
	Earnings Per Common Share
	Net income per common share is determined as follows:
		Three Months Ended March 31
		2014		2013
		(in millions of dollars, except share data)
	Numerator
	Net Income	$	228.9	$	212.6
	Denominator (000s)
	Weighted Average Common Shares - Basic	259,408.50		269,361.10
	Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,301.40		993.3
	Weighted Average Common Shares - Assuming Dilution	260,709.90		270,354.40
	Net Income Per Common Share
	Basic	$	0.88	$	0.79
	Assuming Dilution	$	0.88	$	0.79
	We use the treasury stock method to account for the effect of outstanding stock options, nonvested restricted stock units, and nonvested performance share units on the computation of diluted earnings per share. Under this method, these potential common shares will each have a dilutive effect, as individually measured, when the average market price of Unum Group common stock during the period exceeds the exercise price of the stock options and the grant price of the nonvested restricted stock units and the nonvested performance share units. The outstanding stock options have exercise prices ranging from $11.37 to $26.29, the nonvested restricted stock units have grant prices ranging from $19.38 to $34.73, and the nonvested performance share units have grant prices ranging from $23.97 to $33.86.
	In computing earnings per share assuming dilution, only potential common shares that are dilutive (those that reduce earnings per share) are included. For the three month periods ended March 31, 2014 and 2013 , a de minimis amount and approximately 0.4 million potential common shares, respectively, were excluded in the computation of diluted earnings per share because the impact would be antidilutive, based on then current market prices.
	Common Stock
	Our board of directors has authorized the repurchase of Unum Group's common stock under the following repurchase programs:
		Share Repurchase Program Authorized During
		Dec-13		Jul-12
		(in millions of dollars)
	Authorized Repurchase Amount	$	750	$	750
	Remaining Repurchase Amount at March 31, 2014	$	629.9	$	—
	The December 2013 share repurchase program has an expiration date of June 12, 2015.
	Common stock repurchases, which are classified as treasury stock and accounted for using the cost method, were as follows:
		Three Months Ended March 31
		2014		2013
		(in millions)
	Shares Repurchased	2.9		3.7
	Cost of Shares Repurchased	$	100.1	$	95.1
	Preferred Stock
	Unum Group has 25,000,000 shares of preferred stock authorized with a par value of $0.10 per share. No preferred stock has been issued to date.

Commitments_and_Contingent_Lia

Commitments and Contingent Liabilities	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Commitments and Contingent Liabilities	'
	Commitments and Contingent Liabilities
	Contingent Liabilities
	We are a defendant in a number of litigation matters. In some of these matters, no specified amount is sought. In others, very large or indeterminate amounts, including punitive and treble damages, are asserted. There is a wide variation of pleading practice permitted in the United States courts with respect to requests for monetary damages, including some courts in which no specified amount is required and others which allow the plaintiff to state only that the amount sought is sufficient to invoke the jurisdiction of that court. Further, some jurisdictions permit plaintiffs to allege damages well in excess of reasonably possible verdicts. Based on our extensive experience and that of others in the industry with respect to litigating or resolving claims through settlement over an extended period of time, we believe that the monetary damages asserted in a lawsuit or claim bear little relation to the merits of the case, or the likely disposition value. Therefore, the specific monetary relief sought is not stated.
	Unless indicated otherwise in the descriptions below, reserves have not been established for litigation and contingencies. An estimated loss is accrued when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated.
	Claims Handling Matters
	We and our insurance subsidiaries, in the ordinary course of our business, are engaged in claim litigation where disputes arise as a result of a denial or termination of benefits. Most typically these lawsuits are filed on behalf of a single claimant or policyholder, and in some of these individual actions punitive damages are sought, such as claims alleging bad faith in the handling of insurance claims. For our general claim litigation, we maintain reserves based on experience to satisfy judgments and settlements in the normal course. We expect that the ultimate liability, if any, with respect to general claim litigation, after consideration of the reserves maintained, will not be material to our consolidated financial condition. Nevertheless, given the inherent unpredictability of litigation, it is possible that an adverse outcome in certain claim litigation involving punitive damages could, from time to time, have a material adverse effect on our consolidated results of operations in a period, depending on the results of operations for the particular period.
	From time to time class action allegations are pursued where the claimant or policyholder purports to represent a larger number of individuals who are similarly situated. Since each insurance claim is evaluated based on its own merits, there is rarely a single act or series of actions which can properly be addressed by a class action. Nevertheless, we monitor these cases closely and defend ourselves appropriately where these allegations are made.
	Miscellaneous Matters
	In October 2010, Denise Merrimon, Bobby S. Mowery, and all others similarly situated vs. Unum Life Insurance Company of America, was filed in the United States District Court for the District of Maine. This class action alleges that we breached fiduciary duties owed to certain beneficiaries under certain group life insurance policies when we paid life insurance proceeds by establishing interest-bearing retained asset accounts rather than by mailing checks. Plaintiffs seek to represent a class of beneficiaries under group life insurance contracts that were part of the ERISA employee welfare benefit plans and under which we paid death benefits via retained asset accounts. The plaintiffs' principal theories in the case are: (1) funds held in retained asset accounts were plan assets, and the proceeds earned by us from investing those funds belonged to the beneficiaries, and (2) payment of claims using retained asset accounts did not constitute payment under Maine's late payment statute, requiring us to pay interest on the undrawn retained asset account funds at an annual rate of 18 percent. In February 2012, the District Court issued an opinion rejecting both of plaintiffs' principal theories and ordering judgment for us. At the same time, however, the District Court held that we breached a fiduciary duty to the beneficiaries by failing to pay rates comparable to the best rates available in the market for demand deposits. The District Court also certified a class of people who, during a certain period of time, were beneficiaries under certain group life insurance contracts that were part of ERISA employee welfare benefit plans and were paid death benefits using retained asset accounts. A bench trial was held on the issue of damages in June and July of 2013. In September 2013, the District Court awarded damages based on a benchmark it created by averaging the interest rates paid on money market mutual funds and money market checking accounts. Based on these averages, the District Court found that for certain periods of the class we should have paid additional interest and awarded damages of $12.1 million and prejudgment interest of $1.3 million. Subsequent to this judgment, in September 2013 we filed an appeal to the First Circuit Court of Appeals, and plaintiffs filed a cross appeal. Based on contrary law that has developed recently in similar cases, we believe that we have strong legal arguments to raise on appeal. We have not accrued a loss for the judgment because we have determined that we do not have a probable loss under the applicable accounting standard relating to the accrual of loss contingencies. We cannot predict the timing of a decision or assure the ultimate outcome of our appeal.
	Beginning in 2011, a number of state regulators began requiring insurers to cross-check specified insurance policies with the Social Security Administration’s Death Master File to identify potential matches. If a potential match was identified, insurers were requested to determine if benefits were due, locate beneficiaries, and make payments where appropriate. We initiated this process where requested, and in 2012 we began implementing this process in all states on a forward-looking basis. In addition to implementing this on a forward-looking basis, in 2013 we began an initiative to search for potential claims from previous years. During 2013, we completed our assessment of benefits which we estimate will be paid under this initiative, and as such, established additional reserves for payment of these benefits. Similar to other insurers, we are undergoing an examination by a third party acting on behalf of a number of state treasurers concerning our compliance with the unclaimed property laws of the participating states. We are cooperating fully with this examination, as well as with a Delaware Market Conduct examination and a Voluntary Disclosure Agreement process with the state of Minnesota. The legal and regulatory environment around unclaimed death benefits continues to evolve. It is possible that the current examination and/or similar investigations by other state jurisdictions may result in additional payments to beneficiaries, the payment of abandoned funds under state law, and/or administrative penalties, the total of which may be in excess of the reserves established.
	In December 2012, State of West Virginia ex rel. John D. Perdue v. Provident Life and Accident Insurance Company and State of West Virginia ex rel. John D. Perdue v. Colonial Life & Accident Insurance Company were filed in the Circuit Court of Putnam County, West Virginia. These two separate complaints alleged violations of the West Virginia Uniform Unclaimed Property Act by failing to identify and report all unclaimed insurance policy proceeds due to be escheated to West Virginia.  The complaints sought to examine company records and assess penalties and costs in an undetermined amount. In December 2013, the court dismissed both complaints, holding that the West Virginia Uniform Unclaimed Property Act does not require insurance companies to periodically search the Social Security Administrations' Death Master File or escheat unclaimed life insurance benefits until a claim has been submitted. In January 2014, the plaintiff appealed the dismissal of both complaints.
	In May 2013, a purported class action complaint entitled Ruben Don v. Unum Life Insurance Company of America, Wedner Insurance Group, Inc. dba The Morton Wedner Insurance Agency, and Does 1-30, was filed in the Superior Court of California, County of Los Angeles.  The plaintiff seeks to represent a class of California insureds who were issued long-term care policies containing an inflation protection feature.  The plaintiff alleges we incorrectly administer the inflation protection feature, resulting in an underpayment of benefits.  The complaint makes allegations against us for breach of contract, bad faith, fraud, violation of Business and Professions Code 17200, and injunctive relief. In June 2013, we removed the case to the United States District Court for the Central District of California.  In March 2014, we filed a motion to dismiss the case. Rather than oppose the motion, plaintiff filed an amended purported class action complaint in April 2014 entitled Ruben Don v. Unum Group and Unum Life Insurance Company of America in the United States District Court for the Central District of California. The plaintiff seeks to represent a nationwide class and a California class of insureds who were issued long-term care policies containing an inflation protection feature. Similar to the original complaint, the plaintiff alleges we incorrectly administer the inflation protection feature, resulting in an underpayment of benefits. The complaint makes allegations of breach of contract, bad faith, fraud, violation of Business and Professions Code 17200, and declaratory and injunctive relief. We are in the process of preparing our response to this complaint.
	Summary
	Various lawsuits against us, in addition to those discussed above, have arisen in the normal course of business. Further, state insurance regulatory authorities and other federal and state authorities regularly make inquiries and conduct investigations concerning our compliance with applicable insurance and other laws and regulations.
	Given the complexity and scope of our litigation and regulatory matters, it is not possible to predict the ultimate outcome of all pending investigations or legal proceedings or provide reasonable estimates of potential losses, except if noted in connection with specific matters. It is possible that our results of operations or cash flows in a particular period could be materially affected by an ultimate unfavorable outcome of pending litigation or regulatory matters depending, in part, on our results of operations or cash flows for the particular period. We believe, however, that the ultimate outcome of all pending litigation and regulatory matters, after consideration of applicable reserves and rights to indemnification, should not have a material adverse effect on our financial position.

Debt

Debt	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Debt Disclosure	'
	At March 31, 2014, short-term debt consisted entirely of securities lending agreements.
	We had no amount outstanding on our revolving credit facility at March 31, 2014.
	In March 2014, we issued $350.0 million of unsecured 10-year senior notes in a public offering. The notes have an annual coupon rate of 4.00%.
	During the three months ended March 31, 2014, we made principal payments of $15.0 million on our senior secured non-recourse notes issued by Northwind Holdings, LLC.
	In January 2013, we purchased and retired the outstanding principal of $62.5 million on our senior secured non-recourse notes issued by Tailwind Holdings, LLC, resulting in a before-tax gain of $4.0 million.
	Subsequent to March 31, 2014, we gave notice of our election to redeem on May 15, 2014 a portion of the outstanding principal of the U.S. dollar-denominated debt issued by one of our U.K. subsidiaries. An aggregate principal amount of $145.0 million of the 6.85% debt will be redeemed at a redemption price equal to the greater of the principal amount of the debt redeemed or the make-whole amount, plus in each case any accrued and unpaid interest on the principal amount redeemed. In conjunction with this redemption, we will reclassify the applicable portion of the deferred gain on cash flow hedges from accumulated other comprehensive income to earnings. We expect the redemption to have an immaterial impact on our second quarter of 2014 net income.

Basis_of_Presentation_Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2014
Accounting Policies [Abstract]	'
Basis of Accounting, Policy	'
	The accompanying consolidated financial statements of Unum Group and its subsidiaries (the Company) have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. For further information, refer to the consolidated financial statements and footnotes included in our annual report on Form 10-K for the year ended December 31, 2013.

Accounting_Developments_Polici

Accounting Developments (Policies)	3 Months Ended
	Mar. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
New Accounting Pronouncements Policy	'
	Accounting Updates Outstanding:
	ASC 323 "Investments - Equity Method and Joint Ventures"
	In January 2014, the FASB issued an update to provide guidance on the accounting and reporting for investments in affordable housing projects that qualify for low-income housing tax credits. The amendments in the update permit entities to make an accounting policy election to account for their investments in qualified affordable housing projects using the proportional amortization method if certain conditions are met. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the net investment performance in the income statement as a component of income tax expense (benefit). Additional disclosures concerning investments in qualified affordable housing projects will also be required by the update. The amendments in the update are effective for interim and annual periods beginning on or after December 15, 2014, with early adoption permitted, and are to be applied retrospectively. We have not yet finalized the expected impact on our financial position or results of operations. We expect to adopt this update effective January 1, 2015.

Fair_Values_of_Financial_Instr1

Fair Values of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Carrying Amount and Fair Value of Financial Instruments	'
	Presented as follows are the carrying amounts and fair values of financial instruments. The carrying values of financial instruments such as short-term investments, cash and bank deposits, accounts and premiums receivable, accrued investment income, and short-term debt approximate fair value due to the short-term nature of the instruments. As such, these financial instruments are not included in the following chart.
		31-Mar-14						31-Dec-13
		Carrying			Fair			Carrying			Fair
		Amount			Value			Amount			Value
		(in millions of dollars)
	Assets
	Fixed Maturity Securities	$	43,666.80		$	43,666.80		$	42,344.40		$	42,344.40
	Mortgage Loans	1,843.30			2,009.80			1,815.10			1,980.20
	Policy Loans	3,268.30			3,336.30			3,276.00			3,339.60
	Other Long-term Investments
	Derivatives	10.9			10.9			10.8			10.8
	Equity Securities	15.1			15.1			16.4			16.4
	Miscellaneous Long-term Investments	477.4			477.4			475.2			475.2
	Liabilities
	Policyholders' Funds
	Deferred Annuity Products	$	629.7		$	629.7		$	631.5		$	631.5
	Supplementary Contracts without Life Contingencies	585.7			585.7			563.1			563.1
	Long-term Debt	2,948.20			3,194.50			2,612.00			2,824.40
	Other Liabilities
	Derivatives	117.7			117.7			135.6			135.6
	Embedded Derivative in Modified Coinsurance Arrangement	44.7			44.7			53.2			53.2
	Unfunded Commitments to Investment Partnerships	17.9			17.9			27.2			27.2
Fair Values by Fair Value Heirarchy Input Level	'
	Fair value measurements by input level for financial instruments carried at fair value are as follows:
		March 31, 2014
		Quoted Prices			Significant Other			Significant			Total
		in Active Markets			Observable			Unobservable
		for Identical Assets			Inputs			Inputs
		or Liabilities			(Level 2)			(Level 3)
		(Level 1)
		(in millions of dollars)
	Assets
	Fixed Maturity Securities
	United States Government and Government Agencies and Authorities	$	189.2		$	967.5		$	—		$	1,156.70
	States, Municipalities, and Political Subdivisions	—			1,770.70			156.1			1,926.80
	Foreign Governments	—			1,290.60			80.4			1,371.00
	Public Utilities	709.4			9,783.70			310			10,803.10
	Mortgage/Asset-Backed Securities	—			2,286.30			0.4			2,286.70
	All Other Corporate Bonds	3,912.30			20,698.20			1,473.60			26,084.10
	Redeemable Preferred Stocks	—			14			24.4			38.4
	Total Fixed Maturity Securities	4,810.90			36,811.00			2,044.90			43,666.80
	Other Long-term Investments
	Derivatives
	Interest Rate Swaps	—			8.1			—			8.1
	Foreign Exchange Contracts	—			2.8			—			2.8
	Total Derivatives	—			10.9			—			10.9
	Equity Securities	—			12			3.1			15.1
	Liabilities
	Other Liabilities
	Derivatives
	Interest Rate Swaps	$	—		$	30.9		$	—		$	30.9
	Foreign Exchange Contracts	—			84.8			—			84.8
	Credit Default Swaps	—			2			—			2
	Embedded Derivative in Modified Coinsurance Arrangement	—			—			44.7			44.7
	Total Derivatives	—			117.7			44.7			162.4
		December 31, 2013
		Quoted Prices			Significant Other			Significant			Total
		in Active Markets			Observable			Unobservable
		for Identical Assets			Inputs			Inputs
		or Liabilities			(Level 2)			(Level 3)
		(Level 1)
		(in millions of dollars)
	Assets
	Fixed Maturity Securities
	United States Government and Government Agencies and Authorities	$	144.5		$	1,051.60		$	—		$	1,196.10
	States, Municipalities, and Political Subdivisions	—			1,608.10			175.1			1,783.20
	Foreign Governments	—			1,294.70			78.5			1,373.20
	Public Utilities	396.8			9,802.70			203.5			10,403.00
	Mortgage/Asset-Backed Securities	—			2,038.80			0.5			2,039.30
	All Other Corporate Bonds	1,982.00			21,670.80			1,859.10			25,511.90
	Redeemable Preferred Stocks	—			13.9			23.8			37.7
	Total Fixed Maturity Securities	2,523.30			37,480.60			2,340.50			42,344.40
	Other Long-term Investments
	Derivatives
	Interest Rate Swaps	—			9.2			—			9.2
	Foreign Exchange Contracts	—			1.6			—			1.6
	Total Derivatives	—			10.8			—			10.8
	Equity Securities	—			11.8			4.6			16.4
	Liabilities
	Other Liabilities
	Derivatives
	Interest Rate Swaps	$	—		$	35		$	—		$	35
	Foreign Exchange Contracts	—			98.7			—			98.7
	Credit Default Swaps	—			1.9			—			1.9
	Embedded Derivative in Modified Coinsurance Arrangement	—			—			53.2			53.2
	Total Derivatives	—			135.6			53.2			188.8
Transfers of Assets between Level 1 and Level 2	'
	Transfers of assets between Level 1 and Level 2 are as follows:
		Three Months Ended March 31
		2014						2013
		Transfers into
		Level 1 from			Level 2 from			Level 1 from			Level 2 from
		Level 2			Level 1			Level 2			Level 1
		(in millions of dollars)
	Fixed Maturity Securities
	United States Government and Government Agencies and Authorities	$	163.2		$	121.5		$	256.9		$	—
	States, Municipalities, and Political Subdivisions	—			—			—			19.4
	Public Utilities	452.1			192.8			502.1			53.5
	All Other Corporate Bonds	2,391.50			652.8			2,266.30			1,140.80
	Total Fixed Maturity Securities	$	3,006.80		$	967.1		$	3,025.30		$	1,213.70
	Transfers between Level 1 and Level 2 occurred due to the change in availability of either a TRACE or broker market maker price. Depending on current market conditions, the availability of these Level 1 prices can vary from period to period. For fair value measurements of financial instruments that were transferred either into or out of Level 1 or 2, we reflect the transfers using the fair value at the beginning of the period.
Changes in Assets and Liabilities Measured at Fair Value using Significant Unobservable Inputs	'
	Changes in assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) are as follows:
		Three Months Ended March 31, 2014
					Total Realized and
					Unrealized Investment
					Gains (Losses) Included in
		Beginning			Earnings			Other			Purchases		Sales			Level 3 Transfers					End of
		of Year						Comprehensive													Period
								Income or Loss								Into		Out of
		(in millions of dollars)
	Fixed Maturity Securities
	States, Municipalities, and Political Subdivisions	$	175.1		$	—		$	6.5		$	—	$	—		$	—	$	(25.5	)	$	156.1
	Foreign Governments	78.5			—			1.9			—		—			—		—			80.4
	Public Utilities	203.5			—			5.6			6.6		—			124.5		(30.2		)	310
	Mortgage/Asset-Backed Securities	0.5			—			—			—		(0.1		)	—		—			0.4
	All Other Corporate Bonds	1,859.10			—			24.2			73		(29.6		)	362.9		(816.0		)	1,473.60
	Redeemable Preferred Stocks	23.8			—			0.6			—		—			—		—			24.4
	Total Fixed Maturity Securities	2,340.50			—			38.8			79.6		(29.7		)	487.4		(871.7		)	2,044.90
	Equity Securities	4.6			2.1			(0.1		)	—		(3.5		)	—		—			3.1
	Embedded Derivative in Modified Coinsurance Arrangement	(53.2		)	8.5			—			—		—			—		—			(44.7		)
		Three Months Ended March 31, 2013
					Total Realized and
					Unrealized Investment
					Gains (Losses) Included in
		Beginning			Earnings			Other			Purchases		Sales			Level 3 Transfers					End of
		of Year						Comprehensive													Period
								Income or Loss								Into		Out of
		(in millions of dollars)
	Fixed Maturity Securities
	States, Municipalities, and Political Subdivisions	$	128.7		$	—		$	2.7		$	—	$	—		$	43.4	$	—		$	174.8
	Foreign Governments	82.1			—			0.5			—		—			—		—			82.6
	Public Utilities	574.4			—			1.1			—		(0.1		)	252.3		(425.2		)	402.5
	Mortgage/Asset-Backed Securities	0.5			—			—			—		—			—		—			0.5
	All Other Corporate Bonds	1,177.80			0.8			(8.8		)	30.3		(18.1		)	382.4		(572.1		)	992.3
	Redeemable Preferred Stocks	24.8			—			—			—		—			—		—			24.8
	Total Fixed Maturity Securities	1,988.30			0.8			(4.5		)	30.3		(18.2		)	678.1		(997.3		)	1,677.50
	Equity Securities	4.3			—			—			—		—			—		—			4.3
	Embedded Derivative in Modified Coinsurance Arrangement	(83.9		)	6.4			—			—		—			—		—			(77.5		)
	Realized and unrealized investment gains and losses presented in the preceding tables represent gains and losses only for the time during which the applicable financial instruments were classified as Level 3. The transfers between levels resulted primarily from a change in observability of three inputs used to determine fair values of the securities transferred: (1) transactional data for new issuance and secondary trades, (2) broker/dealer quotes and pricing, primarily related to changes in the level of activity in the market and whether the market was considered orderly, and (3) comparable bond metrics from which to perform an analysis. For fair value measurements of financial instruments that were transferred either into or out of Level 3, we reflect the transfers using the fair value at the beginning of the period. We believe this allows for greater transparency, as all changes in fair value that arise during the reporting period of the transfer are disclosed as a component of our Level 3 reconciliation. Gains for the three months ended March 31, 2014 and 2013 which are included in earnings and are attributable to the change in unrealized gains or losses relating to assets or liabilities valued using significant unobservable inputs and still held at period end were $8.5 million and $6.4 million, respectively. These amounts relate entirely to the changes in fair value of an embedded derivative in a modified coinsurance arrangement which are reported as realized investment gains and losses.
Quantitative Information Regarding Significant Unobservable Inputs	'
	The table below provides quantitative information regarding the significant unobservable inputs used in Level 3 fair value measurements derived from internal models. Certain securities classified as Level 3 are excluded from the table below due to limitations in our ability to obtain the underlying inputs used by external pricing sources.
		31-Mar-14
		Fair Value			Unobservable Input		Range/Weighted Average
		(in millions of dollars)
	Fixed Maturity Securities
	States, Municipalities, and Political Subdivisions - Private	$	122.1		- Comparability Adjustment	(b)	0.25% - 1.25% / 0.74%
	Public Utilities	72.4			- Volatility of Credit	(e)	0.75% - 1.50% / 1.05%
	Mortgage/Asset-Backed Securities - Private	0.4			- Discount for Size	(c)	5.60% - 5.71% / 5.68%
	All Other Corporate Bonds - Private	296.1			- Change in Benchmark Reference	(a)	0.54% - 0.75% / 0.67%
					- Comparability Adjustment	(b)	(0.70)% - (0.40)% / (0.60)%
					- Discount for Size	(c)	0.50% - 0.50% / 0.50%
					- Lack of Marketability	(d)	0.20% - 2.96% / 1.01%
					- Volatility of Credit	(e)	0.40% - 4.00% / 0.85%
					- Market Convention	(f)	Priced at Par
	All Other Corporate Bonds - Public	344.7			- Change in Benchmark Reference	(a)	(0.85%) - (0.85%) / (0.85)%
					- Comparability Adjustment	(b)	0.20% - 1.43% / 0.60%
					- Lack of Marketability	(d)	0.10% - 0.25% / 0.23%
					- Volatility of Credit	(e)	(0.86)% - 1.34% / (0.03)%
	Equity Securities - Private	2.8			- Market Convention	(f)	Priced at Cost or Owner's Equity
	Embedded Derivative in Modified Coinsurance Arrangement	(44.7		)	- Projected Liability Cash Flows	(g)	Actuarial Assumptions
		31-Dec-13
		Fair Value			Unobservable Input		Range/Weighted Average
		(in millions of dollars)
	Fixed Maturity Securities
	States, Municipalities, and Political Subdivisions - Private	$	142.7		- Comparability Adjustment	(b)	0.25% - 1.25% / 0.65%
	Public Utilities	64.3			- Volatility of Credit	(e)	0.75% - 1.25% / 0.92%
	Mortgage/Asset-Backed Securities - Private	0.5			- Discount for Size	(c)	4.93% - 5.03% / 5.01%
	All Other Corporate Bonds - Private	307			- Change in Benchmark Reference	(a)	3.36% - 3.36% / 3.36%
					- Comparability Adjustment	(b)	(0.70)% - (0.40)% / (0.60)%
					- Discount for Size	(c)	0.50% - 0.50% / 0.50%
					- Lack of Marketability	(d)	0.20% - 1.00% / 0.55%
					- Volatility of Credit	(e)	0.07% - 4.00% / 0.84%
					- Market Convention	(f)	Priced at Par
	All Other Corporate Bonds - Public	514.4			- Change in Benchmark Reference	(a)	(0.32)% - 0.25% / 0.04%
					- Comparability Adjustment	(b)	(0.23)% - 1.00% / 0.41%
					- Lack of Marketability	(d)	0.20% - 0.20% / 0.20%
					- Volatility of Credit	(e)	(0.88)% - 0.46% / (0.26)%
	Equity Securities - Private	4.2			- Market Convention	(f)	Priced at Cost or Owner's Equity
	Embedded Derivative in Modified Coinsurance Arrangement	(53.2		)	- Projected Liability Cash Flows	(g)	Actuarial Assumptions
	(a)	Represents basis point adjustments for changes in benchmark spreads associated with various ratings categories
	(b)	Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors
	(c)	Represents basis point adjustments based on issue/issuer size relative to the benchmark
	(d)	Represents basis point adjustments to apply a discount due to the illiquidity of an investment
	(e)	Represents basis point adjustments for credit-specific factors
	(f)	Represents a decision to price based on par value, cost, or owner's equity when limited data is available
	(g)	Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates

Investments_Tables

Investments (Tables)	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Schedule of Available-for-sale Securities Reconciliation	'
	At March 31, 2014 and December 31, 2013, all fixed maturity securities were classified as available-for-sale. The amortized cost and fair values of securities by security type are shown as follows.
		March 31, 2014
		Amortized			Gross				Gross				Fair
		Cost			Unrealized				Unrealized				Value
					Gain				Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	959.1		$	200.1			$	2.5			$	1,156.70
	States, Municipalities, and Political Subdivisions	1,732.30			212.2				17.7				1,926.80
	Foreign Governments	1,205.70			166.3				1				1,371.00
	Public Utilities	9,436.80			1,394.30				28				10,803.10
	Mortgage/Asset-Backed Securities	2,102.50			186.8				2.6				2,286.70
	All Other Corporate Bonds	23,046.60			3,125.50				88				26,084.10
	Redeemable Preferred Stocks	33			5.4				—				38.4
	Total Fixed Maturity Securities	$	38,516.00		$	5,290.60			$	139.8			$	43,666.80
		December 31, 2013
		Amortized			Gross				Gross				Fair
		Cost			Unrealized				Unrealized				Value
					Gain				Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	1,028.60		$	173.1			$	5.6			$	1,196.10
	States, Municipalities, and Political Subdivisions	1,706.00			117.2				40				1,783.20
	Foreign Governments	1,226.40			149.6				2.8				1,373.20
	Public Utilities	9,328.90			1,126.90				52.8				10,403.00
	Mortgage/Asset-Backed Securities	1,858.70			184.6				4				2,039.30
	All Other Corporate Bonds	23,108.00			2,602.60				198.7				25,511.90
	Redeemable Preferred Stocks	33			4.7				—				37.7
	Total Fixed Maturity Securities	$	38,289.60		$	4,358.70			$	303.9			$	42,344.40
Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position	'
	The following charts indicate the length of time our fixed maturity securities have been in a gross unrealized loss position.
		March 31, 2014
		Less Than 12 Months							12 Months or Greater
		Fair			Gross				Fair				Gross
		Value			Unrealized				Value				Unrealized
					Loss								Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	9.2		$	0.5			$	5.8			$	2
	States, Municipalities, and Political Subdivisions	186.3			9.8				55.9				7.9
	Foreign Governments	34.8			1				—				—
	Public Utilities	628			24.2				49.2				3.8
	Mortgage/Asset-Backed Securities	261.4			2.2				2.4				0.4
	All Other Corporate Bonds	1,908.60			66.6				257.1				21.4
	Total Fixed Maturity Securities	$	3,028.30		$	104.3			$	370.4			$	35.5
		December 31, 2013
		Less Than 12 Months							12 Months or Greater
		Fair			Gross				Fair				Gross
		Value			Unrealized				Value				Unrealized
					Loss								Loss
		(in millions of dollars)
	United States Government and Government Agencies and Authorities	$	41.1		$	3.1			$	5.2			$	2.5
	States, Municipalities, and Political Subdivisions	412.5			33.5				37.2				6.5
	Foreign Governments	87.2			2.8				—				—
	Public Utilities	870.6			47.1				58.7				5.7
	Mortgage/Asset-Backed Securities	341			3.6				2.5				0.4
	All Other Corporate Bonds	3,412.30			174				207.4				24.7
	Total Fixed Maturity Securities	$	5,164.70		$	264.1			$	311			$	39.8
Distribution of the Maturity Dates for Fixed Maturity Securities	'
	The following is a distribution of the maturity dates for fixed maturity securities. The maturity dates have not been adjusted for possible calls or prepayments.
		March 31, 2014
		Total			Unrealized Gain Position								Unrealized Loss Position
		Amortized Cost			Gross Gain				Fair Value				Gross Loss				Fair Value
		(in millions of dollars)
	1 year or less	$	841.9		$	21.5			$	854.4			$	—			$	9
	Over 1 year through 5 years	7,186.20			769.6				7,908.90				0.3				46.6
	Over 5 years through 10 years	9,640.00			1,030.00				9,239.50				41.2				1,389.30
	Over 10 years	18,745.40			3,282.70				20,242.40				95.7				1,690.00
		36,413.50			5,103.80				38,245.20				137.2				3,134.90
	Mortgage/Asset-Backed Securities	2,102.50			186.8				2,022.90				2.6				263.8
	Total Fixed Maturity Securities	$	38,516.00		$	5,290.60			$	40,268.10			$	139.8			$	3,398.70
		December 31, 2013
		Total			Unrealized Gain Position								Unrealized Loss Position
		Amortized Cost			Gross Gain				Fair Value				Gross Loss				Fair Value
		(in millions of dollars)
	1 year or less	$	903.9		$	20.6			$	915.5			$	—			$	9
	Over 1 year through 5 years	7,098.20			727.1				7,678.50				0.6				146.2
	Over 5 years through 10 years	9,492.60			940.2				8,137.40				95.8				2,199.60
	Over 10 years	18,936.20			2,486.20				18,441.50				203.5				2,777.40
		36,430.90			4,174.10				35,172.90				299.9				5,132.20
	Mortgage/Asset-Backed Securities	1,858.70			184.6				1,695.80				4				343.5
	Total Fixed Maturity Securities	$	38,289.60		$	4,358.70			$	36,868.70			$	303.9			$	5,475.70
Mortgage Loans by Property Type	'
	Mortgage loans by property type and geographic region are presented below.
		31-Mar-14						31-Dec-13
		(in millions of dollars)
		Carrying			Percent of			Carrying				Percent of
		Amount			Total			Amount				Total
	Property Type
	Apartment	$	74.5		4	%		$	61.1			3.3	%
	Industrial	538			29.2			567.8				31.3
	Office	809.6			43.9			776.5				42.8
	Retail	421.2			22.9			409.7				22.6
	Total	$	1,843.30		100	%		$	1,815.10			100	%
Mortgage Loans by Geographic Region	'
	Region
	New England	$	122.5		6.7	%		$	100.9			5.6	%
	Mid-Atlantic	186.2			10.1			191.5				10.5
	East North Central	227.4			12.3			244.3				13.5
	West North Central	172.8			9.4			162.3				8.9
	South Atlantic	441.1			23.9			447.7				24.7
	East South Central	66.5			3.6			67.7				3.7
	West South Central	206.5			11.2			190.9				10.5
	Mountain	114.7			6.2			101.9				5.6
	Pacific	305.6			16.6			307.9				17
	Total	$	1,843.30		100	%		$	1,815.10			100	%
Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Internal Rating	'
	Mortgage loans, sorted by the applicable credit quality indicators, are as follows:
		March 31 2014			December 31 2013
		(in millions of dollars)
	Internal Rating
	Aa	$	10.6		$	10.8
	A	666.8			683.1
	Baa	1,121.30			1,094.60
	Ba	13.4			13.5
	B	31.2			13.1
	Total	$	1,843.30		$	1,815.10
Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Loan to Value Ratio	'
	Loan-to-Value Ratio
	<=5%	$	815.3		$	777.4
	> 65% <=5%	888.4			867.5
	> 75% <=5%	95.1			107.6
	> 85%	44.5			62.6
	Total	$	1,843.30		$	1,815.10
Activity in the Allowance for Credit Losses	'
	The activity in the allowance for credit losses is as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Balance at Beginning of Year	$	1.5		$	1.5
	Provision	3			—
	Balance at End of Period	$	4.5		$	1.5
Impaired Mortgage Loans	'
	Impaired mortgage loans are as follows:
		March 31, 2014
		(in millions of dollars)
					Unpaid
		Recorded			Principal				Related
		Investment			Balance				Allowance
	With an Allowance Recorded	$	31.2		$	35.7			$	4.5
		December 31, 2013
		(in millions of dollars)
					Unpaid
		Recorded			Principal				Related
		Investment			Balance				Allowance
	With an Allowance Recorded	$	13.1		$	14.6			$	1.5
Schedule of Financial Instrument and Derivative Offsetting	'
	Shown below are our financial instruments that either meet the accounting requirements that allow them to be offset in our balance sheets or that are subject to an enforceable master netting arrangement or similar agreement. Our accounting policy is to not offset these financial instruments in our balance sheets. Net amounts disclosed below have been reduced by the amount of collateral pledged to or received from our counterparties.
			March 31, 2014
			Gross Amount											Gross Amount Not
			of Recognized			Gross Amount				Net Amount				Offset in Balance Sheet
			Financial			Offset in				Presented in				Financial				Cash			Net
			Instruments			Balance Sheet				Balance Sheet				Instruments				Collateral			Amount
			(in millions of dollars)
	Financial Assets:
	Derivatives		$	10.9		$	—			$	10.9			$	(7.9	)		$	(2.8	)	$	0.2
	Securities Lending		187.4			—				187.4				(125.8		)		(61.6		)	—
	Total		$	198.3		$	—			$	198.3			$	(133.7	)		$	(64.4	)	$	0.2
	Financial Liabilities:
	Derivatives		$	117.7		$	—			$	117.7			$	(84.1	)		$	—		$	33.6
	Securities Lending		61.6			—				61.6				(61.6		)		—			—
	Total		$	179.3		$	—			$	179.3			$	(145.7	)		$	—		$	33.6
			December 31, 2013
			Gross Amount											Gross Amount Not
			of Recognized			Gross Amount				Net Amount				Offset in Balance Sheet
			Financial			Offset in				Presented in				Financial				Cash			Net
			Instruments			Balance Sheet				Balance Sheet				Instruments				Collateral			Amount
			(in millions of dollars)
	Financial Assets:
	Derivatives		$	10.8		$	—			$	10.8			$	(9.5	)		$	(1.1	)	$	0.2
	Securities Lending		201.6			—				201.6				(125.1		)		(76.5		)	—
	Total		$	212.4		$	—			$	212.4			$	(134.6	)		$	(77.6	)	$	0.2
	Financial Liabilities:
	Derivatives		$	135.6		$	—			$	135.6			$	(98.6	)		$	—		$	37
	Securities Lending		76.5			—				76.5				(76.5		)		—			—
	Total		$	212.1		$	—			$	212.1			$	(175.1	)		$	—		$	37
Investment Income	'
	Net Investment Income
	Net investment income reported in our consolidated statements of income is as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Fixed Maturity Securities	$	581.1		$	589.9
	Derivative Financial Instruments	9.9			7.7
	Mortgage Loans	28.4			26
	Policy Loans	3.9			3.7
	Other Long-term Investments	3.8			7.7
	Short-term Investments	0.5			0.8
	Gross Investment Income	627.6			635.8
	Less Investment Expenses	8			7.1
	Less Investment Income on Participation Fund Account Assets	3.8			4
	Less Amortization of Tax Credit Partnerships	3.3			3.6
	Net Investment Income	$	612.5		$	621.1
Realized Investment Gains and Losses Reported in Consolidated Statements of Income	'
	Realized Investment Gain and Loss
	Realized investment gains and losses, which for sales are based upon specific identification of the investments sold, are as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Fixed Maturity Securities
	Gross Gains on Sales	$	0.9		$	6.6
	Gross Losses on Sales	(5.4		)	(5.5		)
	Other-Than-Temporary Impairment Loss	—			(0.8		)
	Mortgage Loans and Other Invested Assets
	Gross Gains on Sales	7.4			7.6
	Gross Losses on Sales	(0.6		)	—
	Impairment Loss	(3.0		)	(1.0		)
	Embedded Derivative in Modified Coinsurance Arrangement	8.5			6.4
	Credit Default Swaps	(0.4		)	(0.3		)
	Foreign Currency Transactions	(1.1		)	(2.7		)
	Net Realized Investment Gain	$	6.3		$	10.3

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2014
Notes to Financial Statements [Abstract]	'
Notional Amounts for Each Category of Derivative Activity	'
	The table below summarizes, by notional amounts, the activity for each category of derivatives. The notional amounts represent the basis upon which our counterparty pay and receive amounts are calculated.
		Swaps
		Receive				Receive				Receive		Credit Default		Forwards		Total
		Variable/Pay				Fixed/Pay				Fixed/Pay
		Fixed				Fixed				Variable
		(in millions of dollars)
	Balance at December 31, 2012	$	174			$	508.8			$	750	$	—	$	—	$	1,432.80
	Additions	—				—				—		70		24		94
	Terminations	—				18				40		—		24		82
	Balance at March 31, 2013	174				490.8				710		70		—		1,444.80
	Balance at December 31, 2013	150				630.4				600		97		—		1,477.40
	Additions	—				—				—		—		10		10
	Terminations	—				7.9				—		—		10		17.9
	Balance at March 31, 2014	$	150			$	622.5			$	600	$	97	$	—	$	1,469.50
Location and Fair Values of Derivative Financial Instruments	'
	The following tables summarize the location and fair values of derivative financial instruments, as reported in our consolidated balance sheets.
		March 31, 2014
		Asset Derivatives						Liability Derivatives
		Balance Sheet		Fair				Balance Sheet		Fair
		Location		Value				Location		Value
		(in millions of dollars)
	Designated as Hedging Instruments
	Interest Rate Swaps	Other L-T Investments		$	8.1			Other Liabilities		$	30.9
	Foreign Exchange Contracts	Other L-T Investments		2.8				Other Liabilities		84.8
	Total			$	10.9					$	115.7
	Not Designated as Hedging Instruments
	Credit Default Swaps							Other Liabilities		$	2
	Embedded Derivative in Modified Coinsurance Arrangement							Other Liabilities		44.7
	Total									$	46.7
		December 31, 2013
		Asset Derivatives						Liability Derivatives
		Balance Sheet		Fair				Balance Sheet		Fair
		Location		Value				Location		Value
		(in millions of dollars)
	Designated as Hedging Instruments
	Interest Rate Swaps	Other L-T Investments		$	9.2			Other Liabilities		$	35
	Foreign Exchange Contracts	Other L-T Investments		1.6				Other Liabilities		98.7
	Total			$	10.8					$	133.7
	Not Designated as Hedging Instruments
	Credit Default Swaps							Other Liabilities		$	1.9
	Embedded Derivative in Modified Coinsurance Arrangement							Other Liabilities		53.2
	Total									$	55.1
Location of Gains and Losses on Derivative Instruments Designated as Cash Flow Hedging Instruments	'
	The following table summarizes the location of gains and losses on the effective portion of derivative financial instruments designated as cash flow hedging instruments, as reported in our consolidated statements of income and consolidated statements of comprehensive income.
			Three Months Ended March 31
			2014				2013
			(in millions of dollars)
	Gain (Loss) Recognized in Other Comprehensive Income (Loss) on Derivatives
	Interest Rate Swaps and Forwards		$	—			$	(2.2	)
	Foreign Exchange Contracts		12.9				4.1
		Total	$	12.9			$	1.9
	Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income
	Net Investment Income
		Interest Rate Swaps and Forwards	$	11.7			$	10
		Foreign Exchange Contracts	(1.1		)		(1.7		)
	Net Realized Investment Gain (Loss)
		Interest Rate Swaps	2.5				—
		Foreign Exchange Contracts	(2.1		)		(6.7		)
	Interest and Debt Expense
		Interest Rate Swaps	(0.4		)		(0.4		)
		Total	$	10.6			$	1.2
Location of and Gain (Loss) on Derivatives Not Designated as Hedging Instruments	'
	The following table summarizes the location of gains and losses on our derivatives not designated as hedging instruments, as reported in our consolidated statements of income.
			Three Months Ended March 31
			2014				2013
			(in millions of dollars)
	Net Realized Investment Gain (Loss)
		Credit Default Swaps	$	(0.4	)		$	(0.3	)
		Embedded Derivative in Modified Coinsurance Arrangement	8.5				6.4
		Total	$	8.1			$	6.1

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Tables)	3 Months Ended
	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Schedule of Accumulated Other Comprehensive Income (Loss)	'
	Components of our accumulated other comprehensive income, after tax, and related changes are as follows:
				Net Unrealized Gain on Securities				Net Gain on Cash Flow Hedges				Foreign Currency Translation Adjustment			Unrecognized Pension and Postretirement Benefit Costs			Total
				(in millions of dollars)
	Balance at December 31, 2013			$	135.7			$	396.3			$	(47.1	)	$	(229.9	)	$	255
		Other Comprehensive Income (Loss) Before Reclassifications		187.2				8.5				7.6			(0.2		)	203.1
		Amounts Reclassified from Accumulated Other Comprehensive Income or Loss		2.4				(6.8		)		—			0.7			(3.7		)
		Net Other Comprehensive Income		189.6				1.7				7.6			0.5			199.4
	Balance at March 31, 2014			$	325.3			$	398			$	(39.5	)	$	(229.4	)	$	454.4
	Balance at December 31, 2012			$	873.5			$	401.6			$	(72.6	)	$	(574.5	)	$	628
		Other Comprehensive Income (Loss) Before Reclassifications		(73.3		)		(1.2		)		(69.9		)	1.7			(142.7		)
		Amounts Reclassified from Accumulated Other Comprehensive Income or Loss		(7.8		)		(0.8		)		—			9			0.4
		Net Other Comprehensive Income (Loss)		(81.1		)		(2.0		)		(69.9		)	10.7			(142.3		)
	Balance at March 31, 2013			$	792.4			$	399.6			$	(142.5	)	$	(563.8	)	$	485.7
Schedule of Components of Unrealized Gain (Loss) on Securities	'
	The net unrealized gain on securities consists of the following components:
			31-Mar				31-Dec
			2014				2013				Change
			(in millions of dollars)
	Fixed Maturity Securities		$	5,150.80			$	4,054.80			$	1,096.00
	Other Investments		40.6				55.5				(14.9		)
	Deferred Acquisition Costs		(48.9		)		(41.6		)		(7.3		)
	Reserves for Future Policy and Contract Benefits		(4,939.7		)		(4,108.5		)		(831.2		)
	Reinsurance Recoverable		309.9				263.8				46.1
	Deferred Income Tax		(187.4		)		(88.3		)		(99.1		)
	Total		$	325.3			$	135.7			$	189.6
			31-Mar				31-Dec
			2013				2012				Change
			(in millions of dollars)
	Fixed Maturity Securities		$	6,803.90			$	7,221.50			$	(417.6	)
	Other Investments		72.5				92.8				(20.3		)
	Deferred Acquisition Costs		(61.2		)		(67.0		)		5.8
	Reserves for Future Policy and Contract Benefits		(5,979.7		)		(6,277.5		)		297.8
	Reinsurance Recoverable		353.9				351.5				2.4
	Deferred Income Tax		(397.0		)		(447.8		)		50.8
	Total		$	792.4			$	873.5			$	(81.1	)
Schedule of Reclassifications Out of Accumulated Other Comprehensive Income	'
	Amounts reclassified from accumulated other comprehensive income or loss were recognized in our consolidated statements of income as follows:
				Three Months Ended March 31
				2014				2013
				(in millions of dollars)
	Net Unrealized Gain on Securities
		Net Realized Investment Gain (Loss)
			Gain (Loss) on Sales of Securities and Other Invested Assets	$	(3.7	)		$	12.7
			Other-Than-Temporary Impairment Loss	—				(0.8		)
				(3.7		)		11.9
		Income Tax Expense (Benefit)		(1.3		)		4.1
		Total		$	(2.4	)		$	7.8
	Net Gain on Cash Flow Hedges
		Net Investment Income
			Gain on Interest Rate Swaps and Forwards	$	11.7			$	10
			Loss on Foreign Exchange Contracts	(1.1		)		(1.7		)
		Net Realized Investment Gain (Loss)
			Gain on Interest Rate Swaps	2.5				—
			Loss on Foreign Exchange Contracts	(2.1		)		(6.7		)
		Interest and Debt Expense
			Loss on Interest Rate Swaps	(0.4		)		(0.4		)
				10.6				1.2
		Income Tax Expense		3.8				0.4
		Total		$	6.8			$	0.8
	Unrecognized Pension and Postretirement Benefit Costs
		Other Expenses
			Amortization of Net Actuarial Loss	$	(1.4	)		$	(14.9	)
			Amortization of Prior Service Credit	0.4				1.2
				(1.0		)		(13.7		)
		Income Tax Benefit		(0.3		)		(4.7		)
		Total		$	(0.7	)		$	(9.0	)

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Premium Income by Major Line of Business within Each Segment	'
	Premium income by major line of business within each of our segments is presented as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Unum US
	Group Disability
	Group Long-term Disability	$	383.5		$	392.7
	Group Short-term Disability	137.3			131
	Group Life and Accidental Death & Dismemberment
	Group Life	309.9			302.2
	Accidental Death & Dismemberment	30.6			30.9
	Supplemental and Voluntary
	Individual Disability - Recently Issued	115.9			120.1
	Voluntary Benefits	175.3			162.8
		1,152.50			1,139.70
	Unum UK
	Group Long-term Disability	103			97.9
	Group Life	34.8			31
	Supplemental	13.9			14.9
		151.7			143.8
	Colonial Life
	Accident, Sickness, and Disability	189.1			184.8
	Life	57.4			54.8
	Cancer and Critical Illness	69.9			67.5
		316.4			307.1
	Closed Block
	Individual Disability	161.1			181.8
	Long-term Care	156.5			158.8
	All Other	0.3			(0.3		)
		317.9			340.3
	Total	$	1,938.50		$	1,930.90
Selected Operating Statement Data by Segment	'
	Selected operating statement data by segment is presented as follows:
		Unum US			Unum UK			Colonial Life			Closed Block		Corporate			Total
		(in millions of dollars)
	Three Months Ended March 31, 2014
	Premium Income	$	1,152.50		$	151.7		$	316.4		$	317.9	$	—		$	1,938.50
	Net Investment Income	226.4			33.6			36.9			316.3		(0.7		)	612.5
	Other Income	30.9			(0.1		)	(0.1		)	21.6		1.5			53.8
	Operating Revenue	$	1,409.80		$	185.2		$	353.2		$	655.8	$	0.8		$	2,604.80
	Operating Income (Loss)	$	210.8		$	36.5		$	79.4		$	29.1	$	(34.2	)	$	321.6
	Three Months Ended March 31, 2013
	Premium Income	$	1,139.70		$	143.8		$	307.1		$	340.3	$	—		$	1,930.90
	Net Investment Income	235.7			30.8			39.7			313.1		1.8			621.1
	Other Income	36.7			0.1			—			24.1		1.6			62.5
	Operating Revenue	$	1,412.10		$	174.7		$	346.8		$	677.5	$	3.4		$	2,614.50
	Operating Income (Loss)	$	208.1		$	31.3		$	75.4		$	27.3	$	(33.7	)	$	308.4
Reconciliation of Operating Revenue and Operating Income by Segment to Revenue and Net Income	'
	A reconciliation of "operating revenue" to total revenue and "operating income" to income before income tax is as follows:
		Three Months Ended March 31
		2014			2013
		(in millions of dollars)
	Operating Revenue	$	2,604.80		$	2,614.50
	Net Realized Investment Gain	6.3			10.3
	Total Revenue	$	2,611.10		$	2,624.80
	Operating Income	$	321.6		$	308.4
	Net Realized Investment Gain	6.3			10.3
	Non-operating Retirement-related Loss	(1.4		)	(14.9		)
	Income Before Income Tax	$	326.5		$	303.8
Assets by Segment	'
	Assets by segment are as follows:
		31-Mar			31-Dec
		2014			2013
		(in millions of dollars)
	Unum US	$	18,517.90		$	18,384.30
	Unum UK	3,793.40			3,654.10
	Colonial Life	3,542.50			3,482.90
	Closed Block	32,397.30			31,564.20
	Corporate	2,827.50			2,318.10
	Total	$	61,078.60		$	59,403.60

Employee_Benefit_Plans_Tables

Employee Benefit Plans (Tables)	3 Months Ended
	Mar. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Schedule of Net Benefit Costs	'
	The following table provides the components of the net periodic benefit cost for the defined benefit pension and OPEB plans.
		Three Months Ended March 31
		Pension Benefits
		U.S. Plans						Non U.S. Plans						OPEB
		2014			2013			2014			2013			2014			2013
		(in millions of dollars)
	Service Cost	$	0.9		$	14.9		$	1.1		$	1.1		$	0.1		$	0.2
	Interest Cost	22.5			21.9			2.3			2.1			2			2
	Expected Return on Plan Assets	(29.5		)	(25.5		)	(3.4		)	(3.0		)	(0.2		)	(0.2		)
	Amortization of:
	Net Actuarial Loss	1.3			14.6			0.1			0.3			—			—
	Prior Service Credit	—			—			—			—			(0.4		)	(1.2		)
	Total	$	(4.8	)	$	25.9		$	0.1		$	0.5		$	1.5		$	0.8

Stockholders_Equity_and_Earnin1

Stockholders' Equity and Earnings Per Common Share Stockholders' Equity and Earnings Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2014
Stockholders' Equity Note [Abstract]	'
Schedule of Earnings Per Share, Basic and Diluted	'
	Net income per common share is determined as follows:
		Three Months Ended March 31
		2014		2013
		(in millions of dollars, except share data)
	Numerator
	Net Income	$	228.9	$	212.6
	Denominator (000s)
	Weighted Average Common Shares - Basic	259,408.50		269,361.10
	Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,301.40		993.3
	Weighted Average Common Shares - Assuming Dilution	260,709.90		270,354.40
	Net Income Per Common Share
	Basic	$	0.88	$	0.79
	Assuming Dilution	$	0.88	$	0.79
Authorized Common Stock Repurchase Programs	'
	Our board of directors has authorized the repurchase of Unum Group's common stock under the following repurchase programs:
		Share Repurchase Program Authorized During
		Dec-13		Jul-12
		(in millions of dollars)
	Authorized Repurchase Amount	$	750	$	750
	Remaining Repurchase Amount at March 31, 2014	$	629.9	$	—
	The December 2013 share repurchase program has an expiration date of June 12, 2015.
Share Repurchase Table	'
	Common stock repurchases, which are classified as treasury stock and accounted for using the cost method, were as follows:
		Three Months Ended March 31
		2014		2013
		(in millions)
	Shares Repurchased	2.9		3.7
	Cost of Shares Repurchased	$	100.1	$	95.1

Carrying_Amount_and_Fair_Value

Carrying Amount and Fair Value of Financial Instruments (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets	'	'
Fixed Maturity Securities	$43,666.80	$42,344.40
Mortgage Loans	1,843.30	1,815.10
Policy Loans	3,268.30	3,276
Other Long-term Investments	'	'
Equity Securities	15.1	16.4
Policyholders' Funds	'	'
Long-term Debt	2,948.20	2,612
Other Liabilities	'	'
Unfunded commitment to fund Investment Partnerships	17.9	'
Carrying Amount	'	'
Assets	'	'
Fixed Maturity Securities	43,666.80	42,344.40
Mortgage Loans	1,843.30	1,815.10
Policy Loans	3,268.30	3,276
Other Long-term Investments	'	'
Derivative Assets	10.9	10.8
Equity Securities	15.1	16.4
Miscellaneous Long-Term Investments	477.4	475.2
Policyholders' Funds	'	'
Deferred Annuity Products	629.7	631.5
Supplementary Contracts without Life Contingencies	585.7	563.1
Long-term Debt	2,948.20	2,612
Other Liabilities	'	'
Derivative Liabilities	117.7	135.6
Embedded Derivative in Modified Coinsurance Arrangement	44.7	53.2
Unfunded commitment to fund Investment Partnerships	17.9	27.2
Fair Value	'	'
Assets	'	'
Fixed Maturity Securities	43,666.80	42,344.40
Mortgage Loans	2,009.80	1,980.20
Policy Loans	3,336.30	3,339.60
Other Long-term Investments	'	'
Derivative Assets	10.9	10.8
Equity Securities	15.1	16.4
Miscellaneous Long-Term Investments	477.4	475.2
Policyholders' Funds	'	'
Deferred Annuity Products	629.7	631.5
Supplementary Contracts without Life Contingencies	585.7	563.1
Long-term Debt	3,194.50	2,824.40
Other Liabilities	'	'
Derivative Liabilities	117.7	135.6
Embedded Derivative in Modified Coinsurance Arrangement	44.7	53.2
Unfunded commitment to fund Investment Partnerships	$17.90	$27.20

Fair_Value_Measurements_by_Inp

Fair Value Measurements by Input Level (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Fixed Maturity Securities	'	'
Fixed Maturity Securities	$43,666.80	$42,344.40
Other Long-term Investments	'	'
Equity Securities	15.1	16.4
Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	4,810.90	2,523.30
Other Long-term Investments	'	'
Equity Securities	0	0
Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	36,811	37,480.60
Other Long-term Investments	'	'
Equity Securities	12	11.8
Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	2,044.90	2,340.50
Other Long-term Investments	'	'
Equity Securities	3.1	4.6
Interest Rate Swaps	'	'
Other Long-term Investments	'	'
Derivative Assets	8.1	9.2
Other Liabilities	'	'
Derivative Liabilities	30.9	35
Interest Rate Swaps | Fair Value, Inputs, Level 1	'	'
Other Long-term Investments	'	'
Derivative Assets	0	0
Other Liabilities	'	'
Derivative Liabilities	0	0
Interest Rate Swaps | Fair Value, Inputs, Level 2	'	'
Other Long-term Investments	'	'
Derivative Assets	8.1	9.2
Other Liabilities	'	'
Derivative Liabilities	30.9	35
Interest Rate Swaps | Fair Value, Inputs, Level 3	'	'
Other Long-term Investments	'	'
Derivative Assets	0	0
Other Liabilities	'	'
Derivative Liabilities	0	0
Foreign Exchange Contracts	'	'
Other Long-term Investments	'	'
Derivative Assets	2.8	1.6
Other Liabilities	'	'
Derivative Liabilities	84.8	98.7
Foreign Exchange Contracts | Fair Value, Inputs, Level 1	'	'
Other Long-term Investments	'	'
Derivative Assets	0	0
Other Liabilities	'	'
Derivative Liabilities	0	0
Foreign Exchange Contracts | Fair Value, Inputs, Level 2	'	'
Other Long-term Investments	'	'
Derivative Assets	2.8	1.6
Other Liabilities	'	'
Derivative Liabilities	84.8	98.7
Foreign Exchange Contracts | Fair Value, Inputs, Level 3	'	'
Other Long-term Investments	'	'
Derivative Assets	0	0
Other Liabilities	'	'
Derivative Liabilities	0	0
Derivative Assets	'	'
Other Long-term Investments	'	'
Derivative Assets	10.9	10.8
Derivative Assets | Fair Value, Inputs, Level 1	'	'
Other Long-term Investments	'	'
Derivative Assets	0	0
Derivative Assets | Fair Value, Inputs, Level 2	'	'
Other Long-term Investments	'	'
Derivative Assets	10.9	10.8
Derivative Assets | Fair Value, Inputs, Level 3	'	'
Other Long-term Investments	'	'
Derivative Assets	0	0
Credit Default Swaps	'	'
Other Liabilities	'	'
Derivative Liabilities	2	1.9
Credit Default Swaps | Fair Value, Inputs, Level 1	'	'
Other Liabilities	'	'
Derivative Liabilities	0	0
Credit Default Swaps | Fair Value, Inputs, Level 2	'	'
Other Liabilities	'	'
Derivative Liabilities	2	1.9
Credit Default Swaps | Fair Value, Inputs, Level 3	'	'
Other Liabilities	'	'
Derivative Liabilities	0	0
Embedded Derivative in Modified Coinsurance Arrangement	'	'
Other Liabilities	'	'
Derivative Liabilities	44.7	53.2
Embedded Derivative in Modified Coinsurance Arrangement | Fair Value, Inputs, Level 1	'	'
Other Liabilities	'	'
Derivative Liabilities	0	0
Embedded Derivative in Modified Coinsurance Arrangement | Fair Value, Inputs, Level 2	'	'
Other Liabilities	'	'
Derivative Liabilities	0	0
Embedded Derivative in Modified Coinsurance Arrangement | Fair Value, Inputs, Level 3	'	'
Other Liabilities	'	'
Derivative Liabilities	44.7	53.2
Derivative Liabilities	'	'
Other Liabilities	'	'
Derivative Liabilities	162.4	188.8
Derivative Liabilities | Fair Value, Inputs, Level 1	'	'
Other Liabilities	'	'
Derivative Liabilities	0	0
Derivative Liabilities | Fair Value, Inputs, Level 2	'	'
Other Liabilities	'	'
Derivative Liabilities	117.7	135.6
Derivative Liabilities | Fair Value, Inputs, Level 3	'	'
Other Liabilities	'	'
Derivative Liabilities	44.7	53.2
United States Government and Government Agencies and Authorities	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	1,156.70	1,196.10
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	189.2	144.5
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	967.5	1,051.60
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	0	0
States, Municipalities, and Political Subdivisions	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	1,926.80	1,783.20
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	0	0
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	1,770.70	1,608.10
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	156.1	175.1
Foreign Governments	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	1,371	1,373.20
Foreign Governments | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	0	0
Foreign Governments | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	1,290.60	1,294.70
Foreign Governments | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	80.4	78.5
Public Utilities	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	10,803.10	10,403
Public Utilities | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	709.4	396.8
Public Utilities | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	9,783.70	9,802.70
Public Utilities | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	310	203.5
Mortgage/Asset-backed Securities	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	2,286.70	2,039.30
Mortgage/Asset-backed Securities | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	0	0
Mortgage/Asset-backed Securities | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	2,286.30	2,038.80
Mortgage/Asset-backed Securities | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	0.4	0.5
All Other Corporate Bonds	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	26,084.10	25,511.90
All Other Corporate Bonds | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	3,912.30	1,982
All Other Corporate Bonds | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	20,698.20	21,670.80
All Other Corporate Bonds | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	1,473.60	1,859.10
Redeemable Preferred Stocks	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	38.4	37.7
Redeemable Preferred Stocks | Fair Value, Inputs, Level 1	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	0	0
Redeemable Preferred Stocks | Fair Value, Inputs, Level 2	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	14	13.9
Redeemable Preferred Stocks | Fair Value, Inputs, Level 3	'	'
Fixed Maturity Securities	'	'
Fixed Maturity Securities	$24.40	$23.80

Transfers_of_Assets_between_Le

Transfers of Assets between Level 1 and Level 2 (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Transfers Between Level 1 and Level 2 [Line Items]	'	'
Level 1 to Level 2 Transfers	$967.10	$1,213.70
Level 2 to Level 1 Transfers	3,006.80	3,025.30
United States Government and Government Agencies and Authorities	'	'
Transfers Between Level 1 and Level 2 [Line Items]	'	'
Level 1 to Level 2 Transfers	121.5	0
Level 2 to Level 1 Transfers	163.2	256.9
States, Municipalities, and Political Subdivisions	'	'
Transfers Between Level 1 and Level 2 [Line Items]	'	'
Level 1 to Level 2 Transfers	0	19.4
Level 2 to Level 1 Transfers	0	0
Public Utilities	'	'
Transfers Between Level 1 and Level 2 [Line Items]	'	'
Level 1 to Level 2 Transfers	192.8	53.5
Level 2 to Level 1 Transfers	452.1	502.1
All Other Corporate Bonds	'	'
Transfers Between Level 1 and Level 2 [Line Items]	'	'
Level 1 to Level 2 Transfers	652.8	1,140.80
Level 2 to Level 1 Transfers	$2,391.50	$2,266.30

Changes_in_Assets_and_Liabilit

Changes in Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs (Level 3) (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
States, Municipalities, and Political Subdivisions	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	$175.10	$128.70
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	6.5	2.7
Purchases	0	0
Sales	0	0
Level 3 Transfers Into	0	43.4
Level 3 Transfers Out of	-25.5	0
End of Period	156.1	174.8
Foreign Governments	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	78.5	82.1
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	1.9	0.5
Purchases	0	0
Sales	0	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Period	80.4	82.6
Public Utilities	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	203.5	574.4
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	5.6	1.1
Purchases	6.6	0
Sales	0	-0.1
Level 3 Transfers Into	124.5	252.3
Level 3 Transfers Out of	-30.2	-425.2
End of Period	310	402.5
Mortgage/Asset-backed Securities	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	0.5	0.5
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	0	0
Purchases	0	0
Sales	-0.1	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Period	0.4	0.5
All Other Corporate Bonds	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	1,859.10	1,177.80
Investment Gain (Loss) included in Earnings	0	0.8
Investment Gain (Loss) included in OCI	24.2	-8.8
Purchases	73	30.3
Sales	-29.6	-18.1
Level 3 Transfers Into	362.9	382.4
Level 3 Transfers Out of	-816	-572.1
End of Period	1,473.60	992.3
Redeemable Preferred Stocks	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	23.8	24.8
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	0.6	0
Purchases	0	0
Sales	0	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Period	24.4	24.8
Fixed Maturity Securities	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	2,340.50	1,988.30
Investment Gain (Loss) included in Earnings	0	0.8
Investment Gain (Loss) included in OCI	38.8	-4.5
Purchases	79.6	30.3
Sales	-29.7	-18.2
Level 3 Transfers Into	487.4	678.1
Level 3 Transfers Out of	-871.7	-997.3
End of Period	2,044.90	1,677.50
Equity Securites	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	4.6	4.3
Investment Gain (Loss) included in Earnings	2.1	0
Investment Gain (Loss) included in OCI	-0.1	0
Purchases	0	0
Sales	-3.5	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Period	3.1	4.3
Embedded Derivative in Modified Coinsurance Arrangement	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	'	'
Beginning of Period	-53.2	-83.9
Investment Gain (Loss) included in Earnings	8.5	6.4
Investment Gain (Loss) included in OCI	0	0
Purchases	0	0
Sales	0	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Period	($44.70)	($77.50)

Quantitative_Information_Regar

Quantitative Information Regarding Significant Unobservable Inputs (Details) (Fair Value, Inputs, Level 3, USD $)	3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Embedded Derivative in Modified Coinsurance Arrangement	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	-44.7		-53.2
Embedded Derivative in Modified Coinsurance Arrangement | Projected Cash Flows	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	'Actuarial Assumptions	[1]	'Actuarial Assumptions	[1]
States, Municipalities, and Political Subdivisions	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	122.1		142.7
States, Municipalities, and Political Subdivisions | Minimum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Comparability Adjustments	0.25%	[2]	0.25%	[2]
States, Municipalities, and Political Subdivisions | Maximum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Comparability Adjustments	1.25%	[2]	1.25%	[2]
States, Municipalities, and Political Subdivisions | Weighted Average	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Comparability Adjustments	0.74%	[2]	0.65%	[2]
Public Utilities	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	72.4		64.3
Public Utilities | Minimum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Volatility of Credit	0.75%	[3]	0.75%	[3]
Public Utilities | Maximum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Volatility of Credit	1.50%	[3]	1.25%	[3]
Public Utilities | Weighted Average	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Volatility of Credit	1.05%	[3]	0.92%	[3]
Mortgage/Asset-backed Securities	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	0.4		0.5
Mortgage/Asset-backed Securities | Minimum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Discount for Size	5.60%	[4]	4.93%	[4]
Mortgage/Asset-backed Securities | Maximum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Discount for Size	5.71%	[4]	5.03%	[4]
Mortgage/Asset-backed Securities | Weighted Average	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Discount for Size	5.68%	[4]	5.01%	[4]
All Other Corporate Bonds - Private	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	296.1		307
All Other Corporate Bonds - Private | Market Convention	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	'Priced at Par	[5]	'Priced at Par	[5]
All Other Corporate Bonds - Private | Minimum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Change in Benchmark Reference	0.54%	[6]	3.36%	[6]
Comparability Adjustments	-0.70%	[2]	-0.70%	[2]
Discount for Size	0.50%	[4]	0.50%	[4]
Lack of Marketability	0.20%	[7]	0.20%	[7]
Volatility of Credit	0.40%	[3]	0.07%	[3]
All Other Corporate Bonds - Private | Maximum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Change in Benchmark Reference	0.75%	[6]	3.36%	[6]
Comparability Adjustments	-0.40%	[2]	-0.40%	[2]
Discount for Size	0.50%	[4]	0.50%	[4]
Lack of Marketability	2.96%	[7]	1.00%	[7]
Volatility of Credit	4.00%	[3]	4.00%	[3]
All Other Corporate Bonds - Private | Weighted Average	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Change in Benchmark Reference	0.67%	[6]	3.36%	[6]
Comparability Adjustments	-0.60%	[2]	-0.60%	[2]
Discount for Size	0.50%	[4]	0.50%	[4]
Lack of Marketability	1.01%	[7]	0.55%	[7]
Volatility of Credit	0.85%	[3]	0.84%	[3]
Corporate Bond Securities - Public	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	344.7		514.4
Corporate Bond Securities - Public | Minimum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Change in Benchmark Reference	-0.85%	[6]	-0.32%	[6]
Comparability Adjustments	0.20%	[2]	-0.23%	[2]
Lack of Marketability	0.10%	[7]	0.20%	[7]
Volatility of Credit	-0.86%	[3]	-0.88%	[3]
Corporate Bond Securities - Public | Maximum	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Change in Benchmark Reference	-0.85%	[6]	0.25%	[6]
Comparability Adjustments	1.43%	[2]	1.00%	[2]
Lack of Marketability	0.25%	[7]	0.20%	[7]
Volatility of Credit	1.34%	[3]	0.46%	[3]
Corporate Bond Securities - Public | Weighted Average	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Change in Benchmark Reference	-0.85%	[6]	0.04%	[6]
Comparability Adjustments	0.60%	[2]	0.41%	[2]
Lack of Marketability	0.23%	[7]	0.20%	[7]
Volatility of Credit	-0.03%	[3]	-0.26%	[3]
Equity Securites	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs	2.8		4.2
Equity Securites | Market Convention	'		'
Quantitative Information Regarding Level 3 Inputs	'		'
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	'Priced at Cost or Owner's Equity	[5]	'Priced at Cost or Owner's Equity	[5]
[1]	Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates
[2]	Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors
[3]	Represents basis point adjustments for credit-specific factors
[4]	Represents basis point adjustments based on issue/issuer size relative to the benchmark
[5]	Represents a decision to price based on par value, cost, or owner's equity when limited data is available
[6]	Represents basis point adjustments for changes in benchmark spreads associated with various ratings categories
[7]	Represents basis point adjustments to apply a discount due to the illiquidity of an investment

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Carrying amount of policy loans	$3,268.30	'	$3,276
Long-term Debt	2,948.20	'	2,612
Gain on Embedded Derivative	8.5	6.4	'
Other Than Fair Value Inputs Level 1	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Percentage of Total Fair Value of Fixed Maturities Securities	89.00%	'	'
Fair Value, Inputs, Level 1	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Long-term Debt	1,429.80	'	1,329.20
Percentage of Total Fair Value of Fixed Maturities Securities	11.00%	'	'
Fair Value, Inputs, Level 2	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Long-term Debt	1,764.70	'	1,495.20
Fair Value, Inputs, Level 2 | Pricing Service	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Percentage of Total Fair Value of Fixed Maturities Securities	72.40%	'	'
Fair Value, Inputs, Level 2 | Other Observable Market Data	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Percentage of Total Fair Value of Fixed Maturities Securities	3.60%	'	'
Fair Value Inputs Level 2 Or Level 3	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Percentage of Total Fair Value of Fixed Maturities Securities	13.00%	'	'
Ceded Policy Loans	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Carrying amount of policy loans	$3,034.40	'	$3,043.70
Minimum	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Private Equity Partnership Future Liquidation Term	'1 year	'	'
Maximum	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis	'	'	'
Private Equity Partnership Future Liquidation Term	'10 years	'	'

Amortized_Cost_and_Fair_Values

Amortized Cost and Fair Values of Securities by Security Type (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	$38,516	$38,289.60
Gross Unrealized Gain	5,290.60	4,358.70
Gross Unrealized Loss	139.8	303.9
Fixed Maturity Securities	43,666.80	42,344.40
United States Government and Government Agencies and Authorities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	959.1	1,028.60
Gross Unrealized Gain	200.1	173.1
Gross Unrealized Loss	2.5	5.6
Fixed Maturity Securities	1,156.70	1,196.10
States, Municipalities, and Political Subdivisions	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	1,732.30	1,706
Gross Unrealized Gain	212.2	117.2
Gross Unrealized Loss	17.7	40
Fixed Maturity Securities	1,926.80	1,783.20
Foreign Governments	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	1,205.70	1,226.40
Gross Unrealized Gain	166.3	149.6
Gross Unrealized Loss	1	2.8
Fixed Maturity Securities	1,371	1,373.20
Public Utilities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	9,436.80	9,328.90
Gross Unrealized Gain	1,394.30	1,126.90
Gross Unrealized Loss	28	52.8
Fixed Maturity Securities	10,803.10	10,403
Mortgage/Asset-backed Securities	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	2,102.50	1,858.70
Gross Unrealized Gain	186.8	184.6
Gross Unrealized Loss	2.6	4
Fixed Maturity Securities	2,286.70	2,039.30
All Other Corporate Bonds	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	23,046.60	23,108
Gross Unrealized Gain	3,125.50	2,602.60
Gross Unrealized Loss	88	198.7
Fixed Maturity Securities	26,084.10	25,511.90
Redeemable Preferred Stocks	'	'
Schedule of Available-for-sale Securities	'	'
Available-for-sale Securities, Amortized Cost Basis	33	33
Gross Unrealized Gain	5.4	4.7
Gross Unrealized Loss	0	0
Fixed Maturity Securities	$38.40	$37.70

Length_of_Time_Fixed_Maturity_

Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position (Detail) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	$3,028.30	$5,164.70
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	104.3	264.1
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	370.4	311
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	35.5	39.8
United States Government and Government Agencies and Authorities	'	'
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	9.2	41.1
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	0.5	3.1
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	5.8	5.2
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	2	2.5
States, Municipalities, and Political Subdivisions	'	'
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	186.3	412.5
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	9.8	33.5
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	55.9	37.2
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	7.9	6.5
Foreign Governments	'	'
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	34.8	87.2
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	1	2.8
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	0	0
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	0	0
Public Utilities	'	'
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	628	870.6
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	24.2	47.1
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	49.2	58.7
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	3.8	5.7
Mortgage/Asset-backed Securities	'	'
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	261.4	341
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	2.2	3.6
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	2.4	2.5
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	0.4	0.4
All Other Corporate Bonds	'	'
Schedule of Available-for-sale Securities	'	'
Fair Value of Securities in Continuous Unrealized Loss Possition for Less Than 12 Months	1,908.60	3,412.30
Aggregate Loss Position of Securities in Unrealized Loss Position for Less Than 12 Months	66.6	174
Fair Value of Securities in Continuous Unrealized Loss Possition for Greater Than 12 Months	257.1	207.4
Aggregate Loss Position of Securities in Unrealized Loss Position for Greater Than 12 Months	$21.40	$24.70

Distribution_of_the_Maturity_D

Distribution of the Maturity Dates for Fixed Maturity Securities (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Available-for-Sale Securities, Total Amortized Cost	'	'
1 year or less	$841.90	$903.90
Over 1 year through 5 years	7,186.20	7,098.20
Over 5 years through 10 years	9,640	9,492.60
Over 10 years	18,745.40	18,936.20
Available-for-sale Securities, Debt Maturities, Gross Subtotal	36,413.50	36,430.90
Mortgage/Asset-Backed Securities	2,102.50	1,858.70
Total Fixed Maturity Securities	38,516	38,289.60
Fair Value Maturity Distribution	'	'
Total Fixed Maturity Securities	43,666.80	42,344.40
Fair Value of Fixed Maturity Securities in Unrealized Gain Position	'	'
Available-for-Sale Securities, Unrealized Gain Position, Gross Gain	'	'
1 year or less	21.5	20.6
Over 1 year through 5 years	769.6	727.1
Over 5 years through 10 years	1,030	940.2
Over 10 years	3,282.70	2,486.20
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Gain, Gross Subtotal	5,103.80	4,174.10
Mortgage/Asset-Backed Securities	186.8	184.6
Total Fixed Maturity Securities	5,290.60	4,358.70
Fair Value Maturity Distribution	'	'
1 year or less	854.4	915.5
Over 1 year through 5 years	7,908.90	7,678.50
Over 5 years through 10 years	9,239.50	8,137.40
Over 10 years	20,242.40	18,441.50
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal	38,245.20	35,172.90
Mortgage/Asset-Backed Securities	2,022.90	1,695.80
Total Fixed Maturity Securities	40,268.10	36,868.70
Fair Value of Fixed Maturity Securities in Unrealized Loss Position	'	'
Fair Value Maturity Distribution	'	'
1 year or less	9	9
Over 1 year through 5 years	46.6	146.2
Over 5 years through 10 years	1,389.30	2,199.60
Over 10 years	1,690	2,777.40
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal	3,134.90	5,132.20
Mortgage/Asset-Backed Securities	263.8	343.5
Total Fixed Maturity Securities	3,398.70	5,475.70
Available-for-Sale Securities, Unrealized Loss Position, Gross Loss	'	'
1 year or less	0	0
Over 1 year through 5 years	0.3	0.6
Over 5 years through 10 years	41.2	95.8
Over 10 years	95.7	203.5
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Loss, Gross Subtotal	137.2	299.9
Mortgage/Asset-Backed Securities	2.6	4
Total Fixed Maturity Securities	$139.80	$303.90

Mortgage_Loans_by_Property_Typ

Mortgage Loans by Property Type (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$1,843.30	$1,815.10
Percent of Total	100.00%	100.00%
Apartment	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	74.5	61.1
Percent of Total	4.00%	3.30%
Industrial	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	538	567.8
Percent of Total	29.20%	31.30%
Office	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	809.6	776.5
Percent of Total	43.90%	42.80%
Retail	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$421.20	$409.70
Percent of Total	22.90%	22.60%

Mortgage_Loans_by_Geographic_R

Mortgage Loans by Geographic Region (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$1,843.30	$1,815.10
Percent of Total	100.00%	100.00%
New England	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	122.5	100.9
Percent of Total	6.70%	5.60%
Mid-Atlantic	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	186.2	191.5
Percent of Total	10.10%	10.50%
East North Central	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	227.4	244.3
Percent of Total	12.30%	13.50%
West North Central	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	172.8	162.3
Percent of Total	9.40%	8.90%
South Atlantic	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	441.1	447.7
Percent of Total	23.90%	24.70%
East South Central	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	66.5	67.7
Percent of Total	3.60%	3.70%
West South Central	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	206.5	190.9
Percent of Total	11.20%	10.50%
Mountain	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	114.7	101.9
Percent of Total	6.20%	5.60%
Pacific	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$305.60	$307.90
Percent of Total	16.60%	17.00%

Mortgage_Loans_Sorted_by_Appli

Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Internal rating (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$1,843.30	$1,815.10
AA Credit Rating	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	10.6	10.8
A Credit Rating	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	666.8	683.1
Baa Credit Rating	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	1,121.30	1,094.60
Ba Credit Rating	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	13.4	13.5
B Credit Rating	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$31.20	$13.10

Mortgage_Loans_Sorted_by_Appli1

Mortgage Loans, Sorted by Applicable Credit Quality Indicators, Loan to Value Ratio (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$1,843.30	$1,815.10
Loan to Value Ratio Below or Equal to 65 Percent	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	815.3	777.4
Loan To Value Ratio Above 65 To 75 Percent	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	888.4	867.5
Loan To Value Ratio Above 75 To 85 Percent	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	95.1	107.6
Loan To Value Ratio Above 85 Percent	'	'
Mortgage Loans on Real Estate	'	'
Mortgage Loans	$44.50	$62.60

Activity_in_Allowance_for_Cred

Activity in Allowance for Credit Losses (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Disclosure Activity in Allowance for Credit Losses [Abstract]	'	'
Balance at Beginning of Year	$1.50	$1.50
Provisions	3	0
Balance at End of Period	$4.50	$1.50

Impaired_Mortgage_Loans_Detail

Impaired Mortgage Loans (Detail) (Impaired Fin Receivables with Allowance, USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Impaired Fin Receivables with Allowance	'	'
Recorded Investment	$31.20	$13.10
Unpaid Principal Balance	35.7	14.6
Related Allowance	$4.50	$1.50

Investments_Offsetting_for_Der

Investments Offsetting for Derivatives and Securities Lending Balances (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Offsetting Derivative Assets	'	'
Gross Derivative Assets	$10.90	$10.80
Derivative Assets, Gross Liability Offset	0	0
Derivative Assets, Amount Not Offset Against Collateral	10.9	10.8
Obligation to Return Securities on Derivative Assets	-7.9	-9.5
Obligation to Return Cash on Derivative Assets	-2.8	-1.1
Derivative Assets, Amount Offset Against Collateral	0.2	0.2
Offsetting Securities Borrowed	'	'
Gross Securities Borrowed	187.4	201.6
Securities Borrowed, Liability Offset	0	0
Securities Borrowed	187.4	201.6
Obligation to Return Securities on Securities Borrowed	-125.8	-125.1
Obligation to Return Cash on Securities Borrowed	-61.6	-76.5
Securities Borrowed, Amount Offset Against Collateral	0	0
Offsetting Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed	'	'
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Gross	198.3	212.4
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed, Liability	0	0
Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed	198.3	212.4
Derivative Assets and Securities Lending Assets, Obligation to Return Securities	-133.7	-134.6
Derivative Assets and Securities Lending Assets, Obligation to Return Cash	-64.4	-77.6
Derivative Assets and Securities Lending Assets, Amount Offset Against Collateral	0.2	0.2
Offsetting Derivative Liabilities	'	'
Gross Derivative Liabilities	117.7	135.6
Derivative Liabilities, Gross Asset Offset	0	0
Derivative Liabilities, Amount Not Offset Against Collateral	117.7	135.6
Right to Reclaim Securities on Derivative Liabilities	-84.1	-98.6
Right to Reclaim Cash on Derivative Liabilities	0	0
Derivative Liability, Amount Offset Against Collateral	33.6	37
Offsetting Securities Loaned	'	'
Gross Securities Loaned	61.6	76.5
Securities Loaned, Asset	0	0
Securities Loaned	61.6	76.5
Right to Reclaim Securities on Securities Loaned	-61.6	-76.5
Right to Reclaim Cash on Securities Loaned	0	0
Securities Loaned, Amount Offset Against Collateral	0	0
Derivative Liabilities and Securities Lending Liabilities	'	'
Derivative Liability and Securities Lending Liabilities, Gross	179.3	212.1
Derivative Liability and Securities Lending Liabilities, Asset Offset	0	0
Derivative Liability and Securities Lending Liabilities, Securities Loaned	179.3	212.1
Derivative Liability and Securities Lending Liabilities, Right to Reclaim Securities	-145.7	-175.1
Derivative Liability and Securities Lending Liabilities, Right to Reclaim Cash	0	0
Derivative Liability and Securities Lending Liabilities, Amount Offset Against Collateral	$33.60	$37

Investments_Investment_Income_

Investments Investment Income (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	$627.60	$635.80
Less Investment Expenses	8	7.1
Less Investment Income on PFA Assets	3.8	4
Less Amortization of Tax Credit Partnerships	3.3	3.6
Net Investment Income	612.5	621.1
Fixed Income Securities	'	'
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	581.1	589.9
Derivative	'	'
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	9.9	7.7
Mortgage Receivable	'	'
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	28.4	26
Policy Loans	'	'
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	3.9	3.7
Other Long-term Investments	'	'
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	3.8	7.7
Short-term Investments	'	'
Schedule of Investment Income, Reported Amounts, by Category	'	'
Investment Income, Interest and Dividend	$0.50	$0.80

Realized_Investment_Gains_and_

Realized Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fixed Maturity Securities	'	'
Gross Gains on Sales	$0.90	$6.60
Gross Losses on Sales	-5.4	-5.5
Other-Than-Temporary Impairment Loss	0	-0.8
Mortgage Loans and Other Invested Assets	'	'
Gross Gains on Sales	7.4	7.6
Other Investments Gross Realized Losses	-0.6	0
Impairment Loss	-3	-1
Gain on Embedded Derivative	8.5	6.4
Derivative, Gain (Loss) on Derivative, Net	-0.4	-0.3
Foreign Currency Transactions	-1.1	-2.7
Net Realized Investment Gain	$6.30	$10.30

Investments_Additional_Informa

Investments - Additional Information (Detail) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Schedule of Investments	'	'	'
Fair value of fixed maturity securities	$43,666,800,000	'	$42,344,400,000
Fair value of fixed maturity securities, gross unrealized gain	5,290,600,000	'	4,358,700,000
Fair Value of fixed maturity securities, gross unrealized loss	139,800,000	'	303,900,000
Fixed Maturity Securities Other Than Temporary Impairments in Accumulated Other Comprehensive Income Loss	0	'	0
Commitment to fund private placement fixed maturity securities	60,000,000	'	'
Carrying amount of variable interest entity investments	473,000,000	'	'
Unfunded commitment to fund Investment Partnerships	17,900,000	'	'
Commitment to fund partnership Equity Investments	144,700,000	'	'
Other Long-term Investments	565,000,000	'	566,000,000
Commitments to Fund Special Purpose Entities	0	'	'
Amount Funded to Special Purpose Entity Partnerships	'nor did we fund any amounts to the partnerships	'nor did we fund any amounts to the partnerships	'
Mortgage Loan policy is not to exceed a loan-to-value ratio, percent	75.00%	'	'
Loan to Value Ratio Update Frequency	'3 years	'	'
Mortgage Loan Inspection Frequency	'2 years	'	'
Mortage Loan Policy Debt Service coverage ratio lower range	125.00%	'	'
Mortgage Loans issuance, term years	25	'	'
Number of Changes to Accounting Policy for Estimating Credit Losses on Mortgage Loans	0	0	'
Number of Troubled Debt Restructurings During Period	1	'	'
Pre-Modification Recorded Investment in Troubled Debt Restructuring	21,100,000	'	'
Impaired Financing Receivable, Related Allowance	3,000,000	'	'
Financing Receivable, Recorded Investment, Nonaccrual status	0	'	0
Average Recorded Investment in Impaired Financing Receivable	19,100,000	17,400,000	'
Interest Income on Impaired Financing Receivable, Accrual Method	300,000	200,000	'
Committments to Fund Commercial Mortgage Loans	21,700,000	'	'
Repurchase agreements - Typical Days outstanding	'30	'	'
Minimum percent of the fair value of securities loaned or securities purchased under repurchase agreements be maintained as collateral	102.00%	'	'
Fixed Maturity Securities Loaned to Third Parties	187,400,000	'	201,600,000
Collateral Received in Form of Cash	61,600,000	'	76,500,000
Securities Received as Collateral	132,500,000	'	132,900,000
Outstanding Repurchase Agreements	0	'	0
Nonperforming Financing Receivable	'	'	'
Schedule of Investments	'	'	'
Amount of days past due-DelinquentMortgageLoan	'90 days	'	'
Special Purpose Entity | Bonds	'	'	'
Schedule of Investments	'	'	'
Fair value of fixed maturity securities	138,100,000	'	'
Special Purpose Entity | Partnership Interest	'	'	'
Schedule of Investments	'	'	'
Other Long-term Investments	4,400,000	'	'
Partnership Interests In Tax Credit Investments	'	'	'
Schedule of Investments	'	'	'
Carrying amount of variable interest entity investments	304,800,000	'	'
Equity Method Investments	'	'	'
Schedule of Investments	'	'	'
Carrying amount of variable interest entity investments	168,200,000	'	'
External Credit Rating, Investment Grade	'	'	'
Schedule of Investments	'	'	'
Fair value of fixed maturity securities	40,372,300,000	'	'
Fair value of fixed maturity securities, gross unrealized gain	5,104,700,000	'	'
Fair Value of fixed maturity securities, gross unrealized loss	113,500,000	'	'
Fixed maturity securities in unrealized loss position, percent of total	81.20%	'	'
Number of fixed maturity securities that were in an unrealized loss position	148	'	'
Number of fixed maturity securities in an unrealized loss position continuously for over one year	16	'	'
External Credit Rating, Non Investment Grade	'	'	'
Schedule of Investments	'	'	'
Fair value of fixed maturity securities	3,294,500,000	'	'
Fair value of fixed maturity securities, gross unrealized gain	185,900,000	'	'
Fair Value of fixed maturity securities, gross unrealized loss	$26,300,000	'	'
Fixed maturity securities in unrealized loss position, percent of total	18.80%	'	'
Number of fixed maturity securities that were in an unrealized loss position	38	'	'
Number of fixed maturity securities in an unrealized loss position continuously for over one year	10	'	'

Notional_Amounts_for_Each_Cate

Notional Amounts for Each Category of Derivative Activity (Detail) (USD $)	3 Months Ended				3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
			Credit Default Swaps	Credit Default Swaps	Swaps	Swaps	Swaps	Swaps	Swaps	Swaps	Swaps	Swaps	Forwards	Forwards
					Receive Variable/Pay Fixed	Receive Variable/Pay Fixed	Receive Fixed/Pay Fixed	Receive Fixed/Pay Fixed	Receive Fixed/Pay Variable	Receive Fixed/Pay Variable	Credit Default Swaps	Credit Default Swaps
Derivative	'	'	'	'	'	'	'	'	'	'	'	'	'	'
Balance at beginning of period	$1,477.40	$1,432.80	$97	$97	$150	$174	$630.40	$508.80	$600	$750	$97	$0	$0	$0
Additions	10	94	'	'	0	0	0	0	0	0	0	70	10	24
Terminations	17.9	82	'	'	0	0	7.9	18	0	40	0	0	10	24
Balance at ending of period	$1,469.50	$1,444.80	$97	$97	$150	$174	$622.50	$490.80	$600	$710	$97	$70	$0	$0

Location_and_Fair_Values_of_De

Location and Fair Values of Derivative Financial Instruments (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative	'	'
Asset Derivatives Fair Value	$10.90	$10.80
Liability Derivatives Fair Value	117.7	135.6
Designated as Hedging Instrument | Other Long-term Investments	'	'
Derivative	'	'
Asset Derivatives Fair Value	10.9	10.8
Designated as Hedging Instrument | Other Liability	'	'
Derivative	'	'
Liability Derivatives Fair Value	115.7	133.7
Designated as Hedging Instrument | Interest Rate Swaps | Other Long-term Investments	'	'
Derivative	'	'
Asset Derivatives Fair Value	8.1	9.2
Designated as Hedging Instrument | Interest Rate Swaps | Other Liability	'	'
Derivative	'	'
Liability Derivatives Fair Value	30.9	35
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Long-term Investments	'	'
Derivative	'	'
Asset Derivatives Fair Value	2.8	1.6
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liability	'	'
Derivative	'	'
Liability Derivatives Fair Value	84.8	98.7
Not Designated as Hedging Instrument | Other Liability	'	'
Derivative	'	'
Liability Derivatives Fair Value	46.7	55.1
Not Designated as Hedging Instrument | Credit Default Swaps | Other Liability	'	'
Derivative	'	'
Liability Derivatives Fair Value	2	1.9
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement | Other Liability	'	'
Derivative	'	'
Liability Derivatives Fair Value	$44.70	$53.20

Location_of_Gains_and_Losses_o

Location of Gains and Losses on Derivative Financial Instruments Designated as Cash Flow Hedging Instruments (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$12.90	$1.90
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	10.6	1.2
Interest Rate Swaps	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	0	-2.2
Interest Rate Swaps | Net Investment Income	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	11.7	10
Interest Rate Swaps | Net Realized Investments Gain (Loss)	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	2.5	0
Interest Rate Swaps | Interest and Debt Expense	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	-0.4	-0.4
Foreign Exchange Contracts	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	12.9	4.1
Foreign Exchange Contracts | Net Investment Income	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	-1.1	-1.7
Foreign Exchange Contracts | Net Realized Investments Gain (Loss)	'	'
Derivative Instruments, Gain (Loss)	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	($2.10)	($6.70)

Location_of_and_Gain_Loss_on_D

Location of and Gain (Loss) on Derivative Financial Instruments Not Designated as Hedging Instruments (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net Realized Investment Gain (Loss)	'	'
Credit Default Swap Loss	($0.40)	($0.30)
Gain on Embedded Derivative	8.5	6.4
Gains (Losses) on Derivatives Not Designated as Hedging Instruments	$8.10	$6.10

Derivative_Financial_Instrumen2

Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Derivative	'	'	'	'
Credit Exposure on Derivatives	$0.20	'	'	'
Cash collateral from counterparties	2.8	'	1.1	'
Carrying value of fixed maturity securities posted as collateral to our counterparties	80.4	'	95.6	'
Cash Collateral to counterparties	0	'	0	'
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	117.7	'	135.6	'
Derivative, Notional Amount	1,469.50	1,444.80	1,477.40	1,432.80
Material Ineffectiveness on Cash Flow Hedges	0	0	'	'
Gain from Components Excluded from Assessment of Cash Flow Hedge Effectiveness	0	0	'	'
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	47.3	'	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	10.6	1.2	'	'
Material Ineffectiveness on Fair Value Hedges	0	0	'	'
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	'	'
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as FV Hedge	0	0	'	'
Subsequent Event	'	'	'	'
Derivative	'	'	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	13	'	'	'
Foreign Currency Swap | Cash Flow Hedge	'	'	'	'
Derivative	'	'	'	'
Derivative, Notional Amount	622.5	'	630.4	'
Receive Variable/Pay Fixed | Interest Rate Swaps	'	'	'	'
Derivative	'	'	'	'
Derivative, Notional Amount	150	'	150	'
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	-1.4	-2.4	'	'
Receive Fixed/Pay Variable | Interest Rate Swaps	'	'	'	'
Derivative	'	'	'	'
Derivative, Notional Amount	600	'	600	'
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	-1.6	4.1	'	'
Credit Default Swaps	'	'	'	'
Derivative	'	'	'	'
Derivative, Notional Amount	$97	'	$97	'

Schedule_of_Accumulated_Other_

Schedule of Accumulated Other Comprehensive Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income	'	'
Balance, Beginning of Period	$255	$628
After Tax Other Comprehensive Income Before Reclassifications	203.1	-142.7
Reclassifications from Accumulated Other Comprehensive Income, Net of Tax	-3.7	0.4
Net Other Comprehensive Income (Loss)	199.4	-142.3
Balance, End of Period	454.4	485.7
Net Unrealized Gain on Securities	'	'
Accumulated Other Comprehensive Income	'	'
Balance, Beginning of Period	135.7	873.5
After Tax Other Comprehensive Income Before Reclassifications	187.2	-73.3
Reclassifications from Accumulated Other Comprehensive Income, Net of Tax	2.4	-7.8
Net Other Comprehensive Income (Loss)	189.6	-81.1
Balance, End of Period	325.3	792.4
Net Gain on Cash Flow Hedges	'	'
Accumulated Other Comprehensive Income	'	'
Balance, Beginning of Period	396.3	401.6
After Tax Other Comprehensive Income Before Reclassifications	8.5	-1.2
Reclassifications from Accumulated Other Comprehensive Income, Net of Tax	-6.8	-0.8
Net Other Comprehensive Income (Loss)	1.7	-2
Balance, End of Period	398	399.6
Foreign Currency Translation Adjustment	'	'
Accumulated Other Comprehensive Income	'	'
Balance, Beginning of Period	-47.1	-72.6
After Tax Other Comprehensive Income Before Reclassifications	7.6	-69.9
Reclassifications from Accumulated Other Comprehensive Income, Net of Tax	0	0
Net Other Comprehensive Income (Loss)	7.6	-69.9
Balance, End of Period	-39.5	-142.5
Unrecognized Pension and Postretirement Benefit Costs	'	'
Accumulated Other Comprehensive Income	'	'
Balance, Beginning of Period	-229.9	-574.5
After Tax Other Comprehensive Income Before Reclassifications	-0.2	1.7
Reclassifications from Accumulated Other Comprehensive Income, Net of Tax	0.7	9
Net Other Comprehensive Income (Loss)	0.5	10.7
Balance, End of Period	($229.40)	($563.80)

Schedule_of_Components_of_Unre

Schedule of Components of Unrealized Gain (Loss) on Securities (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Change in Components of Net Unrealized Gain on Securities	'	'
Change in Net Unrealized Gain (Loss) on Securities	$710	($278.50)
Fixed Maturity Securities	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	4,054.80	7,221.50
Change in Net Unrealized Gain (Loss) on Securities	1,096	-417.6
End of Period Balance	5,150.80	6,803.90
Other Investments	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	55.5	92.8
Change in Net Unrealized Gain (Loss) on Securities	-14.9	-20.3
End of Period Balance	40.6	72.5
Deferred Acquisition Costs	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	-41.6	-67
Change in Net Unrealized Gain (Loss) on Securities	-7.3	5.8
End of Period Balance	-48.9	-61.2
Reserve for Future Policy and Contract Benefits	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	-4,108.50	-6,277.50
Change in Net Unrealized Gain (Loss) on Securities	-831.2	297.8
End of Period Balance	-4,939.70	-5,979.70
Reinsurance Recoverable	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	263.8	351.5
Change in Net Unrealized Gain (Loss) on Securities	46.1	2.4
End of Period Balance	309.9	353.9
Deferred Income Tax Charges	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	-88.3	-447.8
Change in Net Unrealized Gain (Loss) on Securities	-99.1	50.8
End of Period Balance	-187.4	-397
Net Unrealized Gain on Securities	'	'
Change in Components of Net Unrealized Gain on Securities	'	'
Beginning of Period Balance	135.7	873.5
Change in Net Unrealized Gain (Loss) on Securities	189.6	-81.1
End of Period Balance	$325.30	$792.40

Schedule_of_Reclassifications_

Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net Unrealized Gain on Securities	'	'
Before Tax Reclassification from AOCI for Sales of Securities	($3.70)	$11.90
After Tax Reclassifications from AOCI for Sales of Securities	-2.4	7.8
Net Gain on Cash Flow Hedges	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	10.6	1.2
After Tax Reclassification from AOCI on Derivatives Instruments	6.8	0.8
Unrecognized Pension and Postretirement Benefit Costs	'	'
Before Tax Pension Plan Reclassification from AOCI	-1	-13.7
After Tax Pension Plan Reclassification from AOCI	-0.7	-9
Net Realized Investments Gain Loss	'	'
Net Unrealized Gain on Securities	'	'
Before Tax Reclassification from AOCI for Sales of Securities	-3.7	12.7
Before Tax Reclassification from AOCI for Write-down of Securities	0	-0.8
Net Realized Investments Gain Loss | Interest Rate Swaps	'	'
Net Gain on Cash Flow Hedges	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	2.5	0
Net Realized Investments Gain Loss | Foreign Exchange Contracts	'	'
Net Gain on Cash Flow Hedges	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	-2.1	-6.7
Net Investment Income | Interest Rate Swaps	'	'
Net Gain on Cash Flow Hedges	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	11.7	10
Net Investment Income | Foreign Exchange Contracts	'	'
Net Gain on Cash Flow Hedges	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	-1.1	-1.7
Interest and Debt Expense | Interest Rate Swaps	'	'
Net Gain on Cash Flow Hedges	'	'
Before Tax Reclassification from AOCI on Derivatives Instruments	-0.4	-0.4
Other Expense	'	'
Unrecognized Pension and Postretirement Benefit Costs	'	'
Before Tax Reclassification from AOCI for Pension Net Actuarial Loss	-1.4	-14.9
Before Tax Reclassification from AOCI for Pension Prior Service Credit	0.4	1.2
Income Tax Expense	'	'
Net Unrealized Gain on Securities	'	'
Income Tax on Reclassifications from AOCI for Sales of Securities	-1.3	4.1
Net Gain on Cash Flow Hedges	'	'
Income Tax on Reclassification from AOCI on Derivatives Instruments	3.8	0.4
Unrecognized Pension and Postretirement Benefit Costs	'	'
Income Tax on Pension Plan Reclassification from AOCI	($0.30)	($4.70)

Premium_Income_by_Major_Line_o

Premium Income by Major Line of Business within Each Segment (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]	'	'
Premium Income	$1,938.50	$1,930.90
Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	1,152.50	1,139.70
Unum U.K.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	151.7	143.8
Colonial Life	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	316.4	307.1
Closed Block	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	317.9	340.3
Group Long term Disability | Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	383.5	392.7
Group Long term Disability | Unum U.K.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	103	97.9
Group Short term Disability | Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	137.3	131
Group Life | Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	309.9	302.2
Group Life | Unum U.K.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	34.8	31
Accidental Death Dismemberment | Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	30.6	30.9
Individual Disability Recently Issued | Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	115.9	120.1
Voluntary Benefits | Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	175.3	162.8
Supplemental and Voluntary Insurance | Unum U.K.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	13.9	14.9
Accident and Health Insurance Segment | Colonial Life	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	189.1	184.8
Life Insurance Product Line | Colonial Life	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	57.4	54.8
Cancer and Critical Illness Colonial | Colonial Life	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	69.9	67.5
Individual Disability Insurance | Closed Block	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	161.1	181.8
Long-term Care | Closed Block	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	156.5	158.8
Other Insurance Product Line | Closed Block	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	$0.30	($0.30)

Selected_Operating_Statement_D

Selected Operating Statement Data by Segment (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting Information [Line Items]	'	'
Premium Income	$1,938.50	$1,930.90
Net Investment Income	612.5	621.1
Other Income	53.8	62.5
Operating Revenue	2,604.80	2,614.50
Operating Income (Loss)	321.6	308.4
Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	1,152.50	1,139.70
Net Investment Income	226.4	235.7
Other Income	30.9	36.7
Operating Revenue	1,409.80	1,412.10
Operating Income (Loss)	210.8	208.1
Unum U.K.	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	151.7	143.8
Net Investment Income	33.6	30.8
Other Income	-0.1	0.1
Operating Revenue	185.2	174.7
Operating Income (Loss)	36.5	31.3
Colonial Life	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	316.4	307.1
Net Investment Income	36.9	39.7
Other Income	-0.1	0
Operating Revenue	353.2	346.8
Operating Income (Loss)	79.4	75.4
Closed Block	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	317.9	340.3
Net Investment Income	316.3	313.1
Other Income	21.6	24.1
Operating Revenue	655.8	677.5
Operating Income (Loss)	29.1	27.3
Corporate	'	'
Segment Reporting Information [Line Items]	'	'
Premium Income	0	0
Net Investment Income	-0.7	1.8
Other Income	1.5	1.6
Operating Revenue	0.8	3.4
Operating Income (Loss)	($34.20)	($33.70)

Reconciliation_of_Operating_Re

Reconciliation of Operating Revenue and Operating Income by Segment to Revenue and Income Before Tax (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Segment Reporting [Abstract]	'	'
Operating Revenue	$2,604.80	$2,614.50
Net Realized Investment Gain	6.3	10.3
Total Revenue	2,611.10	2,624.80
Operating Income	321.6	308.4
Net Realized Investment Gain	6.3	10.3
Non-operating Retirement-related Loss	-1.4	-14.9
Income Before Income Tax	$326.50	$303.80

Assets_by_Segment_Detail

Assets by Segment (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Segment Reporting Information [Line Items]	'	'
Assets	$61,078.60	$59,403.60
Unum U.S.	'	'
Segment Reporting Information [Line Items]	'	'
Assets	18,517.90	18,384.30
Unum U.K.	'	'
Segment Reporting Information [Line Items]	'	'
Assets	3,793.40	3,654.10
Colonial Life	'	'
Segment Reporting Information [Line Items]	'	'
Assets	3,542.50	3,482.90
Closed Block	'	'
Segment Reporting Information [Line Items]	'	'
Assets	32,397.30	31,564.20
Corporate	'	'
Segment Reporting Information [Line Items]	'	'
Assets	$2,827.50	$2,318.10

Segment_Information_Segments_A

Segment Information Segments - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Number of Operating Segments	3

Employee_Benefit_Plans_Net_Per

Employee Benefit Plans Net Periodic Benefit Cost (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
U.S. Plans	'	'
Defined Benefit Plan and Other Postretirement Benefit Plans Disclosure	'	'
Service Cost	$0.90	$14.90
Interest Cost	22.5	21.9
Expected Return on Plan Assets	-29.5	-25.5
Amortization of Net Actuarial Loss	1.3	14.6
Prior Service Credit	0	0
Net Periodic Benefit Cost	-4.8	25.9
U.K. Plans	'	'
Defined Benefit Plan and Other Postretirement Benefit Plans Disclosure	'	'
Service Cost	1.1	1.1
Interest Cost	2.3	2.1
Expected Return on Plan Assets	-3.4	-3
Amortization of Net Actuarial Loss	0.1	0.3
Prior Service Credit	0	0
Net Periodic Benefit Cost	0.1	0.5
OPEB Plan	'	'
Defined Benefit Plan and Other Postretirement Benefit Plans Disclosure	'	'
Service Cost	0.1	0.2
Interest Cost	2	2
Expected Return on Plan Assets	-0.2	-0.2
Amortization of Net Actuarial Loss	0	0
Prior Service Credit	-0.4	-1.2
Net Periodic Benefit Cost	$1.50	$0.80

Net_Income_Per_Common_Share_De

Net Income Per Common Share (Detail) (USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Numerator	'	'
Net Income	$228.90	$212.60
Denominator (000s)	'	'
Weighted Average Number of Shares Outstanding, Basic	259,408,500	269,361,100
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	1,301,400	993,300
Weighted Average Number of Shares Outstanding, Diluted	260,709,900	270,354,400
Net Income Per Common Share	'	'
Basic	$0.88	$0.79
Assuming Dilution	$0.88	$0.79

Stockholders_Equity_and_Earnin2

Stockholders' Equity and Earnings Per Common Share Authorized Share Repurchase Programs (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014
Repurchase Program Authorized in July 2012	'
Authorized Common Stock Repurchase Programs	'
Stock Repurchase Program, Authorized Amount	$750
Stock Repurchase Program, Remaining Authorized Repurchase Amount	0
Repurchase Program Authorized in December 2013	'
Authorized Common Stock Repurchase Programs	'
Stock Repurchase Program, Authorized Amount	750
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$629.90

Stockholders_Equity_and_Earnin3

Stockholders' Equity and Earnings Per Common Share Share Repurchases (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Repurchases of Common Shares [Abstract]	'	'
Number of Shares Repurchased	2.9	3.7
Cost of Shares Repurchased	$100.10	$95.10

Stockholders_Equity_and_Earnin4

Stockholders' Equity and Earnings Per Common Share - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Stockholders Equity and Earnings Per Common Share Additional Information [Abstract]	'	'
Exercise Price Floor on Outstanding Stock Options	$11.37	'
Exercise Price Ceiling on Outstanding Stock Options	$26.29	'
Outstanding Restricted Stock Unit Grant Prices Lower Limit	$19.38	'
Outstanding Restricted Stock Unit Grant Prices Upper Limit	$34.73	'
Outstanding Performance Share Unit Awards Grant Price Range Lower Limit	$23.97	'
Outstanding Performance Share Unit Awards Grant Price Range Upper Limit	$33.86	'
Number of Antidilutive Securities Excluded from Computation of Earnings Per Share	'	400,000
Authorized Shares of Preferred Stock	25,000,000	'
Par Value Per Share of Preferred Stock	$0.10	'
Issued Shares of Preferred Stock	0	'

Commitments_and_Contingent_Lia1

Commitments and Contingent Liabilities - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014
Commitments and Contingent Liabilities Additional Information [Abstract]	'
Interest on undrawn retained asset account funds	18.00%
Loss Contingency, Damages Awarded, Value	$12.10
Loss Contingency, Prejudgment Interest Awarded	$1.30

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Debt Narrative Detail Information	'	'
Amount Outstanding on Revolving Credit Facility	$0	'
Gross Proceeds from Issuance of Long-term Debt	350	'
Repayments of Long-term Debt	15	71.2
Northwind Holdings LLC	'	'
Debt Narrative Detail Information	'	'
Periodic Principal Payments on Long-term Debt	15	'
Tailwind Holdings LLC	'	'
Debt Narrative Detail Information	'	'
Repayments of Long-term Debt	'	62.5
Gain on Extinguishment of Debt	'	4
Debt Issued in the First Quarter of 2014	'	'
Debt Narrative Detail Information	'	'
Interest Rate on Debt	4.00%	'
Subsequent Event	'	'
Debt Narrative Detail Information	'	'
Repayments of Long-term Debt	$145	'
Debt to be Redeemed in the Second Quarter of 2014	'	'
Debt Narrative Detail Information	'	'
Interest Rate on Debt	6.85%	'