Unum (UNM) 10-K 22 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Feb. 21, 2017	Jun. 30, 2016
Document Document and Entity Information [Abstract]
Entity Registrant Name	Unum Group
Trading Symbol	UNM
Entity Central Index Key	5,513
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		229,229,236
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 7.5

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments
Fixed Maturity Securities - at fair value (amortized cost: $39,552.7; $39,658.7)	$ 44,217.3	$ 43,354.4
Mortgage Loans	2,038.9	1,883.6
Policy Loans	3,463.2	3,395.4
Other Long-term Investments	631.5	583
Short-term Investments	780	807.3
Total Investments	51,130.9	50,023.7
Other Assets
Cash and Bank Deposits	100.4	112.9
Accounts and Premiums Receivable	1,610.8	1,598.4
Reinsurance Recoverable	4,858.9	4,725.1
Accrued Investment Income	693.3	702.8
Deferred Acquisition Costs	2,094.2	2,008.5
Goodwill	335.1	230.9
Property and Equipment	500.6	523.9
Other Assets	617.3	637.4
Total Assets	61,941.5	60,563.6
Liabilities
Policy and Contract Benefits	1,507.9	1,484.6
Reserves for Future Policy and Contract Benefits	44,245.9	43,540.6
Unearned Premiums	363.7	384.2
Other Policyholders' Funds	1,623.8	1,674.6
Income Tax Payable	20.6	6
Deferred Income Tax	130.3	91.8
Short-term Debt	0	352
Long-term Debt	2,999.4	2,449.4
Payables for Collateral on Investments	406	415.4
Other Liabilities	1,675.9	1,501.1
Total Liabilities	52,973.5	51,899.7
Commitments and Contingent Liabilities - Note 14
Stockholders' Equity
Common Stock, $0.10 par; authorized: 725,000,000 shares; issued: 303,552,934 and 302,702,811 shares	30.4	30.3
Additional Paid-in Capital	2,272.8	2,247.2
Accumulated Other Comprehensive Income	(51)	16.1
Retained Earnings	8,744	7,995.2
Treasury Stock - at cost: 73,729,992 and 61,785,466 shares	(2,028.2)	(1,624.9)
Total Stockholders' Equity	8,968	8,663.9
Total Liabilities and Stockholders' Equity	$ 61,941.5	$ 60,563.6

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Investments
Amortized Cost of Fixed Maturity Securities	$ 39,552.7	$ 39,658.7
Stockholders' Equity
Common Stock, Par	$ 0.10	$ 0.10
Common Stock, Authorized	725,000,000	725,000,000
Common Stock, Issued	303,552,934	302,702,811
Treasury Stock, Shares	73,729,992	61,785,466

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue
Premium Income	$ 8,357.7	$ 8,082.4	$ 7,797.2
Net Investment Income	2,459	2,481.2	2,492.2
Realized Investment Gain (Loss)
Other-Than-Temporary Impairment Loss on Fixed Maturity Securities	(30.5)	(32.4)	(13.5)
Other Net Realized Investment Gain (Loss)	54.7	(11.4)	29.6
Net Realized Investment Gain (Loss)	24.2	(43.8)	16.1
Other Income	205.6	211.5	219
Total Revenue	11,046.5	10,731.3	10,524.5
Benefits and Expenses
Benefits and Change in Reserves for Future Benefits	6,941.8	6,782.8	7,310.8
Commissions	1,026.7	996.3	935.3
Interest and Debt Expense	166	152.8	167.5
Deferral of Acquisition Costs	(592.4)	(569.7)	(524)
Amortization of Deferred Acquisition Costs	493	482.3	440.8
Compensation Expense	832.1	835.1	820.9
Other Expenses	831.6	813.4	831.2
Total Benefits and Expenses	9,698.8	9,493	9,982.5
Income Before Income Tax	1,347.7	1,238.3	542
Income Tax
Current	385.7	342.1	135.5
Deferred	30.6	29.1	4.4
Total Income Tax	416.3	371.2	139.9
Net Income	$ 931.4	$ 867.1	$ 402.1
Net Income Per Common Share
Basic	$ 3.96	$ 3.51	$ 1.57
Assuming Dilution	$ 3.95	$ 3.50	$ 1.57

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 931.4	$ 867.1	$ 402.1
Other Comprehensive Income (Loss)
Change in Net Unrealized Gain on Securities Before Adjustment (net of tax expense (benefit) of $318.0; $(892.5); $725.8)	661.9	(1,720.9)	1,439.3
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance (net of tax expense (benefit) of $(200.6); $856.6; $(665.1))	(425.6)	1,634.9	(1,284.7)
Change in Net Gain on Cash Flow Hedges (net of tax benefit of $25.4; $4.3; $2.0)	(50.5)	(13)	(5.3)
Change in Foreign Currency Translation Adjustment (net of tax benefit of $-; $0.1; $-)	(180.4)	(60.2)	(66.3)
Change in Unrecognized Pension and Postretirement Benefit Costs (net of tax expense (benefit) of $(34.2); $3.2; $(92.4))	(72.5)	8.9	(171.6)
Total Other Comprehensive Loss	(67.1)	(150.3)	(88.6)
Comprehensive Income	$ 864.3	$ 716.8	$ 313.5

CONSOLIDATED STATEMENTS OF COM6

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Change in Net Unrealized Gain on Securities Before Adjustment, Tax Expense (Benefit)	$ 318	$ (892.5)	$ 725.8
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense (Benefit)	(200.6)	856.6	(665.1)
Change in Net Gain on Cash Flow Hedges, Tax Benefit	25.4	4.3	2
Change in Foreign Currency Translation Adjustment, Tax Benefit	0	0.1	0
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense (Benefit)	$ (34.2)	$ 3.2	$ (92.4)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total		Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock
Balance at Beginning of Year at Dec. 31, 2013			$ 36.1	$ 2,634.1	$ 255	$ 8,064	$ (2,349.3)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			0.1	28.4
Retirement of Treasury Stock	$ (1,451.7)		(6)	(441.3)		(1,004.4)
Other Comprehensive Loss	(88.6)				(88.6)
Net Income	402.1					402.1
Dividends to Stockholders (per common share: $0.77; $0.70; $0.62)						(159.4)
Purchases of Treasury Stock	(300.6)	[1]					(300.6)
Retirement of Stock from Treasury							1,451.7
Balance at End of Year at Dec. 31, 2014	8,521.9		30.2	2,221.2	166.4	7,302.3	(1,198.2)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			0.1	26
Retirement of Treasury Stock			0	0		0
Other Comprehensive Loss	(150.3)				(150.3)
Net Income	867.1					867.1
Dividends to Stockholders (per common share: $0.77; $0.70; $0.62)						(174.2)
Purchases of Treasury Stock	(426.7)	[1]					(426.7)
Retirement of Stock from Treasury							0
Balance at End of Year at Dec. 31, 2015	8,663.9		30.3	2,247.2	16.1	7,995.2	(1,624.9)
Increase (Decrease) in Stockholders' Equity
Common Stock Activity			0.1	25.6
Retirement of Treasury Stock			0	0		0
Other Comprehensive Loss	(67.1)				(67.1)
Net Income	931.4					931.4
Dividends to Stockholders (per common share: $0.77; $0.70; $0.62)						(182.6)
Purchases of Treasury Stock	(403.3)	[1]					(403.3)
Retirement of Stock from Treasury							0
Balance at End of Year at Dec. 31, 2016	$ 8,968		$ 30.4	$ 2,272.8	$ (51)	$ 8,744	$ (2,028.2)
[1]	Includes commissions of $0.2 million, $0.3 million, and $0.1 million for the years ended December 31, 2016, 2015, and 2014, respectively.

CONSOLIDATED STATEMENTS OF STO8

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retained Earnings
Dividends to Stockholders (per common share: $0.77; $0.70; $0.62)	$ 0.77	$ 0.70	$ 0.62

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash Flows from Operating Activities
Net Income	$ 931.4	$ 867.1	$ 402.1
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Change in Receivables	(167.3)	29.3	(21.5)
Change in Deferred Acquisition Costs	(99.4)	(87.4)	(83.2)
Change in Insurance Reserves and Liabilities	368.2	293.9	972.2
Change in Income Taxes	34.7	180.5	(18.6)
Change in Other Accrued Liabilities	125.8	20	105.2
Non-cash Components of Net Investment Income	(187.7)	(194.1)	(195.7)
Net Realized Investment (Gain) Loss	(24.2)	43.8	(16.1)
Depreciation	101.7	99.5	87.9
Other, Net	32.9	39.5	(8.7)
Net Cash Provided by Operating Activities	1,116.1	1,292.1	1,223.6
Cash Flows from Investing Activities
Proceeds from Sales of Fixed Maturity Securities	911.5	880.1	450.1
Proceeds from Maturities of Fixed Maturity Securities	2,197.8	2,417	1,819.4
Proceeds from Sales and Maturities of Other Investments	336.8	347	235
Purchase of Fixed Maturity Securities	(3,362.8)	(4,305.3)	(2,918.4)
Purchase of Other Investments	(576)	(409.5)	(285.2)
Net Sales (Purchases) of Short-term Investments	6.3	170.6	(69.3)
Net Increase (Decrease) in Payables for Collateral on Investments	(9.4)	341.6	(3.8)
Acquisition of Business (Net of Cash Acquired)	(129.2)	(54.3)	0
Net Purchases of Property and Equipment	(85)	(100.2)	(114.5)
Other, Net	0	0	0.1
Net Cash Used by Investing Activities	(710)	(713)	(886.6)
Cash Flows from Financing Activities
Issuance of Long-term Debt	609.1	271.4	347.2
Long-term Debt Repayment	(414)	(226.3)	(186.6)
Cost Related to Early Retirement of Debt	0	0	(13.2)
Issuance of Common Stock	8.5	6.4	12.3
Repurchase of Common Stock	(405.2)	(417.9)	(306)
Dividends Paid to Stockholders	(182.6)	(174.2)	(159.4)
Other, Net	(34.4)	(28.1)	(22.9)
Net Cash Used by Financing Activities	(418.6)	(568.7)	(328.6)
Net Increase (Decrease) in Cash and Bank Deposits	(12.5)	10.4	8.4
Cash and Bank Deposits at Beginning of Year	112.9	102.5	94.1
Cash and Bank Deposits at End of Year	$ 100.4	$ 112.9	$ 102.5

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant Accounting Policies	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). Such accounting principles differ from statutory accounting principles (see Note 15). Intercompany transactions have been eliminated. Description of Business : We are a leading provider of financial protection benefits in the United States and the United Kingdom. Our products include disability, life, accident, critical illness, dental and vision, and other related services. We market our products primarily through the workplace. We have three principal operating business segments: Unum US, Unum UK, and Colonial Life. Our other reporting segments are Closed Block and Corporate. See Note 13 for further discussion of our operating segments. Use of Estimates : The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect amounts reported in the financial statements and accompanying notes. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein. Fixed Maturity Securities : Fixed maturity securities include long-term bonds and redeemable preferred stocks. Our fixed maturity securities are classified as available-for-sale and reported at fair value. Changes in the fair value of available-for-sale fixed maturity securities, except for amounts related to other-than-temporary impairment losses recognized in earnings, are reported as a component of other comprehensive income. These amounts are net of income tax and valuation adjustments to deferred acquisition costs and reserves for future policy and contract benefits which would have been recorded had the related unrealized gain or loss on these securities been realized. Interest income is recorded as part of net investment income when earned, using an effective yield method giving effect to amortization of premium and accretion of discount. Included within fixed maturity securities are mortgage-backed and asset-backed securities. We recognize investment income on these securities using a constant effective yield based on projected prepayments of the underlying loans and the estimated economic life of the securities. Actual prepayment experience is reviewed periodically, and effective yields are recalculated when differences arise between prepayments originally projected and the actual prepayments received and currently projected. The effective yield is recalculated on a retrospective basis, and the adjustment is reflected in net investment income. For fixed maturity securities on which collection of investment income is uncertain, we discontinue the accrual of investment income and recognize investment income when interest and dividends are received. Payment terms specified for fixed maturity securities may include a prepayment penalty for unscheduled payoff of the investment. Prepayment penalties are recognized as investment income when received. In determining when a decline in fair value below amortized cost of a fixed maturity security is other than temporary, we evaluate available information, both positive and negative, in reaching our conclusions. In particular, we 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 all 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 that 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. 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. Other-than-temporary impairment losses on fixed maturity securities which we intend to sell or more likely than not will be required to sell before recovery in value are recognized in earnings and equal the entire difference between the security's amortized cost basis and its fair value. For securities which we do not intend to sell and it is not more likely than not that we will be required to sell before recovery in value, other-than-temporary impairment losses recognized in earnings generally represent the difference between the amortized cost of the security and the present value of our best estimate of cash flows expected to be collected, discounted using the effective interest rate implicit in the security at the date of acquisition. For fixed maturity securities for which we have recognized an other-than-temporary impairment loss through earnings, if through subsequent evaluation there is a significant increase in expected cash flows, the difference between the new amortized cost basis and the cash flows expected to be collected is accreted as net investment income over the remaining life of the investment. See Notes 2 and 3. Mortgage Loans : Mortgage loans are generally held for investment and are carried at amortized cost less an allowance for probable losses. Interest income is accrued on the principal amount of the loan based on the loan's contractual interest rate. Prepayment penalties are recognized as investment income when received. 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. 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. 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 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. Additions and reductions to our allowance for credit losses on mortgage loans are reported as a component of net realized investment gains and losses. We do not purchase mortgage loans with existing credit impairments. See Note 3. Policy Loans : Policy loans are presented at unpaid balances directly related to policyholders. Interest income is accrued on the principal amount of the loan based on the loan's contractual interest rate. Included in policy loans are $3,206.1 million and $3,150.1 million of policy loans ceded to reinsurers at December 31, 2016 and 2015 , respectively. Other Long-term Investments : Other long-term investments are comprised primarily of tax credit partnerships and private equity partnerships. Tax credit partnerships in which we have invested were formed for the purpose of investing in the construction and rehabilitation of low-income housing. Because the partnerships are structured such that there is no return of principal, the primary sources of investment return from our tax credit partnerships are tax credits and tax benefits derived from passive losses on the investments, both of which may exhibit variability over the life of the investment. These partnerships are accounted for using either the proportional or the effective yield method, depending primarily on whether the tax credits are guaranteed through a letter of credit, a tax indemnity agreement, or another similar arrangement. Tax credits received from these partnerships are reported in our consolidated statements of income as either a reduction of premium tax or a reduction of income tax. The amortization of the principal amount invested in these partnerships is reported as a component of either premium tax or income tax. Our investments in private equity partnerships are passive in nature. The underlying investments held by these partnerships include both equity and debt securities and are accounted for using the equity or cost method, depending on the level of ownership and the degree of our influence over partnership operating and financial policies. For partnerships accounted for under the equity method, our portion of partnership earnings is reported as a component of net investment income in our consolidated statements of income. For those partnerships accounted for under the cost method, we record income received from partnership distributions as either a component of net investment income or net realized investment gain or loss, in accordance with the source of the funds distributed from the partnership. See Notes 2 and 3. Short-term Investments : Short-term investments are carried at cost. Short-term investments include investments maturing within one year, such as corporate commercial paper and U.S. Treasury bills, bank term deposits, and other cash accounts and cash equivalents earning interest. See Note 2. Cash and Bank Deposits : Cash and bank deposits include cash on hand and non-interest bearing cash and deposit accounts. Derivative Financial Instruments : Derivative financial instruments (including certain derivative instruments embedded in other contracts) are recognized as either other long-term investments or other liabilities in our consolidated balance sheets and are reported at fair value. The accounting for a derivative depends on whether it has been designated and qualifies as part of a hedging relationship, and further, on the type of hedging relationship. To qualify for hedge accounting, at the inception of the hedging transaction, we formally document the risk management objective and strategy for undertaking the hedging transaction, as well as the designation of the hedge as either a fair value hedge or a cash flow hedge. Included in this documentation is how the hedging instrument is expected to hedge the designated risk(s) related to specific assets or liabilities on the balance sheet or to specific forecasted transactions as well as a description of the method that will be used to retrospectively and prospectively assess the hedging instrument's effectiveness and the method that will be used to measure ineffectiveness. A derivative designated as a hedging instrument must be assessed as being highly effective in offsetting the designated risk(s) of the hedged item. Hedge effectiveness is formally assessed at inception and periodically throughout the life of the designated hedging relationship, using qualitative and quantitative methods. Qualitative methods include comparison of critical terms of the derivative to the hedged item. Quantitative methods include regression or other statistical analysis of changes in fair value or cash flows associated with the hedge relationship. Changes in the fair value of a derivative designated as a fair value hedge, including amounts measured as ineffectiveness, and changes in the fair value of the hedged item attributable to the risk being hedged are recognized in earnings as a component of net realized investment gain or loss during the period of change in fair value. The gain or loss on the termination of a fair value hedge is recognized in earnings as a component of net realized investment gain or loss during the period in which the termination occurs. When interest rate swaps are used in hedge accounting relationships, periodic settlements are recorded in the same income statement line as the related settlements of the hedged items. To the extent it is effective, changes in the fair value of a derivative designated as a cash flow hedge are reported in other comprehensive income and reclassified into earnings and reported on the same income statement line item as the hedged item and in the same period or periods during which the hedged item affects earnings. The ineffective portion of the hedge, if any, is recognized in earnings as a component of net realized investment gain or loss during the period of change in fair value. The gain or loss on the termination of an effective cash flow hedge is reported in other comprehensive income and reclassified into earnings and reported on the same income statement line item as the hedged item and in the same period or periods during which the hedged item affects earnings. Gains or losses on the termination of ineffective fair value or cash flow hedges are reported in earnings as a component of net realized investment gain or loss. In the event a hedged item is disposed of or the anticipated transaction being hedged is no longer likely to occur, we will terminate the related derivative and recognize the gain or loss on termination in current earnings as a component of net realized investment gain or loss. In the event a hedged item is disposed of subsequent to the termination of the hedging transaction, we reclassify any remaining gain or loss on the cash flow hedge out of accumulated other comprehensive income into earnings as a component of the same income statement line item wherein we report the gain or loss on disposition of the hedged item. For a derivative not designated as a hedging instrument, changes in the fair value of the derivative, together with the payment of periodic fees, if applicable, are recognized in earnings as a component of net realized investment gain or loss during the period of change in fair value. Cash flow activity from the settlement of derivative contracts is reported in the consolidated statements of cash flows as a component of proceeds from sales and maturities of other investments. In our consolidated balance sheets, we do not offset fair value amounts recognized for derivatives executed with the same counterparty under a master netting agreement and fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral arising from those master netting agreements. See Notes 2, 3 and 4. Fair Value Measurement : Certain assets and liabilities are reported at fair value in our consolidated balance sheets and in our notes to our consolidated financial statements. We define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Therefore, fair value represents an exit price, not an entry price. The exit price objective applies regardless of our intent and/or ability to sell the asset or transfer the liability at the measurement date. Assets or liabilities with readily available actively 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. When actively quoted prices are not available, fair values are based on quoted prices in markets that are not active, quoted prices for similar but not identical assets or liabilities, or other observable inputs. If observable inputs are not available, unobservable inputs and/or adjustments to observable inputs requiring management judgment are used to determine fair value. We categorize our assets and liabilities measured at estimated fair value into a three-level hierarchy, based on the significance of the inputs. The fair value hierarchy gives the highest priority to inputs which are unadjusted and represent quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). See Note 2. Realized Investment Gains and Losses : Realized investment gains and losses are reported as a component of revenue in the consolidated statements of income and are based upon specific identification of the investments sold. See Note 3. Deferred Acquisition Costs : Incremental direct costs associated with the successful acquisition of new or renewal insurance contracts have been deferred. Such costs include commissions, other agency compensation, certain selection and policy issue expenses, and certain field expenses. Acquisition costs that do not vary with the production of new business, such as commissions on group products which are generally level throughout the life of the policy, are excluded from deferral. Deferred acquisition costs are subject to recoverability testing at the time of policy issue and loss recognition testing in subsequent years. Deferred acquisition costs related to non-interest sensitive policies are amortized in proportion to the premium income we expect to receive over the life of the policies. Deferred acquisition costs related to interest sensitive policies are amortized over the lives of the policies in relation to the present value of estimated gross profits from surrender charges, mortality margins, investment returns, and expense margins. Deviations from projections result in a change to the rate of amortization in the period during which such events occur. Generally, the amortization periods for these policies approximate the estimated lives of the policies. For certain products, policyholders can elect to modify product benefits, features, rights, or coverages by exchanging a contract for a new contract or by amendment, endorsement, or rider to a contract, or by the election of a feature or coverage within a contract. These transactions are known as internal replacement transactions. Internal replacement transactions wherein the modification does not substantially change the policy are accounted for as continuations of the replaced contracts. Unamortized deferred acquisition costs from the original policy continue to be amortized over the expected life of the new policy, and the costs of replacing the policy are accounted for as policy maintenance costs and expensed as incurred. Internal replacement transactions, principally on group contracts, that result in a policy that is substantially changed are accounted for as an extinguishment of the original policy and the issuance of a new policy. Unamortized deferred acquisition costs on the original policy that was replaced are immediately expensed, and the costs of acquiring the new policy are capitalized and amortized in accordance with our accounting policies for deferred acquisition costs. Loss recognition is performed on an annual basis, or more frequently if appropriate, using best estimate assumptions as to future experience as of the date of the test. Insurance contracts are grouped for each major product line within a segment when we perform the loss recognition tests. If loss recognition testing indicates that deferred acquisition costs are not recoverable, the deficiency is charged to expense. Goodwill : Goodwill is the excess of the amount paid to acquire a business over the fair value of the net assets acquired. We review the carrying amount of goodwill for impairment on an annual basis, or more frequently if events or changes in circumstances indicate that the carrying amount might not be recoverable. Goodwill impairment testing compares the fair value of a reporting unit with its carrying amount, including goodwill. The fair values of the reporting units are determined using discounted cash flow models. The critical estimates necessary in determining fair value are projected earnings and the discount rate. We set our discount rate assumption based on an expected risk adjusted cost of capital. If the fair value of the reporting unit to which the goodwill relates is less than the carrying amount of the unamortized goodwill, the impairment charge is determined by calculating the implied fair value of goodwill by assigning the fair value of a reporting unit to all of its assets and liabilities. The carrying amount of goodwill is then reduced with a corresponding charge to expense. Property and Equipment : Property and equipment is reported at cost less accumulated depreciation, which is calculated on the straight-line method over the estimated useful life. The accumulated depreciation for property and equipment was $989.4 million and $902.6 million as of December 31, 2016 and 2015 , respectively. Value of Business Acquired : Value of business acquired represents the present value of future profits recorded in connection with the acquisition of a block of insurance policies. The asset is amortized based upon expected future premium income for non-interest sensitive insurance policies and estimated future gross profits from surrender charges, mortality margins, investment returns, and expense margins for interest sensitive insurance policies. The value of business acquired, which is included in other assets in our consolidated balance sheets, was $31.9 million and $24.0 million at December 31, 2016 and 2015 , respectively. The accumulated amortization for value of business acquired was $119.2 million and $133.1 million as of December 31, 2016 and 2015 , respectively. The amortization of value of business acquired, which is included in other expenses in the consolidated statements of income, was $5.1 million , $4.6 million , and $3.5 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively. We periodically review the carrying amount of value of business acquired using the same methods used to evaluate deferred acquisition costs. Policy and Contract Benefits : Policy and contract benefits represent amounts paid and expected to be paid based on reported losses and estimates of incurred but not reported losses for non-interest sensitive life and accident and health products. For interest sensitive products, benefits are the amounts paid and expected to be paid on insured claims in excess of the policyholders' policy fund balances. Reserves for Policy and Contract Benefits : Policy reserves represent future policy and contract benefits for claims not yet incurred. Policy reserves for non-interest sensitive life and accident and health products are determined using the net level premium method. The reserves are calculated based upon assumptions as to interest, persistency, morbidity, and mortality that were appropriate at the date of issue. Discount rate assumptions are based on actual and expected net investment returns. Persistency assumptions are based on our actual historical experience adjusted for future expectations. Claim incidence and claim resolution rate assumptions related to morbidity and mortality are based on actual experience or industry standards adjusted as appropriate to reflect our actual experience and future expectations. The assumptions vary by plan, year of issue, and policy duration and include a provision for adverse deviation. Policy reserves for group single premium annuities are developed on a net single premium method. The reserves are calculated based on assumptions as to interest, mortality, and retirement that were appropriate at the date of issue. Mortality assumptions are based upon industry standards adjusted as appropriate to reflect our actual experience and future expectations. The assumptions vary by year of issue. Policy reserves for interest sensitive products are principally policyholder account values. Policy reserves require ongoing loss recognition testing. We perform loss recognition tests on our policy reserves annually, or more frequently if appropriate, using best estimate assumptions as of the date of the test, without a provision for adverse deviation. We group the policy reserves for each major product line within a segment when we perform the loss recognition tests. If the policy reserves determined using these best estimate assumptions are higher than our existing policy reserves net of any deferred acquisition cost balance, the existing policy reserves are increased or deferred acquisition costs are reduced to immediately recognize the deficiency. This becomes the new basis for policy reserves going forward, subject to future loss recognition testing. Claim reserves represent future policy and contract benefits for claims that have been incurred or are estimated to have been incurred but not yet reported to us. Our claim reserves relate primarily to disability policies and are calculated based on assumptions as to interest and claim resolution rates that are currently appropriate. Claim resolution rate assumptions are based on our actual experience. The interest rate assumptions used for discounting claim reserves are based on projected portfolio yield rates, after consideration for defaults and investment expenses, for the assets supporting the liabilities for the various product lines. Unlike policy reserves for which assumptions are generally established and locked in at the time of policy issuance, claim reserves are subject to revision as current claim experience and projections of future factors affecting claim experience change. Claim reserves do not include a provision for adverse deviation. See Note 6. Policyholders' Funds : Policyholders' funds represent customer deposits plus interest credited at contract rates. We control interest rate risk by investing in quality assets which have an aggregate duration that closely matches the expected duration of the liabilities. Income Tax : Deferred taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial statement purposes and the amounts used for income tax purposes. Deferred taxes have been measured using enacted statutory income tax rates and laws that are currently in effect. We record deferred tax assets for tax positions taken in the U.S. and other tax jurisdictions based on our assessment of whether a position is more likely than not to be sustained upon examination based solely on its technical merits. A valuation allowance is established for deferred tax assets when it is more likely than not that an amount will not be realized. See Note 7. Short-term and Long-term Debt : Debt is generally carried at the unpaid principal balance, net of unamortized discount or premium and deferred debt issuance costs. Short-term debt consists of debt due within the next twelve months, including that portion of debt otherwise classified as long-term. Original issue discount or premium as well as debt issuance costs are recognized as a component of interest expense over the period the debt is expected to be outstanding. The carrying amount of long-term debt that is part of a fair value hedge program includes an adjustment to reflect the effect of the change in fair value attributable to the risk being hedged. Net interest settlements for fair value hedges on our long-term debt are recognized as a component of interest expense. See Note 8. Treasury Stock and Retirement of Common Stock : Treasury stock is reflected as a reduction of stockholders' equity at cost. When shares are retired, the par value is removed from common stock, and the excess of the repurchase price over par is allocated between additional paid-in capital and retained earnings. See Note 10. Revenue Recognition: Our non-interest sensitive life and accident and health products are long-duration contracts, and premium income is recognized as revenue when due from policyholders. If the contracts are experience rated, the estimated ultimate premium is recognized as revenue over the period of the contract. The estimated ultimate premium, which is revised to reflect current experience, is based on estimated claim costs, expenses, and profit margins. For interest sensitive products, the amounts collected from policyholders are considered deposits, and only the deductions during the period for cost of insurance, policy administration, and surrenders are included in revenue. Policyholders' funds represent funds deposited by contract holders and are not included in revenue. Fees from our administrative-services only and family medical leave products are reported as other income when services are rendered. Reinsurance : We routinely enter into reinsurance agreements with other insurance companies to spread risk and thereby limit losses from large exposures. For each of our reinsurance agreements, we determine if the agreement provides indemnification against loss or liability relating to insurance risk in accordance with applicable accounting standards. If we determine that a reinsurance agreement does not expose the reinsurer to a reasonable possibility of a significant loss from insurance risk, we record the agreement using the deposit method of accounting. Reinsurance activity is accounted for on a basis consistent with the terms of the reinsurance contracts and the accounting used for the original policies issued. Premium income and benefits and change in reserves for future benefits are presented in our consolidated statements of income net of reinsurance ceded. Ceded liabilities for policy and contract benefits, future policy and contract benefits, and unearned premiums are reported on a gross basis in our consolidated balance sheets, as are ceded policy loans. Our reinsurance recoverable includes the balances due from reinsurers under the terms of the reinsurance agreements for these ceded balances as well as settlement amounts currently due. Where applicable, gains or losses on reinsurance transactions are deferred and amortized into earnings based upon expected future premium income for non-interest sensitive insurance policies and estimated future gross profits for interest sensitive insurance policies. The deferred gain on reinsurance included in other liabilities in our consolidated balance sheets at December 31, 2016 and 2015 was $23.8 million and $31.9 million , respectively. Under ceded reinsurance agreements wherein we are not relieved of our legal liability to our policyholders, if the assuming reinsurer is unable to meet its obligations, we remain contingently liable. We evaluate the financial condition of reinsurers and monitor concentration of credit risk to minimize this exposure. We may also require assets in trust, letters of credit, or other acceptable collateral to support our reinsurance recoverable balances. In the event that reinsurers do not meet their obligations to us under the terms of the reinsurance agreements, certain amounts reported in our reinsurance recoverable could become uncollectible, in which case the reinsurance recoverable balances are stated net of allowances for uncollectible reinsurance. See Note 12. Premium Tax Expense : Premium tax expense is included in other expenses in the consolidated statements of income. For the years ended December 31, 2016 , 2015 , and 2014 , premium tax expense was $152.5 million , $146.5 million , and $139.2 million , respectively. Stock-Based Compensation : The cost of stock-based compensation is generally measured based on the grant-date fair value of the award. The Black-Scholes options valuation model is used for estimating the fair value of stock options, and the Monte-Carlo valuation model is used for estimating the fair value of performance share units. Restricted stock units are valued based on the fair value of common stock at the grant date. Stock-based awards are expensed over the requisite service period, or for performance share units over the requisite service period, or remaining service period, if and when it becomes probable tha

Fair Values of Financial Instru

Fair Values of Financial Instruments	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [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 securities lending agreements approximate fair value due to the short-term nature of the instruments. As such, these financial instruments are not included in the following chart. December 31, 2016 December 31, 2015 Carrying Amount Fair Value Carrying Amount Fair Value (in millions of dollars) Assets Fixed Maturity Securities $ 44,217.3 $ 44,217.3 $ 43,354.4 $ 43,354.4 Mortgage Loans 2,038.9 2,122.2 1,883.6 2,013.9 Policy Loans 3,463.2 3,564.2 3,395.4 3,498.0 Other Long-term Investments Derivatives 32.7 32.7 49.8 49.8 Equity Securities 1.2 1.2 1.4 1.4 Miscellaneous Long-term Investments 541.9 541.9 474.4 474.4 Liabilities Policyholders' Funds Deferred Annuity Products $ 597.4 $ 597.4 $ 608.8 $ 608.8 Supplementary Contracts without Life Contingencies 608.8 608.8 641.1 641.1 Short-term Debt — — 352.0 366.2 Long-term Debt 2,999.4 3,175.8 2,449.4 2,645.9 Payables for Collateral on Investments Federal Home Loan Bank (FHLB) Funding Agreements 350.0 350.0 350.0 350.0 Other Liabilities Derivatives 52.8 52.8 50.2 50.2 Embedded Derivative in Modified Coinsurance Arrangement 46.7 46.7 87.6 87.6 Unfunded Commitments to Investment Partnerships 5.0 5.0 5.0 5.0 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 $3,206.1 million and $3,150.1 million as of December 31, 2016 and 2015 , 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 railcar leasing, the financial services industry, mezzanine debt, and bank loans. Distributions received from the funds arise from income generated by the underlying investments as well as the liquidation of the underlying investments. As of December 31, 2016 , we estimate that the underlying assets of the funds will be liquidated over the next one to eleven years. These financial instruments are assigned a Level 3 within the fair value hierarchy. Our shares of FHLB common stock are carried at cost, which approximates fair value. These financial instruments are considered restricted investments and are assigned a Level 2 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. Short-term Debt : Fair values for short-term debt are determined based on prices from independent pricing services that generally use observable inputs for securities or comparable securities in active markets in their valuation techniques. These financial instruments are assigned a Level 1. 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 by pricing services using active trades for which there was current market activity in that specific debt instrument have fair values of $709.8 million and $956.4 million as of December 31, 2016 and 2015 , 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 $2,466.0 million and $1,689.5 million as of December 31, 2016 and 2015 , respectively, and are assigned a Level 2. FHLB Funding Agreements: Funding agreements with the FHLB represent cash advances used for the purpose of investing in fixed maturity securities. Carrying amounts approximate fair value and are assigned a Level 2 within the fair value hierarchy. Unfunded Commitments to Investment Partnerships: Unfunded equity commitments represent amounts that we have committed to fund certain investment partnerships. These commitments are legally binding, subject to the partnerships meeting specified conditions. Carrying amounts approximate fair value and 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 unrestricted 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 2016 , we have applied valuation techniques on a consistent basis to similar assets and liabilities and consistent with those techniques used at year end 2015 . We use observable and unobservable inputs in measuring the fair value of our fixed maturity and equity securities. For securities categorized as Level 1, fair values equal active Trade Reporting and Compliance Engine (TRACE) pricing or unadjusted broker market maker prices. For securities categorized as Level 2 or Level 3, inputs that may be used in valuing each class of securities at any given time period are presented as follows. Actual inputs used to determine fair values will vary for each reporting period depending on the availability of inputs which may, at times, be affected by the lack of market liquidity. Level 2 Level 3 Instrument Observable Inputs Unobservable Inputs United States Government and Government Agencies and Authorities Valuation Techniques Principally the market approach Not applicable Key Inputs Prices obtained from external pricing services States, Municipalities, and Political Subdivisions Valuation Techniques Principally the market approach Principally the market approach Key Inputs Prices obtained from external pricing services Analysis of similar bonds, adjusted for comparability Relevant reports issued by analysts and rating agencies Non-binding broker quotes Audited financial statements Security and issuer level spreads Foreign Governments Valuation Techniques Principally the market approach Principally the market approach Key Inputs Prices obtained from external pricing services Analysis of similar bonds, adjusted for comparability Non-binding broker quotes Non-binding broker quotes Call provisions Security and issuer level spreads Level 2 Level 3 Instrument Observable Inputs Unobservable Inputs Public Utilities Valuation Techniques Principally the market and income approaches Principally the market and income approaches Key Inputs TRACE pricing Change in benchmark reference Prices obtained from external pricing services Analysis of similar bonds, adjusted for comparability Non-binding broker quotes Discount for size - illiquidity Benchmark yields Non-binding broker quotes Transactional data for new issuances and secondary trades Lack of marketability Security cash flows and structures Security and issuer level spreads Recent issuance / supply Volatility of credit Security and issuer level spreads Security creditor ratings/maturity/capital structure/optionality Public covenants Comparative bond analysis Relevant reports issued by analysts and rating agencies Audited financial statements Mortgage/Asset-Backed Securities Valuation Techniques Principally the market and income approaches Principally the market approach Key Inputs Prices obtained from external pricing services Analysis of similar bonds, adjusted for comparability Non-binding broker quotes Non-binding broker quotes Security cash flows and structures Security and issuer level spreads Underlying collateral Prepayment speeds/loan performance/delinquencies Relevant reports issued by analysts and rating agencies Audited financial statements All Other Corporate Bonds Valuation Techniques Principally the market and income approaches Principally the market and income approaches Key Inputs TRACE pricing Change in benchmark reference Prices obtained from external pricing services Analysis of similar bonds, adjusted for comparability Non-binding broker quotes Discount for size - illiquidity Benchmark yields Non-binding broker quotes Transactional data for new issuances and secondary trades Lack of marketability Security cash flows and structures Security and issuer level spreads Recent issuance / supply Volatility of credit Security and issuer level spreads Security creditor ratings/maturity/capital structure/optionality Level 2 Level 3 Instrument Observable Inputs Unobservable Inputs Public covenants Comparative bond analysis Relevant reports issued by analysts and rating agencies Audited financial statements Redeemable Preferred Stocks Valuation Techniques Principally the market approach Principally the market approach Key Inputs Non-binding broker quotes Non-binding broker quotes Benchmark yields Comparative bond analysis Call provisions Relevant reports issued by analysts and rating agencies Audited financial statements Equity Securities Valuation Techniques Principally the market approach Principally the market and income approaches Key Inputs Prices obtained from external pricing services Financial statement analysis Non-binding broker quotes Non-binding broker quotes 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 December 31, 2016 , approximately 9.2 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 90.8 percent of our fixed maturity securities were valued based on non-binding quotes or other observable and unobservable inputs, as discussed below. • Approximately 76.3 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 3.2 percent of our fixed maturity securities were valued based on one or more non-binding broker quotes, 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 11.3 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: December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 454.2 $ 928.2 $ — $ 1,382.4 States, Municipalities, and Political Subdivisions — 2,068.5 89.5 2,158.0 Foreign Governments — 914.7 — 914.7 Public Utilities 108.5 7,648.9 265.3 8,022.7 Mortgage/Asset-Backed Securities — 2,230.4 — 2,230.4 All Other Corporate Bonds 3,507.1 24,500.4 1,459.7 29,467.2 Redeemable Preferred Stocks — 18.7 23.2 41.9 Total Fixed Maturity Securities 4,069.8 38,309.8 1,837.7 44,217.3 Other Long-term Investments Derivatives Foreign Exchange Contracts — 32.7 — 32.7 Equity Securities — — 1.2 1.2 Liabilities Other Liabilities Derivatives Interest Rate Swaps $ — $ 7.6 $ — $ 7.6 Foreign Exchange Contracts — 44.8 — 44.8 Credit Default Swaps — 0.4 — 0.4 Embedded Derivative in Modified Coinsurance Arrangement — — 46.7 46.7 Total Derivatives — 52.8 46.7 99.5 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 97.3 $ 1,367.9 $ — $ 1,465.2 States, Municipalities, and Political Subdivisions — 1,994.9 122.2 2,117.1 Foreign Governments — 998.7 52.9 1,051.6 Public Utilities 59.1 7,687.2 274.1 8,020.4 Mortgage/Asset-Backed Securities — 2,481.5 — 2,481.5 All Other Corporate Bonds 2,770.4 23,992.8 1,408.2 28,171.4 Redeemable Preferred Stocks — 23.4 23.8 47.2 Total Fixed Maturity Securities 2,926.8 38,546.4 1,881.2 43,354.4 Other Long-term Investments Derivatives Interest Rate Swaps — 2.4 — 2.4 Foreign Exchange Contracts — 47.4 — 47.4 Total Derivatives — 49.8 — 49.8 Equity Securities — — 1.4 1.4 Liabilities Other Liabilities Derivatives Interest Rate Swaps $ — $ 12.3 $ — $ 12.3 Foreign Exchange Contracts — 37.6 — 37.6 Credit Default Swaps — 0.3 — 0.3 Embedded Derivative in Modified Coinsurance Arrangement — — 87.6 87.6 Total Derivatives — 50.2 87.6 137.8 Transfers of assets between Level 1 and Level 2 are as follows: Year Ended December 31 2016 2015 Transfers into Level 1 from Level 2 Level 2 from Level 1 Level 1 from Level 2 Level 2 from Level 1 (in millions of dollars) Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 200.0 $ — $ — $ 195.3 Public Utilities 65.9 59.1 7.3 85.1 All Other Corporate Bonds 1,889.0 1,860.3 1,369.2 1,556.7 Total Fixed Maturity Securities $ 2,154.9 $ 1,919.4 $ 1,376.5 $ 1,837.1 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: Year Ended December 31, 2016 Total Realized and Unrealized Investment Gains (Losses) Included in Beginning of Year Earnings Other Comprehensive Income or Loss Purchases Sales Level 3 Transfers End of Year Into Out of (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions $ 122.2 $ — $ 1.9 $ — $ (0.5 ) $ — $ (34.1 ) $ 89.5 Foreign Governments 52.9 — — — — — (52.9 ) — Public Utilities 274.1 — (0.8 ) — (3.7 ) 157.6 (161.9 ) 265.3 All Other Corporate Bonds 1,408.2 1.4 6.9 115.9 (111.2 ) 792.8 (754.3 ) 1,459.7 Redeemable Preferred Stocks 23.8 — (0.6 ) — — — — 23.2 Total Fixed Maturity Securities 1,881.2 1.4 7.4 115.9 (115.4 ) 950.4 (1,003.2 ) 1,837.7 Equity Securities 1.4 — 0.1 — (0.3 ) — — 1.2 Embedded Derivative in Modified Coinsurance Arrangement (87.6 ) 40.9 — — — — — (46.7 ) Year Ended December 31, 2015 Total Realized and Unrealized Investment Gains (Losses) Included in Beginning of Year Earnings Other Comprehensive Income or Loss Purchases Sales Level 3 Transfers End of Year Into Out of (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions $ 140.1 $ (0.1 ) $ (5.3 ) $ 12.0 $ (16.5 ) $ — $ (8.0 ) $ 122.2 Foreign Governments 69.3 — (1.4 ) — (15.0 ) — — 52.9 Public Utilities 315.0 — (6.9 ) 40.0 (2.4 ) 118.5 (190.1 ) 274.1 All Other Corporate Bonds 1,425.3 (7.0 ) (113.2 ) 55.3 (220.8 ) 810.2 (541.6 ) 1,408.2 Redeemable Preferred Stocks 24.9 — (1.1 ) — — — — 23.8 Total Fixed Maturity Securities 1,974.6 (7.1 ) (127.9 ) 107.3 (254.7 ) 928.7 (739.7 ) 1,881.2 Equity Securities 1.4 — — — — — — 1.4 Embedded Derivative in Modified Coinsurance Arrangement (49.9 ) (37.7 ) — — — — — (87.6 ) 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 (losses) which are included in earnings and are attributable to the change in fair value of assets or liabilities valued using significant unobservable inputs and still held at each year end were $40.9 million and $(37.7) million for the years ended December 31, 2016 and 2015 , respectively. These amounts relate entirely to the change in fair value of an embedded derivative in a modified coinsurance arrangement and are reported as a component of 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. December 31, 2016 Fair Value Unobservable Input Range/Weighted Average (in millions of dollars) Fixed Maturity Securities All Other Corporate Bonds - Private $ 310.4 Comparability Adjustment (b) 0.50% - 0.50% / 0.50% Equity Securities - Private 1.1 Market Convention (f) Priced at Cost or Owner's Equity Embedded Derivative in Modified Coinsurance Arrangement (46.7 ) Projected Liability Cash Flows (g) Actuarial Assumptions December 31, 2015 Fair Value Unobservable Input Range/Weighted Average (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions - Private $ 73.3 Change in Benchmark Reference (a) 0.50% - 1.00% / 0.70% States, Municipalities, and Political Subdivisions - Public 12.0 Market Convention (f) Priced at Par All Other Corporate Bonds - Private 151.0 Comparability Adjustment (b) 0.50% - 0.50% / 0.50% All Other Corporate Bonds - Public 36.2 Lack of Marketability (d) 1.00% - 1.00% / 1.00% Equity Securities - Private 1.1 Market Convention (f) Priced at Cost or Owner's Equity Embedded Derivative in Modified Coinsurance Arrangement (87.6 ) 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	12 Months Ended
	Dec. 31, 2016
Notes to Financial Statements [Abstract]
Investments	Fixed Maturity Securities At December 31, 2016 and 2015 , 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: December 31, 2016 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value (in millions of dollars) United States Government and Government Agencies and Authorities $ 1,202.8 $ 183.1 $ 3.5 $ 1,382.4 States, Municipalities, and Political Subdivisions 1,868.0 294.8 4.8 2,158.0 Foreign Governments 714.8 199.9 — 914.7 Public Utilities 6,916.1 1,123.5 16.9 8,022.7 Mortgage/Asset-Backed Securities 2,104.9 134.7 9.2 2,230.4 All Other Corporate Bonds 26,707.1 2,944.0 183.9 29,467.2 Redeemable Preferred Stocks 39.0 3.2 0.3 41.9 Total Fixed Maturity Securities $ 39,552.7 $ 4,883.2 $ 218.6 $ 44,217.3 December 31, 2015 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value (in millions of dollars) United States Government and Government Agencies and Authorities $ 1,265.8 $ 207.3 $ 7.9 $ 1,465.2 States, Municipalities, and Political Subdivisions 1,828.3 293.4 4.6 2,117.1 Foreign Governments 897.2 154.4 — 1,051.6 Public Utilities 6,979.3 1,057.4 16.3 8,020.4 Mortgage/Asset-Backed Securities 2,318.6 167.6 4.7 2,481.5 All Other Corporate Bonds 26,325.5 2,454.1 608.2 28,171.4 Redeemable Preferred Stocks 44.0 3.8 0.6 47.2 Total Fixed Maturity Securities $ 39,658.7 $ 4,338.0 $ 642.3 $ 43,354.4 The following charts indicate the length of time our fixed maturity securities have been in a gross unrealized loss position. December 31, 2016 Less Than 12 Months 12 Months or Greater Fair Value Gross Unrealized Loss Fair Value Gross Unrealized Loss (in millions of dollars) United States Government and Government Agencies and Authorities $ 132.8 $ 3.5 $ — $ — States, Municipalities, and Political Subdivisions 132.2 4.8 — — Public Utilities 260.2 15.3 15.6 1.6 Mortgage/Asset-Backed Securities 513.2 9.1 0.8 0.1 All Other Corporate Bonds 3,621.0 122.1 774.7 61.8 Redeemable Preferred Stocks 7.9 0.1 10.8 0.2 Total Fixed Maturity Securities $ 4,667.3 $ 154.9 $ 801.9 $ 63.7 December 31, 2015 Less Than 12 Months 12 Months or Greater Fair Value Gross Unrealized Loss Fair Value Gross Unrealized Loss (in millions of dollars) United States Government and Government Agencies and Authorities $ 213.5 $ 7.9 $ — $ — States, Municipalities, and Political Subdivisions 112.3 4.3 3.3 0.3 Public Utilities 408.4 14.4 10.3 1.9 Mortgage/Asset-Backed Securities 504.3 4.6 9.0 0.1 All Other Corporate Bonds 6,155.0 464.2 554.7 144.0 Redeemable Preferred Stocks 10.4 0.6 — — Total Fixed Maturity Securities $ 7,403.9 $ 496.0 $ 577.3 $ 146.3 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. December 31, 2016 Total Amortized Cost Unrealized Gain Position Unrealized Loss Position Gross Gain Fair Value Gross Loss Fair Value (in millions of dollars) 1 year or less $ 1,338.8 $ 28.6 $ 1,355.6 $ — $ 11.8 Over 1 year through 5 years 6,231.0 553.5 6,605.6 8.2 170.7 Over 5 years through 10 years 10,991.6 843.8 9,336.2 82.8 2,416.4 Over 10 years 18,886.4 3,322.6 19,734.3 118.4 2,356.3 37,447.8 4,748.5 37,031.7 209.4 4,955.2 Mortgage/Asset-Backed Securities 2,104.9 134.7 1,716.4 9.2 514.0 Total Fixed Maturity Securities $ 39,552.7 $ 4,883.2 $ 38,748.1 $ 218.6 $ 5,469.2 December 31, 2015 Total Amortized Cost Unrealized Gain Position Unrealized Loss Position Gross Gain Fair Value Gross Loss Fair Value (in millions of dollars) 1 year or less $ 1,112.2 $ 20.6 $ 1,098.8 $ 0.2 $ 33.8 Over 1 year through 5 years 6,514.0 554.4 6,649.5 49.8 369.1 Over 5 years through 10 years 10,519.3 746.3 7,124.4 320.5 3,820.7 Over 10 years 19,194.6 2,849.1 18,532.3 267.1 3,244.3 37,340.1 4,170.4 33,405.0 637.6 7,467.9 Mortgage/Asset-Backed Securities 2,318.6 167.6 1,968.2 4.7 513.3 Total Fixed Maturity Securities $ 39,658.7 $ 4,338.0 $ 35,373.2 $ 642.3 $ 7,981.2 At December 31, 2016 , the fair value of investment-grade fixed maturity securities was $40,819.3 million , with a gross unrealized gain of $4,764.5 million and a gross unrealized loss of $151.8 million . The gross unrealized loss on investment-grade fixed maturity securities was 69.4 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 December 31, 2016 , the fair value of below-investment-grade fixed maturity securities was $3,398.0 million , with a gross unrealized gain of $118.7 million and a gross unrealized loss of $66.8 million . The gross unrealized loss on below-investment-grade fixed maturity securities was 30.6 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 December 31, 2016 , 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 that there are positive factors which mitigate credit concerns and that the securities for which we have not recorded an other-than-temporary impairment will recover in value. As of December 31, 2016 , we held 332 individual investment-grade fixed maturity securities and 69 individual below-investment-grade fixed maturity securities that were in an unrealized loss position, of which 16 investment-grade fixed maturity securities and 37 below-investment-grade fixed maturity securities had been in an unrealized loss position continuously for over one year. Of the 332 individual investment-grade securities in an unrealized loss position, 132 are held in the portfolio acquired through our 2016 purchase of H&J Capital, L.L.C., parent of Starmount Life Insurance Company and AlwaysCare Benefits (which collectively we refer to as Starmount). The fair value of the Starmount portfolio was $38.8 million and had a net unrealized loss of $1.5 million at December 31, 2016 . See Note 13. 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 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. We held no fixed maturity securities as of December 31, 2016 and 2015 , for which a portion of an other-than-temporary impairment was recognized in accumulated other comprehensive income. At December 31, 2016 , we had commitments of $30.0 million to fund private placement fixed maturity securities, the amount of which may or may not be funded. 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 December 31, 2016 , the carrying amount of our variable interest entity investments that are not consolidated in our financial statements was $509.3 million , comprised of $165.2 million of tax credit partnerships and $344.1 million of private equity partnerships. These variable interest entity investments are reported as other long-term investments in our consolidated balance sheets. The Company invests in tax credit partnerships primarily for the receipt of income tax credits and tax benefits derived from passive losses on the investments. Amounts recognized in the consolidated statements of income are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Income Tax Credits $ 41.8 $ 41.8 $ 41.8 Amortization, Net of Tax (23.2 ) (23.3 ) (23.2 ) Income Tax Benefit $ 18.6 $ 18.5 $ 18.6 Contractually, we are a limited partner in these tax credit partnerships, and our maximum exposure to loss is limited to the carrying value of our investment, which includes $4.6 million of unfunded unconditional commitments at December 31, 2016 . At December 31, 2016, we also have unfunded unconditional commitments of $0.4 million to fund certain private equity partnerships as well as commitments of $251.9 million , 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 which we contributed into the trust at the time it was established. 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 $151.9 million and $1.0 million , respectively, as of December 31, 2016 and $148.0 million and $0.9 million , respectively, as of December 31, 2015 . 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 December 31, 2016 , we had no commitments to fund the underlying partnership, nor did we fund any amounts to the partnership during the years ended December 31, 2016 , 2015 , and 2014 . 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. December 31 2016 2015 (in millions of dollars) Carrying Percent of Carrying Percent of Amount Total Amount Total Property Type Apartment $ 288.4 14.1 % $ 130.6 6.9 % Industrial 573.6 28.1 574.1 30.5 Office 700.1 34.4 764.7 40.6 Retail 455.4 22.4 392.3 20.8 Other 21.4 1.0 21.9 1.2 Total $ 2,038.9 100.0 % $ 1,883.6 100.0 % Region New England $ 72.7 3.6 % $ 97.6 5.2 % Mid-Atlantic 125.3 6.1 128.8 6.9 East North Central 230.1 11.3 186.4 9.9 West North Central 172.0 8.4 162.6 8.6 South Atlantic 438.3 21.5 409.3 21.7 East South Central 91.6 4.5 79.1 4.2 West South Central 268.7 13.2 237.6 12.6 Mountain 214.1 10.5 196.5 10.4 Pacific 426.1 20.9 385.7 20.5 Total $ 2,038.9 100.0 % $ 1,883.6 100.0 % 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. 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: December 31 2016 2015 (in millions of dollars) Internal Rating Aa $ 0.7 $ 1.1 A 488.2 586.6 Baa 1,506.6 1,285.8 Ba 43.4 10.1 Total $ 2,038.9 $ 1,883.6 Loan-to-Value Ratio <= 65% $ 917.9 $ 937.2 > 65% <= 75% 1,011.5 842.5 > 75% <= 85% 50.8 88.4 > 85% 58.7 15.5 Total $ 2,038.9 $ 1,883.6 A summary of our troubled debt restructurings is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Foreclosure Carrying Amount $ 5.4 $ — $ 18.1 Number of Loans 1 — 1 We had no realized losses on loan foreclosures for the years ended December 31, 2016 , 2015 , and 2014 other than any initial impairment loss recognized prior to foreclosure. During 2016, we foreclosed on a mortgage loan with a carrying value of $5.4 million . We did not recognize a loss at foreclosure as the value of the underlying property exceeded the carrying value of the loan. During 2014, we modified the terms of a mortgage loan with a carrying value of $18.1 million , recognized a $3.0 million realized loss on the troubled debt restructuring, and foreclosed on the property in a subsequent quarter of 2014. At December 31, 2016 and 2015 , we held no mortgage loans that were greater than 90 days past due regarding principal and/or interest payments. 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. The activity in the allowance for credit losses is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Balance at Beginning of Year $ — $ 1.5 $ 1.5 Provision — 0.5 3.0 Charge-offs, Net of Recoveries — (2.0 ) (3.0 ) Balance at End of Year $ — $ — $ 1.5 At December 31, 2014 , we held one impaired mortgage loan with an unpaid principal balance of $14.6 million , a related allowance for credit losses of $1.5 million , and a carrying value of $13.1 million . During 2015, we increased the allowance for credit losses for the impaired loan by $0.5 million and recognized a corresponding investment loss. The loan was repaid in a subsequent quarter of 2015, with an additional de minimis loss recognized at repayment. Our average investment in impaired mortgage loans was $2.2 million , $8.6 million , and $26.7 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively. Interest income recognized on mortgage loans subsequent to impairment was $0.6 million and $1.0 million , for the years ended December 31, 2015 and 2014 , respectively. We did not recognize any interest income during 2016 on mortgage loans subsequent to impairment. At December 31, 2016 , we had commitments of $32.1 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. We may receive cash and/or securities as collateral under these agreements. Cash received as collateral is typically reinvested in short-term investments. If securities are received as collateral, we are not permitted to sell or re-post them. As of December 31, 2016 , the carrying amount of fixed maturity securities loaned to third parties under our securities lending program was $178.5 million , for which we received collateral in the form of cash and securities of $29.9 million and $155.3 million , respectively. As of December 31, 2015 , the carrying amount of fixed maturity securities loaned to third parties under our securities lending program was $181.6 million , for which we received collateral in the form of cash and securities of $29.0 million and $159.3 million , respectively. We had no outstanding repurchase agreements at December 31, 2016 or 2015 . The remaining contractual maturities of our securities lending agreements disaggregated by class of collateral pledged are as follows: December 31 2016 2015 Overnight and Continuous (in millions of dollars) United States Government and Government Agencies and Authorities $ 0.1 $ 1.2 Public Utilities 0.1 4.0 All Other Corporate Bonds 29.7 23.8 Total Borrowings 29.9 29.0 Gross Amount of Recognized Liability for Securities Lending Transactions 29.9 29.0 Amounts Related to Agreements Not Included in Offsetting Disclosure Contained Herein $ — $ — Certain of our U.S. insurance subsidiaries are members of regional FHLBs. Membership, which requires that we purchase a minimum amount of FHLB common stock on which we receive dividends, provides access to low-cost funding. As of December 31, 2016 and 2015, we owned $31.6 million and $30.9 million of FHLB common stock, respectively. Advances from the regional FHLBs for the purpose of purchasing fixed maturity securities totaled $350.0 million as of December 31, 2016 and 2015. The carrying values of fixed maturity securities and commercial mortgage loans posted as collateral to the regional FHLBs were $323.7 million and $288.5 million , respectively as of December 31, 2016 , and $317.2 million and $96.0 million , respectively as of December 31, 2015. Additional common stock purchases may be required, based on the amount of funds we borrow from the FHLBs. 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 4 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. December 31, 2016 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 $ 32.7 $ — $ 32.7 $ (7.3 ) $ (25.4 ) $ — Securities Lending 178.5 — 178.5 (148.6 ) (29.9 ) — Total $ 211.2 $ — $ 211.2 $ (155.9 ) $ (55.3 ) $ — Financial Liabilities: Derivatives $ 52.8 $ — $ 52.8 $ (37.6 ) $ — $ 15.2 Securities Lending 29.9 — 29.9 (29.9 ) — — Total $ 82.7 $ — $ 82.7 $ (67.5 ) $ — $ 15.2 December 31, 2015 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 $ 49.8 $ — $ 49.8 $ (12.8 ) $ (36.4 ) $ 0.6 Securities Lending 181.6 — 181.6 (152.6 ) (29.0 ) — Total $ 231.4 $ — $ 231.4 $ (165.4 ) $ (65.4 ) $ 0.6 Financial Liabilities: Derivatives $ 50.2 $ — $ 50.2 $ (35.6 ) $ — $ 14.6 Securities Lending 29.0 — 29.0 (29.0 ) — — Total $ 79.2 $ — $ 79.2 $ (64.6 ) $ — $ 14.6 Net Investment Income Net investment income reported in our consolidated statements of income is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Fixed Maturity Securities $ 2,293.9 $ 2,327.1 $ 2,344.4 Derivatives 49.8 44.2 40.4 Mortgage Loans 114.0 114.0 109.8 Policy Loans 17.3 16.7 16.3 Other Long-term Investments 22.6 21.6 23.0 Short-term Investments 7.5 3.4 2.4 Gross Investment Income 2,505.1 2,527.0 2,536.3 Less Investment Expenses 31.9 31.2 29.0 Less Investment Income on Participation Fund Account Assets 14.2 14.6 15.1 Net Investment Income $ 2,459.0 $ 2,481.2 $ 2,492.2 Realized Investment Gain and Loss Realized investment gains and losses are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Fixed Maturity Securities Gross Gains on Sales $ 34.3 $ 23.8 $ 9.3 Gross Losses on Sales (17.2 ) (25.6 ) (7.5 ) Other-Than-Temporary Impairment Loss (30.5 ) (32.4 ) (13.5 ) Mortgage Loans and Other Invested Assets Gross Gains on Sales 5.5 16.0 21.2 Gross Losses on Sales (0.7 ) (0.1 ) (0.8 ) Impairment Loss (5.7 ) (5.9 ) (3.4 ) Embedded Derivative in Modified Coinsurance Arrangement 40.9 (37.7 ) 3.3 All Other Derivatives (1.5 ) 35.7 11.0 Foreign Currency Transactions (0.9 ) (17.6 ) (3.5 ) Net Realized Investment Gain (Loss) $ 24.2 $ (43.8 ) $ 16.1

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2016
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, 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. 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 paid, 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. Derivatives not designated as hedging instruments and used to reduce our exposure to foreign currency risk, credit losses on securities owned, and interest rate risk are as follows: • Foreign currency interest rate swaps previously designated as hedges were used to hedge the currency risk of certain foreign currency-denominated fixed maturity securities owned for portfolio diversification. 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. We hold offsetting swaps wherein we agree to pay fixed rate principal and interest payments in the functional currency of the operating segment in exchange for fixed rate foreign currency-denominated payments. • 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. • Interest rate swap is used to effectively convert certain of our floating rate, long-term debt into fixed rate long-term debt. Under this swap agreement, we receive a variable rate of interest and pay a fixed rate of interest. 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 $0.8 million at December 31, 2016 . We held cash collateral from our counterparties of $26.1 million and $36.4 million at December 31, 2016 and 2015 , 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 $35.2 million and $27.3 million at December 31, 2016 and 2015 , respectively. We had no cash posted as collateral to our counterparties at December 31, 2016 and 2015 . See Note 3 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 $52.8 million and $50.2 million at December 31, 2016 and 2015 , 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 Variable/Pay Fixed Receive Fixed/Pay Fixed Receive Fixed/Pay Variable Credit Default Forwards Total (in millions of dollars) Balance at December 31, 2013 $ 150.0 $ 630.4 $ 600.0 $ 97.0 $ — $ 1,477.4 Additions — 250.1 — — 68.0 318.1 Terminations — 40.1 — — 68.0 108.1 Balance at December 31, 2014 150.0 840.4 600.0 97.0 — 1,687.4 Additions — — — 2.0 94.0 96.0 Terminations — 190.1 — 29.0 94.0 313.1 Balance at December 31, 2015 150.0 650.3 600.0 70.0 — 1,470.3 Additions 3.5 — — — 30.0 33.5 Terminations 48.0 33.8 350.0 — 20.0 451.8 Balance at December 31, 2016 $ 105.5 $ 616.5 $ 250.0 $ 70.0 $ 10.0 $ 1,052.0 Cash Flow Hedges As of December 31, 2016 and 2015 , we had $394.1 million and $427.9 million , respectively, notional amount of receive fixed, pay fixed, open current and forward foreign currency interest rate swaps to hedge fixed income foreign currency-denominated securities. During the fourth quarter of 2015, the remaining principal balance of the U.S. dollar-denominated debt issued by one of our U.K. subsidiaries matured, at which time we terminated the related foreign currency swaps with a notional amount of $150.0 million and reclassified the cash flow hedge gain of $8.2 million from accumulated other comprehensive income to realized investment gain in our consolidated statements of income. We also reclassified the remaining deferred cash flow hedge gain of $27.7 million from previously terminated derivatives associated with the hedge of this debt from accumulated other comprehensive income to realized investment gain. During 2014, we redeemed a portion of this debt and reclassified $13.1 million , the applicable portion of the deferred gain on cash flow hedges from the previously terminated derivatives associated with the hedge of this debt, from accumulated other comprehensive income to realized investment gain in our consolidated statements of income. See Note 8. During 2014, we novated certain of our foreign currency interest rate swaps with a notional amount of $97.0 million and a fair value of $(29.5) million to a new counterparty. At the time of novation, these derivatives were effective hedges, and we therefore deferred the unrealized loss into other comprehensive income and will recognize the loss in earnings during the periods in which the hedged items affect earnings. In conjunction with the novation, these derivatives were de-designated as hedges, and subsequent changes in their fair value will be reported in earnings as a component of net realized investment gain or loss. To establish a new effective hedging relationship with the fixed income foreign currency denominated securities previously hedged, we entered into $124.7 million notional amount of foreign currency interest rate swaps during 2014 whereby we receive fixed rate functional currency principal and interest in exchange for fixed rate payments in foreign currency. For the years ended December 31, 2016 , 2015 , and 2014 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 December 31, 2016 , we expect to amortize approximately $58.0 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. Additional amounts that may be reclassified from accumulated other comprehensive income into earnings to offset the earnings impact of foreign currency translation of hedged items are not estimable. As of December 31, 2016 , we are hedging the variability of future cash flows associated with forecasted transactions through the year 2038 . Fair Value Hedges As of December 31, 2016 and 2015 , we had $102.0 million and $150.0 million , respectively, 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 $5.9 million , $5.3 million , and $5.3 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively, with an offsetting gain on the related interest rate swaps. During 2016, we terminated $24.0 million notional amount of receive variable, pay fixed interest rate swaps in connection with the sale of the hedged securities and recorded a loss on the swap terminations of $1.2 million in our consolidated statements of income as a component of net realized investment gains and losses. As of December 31, 2016 and 2015 , we had $250.0 million and $600.0 million , respectively, 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 $2.8 million , $0.1 million , and $(5.5) million for the years ended December 31, 2016 , 2015 , and 2014 , respectively, with an offsetting gain or loss on the related interest rate swaps. During 2016, $350.0 million notional amount of receive fixed, pay variable interest rate swaps matured in conjunction with the maturity of the $350.0 million hedged fixed rate debt. See Note 8. For the years ended December 31, 2016 , 2015 , and 2014 , 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 December 31, 2016 and 2015 , we held $222.4 million notional amount of receive fixed, pay fixed, foreign currency interest rate swaps. During 2014, we entered into $125.4 million notional amount of foreign currency interest rate swaps in conjunction with the previously discussed transaction wherein we de-designated foreign currency interest rate swaps with a notional amount of $97.0 million . These derivatives were not designated as hedges, and as such, changes in fair value related to these derivatives will be reported in earnings as a component of net realized investment gain or loss. We expect the changes in fair value of these derivatives to materially offset the changes in fair value related to the de-designated derivatives. As of December 31, 2016 and 2015 , we held $70.0 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. As of December 31, 2016 , we held $3.5 million notional amount of a receive variable, pay fixed interest rate swap acquired through our purchase of Starmount during 2016. This swap effectively converts Starmount's floating rate long-term debt of $3.5 million into fixed rate debt. See Note 13. 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. December 31, 2016 Asset Derivatives Liability Derivatives Balance Sheet Location Fair Value Balance Sheet Location Fair Value (in millions of dollars) Designated as Hedging Instruments Interest Rate Swaps and Forwards Other L-T Investments $ — Other Liabilities $ 6.9 Foreign Exchange Contracts Other L-T Investments 32.7 Other Liabilities 13.4 Total $ 32.7 $ 20.3 Not Designated as Hedging Instruments Credit Default Swaps Other Liabilities $ 0.4 Interest Rate Swaps Other Liabilities 0.7 Foreign Exchange Contracts Other Liabilities 31.4 Embedded Derivative in Modified Coinsurance Arrangement Other Liabilities 46.7 Total $ 79.2 December 31, 2015 Asset Derivatives Liability Derivatives Balance Sheet Location Fair Value Balance Sheet Location Fair Value (in millions of dollars) Designated as Hedging Instruments Interest Rate Swaps Other L-T Investments $ 2.4 Other Liabilities $ 12.3 Foreign Exchange Contracts Other L-T Investments 47.4 Other Liabilities 6.0 Total $ 49.8 $ 18.3 Not Designated as Hedging Instruments Credit Default Swaps Other Liabilities $ 0.3 Foreign Exchange Contracts Other Liabilities 31.6 Embedded Derivative in Modified Coinsurance Arrangement Other Liabilities 87.6 Total $ 119.5 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. Year Ended December 31 2016 2015 2014 (in millions of dollars) Gain (Loss) Recognized in Other Comprehensive Income (Loss) on Derivatives Interest Rate Swaps and Forwards $ (0.1 ) $ (0.7 ) $ (0.1 ) Foreign Exchange Contracts (22.2 ) 68.1 16.2 Total $ (22.3 ) $ 67.4 $ 16.1 Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Net Investment Income Interest Rate Swaps and Forwards $ 54.5 $ 50.2 $ 47.8 Foreign Exchange Contracts (1.1 ) (1.6 ) (4.2 ) Net Realized Investment Gain (Loss) Interest Rate Swaps 3.2 0.5 4.3 Foreign Exchange Contracts (1.4 ) 36.1 6.9 Interest and Debt Expense Interest Rate Swaps (1.9 ) (1.8 ) (1.8 ) Total $ 53.3 $ 83.4 $ 53.0 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. Year Ended December 31 2016 2015 2014 (in millions of dollars) Net Realized Investment Gain (Loss) Credit Default Swaps $ (0.9 ) $ 0.1 $ (0.3 ) Interest Rate Swaps 0.4 — — Foreign Exchange Contracts 0.2 (0.3 ) (1.8 ) Embedded Derivative in Modified Coinsurance Arrangement 40.9 (37.7 ) 3.3 Total $ 40.6 $ (37.9 ) $ 1.2

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Income	Components of our accumulated other comprehensive income (loss), 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 ) $ 255.0 Other Comprehensive Income (Loss) Before Reclassifications 154.3 31.1 (66.3 ) (216.1 ) (97.0 ) Amounts Reclassified from Accumulated Other Comprehensive Income or Loss 0.3 (36.4 ) — 44.5 8.4 Net Other Comprehensive Income (Loss) 154.6 (5.3 ) (66.3 ) (171.6 ) (88.6 ) Balance at December 31, 2014 290.3 391.0 (113.4 ) (401.5 ) 166.4 Other Comprehensive Income (Loss) Before Reclassifications (114.7 ) 43.3 (60.2 ) 1.3 (130.3 ) Amounts Reclassified from Accumulated Other Comprehensive Income or Loss 28.7 (56.3 ) — 7.6 (20.0 ) Net Other Comprehensive Income (Loss) (86.0 ) (13.0 ) (60.2 ) 8.9 (150.3 ) Balance at December 31, 2015 204.3 378.0 (173.6 ) (392.6 ) 16.1 Other Comprehensive Income (Loss) Before Reclassifications 226.5 (15.8 ) (180.4 ) (82.8 ) (52.5 ) Amounts Reclassified from Accumulated Other Comprehensive Income or Loss 9.8 (34.7 ) — 10.3 (14.6 ) Net Other Comprehensive Income (Loss) 236.3 (50.5 ) (180.4 ) (72.5 ) (67.1 ) Balance at December 31, 2016 $ 440.6 $ 327.5 $ (354.0 ) $ (465.1 ) $ (51.0 ) The net unrealized gain on securities consists of the following components: December 31 Change for the Year Ended December 31 2016 2015 2014 2013 2016 2015 2014 (in millions of dollars) Fixed Maturity Securities $ 4,664.6 $ 3,695.7 $ 6,261.5 $ 4,054.8 $ 968.9 $ (2,565.8 ) $ 2,206.7 Other Investments (22.7 ) (33.7 ) 13.9 55.5 11.0 (47.6 ) (41.6 ) Deferred Acquisition Costs (38.9 ) (29.4 ) (50.8 ) (41.6 ) (9.5 ) 21.4 (9.2 ) Reserves for Future Policy and Contract Benefits (4,253.2 ) (3,578.4 ) (6,150.3 ) (4,108.5 ) (674.8 ) 2,571.9 (2,041.8 ) Reinsurance Recoverable 321.3 263.2 365.0 263.8 58.1 (101.8 ) 101.2 Income Tax (230.5 ) (113.1 ) (149.0 ) (88.3 ) (117.4 ) 35.9 (60.7 ) Total $ 440.6 $ 204.3 $ 290.3 $ 135.7 $ 236.3 $ (86.0 ) $ 154.6 Amounts reclassified from accumulated other comprehensive income (loss) were recognized in our consolidated statements of income as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Net Unrealized Gain on Securities Net Realized Investment Gain (Loss) Gain (Loss) on Sales of Securities and Other Invested Assets $ 15.3 $ (12.2 ) $ 12.6 Other-Than-Temporary Impairment Loss (30.5 ) (32.4 ) (13.5 ) (15.2 ) (44.6 ) (0.9 ) Income Tax Benefit (5.4 ) (15.9 ) (0.6 ) Total $ (9.8 ) $ (28.7 ) $ (0.3 ) Net Gain on Cash Flow Hedges Net Investment Income Gain on Interest Rate Swaps and Forwards $ 54.5 $ 50.2 $ 47.8 Loss on Foreign Exchange Contracts (1.1 ) (1.6 ) (4.2 ) Net Realized Investment Gain (Loss) Gain on Interest Rate Swaps 3.2 0.5 4.3 Gain (Loss) on Foreign Exchange Contracts (1.4 ) 36.1 6.9 Interest and Debt Expense Loss on Interest Rate Swaps (1.9 ) (1.8 ) (1.8 ) 53.3 83.4 53.0 Income Tax Expense 18.6 27.1 16.6 Total $ 34.7 $ 56.3 $ 36.4 Unrecognized Pension and Postretirement Benefit Costs Other Expenses Amortization of Net Actuarial Loss $ (16.3 ) $ (11.9 ) $ (5.6 ) Amortization of Prior Service Credit 0.5 0.3 1.7 Settlement Loss — — (64.4 ) (15.8 ) (11.6 ) (68.3 ) Income Tax Benefit (5.5 ) (4.0 ) (23.8 ) Total $ (10.3 ) $ (7.6 ) $ (44.5 )

Liability for Unpaid Claims

Liability for Unpaid Claims	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Liability for Unpaid Claims Disclosure	Changes in the liability for unpaid claims and claim adjustment expenses are as follows: 2016 2015 2014 (in millions of dollars) Balance at January 1 $ 23,796.1 $ 24,194.0 $ 24,535.6 Less Reinsurance Recoverable 2,064.6 2,066.9 2,072.8 Net Balance at January 1 21,731.5 22,127.1 22,462.8 Incurred Related to Current Year 5,243.0 5,058.1 4,851.5 Prior Years Interest 1,136.7 1,177.6 1,214.7 All Other Incurred (198.3 ) (111.6 ) (13.5 ) Foreign Currency (340.2 ) (119.5 ) (138.7 ) Total Incurred 5,841.2 6,004.6 5,914.0 Paid Related to Current Year (2,035.4 ) (1,853.7 ) (1,702.3 ) Prior Years (4,451.4 ) (4,546.5 ) (4,547.4 ) Total Paid (6,486.8 ) (6,400.2 ) (6,249.7 ) Net Balance at December 31 21,085.9 21,731.5 22,127.1 Plus Reinsurance Recoverable 2,163.6 2,064.6 2,066.9 Balance at December 31 $ 23,249.5 $ 23,796.1 $ 24,194.0 The majority of the net balances are related to disability claims with long-tail payouts on which interest earned on assets backing liabilities is an integral part of pricing and reserving. Interest accrued on prior year reserves has been calculated on the opening reserve balance less one-half year's cash payments at our average reserve discount rate used during 2016 , 2015 , and 2014 . "Incurred Related to Prior Years - All Other Incurred" for 2014 shown in the preceding chart includes the reserve adjustment as discussed in the following paragraph, which impacts the comparability of 2014 to the other years presented. Excluding that adjustment, the variability exhibited year over year is caused primarily by the level of claim resolutions in the period relative to the long-term expectations reflected in the reserves. Our claim resolution rate assumption used in determining reserves is our expectation of the resolution rate we will experience over the life of the block of business and will vary from actual experience in any one period, both favorably and unfavorably. 2014 Long-term Care Reserve Increase Policy reserves for our long-term care block of business are determined using the gross premium valuation method and, prior to 2014, were valued based on assumptions established as of December 31, 2011, the date of the initial loss recognition. Gross premium valuation assumptions do not change after the date of loss recognition unless reserves are again determined to be deficient. We undertake a review of policy reserve adequacy annually during the fourth quarter of each year, or more frequently if appropriate, using best estimate assumptions as of the date of the review. Included in our 2014 review was an analysis of our reserve assumptions, including those for the discount rate, mortality and morbidity rates, persistency, and premium rate increases. Our analysis of reserve discount rate assumptions considered the continued historic low interest rate environment, future market expectations, and our view of future portfolio yields. The assumptions we established in 2011 were set at a level that we estimated would be sustainable in a low interest rate environment for three to five years, with improvements in market yields beginning after the third year. Since that time, however, interest rates had continued to hover near historic lows, and credit spreads had tightened. Our assumption update for mortality incorporated the last three years of Company-specific experience and emerging trends as well as industry data, where available and appropriate, and reflected improvements in life expectancies beyond what was initially anticipated in 2011. Our morbidity assumptions were updated to reflect trends from our own emerging Company experience in claim incidence and terminations, as well as trends based on available and appropriate industry data and studies. Our premium rate increase assumptions were updated to reflect progress-to-date and our on-going rate increase strategy. Based on our analysis at that time, we lowered the discount rate assumption to reflect the low interest rate environment and our revised expectation of future investment portfolio yield rates. Our revised assumptions anticipated the low interest rate environment persisting for the next three to five years, with a return to more historical averages over the following five year period. We updated our mortality assumptions to reflect emerging experience due to an increase in life expectancies which increases the ultimate number of people who will utilize long-term care benefits and also lengthens the amount of time a claimant may receive long-term care benefits. We changed our morbidity assumptions to reflect emerging industry experience as well as our own Company experience, and we updated our projection of future premium rate increase approvals. Using our revised best estimate assumptions, as of December 31, 2014, we determined that our policy and claim reserves should be increased $698.2 million to reflect our current estimate of future benefit obligations. Of this amount, $85.8 million was related to claim reserves, which can be attributed to prior year incurred claims, thereby impacting the results shown in the preceding chart. Reconciliation A reconciliation of policy and contract benefits and reserves for future policy and contract benefits as reported in our consolidated balance sheets to the liability for unpaid claims and claim adjustment expenses is as follows: December 31 2016 2015 2014 (in millions of dollars) Policy and Contract Benefits $ 1,507.9 $ 1,484.6 $ 1,529.3 Reserves for Future Policy and Contract Benefits 44,245.9 43,540.6 45,929.4 Total 45,753.8 45,025.2 47,458.7 Less: Life Reserves for Future Policy and Contract Benefits 8,078.2 7,946.3 7,850.9 Accident and Health Active Life Reserves 10,172.9 9,704.4 9,263.5 Adjustment Related to Unrealized Investment Gains and Losses 4,253.2 3,578.4 6,150.3 Liability for Unpaid Claims and Claim Adjustment Expenses $ 23,249.5 $ 23,796.1 $ 24,194.0 The adjustment related to unrealized investment gains and losses reflects the changes that would be necessary to policyholder liabilities if the unrealized investment gains and losses related to the corresponding available-for-sale securities had been realized. Changes in this adjustment are reported as a component of other comprehensive income or loss.

Income Tax

Income Tax	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Tax Disclosure	Income Tax Total income tax expense (benefit) is allocated as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Net Income $ 416.3 $ 371.2 $ 139.9 Stockholders' Equity - Additional Paid-in Capital Stock-Based Compensation (0.3 ) (3.6 ) (3.0 ) Stockholders' Equity - Accumulated Other Comprehensive Income Change in Net Unrealized Gain on Securities Before Adjustment 318.0 (892.5 ) 725.8 Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance (200.6 ) 856.6 (665.1 ) Change in Net Gain on Cash Flow Hedges (25.4 ) (4.3 ) (2.0 ) Change in Foreign Currency Translation Adjustment — (0.1 ) — Change in Unrecognized Pension and Postretirement Benefit Costs (34.2 ) 3.2 (92.4 ) Total $ 473.8 $ 330.5 $ 103.2 A reconciliation of the income tax provision at the U.S. federal statutory rate to the income tax rate as reported in our consolidated statements of income is as follows: Year Ended December 31 2016 2015 2014 Statutory Income Tax 35.0 % 35.0 % 35.0 % Foreign Rate Differential, Inclusive of Foreign Rate Changes (2.2 ) (2.5 ) (4.0 ) Tax Credits (1.6 ) (1.4 ) (4.5 ) Other Items, Net (0.3 ) (1.1 ) (0.7 ) Effective Tax 30.9 % 30.0 % 25.8 % In 2014, our U.S. earnings included a long-term care reserve charge that resulted in a larger proportion of our 2014 earnings derived from our foreign operations and taxed at the lower rate, therefore reducing our overall effective tax rate. Our net deferred tax liability consists of the following: December 31 2016 2015 (in millions of dollars) Deferred Tax Liability Deferred Acquisition Costs $ 174.9 $ 140.4 Fixed Assets 80.7 87.1 Invested Assets 1,427.6 1,128.4 Other 63.2 55.4 Gross Deferred Tax Liability 1,746.4 1,411.3 Deferred Tax Asset Reserves 1,308.5 1,060.5 Employee Benefits 307.4 246.0 Other 17.4 14.3 Gross Deferred Tax Asset 1,633.3 1,320.8 Less: Valuation Allowance 17.2 1.3 Net Deferred Tax Asset 1,616.1 1,319.5 Net Deferred Tax Liability $ 130.3 $ 91.8 Our consolidated statements of income include amounts subject to both domestic and foreign taxation. The income and related tax expense (benefit) are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Income Before Tax Domestic $ 1,215.8 $ 1,057.8 $ 391.7 Foreign 131.9 180.5 150.3 Total $ 1,347.7 $ 1,238.3 $ 542.0 Current Tax Expense (Benefit) Federal $ 414.8 $ 280.5 $ 160.6 State and Local 0.3 — — Foreign (29.4 ) 61.6 (25.1 ) Total 385.7 342.1 135.5 Deferred Tax Expense (Benefit) Federal (14.6 ) 56.9 (50.5 ) State and Local (2.1 ) — — Foreign 47.3 (27.8 ) 54.9 Total 30.6 29.1 4.4 Total $ 416.3 $ 371.2 $ 139.9 The U.K. government enacted income tax rate reductions during 2016 and 2015. During 2016, the rate effective April 2020 was reduced to 17 percent . During 2015, the rate was reduced from 20 percent to 19 percent effective April 2017, and to 18 percent effective April 2020. Although the rate reductions in each instance became or will become effective during a subsequent year, we are required to adjust deferred tax assets and liabilities through income on the date of enactment of a rate change. As a result, we recorded income tax benefits of $4.5 million and $6.5 million for the tax rate reductions enacted during 2016 and 2015, respectively. We have not provided U.S. deferred taxes on the cumulative earnings of our non-U.S. subsidiaries. We consider these unremitted earnings to be permanently invested as they relate to ongoing operations of our non-U.S. subsidiaries. We do not intend to repatriate these earnings to fund our U.S. operations as we expect that future domestic cash flow generation will be sufficient to meet future domestic cash needs. As of December 31, 2016 , we had not recorded a deferred tax liability on approximately $1 billion of the excess of the U.S. GAAP carrying value over the tax basis of investments in non-U.S. subsidiaries that is considered permanent in duration. This amount becomes taxable upon repatriation of assets from a foreign subsidiary or a sale or liquidation of foreign subsidiaries. Should we sell the stock in our non-U.S. subsidiaries for an amount equal to the U.S. GAAP carrying value, we would recognize tax expense of approximately $200 million , assuming our ability to fully utilize foreign tax credits. Our consolidated statements of income include the following changes in unrecognized tax benefits: December 31 2016 2015 2014 (in millions of dollars) Balance at Beginning of Year $ 0.8 $ 19.8 $ 18.4 Additions for Tax Positions Related to Prior Years 0.7 — 1.7 Additions for Tax Positions Related to Current Year — — 0.3 Settlements with Tax Authorities — (19.0 ) (0.6 ) Balance at End of Year 1.5 0.8 19.8 Less Tax Attributable to Temporary Items Included Above — — (10.4 ) Total Unrecognized Tax Benefits That if Recognized Would Affect the Effective Tax Rate $ 1.5 $ 0.8 $ 9.4 Included in the balance at December 31, 2014 was $10.4 million of unrecognized tax benefits for tax positions for which the ultimate deductibility was highly certain but for which there was uncertainty about the timing of such deductibility. Other than potential interest and penalties, the disallowance of the shorter deductibility period would not have affected our results of operations but would have accelerated the payment of cash to the taxing authority. We recognize interest expense and penalties, if applicable, related to unrecognized tax benefits in tax expense net of federal income tax. We recognized a de minimis amount of interest expense related to unrecognized tax benefits during 2016. We recognized an increase (reduction) in interest expense related to unrecognized tax benefits of $(1.0) million and $0.2 million during 2015 and 2014 , respectively. We held a de minimis liability in our consolidated balance sheets for accrued interest and penalties related to unrecognized tax benefits at December 31, 2016 and 2015 . At December 31, 2014, we held a liability of $1.0 million . There are no positions for which it is reasonably possible that unrecognized tax benefits could materially increase or decrease within the next 12 months. We file federal and state income tax returns in the United States and in foreign jurisdictions. During 2015, we settled our Internal Revenue Service (IRS) audit for 2009 and 2010 and resolved a claim for refund we filed related to tax credits for years 2003 through 2012. As a result, we recognized a tax benefit of $6.8 million in our consolidated statements of income and paid an immaterial amount of additional tax. Tax years subsequent to 2012 remain subject to examination by the IRS, and tax years subsequent to 2014 remain subject to examination in major foreign jurisdictions. We believe sufficient provision has been made for all potential adjustments for years that are not closed by the statute of limitations in all major tax jurisdictions and that any such adjustments would not have a material adverse effect on our financial position, liquidity, or results of operations. We file state income tax returns in nearly every state in the United States. Tax years subsequent to 2011 remain subject to examination depending on the statute of limitation established by the various states, which is generally three to four years. Tax years subsequent to 2009 remain subject to examination in California. As of the date of the acquisition of Starmount, we recorded a net operating loss carryforward of $2.5 million and an alternative minimum tax credit carryforward of $0.6 million . During 2016, we recognized a net operating loss benefit of $1.2 million . The alternative minimum tax credit carryforward does not expire, and the remaining net operating loss carryforward of $1.3 million will expire between 2023 and 2035 ; however, we expect to utilize both within the next two tax years. We have net operating loss carryforwards for state and local income tax of approximately $160 million which will expire between 2017 and 2036 . We record valuation allowances to reduce deferred tax assets to the amount that is more likely than not to be realized. Our valuation allowance was $17.2 million and $1.3 million at December 31, 2016 and 2015, respectively. During 2016, we recorded a cumulative deferred tax asset for future state income tax benefits of $18.7 million , net of federal tax benefit, and recorded a corresponding valuation allowance of $16.3 million to reduce the deferred tax asset to the amount that is more likely than not to be realized, $1.5 million of which was recorded in other comprehensive income. During 2015, we recorded a valuation allowance of $1.3 million related to unrealized tax losses on buildings which we own and occupy in the U.K. Total income taxes paid net of refunds during 2016 , 2015 , and 2014 were $384.3 million , $189.1 million , and $155.7 million , respectively.

Debt

Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Debt Disclosure	Debt Debt consists of the following: December 31 2016 2015 Interest Rates Maturities (in millions of dollars) Long-term Debt Outstanding Principal Senior Secured Notes issued 2007 Variable 2037 $ 260.0 $ 324.0 Senior Secured Notes acquired 2016 Variable 2038 3.5 — Senior Notes issued 1998 7.000% 2018 200.0 200.0 Senior Notes issued 1998 6.750 - 7.250% 2028 365.8 365.8 Senior Notes issued 2002 7.375% 2032 39.5 39.5 Senior Notes issued 2010 5.625% 2020 400.0 400.0 Senior Notes issued 2012 and 2016 5.750% 2042 500.0 250.0 Senior Notes issued 2014 4.000% 2024 350.0 350.0 Senior Notes issued 2015 3.875% 2025 275.0 275.0 Senior Notes issued 2016 3.000% 2021 350.0 — Medium-term Notes issued 1990 - 1996 7.000 - 7.190% 2023 - 2028 50.8 50.8 Junior Subordinated Debt Securities issued 1998 7.405% 2038 226.5 226.5 Fair Value Hedges Adjustment (3.1 ) (2.7 ) Less: Unamortized Net Premium (Discount) 9.8 (3.8 ) Unamortized Debt Issuance Costs (28.4 ) (25.7 ) Total Long-term Debt 2,999.4 2,449.4 Short-term Debt Outstanding Principal Senior Notes issued 2009 7.125% 2016 — 350.0 Fair Value Hedges Adjustment — 2.4 Less Unamortized Debt Issuance Costs — (0.4 ) Total Short-term Debt — 352.0 Total Debt $ 2,999.4 $ 2,801.4 Collateralized debt is comprised of our senior secured notes and ranks highest in priority, followed by unsecured notes, which consist of senior notes and medium-term notes, followed by junior subordinated debt securities. The senior notes due 2018 and medium-term notes are non-callable and the junior subordinated debt securities are callable under limited, specified circumstances. The remaining debt is callable and may be redeemed, in whole or in part, at any time. The aggregate contractual principal maturities are $200.0 million in 2018, $400.0 million in 2020, $350.0 million in 2021, and $2,071.1 million thereafter. Senior Secured Notes In 2007, Northwind Holdings, LLC (Northwind Holdings), a wholly-owned subsidiary of Unum Group, issued $800.0 million of insured, senior secured notes (the Northwind notes) in a private offering. The Northwind notes bear interest at a floating rate equal to the three-month LIBOR plus 0.78% . Northwind Holdings’ ability to meet its obligations to pay principal, interest, and other amounts due on the Northwind notes will be dependent principally on its receipt of dividends from Northwind Reinsurance Company (Northwind Re), the sole subsidiary of Northwind Holdings. Northwind Re reinsured the risks attributable to specified individual disability insurance policies issued by or reinsured by Provident Life and Accident Insurance Company, Unum Life Insurance Company of America, and The Paul Revere Life Insurance Company (collectively, the ceding insurers) pursuant to separate reinsurance agreements between Northwind Re and each of the ceding insurers. The ability of Northwind Re to pay dividends to Northwind Holdings will depend on its satisfaction of applicable regulatory requirements and the performance of the reinsured policies. Recourse for the payment of principal, interest and other amounts due on the Northwind notes is limited to the collateral for the Northwind notes and the other assets, if any, of Northwind Holdings. The collateral consists of a first priority, perfected security interest in (a) the debt service coverage account (DSCA) that Northwind Holdings is required to maintain in accordance with the indenture pursuant to which the Northwind notes were issued (the Northwind indenture), (b) the capital stock of Northwind Re and the dividends and distributions on such capital stock, and (c) Northwind Holdings' rights under the transaction documents related to the Northwind notes to which Northwind Holdings is a party. At December 31, 2016 , the amount in the DSCA was $27.6 million . None of Unum Group, the ceding insurers, Northwind Re, or any other affiliate of Northwind Holdings is an obligor or guarantor with respect to the Northwind notes. Northwind Holdings is required to repay a portion of the outstanding principal under the Northwind notes at par on the quarterly scheduled payment dates under the Northwind notes in an amount equal to the lesser of (i) a targeted amortization amount as defined in the Northwind indenture and (ii) the amount of the remaining available funds in the DSCA minus an amount equal to the minimum balance that is required to be maintained in the DSCA under the Northwind indenture, provided that Northwind Holdings has sufficient funds available to pay its other expenses, including interest payments on the Northwind notes, and to maintain the minimum balance in the DSCA as required under the Northwind indenture. During 2016 , 2015 , and 2014 , Northwind Holdings made principal payments of $64.0 million , $74.4 million , and $41.6 million , respectively, on the Northwind notes. In conjunction with the purchase of Starmount in 2016, we acquired $3.5 million of senior secured floating rate notes due 2038. The notes, issued by Starmount Life Insurance Company, are secured by Starmount's home office building and are guaranteed by H&J Capital L.L.C, parent company of Starmount Life Insurance Company and a wholly-owned subsidiary of Unum Group. Upon issuance, Starmount entered into a receive variable, pay fixed interest rate swap which effectively converted the notes into fixed rate debt. See Notes 4 and 13. Unsecured Notes In September 2016, our $350.0 million 7.125% senior unsecured notes matured. In May 2016, we issued a total of $600.0 million aggregate principal amount of senior notes: (i) $350.0 million aggregate principal amount of senior notes due in 2021 with an annual coupon rate of 3.00% , and (ii) $250.0 million aggregate principal amount of senior notes due in 2042 with an annual coupon rate of 5.75% , pursuant to a reopening of the $250.0 million aggregate principal amount outstanding of our 5.75% senior notes due 2042 issued in 2012. Both issuances are callable at or above par and rank equally in the right of payment with all of our other unsecured and unsubordinated debt. In 2014, we purchased and retired $145.0 million principal of our 6.85% notes, including a make-whole amount of $13.2 million , for a total cost of $158.2 million . In conjunction with this retirement, we reclassified $13.1 million of the deferred gain on previously terminated derivatives associated with the hedge of this debt from accumulated other comprehensive income to realized investment gain in our consolidated statements of income. The remaining $151.9 million balance of these notes matured in November 2015. Fair Value Hedges As of December 31, 2016 and 2015 , we had $250.0 million and $600.0 million , respectively, notional amount interest rate swaps which effectively convert certain of our unsecured senior notes into floating rate debt. Under these agreements, we receive fixed rates of interest and pay variable rates of interest, based off of three-month LIBOR. See Note 4 for further information on our interest rate swaps. Junior Subordinated Debt Securities In 1998, Provident Financing Trust I (the trust), a 100 percent -owned finance subsidiary of Unum Group, issued $300.0 million of 7.405% capital securities in a public offering. These capital securities are fully and unconditionally guaranteed by Unum Group, have a liquidation value of $1,000 per capital security, and have a mandatory redemption feature under certain circumstances. Unum Group issued 7.405% junior subordinated deferrable interest debentures to the trust in connection with the capital securities offering. The debentures mature in 2038. The sole assets of the trust are the junior subordinated debt securities. Interest Paid Interest paid on long-term and short-term debt and related securities during 2016 , 2015 , and 2014 was $153.6 million , $146.9 million , and $145.9 million , respectively. Credit Facility In March 2016, we amended the terms of our five -year, $400.0 million unsecured revolving credit facility, which was previously set to expire in 2018, to extend through March 2021. Under the terms of the agreement, we may request that the credit facility be increased up to $600.0 million . Borrowings under the credit facility are for general corporate uses and are subject to financial covenants, negative covenants, and events of default that are customary. The credit facility provides for borrowing at an interest rate based either on the prime rate or LIBOR. In addition, the credit facility provides for the issuance of letters of credit subject to certain terms and limitations. At December 31, 2016 and 2015 , letters of credit totaling $2.1 million had been issued from the credit facility, but there were no borrowed amounts outstanding.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Benefits Disclosure	Employee Benefit Plans Defined Benefit Pension and Other Postretirement Benefit (OPEB) Plans We sponsor several defined benefit pension and OPEB plans for our employees, including non-qualified pension plans. The U.S. qualified and non-qualified defined benefit pension plans comprise the majority of our total benefit obligation and benefit cost. We maintain a separate defined benefit plan for eligible employees in our U.K. operation. The U.S. defined benefit pension plans were closed to new entrants on December 31, 2013, the OPEB plan was closed to new entrants on December 31, 2012, and the U.K. plan was closed to new entrants on December 31, 2002. Amendments to Pension Plan In 2015, we amended our U.S. qualified defined benefit pension plan to increase the eligibility limit from $10,000 to $100,000 for a participant who terminates from the plan after December 31, 2015 and elects to receive a lump-sum settlement of his or her entire accrued pension benefit. As a result of this plan amendment, we recognized a decrease in the net pension liability of $7.5 million , with a corresponding prior service credit included in accumulated other comprehensive income. In 2014, we amended our U.S. qualified defined benefit pension plan to allow a limited-time offer of benefit payouts to eligible former employees with a vested right to a pension benefit. The offer provided eligible former employees, regardless of age, with an option to elect to receive a lump-sum settlement of his or her entire accrued pension benefit in December 2014 or to elect receipt of monthly pension benefits commencing in January 2015. For those who elected to receive lump-sum settlements, we made payments totaling $214.5 million from plan assets in December 2014. We recognized a before-tax settlement loss of $64.4 million in earnings during 2014, with a corresponding reduction in the unrecognized actuarial loss included in accumulated other comprehensive income that pertained to the settled benefit obligation. Amendment to OPEB Plan Effective August 1, 2016, we amended the retiree medical benefits portion of our OPEB plan to transition a majority of participants to a private exchange for their health insurance coverage. Prior to the plan amendment, participants paid a subsidized premium for their health insurance coverage, but if they elect to continue participation in the plan they will now purchase coverage on a private exchange and will subsequently be reimbursed through a Health Reimbursement Account (HRA) for an amount equivalent to the subsidy that was previously provided. Participants who continued in the plan received a one-time subsidy to minimize the initial out-of-pocket cost of purchasing health insurance. The amendment did not materially change the benefit obligation of the plan. Amortization Period of Actuarial Gain or Loss and Prior Service Cost or Credit Because all participants in the U.S. and U.K. pension plans are considered inactive, we amortize the net actuarial loss and prior service credit for these plans over the average remaining life expectancy of the plans. As of December 31, 2016 , the estimate of the average remaining life expectancy of the plans was approximately 25 years for the U.S. plan and 33 years for U.K. plan. The following table provides the changes in the benefit obligation and fair value of plan assets and the funded status of the plans. Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 (in millions of dollars) Change in Benefit Obligation Benefit Obligation at Beginning of Year $ 1,808.2 $ 1,892.6 $ 203.8 $ 226.9 $ 160.4 $ 173.9 Service Cost 7.0 3.8 — — — — Interest Cost 85.2 82.2 7.0 7.9 7.2 7.2 Plan Participant Contributions — — — — 4.0 4.6 Actuarial (Gain) Loss 123.6 (103.6 ) 55.0 (14.7 ) (4.4 ) (9.1 ) Benefits and Expenses Paid (68.7 ) (59.3 ) (4.5 ) (4.6 ) (15.6 ) (16.2 ) Plan Amendment — (7.5 ) — — (3.7 ) — Change in Foreign Exchange Rates — — (38.3 ) (11.7 ) — — Benefit Obligation at End of Year $ 1,955.3 $ 1,808.2 $ 223.0 $ 203.8 $ 147.9 $ 160.4 Accumulated Benefit Obligation at December 31 $ 1,955.3 $ 1,808.2 $ 213.4 $ 194.8 N/A N/A Change in Fair Value of Plan Assets Fair Value of Plan Assets at Beginning of Year $ 1,403.3 $ 1,473.7 $ 231.5 $ 246.3 $ 11.2 $ 11.3 Actual Return on Plan Assets 112.3 (17.5 ) 42.5 2.9 0.1 0.3 Employer Contributions 7.2 6.4 — — 11.1 11.2 Plan Participant Contributions — — — — 4.0 4.6 Benefits and Expenses Paid (68.7 ) (59.3 ) (4.5 ) (4.6 ) (15.6 ) (16.2 ) Change in Foreign Exchange Rates — — (41.1 ) (13.1 ) — — Fair Value of Plan Assets at End of Year $ 1,454.1 $ 1,403.3 $ 228.4 $ 231.5 $ 10.8 $ 11.2 Underfunded (Overfunded) Status $ 501.2 $ 404.9 $ (5.4 ) $ (27.7 ) $ 137.1 $ 149.2 The amounts recognized in our consolidated balance sheets for our pension and OPEB plans at December 31, 2016 and 2015 are as follows. Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 (in millions of dollars) Current Liability $ 7.0 $ 5.9 $ — $ — $ 13.1 $ 13.0 Noncurrent Liability 494.2 399.0 — — 124.0 136.2 Noncurrent Asset — — (5.4 ) (27.7 ) — — Underfunded (Overfunded) Status $ 501.2 $ 404.9 $ (5.4 ) $ (27.7 ) $ 137.1 $ 149.2 Unrecognized Pension and Postretirement Benefit Costs Net Actuarial Gain (Loss) $ (702.1 ) $ (604.2 ) $ (44.0 ) $ (28.1 ) $ 10.1 $ 6.2 Prior Service Credit 7.2 7.5 — — 3.9 0.4 (694.9 ) (596.7 ) (44.0 ) (28.1 ) 14.0 6.6 Income Tax 243.6 208.8 10.9 8.9 5.3 7.9 Total Included in Accumulated Other Comprehensive Income (Loss) $ (451.3 ) $ (387.9 ) $ (33.1 ) $ (19.2 ) $ 19.3 $ 14.5 The following table provides the changes recognized in other comprehensive income for the years ended December 31, 2016 and 2015 . Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 (in millions of dollars) Accumulated Other Comprehensive Income (Loss) at Beginning of Year $ (387.9 ) $ (385.5 ) $ (19.2 ) $ (25.0 ) $ 14.5 $ 9.0 Net Actuarial Gain (Loss) Amortization 16.2 11.6 0.1 0.3 — — All Other Changes (114.1 ) (22.8 ) (16.0 ) 7.0 3.9 8.8 Prior Service Credit (Cost) Amortization (0.3 ) — — — (0.2 ) (0.3 ) Plan Amendment — 7.5 — — 3.7 — Change in Income Tax 34.8 1.3 2.0 (1.5 ) (2.6 ) (3.0 ) Accumulated Other Comprehensive Income (Loss) at End of Year $ (451.3 ) $ (387.9 ) $ (33.1 ) $ (19.2 ) $ 19.3 $ 14.5 Plan Assets The objective of our U.S. pension and OPEB plans is to maximize long-term return, within acceptable risk levels, in a manner that is consistent with the fiduciary standards of the Employee Retirement Income Security Act (ERISA), while maintaining sufficient liquidity to pay current benefits and expenses. Our U.S. qualified defined benefit pension plan assets include a diversified blend of domestic, international, global, and emerging market equity securities, fixed income securities, opportunistic credit securities, real estate investments, alternative investments, and cash equivalents. Equity securities are comprised of funds and individual securities that are designed to track the respective indices specified below. International and global equity funds may allocate a certain percentage of assets to forward currency contracts. Fixed income securities include U.S. government and agency asset-backed securities, corporate investment-grade bonds, private placement securities, and bonds issued by states or other municipalities. Opportunistic credits consist of investments in funds that hold varied fixed income investments purchased at depressed values with the intention to later sell those investments for a gain. Real estate investments consist primarily of funds that hold commercial real estate investments. Alternative investments, which include private equity direct investments, private equity funds of funds, and hedge funds of funds, utilize proprietary strategies that are intended to have a low correlation to the U.S. stock market. Prohibited investments include, but are not limited to, unlisted securities, futures contracts, options, short sales, and investments in securities issued by Unum Group or its affiliates. The invested asset classes, asset types, and benchmark indices for our U.S. qualified defined benefit pension plan is as follows. We target approximately 33 percent to equity securities, 40 percent to fixed income securities, and 27 percent to opportunistic credits, alternative, and real estate investments. Asset Class Asset Type Benchmark Indices Equity Securities Collective fund; Individual holdings Standard & Poor's 500; Russell 2000 Value and Growth; MSCI Europe Australasia Far East Small Cap; MSCI Emerging Markets; MSCI World and World Minimum Volatility; FTSE RAFI All-World Low Volatility Fixed Income Individual holdings Bloomberg Barclays Long Government/Corporate Index Opportunistic Credits Collective fund Custom Index Real Estate Collective fund National Council of Real Estate Investment Fund Open-end Diversified Core Equity Index Alternative Investments (Hedge and Private Equity) Fund of funds; Direct investments Hedge Fund Research Institute Fund of Funds; Russell 2000 Assets for our U.K. pension plan are primarily invested in a pooled diversified growth fund. This fund invests in assets such as global equities, hedge funds, commodities, below-investment-grade fixed income securities, and currencies. The objectives of the fund are to generate capital appreciation over the course of a complete economic and market cycle and to deliver equity-like returns in the medium-to-long term while maintaining approximately two thirds of the volatility of equity markets. Performance of this fund is measured against the U.K. inflation rate plus four percent. The remaining assets in the U.K. plan are invested in leveraged interest rate and inflation swap and gilt funds of varying durations designed to broadly match the interest rate and inflation sensitivities of the plan's liabilities. The current target allocation for the assets is 65 percent diversified growth assets and 35 percent interest rate and inflation swap funds. There are no categories of investments that are specifically prohibited by the U.K. plan, but there are general guidelines that ensure prudent investment action is taken. Such guidelines include the prevention of the plan from using derivatives for speculative purposes and limiting the concentration of risk in any one type of investment. Assets for the OPEB plan are invested in life insurance contracts issued by one of our insurance subsidiaries. The assets support life insurance benefits payable to certain former retirees covered under the OPEB plan. The terms of these contracts are consistent in all material respects with those the subsidiary offers to unaffiliated parties that are similarly situated. There are no categories of investments specifically prohibited by the OPEB plan. We believe our investment portfolios are well diversified by asset class and sector, with no undue risk concentrations in any one category. The categorization of fair value measurements by input level for the invested assets in our U.S. pension plans is shown below. The carrying values of investment-related receivables and payables approximate fair value due to the short-term nature of the securities and are not included in the following chart. Investments valued using net asset value (NAV) as a practical expedient are not required to be categorized by input level, but these investments are included as follows to reconcile to total invested assets. Prior year amounts have been reclassified to conform to current year presentation. December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) NAV as a Practical Total (in millions of dollars) Invested Assets Equity Securities: U.S. Large Cap $ — $ — $ — $ 85.5 $ 85.5 U.S. Small Cap 50.2 — — — 50.2 Global — — — 259.7 259.7 International — — — 26.3 26.3 Emerging Markets — — — 49.6 49.6 Fixed Income Securities: U.S. Government and Agencies 227.8 11.1 — — 238.9 Corporate — 303.6 — — 303.6 State and Municipal Securities — 2.0 — — 2.0 Opportunistic Credits — — — 181.8 181.8 Real Estate — — — 88.9 88.9 Alternative Investments: Private Equity Direct Investments — — — 37.4 37.4 Private Equity Funds of Funds — — — 32.0 32.0 Hedge Funds of Funds — — — 72.1 72.1 Cash Equivalents 21.2 — — — 21.2 Total Invested Assets $ 299.2 $ 316.7 $ — $ 833.3 $ 1,449.2 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) NAV as a Practical Total (in millions of dollars) Invested Assets Equity Securities: U.S. Large Cap $ — $ — $ — $ 176.2 $ 176.2 U.S. Mid Cap — — — 55.0 55.0 U.S. Small Cap 56.9 — — — 56.9 International 63.7 — — 62.9 126.6 Emerging Markets — — — 35.5 35.5 Fixed Income Securities: U.S. Government and Agencies 231.5 12.8 — — 244.3 Corporate — 291.4 — — 291.4 State and Municipal Securities — 2.1 — — 2.1 Opportunistic Credits — — — 163.5 163.5 Real Estate — — — 83.5 83.5 Alternative Investments: Private Equity Direct Investments — — — 30.4 30.4 Private Equity Funds of Funds — — — 35.3 35.3 Hedge Funds of Funds — — — 70.9 70.9 Cash Equivalents 28.0 — — — 28.0 Total Invested Assets $ 380.1 $ 306.3 $ — $ 713.2 $ 1,399.6 Level 1 investments consist of individual holdings and funds that are valued based on unadjusted quoted prices from active markets for identical securities. Level 2 investments consist of individual holdings that are valued using observable inputs through market corroborated pricing. Certain equity, opportunistic credit, and real estate investments are valued based on the NAV of the underlying holdings. We made no adjustments to the NAV for 2016 or 2015 . These investments have no unfunded commitments and no specific redemption restrictions. Alternative investments are valued based on NAV in a period ranging from one month to one quarter in arrears. We evaluate the need for adjustments to the NAV based on market conditions and discussions with fund managers in the period subsequent to the valuation date and prior to issuance of the financial statements. We made no adjustments to the NAV for 2016 or 2015 . The private equity direct investments and private equity funds of funds generally cannot be redeemed by investors, and distributions are received following the maturity of the underlying assets. It is estimated that these underlying assets will mature between five and eight years from the date of initial investment. Redemptions on the hedge funds of funds can be made on either a quarterly or bi-annual basis, depending on the fund, with prior notice of at least 90 calendar days. The categorization of fair value measurements by input level for the invested assets in our U.K. pension plan is shown below. Investments valued using NAV as a practical expedient are not required to be categorized by input level, but these investments are included as follows to reconcile to total invested assets. Prior year amounts have been reclassified to conform to current year presentation. December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) NAV as a Practical Total (in millions of dollars) Plan Assets Diversified Growth Assets $ — $ — $ — $ 140.1 $ 140.1 Fixed Interest and Index-linked Securities 79.9 — — 7.5 87.4 Cash Equivalents 0.9 — — — 0.9 Total Plan Assets $ 80.8 $ — $ — $ 147.6 $ 228.4 December 31, 2015 Quoted Prices Significant Significant NAV as a Practical Total (in millions of dollars) Plan Assets Diversified Growth Assets $ — $ — $ — $ 156.3 $ 156.3 Fixed Interest and Index-linked Securities 62.2 — — 5.3 67.5 Cash Equivalents 7.7 — — — 7.7 Total Plan Assets $ 69.9 $ — $ — $ 161.6 $ 231.5 Level 1 fixed interest and index-linked securities consist of individual funds that are valued based on unadjusted quoted prices from active markets for identical securities. Diversified growth assets and certain fixed interest and index-linked securities are valued based on the NAV of the underlying holdings. We made no adjustments to the NAV for 2016 or 2015 . These investments have no unfunded commitments and no specific redemption restrictions. The categorization of fair value measurements by input level for the assets in our OPEB plan is as follows: December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Life Insurance Contracts $ — $ — $ 10.8 $ 10.8 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Life Insurance Contracts $ — $ — $ 11.2 $ 11.2 The fair value is represented by the actuarial present value of future cash flows of the contracts. Changes in our OPEB plan assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the years ended December 31, 2016 and 2015 are as follows: Year Ended December 31, 2016 Beginning of Year Actual Return on Plan Assets Contributions Net Benefits and Expenses Paid End of Year (in millions of dollars) Life Insurance Contracts $ 11.2 $ 0.1 $ 15.1 $ (15.6 ) $ 10.8 Year Ended December 31, 2015 Beginning of Year Actual Return on Plan Assets Contributions Net Benefits and Expenses Paid End of Year (in millions of dollars) Life Insurance Contracts $ 11.3 $ 0.3 $ 15.8 $ (16.2 ) $ 11.2 For the years ended December 31, 2016 and 2015 , the actual return on plan assets relates solely to investments still held at the reporting date. There were no transfers into or out of Level 3 during 2016 or 2015 . Measurement Assumptions We use a December 31 measurement date for each of our plans. The weighted average assumptions used in the measurement of our benefit obligations as of December 31 and our net periodic benefit costs for the years ended December 31 are as follows: Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 Benefit Obligations Discount Rate 4.40 % 4.80 % 2.70 % 3.80 % 4.20 % 4.70 % Rate of Compensation Increase N/A N/A 3.80 % 3.60 % N/A N/A Net Periodic Benefit Cost Discount Rate 4.80 % 4.40 % 3.80 % 3.60 % 4.70 % 4.30 % Expected Return on Plan Assets 7.50 % 7.50 % 4.90 % 5.20 % 5.75 % 5.75 % Rate of Compensation Increase N/A N/A 3.60 % 3.60 % N/A N/A We set the discount rate assumption annually for each of our retirement-related benefit plans at the measurement date to reflect the yield on a portfolio of high quality fixed income corporate debt instruments matched against the projected cash flows for future benefits. Our long-term rate of return on plan assets assumption is selected from a range of probable return outcomes generated by statistical analysis of the asset portfolio. Our expectations for the future investment returns of the asset categories are based on a combination of historical market performance, evaluations of investment forecasts obtained from external consultants and economists, and current market yields. The methodology underlying the return assumption includes the various elements of the expected return for each asset class such as long-term rates of return, volatility of returns, and the correlation of returns between various asset classes. The expected return for the total portfolio is calculated based on the plan's strategic asset allocation. Investment risk is measured and monitored on an ongoing basis through annual liability measurements, periodic asset/liability studies, and quarterly investment portfolio reviews. Risk tolerance is established through consideration of plan liabilities, plan funded status, and corporate financial condition. Our mortality rate assumption reflects our best estimate, as of the measurement date, of the life expectancies of plan participants in order to determine the expected length of time for benefit payments. We derive our assumptions from industry mortality tables. The expected return assumption for the life insurance reserve for our OPEB plan at December 31, 2016 and 2015 is 5.75 percent , which is based on full investment in fixed income securities with an average book yield of 4.99 percent and 5.24 percent in 2016 and 2015 , respectively. The rate of compensation increase assumption for our U.K. pension plan is generally based on periodic studies of compensation trends. At December 31, 2016 and 2015 , the annual rates of increase in the per capita cost of covered postretirement health care benefits assumed for the next calendar year are 7.00 percent and 7.50 percent , respectively, for benefits payable to both retirees prior to Medicare eligibility as well as Medicare eligible retirees. The rates are assumed to change gradually to 5.00 percent by 2021 for measurement at December 31, 2016 and remain at that level thereafter. The annual rates of increase in the per capita cost of covered postretirement health benefits do not apply to retirees whose postretirement health care benefits are provided through an exchange. Net Periodic Benefit Cost The following table provides the components of the net periodic benefit cost for the years ended December 31. Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2014 2016 2015 2014 2016 2015 2014 (in millions of dollars) Service Cost $ 7.0 $ 3.8 $ 3.7 $ — $ — $ 2.3 $ — $ — $ 0.3 Interest Cost 85.2 82.2 89.9 7.0 7.9 9.1 7.2 7.2 7.9 Expected Return on Plan Assets (102.8 ) (108.9 ) (117.8 ) (10.0 ) (12.4 ) (13.7 ) (0.6 ) (0.7 ) (0.7 ) Amortization of: Net Actuarial Loss 16.2 11.6 5.2 0.1 0.3 0.4 — — — Prior Service Credit (0.3 ) — — — — — (0.2 ) (0.3 ) (1.7 ) Plan Amendment — — — — — — 0.9 — — Settlement — — 64.4 — — — — — — Total Net Periodic Benefit Cost $ 5.3 $ (11.3 ) $ 45.4 $ (2.9 ) $ (4.2 ) $ (1.9 ) $ 7.3 $ 6.2 $ 5.8 A one percent increase or decrease in the assumed health care cost trend rate at December 31, 2016 would have increased (decreased) the service cost and interest cost by $0.2 million and $(0.2) million , respectively, and the postretirement benefit obligation by $0.9 million and $(0.8) million , respectively. The unrecognized net actuarial loss and the prior service credit included in accumulated other comprehensive income and expected to be amortized and included in net periodic pension cost during 2017 is $20.2 million and $0.7 million before tax, respectively. Benefit Payments The following table provides expected benefit payments, which reflect expected future service, as appropriate. Pension Benefits U.S. Plans U.K. Plan OPEB (in millions of dollars) Year Gross Subsidy Payments Net 2017 $ 71.8 $ 4.5 $ 13.6 $ 0.3 $ 13.3 2018 74.4 4.8 13.2 0.2 13.0 2019 76.9 4.8 12.8 0.2 12.6 2020 80.6 5.1 12.3 0.2 12.1 2021 84.3 5.4 11.9 0.2 11.7 2022-2026 476.9 32.5 50.9 0.7 50.2 Funding Policy The funding policy for our U.S. qualified defined benefit plan is to contribute annually an amount at least equal to the minimum annual contribution required under ERISA and other applicable laws, but generally not greater than the maximum amount that can be deducted for federal income tax purposes. We had no regulatory contribution requirements for our U.S. qualified defined benefit plan in 2016 and made no voluntary contributions during 2016 . We do not expect to make any contributions in 2017 . The funding policy for our U.S. non-qualified defined benefit pension plan is to contribute the amount of the benefit payments made during the year. Our expected return on plan assets and discount rate will not affect the cash contributions we are required to make to our U.S. pension and OPEB plans because such contributions are determined under the minimum funding requirements as set forth in ERISA. We made no contributions to our U.K. plan during 2016 , nor do we expect to make any contributions in 2017, either voluntary or those required to meet the minimum funding requirements under U.K. legislation. Our OPEB plan represents a non-vested, non-guaranteed obligation, and current regulations do not require specific funding levels for these benefits, which are comprised of retiree life, medical, and dental benefits. It is our practice to use general assets to pay medical and dental claims as they come due in lieu of utilizing plan assets for the medical and dental benefit portions of our OPEB plan. Defined Contribution Plans We offer a 401(k) plan to all eligible U.S. employees under which a portion of employee contributions is matched. We match dollar-for-dollar up to 5.0 percent of base salary and any recognized sales and performance-based incentive compensation for employee contributions into the plan. We also make an additional non-elective contribution of 4.5 percent of earnings for all eligible employees and a separate transition contribution for eligible employees who met certain age and years of service criteria as of December 31, 2013. The 401(k) plan remains in compliance with ERISA guidelines and continues to qualify for a “safe harbor” from annual discrimination testing. We also offer a defined contribution plan to all eligible U.K. employees under which a portion of employee contributions is matched. Effective July 1, 2014, we increased benefits under the defined contribution plan wherein we match two pounds for every one pound on the first 1.0 percent of employee contributions into the plan and match additional employee contributions pound-for-pound up to 5.0 percent of base salary. We previously matched pound-for-pound up to 5.0 percent of base salary for employee contributions into the defined contribution plan and made an additional non-elective contribution of 5.0 percent of base salary. Also effective July 1, 2014, we increased the non-elective contribution to 6.0 percent of base salary for all eligible employees, and a separate transition contribution was made for all eligible employees through March 31, 2016. During the years ended December 31, 2016 , 2015 , and 2014 , we recognized costs of $72.2 million , $71.5 million , and $76.0 million , respectively, for our U.S. defined contribution plan and $4.9 million , $5.7 million , and $5.0 million , respectively, for our U.K. defined contribution plan.

Stockholders' Equity and Earnin

Stockholders' Equity and Earnings Per Common Share	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity and Earnings Per Common Share [Abstract]
Earnings Per Share Disclosure	Earnings Per Common Share Net income per common share is determined as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars, except share data) Numerator Net Income $ 931.4 $ 867.1 $ 402.1 Denominator (000s) Weighted Average Common Shares - Basic 235,445.7 246,986.7 255,525.9 Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards 533.5 868.0 1,126.9 Weighted Average Common Shares - Assuming Dilution 235,979.2 247,854.7 256,652.8 Net Income Per Common Share Basic $ 3.96 $ 3.51 $ 1.57 Assuming Dilution $ 3.95 $ 3.50 $ 1.57 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 $27.85 to $36.36 ; and the nonvested performance share units have grant prices ranging from $27.85 to $34.08 . See Note 11. In computing earnings per share assuming dilution, only potential common shares that are dilutive (those that reduce earnings per share) are included. Potential common shares not included in the computation of diluted earnings per share because the impact would be antidilutive, based on then current market prices, approximated 0.4 million , 0.3 million , and 0.1 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively.
Stockholders' Equity Disclosure	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 May 2016 May 2015 December 2013 (in millions of dollars) Authorized Repurchase Amount $ 750.0 $ 750.0 $ 750.0 Remaining Repurchase Amount at Year End 2016 $ 495.7 $ — $ — The May 2016 share repurchase program has an expiration date of November 26, 2017 . Common stock repurchases, which are accounted for using the cost method and classified as treasury stock until otherwise retired, were as follows: Year Ended December 31 2016 2015 2014 (in millions) Shares Repurchased 11.9 12.3 8.7 Cost of Shares Repurchased (1) $ 403.3 $ 426.7 $ 300.6 (1) Includes commissions of $0.2 million , $0.3 million , and $0.1 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively. During 2014, we retired 60.0 million shares of our treasury stock with an average total cost of $1,451.7 million . Preferred Stock Unum Group has 25.0 million shares of preferred stock authorized with a par value of $0.10 per share. No preferred stock has been issued to date.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments	Stock-Based Compensation Description of Stock Plans Under the Stock Incentive Plan of 2012 (the 2012 Plan), up to 20 million shares of common stock are available for awards to our employees, officers, consultants, and directors. Awards may be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each full-value award, defined as any award other than a stock option or stock appreciation right, is counted as 1.76 shares. The exercise price for stock options issued cannot be less than the fair value of the underlying common stock as of the grant date. Stock options generally have a term of eight years after the date of grant and fully vest after three years. At December 31, 2016 , approximately 14.2 million shares were available for future grants under the 2012 Plan. Under the Stock Incentive Plan of 2007 (the 2007 Plan), which was terminated in May 2012 for purposes of any further grants, up to 35 million shares of common stock were available for awards to our employees, officers, consultants, and directors. Awards could be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each full-value award, defined as any award other than a stock option or stock appreciation right, is counted as 2.7 shares. Awards granted before the termination of the 2007 Plan remain outstanding in accordance with the plan's terms. Stock options generally have a term of eight years after the date of grant and fully vest after three years. We issue new shares of common stock for all of our stock plan vestings and exercises. Performance Share Units (PSUs) Activity for PSUs classified as equity is as follows: Weighted Average Shares Grant Date (000s) Fair Value Outstanding at December 31, 2015 383 $ 35.05 Granted 219 28.41 Vested (167 ) 34.79 Forfeited (6 ) 32.54 Outstanding at December 31, 2016 429 31.80 During 2016 , 2015 , and 2014 , we issued PSUs with a weighted average grant date fair value per share of $28.41 , $35.13 , and $34.72 , respectively. Vesting for the PSUs occurs at the end of a three-year period and is contingent upon our achievement of prospective company performance goals and our total shareholder return relative to a board-approved peer group during the three -year period. Actual perform ance, including modification for relative total shareholder return, may result in the ultimate award of 40 to 180 percent of the initial number of PSUs issued, with the potential for no award if company performance goals are not achieved during the three-year period. Forfeitable dividend equivalents on PSUs are accrued in the form of additional PSUs. PSU shares in the preceding table represent aggregate initial target awards and accrued dividend equivalents and do not reflect potential increases or decreases resulting from the performance factor determined after the end of the performance periods. At December 31, 2016 , the three -year performance period for the 2014 PSU grant was completed, but the performance factor had not yet been applied. Vested amounts in the preceding table represent vested PSUs for which the 2014 through 2016 performance factor will be applied during the first quarter of 2017, with distribution of the stock thereafter. At December 31, 2016 , w e had approximately $7.4 million of unrecognized compensation cost related to PSUs that will be recognized over a weighted average period of 1.5 years . The estimated compensation expense is adjusted for actual performance experience and is recognized ratably during the service period, or remaining service period, if and when it becomes probable that the performance conditions will be satisfied. Compensation cost for PSUs subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period. The fair value of PSUs is estimated on the date of initial grant using the Monte-Carlo simulation m odel. Key assumptions used to value PSUs granted during the years shown are as follows: Year Ended December 31 2016 2015 2014 Expected Volatility (based on our and our peer group historical daily stock prices) 22 % 22 % 31 % Expected Life (equals the performance period) 3.0 years 3.0 years 3.0 years Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant) 0.88 % 0.91 % 0.65 % Restricted Stock Units (RSUs) Activity for RSUs classified as equity is as follows: Weighted Average Shares Grant Date (000s) Fair Value Outstanding at December 31, 2015 866 $ 32.40 Granted 632 28.80 Vested (587 ) 31.22 Forfeited (33 ) 30.64 Outstanding at December 31, 2016 878 30.66 During 2016 , 2015 , and 2014 , we issued RSUs with a weighted average grant date fair value per share of $28.80 , $34.08 , and $33.77 , respectively. RSUs vest over a one to three -year service period, beginning at the date of grant, and the compensation cost is recognized ratably during the vesting period. Forfeitable dividend equivalents on RSUs are accrued in the form of additional RSUs. Compensation cost for RSUs subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period. The total fair value of shares vested during 2016 , 2015 , and 2014 was $18.3 million , $21.4 million , and $19.8 million , respectively. At December 31, 2016 , we had $13.0 million of unrecognized compensation cost related to RSUs that will be recognized over a weighted average period of 0.9 years . Cash-Settled Awards There were no outstanding cash-settled awards at December 31, 2016 and 2015 . All cash-settled awards were fully vested at December 31, 2015 . Fully vested awards not distributed in 2015 were paid in 2016 . The amount paid per unit awarded was equal to the price per share of Unum Group's common stock at settlement of the award, and as such, we measured the value of the award each reporting period based on the current stock price. The effects of changes in the stock price during the service period were recognized as compensation cost over the service period. Changes in the amount of the liability due to stock price changes after the service period were recognized as compensation cost during the period in which the changes occurred. At December 31, 2016, we had no unrecognized compensation cost related to cash-settled awards. Year Ended December 31 2016 2015 2014 (in millions of dollars, except per unit data) Weighted Average Grant Date Fair Value per Unit Granted $ — $ 33.92 $ 33.85 Total Fair Value of Units Vested $ — $ 4.9 $ 2.1 Total Fair Value of Units Paid $ 2.4 $ 2.5 $ 2.9 Stock Options Stock option activity is summarized as follows: Remaining Intrinsic Shares Weighted Average Contractual Term Value (000s) Exercise Price (in years) (in millions) Outstanding at December 31, 2015 759 $ 23.02 Exercised (242 ) 21.01 Outstanding at December 31, 2016 517 23.97 2.7 $ 10.3 Exercisable at December 31, 2016 517 $ 23.97 2.7 $ 10.3 All outstanding stock options at December 31, 2016 have vested. Stock options vest over a one to three -year service period, beginning at the date of grant, and the compensation cost is recognized ratably during the vesting period. Compensation cost for stock options subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period. At December 31, 2016 , we had no unrecognized compensation cost related to stock options. The intrinsic value of options exercised and fair value of options vested are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Total Intrinsic Value of Options Exercised $ 3.4 $ 5.6 $ 4.0 Total Fair Value of Options Vested $ 0.1 $ 1.1 $ 2.4 There were no stock options granted in the years 2014 through 2016 . Expense Compensation expense for the stock plans, as reported in our consolidated statements of income, is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Performance Share Units $ 6.6 $ 4.5 $ 2.5 Restricted Stock Units and Cash-Settled Awards 14.9 18.6 19.0 Stock Options — 0.2 0.6 Other 0.4 0.5 0.5 Total Compensation Expense, Before Income Tax $ 21.9 $ 23.8 $ 22.6 Total Compensation Expense, Net of Income Tax $ 14.4 $ 15.7 $ 14.9 Cash received under all share-based payment arrangements for the years ended December 31, 2016 , 2015 , and 2014 was $8.5 million , $6.4 million , and $12.3 million , respectively.

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance Thirteen major companies account for approximately 91 percent of our reinsurance recoverable at December 31, 2016 , and all are rated A or better by A.M. Best Company (AM Best) or are fully securitized by letters of credit or investment-grade fixed maturity securities held in trust. Approximately eight percent of our reinsurance recoverable relates to business reinsured either with companies rated A- or better by AM Best, with overseas entities with equivalent ratings or backed by letters of credit or trust agreements, or through reinsurance arrangements wherein we retain the assets in our general account. The remaining one percent of our reinsurance recoverable is held by companies either rated below A- by AM Best or not rated. Reinsurance data is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Direct Premium Income $ 8,385.0 $ 8,151.9 $ 7,899.3 Reinsurance Assumed 236.3 202.8 189.8 Reinsurance Ceded (263.6 ) (272.3 ) (291.9 ) Net Premium Income $ 8,357.7 $ 8,082.4 $ 7,797.2 Ceded Benefits and Change in Reserves for Future Benefits $ 648.3 $ 662.7 $ 662.7 Effective October 1, 2016, we entered into a reinsurance agreement under which we ceded 30 percent of the risk for certain blocks of Unum US individual disability policies, as well as some related claims development risk for a limited period of time. The agreement is on a non-proportional modified coinsurance basis with a provision for experience refunds.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	Segment Information We have three principal operating business segments: Unum US, Unum UK, and Colonial Life. Our other segments are Closed Block and Corporate. The Unum US segment includes group long-term and short-term disability insurance, group life and accidental death and dismemberment products, and supplemental and voluntary lines of business. The supplemental and voluntary lines of business are comprised of individual disability, voluntary benefits, and dental and vision products. These products are marketed through our field sales personnel who work in conjunction with independent brokers and consultants. The Unum UK segment includes insurance for group long-term disability, group life, and supplemental lines of business, which include dental, individual disability, and critical illness products. Unum UK's products are sold primarily in the United Kingdom through field sales personnel and independent brokers and consultants. The Colonial Life segment includes insurance for accident, sickness, and disability products, life products, and cancer and critical illness products marketed to employees, on both a group and an individual basis, at the workplace through an independent contractor agency sales force and brokers. The Closed Block segment consists of individual disability, group and individual long-term care, and other insurance products no longer actively marketed. The individual disability line of business in this segment generally consists of policies we sold prior to the mid-1990s and entirely discontinued selling in 2004, other than update features contractually allowable on existing policies. We discontinued offering individual long-term care in 2009 and group long-term care in 2012. Other insurance products include group pension, individual life and corporate-owned life insurance, reinsurance pools and management operations, and other miscellaneous product lines. The Corporate segment includes investment income on corporate assets not specifically allocated to a line of business, interest expense on corporate debt other than non-recourse debt, and certain other corporate income and expense not allocated to a line of business. Acquisitions of Business In August 2016, we acquired 100 percent of the shares and voting interests in H&J Capital, L.L.C., parent of Starmount Life Insurance Company and AlwaysCare Benefits (Starmount) , for a total cash purchase price of $140.3 million plus contingent cash consideration of $10.0 million to be paid in two increments of $5.0 million each, at 18 and 24 months from the date of acquisition upon satisfaction of certain conditions. Starmount Life Insurance Company is an independent provider of dental and vision insurance in the U.S. workplace, and AlwaysCare Benefits is a nationally licensed, third-party administrator. The acquisition of Starmount will broaden our employee benefit offerings in the U.S. Starmount's dental and vision products and new dental and vision products to be marketed by Unum US are reported in our Unum US segment within our supplemental and voluntary product lines. Colonial Life dental and vision products are expected to be introduced in 2018 and will be reported in our Colonial Life segment. Starmount's revenues totaled $129.9 million in 2015. Total assets were valued at $93.1 million as of the acquisition date and were primarily comprised of bonds, cash, accounts receivable, and intangible assets attributable to the value of business acquired and the value of existing state licenses. Total liabilities were valued at $55.7 million as of the acquisition date and were primarily comprised of outstanding claim liabilities and reserves for future claims. The total purchase price exceeded the fair value of the identifiable net assets by $111.2 million and has been identified as goodwill, primarily attributable to the value of adding dental and vision to our current employee benefit offerings. Goodwill was allocated to the reporting units expected to benefit from the acquisition. Approximately 75 percent was allocated to our Unum US supplemental and voluntary product lines and approximately 25 percent to Colonial Life. The goodwill is not deductible for income tax purposes except upon disposition of the acquired entity. This acquisition, the results of which are included in our consolidated financial statements for the period subsequent to the date of acquisition, did not have a material impact on revenue or operating results for 2016. In September 2015, we acquired 100 percent of the common shares and voting interests in National Dental Plan Limited and associated companies (National Dental) for a total cash purchase price of £35.9 million or $54.3 million . National Dental, a provider of dental insurance in the U.K. workplace, is reported in our Unum UK segment as part of our supplemental product line. The acquisition of National Dental extends our market reach, broadening our employee benefit offerings in the U.K. National Dental's revenues totaled £14.7 million , or $24.2 million , in 2014. Total assets were £18.6 million , or $28.1 million as of the acquisition date, and were primarily comprised of short-term investments, accounts receivable, and intangible assets attributable to benefits derived from National Dental's customer relationships and dental provider network. Total liabilities were £5.0 million , or $7.5 million as of the acquisition date, and were primarily comprised of outstanding claims liabilities, unearned premiums, and a deferred tax liability. The purchase price exceeded the fair value of the identifiable net assets by £22.3 million , or $33.7 million , and has been identified as goodwill, primarily attributable to the value of adding dental to our current employee benefit offerings. The goodwill is not deductible for income tax purposes except upon disposition of the acquired entity. This acquisition, the results of which are included in our consolidated financial statements for the period subsequent to the date of acquisition, did not have a material impact on revenue or operating results for 2015. Segment information is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Premium Income Unum US Group Disability Group Long-term Disability $ 1,726.6 $ 1,644.7 $ 1,553.5 Group Short-term Disability 626.1 607.4 558.1 Group Life and Accidental Death & Dismemberment Group Life 1,410.0 1,347.4 1,262.3 Accidental Death & Dismemberment 140.3 131.7 125.9 Supplemental and Voluntary Individual Disability 480.3 478.9 466.1 Voluntary Benefits 796.5 749.9 693.8 Dental and Vision 61.1 — — 5,240.9 4,960.0 4,659.7 Unum UK Group Long-term Disability 355.2 397.4 418.9 Group Life 105.7 121.5 133.2 Supplemental 68.4 57.3 55.1 529.3 576.2 607.2 Colonial Life Accident, Sickness, and Disability 830.0 789.0 759.8 Life 273.8 252.4 231.8 Cancer and Critical Illness 313.3 297.2 282.1 1,417.1 1,338.6 1,273.7 Closed Block Individual Disability 521.9 572.4 624.8 Long-term Care 643.9 633.5 630.9 All Other 4.6 1.7 0.9 1,170.4 1,207.6 1,256.6 Total Premium Income $ 8,357.7 $ 8,082.4 $ 7,797.2 Unum US Unum UK Colonial Life Closed Block Corporate Total (in millions of dollars) Year Ended December 31, 2016 Premium Income $ 5,240.9 $ 529.3 $ 1,417.1 $ 1,170.4 $ — $ 8,357.7 Net Investment Income 828.7 118.1 141.5 1,352.2 18.5 2,459.0 Other Income 113.3 0.2 1.2 86.0 4.9 205.6 Operating Revenue $ 6,182.9 $ 647.6 $ 1,559.8 $ 2,608.6 $ 23.4 $ 11,022.3 Operating Income (Loss) $ 914.2 $ 128.6 $ 314.2 $ 129.5 $ (146.7 ) $ 1,339.8 Interest and Debt Expense $ — $ — $ — $ 6.9 $ 159.1 $ 166.0 Depreciation and Amortization $ 353.0 $ 16.4 $ 222.9 $ 6.9 $ 1.0 $ 600.2 Year Ended December 31, 2015 Premium Income $ 4,960.0 $ 576.2 $ 1,338.6 $ 1,207.6 $ — $ 8,082.4 Net Investment Income 865.3 124.9 145.4 1,320.0 25.6 2,481.2 Other Income 119.2 — 0.1 89.3 2.9 211.5 Operating Revenue $ 5,944.5 $ 701.1 $ 1,484.1 $ 2,616.9 $ 28.5 $ 10,775.1 Operating Income (Loss) $ 850.0 $ 140.6 $ 309.1 $ 119.1 $ (124.8 ) $ 1,294.0 Interest and Debt Expense $ — $ — $ — $ 6.6 $ 146.2 $ 152.8 Depreciation and Amortization $ 347.0 $ 18.0 $ 214.6 $ 6.6 $ 0.9 $ 587.1 Year Ended December 31, 2014 Premium Income $ 4,659.7 $ 607.2 $ 1,273.7 $ 1,256.6 $ — $ 7,797.2 Net Investment Income 878.9 151.0 145.5 1,281.5 35.3 2,492.2 Other Income 122.1 — 0.1 91.8 5.0 219.0 Operating Revenue $ 5,660.7 $ 758.2 $ 1,419.3 $ 2,629.9 $ 40.3 $ 10,508.4 Operating Income (Loss) $ 844.9 $ 147.8 $ 299.0 $ 120.0 $ (104.4 ) $ 1,307.3 Interest and Debt Expense Excluding Costs Related to Early Retirement of Debt $ — $ — $ — $ 7.3 $ 147.0 $ 154.3 Depreciation and Amortization $ 314.2 $ 19.2 $ 194.1 $ 5.9 $ 1.0 $ 534.4 Colonial Unum US Unum UK Life Total (in millions of dollars) Deferred Acquisition Costs Year Ended December 31, 2016 Beginning of Year $ 1,136.4 $ 27.1 $ 845.0 $ 2,008.5 Capitalization 314.1 8.2 270.1 592.4 Amortization (275.2 ) (9.7 ) (208.1 ) (493.0 ) Adjustment Related to Unrealized Investment Gains and Losses 1.2 — (10.7 ) (9.5 ) Foreign Currency — (4.2 ) — (4.2 ) End of Year $ 1,176.5 $ 21.4 $ 896.3 $ 2,094.2 Year Ended December 31, 2015 Beginning of Year $ 1,096.5 $ 30.4 $ 774.4 $ 1,901.3 Capitalization 307.3 9.6 252.8 569.7 Amortization (272.3 ) (11.3 ) (198.7 ) (482.3 ) Adjustment Related to Unrealized Investment Gains and Losses 4.9 — 16.5 21.4 Foreign Currency — (1.6 ) — (1.6 ) End of Year $ 1,136.4 $ 27.1 $ 845.0 $ 2,008.5 Year Ended December 31, 2014 Beginning of Year $ 1,051.5 $ 34.3 $ 743.4 $ 1,829.2 Capitalization 292.7 10.5 220.8 524.0 Amortization (248.1 ) (12.5 ) (180.2 ) (440.8 ) Adjustment Related to Unrealized Investment Gains and Losses 0.4 — (9.6 ) (9.2 ) Foreign Currency — (1.9 ) — (1.9 ) End of Year $ 1,096.5 $ 30.4 $ 774.4 $ 1,901.3 December 31 2016 2015 (in millions of dollars) Assets Unum US $ 18,036.6 $ 18,242.4 Unum UK 3,101.4 3,432.4 Colonial Life 3,923.2 3,776.8 Closed Block 33,734.3 33,000.9 Corporate 3,146.0 2,111.1 Total Assets $ 61,941.5 $ 60,563.6 Revenue is primarily derived from sources in the United States and the United Kingdom. There are no material revenues or assets attributable to foreign operations other than those reported in our Unum UK segment. We report goodwill in our Unum US, Unum UK, and Colonial Life segments, which are the segments expected to benefit from the originating business combinations. At December 31, 2016 and 2015 , goodwill was $335.1 million and $230.9 million , respectively, with $271.1 million and $187.6 million , respectively, attributable to Unum US, $36.3 million and $43.3 million , respectively, attributable to Unum UK, and $27.7 million in 2016 attributable to Colonial Life. Changes in the goodwill balances for our Unum US and Colonial Life segments are attributable to the acquisition of Starmount, while changes in our Unum UK segment result from fluctuation in foreign currency exchange rates. Stockholders' equity is allocated to the operating segments on the basis of an internal allocation formula that reflects the volume and risk components of each operating segment's business and aligns allocated equity with our target capital levels for regulatory and rating agency purposes. We modify this formula periodically to recognize changes in the views of capital requirements. We measure and analyze our segment performance on the basis of "operating revenue" and "operating income" or "operating loss", which differ from total revenue and income before income tax as presented in our consolidated statements of income due to the exclusion of net realized investment gains and losses and non-operating retirement-related gains or losses as specified in the reconciliations below. We believe operating revenue and operating income or loss are better performance measures and better indicators of the revenue and profitability and underlying trends in our business. These performance measures are in accordance with GAAP guidance for segment reporting, but they should not be viewed as a substitute for total revenue, income before income tax, or net income. Realized investment gains or losses depend on market conditions and do not necessarily relate to decisions regarding the underlying business of our segments. Our investment focus is on investment income to support our insurance liabilities as opposed to the generation of realized investment gains or losses. Although we may experience realized investment gains or losses which will affect future earnings levels, a long-term focus is necessary to maintain profitability over the life of the business since our underlying business is long-term in nature, and we need to earn the interest rates assumed in calculating our liabilities. The amortization of prior period actuarial gains or losses, a component of the net periodic benefit cost for our pensions and other postretirement benefit plans, is driven by market performance as well as plan amendments and is not indicative of the operational results of our businesses. We believe that excluding the amortization of prior period gains or losses, as well as the 2014 settlement loss resulting from our pension plan amendment, from operating income or loss provides investors with additional information for comparison and analysis of our operating results. Although we manage our non-operating retirement-related gains or losses separately from the operational performance of our business, these gains or losses impact the overall profitability of our company and have historically increased or decreased over time, depending on plan amendments and market conditions and the resulting impact on the actuarial gains or losses in our pensions and other postretirement benefit plans. We believe that excluding the 2014 costs related to the early retirement of debt is appropriate because in conjunction with the debt redemption, we recognized in realized investment gains and losses a deferred gain from previously terminated derivatives which were associated with the hedge of this debt. The amount recognized as a realized investment gain, which basically offsets the cost of the debt redemption, is also excluded from our non-GAAP financial measures since we analyze our performance excluding amounts reported as realized investment gains or losses. We believe it provides investors with a more realistic view of our overall profitability if we are consistent in excluding both the cost of the debt retirement as well as the gain on the hedge of the debt. We may at other times exclude certain other items from our discussion of financial ratios and metrics in order to enhance the understanding and comparability of our operational performance and the underlying fundamentals, but this exclusion is not an indication that similar items may not recur and does not replace net income or net loss as a measure of our overall profitability. A reconciliation of total revenue to "operating revenue" and income before income tax to "operating income" is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Total Revenue $ 11,046.5 $ 10,731.3 $ 10,524.5 Excluding: Net Realized Investment Gain (Loss) 24.2 (43.8 ) 16.1 Operating Revenue $ 11,022.3 $ 10,775.1 $ 10,508.4 Income Before Income Tax $ 1,347.7 $ 1,238.3 $ 542.0 Excluding: Net Realized Investment Gain (Loss) 24.2 (43.8 ) 16.1 Non-operating Retirement-related Loss (16.3 ) (11.9 ) (70.0 ) Costs Related to Early Retirement of Debt for Corporate — — (13.2 ) Long-term Care Reserve Increase for Closed Block — — (698.2 ) Operating Income $ 1,339.8 $ 1,294.0 $ 1,307.3

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies Disclosure	Commitments We have noncancelable lease obligations on certain office space and equipment. As of December 31, 2016 , the aggregate net minimum lease payments were $189.6 million payable as follows: $50.8 million in 2017 , $25.8 million in 2018 , $22.5 million in 2019 , $18.0 million in 2020 , $13.9 million in 2021 , and $58.6 million thereafter. Rental expense for the years ended December 31, 2016 , 2015 , and 2014 was $51.4 million , $42.5 million , and $44.2 million , respectively. At December 31, 2016 , we had unfunded commitments of $314.0 million for certain of our investments, the amount of which may or may not be funded. 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 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 involving the same issue. 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 June 2015, the appellate court reinstated the case, holding that the West Virginia Uniform Unclaimed Property Act requires insurers to make reasonable efforts to determine whether their insureds are still living. The case was remanded to the trial court where we answered the complaints. In December 2016, we filed a motion to dismiss as a result of legislation enacted after the appellate court’s decision in 2015. A hearing on that motion is scheduled for March 2017. In May 2013, a purported class action complaint was filed in the Superior Court of California, County of Los Angeles. The plaintiff sought to represent a class of California insureds who were issued long-term care policies containing an inflation protection feature. The plaintiff alleged we incorrectly administered the inflation protection feature, resulting in an underpayment of benefits. The complaint made allegations against us for breach of contract, bad faith, fraud, violation of Business and Professions Code 17200, and injunctive relief. We removed the case to the United States District Court for the Central District of California, and plaintiff filed an amended complaint on behalf of a nationwide class of insureds who were issued long-term care policies containing an inflation protection feature. After we answered the complaint, the court permitted the plaintiff to file another amended complaint entitled Michael Don, Executor of The Estate of Ruben Don, Leroy Little, by and through his Guardian ad Litem Tamara Pelham, and Carolyn Little v. Unum Group, and Unum Life Insurance Company of America containing similar allegations. In April 2015, we again answered the complaint. The plaintiffs filed a motion seeking certification of five subclasses, and we filed our opposition. In February 2016, the plaintiffs filed a motion for preliminary approval of settlement for a class of certain insureds issued long-term care policies containing an inflation protection feature as well as certain insureds who requested copies of their long-term care policies. In July 2016, the court issued a final order approving the settlement and dismissing the case. We adjusted our previously accrued estimated loss contingency as a result of the final settlement, the amount of which was immaterial to our consolidated financial position and results of operations. In 2009, a Pennsylvania-based insurance company and its affiliates were ordered into rehabilitation, and the Pennsylvania Insurance Commissioner, who was appointed as the Rehabilitator, filed petitions for liquidation with the Commonwealth Court of Pennsylvania. Under Pennsylvania law, payment of covered claims and other related insurance obligations are provided, within prescribed limits, by state guaranty associations. These guaranty associations assess fees to meet these obligations on insurance companies that sell insurance within the state, which are generally based on a company's pro rata portion of average premiums written or received for several years prior to the insolvency. Under Pennsylvania statutes, an insurer is declared insolvent only after it is placed under an order of liquidation by a court of competent jurisdiction with a finding for insolvency. We expect the formal order of liquidation to be issued during the first quarter of 2017, and as such, we would then be subject to an assessment by those guaranty associations that are responsible for policyholder claims. In the period during which the formal order of liquidation is issued, we expect to accrue an estimated loss contingency in the range of $ 12 million to $ 15 million . This amount is net of expected recoverable premium tax offsets and net of income tax. We do not believe our exposure to potential assessment is material to our consolidated financial position, cash flows, or results of operations. 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.

Statutory Financial Information

Statutory Financial Information	12 Months Ended
	Dec. 31, 2016
Statutory Financial Information [Abstract]
Statutory Financial Information	Statutory Financial Information Statutory Net Income, Capital and Surplus, and Dividends Statutory net income for U.S. life insurance companies is reported in conformity with statutory accounting principles prescribed by the National Association of Insurance Commissioners (NAIC) and adopted by applicable domiciliary state laws. The commissioners of the states of domicile have the right to permit other specific practices that may deviate from prescribed practices. Our traditional U.S. life insurance subsidiaries have no prescribed or permitted statutory accounting practices that differ materially from statutory accounting principles prescribed by the NAIC. Certain of our traditional U.S. life insurance subsidiaries cede blocks of business to Northwind Re and Fairwind Insurance Company (Fairwind), both of which are affiliated captive reinsurance subsidiaries (captive reinsurers) domiciled in the United States, with Unum Group as the ultimate parent. These captive reinsurers were established for the limited purpose of reinsuring risks attributable to specified policies issued or reinsured by our life insurance subsidiaries. During 2015, Tailwind Reinsurance Company (Tailwind Re), also an affiliated captive reinsurance subsidiary domiciled in the United States, merged with one of our traditional U.S. life insurance subsidiaries, with the traditional U.S. life insurance subsidiary remaining as the surviving company. Following the merger, the majority of the block of business previously ceded to Tailwind Re was ceded to an unaffiliated reinsurer. These two transactions did not materially impact the statutory results of operations, capital adequacy, or ability of our insurance subsidiaries to pay dividends to Unum Group. Fairwind, which is domiciled in the State of Vermont, is required to follow GAAP in accordance with Vermont reporting requirements for pure captive insurance companies, unless the commissioner permits the use of some other basis of accounting. Fairwind has permission from Vermont to follow accounting practices that are generally consistent with current NAIC statutory accounting principles for its insurance reserves and invested assets supporting reserves. All other assets and liabilities are accounted for in accordance with GAAP, as prescribed by Vermont, which allows for the full recognition of deferred tax assets which are more likely than not to be realized. Statutory accounting principles have a stricter limitation for the recognition of deferred tax assets. The impact of following the prescribed and permitted practices of Vermont rather than statutory accounting principles prescribed by the NAIC resulted in higher capital and surplus for Fairwind of approximately $213 million and $208 million as of December 31, 2016 and 2015 , respectively. Northwind Re has no material state prescribed accounting practices that differ from statutory accounting principles prescribed by the NAIC. The operating results and capital and surplus of our traditional U.S. life insurance subsidiaries and our captive reinsurers, prepared in accordance with prescribed or permitted accounting practices of the NAIC or states of domicile, are presented separately below. Year Ended December 31 2016 2015 2014 (in millions of dollars) Combined Net Income (Loss) Traditional U.S. Life Insurance Subsidiaries $ 855.1 $ 653.7 $ 628.9 Captive Reinsurers $ 48.4 $ (56.3 ) $ (129.3 ) Combined Net Gain (Loss) from Operations Traditional U.S. Life Insurance Subsidiaries $ 884.6 $ 689.2 $ 623.9 Captive Reinsurers $ 50.6 $ (54.3 ) $ (130.2 ) December 31 2016 2015 (in millions of dollars) Combined Capital and Surplus Traditional U.S. Life Insurance Subsidiaries $ 3,626.9 $ 3,470.3 Captive Reinsurers $ 1,726.7 $ 1,672.3 As derived from the most recent annual statutory basis financial statements filed with insurance regulators, the statutory net income and statutory capital and surplus of our United Kingdom insurance subsidiary, Unum Limited, were £60.6 million and £441.5 million , respectively. Risk‑based capital (RBC) standards for U.S. life insurance companies are prescribed by the NAIC. The domiciliary states of our U.S. insurance subsidiaries have all adopted a version of the RBC model formula of the NAIC, which prescribes a system for assessing the adequacy of statutory capital and surplus for all life and health insurers. The basis of the system is a risk-based formula that applies prescribed factors to the various risk elements in a life and health insurer's business to report a minimum capital requirement proportional to the amount of risk assumed by the insurer. The life and health RBC formula is designed to measure annually (i) the risk of loss from asset defaults and asset value fluctuations, (ii) the risk of loss from adverse mortality and morbidity experience, (iii) the risk of loss from mismatching of asset and liability cash flow due to changing interest rates, and (iv) business risks. The formula is used as an early warning tool to identify companies that are potentially inadequately capitalized. State insurance laws grant insurance regulators the authority to require various actions by, or take various actions against, insurers whose total adjusted capital does not meet or exceed certain RBC levels. The total adjusted capital of each of our U.S. insurance subsidiaries at December 31, 2016 is in excess of those RBC levels. Restrictions under applicable state insurance laws limit the amount of dividends that can be paid to a parent company from its insurance subsidiaries in any 12-month period without prior approval by regulatory authorities. For life insurance companies domiciled in the U.S., that limitation generally equals, depending on the state of domicile, either ten percent of an insurer's statutory surplus with respect to policyholders as of the preceding year end or the statutory net gain from operations, excluding realized investment gains and losses, of the preceding year. The payment of dividends to a parent company from a life insurance subsidiary is generally further limited to the amount of unassigned funds. Based on the restrictions under current law, $859.3 million is available, without prior approval by regulatory authorities, during 2017 for the payment of dividends to Unum Group from its traditional U.S. life insurance subsidiaries. The ability of our captive insurers to pay dividends to their respective parent companies will depend on their satisfaction of applicable regulatory requirements and on the performance of the business reinsured. We also have the ability to receive dividends from Unum Limited, subject to applicable insurance company regulations and capital guidance in the United Kingdom. As of January 1, 2016, Solvency II, a European Union directive that prescribes new capital requirements and risk management standards for the European insurance industry, replaced the previous capital requirements for Unum Limited. There was no material change to capital requirements or to solvency ratios. We have £271.0 million available for the payment of dividends from Unum Limited during 2017 , subject to regulatory approval. Deposits At December 31, 2016 and 2015 , our U.S. insurance subsidiaries had on deposit with U.S. regulatory authorities securities with a book value of $194.9 million and $284.1 million , respectively, held for the protection of policyholders.

Unaudited Quarterly Results

Unaudited Quarterly Results	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	The following is a summary of our unaudited quarterly results of operations for 2016 and 2015 : 2016 4 th 3 rd 2 nd 1 st (in millions of dollars, except share data) Premium Income $ 2,099.2 $ 2,089.4 $ 2,081.6 $ 2,087.5 Net Investment Income 617.9 611.4 623.3 606.4 Net Realized Investment Gain (Loss) 28.4 11.0 5.3 (20.5 ) Total Revenue 2,796.5 2,763.3 2,761.3 2,725.4 Income Before Income Tax 371.2 332.1 340.2 304.2 Net Income 248.0 236.0 236.8 210.6 Net Income Per Common Share Basic 1.07 1.01 1.00 0.88 Assuming Dilution 1.07 1.01 1.00 0.88 2015 4 th 3 rd 2 nd 1 st (in millions of dollars, except share data) Premium Income $ 2,037.8 $ 2,020.8 $ 2,017.5 $ 2,006.3 Net Investment Income 636.4 612.1 630.7 602.0 Net Realized Investment Gain (Loss) (2.7 ) (26.6 ) 0.8 (15.3 ) Total Revenue 2,722.4 2,657.8 2,703.7 2,647.4 Income Before Income Tax 316.6 298.9 319.8 303.0 Net Income 226.1 203.8 224.3 212.9 Net Income Per Common Share Basic 0.93 0.83 0.90 0.85 Assuming Dilution 0.93 0.83 0.90 0.84

Schedule I - Summary of Investm

Schedule I - Summary of Investments, Other Than Investments in Related Parties Schedule I - Summary of Investments, Other Than Investments in Related Parties	12 Months Ended
	Dec. 31, 2016
Summary of Investments, Other than Investments in Related Parties [Abstract]
Summary of Investments, Other Than Investments in Related Parties	SCHEDULE I--SUMMARY OF INVESTMENTS - OTHER THAN INVESTMENTS IN RELATED PARTIES Unum Group and Subsidiaries Type of Investment Cost or Amortized Cost (1) Fair Value Amount shown on the balance sheet (in millions of dollars) Fixed Maturity Securities: Bonds United States Government and Government Agencies and Authorities $ 1,202.8 $ 1,382.4 $ 1,382.4 States, Municipalities, and Political Subdivisions 1,868.0 2,158.0 2,158.0 Foreign Governments 714.8 914.7 914.7 Public Utilities 6,916.1 8,022.7 8,022.7 Mortgage/Asset-Backed Securities 2,104.9 2,230.4 2,230.4 All Other Corporate Bonds 26,707.1 29,467.2 29,467.2 Redeemable Preferred Stocks 39.0 41.9 41.9 Total Fixed Maturity Securities 39,552.7 $ 44,217.3 44,217.3 Mortgage Loans 2,038.9 2,038.9 Policy Loans 3,463.2 3,463.2 Other Long-term Investments Derivatives — 32.7 (2) Equity Securities 1.1 1.2 Miscellaneous Long-term Investments 589.3 597.6 (3) Short-term Investments 780.0 780.0 Total Investments $ 46,425.2 $ 51,130.9 (1) The amortized cost for fixed maturity securities and mortgage loans represents original cost reduced by repayments, write-downs from other-than-temporary declines in fair value, amortization of premiums, and/or accretion of discounts. (2) Derivatives are carried at fair value. (3) The difference between amortized cost and carrying value primarily results from changes in the partnership owner's equity since acquisition.

Schedule II Condensed Finacial

Schedule II Condensed Finacial Information of Registrant	12 Months Ended
	Dec. 31, 2016
Schedule II - Condensed Financial Info [Abstract]
Condensed Financial Information of Parent Company Only Disclosure	SCHEDULE II--CONDENSED FINANCIAL INFORMATION OF REGISTRANT Unum Group (Parent Company) BALANCE SHEETS December 31 2016 2015 (in millions of dollars) As Adjusted Assets Fixed Maturity Securities - at fair value (amortized cost: $215.1; $273.7) $ 214.2 $ 273.4 Other Long-term Investments 49.0 22.7 Short-term Investments 377.9 288.1 Investment in Subsidiaries 11,340.7 10,689.1 Deferred Income Tax 210.7 160.1 Other Assets 473.9 546.4 Total Assets $ 12,666.4 $ 11,979.8 Liabilities and Stockholders' Equity Liabilities Short-term Debt $ — $ 352.0 Long-term Debt 2,735.9 2,125.4 Pension and Postretirement Benefits 638.3 554.1 Other Liabilities 324.2 284.4 Total Liabilities 3,698.4 3,315.9 Stockholders' Equity Common Stock 30.4 30.3 Additional Paid-in Capital 2,272.8 2,247.2 Accumulated Other Comprehensive Income (Loss) (51.0 ) 16.1 Retained Earnings 8,744.0 7,995.2 Treasury Stock (2,028.2 ) (1,624.9 ) Total Stockholders' Equity 8,968.0 8,663.9 Total Liabilities and Stockholders' Equity $ 12,666.4 $ 11,979.8 See notes to condensed financial information. SCHEDULE II--CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Continued) Unum Group (Parent Company) STATEMENTS OF INCOME Year Ended December 31 2016 2015 2014 (in millions of dollars) Cash Dividends from Subsidiaries $ 676.5 $ 671.8 $ 645.2 Other Income 58.4 52.8 116.3 Total Revenue 734.9 724.6 761.5 Interest and Debt Expense 160.1 137.5 132.4 Other Expenses 32.3 16.7 66.0 Total Expenses 192.4 154.2 198.4 Income of Parent Company Before Income Tax 542.5 570.4 563.1 Income Tax Benefit (20.2 ) (16.2 ) (24.5 ) Income of Parent Company 562.7 586.6 587.6 Equity in Undistributed Earnings (Loss) of Subsidiaries 368.7 280.5 (185.5 ) Net Income 931.4 867.1 402.1 Other Comprehensive Loss, Net of Tax (67.1 ) (150.3 ) (88.6 ) Comprehensive Income $ 864.3 $ 716.8 $ 313.5 See notes to condensed financial information. SCHEDULE II--CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Continued) Unum Group (Parent Company) STATEMENTS OF CASH FLOWS Year Ended December 31 2016 2015 2014 (in millions of dollars) Cash Provided by Operating Activities $ 685.4 $ 672.2 $ 683.0 Cash Flows from Investing Activities Proceeds from Sales of Fixed Maturity Securities 2.6 7.8 25.0 Proceeds from Maturities of Fixed Maturity Securities 111.2 112.2 76.1 Proceeds from Sales and Maturities of Other Investments 0.4 26.4 31.9 Purchase of Fixed Maturity Securities (56.5 ) (233.7 ) (118.9 ) Purchase of Other Investments (23.3 ) — (19.0 ) Net Sales (Purchases) of Short-term Investments (89.8 ) 38.1 (162.1 ) Cash Distributions to Subsidiaries (143.6 ) (231.0 ) (316.1 ) Net Purchases of Property and Equipment (55.5 ) (78.9 ) (102.5 ) Acquisition of Business (140.3 ) — — Other, Net 0.2 0.1 (0.2 ) Cash Used by Investing Activities (394.6 ) (359.0 ) (585.8 ) Cash Flows from Financing Activities Issuance of Long-term Debt 609.1 271.4 347.2 Long-term Debt Repayment (350.0 ) — — Issuance of Common Stock 8.5 6.4 12.3 Repurchase of Common Stock (405.2 ) (417.9 ) (306.0 ) Dividends Paid to Stockholders (182.6 ) (174.2 ) (159.4 ) Other, Net (1.0 ) 2.9 1.9 Cash Used by Financing Activities (321.2 ) (311.4 ) (104.0 ) Increase (Decrease) in Cash $ (30.4 ) $ 1.8 $ (6.8 ) See notes to condensed financial information. SCHEDULE II--CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Continued) Unum Group (Parent Company) NOTES TO CONDENSED FINANCIAL INFORMATION Note 1 - Basis of Presentation The accompanying condensed financial statements should be read in conjunction with the consolidated financial statements and notes thereto of Unum Group and subsidiaries. Note 2 - Debt Debt consists of the following: December 31 2016 2015 Interest Rates Maturities (in millions of dollars) Long-term Debt Outstanding Principal Senior Notes issued 1998 7.000% 2018 $ 200.0 $ 200.0 Senior Notes issued 1998 6.750 - 7.250% 2028 365.8 365.8 Senior Notes issued 2002 7.375% 2032 39.5 39.5 Senior Notes issued 2010 5.625% 2020 400.0 400.0 Senior Notes issued 2012 and 2016 5.750% 2042 500.0 250.0 Senior Notes issued 2014 4.000% 2024 350.0 350.0 Senior Notes issued 2015 3.875% 2025 275.0 275.0 Senior Notes issued 2016 3.000% 2021 350.0 — Medium-term Notes issued 1990 - 1996 7.000 - 7.190% 2023 - 2028 50.8 50.8 Junior Subordinated Debt Securities issued 1998 7.405% 2038 226.5 226.5 Fair Value Hedges Adjustment (3.1 ) (2.7 ) Less: Unamortized Net Premium (Discount) 9.8 (3.8 ) Unamortized Debt Issuance Costs (28.4 ) (25.7 ) Total Long-term Debt 2,735.9 2,125.4 Short-term Debt Outstanding Principal Senior Notes issued 2009 7.125% 2016 — 350.0 Fair Value Hedges Adjustment — 2.4 Less Unamortized Debt Issuance Costs — (0.4 ) Total Short-term Debt — 352.0 Total Debt $ 2,735.9 $ 2,477.4 The senior notes due 2018 and the medium-term notes are non-callable. The junior subordinated debt securities are callable under limited, specified circumstances. The remaining debt is callable and may be redeemed, in whole or in part, at any time. The aggregate contractual principal maturities are $200.0 million in 2018, $400.0 million in 2020, $350.0 million in 2021, and $1,807.6 million thereafter. Fair Value Hedges As of December 31, 2016 and 2015 , we had $250.0 million and $600.0 million , respectively, notional amount interest rate swaps which effectively convert certain of our unsecured senior notes into floating rate debt. Under these agreements, we receive fixed rates of interest and pay variable rates of interest, based off of the three-month LIBOR. SCHEDULE II--CONDENSED FINANCIAL INFORMATION OF REGISTRANT (Continued) Unum Group (Parent Company) NOTES TO CONDENSED FINANCIAL INFORMATION - CONTINUED Junior Subordinated Debt Securities In 1998, Provident Financing Trust I (the trust), a 100 percent-owned finance subsidiary of Unum Group, issued $300.0 million of 7.405% capital securities in a public offering. These capital securities are fully and unconditionally guaranteed by Unum Group, have a liquidation value of $1,000 per capital security, and have a mandatory redemption feature under certain circumstances. Unum Group issued 7.405% junior subordinated deferrable interest debentures to the trust in connection with the capital securities offering. The debentures mature in 2038. The sole assets of the trust are the junior subordinated debt securities. Interest Paid Interest paid on debt and related securities during 2016 , 2015 , and 2014 was $147.8 million , $130.9 million , and $123.6 million , respectively. Credit Facility In 2016, we amended the terms of our five-year, $400.0 million unsecured revolving credit facility, which was previously set to expire in 2018, to extend through March 2021. Under the terms of the agreement, we may request that the credit facility be increased up to $600.0 million . Borrowings under the credit facility are for general corporate uses and are subject to financial covenants, negative covenants, and events of default that are customary. The credit facility provides for borrowing at an interest rate based either on the prime rate or LIBOR. In addition, the credit facility provides for the issuance of letters of credit subject to certain terms and limitations. At December 31, 2016 and 2015 , letters of credit totaling $2.1 million had been issued from the credit facility, but there were no borrowed amounts outstanding. Note 3 - Guarantees In 2005, UnumProvident Finance Company plc, a wholly-owned subsidiary of Unum Group, issued $400.0 million of 6.85% senior debentures. The remaining balance on these debentures, which we had fully and unconditionally guaranteed, matured in 2015.

Schedule III Supplementary Insu

Schedule III Supplementary Insurance Information	12 Months Ended
	Dec. 31, 2016
Schedule III - Supplementary Insurance Info [Abstract]
Supplementary Insurance Information, for Insurance Companies Disclosure	SCHEDULE III--SUPPLEMENTARY INSURANCE INFORMATION Unum Group and Subsidiaries Segment Deferred Acquisition Costs Reserves for Future Policy Contract Benefits Unearned Premiums Policy and Contract Benefits (in millions of dollars) December 31, 2016 Unum US $ 1,176.5 $ 11,312.6 $ 46.9 $ 977.2 Unum UK 21.4 2,127.9 110.3 102.4 Colonial Life 896.3 2,103.5 33.5 195.8 Closed Block — 28,701.9 173.0 232.5 Total $ 2,094.2 $ 44,245.9 $ 363.7 $ 1,507.9 December 31, 2015 Unum US $ 1,136.4 $ 11,273.5 $ 45.5 $ 940.8 Unum UK 27.1 2,377.5 128.2 114.3 Colonial Life 845.0 1,989.8 32.0 191.2 Closed Block — 27,899.8 178.5 238.3 Total $ 2,008.5 $ 43,540.6 $ 384.2 $ 1,484.6 SCHEDULE III--SUPPLEMENTARY INSURANCE INFORMATION Unum Group and Subsidiaries (continued from preceding page) Segment Premium Income Net Investment Income (1) Benefits and Change in Reserves for Future Benefits (2) Amortization of Deferred Acquisition Costs All Other Expenses (3) Premiums Written (4) (in millions of dollars) December 31, 2016 Unum US $ 5,240.9 $ 828.7 $ 3,624.3 $ 275.2 $ 1,369.2 $ 3,564.4 Unum UK 529.3 118.1 367.4 9.7 141.9 435.4 Colonial Life 1,417.1 141.5 726.4 208.1 311.1 1,145.0 Closed Block 1,170.4 1,352.2 2,223.7 — 255.4 1,161.8 Corporate — 18.5 — — 186.4 — Total $ 8,357.7 $ 2,459.0 $ 6,941.8 $ 493.0 $ 2,264.0 December 31, 2015 Unum US $ 4,960.0 $ 865.3 $ 3,476.7 $ 272.3 $ 1,345.5 $ 3,353.8 Unum UK 576.2 124.9 394.8 11.3 154.4 453.0 Colonial Life 1,338.6 145.4 683.0 198.7 293.3 1,088.3 Closed Block 1,207.6 1,320.0 2,228.3 — 269.5 1,198.5 Corporate — 25.6 — — 165.2 — Total $ 8,082.4 $ 2,481.2 $ 6,782.8 $ 482.3 $ 2,227.9 December 31, 2014 Unum US $ 4,659.7 $ 878.9 $ 3,288.1 $ 248.1 $ 1,279.6 $ 3,144.1 Unum UK 607.2 151.0 431.0 12.5 166.9 479.9 Colonial Life 1,273.7 145.5 660.6 180.2 279.5 1,042.7 Closed Block 1,256.6 1,281.5 2,931.1 — 277.0 1,248.6 Corporate — 35.3 — — 227.9 — Total $ 7,797.2 $ 2,492.2 $ 7,310.8 $ 440.8 $ 2,230.9 (1) Net investment income is allocated based upon segmentation. Each segment has its own specifically identified assets and receives the investment income generated by those assets. (2) Included in 2014 is a reserve charge of $698.2 million in the Closed Block segment related to our long-term care business. (3) Includes commissions; interest and debt expense; deferral of acquisition costs; compensation expense; non-operating retirement related loss, which in 2014 included a settlement loss of $64.4 million in the Corporate segment related to a pension plan amendment; and other expenses. Where not directly attributable to a segment, expenses are generally allocated based on activity levels, time information, and usage statistics. (4) Excludes life insurance.

Schedule IV Reinsurance

Schedule IV Reinsurance	12 Months Ended
	Dec. 31, 2016
Schedule IV - Reinsurance [Abstract]
Supplemental Schedule of Reinsurance Premiums for Insurance Companies	SCHEDULE IV--REINSURANCE Unum Group and Subsidiaries Gross Amount Ceded to Other Companies Assumed from Other Companies Net Amount Percentage Amount Assumed to Net (in millions of dollars) Year Ended December 31, 2016 Life Insurance in Force $ 854,783.9 $ 31,882.5 $ 1,004.7 $ 823,906.1 0.1 % Premium Income: Life Insurance $ 2,202.6 $ 151.3 $ 9.7 $ 2,061.0 0.5 % Accident, Health, and Other Insurance 6,182.4 112.3 226.6 6,296.7 3.6 % Total $ 8,385.0 $ 263.6 $ 236.3 $ 8,357.7 2.8 % Year Ended December 31, 2015 Life Insurance in Force $ 827,515.2 $ 24,062.6 $ 993.5 $ 804,446.1 0.1 % Premium Income: Life Insurance $ 2,150.1 $ 176.3 $ 9.4 $ 1,983.2 0.5 % Accident, Health, and Other Insurance 6,001.8 96.0 193.4 6,099.2 3.2 % Total $ 8,151.9 $ 272.3 $ 202.8 $ 8,082.4 2.5 % Year Ended December 31, 2014 Life Insurance in Force $ 790,952.1 $ 24,416.7 $ 999.7 $ 767,535.1 0.1 % Premium Income: Life Insurance $ 2,056.4 $ 194.8 $ 9.6 $ 1,871.2 0.5 % Accident, Health, and Other Insurance 5,842.9 97.1 180.2 5,926.0 3.0 % Total $ 7,899.3 $ 291.9 $ 189.8 $ 7,797.2 2.4 %

Schedule V Valuation and Qualif

Schedule V Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2016
Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	SCHEDULE V--VALUATION AND QUALIFYING ACCOUNTS Unum Group and Subsidiaries Description Balance at Beginning of Period Additions Charged to Costs and Expenses Additions Charged to Other Accounts (1) Deductions (2) Balance at End of Period (in millions of dollars) Year Ended December 31, 2016 Real Estate reserve (deducted from other long-term investments) $ 1.2 $ 3.0 $ — $ — $ 4.2 Allowance for doubtful accounts (deducted from accounts and premiums receivable) $ 6.2 $ 3.1 $ — $ 3.1 $ 6.2 Year Ended December 31, 2015 Real Estate reserve (deducted from other long-term investments) $ 0.3 $ 1.2 $ — $ 0.3 $ 1.2 Allowance for doubtful accounts (deducted from accounts and premiums receivable) $ 6.4 $ 1.7 $ — $ 1.9 $ 6.2 Year Ended December 31, 2014 Real Estate reserve (deducted from other long-term investments) $ 1.8 $ 0.4 $ — $ 1.9 $ 0.3 Allowance for doubtful accounts (deducted from accounts and premiums receivable) $ 5.6 $ 1.4 $ 0.3 $ 0.9 $ 6.4 (1) Additions charged to other accounts are comprised of amounts related to fluctuations in the foreign currency exchange rate. (2) Deductions include amounts deemed to reduce exposure of probable losses, amounts deemed uncollectible, and amounts related to fluctuations in the foreign currency exchange rate. See Notes 3 and 7 of the "Notes to Consolidated Financial Statements" contained herein in Item 8 for a discussion of the mortgage loan allowance for credit losses and the deferred tax asset valuation allowance not included in the amounts reported above.

Signficant Accounting Policies

Signficant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	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). Such accounting principles differ from statutory accounting principles (see Note 15). Intercompany transactions have been eliminated.
Use of Estimates	Use of Estimates : The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect amounts reported in the financial statements and accompanying notes. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein.
Fixed Maturity Securities	Fixed Maturity Securities : Fixed maturity securities include long-term bonds and redeemable preferred stocks. Our fixed maturity securities are classified as available-for-sale and reported at fair value. Changes in the fair value of available-for-sale fixed maturity securities, except for amounts related to other-than-temporary impairment losses recognized in earnings, are reported as a component of other comprehensive income. These amounts are net of income tax and valuation adjustments to deferred acquisition costs and reserves for future policy and contract benefits which would have been recorded had the related unrealized gain or loss on these securities been realized. Interest income is recorded as part of net investment income when earned, using an effective yield method giving effect to amortization of premium and accretion of discount. Included within fixed maturity securities are mortgage-backed and asset-backed securities. We recognize investment income on these securities using a constant effective yield based on projected prepayments of the underlying loans and the estimated economic life of the securities. Actual prepayment experience is reviewed periodically, and effective yields are recalculated when differences arise between prepayments originally projected and the actual prepayments received and currently projected. The effective yield is recalculated on a retrospective basis, and the adjustment is reflected in net investment income. For fixed maturity securities on which collection of investment income is uncertain, we discontinue the accrual of investment income and recognize investment income when interest and dividends are received. Payment terms specified for fixed maturity securities may include a prepayment penalty for unscheduled payoff of the investment. Prepayment penalties are recognized as investment income when received. In determining when a decline in fair value below amortized cost of a fixed maturity security is other than temporary, we evaluate available information, both positive and negative, in reaching our conclusions. In particular, we 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 all 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 that 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. 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. Other-than-temporary impairment losses on fixed maturity securities which we intend to sell or more likely than not will be required to sell before recovery in value are recognized in earnings and equal the entire difference between the security's amortized cost basis and its fair value. For securities which we do not intend to sell and it is not more likely than not that we will be required to sell before recovery in value, other-than-temporary impairment losses recognized in earnings generally represent the difference between the amortized cost of the security and the present value of our best estimate of cash flows expected to be collected, discounted using the effective interest rate implicit in the security at the date of acquisition. For fixed maturity securities for which we have recognized an other-than-temporary impairment loss through earnings, if through subsequent evaluation there is a significant increase in expected cash flows, the difference between the new amortized cost basis and the cash flows expected to be collected is accreted as net investment income over the remaining life of the investment. See Notes 2 and 3.
Mortgage Loans	Mortgage Loans : Mortgage loans are generally held for investment and are carried at amortized cost less an allowance for probable losses. Interest income is accrued on the principal amount of the loan based on the loan's contractual interest rate. Prepayment penalties are recognized as investment income when received. 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. 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. 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 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. Additions and reductions to our allowance for credit losses on mortgage loans are reported as a component of net realized investment gains and losses. We do not purchase mortgage loans with existing credit impairments. See Note 3.
Policy Loans	Policy Loans : Policy loans are presented at unpaid balances directly related to policyholders. Interest income is accrued on the principal amount of the loan based on the loan's contractual interest rate. Included in policy loans are $3,206.1 million and $3,150.1 million of policy loans ceded to reinsurers at December 31, 2016 and 2015 , respectively.
Other Investments	Other Long-term Investments : Other long-term investments are comprised primarily of tax credit partnerships and private equity partnerships. Tax credit partnerships in which we have invested were formed for the purpose of investing in the construction and rehabilitation of low-income housing. Because the partnerships are structured such that there is no return of principal, the primary sources of investment return from our tax credit partnerships are tax credits and tax benefits derived from passive losses on the investments, both of which may exhibit variability over the life of the investment. These partnerships are accounted for using either the proportional or the effective yield method, depending primarily on whether the tax credits are guaranteed through a letter of credit, a tax indemnity agreement, or another similar arrangement. Tax credits received from these partnerships are reported in our consolidated statements of income as either a reduction of premium tax or a reduction of income tax. The amortization of the principal amount invested in these partnerships is reported as a component of either premium tax or income tax. Our investments in private equity partnerships are passive in nature. The underlying investments held by these partnerships include both equity and debt securities and are accounted for using the equity or cost method, depending on the level of ownership and the degree of our influence over partnership operating and financial policies. For partnerships accounted for under the equity method, our portion of partnership earnings is reported as a component of net investment income in our consolidated statements of income. For those partnerships accounted for under the cost method, we record income received from partnership distributions as either a component of net investment income or net realized investment gain or loss, in accordance with the source of the funds distributed from the partnership. See Notes 2 and 3. Short-term Investments : Short-term investments are carried at cost. Short-term investments include investments maturing within one year, such as corporate commercial paper and U.S. Treasury bills, bank term deposits, and other cash accounts and cash equivalents earning interest. See Note 2.
Cash and Bank Deposits	Cash and Bank Deposits : Cash and bank deposits include cash on hand and non-interest bearing cash and deposit accounts.
Derivative Financial Instruments	Derivative Financial Instruments : Derivative financial instruments (including certain derivative instruments embedded in other contracts) are recognized as either other long-term investments or other liabilities in our consolidated balance sheets and are reported at fair value. The accounting for a derivative depends on whether it has been designated and qualifies as part of a hedging relationship, and further, on the type of hedging relationship. To qualify for hedge accounting, at the inception of the hedging transaction, we formally document the risk management objective and strategy for undertaking the hedging transaction, as well as the designation of the hedge as either a fair value hedge or a cash flow hedge. Included in this documentation is how the hedging instrument is expected to hedge the designated risk(s) related to specific assets or liabilities on the balance sheet or to specific forecasted transactions as well as a description of the method that will be used to retrospectively and prospectively assess the hedging instrument's effectiveness and the method that will be used to measure ineffectiveness. A derivative designated as a hedging instrument must be assessed as being highly effective in offsetting the designated risk(s) of the hedged item. Hedge effectiveness is formally assessed at inception and periodically throughout the life of the designated hedging relationship, using qualitative and quantitative methods. Qualitative methods include comparison of critical terms of the derivative to the hedged item. Quantitative methods include regression or other statistical analysis of changes in fair value or cash flows associated with the hedge relationship. Changes in the fair value of a derivative designated as a fair value hedge, including amounts measured as ineffectiveness, and changes in the fair value of the hedged item attributable to the risk being hedged are recognized in earnings as a component of net realized investment gain or loss during the period of change in fair value. The gain or loss on the termination of a fair value hedge is recognized in earnings as a component of net realized investment gain or loss during the period in which the termination occurs. When interest rate swaps are used in hedge accounting relationships, periodic settlements are recorded in the same income statement line as the related settlements of the hedged items. To the extent it is effective, changes in the fair value of a derivative designated as a cash flow hedge are reported in other comprehensive income and reclassified into earnings and reported on the same income statement line item as the hedged item and in the same period or periods during which the hedged item affects earnings. The ineffective portion of the hedge, if any, is recognized in earnings as a component of net realized investment gain or loss during the period of change in fair value. The gain or loss on the termination of an effective cash flow hedge is reported in other comprehensive income and reclassified into earnings and reported on the same income statement line item as the hedged item and in the same period or periods during which the hedged item affects earnings. Gains or losses on the termination of ineffective fair value or cash flow hedges are reported in earnings as a component of net realized investment gain or loss. In the event a hedged item is disposed of or the anticipated transaction being hedged is no longer likely to occur, we will terminate the related derivative and recognize the gain or loss on termination in current earnings as a component of net realized investment gain or loss. In the event a hedged item is disposed of subsequent to the termination of the hedging transaction, we reclassify any remaining gain or loss on the cash flow hedge out of accumulated other comprehensive income into earnings as a component of the same income statement line item wherein we report the gain or loss on disposition of the hedged item. For a derivative not designated as a hedging instrument, changes in the fair value of the derivative, together with the payment of periodic fees, if applicable, are recognized in earnings as a component of net realized investment gain or loss during the period of change in fair value. Cash flow activity from the settlement of derivative contracts is reported in the consolidated statements of cash flows as a component of proceeds from sales and maturities of other investments. In our consolidated balance sheets, we do not offset fair value amounts recognized for derivatives executed with the same counterparty under a master netting agreement and fair value amounts recognized for the right to reclaim cash collateral or the obligation to return cash collateral arising from those master netting agreements. See Notes 2, 3 and 4.
Fair Value Measurement	Fair Value Measurement : Certain assets and liabilities are reported at fair value in our consolidated balance sheets and in our notes to our consolidated financial statements. We define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Therefore, fair value represents an exit price, not an entry price. The exit price objective applies regardless of our intent and/or ability to sell the asset or transfer the liability at the measurement date. Assets or liabilities with readily available actively 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. When actively quoted prices are not available, fair values are based on quoted prices in markets that are not active, quoted prices for similar but not identical assets or liabilities, or other observable inputs. If observable inputs are not available, unobservable inputs and/or adjustments to observable inputs requiring management judgment are used to determine fair value. We categorize our assets and liabilities measured at estimated fair value into a three-level hierarchy, based on the significance of the inputs. The fair value hierarchy gives the highest priority to inputs which are unadjusted and represent quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). See Note 2.
Realized Investment Gains and Losses	Realized Investment Gains and Losses : Realized investment gains and losses are reported as a component of revenue in the consolidated statements of income and are based upon specific identification of the investments sold. See Note 3.
Deferred Acquisition Costs	Deferred Acquisition Costs : Incremental direct costs associated with the successful acquisition of new or renewal insurance contracts have been deferred. Such costs include commissions, other agency compensation, certain selection and policy issue expenses, and certain field expenses. Acquisition costs that do not vary with the production of new business, such as commissions on group products which are generally level throughout the life of the policy, are excluded from deferral. Deferred acquisition costs are subject to recoverability testing at the time of policy issue and loss recognition testing in subsequent years. Deferred acquisition costs related to non-interest sensitive policies are amortized in proportion to the premium income we expect to receive over the life of the policies. Deferred acquisition costs related to interest sensitive policies are amortized over the lives of the policies in relation to the present value of estimated gross profits from surrender charges, mortality margins, investment returns, and expense margins. Deviations from projections result in a change to the rate of amortization in the period during which such events occur. Generally, the amortization periods for these policies approximate the estimated lives of the policies. For certain products, policyholders can elect to modify product benefits, features, rights, or coverages by exchanging a contract for a new contract or by amendment, endorsement, or rider to a contract, or by the election of a feature or coverage within a contract. These transactions are known as internal replacement transactions. Internal replacement transactions wherein the modification does not substantially change the policy are accounted for as continuations of the replaced contracts. Unamortized deferred acquisition costs from the original policy continue to be amortized over the expected life of the new policy, and the costs of replacing the policy are accounted for as policy maintenance costs and expensed as incurred. Internal replacement transactions, principally on group contracts, that result in a policy that is substantially changed are accounted for as an extinguishment of the original policy and the issuance of a new policy. Unamortized deferred acquisition costs on the original policy that was replaced are immediately expensed, and the costs of acquiring the new policy are capitalized and amortized in accordance with our accounting policies for deferred acquisition costs. Loss recognition is performed on an annual basis, or more frequently if appropriate, using best estimate assumptions as to future experience as of the date of the test. Insurance contracts are grouped for each major product line within a segment when we perform the loss recognition tests. If loss recognition testing indicates that deferred acquisition costs are not recoverable, the deficiency is charged to expense.
Goodwill	Goodwill : Goodwill is the excess of the amount paid to acquire a business over the fair value of the net assets acquired. We review the carrying amount of goodwill for impairment on an annual basis, or more frequently if events or changes in circumstances indicate that the carrying amount might not be recoverable. Goodwill impairment testing compares the fair value of a reporting unit with its carrying amount, including goodwill. The fair values of the reporting units are determined using discounted cash flow models. The critical estimates necessary in determining fair value are projected earnings and the discount rate. We set our discount rate assumption based on an expected risk adjusted cost of capital. If the fair value of the reporting unit to which the goodwill relates is less than the carrying amount of the unamortized goodwill, the impairment charge is determined by calculating the implied fair value of goodwill by assigning the fair value of a reporting unit to all of its assets and liabilities. The carrying amount of goodwill is then reduced with a corresponding charge to expense.
Property and Equipment	Property and Equipment : Property and equipment is reported at cost less accumulated depreciation, which is calculated on the straight-line method over the estimated useful life. The accumulated depreciation for property and equipment was $989.4 million and $902.6 million as of December 31, 2016 and 2015 , respectively.
Value of Business Acquired	Value of Business Acquired : Value of business acquired represents the present value of future profits recorded in connection with the acquisition of a block of insurance policies. The asset is amortized based upon expected future premium income for non-interest sensitive insurance policies and estimated future gross profits from surrender charges, mortality margins, investment returns, and expense margins for interest sensitive insurance policies. The value of business acquired, which is included in other assets in our consolidated balance sheets, was $31.9 million and $24.0 million at December 31, 2016 and 2015 , respectively. The accumulated amortization for value of business acquired was $119.2 million and $133.1 million as of December 31, 2016 and 2015 , respectively. The amortization of value of business acquired, which is included in other expenses in the consolidated statements of income, was $5.1 million , $4.6 million , and $3.5 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively. We periodically review the carrying amount of value of business acquired using the same methods used to evaluate deferred acquisition costs.
Policy and Contract Benefits	Policy and Contract Benefits : Policy and contract benefits represent amounts paid and expected to be paid based on reported losses and estimates of incurred but not reported losses for non-interest sensitive life and accident and health products. For interest sensitive products, benefits are the amounts paid and expected to be paid on insured claims in excess of the policyholders' policy fund balances.
Reserves for Policy and Contract Benefits	Reserves for Policy and Contract Benefits : Policy reserves represent future policy and contract benefits for claims not yet incurred. Policy reserves for non-interest sensitive life and accident and health products are determined using the net level premium method. The reserves are calculated based upon assumptions as to interest, persistency, morbidity, and mortality that were appropriate at the date of issue. Discount rate assumptions are based on actual and expected net investment returns. Persistency assumptions are based on our actual historical experience adjusted for future expectations. Claim incidence and claim resolution rate assumptions related to morbidity and mortality are based on actual experience or industry standards adjusted as appropriate to reflect our actual experience and future expectations. The assumptions vary by plan, year of issue, and policy duration and include a provision for adverse deviation. Policy reserves for group single premium annuities are developed on a net single premium method. The reserves are calculated based on assumptions as to interest, mortality, and retirement that were appropriate at the date of issue. Mortality assumptions are based upon industry standards adjusted as appropriate to reflect our actual experience and future expectations. The assumptions vary by year of issue. Policy reserves for interest sensitive products are principally policyholder account values. Policy reserves require ongoing loss recognition testing. We perform loss recognition tests on our policy reserves annually, or more frequently if appropriate, using best estimate assumptions as of the date of the test, without a provision for adverse deviation. We group the policy reserves for each major product line within a segment when we perform the loss recognition tests. If the policy reserves determined using these best estimate assumptions are higher than our existing policy reserves net of any deferred acquisition cost balance, the existing policy reserves are increased or deferred acquisition costs are reduced to immediately recognize the deficiency. This becomes the new basis for policy reserves going forward, subject to future loss recognition testing. Claim reserves represent future policy and contract benefits for claims that have been incurred or are estimated to have been incurred but not yet reported to us. Our claim reserves relate primarily to disability policies and are calculated based on assumptions as to interest and claim resolution rates that are currently appropriate. Claim resolution rate assumptions are based on our actual experience. The interest rate assumptions used for discounting claim reserves are based on projected portfolio yield rates, after consideration for defaults and investment expenses, for the assets supporting the liabilities for the various product lines. Unlike policy reserves for which assumptions are generally established and locked in at the time of policy issuance, claim reserves are subject to revision as current claim experience and projections of future factors affecting claim experience change. Claim reserves do not include a provision for adverse deviation. See Note 6.
Policyholders' Funds	Policyholders' Funds : Policyholders' funds represent customer deposits plus interest credited at contract rates. We control interest rate risk by investing in quality assets which have an aggregate duration that closely matches the expected duration of the liabilities.
Income Tax	Income Tax : Deferred taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial statement purposes and the amounts used for income tax purposes. Deferred taxes have been measured using enacted statutory income tax rates and laws that are currently in effect. We record deferred tax assets for tax positions taken in the U.S. and other tax jurisdictions based on our assessment of whether a position is more likely than not to be sustained upon examination based solely on its technical merits. A valuation allowance is established for deferred tax assets when it is more likely than not that an amount will not be realized. See Note 7.
Short-term and Long-term Debt	Short-term and Long-term Debt : Debt is generally carried at the unpaid principal balance, net of unamortized discount or premium and deferred debt issuance costs. Short-term debt consists of debt due within the next twelve months, including that portion of debt otherwise classified as long-term. Original issue discount or premium as well as debt issuance costs are recognized as a component of interest expense over the period the debt is expected to be outstanding. The carrying amount of long-term debt that is part of a fair value hedge program includes an adjustment to reflect the effect of the change in fair value attributable to the risk being hedged. Net interest settlements for fair value hedges on our long-term debt are recognized as a component of interest expense. See Note 8.
Treasury Stock and Retirement of Common Stock	Treasury Stock and Retirement of Common Stock : Treasury stock is reflected as a reduction of stockholders' equity at cost. When shares are retired, the par value is removed from common stock, and the excess of the repurchase price over par is allocated between additional paid-in capital and retained earnings. See Note 10.
Revenue Recognition	Revenue Recognition: Our non-interest sensitive life and accident and health products are long-duration contracts, and premium income is recognized as revenue when due from policyholders. If the contracts are experience rated, the estimated ultimate premium is recognized as revenue over the period of the contract. The estimated ultimate premium, which is revised to reflect current experience, is based on estimated claim costs, expenses, and profit margins. For interest sensitive products, the amounts collected from policyholders are considered deposits, and only the deductions during the period for cost of insurance, policy administration, and surrenders are included in revenue. Policyholders' funds represent funds deposited by contract holders and are not included in revenue.
Revenue from Service Fees	Fees from our administrative-services only and family medical leave products are reported as other income when services are rendered.
Reinsurance	Reinsurance : We routinely enter into reinsurance agreements with other insurance companies to spread risk and thereby limit losses from large exposures. For each of our reinsurance agreements, we determine if the agreement provides indemnification against loss or liability relating to insurance risk in accordance with applicable accounting standards. If we determine that a reinsurance agreement does not expose the reinsurer to a reasonable possibility of a significant loss from insurance risk, we record the agreement using the deposit method of accounting. Reinsurance activity is accounted for on a basis consistent with the terms of the reinsurance contracts and the accounting used for the original policies issued. Premium income and benefits and change in reserves for future benefits are presented in our consolidated statements of income net of reinsurance ceded. Ceded liabilities for policy and contract benefits, future policy and contract benefits, and unearned premiums are reported on a gross basis in our consolidated balance sheets, as are ceded policy loans. Our reinsurance recoverable includes the balances due from reinsurers under the terms of the reinsurance agreements for these ceded balances as well as settlement amounts currently due. Where applicable, gains or losses on reinsurance transactions are deferred and amortized into earnings based upon expected future premium income for non-interest sensitive insurance policies and estimated future gross profits for interest sensitive insurance policies. The deferred gain on reinsurance included in other liabilities in our consolidated balance sheets at December 31, 2016 and 2015 was $23.8 million and $31.9 million , respectively. Under ceded reinsurance agreements wherein we are not relieved of our legal liability to our policyholders, if the assuming reinsurer is unable to meet its obligations, we remain contingently liable. We evaluate the financial condition of reinsurers and monitor concentration of credit risk to minimize this exposure. We may also require assets in trust, letters of credit, or other acceptable collateral to support our reinsurance recoverable balances. In the event that reinsurers do not meet their obligations to us under the terms of the reinsurance agreements, certain amounts reported in our reinsurance recoverable could become uncollectible, in which case the reinsurance recoverable balances are stated net of allowances for uncollectible reinsurance. See Note 12.
Premium Tax Expense	Premium Tax Expense : Premium tax expense is included in other expenses in the consolidated statements of income. For the years ended December 31, 2016 , 2015 , and 2014 , premium tax expense was $152.5 million , $146.5 million , and $139.2 million , respectively.
Stock-Based Compensation	Stock-Based Compensation : The cost of stock-based compensation is generally measured based on the grant-date fair value of the award. The Black-Scholes options valuation model is used for estimating the fair value of stock options, and the Monte-Carlo valuation model is used for estimating the fair value of performance share units. Restricted stock units are valued based on the fair value of common stock at the grant date. Stock-based awards are expensed over the requisite service period, or for performance share units over the requisite service period, or remaining service period, if and when it becomes probable that the performance conditions will be satisfied, with an offsetting increase to additional paid-in capital in stockholders' equity. See Note 11.
Earnings Per Share	Earnings Per Share : We compute basic earnings per share by dividing net income by the weighted average number of common shares outstanding for the period. Earnings per share assuming dilution is computed by dividing net income by the weighted average number of shares outstanding for the period plus the shares representing the dilutive effect of stock-based awards. In computing earnings per share assuming dilution, only potential common shares resulting from stock-based awards that are dilutive (those that reduce earnings per share) are included. We use the treasury stock method to account for the effect of outstanding stock options and nonvested stock awards on the computation of earnings per share assuming dilution. See Note 10.
Translation of Foreign Curency	Translation of Foreign Currency : Revenues and expenses of our foreign operations are translated at average exchange rates. Assets and liabilities are translated at the rate of exchange on the balance sheet dates. The translation gain or loss is generally reported in accumulated other comprehensive income, net of deferred tax. We do not provide for deferred taxes to the extent unremitted foreign earnings are deemed permanently invested.
Accounting for Participating Individual Life Insurance	Accounting for Participating Individual Life Insurance : Participating policies issued by one of our subsidiaries prior to its 1986 conversion from a mutual to a stock life insurance company will remain participating as long as the policies remain in-force. A Participation Fund Account (PFA) was established for the benefit of all such individual participating life and annuity policies and contracts. The assets of the PFA provide for the benefit, dividend, and certain expense obligations of the participating individual life insurance policies and annuity contracts. The assets of the PFA were $331.1 million and $338.8 million at December 31, 2016 and 2015 , respectively.
Accounting Updates Outstanding	Accounting Updates Outstanding: ASC Description Date of Adoption Effect on Financial Statements ASC 944 "Financial Services - Insurance" This update changes the disclosure requirements for certain insurance contracts. These changes include a requirement to disclose the rollforward of the liability for unpaid claims and claim adjustment expenses in both interim and annual reporting periods for long-duration and short-duration insurance contracts. Additional claims disclosures will also be required for short-duration contracts. The guidance is to be applied retrospectively. January 1, 2016 for annual reporting period disclosures and January 1, 2017 for interim reporting period disclosures. The annual reporting period disclosure requirements effective January 1, 2016 are applicable to only to certain of our individual dental products. The amount of reserves for policy and contract benefits held for these products is immaterial, and we therefore did not alter our current disclosures. We will adopt the interim reporting period disclosure requirements effective January 1, 2017. The adoption of this update will have no effect on our financial position or results of operations. ASC 718 "Compensation - Stock Compensation" This update changes the accounting and disclosure requirements for certain aspects of share-based payments to employees. The update requires all income tax effects of stock-based compensation awards to be recognized in the income statement when the awards vest or are settled. The update also allows an employer to repurchase more of an employee's shares than it can today for tax withholding purposes without triggering liability accounting and to make a policy election to account for forfeitures as they occur. Transition guidance for the amendments varies between the retrospective, modified retrospective, and prospective methods depending on the specific requirement of the update. Early adoption is also permitted. January 1, 2017 The adoption of this update will not have a material effect on our financial position or results of operations. During periods in which the vesting date fair value differs from the grant date fair value of certain stock-based compensation awards, we may experience volatility in the income tax recognized in our results of operations. ASC 230 "Statement of Cash Flows" This update provides clarifying guidance intended to reduce the diversity in practice in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. The update addresses eight specific cash flow issues that relate to various transactions. The guidance is to be applied retrospectively, with early adoption permitted. January 1, 2018 The adoption of this update will result in reclassifications to certain cash receipts and payments within our consolidated statements of cash flows but will have no effect on our financial position or results of operations. ASC Description Date of Adoption Effect on Financial Statements ASC 606 "Revenue from Contracts with Customers" This update supersedes virtually all existing guidance regarding the recognition of revenue from customers. Specifically excluded from the scope of this update are contracts under ASC 944, which includes insurance contracts, although our fee-based service products, which represent less than one percent of 2016 total revenue, are included within the scope. The core principle of this guidance is that revenue recognition should depict the transfer of goods or services to customers in an amount that reflects the consideration to which an entity expects to be entitled in exchange for those goods or services. The guidance is to be applied retrospectively. January 1, 2018 The adoption of this update will not have a material effect on our financial position or results of operations. ASC 740 "Income Taxes" This update eliminates the exception that requires intra-entity asset transfers other than inventory to be deferred until the transferred asset is sold to a third party or otherwise recovered through use. It requires recognition of tax expense from the sale of the asset in the seller’s tax jurisdiction when the transfer occurs, even though the pre-tax effects of that transaction are eliminated in consolidation. The guidance is to be applied retrospectively. January 1, 2018 We have not yet determined the expected impact on our financial position or results of operations. ASC 825 "Financial Instruments - Overall" This update changes the accounting and disclosure requirements for certain financial instruments. These changes include a requirement to measure equity investments, other than those that result in consolidation or are accounted for under the equity method, at fair value through net income unless the investment qualifies for certain practicability exceptions. In addition, the update clarifies guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from unrealized losses on available-for-sale fixed maturity securities. Changes also include the modification of certain disclosures around the fair value of financial instruments, including the requirement for separate presentation of financial assets and liabilities by measurement category, as well as the elimination of certain disclosures around methods and significant assumptions used to estimate fair value. The guidance is to be applied retrospectively. January 1, 2018 We have not yet determined the expected impact on our financial position or results of operations. ASC 842 "Leases" This update changes the accounting for leases, requiring lessees to report most leases on their balance sheets, regardless of whether the lease is classified as a finance lease or an operating lease. For lessees, the initial lease liability is equal to the present value of lease payments, and a corresponding asset, adjusted for certain items, is also recorded. Expense recognition for lessees will remain similar to current accounting requirements for capital and operating leases. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is to be applied using a modified retrospective approach at the beginning of the earliest comparative period presented. January 1, 2019 We have not yet determined the expected impact on our financial position or results of operations. ASC Description Date of Adoption Effect on Financial Statements ASC 350 "Intangibles - Goodwill and Other" This update eliminates the requirement to calculate the implied fair value of goodwill (the second step in the current two-step test) to measure a goodwill impairment charge. Instead, entities should perform the goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the excess of the carrying amount over the fair value, with the loss not to exceed the total amount of goodwill allocated to that reporting unit. The guidance is to be applied prospectively, with early adoption permitted for goodwill impairment tests performed on testing dates after January 1, 2017. January 1, 2020 The adoption of this update will not have a material effect on our financial position or results of operations. ASC 326 "Financial Instruments - Credit Losses" This update amends the guidance on the impairment of financial instruments. The update adds an impairment model known as the current expected credit loss model that is based on expected losses rather than incurred losses and will generally result in earlier recognition of allowances for losses. The current expected credit loss model applies to financial instruments such as mortgage loans, fixed maturity securities classified as held-to-maturity, and certain receivables. The update also modifies the other-than-temporary impairment model used for available-for-sale fixed maturity securities such that credit losses are recognized as an allowance rather than as a reduction in the amortized cost of the security. The reversal of previously recognized credit losses on available-for-sale fixed maturity securities is allowed under specified circumstances. Additional disclosures will also be required, including information used to develop the allowance for losses. The guidance is to be applied to most instruments in scope using a modified retrospective approach at the beginning of the earliest comparative period presented. For available-for-sale fixed maturity securities, the update is applied prospectively. Other-than-temporary impairment losses recognized on available-for-sale fixed maturity securities prior to adoption of the update cannot be reversed. January 1, 2020 We have not yet determined the expected impact on our financial position or results of operations.

Significant Accounting Polici32

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of New Accounting Pronouncements	Accounting Updates Adopted in 2016: Accounting Standards Codification (ASC) Description Date of Adoption Effect on Financial Statements ASC 820 "Fair Value Measurement" This update eliminated the requirement to categorize within the fair value hierarchy table investments whose fair value is measured at net asset value using the practical expedient. Instead, entities are required to disclose the fair value of these investments so that financial statement users can reconcile amounts reported in the fair value hierarchy table to the amounts reported on the consolidated balance sheets. The guidance is to be applied retrospectively. January 1, 2016 The adoption of this update modified certain of our annual reporting period disclosures for invested assets held in our employee benefit plans but had no effect on our financial position or results of operations. ASC 835 "Interest - Imputation of Interest" This update simplified the presentation of deferred debt issuance costs by requiring these costs to be presented in the balance sheet as a reduction of the carrying amount of the debt liability to which the deferred costs relate, rather than classifying the deferred costs as an asset. This classification is consistent with the treatment of debt discounts. We applied the amendments in the update retrospectively, adjusting all prior periods in our consolidated financial statements and accompanying notes. January 1, 2016 The adoption of this update resulted in the following reclassification adjustments to our consolidated balance sheets but had no effect on our financial position or results of operations. December 31, 2015 Historical Accounting Method As Adjusted Effect of Change (in millions of dollars) Consolidated Balance Sheets Short-term Debt $ 352.4 $ 352.0 $ (0.4 ) Long-term Debt 2,475.1 2,449.4 (25.7 ) Other Assets 663.5 637.4 (26.1 ) Accounting Updates Adopted in 2015: ASC Description Date of Adoption Effect on Financial Statements ASC 860 "Transfers and Servicing" This update changed the accounting for repurchase-to-maturity transactions and linked repurchase financings to secured borrowing accounting, which is consistent with the accounting for other repurchase agreements. The update also required disclosures for repurchase agreements, securities lending transactions, and repurchase-to-maturity transactions. January 1, 2015, except for certain disclosures, which were effective April 1, 2015. The adoption of this update expanded our disclosures, but had no effect on our financial position or results of operations. ASC 323 "Investments - Equity Method and Joint Ventures" This update permitted entities to make an accounting policy election to account for 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 were also required. January 1, 2015 The adoption of this update resulted in the retrospective adjustment of all prior periods in our consolidated financial statements and accompanying notes.

Fair Values of Financial Inst33

Fair Values of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [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 securities lending agreements approximate fair value due to the short-term nature of the instruments. As such, these financial instruments are not included in the following chart. December 31, 2016 December 31, 2015 Carrying Amount Fair Value Carrying Amount Fair Value (in millions of dollars) Assets Fixed Maturity Securities $ 44,217.3 $ 44,217.3 $ 43,354.4 $ 43,354.4 Mortgage Loans 2,038.9 2,122.2 1,883.6 2,013.9 Policy Loans 3,463.2 3,564.2 3,395.4 3,498.0 Other Long-term Investments Derivatives 32.7 32.7 49.8 49.8 Equity Securities 1.2 1.2 1.4 1.4 Miscellaneous Long-term Investments 541.9 541.9 474.4 474.4 Liabilities Policyholders' Funds Deferred Annuity Products $ 597.4 $ 597.4 $ 608.8 $ 608.8 Supplementary Contracts without Life Contingencies 608.8 608.8 641.1 641.1 Short-term Debt — — 352.0 366.2 Long-term Debt 2,999.4 3,175.8 2,449.4 2,645.9 Payables for Collateral on Investments Federal Home Loan Bank (FHLB) Funding Agreements 350.0 350.0 350.0 350.0 Other Liabilities Derivatives 52.8 52.8 50.2 50.2 Embedded Derivative in Modified Coinsurance Arrangement 46.7 46.7 87.6 87.6 Unfunded Commitments to Investment Partnerships 5.0 5.0 5.0 5.0
Fair Values by Fair Value Hierarchy Input Level	Fair value measurements by input level for financial instruments carried at fair value are as follows: December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 454.2 $ 928.2 $ — $ 1,382.4 States, Municipalities, and Political Subdivisions — 2,068.5 89.5 2,158.0 Foreign Governments — 914.7 — 914.7 Public Utilities 108.5 7,648.9 265.3 8,022.7 Mortgage/Asset-Backed Securities — 2,230.4 — 2,230.4 All Other Corporate Bonds 3,507.1 24,500.4 1,459.7 29,467.2 Redeemable Preferred Stocks — 18.7 23.2 41.9 Total Fixed Maturity Securities 4,069.8 38,309.8 1,837.7 44,217.3 Other Long-term Investments Derivatives Foreign Exchange Contracts — 32.7 — 32.7 Equity Securities — — 1.2 1.2 Liabilities Other Liabilities Derivatives Interest Rate Swaps $ — $ 7.6 $ — $ 7.6 Foreign Exchange Contracts — 44.8 — 44.8 Credit Default Swaps — 0.4 — 0.4 Embedded Derivative in Modified Coinsurance Arrangement — — 46.7 46.7 Total Derivatives — 52.8 46.7 99.5 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 97.3 $ 1,367.9 $ — $ 1,465.2 States, Municipalities, and Political Subdivisions — 1,994.9 122.2 2,117.1 Foreign Governments — 998.7 52.9 1,051.6 Public Utilities 59.1 7,687.2 274.1 8,020.4 Mortgage/Asset-Backed Securities — 2,481.5 — 2,481.5 All Other Corporate Bonds 2,770.4 23,992.8 1,408.2 28,171.4 Redeemable Preferred Stocks — 23.4 23.8 47.2 Total Fixed Maturity Securities 2,926.8 38,546.4 1,881.2 43,354.4 Other Long-term Investments Derivatives Interest Rate Swaps — 2.4 — 2.4 Foreign Exchange Contracts — 47.4 — 47.4 Total Derivatives — 49.8 — 49.8 Equity Securities — — 1.4 1.4 Liabilities Other Liabilities Derivatives Interest Rate Swaps $ — $ 12.3 $ — $ 12.3 Foreign Exchange Contracts — 37.6 — 37.6 Credit Default Swaps — 0.3 — 0.3 Embedded Derivative in Modified Coinsurance Arrangement — — 87.6 87.6 Total Derivatives — 50.2 87.6 137.8
Transfers of Assets between Level 1 and Level 2	Transfers of assets between Level 1 and Level 2 are as follows: Year Ended December 31 2016 2015 Transfers into Level 1 from Level 2 Level 2 from Level 1 Level 1 from Level 2 Level 2 from Level 1 (in millions of dollars) Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 200.0 $ — $ — $ 195.3 Public Utilities 65.9 59.1 7.3 85.1 All Other Corporate Bonds 1,889.0 1,860.3 1,369.2 1,556.7 Total Fixed Maturity Securities $ 2,154.9 $ 1,919.4 $ 1,376.5 $ 1,837.1 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	Changes in assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) are as follows: Year Ended December 31, 2016 Total Realized and Unrealized Investment Gains (Losses) Included in Beginning of Year Earnings Other Comprehensive Income or Loss Purchases Sales Level 3 Transfers End of Year Into Out of (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions $ 122.2 $ — $ 1.9 $ — $ (0.5 ) $ — $ (34.1 ) $ 89.5 Foreign Governments 52.9 — — — — — (52.9 ) — Public Utilities 274.1 — (0.8 ) — (3.7 ) 157.6 (161.9 ) 265.3 All Other Corporate Bonds 1,408.2 1.4 6.9 115.9 (111.2 ) 792.8 (754.3 ) 1,459.7 Redeemable Preferred Stocks 23.8 — (0.6 ) — — — — 23.2 Total Fixed Maturity Securities 1,881.2 1.4 7.4 115.9 (115.4 ) 950.4 (1,003.2 ) 1,837.7 Equity Securities 1.4 — 0.1 — (0.3 ) — — 1.2 Embedded Derivative in Modified Coinsurance Arrangement (87.6 ) 40.9 — — — — — (46.7 ) Year Ended December 31, 2015 Total Realized and Unrealized Investment Gains (Losses) Included in Beginning of Year Earnings Other Comprehensive Income or Loss Purchases Sales Level 3 Transfers End of Year Into Out of (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions $ 140.1 $ (0.1 ) $ (5.3 ) $ 12.0 $ (16.5 ) $ — $ (8.0 ) $ 122.2 Foreign Governments 69.3 — (1.4 ) — (15.0 ) — — 52.9 Public Utilities 315.0 — (6.9 ) 40.0 (2.4 ) 118.5 (190.1 ) 274.1 All Other Corporate Bonds 1,425.3 (7.0 ) (113.2 ) 55.3 (220.8 ) 810.2 (541.6 ) 1,408.2 Redeemable Preferred Stocks 24.9 — (1.1 ) — — — — 23.8 Total Fixed Maturity Securities 1,974.6 (7.1 ) (127.9 ) 107.3 (254.7 ) 928.7 (739.7 ) 1,881.2 Equity Securities 1.4 — — — — — — 1.4 Embedded Derivative in Modified Coinsurance Arrangement (49.9 ) (37.7 ) — — — — — (87.6 ) 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 (losses) which are included in earnings and are attributable to the change in fair value of assets or liabilities valued using significant unobservable inputs and still held at each year end were $40.9 million and $(37.7) million for the years ended December 31, 2016 and 2015 , respectively. These amounts relate entirely to the change in fair value of an embedded derivative in a modified coinsurance arrangement and are reported as a component of 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. December 31, 2016 Fair Value Unobservable Input Range/Weighted Average (in millions of dollars) Fixed Maturity Securities All Other Corporate Bonds - Private $ 310.4 Comparability Adjustment (b) 0.50% - 0.50% / 0.50% Equity Securities - Private 1.1 Market Convention (f) Priced at Cost or Owner's Equity Embedded Derivative in Modified Coinsurance Arrangement (46.7 ) Projected Liability Cash Flows (g) Actuarial Assumptions December 31, 2015 Fair Value Unobservable Input Range/Weighted Average (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions - Private $ 73.3 Change in Benchmark Reference (a) 0.50% - 1.00% / 0.70% States, Municipalities, and Political Subdivisions - Public 12.0 Market Convention (f) Priced at Par All Other Corporate Bonds - Private 151.0 Comparability Adjustment (b) 0.50% - 0.50% / 0.50% All Other Corporate Bonds - Public 36.2 Lack of Marketability (d) 1.00% - 1.00% / 1.00% Equity Securities - Private 1.1 Market Convention (f) Priced at Cost or Owner's Equity Embedded Derivative in Modified Coinsurance Arrangement (87.6 ) 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)	12 Months Ended
	Dec. 31, 2016
Notes to Financial Statements [Abstract]
Amortized Cost and Fair Values of Securities by Security Type	At December 31, 2016 and 2015 , 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: December 31, 2016 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value (in millions of dollars) United States Government and Government Agencies and Authorities $ 1,202.8 $ 183.1 $ 3.5 $ 1,382.4 States, Municipalities, and Political Subdivisions 1,868.0 294.8 4.8 2,158.0 Foreign Governments 714.8 199.9 — 914.7 Public Utilities 6,916.1 1,123.5 16.9 8,022.7 Mortgage/Asset-Backed Securities 2,104.9 134.7 9.2 2,230.4 All Other Corporate Bonds 26,707.1 2,944.0 183.9 29,467.2 Redeemable Preferred Stocks 39.0 3.2 0.3 41.9 Total Fixed Maturity Securities $ 39,552.7 $ 4,883.2 $ 218.6 $ 44,217.3 December 31, 2015 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value (in millions of dollars) United States Government and Government Agencies and Authorities $ 1,265.8 $ 207.3 $ 7.9 $ 1,465.2 States, Municipalities, and Political Subdivisions 1,828.3 293.4 4.6 2,117.1 Foreign Governments 897.2 154.4 — 1,051.6 Public Utilities 6,979.3 1,057.4 16.3 8,020.4 Mortgage/Asset-Backed Securities 2,318.6 167.6 4.7 2,481.5 All Other Corporate Bonds 26,325.5 2,454.1 608.2 28,171.4 Redeemable Preferred Stocks 44.0 3.8 0.6 47.2 Total Fixed Maturity Securities $ 39,658.7 $ 4,338.0 $ 642.3 $ 43,354.4
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. December 31, 2016 Less Than 12 Months 12 Months or Greater Fair Value Gross Unrealized Loss Fair Value Gross Unrealized Loss (in millions of dollars) United States Government and Government Agencies and Authorities $ 132.8 $ 3.5 $ — $ — States, Municipalities, and Political Subdivisions 132.2 4.8 — — Public Utilities 260.2 15.3 15.6 1.6 Mortgage/Asset-Backed Securities 513.2 9.1 0.8 0.1 All Other Corporate Bonds 3,621.0 122.1 774.7 61.8 Redeemable Preferred Stocks 7.9 0.1 10.8 0.2 Total Fixed Maturity Securities $ 4,667.3 $ 154.9 $ 801.9 $ 63.7 December 31, 2015 Less Than 12 Months 12 Months or Greater Fair Value Gross Unrealized Loss Fair Value Gross Unrealized Loss (in millions of dollars) United States Government and Government Agencies and Authorities $ 213.5 $ 7.9 $ — $ — States, Municipalities, and Political Subdivisions 112.3 4.3 3.3 0.3 Public Utilities 408.4 14.4 10.3 1.9 Mortgage/Asset-Backed Securities 504.3 4.6 9.0 0.1 All Other Corporate Bonds 6,155.0 464.2 554.7 144.0 Redeemable Preferred Stocks 10.4 0.6 — — Total Fixed Maturity Securities $ 7,403.9 $ 496.0 $ 577.3 $ 146.3
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. December 31, 2016 Total Amortized Cost Unrealized Gain Position Unrealized Loss Position Gross Gain Fair Value Gross Loss Fair Value (in millions of dollars) 1 year or less $ 1,338.8 $ 28.6 $ 1,355.6 $ — $ 11.8 Over 1 year through 5 years 6,231.0 553.5 6,605.6 8.2 170.7 Over 5 years through 10 years 10,991.6 843.8 9,336.2 82.8 2,416.4 Over 10 years 18,886.4 3,322.6 19,734.3 118.4 2,356.3 37,447.8 4,748.5 37,031.7 209.4 4,955.2 Mortgage/Asset-Backed Securities 2,104.9 134.7 1,716.4 9.2 514.0 Total Fixed Maturity Securities $ 39,552.7 $ 4,883.2 $ 38,748.1 $ 218.6 $ 5,469.2 December 31, 2015 Total Amortized Cost Unrealized Gain Position Unrealized Loss Position Gross Gain Fair Value Gross Loss Fair Value (in millions of dollars) 1 year or less $ 1,112.2 $ 20.6 $ 1,098.8 $ 0.2 $ 33.8 Over 1 year through 5 years 6,514.0 554.4 6,649.5 49.8 369.1 Over 5 years through 10 years 10,519.3 746.3 7,124.4 320.5 3,820.7 Over 10 years 19,194.6 2,849.1 18,532.3 267.1 3,244.3 37,340.1 4,170.4 33,405.0 637.6 7,467.9 Mortgage/Asset-Backed Securities 2,318.6 167.6 1,968.2 4.7 513.3 Total Fixed Maturity Securities $ 39,658.7 $ 4,338.0 $ 35,373.2 $ 642.3 $ 7,981.2
Low Income Housing Tax Credits	The Company invests in tax credit partnerships primarily for the receipt of income tax credits and tax benefits derived from passive losses on the investments. Amounts recognized in the consolidated statements of income are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Income Tax Credits $ 41.8 $ 41.8 $ 41.8 Amortization, Net of Tax (23.2 ) (23.3 ) (23.2 ) Income Tax Benefit $ 18.6 $ 18.5 $ 18.6
Mortgage Loans by Property Type and Geographic Region	Mortgage loans by property type and geographic region are presented below. December 31 2016 2015 (in millions of dollars) Carrying Percent of Carrying Percent of Amount Total Amount Total Property Type Apartment $ 288.4 14.1 % $ 130.6 6.9 % Industrial 573.6 28.1 574.1 30.5 Office 700.1 34.4 764.7 40.6 Retail 455.4 22.4 392.3 20.8 Other 21.4 1.0 21.9 1.2 Total $ 2,038.9 100.0 % $ 1,883.6 100.0 % Region New England $ 72.7 3.6 % $ 97.6 5.2 % Mid-Atlantic 125.3 6.1 128.8 6.9 East North Central 230.1 11.3 186.4 9.9 West North Central 172.0 8.4 162.6 8.6 South Atlantic 438.3 21.5 409.3 21.7 East South Central 91.6 4.5 79.1 4.2 West South Central 268.7 13.2 237.6 12.6 Mountain 214.1 10.5 196.5 10.4 Pacific 426.1 20.9 385.7 20.5 Total $ 2,038.9 100.0 % $ 1,883.6 100.0 %
Mortgage Loans by Credit Quality Indicators	Mortgage loans, sorted by the applicable credit quality indicators, are as follows: December 31 2016 2015 (in millions of dollars) Internal Rating Aa $ 0.7 $ 1.1 A 488.2 586.6 Baa 1,506.6 1,285.8 Ba 43.4 10.1 Total $ 2,038.9 $ 1,883.6 Loan-to-Value Ratio <= 65% $ 917.9 $ 937.2 > 65% <= 75% 1,011.5 842.5 > 75% <= 85% 50.8 88.4 > 85% 58.7 15.5 Total $ 2,038.9 $ 1,883.6
Troubled Debt Restructurings on Financing Receivables	A summary of our troubled debt restructurings is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Foreclosure Carrying Amount $ 5.4 $ — $ 18.1 Number of Loans 1 — 1
Activity in the Allowance for Credit Losses	The activity in the allowance for credit losses is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Balance at Beginning of Year $ — $ 1.5 $ 1.5 Provision — 0.5 3.0 Charge-offs, Net of Recoveries — (2.0 ) (3.0 ) Balance at End of Year $ — $ — $ 1.5
Remaining Contractual Maturity of Securities Lending Agreements	The remaining contractual maturities of our securities lending agreements disaggregated by class of collateral pledged are as follows: December 31 2016 2015 Overnight and Continuous (in millions of dollars) United States Government and Government Agencies and Authorities $ 0.1 $ 1.2 Public Utilities 0.1 4.0 All Other Corporate Bonds 29.7 23.8 Total Borrowings 29.9 29.0 Gross Amount of Recognized Liability for Securities Lending Transactions 29.9 29.0 Amounts Related to Agreements Not Included in Offsetting Disclosure Contained Herein $ — $ —
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. December 31, 2016 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 $ 32.7 $ — $ 32.7 $ (7.3 ) $ (25.4 ) $ — Securities Lending 178.5 — 178.5 (148.6 ) (29.9 ) — Total $ 211.2 $ — $ 211.2 $ (155.9 ) $ (55.3 ) $ — Financial Liabilities: Derivatives $ 52.8 $ — $ 52.8 $ (37.6 ) $ — $ 15.2 Securities Lending 29.9 — 29.9 (29.9 ) — — Total $ 82.7 $ — $ 82.7 $ (67.5 ) $ — $ 15.2 December 31, 2015 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 $ 49.8 $ — $ 49.8 $ (12.8 ) $ (36.4 ) $ 0.6 Securities Lending 181.6 — 181.6 (152.6 ) (29.0 ) — Total $ 231.4 $ — $ 231.4 $ (165.4 ) $ (65.4 ) $ 0.6 Financial Liabilities: Derivatives $ 50.2 $ — $ 50.2 $ (35.6 ) $ — $ 14.6 Securities Lending 29.0 — 29.0 (29.0 ) — — Total $ 79.2 $ — $ 79.2 $ (64.6 ) $ — $ 14.6
Net Investment Income	Net Investment Income Net investment income reported in our consolidated statements of income is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Fixed Maturity Securities $ 2,293.9 $ 2,327.1 $ 2,344.4 Derivatives 49.8 44.2 40.4 Mortgage Loans 114.0 114.0 109.8 Policy Loans 17.3 16.7 16.3 Other Long-term Investments 22.6 21.6 23.0 Short-term Investments 7.5 3.4 2.4 Gross Investment Income 2,505.1 2,527.0 2,536.3 Less Investment Expenses 31.9 31.2 29.0 Less Investment Income on Participation Fund Account Assets 14.2 14.6 15.1 Net Investment Income $ 2,459.0 $ 2,481.2 $ 2,492.2
Realized Investment Gains and Losses Reported in Consolidated Statements of Income	Realized Investment Gain and Loss Realized investment gains and losses are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Fixed Maturity Securities Gross Gains on Sales $ 34.3 $ 23.8 $ 9.3 Gross Losses on Sales (17.2 ) (25.6 ) (7.5 ) Other-Than-Temporary Impairment Loss (30.5 ) (32.4 ) (13.5 ) Mortgage Loans and Other Invested Assets Gross Gains on Sales 5.5 16.0 21.2 Gross Losses on Sales (0.7 ) (0.1 ) (0.8 ) Impairment Loss (5.7 ) (5.9 ) (3.4 ) Embedded Derivative in Modified Coinsurance Arrangement 40.9 (37.7 ) 3.3 All Other Derivatives (1.5 ) 35.7 11.0 Foreign Currency Transactions (0.9 ) (17.6 ) (3.5 ) Net Realized Investment Gain (Loss) $ 24.2 $ (43.8 ) $ 16.1

Derivative Financial Instrume35

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
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 Variable/Pay Fixed Receive Fixed/Pay Fixed Receive Fixed/Pay Variable Credit Default Forwards Total (in millions of dollars) Balance at December 31, 2013 $ 150.0 $ 630.4 $ 600.0 $ 97.0 $ — $ 1,477.4 Additions — 250.1 — — 68.0 318.1 Terminations — 40.1 — — 68.0 108.1 Balance at December 31, 2014 150.0 840.4 600.0 97.0 — 1,687.4 Additions — — — 2.0 94.0 96.0 Terminations — 190.1 — 29.0 94.0 313.1 Balance at December 31, 2015 150.0 650.3 600.0 70.0 — 1,470.3 Additions 3.5 — — — 30.0 33.5 Terminations 48.0 33.8 350.0 — 20.0 451.8 Balance at December 31, 2016 $ 105.5 $ 616.5 $ 250.0 $ 70.0 $ 10.0 $ 1,052.0
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. December 31, 2016 Asset Derivatives Liability Derivatives Balance Sheet Location Fair Value Balance Sheet Location Fair Value (in millions of dollars) Designated as Hedging Instruments Interest Rate Swaps and Forwards Other L-T Investments $ — Other Liabilities $ 6.9 Foreign Exchange Contracts Other L-T Investments 32.7 Other Liabilities 13.4 Total $ 32.7 $ 20.3 Not Designated as Hedging Instruments Credit Default Swaps Other Liabilities $ 0.4 Interest Rate Swaps Other Liabilities 0.7 Foreign Exchange Contracts Other Liabilities 31.4 Embedded Derivative in Modified Coinsurance Arrangement Other Liabilities 46.7 Total $ 79.2 December 31, 2015 Asset Derivatives Liability Derivatives Balance Sheet Location Fair Value Balance Sheet Location Fair Value (in millions of dollars) Designated as Hedging Instruments Interest Rate Swaps Other L-T Investments $ 2.4 Other Liabilities $ 12.3 Foreign Exchange Contracts Other L-T Investments 47.4 Other Liabilities 6.0 Total $ 49.8 $ 18.3 Not Designated as Hedging Instruments Credit Default Swaps Other Liabilities $ 0.3 Foreign Exchange Contracts Other Liabilities 31.6 Embedded Derivative in Modified Coinsurance Arrangement Other Liabilities 87.6 Total $ 119.5
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. Year Ended December 31 2016 2015 2014 (in millions of dollars) Gain (Loss) Recognized in Other Comprehensive Income (Loss) on Derivatives Interest Rate Swaps and Forwards $ (0.1 ) $ (0.7 ) $ (0.1 ) Foreign Exchange Contracts (22.2 ) 68.1 16.2 Total $ (22.3 ) $ 67.4 $ 16.1 Gain (Loss) Reclassified from Accumulated Other Comprehensive Income into Income Net Investment Income Interest Rate Swaps and Forwards $ 54.5 $ 50.2 $ 47.8 Foreign Exchange Contracts (1.1 ) (1.6 ) (4.2 ) Net Realized Investment Gain (Loss) Interest Rate Swaps 3.2 0.5 4.3 Foreign Exchange Contracts (1.4 ) 36.1 6.9 Interest and Debt Expense Interest Rate Swaps (1.9 ) (1.8 ) (1.8 ) Total $ 53.3 $ 83.4 $ 53.0
Gains and Losses 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. Year Ended December 31 2016 2015 2014 (in millions of dollars) Net Realized Investment Gain (Loss) Credit Default Swaps $ (0.9 ) $ 0.1 $ (0.3 ) Interest Rate Swaps 0.4 — — Foreign Exchange Contracts 0.2 (0.3 ) (1.8 ) Embedded Derivative in Modified Coinsurance Arrangement 40.9 (37.7 ) 3.3 Total $ 40.6 $ (37.9 ) $ 1.2

Accumulated Other Comprehensi36

Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income	Components of our accumulated other comprehensive income (loss), 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 ) $ 255.0 Other Comprehensive Income (Loss) Before Reclassifications 154.3 31.1 (66.3 ) (216.1 ) (97.0 ) Amounts Reclassified from Accumulated Other Comprehensive Income or Loss 0.3 (36.4 ) — 44.5 8.4 Net Other Comprehensive Income (Loss) 154.6 (5.3 ) (66.3 ) (171.6 ) (88.6 ) Balance at December 31, 2014 290.3 391.0 (113.4 ) (401.5 ) 166.4 Other Comprehensive Income (Loss) Before Reclassifications (114.7 ) 43.3 (60.2 ) 1.3 (130.3 ) Amounts Reclassified from Accumulated Other Comprehensive Income or Loss 28.7 (56.3 ) — 7.6 (20.0 ) Net Other Comprehensive Income (Loss) (86.0 ) (13.0 ) (60.2 ) 8.9 (150.3 ) Balance at December 31, 2015 204.3 378.0 (173.6 ) (392.6 ) 16.1 Other Comprehensive Income (Loss) Before Reclassifications 226.5 (15.8 ) (180.4 ) (82.8 ) (52.5 ) Amounts Reclassified from Accumulated Other Comprehensive Income or Loss 9.8 (34.7 ) — 10.3 (14.6 ) Net Other Comprehensive Income (Loss) 236.3 (50.5 ) (180.4 ) (72.5 ) (67.1 ) Balance at December 31, 2016 $ 440.6 $ 327.5 $ (354.0 ) $ (465.1 ) $ (51.0 )
Schedule of Components of Unrealized Gain on Securities	The net unrealized gain on securities consists of the following components: December 31 Change for the Year Ended December 31 2016 2015 2014 2013 2016 2015 2014 (in millions of dollars) Fixed Maturity Securities $ 4,664.6 $ 3,695.7 $ 6,261.5 $ 4,054.8 $ 968.9 $ (2,565.8 ) $ 2,206.7 Other Investments (22.7 ) (33.7 ) 13.9 55.5 11.0 (47.6 ) (41.6 ) Deferred Acquisition Costs (38.9 ) (29.4 ) (50.8 ) (41.6 ) (9.5 ) 21.4 (9.2 ) Reserves for Future Policy and Contract Benefits (4,253.2 ) (3,578.4 ) (6,150.3 ) (4,108.5 ) (674.8 ) 2,571.9 (2,041.8 ) Reinsurance Recoverable 321.3 263.2 365.0 263.8 58.1 (101.8 ) 101.2 Income Tax (230.5 ) (113.1 ) (149.0 ) (88.3 ) (117.4 ) 35.9 (60.7 ) Total $ 440.6 $ 204.3 $ 290.3 $ 135.7 $ 236.3 $ (86.0 ) $ 154.6
Schedule of Reclassification out of Accumulated Other Comprehensive Income	Amounts reclassified from accumulated other comprehensive income (loss) were recognized in our consolidated statements of income as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Net Unrealized Gain on Securities Net Realized Investment Gain (Loss) Gain (Loss) on Sales of Securities and Other Invested Assets $ 15.3 $ (12.2 ) $ 12.6 Other-Than-Temporary Impairment Loss (30.5 ) (32.4 ) (13.5 ) (15.2 ) (44.6 ) (0.9 ) Income Tax Benefit (5.4 ) (15.9 ) (0.6 ) Total $ (9.8 ) $ (28.7 ) $ (0.3 ) Net Gain on Cash Flow Hedges Net Investment Income Gain on Interest Rate Swaps and Forwards $ 54.5 $ 50.2 $ 47.8 Loss on Foreign Exchange Contracts (1.1 ) (1.6 ) (4.2 ) Net Realized Investment Gain (Loss) Gain on Interest Rate Swaps 3.2 0.5 4.3 Gain (Loss) on Foreign Exchange Contracts (1.4 ) 36.1 6.9 Interest and Debt Expense Loss on Interest Rate Swaps (1.9 ) (1.8 ) (1.8 ) 53.3 83.4 53.0 Income Tax Expense 18.6 27.1 16.6 Total $ 34.7 $ 56.3 $ 36.4 Unrecognized Pension and Postretirement Benefit Costs Other Expenses Amortization of Net Actuarial Loss $ (16.3 ) $ (11.9 ) $ (5.6 ) Amortization of Prior Service Credit 0.5 0.3 1.7 Settlement Loss — — (64.4 ) (15.8 ) (11.6 ) (68.3 ) Income Tax Benefit (5.5 ) (4.0 ) (23.8 ) Total $ (10.3 ) $ (7.6 ) $ (44.5 )

Liability for Unpaid Claims (Ta

Liability for Unpaid Claims (Tables)	12 Months Ended
	Dec. 31, 2016
Insurance [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	Changes in the liability for unpaid claims and claim adjustment expenses are as follows: 2016 2015 2014 (in millions of dollars) Balance at January 1 $ 23,796.1 $ 24,194.0 $ 24,535.6 Less Reinsurance Recoverable 2,064.6 2,066.9 2,072.8 Net Balance at January 1 21,731.5 22,127.1 22,462.8 Incurred Related to Current Year 5,243.0 5,058.1 4,851.5 Prior Years Interest 1,136.7 1,177.6 1,214.7 All Other Incurred (198.3 ) (111.6 ) (13.5 ) Foreign Currency (340.2 ) (119.5 ) (138.7 ) Total Incurred 5,841.2 6,004.6 5,914.0 Paid Related to Current Year (2,035.4 ) (1,853.7 ) (1,702.3 ) Prior Years (4,451.4 ) (4,546.5 ) (4,547.4 ) Total Paid (6,486.8 ) (6,400.2 ) (6,249.7 ) Net Balance at December 31 21,085.9 21,731.5 22,127.1 Plus Reinsurance Recoverable 2,163.6 2,064.6 2,066.9 Balance at December 31 $ 23,249.5 $ 23,796.1 $ 24,194.0
Reconciliation of Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits to Balance Sheet Amounts	A reconciliation of policy and contract benefits and reserves for future policy and contract benefits as reported in our consolidated balance sheets to the liability for unpaid claims and claim adjustment expenses is as follows: December 31 2016 2015 2014 (in millions of dollars) Policy and Contract Benefits $ 1,507.9 $ 1,484.6 $ 1,529.3 Reserves for Future Policy and Contract Benefits 44,245.9 43,540.6 45,929.4 Total 45,753.8 45,025.2 47,458.7 Less: Life Reserves for Future Policy and Contract Benefits 8,078.2 7,946.3 7,850.9 Accident and Health Active Life Reserves 10,172.9 9,704.4 9,263.5 Adjustment Related to Unrealized Investment Gains and Losses 4,253.2 3,578.4 6,150.3 Liability for Unpaid Claims and Claim Adjustment Expenses $ 23,249.5 $ 23,796.1 $ 24,194.0 The adjustment related to unrealized investment gains and losses reflects the changes that would be necessary to policyholder liabilities if the unrealized investment gains and losses related to the corresponding available-for-sale securities had been realized. Changes in this adjustment are reported as a component of other comprehensive income or loss.

Income Tax (Tables)

Income Tax (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit)	Total income tax expense (benefit) is allocated as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Net Income $ 416.3 $ 371.2 $ 139.9 Stockholders' Equity - Additional Paid-in Capital Stock-Based Compensation (0.3 ) (3.6 ) (3.0 ) Stockholders' Equity - Accumulated Other Comprehensive Income Change in Net Unrealized Gain on Securities Before Adjustment 318.0 (892.5 ) 725.8 Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance (200.6 ) 856.6 (665.1 ) Change in Net Gain on Cash Flow Hedges (25.4 ) (4.3 ) (2.0 ) Change in Foreign Currency Translation Adjustment — (0.1 ) — Change in Unrecognized Pension and Postretirement Benefit Costs (34.2 ) 3.2 (92.4 ) Total $ 473.8 $ 330.5 $ 103.2
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of the income tax provision at the U.S. federal statutory rate to the income tax rate as reported in our consolidated statements of income is as follows: Year Ended December 31 2016 2015 2014 Statutory Income Tax 35.0 % 35.0 % 35.0 % Foreign Rate Differential, Inclusive of Foreign Rate Changes (2.2 ) (2.5 ) (4.0 ) Tax Credits (1.6 ) (1.4 ) (4.5 ) Other Items, Net (0.3 ) (1.1 ) (0.7 ) Effective Tax 30.9 % 30.0 % 25.8 %
Schedule of Deferred Tax Assets and Liabilities	Our net deferred tax liability consists of the following: December 31 2016 2015 (in millions of dollars) Deferred Tax Liability Deferred Acquisition Costs $ 174.9 $ 140.4 Fixed Assets 80.7 87.1 Invested Assets 1,427.6 1,128.4 Other 63.2 55.4 Gross Deferred Tax Liability 1,746.4 1,411.3 Deferred Tax Asset Reserves 1,308.5 1,060.5 Employee Benefits 307.4 246.0 Other 17.4 14.3 Gross Deferred Tax Asset 1,633.3 1,320.8 Less: Valuation Allowance 17.2 1.3 Net Deferred Tax Asset 1,616.1 1,319.5 Net Deferred Tax Liability $ 130.3 $ 91.8
Schedule of Income before Income Tax, Domestic and Foreign	Our consolidated statements of income include amounts subject to both domestic and foreign taxation. The income and related tax expense (benefit) are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Income Before Tax Domestic $ 1,215.8 $ 1,057.8 $ 391.7 Foreign 131.9 180.5 150.3 Total $ 1,347.7 $ 1,238.3 $ 542.0 Current Tax Expense (Benefit) Federal $ 414.8 $ 280.5 $ 160.6 State and Local 0.3 — — Foreign (29.4 ) 61.6 (25.1 ) Total 385.7 342.1 135.5 Deferred Tax Expense (Benefit) Federal (14.6 ) 56.9 (50.5 ) State and Local (2.1 ) — — Foreign 47.3 (27.8 ) 54.9 Total 30.6 29.1 4.4 Total $ 416.3 $ 371.2 $ 139.9
Summary of Positions for which Significant Change in Unrecognized Tax Benefits is Reasonably Possible	Our consolidated statements of income include the following changes in unrecognized tax benefits: December 31 2016 2015 2014 (in millions of dollars) Balance at Beginning of Year $ 0.8 $ 19.8 $ 18.4 Additions for Tax Positions Related to Prior Years 0.7 — 1.7 Additions for Tax Positions Related to Current Year — — 0.3 Settlements with Tax Authorities — (19.0 ) (0.6 ) Balance at End of Year 1.5 0.8 19.8 Less Tax Attributable to Temporary Items Included Above — — (10.4 ) Total Unrecognized Tax Benefits That if Recognized Would Affect the Effective Tax Rate $ 1.5 $ 0.8 $ 9.4

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Schedule of Debt	Debt consists of the following: December 31 2016 2015 Interest Rates Maturities (in millions of dollars) Long-term Debt Outstanding Principal Senior Secured Notes issued 2007 Variable 2037 $ 260.0 $ 324.0 Senior Secured Notes acquired 2016 Variable 2038 3.5 — Senior Notes issued 1998 7.000% 2018 200.0 200.0 Senior Notes issued 1998 6.750 - 7.250% 2028 365.8 365.8 Senior Notes issued 2002 7.375% 2032 39.5 39.5 Senior Notes issued 2010 5.625% 2020 400.0 400.0 Senior Notes issued 2012 and 2016 5.750% 2042 500.0 250.0 Senior Notes issued 2014 4.000% 2024 350.0 350.0 Senior Notes issued 2015 3.875% 2025 275.0 275.0 Senior Notes issued 2016 3.000% 2021 350.0 — Medium-term Notes issued 1990 - 1996 7.000 - 7.190% 2023 - 2028 50.8 50.8 Junior Subordinated Debt Securities issued 1998 7.405% 2038 226.5 226.5 Fair Value Hedges Adjustment (3.1 ) (2.7 ) Less: Unamortized Net Premium (Discount) 9.8 (3.8 ) Unamortized Debt Issuance Costs (28.4 ) (25.7 ) Total Long-term Debt 2,999.4 2,449.4 Short-term Debt Outstanding Principal Senior Notes issued 2009 7.125% 2016 — 350.0 Fair Value Hedges Adjustment — 2.4 Less Unamortized Debt Issuance Costs — (0.4 ) Total Short-term Debt — 352.0 Total Debt $ 2,999.4 $ 2,801.4

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans
Schedule of Changes in Projected Benefit Obligations and Fair Value of Plan Assets	The following table provides the changes in the benefit obligation and fair value of plan assets and the funded status of the plans. Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 (in millions of dollars) Change in Benefit Obligation Benefit Obligation at Beginning of Year $ 1,808.2 $ 1,892.6 $ 203.8 $ 226.9 $ 160.4 $ 173.9 Service Cost 7.0 3.8 — — — — Interest Cost 85.2 82.2 7.0 7.9 7.2 7.2 Plan Participant Contributions — — — — 4.0 4.6 Actuarial (Gain) Loss 123.6 (103.6 ) 55.0 (14.7 ) (4.4 ) (9.1 ) Benefits and Expenses Paid (68.7 ) (59.3 ) (4.5 ) (4.6 ) (15.6 ) (16.2 ) Plan Amendment — (7.5 ) — — (3.7 ) — Change in Foreign Exchange Rates — — (38.3 ) (11.7 ) — — Benefit Obligation at End of Year $ 1,955.3 $ 1,808.2 $ 223.0 $ 203.8 $ 147.9 $ 160.4 Accumulated Benefit Obligation at December 31 $ 1,955.3 $ 1,808.2 $ 213.4 $ 194.8 N/A N/A Change in Fair Value of Plan Assets Fair Value of Plan Assets at Beginning of Year $ 1,403.3 $ 1,473.7 $ 231.5 $ 246.3 $ 11.2 $ 11.3 Actual Return on Plan Assets 112.3 (17.5 ) 42.5 2.9 0.1 0.3 Employer Contributions 7.2 6.4 — — 11.1 11.2 Plan Participant Contributions — — — — 4.0 4.6 Benefits and Expenses Paid (68.7 ) (59.3 ) (4.5 ) (4.6 ) (15.6 ) (16.2 ) Change in Foreign Exchange Rates — — (41.1 ) (13.1 ) — — Fair Value of Plan Assets at End of Year $ 1,454.1 $ 1,403.3 $ 228.4 $ 231.5 $ 10.8 $ 11.2 Underfunded (Overfunded) Status $ 501.2 $ 404.9 $ (5.4 ) $ (27.7 ) $ 137.1 $ 149.2
Schedule of Amounts Recognized in Balance Sheet	The amounts recognized in our consolidated balance sheets for our pension and OPEB plans at December 31, 2016 and 2015 are as follows. Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 (in millions of dollars) Current Liability $ 7.0 $ 5.9 $ — $ — $ 13.1 $ 13.0 Noncurrent Liability 494.2 399.0 — — 124.0 136.2 Noncurrent Asset — — (5.4 ) (27.7 ) — — Underfunded (Overfunded) Status $ 501.2 $ 404.9 $ (5.4 ) $ (27.7 ) $ 137.1 $ 149.2 Unrecognized Pension and Postretirement Benefit Costs Net Actuarial Gain (Loss) $ (702.1 ) $ (604.2 ) $ (44.0 ) $ (28.1 ) $ 10.1 $ 6.2 Prior Service Credit 7.2 7.5 — — 3.9 0.4 (694.9 ) (596.7 ) (44.0 ) (28.1 ) 14.0 6.6 Income Tax 243.6 208.8 10.9 8.9 5.3 7.9 Total Included in Accumulated Other Comprehensive Income (Loss) $ (451.3 ) $ (387.9 ) $ (33.1 ) $ (19.2 ) $ 19.3 $ 14.5
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	The following table provides the changes recognized in other comprehensive income for the years ended December 31, 2016 and 2015 . Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 (in millions of dollars) Accumulated Other Comprehensive Income (Loss) at Beginning of Year $ (387.9 ) $ (385.5 ) $ (19.2 ) $ (25.0 ) $ 14.5 $ 9.0 Net Actuarial Gain (Loss) Amortization 16.2 11.6 0.1 0.3 — — All Other Changes (114.1 ) (22.8 ) (16.0 ) 7.0 3.9 8.8 Prior Service Credit (Cost) Amortization (0.3 ) — — — (0.2 ) (0.3 ) Plan Amendment — 7.5 — — 3.7 — Change in Income Tax 34.8 1.3 2.0 (1.5 ) (2.6 ) (3.0 ) Accumulated Other Comprehensive Income (Loss) at End of Year $ (451.3 ) $ (387.9 ) $ (33.1 ) $ (19.2 ) $ 19.3 $ 14.5
Fair Values by Fair Value Hierarchy Input Level	Fair value measurements by input level for financial instruments carried at fair value are as follows: December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 454.2 $ 928.2 $ — $ 1,382.4 States, Municipalities, and Political Subdivisions — 2,068.5 89.5 2,158.0 Foreign Governments — 914.7 — 914.7 Public Utilities 108.5 7,648.9 265.3 8,022.7 Mortgage/Asset-Backed Securities — 2,230.4 — 2,230.4 All Other Corporate Bonds 3,507.1 24,500.4 1,459.7 29,467.2 Redeemable Preferred Stocks — 18.7 23.2 41.9 Total Fixed Maturity Securities 4,069.8 38,309.8 1,837.7 44,217.3 Other Long-term Investments Derivatives Foreign Exchange Contracts — 32.7 — 32.7 Equity Securities — — 1.2 1.2 Liabilities Other Liabilities Derivatives Interest Rate Swaps $ — $ 7.6 $ — $ 7.6 Foreign Exchange Contracts — 44.8 — 44.8 Credit Default Swaps — 0.4 — 0.4 Embedded Derivative in Modified Coinsurance Arrangement — — 46.7 46.7 Total Derivatives — 52.8 46.7 99.5 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Fixed Maturity Securities United States Government and Government Agencies and Authorities $ 97.3 $ 1,367.9 $ — $ 1,465.2 States, Municipalities, and Political Subdivisions — 1,994.9 122.2 2,117.1 Foreign Governments — 998.7 52.9 1,051.6 Public Utilities 59.1 7,687.2 274.1 8,020.4 Mortgage/Asset-Backed Securities — 2,481.5 — 2,481.5 All Other Corporate Bonds 2,770.4 23,992.8 1,408.2 28,171.4 Redeemable Preferred Stocks — 23.4 23.8 47.2 Total Fixed Maturity Securities 2,926.8 38,546.4 1,881.2 43,354.4 Other Long-term Investments Derivatives Interest Rate Swaps — 2.4 — 2.4 Foreign Exchange Contracts — 47.4 — 47.4 Total Derivatives — 49.8 — 49.8 Equity Securities — — 1.4 1.4 Liabilities Other Liabilities Derivatives Interest Rate Swaps $ — $ 12.3 $ — $ 12.3 Foreign Exchange Contracts — 37.6 — 37.6 Credit Default Swaps — 0.3 — 0.3 Embedded Derivative in Modified Coinsurance Arrangement — — 87.6 87.6 Total Derivatives — 50.2 87.6 137.8
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	Changes in assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) are as follows: Year Ended December 31, 2016 Total Realized and Unrealized Investment Gains (Losses) Included in Beginning of Year Earnings Other Comprehensive Income or Loss Purchases Sales Level 3 Transfers End of Year Into Out of (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions $ 122.2 $ — $ 1.9 $ — $ (0.5 ) $ — $ (34.1 ) $ 89.5 Foreign Governments 52.9 — — — — — (52.9 ) — Public Utilities 274.1 — (0.8 ) — (3.7 ) 157.6 (161.9 ) 265.3 All Other Corporate Bonds 1,408.2 1.4 6.9 115.9 (111.2 ) 792.8 (754.3 ) 1,459.7 Redeemable Preferred Stocks 23.8 — (0.6 ) — — — — 23.2 Total Fixed Maturity Securities 1,881.2 1.4 7.4 115.9 (115.4 ) 950.4 (1,003.2 ) 1,837.7 Equity Securities 1.4 — 0.1 — (0.3 ) — — 1.2 Embedded Derivative in Modified Coinsurance Arrangement (87.6 ) 40.9 — — — — — (46.7 ) Year Ended December 31, 2015 Total Realized and Unrealized Investment Gains (Losses) Included in Beginning of Year Earnings Other Comprehensive Income or Loss Purchases Sales Level 3 Transfers End of Year Into Out of (in millions of dollars) Fixed Maturity Securities States, Municipalities, and Political Subdivisions $ 140.1 $ (0.1 ) $ (5.3 ) $ 12.0 $ (16.5 ) $ — $ (8.0 ) $ 122.2 Foreign Governments 69.3 — (1.4 ) — (15.0 ) — — 52.9 Public Utilities 315.0 — (6.9 ) 40.0 (2.4 ) 118.5 (190.1 ) 274.1 All Other Corporate Bonds 1,425.3 (7.0 ) (113.2 ) 55.3 (220.8 ) 810.2 (541.6 ) 1,408.2 Redeemable Preferred Stocks 24.9 — (1.1 ) — — — — 23.8 Total Fixed Maturity Securities 1,974.6 (7.1 ) (127.9 ) 107.3 (254.7 ) 928.7 (739.7 ) 1,881.2 Equity Securities 1.4 — — — — — — 1.4 Embedded Derivative in Modified Coinsurance Arrangement (49.9 ) (37.7 ) — — — — — (87.6 ) 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 (losses) which are included in earnings and are attributable to the change in fair value of assets or liabilities valued using significant unobservable inputs and still held at each year end were $40.9 million and $(37.7) million for the years ended December 31, 2016 and 2015 , respectively. These amounts relate entirely to the change in fair value of an embedded derivative in a modified coinsurance arrangement and are reported as a component of realized investment gains and losses.
Schedule of Assumptions Used	We use a December 31 measurement date for each of our plans. The weighted average assumptions used in the measurement of our benefit obligations as of December 31 and our net periodic benefit costs for the years ended December 31 are as follows: Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2016 2015 2016 2015 Benefit Obligations Discount Rate 4.40 % 4.80 % 2.70 % 3.80 % 4.20 % 4.70 % Rate of Compensation Increase N/A N/A 3.80 % 3.60 % N/A N/A Net Periodic Benefit Cost Discount Rate 4.80 % 4.40 % 3.80 % 3.60 % 4.70 % 4.30 % Expected Return on Plan Assets 7.50 % 7.50 % 4.90 % 5.20 % 5.75 % 5.75 % Rate of Compensation Increase N/A N/A 3.60 % 3.60 % N/A N/A
Schedule of Net Benefit Costs	Net Periodic Benefit Cost The following table provides the components of the net periodic benefit cost for the years ended December 31. Pension Benefits U.S. Plans U.K. Plan OPEB 2016 2015 2014 2016 2015 2014 2016 2015 2014 (in millions of dollars) Service Cost $ 7.0 $ 3.8 $ 3.7 $ — $ — $ 2.3 $ — $ — $ 0.3 Interest Cost 85.2 82.2 89.9 7.0 7.9 9.1 7.2 7.2 7.9 Expected Return on Plan Assets (102.8 ) (108.9 ) (117.8 ) (10.0 ) (12.4 ) (13.7 ) (0.6 ) (0.7 ) (0.7 ) Amortization of: Net Actuarial Loss 16.2 11.6 5.2 0.1 0.3 0.4 — — — Prior Service Credit (0.3 ) — — — — — (0.2 ) (0.3 ) (1.7 ) Plan Amendment — — — — — — 0.9 — — Settlement — — 64.4 — — — — — — Total Net Periodic Benefit Cost $ 5.3 $ (11.3 ) $ 45.4 $ (2.9 ) $ (4.2 ) $ (1.9 ) $ 7.3 $ 6.2 $ 5.8
Schedule of Expected Benefit Payments	The following table provides expected benefit payments, which reflect expected future service, as appropriate. Pension Benefits U.S. Plans U.K. Plan OPEB (in millions of dollars) Year Gross Subsidy Payments Net 2017 $ 71.8 $ 4.5 $ 13.6 $ 0.3 $ 13.3 2018 74.4 4.8 13.2 0.2 13.0 2019 76.9 4.8 12.8 0.2 12.6 2020 80.6 5.1 12.3 0.2 12.1 2021 84.3 5.4 11.9 0.2 11.7 2022-2026 476.9 32.5 50.9 0.7 50.2
Pension Benefits, U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Values by Fair Value Hierarchy Input Level	The categorization of fair value measurements by input level for the invested assets in our U.S. pension plans is shown below. The carrying values of investment-related receivables and payables approximate fair value due to the short-term nature of the securities and are not included in the following chart. Investments valued using net asset value (NAV) as a practical expedient are not required to be categorized by input level, but these investments are included as follows to reconcile to total invested assets. Prior year amounts have been reclassified to conform to current year presentation. December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) NAV as a Practical Total (in millions of dollars) Invested Assets Equity Securities: U.S. Large Cap $ — $ — $ — $ 85.5 $ 85.5 U.S. Small Cap 50.2 — — — 50.2 Global — — — 259.7 259.7 International — — — 26.3 26.3 Emerging Markets — — — 49.6 49.6 Fixed Income Securities: U.S. Government and Agencies 227.8 11.1 — — 238.9 Corporate — 303.6 — — 303.6 State and Municipal Securities — 2.0 — — 2.0 Opportunistic Credits — — — 181.8 181.8 Real Estate — — — 88.9 88.9 Alternative Investments: Private Equity Direct Investments — — — 37.4 37.4 Private Equity Funds of Funds — — — 32.0 32.0 Hedge Funds of Funds — — — 72.1 72.1 Cash Equivalents 21.2 — — — 21.2 Total Invested Assets $ 299.2 $ 316.7 $ — $ 833.3 $ 1,449.2 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) NAV as a Practical Total (in millions of dollars) Invested Assets Equity Securities: U.S. Large Cap $ — $ — $ — $ 176.2 $ 176.2 U.S. Mid Cap — — — 55.0 55.0 U.S. Small Cap 56.9 — — — 56.9 International 63.7 — — 62.9 126.6 Emerging Markets — — — 35.5 35.5 Fixed Income Securities: U.S. Government and Agencies 231.5 12.8 — — 244.3 Corporate — 291.4 — — 291.4 State and Municipal Securities — 2.1 — — 2.1 Opportunistic Credits — — — 163.5 163.5 Real Estate — — — 83.5 83.5 Alternative Investments: Private Equity Direct Investments — — — 30.4 30.4 Private Equity Funds of Funds — — — 35.3 35.3 Hedge Funds of Funds — — — 70.9 70.9 Cash Equivalents 28.0 — — — 28.0 Total Invested Assets $ 380.1 $ 306.3 $ — $ 713.2 $ 1,399.6
Pension Benefits, Non U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Values by Fair Value Hierarchy Input Level	The categorization of fair value measurements by input level for the invested assets in our U.K. pension plan is shown below. Investments valued using NAV as a practical expedient are not required to be categorized by input level, but these investments are included as follows to reconcile to total invested assets. Prior year amounts have been reclassified to conform to current year presentation. December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) NAV as a Practical Total (in millions of dollars) Plan Assets Diversified Growth Assets $ — $ — $ — $ 140.1 $ 140.1 Fixed Interest and Index-linked Securities 79.9 — — 7.5 87.4 Cash Equivalents 0.9 — — — 0.9 Total Plan Assets $ 80.8 $ — $ — $ 147.6 $ 228.4 December 31, 2015 Quoted Prices Significant Significant NAV as a Practical Total (in millions of dollars) Plan Assets Diversified Growth Assets $ — $ — $ — $ 156.3 $ 156.3 Fixed Interest and Index-linked Securities 62.2 — — 5.3 67.5 Cash Equivalents 7.7 — — — 7.7 Total Plan Assets $ 69.9 $ — $ — $ 161.6 $ 231.5
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Values by Fair Value Hierarchy Input Level	The categorization of fair value measurements by input level for the assets in our OPEB plan is as follows: December 31, 2016 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Life Insurance Contracts $ — $ — $ 10.8 $ 10.8 December 31, 2015 Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total (in millions of dollars) Assets Life Insurance Contracts $ — $ — $ 11.2 $ 11.2
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation	The fair value is represented by the actuarial present value of future cash flows of the contracts. Changes in our OPEB plan assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the years ended December 31, 2016 and 2015 are as follows: Year Ended December 31, 2016 Beginning of Year Actual Return on Plan Assets Contributions Net Benefits and Expenses Paid End of Year (in millions of dollars) Life Insurance Contracts $ 11.2 $ 0.1 $ 15.1 $ (15.6 ) $ 10.8 Year Ended December 31, 2015 Beginning of Year Actual Return on Plan Assets Contributions Net Benefits and Expenses Paid End of Year (in millions of dollars) Life Insurance Contracts $ 11.3 $ 0.3 $ 15.8 $ (16.2 ) $ 11.2

Stockholders' Equity and Earn41

Stockholders' Equity and Earnings Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2016
Stockholders' Equity and Earnings Per Common Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	Net income per common share is determined as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars, except share data) Numerator Net Income $ 931.4 $ 867.1 $ 402.1 Denominator (000s) Weighted Average Common Shares - Basic 235,445.7 246,986.7 255,525.9 Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards 533.5 868.0 1,126.9 Weighted Average Common Shares - Assuming Dilution 235,979.2 247,854.7 256,652.8 Net Income Per Common Share Basic $ 3.96 $ 3.51 $ 1.57 Assuming Dilution $ 3.95 $ 3.50 $ 1.57
Treasury Stock Transactions	Our board of directors has authorized the repurchase of Unum Group's common stock under the following repurchase programs: Share Repurchase Program Authorized During May 2016 May 2015 December 2013 (in millions of dollars) Authorized Repurchase Amount $ 750.0 $ 750.0 $ 750.0 Remaining Repurchase Amount at Year End 2016 $ 495.7 $ — $ — The May 2016 share repurchase program has an expiration date of November 26, 2017 . Common stock repurchases, which are accounted for using the cost method and classified as treasury stock until otherwise retired, were as follows: Year Ended December 31 2016 2015 2014 (in millions) Shares Repurchased 11.9 12.3 8.7 Cost of Shares Repurchased (1) $ 403.3 $ 426.7 $ 300.6 (1) Includes commissions of $0.2 million , $0.3 million , and $0.1 million for the years ended December 31, 2016 , 2015 , and 2014 , respectively.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award
Schedule of Compensation Cost for Share-based Payment Arrangements	Compensation expense for the stock plans, as reported in our consolidated statements of income, is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Performance Share Units $ 6.6 $ 4.5 $ 2.5 Restricted Stock Units and Cash-Settled Awards 14.9 18.6 19.0 Stock Options — 0.2 0.6 Other 0.4 0.5 0.5 Total Compensation Expense, Before Income Tax $ 21.9 $ 23.8 $ 22.6 Total Compensation Expense, Net of Income Tax $ 14.4 $ 15.7 $ 14.9
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award
Activity for PSUs Classified as Equity	Activity for PSUs classified as equity is as follows: Weighted Average Shares Grant Date (000s) Fair Value Outstanding at December 31, 2015 383 $ 35.05 Granted 219 28.41 Vested (167 ) 34.79 Forfeited (6 ) 32.54 Outstanding at December 31, 2016 429 31.80
Valuation Assumptions on PSU Grants	The fair value of PSUs is estimated on the date of initial grant using the Monte-Carlo simulation m odel. Key assumptions used to value PSUs granted during the years shown are as follows: Year Ended December 31 2016 2015 2014 Expected Volatility (based on our and our peer group historical daily stock prices) 22 % 22 % 31 % Expected Life (equals the performance period) 3.0 years 3.0 years 3.0 years Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant) 0.88 % 0.91 % 0.65 %
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Activity for Restricted Stock Units	Activity for RSUs classified as equity is as follows: Weighted Average Shares Grant Date (000s) Fair Value Outstanding at December 31, 2015 866 $ 32.40 Granted 632 28.80 Vested (587 ) 31.22 Forfeited (33 ) 30.64 Outstanding at December 31, 2016 878 30.66
Cash Settled Awards
Share-based Compensation Arrangement by Share-based Payment Award
Fair Value and Intrinsic Value of Cash Settled Awards and Stock Options	Year Ended December 31 2016 2015 2014 (in millions of dollars, except per unit data) Weighted Average Grant Date Fair Value per Unit Granted $ — $ 33.92 $ 33.85 Total Fair Value of Units Vested $ — $ 4.9 $ 2.1 Total Fair Value of Units Paid $ 2.4 $ 2.5 $ 2.9
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Fair Value and Intrinsic Value of Cash Settled Awards and Stock Options	The intrinsic value of options exercised and fair value of options vested are as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Total Intrinsic Value of Options Exercised $ 3.4 $ 5.6 $ 4.0 Total Fair Value of Options Vested $ 0.1 $ 1.1 $ 2.4
Schedule of Stock Option Activity	Stock option activity is summarized as follows: Remaining Intrinsic Shares Weighted Average Contractual Term Value (000s) Exercise Price (in years) (in millions) Outstanding at December 31, 2015 759 $ 23.02 Exercised (242 ) 21.01 Outstanding at December 31, 2016 517 23.97 2.7 $ 10.3 Exercisable at December 31, 2016 517 $ 23.97 2.7 $ 10.3

Reinsurance (Tables)

Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2016
Reinsurance Disclosures [Abstract]
Reinsurance Premiums for Insurance Companies	Reinsurance data is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Direct Premium Income $ 8,385.0 $ 8,151.9 $ 7,899.3 Reinsurance Assumed 236.3 202.8 189.8 Reinsurance Ceded (263.6 ) (272.3 ) (291.9 ) Net Premium Income $ 8,357.7 $ 8,082.4 $ 7,797.2 Ceded Benefits and Change in Reserves for Future Benefits $ 648.3 $ 662.7 $ 662.7

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Premium Income by Major Line of Business within Each Segment	Segment information is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Premium Income Unum US Group Disability Group Long-term Disability $ 1,726.6 $ 1,644.7 $ 1,553.5 Group Short-term Disability 626.1 607.4 558.1 Group Life and Accidental Death & Dismemberment Group Life 1,410.0 1,347.4 1,262.3 Accidental Death & Dismemberment 140.3 131.7 125.9 Supplemental and Voluntary Individual Disability 480.3 478.9 466.1 Voluntary Benefits 796.5 749.9 693.8 Dental and Vision 61.1 — — 5,240.9 4,960.0 4,659.7 Unum UK Group Long-term Disability 355.2 397.4 418.9 Group Life 105.7 121.5 133.2 Supplemental 68.4 57.3 55.1 529.3 576.2 607.2 Colonial Life Accident, Sickness, and Disability 830.0 789.0 759.8 Life 273.8 252.4 231.8 Cancer and Critical Illness 313.3 297.2 282.1 1,417.1 1,338.6 1,273.7 Closed Block Individual Disability 521.9 572.4 624.8 Long-term Care 643.9 633.5 630.9 All Other 4.6 1.7 0.9 1,170.4 1,207.6 1,256.6 Total Premium Income $ 8,357.7 $ 8,082.4 $ 7,797.2
Selected Operating Statement Data by Segment	Unum US Unum UK Colonial Life Closed Block Corporate Total (in millions of dollars) Year Ended December 31, 2016 Premium Income $ 5,240.9 $ 529.3 $ 1,417.1 $ 1,170.4 $ — $ 8,357.7 Net Investment Income 828.7 118.1 141.5 1,352.2 18.5 2,459.0 Other Income 113.3 0.2 1.2 86.0 4.9 205.6 Operating Revenue $ 6,182.9 $ 647.6 $ 1,559.8 $ 2,608.6 $ 23.4 $ 11,022.3 Operating Income (Loss) $ 914.2 $ 128.6 $ 314.2 $ 129.5 $ (146.7 ) $ 1,339.8 Interest and Debt Expense $ — $ — $ — $ 6.9 $ 159.1 $ 166.0 Depreciation and Amortization $ 353.0 $ 16.4 $ 222.9 $ 6.9 $ 1.0 $ 600.2 Year Ended December 31, 2015 Premium Income $ 4,960.0 $ 576.2 $ 1,338.6 $ 1,207.6 $ — $ 8,082.4 Net Investment Income 865.3 124.9 145.4 1,320.0 25.6 2,481.2 Other Income 119.2 — 0.1 89.3 2.9 211.5 Operating Revenue $ 5,944.5 $ 701.1 $ 1,484.1 $ 2,616.9 $ 28.5 $ 10,775.1 Operating Income (Loss) $ 850.0 $ 140.6 $ 309.1 $ 119.1 $ (124.8 ) $ 1,294.0 Interest and Debt Expense $ — $ — $ — $ 6.6 $ 146.2 $ 152.8 Depreciation and Amortization $ 347.0 $ 18.0 $ 214.6 $ 6.6 $ 0.9 $ 587.1 Year Ended December 31, 2014 Premium Income $ 4,659.7 $ 607.2 $ 1,273.7 $ 1,256.6 $ — $ 7,797.2 Net Investment Income 878.9 151.0 145.5 1,281.5 35.3 2,492.2 Other Income 122.1 — 0.1 91.8 5.0 219.0 Operating Revenue $ 5,660.7 $ 758.2 $ 1,419.3 $ 2,629.9 $ 40.3 $ 10,508.4 Operating Income (Loss) $ 844.9 $ 147.8 $ 299.0 $ 120.0 $ (104.4 ) $ 1,307.3 Interest and Debt Expense Excluding Costs Related to Early Retirement of Debt $ — $ — $ — $ 7.3 $ 147.0 $ 154.3 Depreciation and Amortization $ 314.2 $ 19.2 $ 194.1 $ 5.9 $ 1.0 $ 534.4
Deferred Policy Acquisition Costs by Segment	Colonial Unum US Unum UK Life Total (in millions of dollars) Deferred Acquisition Costs Year Ended December 31, 2016 Beginning of Year $ 1,136.4 $ 27.1 $ 845.0 $ 2,008.5 Capitalization 314.1 8.2 270.1 592.4 Amortization (275.2 ) (9.7 ) (208.1 ) (493.0 ) Adjustment Related to Unrealized Investment Gains and Losses 1.2 — (10.7 ) (9.5 ) Foreign Currency — (4.2 ) — (4.2 ) End of Year $ 1,176.5 $ 21.4 $ 896.3 $ 2,094.2 Year Ended December 31, 2015 Beginning of Year $ 1,096.5 $ 30.4 $ 774.4 $ 1,901.3 Capitalization 307.3 9.6 252.8 569.7 Amortization (272.3 ) (11.3 ) (198.7 ) (482.3 ) Adjustment Related to Unrealized Investment Gains and Losses 4.9 — 16.5 21.4 Foreign Currency — (1.6 ) — (1.6 ) End of Year $ 1,136.4 $ 27.1 $ 845.0 $ 2,008.5 Year Ended December 31, 2014 Beginning of Year $ 1,051.5 $ 34.3 $ 743.4 $ 1,829.2 Capitalization 292.7 10.5 220.8 524.0 Amortization (248.1 ) (12.5 ) (180.2 ) (440.8 ) Adjustment Related to Unrealized Investment Gains and Losses 0.4 — (9.6 ) (9.2 ) Foreign Currency — (1.9 ) — (1.9 ) End of Year $ 1,096.5 $ 30.4 $ 774.4 $ 1,901.3
Assets by Segment	December 31 2016 2015 (in millions of dollars) Assets Unum US $ 18,036.6 $ 18,242.4 Unum UK 3,101.4 3,432.4 Colonial Life 3,923.2 3,776.8 Closed Block 33,734.3 33,000.9 Corporate 3,146.0 2,111.1 Total Assets $ 61,941.5 $ 60,563.6
Reconciliation of Operating Revenue and Operating Income by Segment to Total Revenue and Income Before Income Tax	A reconciliation of total revenue to "operating revenue" and income before income tax to "operating income" is as follows: Year Ended December 31 2016 2015 2014 (in millions of dollars) Total Revenue $ 11,046.5 $ 10,731.3 $ 10,524.5 Excluding: Net Realized Investment Gain (Loss) 24.2 (43.8 ) 16.1 Operating Revenue $ 11,022.3 $ 10,775.1 $ 10,508.4 Income Before Income Tax $ 1,347.7 $ 1,238.3 $ 542.0 Excluding: Net Realized Investment Gain (Loss) 24.2 (43.8 ) 16.1 Non-operating Retirement-related Loss (16.3 ) (11.9 ) (70.0 ) Costs Related to Early Retirement of Debt for Corporate — — (13.2 ) Long-term Care Reserve Increase for Closed Block — — (698.2 ) Operating Income $ 1,339.8 $ 1,294.0 $ 1,307.3

Statutory Financial Informati45

Statutory Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Statutory Financial Information [Abstract]
Statutory Earnings and Surplus	The operating results and capital and surplus of our traditional U.S. life insurance subsidiaries and our captive reinsurers, prepared in accordance with prescribed or permitted accounting practices of the NAIC or states of domicile, are presented separately below. Year Ended December 31 2016 2015 2014 (in millions of dollars) Combined Net Income (Loss) Traditional U.S. Life Insurance Subsidiaries $ 855.1 $ 653.7 $ 628.9 Captive Reinsurers $ 48.4 $ (56.3 ) $ (129.3 ) Combined Net Gain (Loss) from Operations Traditional U.S. Life Insurance Subsidiaries $ 884.6 $ 689.2 $ 623.9 Captive Reinsurers $ 50.6 $ (54.3 ) $ (130.2 ) December 31 2016 2015 (in millions of dollars) Combined Capital and Surplus Traditional U.S. Life Insurance Subsidiaries $ 3,626.9 $ 3,470.3 Captive Reinsurers $ 1,726.7 $ 1,672.3

Unaudited Quarterly Results (Ta

Unaudited Quarterly Results (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	The following is a summary of our unaudited quarterly results of operations for 2016 and 2015 : 2016 4 th 3 rd 2 nd 1 st (in millions of dollars, except share data) Premium Income $ 2,099.2 $ 2,089.4 $ 2,081.6 $ 2,087.5 Net Investment Income 617.9 611.4 623.3 606.4 Net Realized Investment Gain (Loss) 28.4 11.0 5.3 (20.5 ) Total Revenue 2,796.5 2,763.3 2,761.3 2,725.4 Income Before Income Tax 371.2 332.1 340.2 304.2 Net Income 248.0 236.0 236.8 210.6 Net Income Per Common Share Basic 1.07 1.01 1.00 0.88 Assuming Dilution 1.07 1.01 1.00 0.88 2015 4 th 3 rd 2 nd 1 st (in millions of dollars, except share data) Premium Income $ 2,037.8 $ 2,020.8 $ 2,017.5 $ 2,006.3 Net Investment Income 636.4 612.1 630.7 602.0 Net Realized Investment Gain (Loss) (2.7 ) (26.6 ) 0.8 (15.3 ) Total Revenue 2,722.4 2,657.8 2,703.7 2,647.4 Income Before Income Tax 316.6 298.9 319.8 303.0 Net Income 226.1 203.8 224.3 212.9 Net Income Per Common Share Basic 0.93 0.83 0.90 0.85 Assuming Dilution 0.93 0.83 0.90 0.84

Schedule II Condensed Financial

Schedule II Condensed Financial Information of Registrant (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule II - Condensed Financial Information of Registrant Balance Sheet [Abstract]
Condensed Financial Information of Parent Company Only Balance Sheets	BALANCE SHEETS December 31 2016 2015 (in millions of dollars) As Adjusted Assets Fixed Maturity Securities - at fair value (amortized cost: $215.1; $273.7) $ 214.2 $ 273.4 Other Long-term Investments 49.0 22.7 Short-term Investments 377.9 288.1 Investment in Subsidiaries 11,340.7 10,689.1 Deferred Income Tax 210.7 160.1 Other Assets 473.9 546.4 Total Assets $ 12,666.4 $ 11,979.8 Liabilities and Stockholders' Equity Liabilities Short-term Debt $ — $ 352.0 Long-term Debt 2,735.9 2,125.4 Pension and Postretirement Benefits 638.3 554.1 Other Liabilities 324.2 284.4 Total Liabilities 3,698.4 3,315.9 Stockholders' Equity Common Stock 30.4 30.3 Additional Paid-in Capital 2,272.8 2,247.2 Accumulated Other Comprehensive Income (Loss) (51.0 ) 16.1 Retained Earnings 8,744.0 7,995.2 Treasury Stock (2,028.2 ) (1,624.9 ) Total Stockholders' Equity 8,968.0 8,663.9 Total Liabilities and Stockholders' Equity $ 12,666.4 $ 11,979.8 See notes to condensed financial information.
Condensed Financial Information of Parent Company Only Statement of Earnings	STATEMENTS OF INCOME Year Ended December 31 2016 2015 2014 (in millions of dollars) Cash Dividends from Subsidiaries $ 676.5 $ 671.8 $ 645.2 Other Income 58.4 52.8 116.3 Total Revenue 734.9 724.6 761.5 Interest and Debt Expense 160.1 137.5 132.4 Other Expenses 32.3 16.7 66.0 Total Expenses 192.4 154.2 198.4 Income of Parent Company Before Income Tax 542.5 570.4 563.1 Income Tax Benefit (20.2 ) (16.2 ) (24.5 ) Income of Parent Company 562.7 586.6 587.6 Equity in Undistributed Earnings (Loss) of Subsidiaries 368.7 280.5 (185.5 ) Net Income 931.4 867.1 402.1 Other Comprehensive Loss, Net of Tax (67.1 ) (150.3 ) (88.6 ) Comprehensive Income $ 864.3 $ 716.8 $ 313.5 See notes to condensed financial information.
Condensed Financial Information of Parent Company Only Statements of Cash Flows	STATEMENTS OF CASH FLOWS Year Ended December 31 2016 2015 2014 (in millions of dollars) Cash Provided by Operating Activities $ 685.4 $ 672.2 $ 683.0 Cash Flows from Investing Activities Proceeds from Sales of Fixed Maturity Securities 2.6 7.8 25.0 Proceeds from Maturities of Fixed Maturity Securities 111.2 112.2 76.1 Proceeds from Sales and Maturities of Other Investments 0.4 26.4 31.9 Purchase of Fixed Maturity Securities (56.5 ) (233.7 ) (118.9 ) Purchase of Other Investments (23.3 ) — (19.0 ) Net Sales (Purchases) of Short-term Investments (89.8 ) 38.1 (162.1 ) Cash Distributions to Subsidiaries (143.6 ) (231.0 ) (316.1 ) Net Purchases of Property and Equipment (55.5 ) (78.9 ) (102.5 ) Acquisition of Business (140.3 ) — — Other, Net 0.2 0.1 (0.2 ) Cash Used by Investing Activities (394.6 ) (359.0 ) (585.8 ) Cash Flows from Financing Activities Issuance of Long-term Debt 609.1 271.4 347.2 Long-term Debt Repayment (350.0 ) — — Issuance of Common Stock 8.5 6.4 12.3 Repurchase of Common Stock (405.2 ) (417.9 ) (306.0 ) Dividends Paid to Stockholders (182.6 ) (174.2 ) (159.4 ) Other, Net (1.0 ) 2.9 1.9 Cash Used by Financing Activities (321.2 ) (311.4 ) (104.0 ) Increase (Decrease) in Cash $ (30.4 ) $ 1.8 $ (6.8 ) See notes to condensed financial information.
Schedule of Debt Instruments Parent Company Only	Debt consists of the following: December 31 2016 2015 Interest Rates Maturities (in millions of dollars) Long-term Debt Outstanding Principal Senior Notes issued 1998 7.000% 2018 $ 200.0 $ 200.0 Senior Notes issued 1998 6.750 - 7.250% 2028 365.8 365.8 Senior Notes issued 2002 7.375% 2032 39.5 39.5 Senior Notes issued 2010 5.625% 2020 400.0 400.0 Senior Notes issued 2012 and 2016 5.750% 2042 500.0 250.0 Senior Notes issued 2014 4.000% 2024 350.0 350.0 Senior Notes issued 2015 3.875% 2025 275.0 275.0 Senior Notes issued 2016 3.000% 2021 350.0 — Medium-term Notes issued 1990 - 1996 7.000 - 7.190% 2023 - 2028 50.8 50.8 Junior Subordinated Debt Securities issued 1998 7.405% 2038 226.5 226.5 Fair Value Hedges Adjustment (3.1 ) (2.7 ) Less: Unamortized Net Premium (Discount) 9.8 (3.8 ) Unamortized Debt Issuance Costs (28.4 ) (25.7 ) Total Long-term Debt 2,735.9 2,125.4 Short-term Debt Outstanding Principal Senior Notes issued 2009 7.125% 2016 — 350.0 Fair Value Hedges Adjustment — 2.4 Less Unamortized Debt Issuance Costs — (0.4 ) Total Short-term Debt — 352.0 Total Debt $ 2,735.9 $ 2,477.4

Significant Accounting Polici48

Significant Accounting Policies Schedule of New Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle
Short-term Debt	$ 0	$ 352
Long-term Debt	2,999.4	2,449.4
Other Assets	$ 617.3	637.4
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle
Short-term Debt		352.4
Long-term Debt		2,475.1
Other Assets		663.5
Accounting Standards Update 2015-03 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Short-term Debt		(0.4)
Long-term Debt		(25.7)
Other Assets		$ (26.1)

Significant Accounting Polici49

Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)Integer	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Operating Segments | Integer	3
Ceded Policy Loans	$ 3,206.1	$ 3,150.1
Accumulated Depreciation for Property and Equipment	989.4	902.6
Value of Business Acquired	31.9	24
Accumulated Amortization of Value of Business Acquired	119.2	133.1
Amortization of Value of Business Acquired	5.1	4.6	$ 3.5
Deferred Gain on Reinsurance	23.8	31.9
Premium tax expense	152.5	146.5	$ 139.2
Participation Fund Account Assets (PFA)	$ 331.1	$ 338.8

Carrying Amount and Fair Value

Carrying Amount and Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Assets
Fixed Maturity Securities	$ 44,217.3	$ 43,354.4
Mortgage Loans	2,038.9	1,883.6
Policy Loans	3,463.2	3,395.4
Other Long-term Investments
Derivative Assets	32.7	49.8
Equity Securities	1.2	1.4
Policyholders' Funds
Long-term Debt	2,999.4	2,449.4
Advances from FHLB	350	350
Other Liabilities
Derivative Liabilities	99.5	137.8
Carrying Amount
Assets
Fixed Maturity Securities	44,217.3	43,354.4
Mortgage Loans	2,038.9	1,883.6
Policy Loans	3,463.2	3,395.4
Other Long-term Investments
Derivative Assets	32.7	49.8
Equity Securities	1.2	1.4
Miscellaneous Long-Term Investments	541.9	474.4
Policyholders' Funds
Deferred Annuity Products	597.4	608.8
Supplementary Contracts without Life Contingencies	608.8	641.1
Short-term Debt	0	352
Long-term Debt	2,999.4	2,449.4
Advances from FHLB	350	350
Other Liabilities
Derivative Liabilities	52.8	50.2
Embedded Derivative in Modified Coinsurance Arrangement	46.7	87.6
Unfunded commitment to fund Investment Partnerships	5	5
Fair Value
Assets
Fixed Maturity Securities	44,217.3	43,354.4
Mortgage Loans	2,122.2	2,013.9
Policy Loans	3,564.2	3,498
Other Long-term Investments
Derivative Assets	32.7	49.8
Equity Securities	1.2	1.4
Miscellaneous Long-Term Investments	541.9	474.4
Policyholders' Funds
Deferred Annuity Products	597.4	608.8
Supplementary Contracts without Life Contingencies	608.8	641.1
Short-term Debt	0	366.2
Long-term Debt	3,175.8	2,645.9
Advances from FHLB	350	350
Other Liabilities
Derivative Liabilities	52.8	50.2
Embedded Derivative in Modified Coinsurance Arrangement	46.7	87.6
Unfunded commitment to fund Investment Partnerships	$ 5	$ 5

Fair Value Measurements by Inpu

Fair Value Measurements by Input Level (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fixed Maturity Securities
Fixed Maturity Securities	$ 44,217.3	$ 43,354.4
Derivatives
Derivative Assets	32.7	49.8
Equity Securities	1.2	1.4
Derivatives
Derivative Liabilities	99.5	137.8
Fair Value, Inputs, Level 1
Fixed Maturity Securities
Fixed Maturity Securities	4,069.8	2,926.8
Derivatives
Derivative Assets		0
Equity Securities	0	0
Derivatives
Derivative Liabilities	0	0
Fair Value, Inputs, Level 2
Fixed Maturity Securities
Fixed Maturity Securities	38,309.8	38,546.4
Derivatives
Derivative Assets		49.8
Equity Securities	0	0
Derivatives
Derivative Liabilities	52.8	50.2
Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	1,837.7	1,881.2
Derivatives
Derivative Assets		0
Equity Securities	1.2	1.4
Derivatives
Derivative Liabilities	46.7	87.6
Interest Rate Swaps
Derivatives
Derivative Assets		2.4
Derivatives
Derivative Liabilities	7.6	12.3
Interest Rate Swaps | Fair Value, Inputs, Level 1
Derivatives
Derivative Assets		0
Derivatives
Derivative Liabilities	0	0
Interest Rate Swaps | Fair Value, Inputs, Level 2
Derivatives
Derivative Assets		2.4
Derivatives
Derivative Liabilities	7.6	12.3
Interest Rate Swaps | Fair Value, Inputs, Level 3
Derivatives
Derivative Assets		0
Derivatives
Derivative Liabilities	0	0
Foreign Exchange Contracts
Derivatives
Derivative Assets	32.7	47.4
Derivatives
Derivative Liabilities	44.8	37.6
Foreign Exchange Contracts | Fair Value, Inputs, Level 1
Derivatives
Derivative Assets	0	0
Derivatives
Derivative Liabilities	0	0
Foreign Exchange Contracts | Fair Value, Inputs, Level 2
Derivatives
Derivative Assets	32.7	47.4
Derivatives
Derivative Liabilities	44.8	37.6
Foreign Exchange Contracts | Fair Value, Inputs, Level 3
Derivatives
Derivative Assets	0	0
Derivatives
Derivative Liabilities	0	0
Credit Default Swaps
Derivatives
Derivative Liabilities	0.4	0.3
Credit Default Swaps | Fair Value, Inputs, Level 1
Derivatives
Derivative Liabilities	0	0
Credit Default Swaps | Fair Value, Inputs, Level 2
Derivatives
Derivative Liabilities	0.4	0.3
Credit Default Swaps | Fair Value, Inputs, Level 3
Derivatives
Derivative Liabilities	0	0
Embedded Derivative in Modified Coinsurance Arrangement
Derivatives
Derivative Liabilities	46.7	87.6
Embedded Derivative in Modified Coinsurance Arrangement | Fair Value, Inputs, Level 1
Derivatives
Derivative Liabilities	0	0
Embedded Derivative in Modified Coinsurance Arrangement | Fair Value, Inputs, Level 2
Derivatives
Derivative Liabilities	0	0
Embedded Derivative in Modified Coinsurance Arrangement | Fair Value, Inputs, Level 3
Derivatives
Derivative Liabilities	46.7	87.6
United States Government and Government Agencies and Authorities
Fixed Maturity Securities
Fixed Maturity Securities	1,382.4	1,465.2
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 1
Fixed Maturity Securities
Fixed Maturity Securities	454.2	97.3
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 2
Fixed Maturity Securities
Fixed Maturity Securities	928.2	1,367.9
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	2,158	2,117.1
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	2,068.5	1,994.9
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	89.5	122.2
Foreign Governments
Fixed Maturity Securities
Fixed Maturity Securities	914.7	1,051.6
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	914.7	998.7
Foreign Governments | Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	0	52.9
Public Utilities
Fixed Maturity Securities
Fixed Maturity Securities	8,022.7	8,020.4
Public Utilities | Fair Value, Inputs, Level 1
Fixed Maturity Securities
Fixed Maturity Securities	108.5	59.1
Public Utilities | Fair Value, Inputs, Level 2
Fixed Maturity Securities
Fixed Maturity Securities	7,648.9	7,687.2
Public Utilities | Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	265.3	274.1
Mortgage/Asset-backed Securities
Fixed Maturity Securities
Fixed Maturity Securities	2,230.4	2,481.5
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	2,230.4	2,481.5
Mortgage/Asset-backed Securities | Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	0	0
Corporate Debt Securities
Fixed Maturity Securities
Fixed Maturity Securities	29,467.2	28,171.4
Corporate Debt Securities | Fair Value, Inputs, Level 1
Fixed Maturity Securities
Fixed Maturity Securities	3,507.1	2,770.4
Corporate Debt Securities | Fair Value, Inputs, Level 2
Fixed Maturity Securities
Fixed Maturity Securities	24,500.4	23,992.8
Corporate Debt Securities | Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	1,459.7	1,408.2
Redeemable Preferred Stocks
Fixed Maturity Securities
Fixed Maturity Securities	41.9	47.2
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	18.7	23.4
Redeemable Preferred Stocks | Fair Value, Inputs, Level 3
Fixed Maturity Securities
Fixed Maturity Securities	$ 23.2	$ 23.8

Transfers of Assets between Lev

Transfers of Assets between Level 1 and Level 2 (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Transfers Between Level 1 and Level 2
Level 1 from Level 2 Transfers	$ 2,154.9	$ 1,376.5
Level 2 from Level 1 Transfers	1,919.4	1,837.1
United States Government and Government Agencies and Authorities
Transfers Between Level 1 and Level 2
Level 1 from Level 2 Transfers	200	0
Level 2 from Level 1 Transfers	0	195.3
Public Utilities
Transfers Between Level 1 and Level 2
Level 1 from Level 2 Transfers	65.9	7.3
Level 2 from Level 1 Transfers	59.1	85.1
Corporate Debt Securities
Transfers Between Level 1 and Level 2
Level 1 from Level 2 Transfers	1,889	1,369.2
Level 2 from Level 1 Transfers	$ 1,860.3	$ 1,556.7

Changes in Assets and Liabiliti

Changes in Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs (Level 3) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
States, Municipalities, and Political Subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	$ 122.2	$ 140.1
Investment Gain (Loss) included in Earnings	0	(0.1)
Investment Gain (Loss) included in OCI	1.9	(5.3)
Investment Purchases	0	12
Investment Sales	(0.5)	(16.5)
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	(34.1)	(8)
Ending Balance of Assets Measured with Unobservable Inputs	89.5	122.2
Foreign Governments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	52.9	69.3
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	0	(1.4)
Investment Purchases	0	0
Investment Sales	0	(15)
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	(52.9)	0
Ending Balance of Assets Measured with Unobservable Inputs	0	52.9
Public Utilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	274.1	315
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	(0.8)	(6.9)
Investment Purchases	0	40
Investment Sales	(3.7)	(2.4)
Level 3 Transfers Into	157.6	118.5
Level 3 Transfers Out of	(161.9)	(190.1)
Ending Balance of Assets Measured with Unobservable Inputs	265.3	274.1
Corporate Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	1,408.2	1,425.3
Investment Gain (Loss) included in Earnings	1.4	(7)
Investment Gain (Loss) included in OCI	6.9	(113.2)
Investment Purchases	115.9	55.3
Investment Sales	(111.2)	(220.8)
Level 3 Transfers Into	792.8	810.2
Level 3 Transfers Out of	(754.3)	(541.6)
Ending Balance of Assets Measured with Unobservable Inputs	1,459.7	1,408.2
Redeemable Preferred Stocks
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	23.8	24.9
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	(0.6)	(1.1)
Investment Purchases	0	0
Investment Sales	0	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
Ending Balance of Assets Measured with Unobservable Inputs	23.2	23.8
Fixed Maturity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	1,881.2	1,974.6
Investment Gain (Loss) included in Earnings	1.4	(7.1)
Investment Gain (Loss) included in OCI	7.4	(127.9)
Investment Purchases	115.9	107.3
Investment Sales	(115.4)	(254.7)
Level 3 Transfers Into	950.4	928.7
Level 3 Transfers Out of	(1,003.2)	(739.7)
Ending Balance of Assets Measured with Unobservable Inputs	1,837.7	1,881.2
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	1.4	1.4
Investment Gain (Loss) included in Earnings	0	0
Investment Gain (Loss) included in OCI	0.1	0
Investment Purchases	0	0
Investment Sales	(0.3)	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
Ending Balance of Assets Measured with Unobservable Inputs	1.2	1.4
Embedded Derivative in Modified Coinsurance Arrangement
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Derivatives Measured with Unobservable Inputs, Beginning Balance	(87.6)	(49.9)
Derivative Liability Gain (Loss) Included in Earnings	40.9	(37.7)
Derivative Liability Gain (Loss) Included in OCI	0	0
Derivative Purchases	0	0
Derivative Sales	0	0
Derivative Transfers Into Level 3	0	0
Derivative Transfers Out of Level 3	0	0
Derivatives Measured with Unobservable Inputs, Ending Balance	$ (46.7)	$ (87.6)

Quantitative Information Regard

Quantitative Information Regarding Significant Unobservable Inputs (Details) - Fair Value, Inputs, Level 3 - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Embedded Derivative Liability
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs		$ (46.7)	$ (87.6)
Embedded Derivative Liability | Projected Cash Flows
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	[1]	Actuarial Assumptions	Actuarial Assumptions
All Other Corporate Bonds - Private
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs		$ 310.4	$ 151
All Other Corporate Bonds - Private | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	[2]	Priced at Par	Priced at Par
All Other Corporate Bonds - Private | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Comparability Adjustments	[3]	0.50%	0.50%
Discount for Size	[4]	0.50%	0.50%
Lack of Marketability	[5]	0.20%	1.00%
Volatility of Credit	[6]	0.20%	0.25%
All Other Corporate Bonds - Private | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Comparability Adjustments	[3]	0.50%	0.50%
Discount for Size	[4]	0.50%	0.50%
Lack of Marketability	[5]	0.25%	2.00%
Volatility of Credit	[6]	6.04%	5.56%
All Other Corporate Bonds - Private | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Comparability Adjustments	[3]	0.50%	0.50%
Discount for Size	[4]	0.50%	0.50%
Lack of Marketability	[5]	0.23%	1.75%
Volatility of Credit	[6]	0.70%	0.94%
Equity Securities
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs		$ 1.1	$ 1.1
Equity Securities | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	[2]	Priced at Cost or Owner's Equity	Priced at Cost or Owner's Equity
States, Municipalities, and Political Subdivisions - Private
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs			$ 73.3
States, Municipalities, and Political Subdivisions - Private | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference	[7]		0.50%
States, Municipalities, and Political Subdivisions - Private | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference	[7]		1.00%
States, Municipalities, and Political Subdivisions - Private | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Change in Benchmark Reference	[7]		0.70%
States, Municipalities, and Political Subdivisions - Public
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs			$ 12
States, Municipalities, and Political Subdivisions - Public | Market Convention
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Significant Assumptions to Calculating Fair Value of Level 3 Instrument	[2]		Priced at Par
All Other Corporate Bonds - Public
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Fair Value of Financial Instrument Using Internally Derived Unobservable Inputs			$ 36.2
All Other Corporate Bonds - Public | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Lack of Marketability	[5]		1.00%
All Other Corporate Bonds - Public | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Lack of Marketability	[5]		1.00%
All Other Corporate Bonds - Public | Weighted Average
Fair Value Inputs, Assets and Liabilities, Quantitative Information
Lack of Marketability	[5]		1.00%
[1]	Represents various actuarial assumptions required to derive the liability cash flows including incidence, termination, and lapse rates
[2]	Represents a decision to price based on par value, cost, or owner's equity when limited data is available
[3]	Represents basis point adjustments for changes in benchmark spreads associated with various industry sectors
[4]	Represents basis point adjustments based on issue/issuer size relative to the benchmark
[5]	Represents basis point adjustments to apply a discount due to the illiquidity of an investment
[6]	Represents basis point adjustments for credit-specific factors
[7]	Represents basis point adjustments for changes in benchmark spreads associated with various ratings categories

Fair Value of Financial Instrum

Fair Value of Financial Instruments Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Ceded Policy Loans	$ 3,206.1	$ 3,150.1
Long-term Debt	2,999.4	2,449.4
Gain (Loss) on Embedded Derivative	$ 40.9	(37.7)	$ 3.3
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	90.80%
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt	$ 709.8	956.4
Percentage of Total Fair Value of Fixed Maturities Securities	9.20%
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Long-term Debt	$ 2,466	$ 1,689.5
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	76.30%
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	3.20%
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	11.30%
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	11 years

Amortized Cost and Fair Values

Amortized Cost and Fair Values of Securities by Security Type (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	$ 39,552.7	$ 39,658.7
Fair value of Fixed Maturity Securities	44,217.3	43,354.4
United States Government and Government Agencies and Authorities
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	1,202.8	1,265.8
Accumulated Gross Unrealized Gain on Securities	183.1	207.3
Accumulated Gross Unrealized Loss on Securities	3.5	7.9
Fair value of Fixed Maturity Securities	1,382.4	1,465.2
States, Municipalities, and Political Subdivisions
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	1,868	1,828.3
Accumulated Gross Unrealized Gain on Securities	294.8	293.4
Accumulated Gross Unrealized Loss on Securities	4.8	4.6
Fair value of Fixed Maturity Securities	2,158	2,117.1
Foreign Governments
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	714.8	897.2
Accumulated Gross Unrealized Gain on Securities	199.9	154.4
Accumulated Gross Unrealized Loss on Securities	0	0
Fair value of Fixed Maturity Securities	914.7	1,051.6
Public Utilities
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	6,916.1	6,979.3
Accumulated Gross Unrealized Gain on Securities	1,123.5	1,057.4
Accumulated Gross Unrealized Loss on Securities	16.9	16.3
Fair value of Fixed Maturity Securities	8,022.7	8,020.4
Mortgage/Asset-backed Securities
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	2,104.9	2,318.6
Accumulated Gross Unrealized Gain on Securities	134.7	167.6
Accumulated Gross Unrealized Loss on Securities	9.2	4.7
Fair value of Fixed Maturity Securities	2,230.4	2,481.5
All Other Corporate Bonds
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	26,707.1	26,325.5
Accumulated Gross Unrealized Gain on Securities	2,944	2,454.1
Accumulated Gross Unrealized Loss on Securities	183.9	608.2
Fair value of Fixed Maturity Securities	29,467.2	28,171.4
Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	39	44
Accumulated Gross Unrealized Gain on Securities	3.2	3.8
Accumulated Gross Unrealized Loss on Securities	0.3	0.6
Fair value of Fixed Maturity Securities	41.9	47.2
Fixed Maturity Securities
Schedule of Available-for-sale Securities
Amortized Cost of Fixed Maturity Securities	39,552.7	39,658.7
Accumulated Gross Unrealized Gain on Securities	4,883.2	4,338
Accumulated Gross Unrealized Loss on Securities	218.6	642.3
Fair value of Fixed Maturity Securities	$ 44,217.3	$ 43,354.4

Length of Time Fixed Maturity S

Length of Time Fixed Maturity Securities had been in a Gross Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	$ 4,667.3	$ 7,403.9
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	154.9	496
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	801.9	577.3
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	63.7	146.3
United States Government and Government Agencies and Authorities
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	132.8	213.5
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	3.5	7.9
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	0	0
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	0	0
States, Municipalities, and Political Subdivisions
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	132.2	112.3
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	4.8	4.3
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	0	3.3
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	0	0.3
Public Utilities
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	260.2	408.4
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	15.3	14.4
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	15.6	10.3
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	1.6	1.9
Mortgage/Asset-backed Securities
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	513.2	504.3
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	9.1	4.6
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	0.8	9
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	0.1	0.1
All Other Corporate Bonds
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	3,621	6,155
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	122.1	464.2
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	774.7	554.7
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	61.8	144
Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	7.9	10.4
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Less than Twelve Months	0.1	0.6
Fair Value of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	10.8	0
Accumulated Loss of Fixed Maturity Securities in Unrealized Loss Position Twelve Months or Longer	$ 0.2	$ 0

Distribution of the Maturity Da

Distribution of the Maturity Dates for Fixed Maturity Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Available-for-Sale Securities, Total Amortized Cost
1 year or less	$ 1,338.8	$ 1,112.2
Over 1 year through 5 years	6,231	6,514
Over 5 years through 10 years	10,991.6	10,519.3
Over 10 years	18,886.4	19,194.6
Available-for-sale Securities, Debt Maturities, Gross Subtotal	37,447.8	37,340.1
Mortgage/Asset-Backed Securities	2,104.9	2,318.6
Amortized Cost of Fixed Maturity Securities	39,552.7	39,658.7
Fair Value Maturity Distribution [Abstract]
Total Fixed Maturity Securities	44,217.3	43,354.4
Fair Value of Fixed Maturity Securities in Unrealized Gain Position
Available-for-Sale Securities, Unrealized Gain Position, Gross Gain
1 year or less	28.6	20.6
Over 1 year through 5 years	553.5	554.4
Over 5 years through 10 years	843.8	746.3
Over 10 years	3,322.6	2,849.1
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Gain, Gross Subtotal	4,748.5	4,170.4
Mortgage/Asset-Backed Securities	134.7	167.6
Total Fixed Maturity Securities	4,883.2	4,338
Fair Value Maturity Distribution [Abstract]
1 year or less	1,355.6	1,098.8
Over 1 year through 5 years	6,605.6	6,649.5
Over 5 years through 10 years	9,336.2	7,124.4
Over 10 years	19,734.3	18,532.3
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal	37,031.7	33,405
Mortgage/Asset-Backed Securities	1,716.4	1,968.2
Total Fixed Maturity Securities	38,748.1	35,373.2
Fair Value of Fixed Maturity Securities in Unrealized Loss Position
Fair Value Maturity Distribution [Abstract]
1 year or less	11.8	33.8
Over 1 year through 5 years	170.7	369.1
Over 5 years through 10 years	2,416.4	3,820.7
Over 10 years	2,356.3	3,244.3
Available-for-sale Securities, Debt Maturities, Fair Value, Gross Subtotal	4,955.2	7,467.9
Mortgage/Asset-Backed Securities	514	513.3
Total Fixed Maturity Securities	5,469.2	7,981.2
Available-for-Sale Securities, Unrealized Loss Position, Gross Loss
1 year or less	0	0.2
Over 1 year through 5 years	8.2	49.8
Over 5 years through 10 years	82.8	320.5
Over 10 years	118.4	267.1
Available-For-Sale Securities, Debt Maturities Unrealized Gain Position, Gross Loss, Gross Subtotal	209.4	637.6
Mortgage/Asset-Backed Securities	9.2	4.7
Total Fixed Maturity Securities	$ 218.6	$ 642.3

Investments Low Income Housing

Investments Low Income Housing Tax Credits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Low Income Housing Tax Credits [Abstract]
Affordable Housing Tax Credits	$ 41.8	$ 41.8	$ 41.8
Amortization of Affordable Housing Tax Credit Investments	(23.2)	(23.3)	(23.2)
Tax Benefits from Low Income Housing Investments	$ 18.6	$ 18.5	$ 18.6

Mortgage Loans by Property Type

Mortgage Loans by Property Type and Geographic Region (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate
Mortgage Loans	$ 2,038.9	$ 1,883.6
Percent of Total	100.00%	100.00%
New England
Mortgage Loans on Real Estate
Mortgage Loans	$ 72.7	$ 97.6
Percent of Total	3.60%	5.20%
Mid-Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	$ 125.3	$ 128.8
Percent of Total	6.10%	6.90%
East North Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 230.1	$ 186.4
Percent of Total	11.30%	9.90%
West North Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 172	$ 162.6
Percent of Total	8.40%	8.60%
South Atlantic
Mortgage Loans on Real Estate
Mortgage Loans	$ 438.3	$ 409.3
Percent of Total	21.50%	21.70%
East South Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 91.6	$ 79.1
Percent of Total	4.50%	4.20%
West South Central
Mortgage Loans on Real Estate
Mortgage Loans	$ 268.7	$ 237.6
Percent of Total	13.20%	12.60%
Mountain
Mortgage Loans on Real Estate
Mortgage Loans	$ 214.1	$ 196.5
Percent of Total	10.50%	10.40%
Pacific
Mortgage Loans on Real Estate
Mortgage Loans	$ 426.1	$ 385.7
Percent of Total	20.90%	20.50%
Apartment
Mortgage Loans on Real Estate
Mortgage Loans	$ 288.4	$ 130.6
Percent of Total	14.10%	6.90%
Industrial
Mortgage Loans on Real Estate
Mortgage Loans	$ 573.6	$ 574.1
Percent of Total	28.10%	30.50%
Office
Mortgage Loans on Real Estate
Mortgage Loans	$ 700.1	$ 764.7
Percent of Total	34.40%	40.60%
Retail
Mortgage Loans on Real Estate
Mortgage Loans	$ 455.4	$ 392.3
Percent of Total	22.40%	20.80%
Other Property
Mortgage Loans on Real Estate
Mortgage Loans	$ 21.4	$ 21.9
Percent of Total	1.00%	1.20%

Mortgage Loans, Sorted by Appli

Mortgage Loans, Sorted by Applicable Credit Quality Indicators (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Mortgage Loans on Real Estate
Mortgage Loans	$ 2,038.9	$ 1,883.6
Aa Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	0.7	1.1
A Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	488.2	586.6
Baa Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	1,506.6	1,285.8
Ba Credit Rating
Mortgage Loans on Real Estate
Mortgage Loans	43.4	10.1
Loan to Value Ratio Below or Equal to 65 Percent
Mortgage Loans on Real Estate
Mortgage Loans	917.9	937.2
Loan To Value Ratio Above 65 To 75 Percent
Mortgage Loans on Real Estate
Mortgage Loans	1,011.5	842.5
Loan To Value Ratio Above 75 To 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans	50.8	88.4
Loan To Value Ratio Above 85 Percent
Mortgage Loans on Real Estate
Mortgage Loans	$ 58.7	$ 15.5

Investments Troubled Debt Restr

Investments Troubled Debt Restructurings on Financing Receivables (Details) - Commercial Real Estate Portfolio Segment $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Financing Receivable Modifications
Recorded Investment in Mortgage Loan Modifications Due to Foreclosure	$ 5.4	$ 0	$ 18.1
Number of Modifications Due to Loan Foreclosure	1	0	1

Activity in Allowance for Credi

Activity in Allowance for Credit Losses (Detail) - Commercial Real Estate Portfolio Segment - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses
Balance at Beginning of Year	$ 0	$ 1.5	$ 1.5
Provisions	0	0.5	3
Charge-offs, Net of Recoveries	0	(2)	(3)
Balance at End of Period	$ 0	$ 0	$ 1.5

Investments Remaining Contractu

Investments Remaining Contractual Maturity of Security Lending Agreements (Details) - Overnight and Continuous - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Transfer of Certain Financial Assets Accounted for as Secured Borrowings
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	$ 29.9	$ 29
Securities Loaned and Securities Sold under Agreement to Repurchase, Gross Including Not Subject to Master Netting Arrangement	29.9	29
Secured Borrowings, Gross, Difference, Amount	0	0
United States Government and Government Agencies and Authorities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0.1	1.2
Public Utilities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	0.1	4
All Other Corporate Bonds
Transfer of Certain Financial Assets Accounted for as Secured Borrowings
Securities Loaned, Including Not Subject to Master Netting Arrangement and Assets other than Securities Transferred	$ 29.7	$ 23.8

Investments Offsetting for Deri

Investments Offsetting for Derivatives and Securities Lending Balances (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Offsetting Derivative Assets
Gross Derivative Asset	$ 32.7	$ 49.8
Derivative Liabilities Offsetting Derivative Assets in Balance Sheet	0	0
Net Derivative Assets Reported in Balance Sheet	32.7	49.8
Securities Received as Collateral on Derivative Assets	(7.3)	(12.8)
Cash collateral from counterparties	(25.4)	(36.4)
Derivative Assets Net of Collateral	0	0.6
Offsetting Securities Borrowed
Gross Securities Borrowed	178.5	181.6
Liabilities Offsetting Securities Borrowed in Balance Sheet	0	0
Net Securities Borrowed Reported in Balance Sheet	178.5	181.6
Securities Received as Collateral on Securities Borrowed	(148.6)	(152.6)
Cash Received as Collateral on Securities Borrowed	(29.9)	(29)
Securities Borrowed Net of Collateral	0	0
Offsetting Financial Assets
Gross Financial Assets	211.2	231.4
Financial Liabilities Offsetting Financial Assets in Balance Sheet	0	0
Net Financial Assets Reported in Balance Sheet	211.2	231.4
Securities Received as Collateral on Financial Assets	(155.9)	(165.4)
Cash Received as Collateral on Financial Assets	(55.3)	(65.4)
Financial Assets Net of Collateral	0	0.6
Offsetting Derivative Liabilities
Net Derivative Liabilities Reported in Balance Sheet	99.5	137.8
Cash Collateral to counterparties	0	0
Offsetting Securities Loaned
Gross Securities Loaned	29.9	29
Assets Offsetting Securities Loaned in Balance Sheet	0	0
Net Securities Loaned Reported in Balance Sheet	29.9	29
Securities Given as Collateral on Securities Loaned	(29.9)	(29)
Cash Given as Collateral on Securities Loaned	0	0
Securities Loaned Net of Collateral	0	0
Offsetting Financial Liabilities
Gross Financial Liability	82.7	79.2
Financial Assets Offsetting Financial Liabilities in Balance Sheet	0	0
Net Financial Liabilities Reported in Balance Sheet	82.7	79.2
Securities Given as Collateral on Financial Liabilities	(67.5)	(64.6)
Cash Given as Collateral on Financial Liabilities	0	0
Financial Liabilities Net of Collateral	15.2	14.6
Over the Counter
Offsetting Derivative Liabilities
Gross Derivative Liability	52.8	50.2
Derivative Assets Offsetting Derivative Liabilities in Balance Sheet	0	0
Net Derivative Liabilities Reported in Balance Sheet	52.8	50.2
Securities Given as Collateral on Derivative Liabilities	(37.6)	(35.6)
Cash Collateral to counterparties	0	0
Derivative Liabilities Net of Collateral	$ 15.2	$ 14.6

Investments Investment Income (

Investments Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Investment Income
Investment Income, Interest and Dividend									$ 2,505.1	$ 2,527	$ 2,536.3
Less Investment Expenses									31.9	31.2	29
Less Investment Income on PFA Assets									14.2	14.6	15.1
Net Investment Income	$ 617.9	$ 611.4	$ 623.3	$ 606.4	$ 636.4	$ 612.1	$ 630.7	$ 602	2,459	2,481.2	2,492.2
Fixed Maturity Securities
Net Investment Income
Investment Income, Interest and Dividend									2,293.9	2,327.1	2,344.4
Derivatives
Net Investment Income
Investment Income, Interest and Dividend									49.8	44.2	40.4
Mortgage Loans
Net Investment Income
Investment Income, Interest and Dividend									114	114	109.8
Policy Loans
Net Investment Income
Investment Income, Interest and Dividend									17.3	16.7	16.3
Other Long-term Investments
Net Investment Income
Investment Income, Interest and Dividend									22.6	21.6	23
Short-term Investments
Net Investment Income
Investment Income, Interest and Dividend									$ 7.5	$ 3.4	$ 2.4

Realized Investment Gains and L

Realized Investment Gains and Losses Reported in Consolidated Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fixed Maturity Securities
Gross Gains on Sales									$ 34.3	$ 23.8	$ 9.3
Gross Losses on Sales									(17.2)	(25.6)	(7.5)
Other-Than-Temporary Impairment Loss									(30.5)	(32.4)	(13.5)
Mortgage Loans and Other Invested Assets
Gross Gains on Sales									5.5	16	21.2
Gross Losses on Sales									(0.7)	(0.1)	(0.8)
Impairment Loss									(5.7)	(5.9)	(3.4)
Gain (Loss) on Embedded Derivative									40.9	(37.7)	3.3
All Other Derivatives									(1.5)	35.7	11
Foreign Currency Transactions									(0.9)	(17.6)	(3.5)
Net Realized Investment Gain (Loss)	$ 28.4	$ 11	$ 5.3	$ (20.5)	$ (2.7)	$ (26.6)	$ 0.8	$ (15.3)	$ 24.2	$ (43.8)	$ 16.1

Investments - Additional Inform

Investments - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Schedule of Investments
Fair value of Fixed Maturity Securities	$ 44,217,300,000	$ 43,354,400,000
Fixed Maturity Securities Other Than Temporary Impairments in Accumulated Other Comprehensive Income Loss	0	0
Commitment to fund private placement fixed maturity securities	30,000,000
Carrying amount of variable interest entity investments	509,300,000
Commitments to Qualified Affordable Housing Project Investments	4,600,000
Unfunded Unconditional Commitment to Fund Private Equity Partnerships	400,000
Commitment to fund partnership Equity Investments	251,900,000
Other Long-term Investments	631,500,000	$ 583,000,000
Commitments to Fund Special Purpose Entities	$ 0
Amount Funded to Special Purpose Entity Partnerships	nor did we fund any amounts to the partnership	nor did we fund any amounts to the partnership	nor did we fund any amounts to the partnership
Mortgage Loan policy is not to exceed a loan-to-value ratio, percent	75.00%
Loan to Value Ratio Update Frequency	three
Mortgage Loan Inspection Frequency	two
Mortage Loan Policy Debt Service coverage ratio lower range	125.00%
Mortgage Loans issuance, term years	25
Foreclosed Real Estate Expense	$ 0	$ 0	$ 0
Financing Receivable, Recorder Investment, Nonaccrual status	0	0
Number of Changes to Accounting Policy for Estimating Credit Losses on Mortgage Loans	0
Average Recorded Investment of Impaired Mortgage Loans	$ 2,200,000	$ 8,600,000	26,700,000
Interest Income on Mortgage Loans Subsequent to Impairment		600,000	1,000,000
Committments to Fund Commercial Mortgage Loans	$ 32,100,000
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%
Gross Securities Borrowed	$ 178,500,000	181,600,000
Outstanding Repurchase Agreements	0	0
Federal Home Loan Bank Stock	31,600,000	30,900,000
Advances from FHLB	350,000,000	350,000,000
Off Balance Sheet Amount
Schedule of Investments
Cash Collateral for Borrowed Securities	29,900,000	29,000,000
Securities Received as Collateral	155,300,000	159,300,000
Commercial Real Estate Portfolio Segment
Schedule of Investments
Unpaid Principal Balance of Impaired Mortgage Loan			14,600,000
Financing Receivable, Allowance for Credit Losses	0	0	1,500,000	$ 1,500,000
Impaired Financing Receivable, with Related Allowance, Recorded Investment			13,100,000
Provisions	0	500,000	3,000,000
Special Purpose Entity | Bonds
Schedule of Investments
Fair value of Fixed Maturity Securities	151,900,000	148,000,000
Special Purpose Entity | Partnership Interest
Schedule of Investments
Other Long-term Investments	1,000,000	900,000
Partnership Interests In Tax Credit Investments
Schedule of Investments
Carrying amount of variable interest entity investments	165,200,000
Equity Method Investments
Schedule of Investments
Carrying amount of variable interest entity investments	344,100,000
External Credit Rating, Investment Grade
Schedule of Investments
Fair value of Fixed Maturity Securities	40,819,300,000
Accumulated Gross Unrealized Gain on Securities	4,764,500,000
Accumulated Gross Unrealized Loss on Securities	$ 151,800,000
Percent of Fixed Maturity Securities in Unrealized Loss Position	69.40%
Number of fixed maturity securities that were in an unrealized loss position	332
Number of fixed maturity securities in an unrealized loss position continuously for over one year	16
External Credit Rating, Below-Investment-Grade
Schedule of Investments
Fair value of Fixed Maturity Securities	$ 3,398,000,000
Accumulated Gross Unrealized Gain on Securities	118,700,000
Accumulated Gross Unrealized Loss on Securities	$ 66,800,000
Percent of Fixed Maturity Securities in Unrealized Loss Position	30.60%
Number of fixed maturity securities that were in an unrealized loss position	69
Number of fixed maturity securities in an unrealized loss position continuously for over one year	37
Collateralized Mortgage Backed Securities
Schedule of Investments
Collateral Pledged to FHLB	$ 288,500,000	96,000,000
Fixed Maturity Securities
Schedule of Investments
Fair value of Fixed Maturity Securities	44,217,300,000	43,354,400,000
Accumulated Gross Unrealized Gain on Securities	4,883,200,000	4,338,000,000
Accumulated Gross Unrealized Loss on Securities	218,600,000	642,300,000
Collateral Pledged to FHLB	323,700,000	317,200,000
Commercial Real Estate Portfolio Segment
Schedule of Investments
Recorded Investment in Mortgage Loan Modifications Due to Foreclosure	5,400,000	$ 0	18,100,000
Provisions			$ 3,000,000
Starmount
Schedule of Investments
Fair value of Fixed Maturity Securities	38,800,000
Available-for-sale Securities, Gross Unrealized Gain (Loss)	$ 1,500,000
Starmount | External Credit Rating, Investment Grade
Schedule of Investments
Number of fixed maturity securities that were in an unrealized loss position	132

Notional Amounts for Each Categ

Notional Amounts for Each Category of Derivative Activity (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative
Balance at beginning of period	$ 1,470.3	$ 1,687.4	$ 1,477.4
Additions	33.5	96	318.1
Terminations	451.8	313.1	108.1
Balance at ending of period	1,052	1,470.3	1,687.4
Swaps | Receive Variable/Pay Fixed
Derivative
Balance at beginning of period	150	150	150
Additions	3.5	0	0
Terminations	48	0	0
Balance at ending of period	105.5	150	150
Swaps | Receive Fixed/Pay Fixed
Derivative
Balance at beginning of period	650.3	840.4	630.4
Additions	0	0	250.1
Terminations	33.8	190.1	40.1
Balance at ending of period	616.5	650.3	840.4
Swaps | Receive Fixed/Pay Variable
Derivative
Balance at beginning of period	600	600	600
Additions	0	0	0
Terminations	350	0	0
Balance at ending of period	250	600	600
Swaps | Credit Default Swaps
Derivative
Balance at beginning of period	70	97	97
Additions	0	2	0
Terminations	0	29	0
Balance at ending of period	70	70	97
Forwards
Derivative
Balance at beginning of period	0	0	0
Additions	30	94	68
Terminations	20	94	68
Balance at ending of period	$ 10	$ 0	$ 0

Location and Fair Values of Der

Location and Fair Values of Derivative Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative
Asset Derivatives Fair Value	$ 32.7	$ 49.8
Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	32.7	49.8
Designated as Hedging Instrument | Other Liability
Derivative
Liability Derivatives Fair Value	20.3	18.3
Designated as Hedging Instrument | Interest Rate Swaps | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	0	2.4
Designated as Hedging Instrument | Interest Rate Swaps | Other Liability
Derivative
Liability Derivatives Fair Value	6.9	12.3
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	32.7	47.4
Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liability
Derivative
Liability Derivatives Fair Value	13.4	6
Not Designated as Hedging Instrument | Other Liability
Derivative
Liability Derivatives Fair Value	79.2	119.5
Not Designated as Hedging Instrument | Interest Rate Swaps | Other Liability
Derivative
Liability Derivatives Fair Value	0.7
Not Designated as Hedging Instrument | Foreign Exchange Contracts | Other Liability
Derivative
Liability Derivatives Fair Value	31.4	31.6
Not Designated as Hedging Instrument | Credit Risk Contract | Other Liability
Derivative
Liability Derivatives Fair Value	0.4	0.3
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement | Other Liability
Derivative
Liability Derivatives Fair Value	$ 46.7	$ 87.6

Location of Gains and Losses on

Location of Gains and Losses on Derivative Instruments Designated as Cash Flow Hedging Instruments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss)
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (22.3)	$ 67.4	$ 16.1
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	53.3	83.4	53
Interest Rate Swaps
Derivative Instruments, Gain (Loss)
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(0.1)	(0.7)	(0.1)
Foreign Exchange Contracts
Derivative Instruments, Gain (Loss)
Gain (Loss) Recognized in OCI on Derivatives (Effective Portion)	(22.2)	68.1	16.2
Investment Income | Interest Rate Swaps
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	54.5	50.2	47.8
Investment Income | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1.1)	(1.6)	(4.2)
Net Realized Investments Gain Loss | Interest Rate Swaps
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	3.2	0.5	4.3
Net Realized Investments Gain Loss | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	(1.4)	36.1	6.9
Interest Expense | Interest Rate Swaps
Derivative Instruments, Gain (Loss)
Gain (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (1.9)	$ (1.8)	$ (1.8)

Gains and Losses on Derivatives

Gains and Losses on Derivatives Not Designated as Hedging Instruments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Realized Investment Gain (Loss)
Net Gain (Loss) on Derivatives	$ (1.5)	$ 35.7	$ 11
Not Designated as Hedging Instrument
Net Realized Investment Gain (Loss)
Net Gain (Loss) on Derivatives	40.6	(37.9)	1.2
Not Designated as Hedging Instrument | Credit Default Swaps
Net Realized Investment Gain (Loss)
Net Gain (Loss) on Derivatives	(0.9)	0.1	(0.3)
Not Designated as Hedging Instrument | Interest Rate Swaps
Net Realized Investment Gain (Loss)
Net Gain (Loss) on Derivatives	0.4	0	0
Not Designated as Hedging Instrument | Foreign Exchange Contracts
Net Realized Investment Gain (Loss)
Net Gain (Loss) on Derivatives	0.2	(0.3)	(1.8)
Not Designated as Hedging Instrument | Embedded Derivative in Modified Coinsurance Arrangement
Net Realized Investment Gain (Loss)
Net Gain (Loss) on Derivatives	$ 40.9	$ (37.7)	$ 3.3

Derivative Financial Instrume73

Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative
Credit Exposure on Derivatives	$ 0.8
Cash collateral from counterparties	25.4	$ 36.4
Carrying value of fixed maturity securities posted as collateral to our counterparties	35.2	27.3
Cash Collateral to counterparties	0	0
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	52.8	50.2
Notional Amount of Derivatives	1,052	1,470.3	$ 1,687.4	$ 1,477.4
Notional Amount Of Derivatives Terminations	451.8	313.1	108.1
Material Ineffectiveness on Cash Flow Hedges	0	0	0
Gain from Components Excluded from Assessment of Cash Flow Hedge Effectiveness	0	0	0
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	$ 58
Maximum Length of Time Hedged in Cash Flow Hedge	22 years
Loss on Contract Termination	$ 1.2
Material Ineffectiveness on Fair Value Hedges	0	0	0
Gain (Loss) from Components Excluded from Assessment of Fair Value Hedge Effectiveness, Net	0	0	0
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as FV Hedge	0
Derivative, Amount of Hedged Item	3.5
Foreign Exchange Contracts
Derivative
Hedge Gain Reclassification from AOCI to Earnings		8.2	13.1
Novated Foreign Currency Interest Rate Swap
Derivative
Notional Amount of Derivatives			97
Receive Variable/Pay Fixed
Derivative
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	5.9	5.3	5.3
Receive Fixed/Pay Variable
Derivative
Notional Amount of Derivatives	250	600
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	2.8	0.1	(5.5)
Receive Variable/Pay Fixed | Swaps
Derivative
Notional Amount of Derivatives	105.5	150	150	150
Notional Amount Of Derivatives Terminations	48	0	0
Credit Default Swaps | Swaps
Derivative
Notional Amount of Derivatives	70	70	97	$ 97
Notional Amount Of Derivatives Terminations	0	29	0
Not Designated as Hedging Instrument | Interest Rate Swaps
Derivative
Notional Amount of Derivatives	222.4	222.4
Not Designated as Hedging Instrument | Foreign Currency Swap
Derivative
Notional Amount of Derivatives			125.4
Not Designated as Hedging Instrument | Receive Variable/Pay Fixed
Derivative
Notional Amount of Derivatives	3.5
Not Designated as Hedging Instrument | Credit Default Swaps
Derivative
Notional Amount of Derivatives	70	70
Long-term Debt
Derivative
Hedge Gain Reclassification from AOCI to Earnings		27.7	13.1
Cash Flow Hedging | Interest Rate Swaps
Derivative
Notional Amount of Derivatives	394.1	427.9
Notional Amount Of Derivatives Terminations		150
Cash Flow Hedging | Novated Foreign Currency Interest Rate Swap
Derivative
Gross Derivative Liability			(29.5)
Cash Flow Hedging | Designated as Hedging Instrument | Foreign Currency Swap
Derivative
Notional Amount of Derivatives			$ 124.7
Fair Value Hedging | Receive Variable/Pay Fixed
Derivative
Notional Amount of Derivatives	102	150
Fair Value Hedging | Receive Fixed/Pay Variable
Derivative
Notional Amount of Derivatives	250	$ 600
Notional Amount of Derivatives Matured	350
Amount of Hedged Item, Matured	350
Fair Value Hedging | Receive Variable/Pay Fixed | Swaps
Derivative
Notional Amount Of Derivatives Terminations	24
Net
Derivative
Cash collateral from counterparties	$ 26.1

Schedule of Accumulated Other C

Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Year	$ 16.1	$ 166.4	$ 255
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(52.5)	(130.3)	(97)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(14.6)	(20)	8.4
Net Other Comprehensive Income (Loss)	(67.1)	(150.3)	(88.6)
Balance at End of Year	(51)	16.1	166.4
Net Unrealized Gain on Securities
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Year	204.3	290.3	135.7
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	226.5	(114.7)	154.3
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	9.8	28.7	0.3
Net Other Comprehensive Income (Loss)	236.3	(86)	154.6
Balance at End of Year	440.6	204.3	290.3
Net Gain on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Year	378	391	396.3
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(15.8)	43.3	31.1
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(34.7)	(56.3)	(36.4)
Net Other Comprehensive Income (Loss)	(50.5)	(13)	(5.3)
Balance at End of Year	327.5	378	391
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Year	(173.6)	(113.4)	(47.1)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(180.4)	(60.2)	(66.3)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0	0	0
Net Other Comprehensive Income (Loss)	(180.4)	(60.2)	(66.3)
Balance at End of Year	(354)	(173.6)	(113.4)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Balance at Beginning of Year	(392.6)	(401.5)	(229.9)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(82.8)	1.3	(216.1)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	10.3	7.6	44.5
Net Other Comprehensive Income (Loss)	(72.5)	8.9	(171.6)
Balance at End of Year	$ (465.1)	$ (392.6)	$ (401.5)

Schedule of Components of Unrea

Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain (Loss) on Securities	$ 661.9	$ (1,720.9)	$ 1,439.3
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	3,695.7	6,261.5	4,054.8
Change in Net Unrealized Gain (Loss) on Securities	968.9	(2,565.8)	2,206.7
End of Year Balance	4,664.6	3,695.7	6,261.5
Other Investments
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(33.7)	13.9	55.5
Change in Net Unrealized Gain (Loss) on Securities	11	(47.6)	(41.6)
End of Year Balance	(22.7)	(33.7)	13.9
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(29.4)	(50.8)	(41.6)
Change in Net Unrealized Gain (Loss) on Securities	(9.5)	21.4	(9.2)
End of Year Balance	(38.9)	(29.4)	(50.8)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(3,578.4)	(6,150.3)	(4,108.5)
Change in Net Unrealized Gain (Loss) on Securities	(674.8)	2,571.9	(2,041.8)
End of Year Balance	(4,253.2)	(3,578.4)	(6,150.3)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	263.2	365	263.8
Change in Net Unrealized Gain (Loss) on Securities	58.1	(101.8)	101.2
End of Year Balance	321.3	263.2	365
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(113.1)	(149)	(88.3)
Change in Net Unrealized Gain (Loss) on Securities	(117.4)	35.9	(60.7)
End of Year Balance	(230.5)	(113.1)	(149)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	204.3	290.3	135.7
Change in Net Unrealized Gain (Loss) on Securities	236.3	(86)	154.6
End of Year Balance	$ 440.6	$ 204.3	$ 290.3

Schedule of Reclassifications O

Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Net Realized Investment Gain (Loss)									$ 54.7	$ (11.4)	$ 29.6
Other-Than-Temporary Impairment Loss									(30.5)	(32.4)	(13.5)
Net Investment Income	$ 617.9	$ 611.4	$ 623.3	$ 606.4	$ 636.4	$ 612.1	$ 630.7	$ 602	2,459	2,481.2	2,492.2
Interest and Debt Expense									(166)	(152.8)	(167.5)
Other Expenses									(831.6)	(813.4)	(831.2)
Income Before Income Tax	371.2	332.1	340.2	304.2	316.6	298.9	319.8	303	1,347.7	1,238.3	542
Income Tax Expense (Benefit)									416.3	371.2	139.9
Net Income	$ 248	$ 236	$ 236.8	$ 210.6	$ 226.1	$ 203.8	$ 224.3	$ 212.9	931.4	867.1	402.1
Reclassification out of Accumulated Other Comprehensive Income | Net Unrealized Gain on Securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Net Realized Investment Gain (Loss)									15.3	(12.2)	12.6
Other-Than-Temporary Impairment Loss									(30.5)	(32.4)	(13.5)
Income Before Income Tax									(15.2)	(44.6)	(0.9)
Income Tax Expense (Benefit)									(5.4)	(15.9)	(0.6)
Net Income									(9.8)	(28.7)	(0.3)
Reclassification out of Accumulated Other Comprehensive Income | Net Gain on Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax									53.3	83.4	53
Income Tax Expense (Benefit)									18.6	27.1	16.6
Net Income									34.7	56.3	36.4
Reclassification out of Accumulated Other Comprehensive Income | Net Gain on Cash Flow Hedges | Interest Rate Swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Net Realized Investment Gain (Loss)									3.2	0.5	4.3
Net Investment Income									54.5	50.2	47.8
Interest and Debt Expense									(1.9)	(1.8)	(1.8)
Reclassification out of Accumulated Other Comprehensive Income | Net Gain on Cash Flow Hedges | Foreign Exchange Contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Net Realized Investment Gain (Loss)									(1.4)	36.1	6.9
Net Investment Income									(1.1)	(1.6)	(4.2)
Reclassification out of Accumulated Other Comprehensive Income | Net Actuarial Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses									(16.3)	(11.9)	(5.6)
Reclassification out of Accumulated Other Comprehensive Income | Prior Service Credit
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses									0.5	0.3	1.7
Reclassification out of Accumulated Other Comprehensive Income | Pension Settlement Loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Other Expenses									0	0	(64.4)
Reclassification out of Accumulated Other Comprehensive Income | Unrecognized Pension and Postretirement Benefit Costs
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income Before Income Tax									(15.8)	(11.6)	(68.3)
Income Tax Expense (Benefit)									(5.5)	(4)	(23.8)
Net Income									$ (10.3)	$ (7.6)	$ (44.5)

Liability for Unpaid Claims and

Liability for Unpaid Claims and Claims Adjustment Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense
Balance at January 1	$ 23,796.1	$ 24,194	$ 24,535.6
Less Reinsurance Recoverable	2,064.6	2,066.9	2,072.8
Net Balance at January 1	21,731.5	22,127.1	22,462.8
Incurred Related to
Current Year	5,243	5,058.1	4,851.5
Paid Related to
Current Year	(2,035.4)	(1,853.7)	(1,702.3)
Prior Years	(4,451.4)	(4,546.5)	(4,547.4)
Total Paid	(6,486.8)	(6,400.2)	(6,249.7)
Net Balance at December 31	21,085.9	21,731.5	22,127.1
Plus Reinsurance Recoverable	2,163.6	2,064.6	2,066.9
Balance at December 31	23,249.5	23,796.1	24,194
Amount Related to Interest
Incurred Related to
Prior Years	1,136.7	1,177.6	1,214.7
Incurred Claims
Incurred Related to
Prior Years	(198.3)	(111.6)	(13.5)
Foreign Currency
Incurred Related to
Prior Years	(340.2)	(119.5)	(138.7)
Operating Expense
Incurred Related to
Total Incurred	$ 5,841.2	$ 6,004.6	$ 5,914

Reconciliation of Policy and Co

Reconciliation of Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Insurance [Abstract]
Policy and Contract Benefits	$ 1,507.9	$ 1,484.6	$ 1,529.3
Reserves for Future Policy and Contract Benefits	44,245.9	43,540.6	45,929.4
Total Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits	45,753.8	45,025.2	47,458.7
Life Reserves for Future Policy and Contract Benefits	8,078.2	7,946.3	7,850.9
Accident and Health Active Life Reserves	10,172.9	9,704.4	9,263.5
Adjustment Related to Unrealized Investment Gains and Losses	4,253.2	3,578.4	6,150.3
Liability for Claims and Claims Adjustment Expense	$ 23,249.5	$ 23,796.1	$ 24,194	$ 24,535.6

Liability for Unpaid Claims - A

Liability for Unpaid Claims - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Closed Block | Long-term Care
Liability for Unpaid Claims and CAE Narrative Information
Reserve Increase for Long-term Care, Before Tax	$ 698.2
Claim Reserve Prior Year
Liability for Unpaid Claims and CAE Narrative Information
Reserve Increase for Long-term Care, Before Tax	$ 85.8

Income Tax Expense (Benefit) (D

Income Tax Expense (Benefit) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Abstract]
Income Tax Expense	$ 416.3	$ 371.2	$ 139.9
Additional Paid in Capital
Stock-Based Compensation	(0.3)	(3.6)	(3)
Other Comprehensive Income (Loss), Tax
Other Comprehensive Income (Loss), Unrealized Holding Gain on Securities Arising During Period, Tax	318	(892.5)	725.8
Change in Adjustment to Deferred Acquisition Costs and Reserves for Future Policy and Contract Benefits, Net of Reinsurance, Tax Expense	(200.6)	856.6	(665.1)
Change in Net Gain on Cash Flow Hedges	(25.4)	(4.3)	(2)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	0	(0.1)	0
Change in Unrecognized Pension and Postretirement Benefit Costs	(34.2)	3.2	(92.4)
Total	$ 473.8	$ 330.5	$ 103.2

Reconciliation of income tax co

Reconciliation of income tax computed at US Federal tax rates (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Abstract]
Statutory Income Tax	35.00%	35.00%	35.00%
Foreign Rate Differential, Inclusive of Foreign Rate Changes	(2.20%)	(2.50%)	(4.00%)
Tax Credits	(1.60%)	(1.40%)	(4.50%)
Other Items, Net	(0.30%)	(1.10%)	(0.70%)
Effective Tax	30.90%	30.00%	25.80%

Schedule of deferred income tax

Schedule of deferred income tax assets and liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Abstract]
Deferred Acquisition Cost	$ 174.9	$ 140.4
Deferred Tax Liabilities for Fixed Assets	80.7	87.1
Deferred Tax Liabilities on Invested Assets	1,427.6	1,128.4
Other	63.2	55.4
Gross Deferred Tax Liability	1,746.4	1,411.3
Reserves	1,308.5	1,060.5
Employee Benefits	307.4	246
Other	17.4	14.3
Gross Deferred Tax Asset	1,633.3	1,320.8
Less: Valuation Allowance	17.2	1.3
Net Deferred Tax Asset	1,616.1	1,319.5
Net Deferred Tax Liability	$ 130.3	$ 91.8

Schedule of Income subject to d

Schedule of Income subject to domestic and foreign taxation (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Abstract]
Income Before Tax United States - Federal and State									$ 1,215.8	$ 1,057.8	$ 391.7
Income Before Tax Foreign									131.9	180.5	150.3
Income Before Income Tax	$ 371.2	$ 332.1	$ 340.2	$ 304.2	$ 316.6	$ 298.9	$ 319.8	$ 303	1,347.7	1,238.3	542
Current Tax Expense United States - Federal									414.8	280.5	160.6
Current State and Local Tax Expense (Benefit)									0.3	0	0
Current Tax Expense Foreign									(29.4)	61.6	(25.1)
Income Tax - Current									385.7	342.1	135.5
Deferred Tax Expense (Benefit) United States - Federal									(14.6)	56.9	(50.5)
Deferred State and Local Income Tax Expense (Benefit)									(2.1)	0	0
Deferred Tax Expense (Benefit) Foreign									47.3	(27.8)	54.9
Income Tax - Deferred									30.6	29.1	4.4
Income Tax Expense									$ 416.3	$ 371.2	$ 139.9

Unrecognized tax benefits (Deta

Unrecognized tax benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax [Abstract]
Balance at Beginning of Year	$ 0.8	$ 19.8	$ 18.4
Additions to Tax Positions Taken During Prior Years	0.7	0	1.7
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	0	0	0.3
Settlements with Tax Authorities	0	(19)	(0.6)
Balance at End of Year	1.5	0.8	19.8
Less Tax Attributable to Temporary Items Included Above	0	0	(10.4)
Total Unrecognized Tax Benefits that if Recognized Would Affect the Effective Tax Rate	$ 1.5	$ 0.8	$ 9.4

Income Tax Additional Informati

Income Tax Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)Rate	Dec. 31, 2015USD ($)Rate	Dec. 31, 2014USD ($)	Aug. 01, 2016USD ($)
Federal Income Tax Note
2020 UK Tax Rate | Rate	17.00%
2015 UK Tax Rate | Rate		20.00%
2017 UK Tax Rate | Rate		19.00%
2020 UK Tax Rate Prior to 2016 Enactment | Rate		18.00%
Income Tax Benefit from Enacted Tax Rate Changes	$ 4,500,000	$ 6,500,000
Excess of Financial Reporting Carrying Amount Over the Tax Basis of Investments in Foreign Subsidiaries, Provision Not Practicable	1,000,000,000
Tax Expense Not Recognized Due To Permanent Differences	200,000,000
Liability for unrecognized tax benefits			$ 10,400,000
Unrecognized Tax Benefits, Interest on Income Taxes Expense		(1,000,000)	200,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued			1,000,000
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority		(6,800,000)
Operating Loss Carryforwards	$ 1,300,000			$ 2,500,000
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax				$ 600,000
Net Operating Loss Benefit	1,200,000
Valuation Allowance on Deferred Tax Assets	$ 17,200,000	1,300,000
Deferred Tax Assets, State Taxes	18,700,000
Income Taxes Paid, Net	384,300,000	$ 189,100,000	$ 155,700,000
State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards	160,000,000
Valuation Allowance on Deferred Tax Assets	$ 16,300,000
Minimum
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2023
Minimum | State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2017
Maximum
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2035
Maximum | State and Local Jurisdiction
Federal Income Tax Note
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036
Other Comprehensive Income (Loss) | State and Local Jurisdiction
Federal Income Tax Note
Valuation Allowance on Deferred Tax Assets	$ 1,500,000

Debt Schedule (Detail)

Debt Schedule (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument
Long-term Debt, Excluding Current Maturities		$ 2,999.4		$ 2,449.4
Debt Instrument, Unamortized Premium (Discount), Net		9.8		(3.8)
Debt Issuance Costs, Noncurrent, Net		(28.4)		(25.7)
Current Maturities of Long-term Debt		0		352
Debt Issuance Costs, Current, Net		0		(0.4)
Long-term Debt		2,999.4		2,801.4
Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Long-term Debt, Excluding Current Maturities		(3.1)		(2.7)
Current Maturities of Long-term Debt		0		2.4
Secured Notes Issued in 2007 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		260		324
Interest Rate Terms	Variable
Year of Maturity	Dec. 31, 2037
Secured Notes acquired 2016 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		3.5		0
Interest Rate Terms	Variable
Year of Maturity	Apr. 8, 2038
Notes Issued in 1998 with 2018 Maturity Date | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		200		200
Stated Interest Rate of Debt			7.00%
Year of Maturity	Dec. 31, 2018
Notes Issued in 1998 with 2028 Maturity Date | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		365.8		365.8
Interest Rate Terms	6.750 - 7.250%
Year of Maturity	Dec. 31, 2028
Notes Issued in 1998 with 2028 Maturity Date | Minimum | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			6.75%
Notes Issued in 1998 with 2028 Maturity Date | Maximum | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.25%
Notes Issued in 2002 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		39.5		39.5
Stated Interest Rate of Debt			7.375%
Year of Maturity	Dec. 31, 2032
Notes Issued in 2010 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		400		400
Stated Interest Rate of Debt			5.625%
Year of Maturity	Dec. 31, 2020
Notes Payable due 2042
Debt Instrument
Stated Interest Rate of Debt			5.75%
Notes Payable due 2042 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		500		250
Stated Interest Rate of Debt			5.75%
Year of Maturity	Dec. 31, 2042
Notes Issued in 2014 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		350		350
Stated Interest Rate of Debt			4.00%
Year of Maturity	Dec. 31, 2024
Notes Issued in 2015 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		275		275
Stated Interest Rate of Debt			3.875%
Year of Maturity	Dec. 31, 2025
Notes Issued in 2016 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		350		0
Stated Interest Rate of Debt			3.00%
Year of Maturity	May 15, 2021
Notes Issued 1990 to 1996 | Medium-term Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities		50.8		50.8
Interest Rate Terms	7.000 - 7.190%
Debt Instrument, Maturity Date Range, Start	Dec. 31, 2023
Debt Instrument, Maturity Date Range, End	Dec. 31, 2028
Notes Issued 1990 to 1996 | Minimum | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.00%
Notes Issued 1990 to 1996 | Maximum | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.19%
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt
Debt Instrument
Long-term Debt, Excluding Current Maturities		226.5		226.5
Stated Interest Rate of Debt	7.405%		7.405%
Year of Maturity	Dec. 31, 2038
Notes Issued in 2009
Debt Instrument
Current Maturities of Long-term Debt		$ 0		$ 350
Stated Interest Rate of Debt			7.125%
Year of Maturity	Sep. 30, 2016

Debt - Additional Information D

Debt - Additional Information Domain (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2007	Dec. 31, 1998	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2013
Debt Narrative Detail Information
Repayments of Principal in 2018							$ 200
Repayments of Principal in 2020							400
Repayments of Principal in 2021							350
Repayments of Principal Thereafter							2,071.1
Long-term Debt, Excluding Current Maturities		$ 2,449.4					2,999.4
Current Maturities of Long-term Debt		352					0
Proceeds from Issuance of Debt	$ 600
Payments of Debt Extinguishment Costs	$ 0	0	$ 13.2
Notional Amount of Derivatives		1,470.3	1,687.4				1,052		$ 1,477.4
Unum Group Percentage Ownership of Provident Financing Trust	100.00%
Interest Paid	$ 153.6	146.9	145.9
Line of Credit Facility, Maximum Borrowing Capacity							400
Line Of Credit Facility Maximum Borrowing Capacity If Requested							600
Letters of Credit Outstanding		2.1					2.1
Amount Outstanding on Line of Credit		0					0
Receive Fixed/Pay Variable
Debt Narrative Detail Information
Notional Amount of Derivatives		600					250
Northwind Holdings LLC
Debt Narrative Detail Information
Proceeds from Issuance of Senior Long-term Debt				$ 800
Basis Spread on LIBOR	0.78%
Debt service coverage account (DSCA)							27.6
Periodic Principal Payments	$ 64	$ 74.4	41.6
Long-term Debt
Debt Narrative Detail Information
Stated Interest Rate of Debt		6.85%
Extinguishment of Debt, Amount		$ 145
Payments of Debt Extinguishment Costs		13.2
Repayment of Long-term Debt, Including Cost of Make-whole Call Premium		158.2
Hedge Gain Reclassification from AOCI to Earnings		27.7	$ 13.1
Secured Notes acquired 2016 | Senior Notes
Debt Narrative Detail Information
Long-term Debt, Excluding Current Maturities		0					3.5
Notes Issued in 2009
Debt Narrative Detail Information
Current Maturities of Long-term Debt		350					0
Stated Interest Rate of Debt								7.125%
Notes Payable Due 2021
Debt Narrative Detail Information
Stated Interest Rate of Debt								3.00%
Proceeds from Issuance of Debt	350
Notes Payable due 2042
Debt Narrative Detail Information
Stated Interest Rate of Debt								5.75%
Proceeds from Issuance of Debt	$ 250
Notes Payable due 2042 | Senior Notes
Debt Narrative Detail Information
Long-term Debt, Excluding Current Maturities		250					500
Stated Interest Rate of Debt								5.75%
Notes Issued in 2012
Debt Narrative Detail Information
Long-term Debt, Excluding Current Maturities							250
Stated Interest Rate of Debt								5.75%
Notes Issued in 2005
Debt Narrative Detail Information
Current Maturities of Long-term Debt		151.9
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt
Debt Narrative Detail Information
Proceeds from Issuance of Senior Long-term Debt					$ 300
Long-term Debt, Excluding Current Maturities		$ 226.5					$ 226.5
Stated Interest Rate of Debt	7.405%							7.405%
Liquidation value per capital security						$ 1,000

Employee Benefit Plans Change i

Employee Benefit Plans Change in Projected Benefit Obligation Amount (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits, U.S. Plans
Defined Benefit Plan, Change in Benefit Obligation
Benefit Obligation at Beginning of Year	$ 1,808.2	$ 1,892.6
Service Cost	7	3.8	$ 3.7
Interest Cost	85.2	82.2	89.9
Contributions by Plan Participants	0	0
Defined Benefit Plan, Actuarial Gain (Loss)	123.6	(103.6)
Net Benefit Expenses Paid	(68.7)	(59.3)
Plan Amendments	0	(7.5)
Change in Foreign Exchange Rates	0	0
Benefit Obligation at End of Year	1,955.3	1,808.2	1,892.6
Accumulated Benefit Obligation	1,955.3	1,808.2
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair Value of Plan Assets at Beginning of Year	1,403.3	1,473.7
Defined Benefit Plan, Actual Return on Plan Assets	112.3	(17.5)
Employer Contributions to Defined Benefit Plan	7.2	6.4
Contributions by Plan Participants	0	0
Net Benefit Expenses Paid	(68.7)	(59.3)
Effect of Foreign Exchange Rates on Plan Assets	0	0
Fair Value of Plan Assets at End of Year	1,454.1	1,403.3	1,473.7
Funded Status of Plan	501.2	404.9
Pension Benefits, Non U.S. Plans
Defined Benefit Plan, Change in Benefit Obligation
Benefit Obligation at Beginning of Year	203.8	226.9
Service Cost	0	0	2.3
Interest Cost	7	7.9	9.1
Contributions by Plan Participants	0	0
Defined Benefit Plan, Actuarial Gain (Loss)	55	(14.7)
Net Benefit Expenses Paid	(4.5)	(4.6)
Plan Amendments	0	0
Change in Foreign Exchange Rates	(38.3)	(11.7)
Benefit Obligation at End of Year	223	203.8	226.9
Accumulated Benefit Obligation	213.4	194.8
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair Value of Plan Assets at Beginning of Year	231.5	246.3
Defined Benefit Plan, Actual Return on Plan Assets	42.5	2.9
Employer Contributions to Defined Benefit Plan	0	0
Contributions by Plan Participants	0	0
Net Benefit Expenses Paid	(4.5)	(4.6)
Effect of Foreign Exchange Rates on Plan Assets	(41.1)	(13.1)
Fair Value of Plan Assets at End of Year	228.4	231.5	246.3
Funded Status of Plan	(5.4)	(27.7)
Other Postretirement Benefit Plans
Defined Benefit Plan, Change in Benefit Obligation
Benefit Obligation at Beginning of Year	160.4	173.9
Service Cost	0	0	0.3
Interest Cost	7.2	7.2	7.9
Contributions by Plan Participants	4	4.6
Defined Benefit Plan, Actuarial Gain (Loss)	(4.4)	(9.1)
Net Benefit Expenses Paid	(15.6)	(16.2)
Plan Amendments	(3.7)	0
Change in Foreign Exchange Rates	0	0
Benefit Obligation at End of Year	147.9	160.4	173.9
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair Value of Plan Assets at Beginning of Year	11.2	11.3
Defined Benefit Plan, Actual Return on Plan Assets	0.1	0.3
Employer Contributions to Defined Benefit Plan	11.1	11.2
Contributions by Plan Participants	4	4.6
Net Benefit Expenses Paid	(15.6)	(16.2)
Effect of Foreign Exchange Rates on Plan Assets	0	0
Fair Value of Plan Assets at End of Year	10.8	11.2	$ 11.3
Funded Status of Plan	$ 137.1	$ 149.2

Employee Benefit Plans Amounts

Employee Benefit Plans Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits, U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Current Pension Liability	$ 7	$ 5.9
Noncurrent Pension Liability	494.2	399
Noncurrent Pension Asset	0	0
Funded Status of Plan	501.2	404.9
Net Actuarial Gain (Loss) in Balance Sheet	(702.1)	(604.2)
Prior Service Credit in Balance Sheet	7.2	7.5
Pension Recognized in Balance Sheet, Gross of Deferred Tax	(694.9)	(596.7)
Pension Deferred Tax Asset in Balance Sheet	243.6	208.8
Pension Recognized in Balance Sheet, Net of Deferred Tax	(451.3)	(387.9)	$ (385.5)
Pension Benefits, Non U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Current Pension Liability	0	0
Noncurrent Pension Liability	0	0
Noncurrent Pension Asset	(5.4)	(27.7)
Funded Status of Plan	(5.4)	(27.7)
Net Actuarial Gain (Loss) in Balance Sheet	(44)	(28.1)
Prior Service Credit in Balance Sheet	0	0
Pension Recognized in Balance Sheet, Gross of Deferred Tax	(44)	(28.1)
Pension Deferred Tax Asset in Balance Sheet	10.9	8.9
Pension Recognized in Balance Sheet, Net of Deferred Tax	(33.1)	(19.2)	(25)
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Current Pension Liability	13.1	13
Noncurrent Pension Liability	124	136.2
Noncurrent Pension Asset	0	0
Funded Status of Plan	137.1	149.2
Net Actuarial Gain (Loss) in Balance Sheet	10.1	6.2
Prior Service Credit in Balance Sheet	3.9	0.4
Pension Recognized in Balance Sheet, Gross of Deferred Tax	14	6.6
Pension Deferred Tax Asset in Balance Sheet	5.3	7.9
Pension Recognized in Balance Sheet, Net of Deferred Tax	$ 19.3	$ 14.5	$ 9

Employee Benefit Plans Amount90

Employee Benefit Plans Amounts Recognized in Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits, U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Pension Recognized in Balance Sheet, Net of Deferred Tax	$ (387.9)	$ (385.5)
Amortization of Net Actuarial Loss	16.2	11.6	$ 5.2
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	(114.1)	(22.8)
Amortization of Prior Service Cost (Credit)	(0.3)	0	0
Plan Amendments	0	7.5
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense	34.8	1.3
Pension Recognized in Balance Sheet, Net of Deferred Tax	(451.3)	(387.9)	(385.5)
Pension Benefits, Non U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Pension Recognized in Balance Sheet, Net of Deferred Tax	(19.2)	(25)
Amortization of Net Actuarial Loss	0.1	0.3	0.4
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	(16)	7
Amortization of Prior Service Cost (Credit)	0	0	0
Plan Amendments	0	0
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense	2	(1.5)
Pension Recognized in Balance Sheet, Net of Deferred Tax	(33.1)	(19.2)	(25)
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Pension Recognized in Balance Sheet, Net of Deferred Tax	14.5	9
Amortization of Net Actuarial Loss	0	0	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, before Tax	3.9	8.8
Amortization of Prior Service Cost (Credit)	(0.2)	(0.3)	(1.7)
Plan Amendments	3.7	0
Change in Unrecognized Pension and Postretirement Benefit Costs, Tax Expense	(2.6)	(3)
Pension Recognized in Balance Sheet, Net of Deferred Tax	$ 19.3	$ 14.5	$ 9

Employee Benefit Plans US Pensi

Employee Benefit Plans US Pension Assets, Fair Value Measurement by Input Level (Details) - Pension Benefits, U.S. Plans - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	$ 1,449.2	$ 1,399.6
Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	299.2	380.1
Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	316.7	306.3
Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	833.3	713.2
Equity Securities | U.S. Large Cap
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	85.5	176.2
Equity Securities | U.S. Large Cap | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | U.S. Large Cap | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | U.S. Large Cap | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | U.S. Large Cap | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	85.5	176.2
Equity Securities | U.S. Mid Cap
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets		55
Equity Securities | U.S. Mid Cap | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets		0
Equity Securities | U.S. Mid Cap | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets		0
Equity Securities | U.S. Mid Cap | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets		0
Equity Securities | U.S. Mid Cap | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets		55
Equity Securities | U.S. Small Cap
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	50.2	56.9
Equity Securities | U.S. Small Cap | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	50.2	56.9
Equity Securities | U.S. Small Cap | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | U.S. Small Cap | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | U.S. Small Cap | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | Global Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	259.7
Equity Securities | Global Equity Securities | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0
Equity Securities | Global Equity Securities | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0
Equity Securities | Global Equity Securities | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0
Equity Securities | Global Equity Securities | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	259.7
Equity Securities | International Securities
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	26.3	126.6
Equity Securities | International Securities | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	63.7
Equity Securities | International Securities | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | International Securities | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | International Securities | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	26.3	62.9
Equity Securities | Emerging Markets
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	49.6	35.5
Equity Securities | Emerging Markets | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | Emerging Markets | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | Emerging Markets | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Equity Securities | Emerging Markets | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	49.6	35.5
United States Government and Government Agencies and Authorities
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	238.9	244.3
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	227.8	231.5
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	11.1	12.8
United States Government and Government Agencies and Authorities | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
United States Government and Government Agencies and Authorities | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Corporate Debt Securities
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	303.6	291.4
Corporate Debt Securities | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Corporate Debt Securities | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	303.6	291.4
Corporate Debt Securities | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Corporate Debt Securities | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
States, Municipalities, and Political Subdivisions
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	2	2.1
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	2	2.1
States, Municipalities, and Political Subdivisions | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
States, Municipalities, and Political Subdivisions | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Opportunistic Credits
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	181.8	163.5
Opportunistic Credits | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Opportunistic Credits | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Opportunistic Credits | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Opportunistic Credits | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	181.8	163.5
Real Estate
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	88.9	83.5
Real Estate | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Real Estate | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Real Estate | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Real Estate | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	88.9	83.5
Private Equity Direct Investments
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	37.4	30.4
Private Equity Direct Investments | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Private Equity Direct Investments | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Private Equity Direct Investments | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Private Equity Direct Investments | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	37.4	30.4
Private Equity Funds
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	32	35.3
Private Equity Funds | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Private Equity Funds | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Private Equity Funds | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Private Equity Funds | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	32	35.3
Hedge Funds
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	72.1	70.9
Hedge Funds | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Hedge Funds | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Hedge Funds | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Hedge Funds | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	72.1	70.9
Cash and Cash Equivalents
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	21.2	28
Cash and Cash Equivalents | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	21.2	28
Cash and Cash Equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Cash and Cash Equivalents | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	0	0
Cash and Cash Equivalents | NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Fair Value of Invested Pension Assets	$ 0	$ 0

Employee Benefit Plans UK Pensi

Employee Benefit Plans UK Pension Assets, Fair Value Measurement by Input Level (Details) - Pension Benefits, Non U.S. Plans - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	$ 140.1	$ 156.3
Fixed Interest and Index-linked Securities	87.4	67.5
Cash Equivalents	0.9	7.7
Fair Value of Plan Assets	228.4	231.5	$ 246.3
Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	0	0
Fixed Interest and Index-linked Securities	79.9	62.2
Cash Equivalents	0.9	7.7
Fair Value of Plan Assets	80.8	69.9
Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	0	0
Fixed Interest and Index-linked Securities	0	0
Cash Equivalents	0	0
Fair Value of Plan Assets	0	0
Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	0	0
Fixed Interest and Index-linked Securities	0	0
Cash Equivalents	0	0
Fair Value of Plan Assets	0	0
NAV as a Practical Expedient
Defined Benefit Plans and Other Postretirement Benefit Plans
Diversified Growth Assets	140.1	156.3
Fixed Interest and Index-linked Securities	7.5	5.3
Cash Equivalents	0	0
Fair Value of Plan Assets	$ 147.6	$ 161.6

Employee Benefit Plans OPEB Pla

Employee Benefit Plans OPEB Plan Assets, Fair Value Measurements by Input Level (Details) - Other Postretirement Benefit Plans - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans
Life Settlement Contracts, Fair Value Method, Face Value	$ 10.8	$ 11.2
Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans
Life Settlement Contracts, Fair Value Method, Face Value	0	0
Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans
Life Settlement Contracts, Fair Value Method, Face Value	0	0
Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans
Life Settlement Contracts, Fair Value Method, Face Value	$ 10.8	$ 11.2

Employee Benefit Plans OPEB Cha

Employee Benefit Plans OPEB Changes in Assets Measured at Fair Value Using Signficant Unobservable Inputs (Details) - Other Postretirement Benefit Plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Contributions by Plan Participants	$ 4	$ 4.6
Net Benefit Expenses Paid	(15.6)	(16.2)
Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	11.2	11.3
Actual Return on Plan Assets Still Held	0.1	0.3
Contributions by Plan Participants	15.1	15.8
Net Benefit Expenses Paid	(15.6)	(16.2)
Ending Balance of Assets Measured with Unobservable Inputs	$ 10.8	$ 11.2

Employee Benefit Plans Measurem

Employee Benefit Plans Measurement Assumptions (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016Rate	Dec. 31, 2015
Pension Benefits, U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Discount Rate Assumptions Used Calculating Benefit Obligation	4.40%	4.40%	4.80%
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost	4.80%		4.40%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost	7.50%		7.50%
Pension Benefits, Non U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Discount Rate Assumptions Used Calculating Benefit Obligation	2.70%	2.70%	3.80%
Rate of Compensation Increase Assumptions Used Calculating Benefit Obligation	3.80%	3.80%	3.60%
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost	3.80%		3.60%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost	4.90%		5.20%
Rate of Compensation Increase Assumptions Used Calculating Net Periodic Benefit Cost	3.60%		3.60%
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Discount Rate Assumptions Used Calculating Benefit Obligation	4.20%	4.20%	4.70%
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost	4.70%		4.30%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost	5.75%	5.75%	5.75%

Employee Benefit Plans Net Peri

Employee Benefit Plans Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits, U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Service Cost	$ 7	$ 3.8	$ 3.7
Interest Cost	85.2	82.2	89.9
Expected Return on Plan Assets	(102.8)	(108.9)	(117.8)
Amortization of Net Actuarial Loss	16.2	11.6	5.2
Amortization of Prior Service Cost (Credit)	(0.3)	0	0
Plan Amendment, Other Costs	0	0	0
Pension Settlement Costs	0	0	64.4
Net Periodic Benefit Cost	5.3	(11.3)	45.4
Pension Benefits, Non U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Service Cost	0	0	2.3
Interest Cost	7	7.9	9.1
Expected Return on Plan Assets	(10)	(12.4)	(13.7)
Amortization of Net Actuarial Loss	0.1	0.3	0.4
Amortization of Prior Service Cost (Credit)	0	0	0
Plan Amendment, Other Costs	0	0	0
Pension Settlement Costs	0	0	0
Net Periodic Benefit Cost	(2.9)	(4.2)	(1.9)
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Service Cost	0	0	0.3
Interest Cost	7.2	7.2	7.9
Expected Return on Plan Assets	(0.6)	(0.7)	(0.7)
Amortization of Net Actuarial Loss	0	0	0
Amortization of Prior Service Cost (Credit)	(0.2)	(0.3)	(1.7)
Plan Amendment, Other Costs	0.9	0	0
Pension Settlement Costs	0	0	0
Net Periodic Benefit Cost	$ 7.3	$ 6.2	$ 5.8

Employee Benefit Plans Expected

Employee Benefit Plans Expected Benefit Payments (Details) $ in Millions	Dec. 31, 2016USD ($)
Pension Benefits, U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Benefit Payments in Year One	$ 71.8
Benefit Payments in Year Two	74.4
Benefit Payments in Year Three	76.9
Benefit Payments in Year Four	80.6
Benefit Payments in Year Five	84.3
Benefit Payments in Five Fiscal Years Thereafter	476.9
Pension Benefits, Non U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Benefit Payments in Year One	4.5
Benefit Payments in Year Two	4.8
Benefit Payments in Year Three	4.8
Benefit Payments in Year Four	5.1
Benefit Payments in Year Five	5.4
Benefit Payments in Five Fiscal Years Thereafter	32.5
Other Postretirement Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans
Benefit Payments in Year One	13.6
Prescription Drug Subsidy Receipts in Year One	0.3
Net OPEB Payments in Year One	13.3
Benefit Payments in Year Two	13.2
Prescription Drug Subsidy Receipts in Year Two	0.2
Net OPEB Payments in Year Two	13
Benefit Payments in Year Three	12.8
Prescription Drug Subsidy Receipts in Year Three	0.2
Net OPEB Payments in Year Three	12.6
Benefit Payments in Year Four	12.3
Prescription Drug Subsidy Receipts in Year Four	0.2
Net OPEB Payments in Year Four	12.1
Benefit Payments in Year Five	11.9
Prescription Drug Subsidy Receipts in Year Five	0.2
Net OPEB Payments in Year Five	11.7
Benefit Payments in Five Fiscal Years Thereafter	50.9
Prescription Drug Subsidy Receipts in Five Fiscal Years Thereafter	0.7
Net OPEB Payments in Five Fiscal Years Thereafter	$ 50.2

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016USD ($)	Dec. 31, 2016GBP (£)	Dec. 31, 2016Rate	Dec. 31, 2015USD ($)Rate	Dec. 31, 2014USD ($)
Pension and Other Postretirement Benefits Disclosure
Health Care Cost Trend Rate Assumed for Next Fiscal Year | Rate					7.00%	7.50%
Ultimate Health Care Cost Trend Rate | Rate					5.00%
Effect of One Percentage Point Increase on Service and Interest Cost Components			$ 200,000
Effect of One Percentage Point Decrease on Service and Interest Cost Components			(200,000)
Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation			900,000
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation			(800,000)
Future Amortization of Actuarial Gain (Loss)			20,200,000
Future Amortization of Prior Service Cost (Credit)			700,000
Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		7.50%				7.50%
Plan Amendments			0			$ 7,500,000
Pension Plan Lump-sum Settlement Payment							$ 214,500,000
Pension Settlement Costs			0			$ 0	64,400,000
Average Remaining Life Expectancy of Plan Participants	25 years
General Discussion of Pension and Other Postretirement Benefits	We had no regulatory contribution requirements for our U.S. qualified defined benefit plan in 2016
Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		4.90%				5.20%
Plan Amendments			0			$ 0
Pension Settlement Costs			0			$ 0	0
Average Remaining Life Expectancy of Plan Participants	33 years
Pension Contributions			0
Other Postretirement Benefit Plans
Pension and Other Postretirement Benefits Disclosure
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		5.75%			5.75%	5.75%
Plan Amendments			3,700,000			$ 0
Pension Settlement Costs			0			0	0
Level 3 Transfers Into			0			0
Level 3 Transfers Out of			0			$ 0
Interest Rate During Period		4.99%				5.24%
Health Care Cost Trend Rate Assumed for Next Fiscal Year | Rate						7.50%
Diversified Growth Assets | Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					65.00%
Equity Securities | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					33.00%
Interest Rate Contract | Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					35.00%
Fixed Maturity Securities | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					40.00%
Alternative Investments | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					27.00%
Minimum
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	1 year
Minimum | Private Equity Funds | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	5 years
Maximum
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	11 years
Maximum | Private Equity Funds | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	8 years
U.S. Defined Contribution Plan
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay | Rate					5.00%
Employer Discretionary Contribution Percentage of earnings | Rate					4.50%
Cost Recognized			72,200,000			$ 71,500,000	$ 76,000,000
Non U.S. Defined Contribution Plan
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay		5.00%					5.00%
Employer Discretionary Contribution Percentage of earnings		6.00%					5.00%
Employer Matching Contribution for Every Pound on the First One Percent of Employee Contributions | £				£ 2
Employee Contribution Percentage Received 2-for-1 Employer Match		1.00%
Cost Recognized			$ 4,900,000			$ 5,700,000	$ 5,000,000

Basic and Diluted Earnings Per

Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator
Net Income	$ 248	$ 236	$ 236.8	$ 210.6	$ 226.1	$ 203.8	$ 224.3	$ 212.9	$ 931.4	$ 867.1	$ 402.1
Denominator
Weighted Average Common Shares - Basic									235,445,700	246,986,700	255,525,900
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards									533,500	868,000	1,126,900
Weighted Average Common Shares - Assuming Dilution									235,979,200	247,854,700	256,652,800
Net Income Per Common Share
Basic	$ 1.07	$ 1.01	$ 1	$ 0.88	$ 0.93	$ 0.83	$ 0.90	$ 0.85	$ 3.96	$ 3.51	$ 1.57
Assuming Dilution	$ 1.07	$ 1.01	$ 1	$ 0.88	$ 0.93	$ 0.83	$ 0.90	$ 0.84	$ 3.95	$ 3.50	$ 1.57

Treasury Stock Transactions (De

Treasury Stock Transactions (Details) - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity, Class of Treasury Stock
Expiration Date of Share Repurchase Program Authorized in May 2016		Nov. 26, 2017
Number of Treasury Shares Repurchased		11.9	12.3	8.7
Cost of Shares Repurchased	[1]	$ 403.3	$ 426.7	$ 300.6
Commission Paid on Stock Repurchases		0.2	$ 0.3	$ 0.1
Repurchase Program Authorized in May 2016
Equity, Class of Treasury Stock
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program		750
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program		495.7
Repurchase Program Authorized in May 2015
Equity, Class of Treasury Stock
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program		750
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program		0
Repurchase Program Authorized in December 2013
Equity, Class of Treasury Stock
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program		750
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program		$ 0
[1]	Includes commissions of $0.2 million, $0.3 million, and $0.1 million for the years ended December 31, 2016, 2015, and 2014, respectively.

Stockholders' Equity and Ear101

Stockholders' Equity and Earnings Per Common Share - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	27.85
Outstanding Restricted Stock Unit Grant Prices Upper Limit	36.36
Outstanding Performance Share Unit Awards Grant Price Range Lower Limit	27.85
Outstanding Performance Share Unit Awards Grant Price Range Upper Limit	$ 34.08
Antidilutive Securities Excluded from Computation of Earnings Per Share	400,000	300,000	100,000
Shares of Treasury Stock Retired			60,000,000
Cost of Retired Treasury Stock			$ 1,451.7
Authorized Shares of Preferred Stock	25,000,000
Par Value Per Share of Preferred Stock	$ 0.1
Issued Shares of Preferred Stock	0

Stock-Based Compensation - Acti

Stock-Based Compensation - Activity for PSUs Classified as Equity (Details) - Performance Share Units - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Weighted Average Grant Date Fair Value at Beginning of Period	$ 35.05
Weighted Average Grant Date Fair Value of Shares Granted	28.41	$ 35.13	$ 34.72
Weighted Average Grant Date Fair Value of Shares Vested	34.79
Weighted Average Grant Date Fair Value of Shares Forfeited	32.54
Weighted Average Grant Date Fair Value at End of Period	$ 31.80	$ 35.05
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares
Shares Outstanding Beginning Balance	383
Shares Granted	219
Shares Vested	(167)
Shares Forfeited	(6)
Shares Outstanding Ending Balance	429	383

Stock-Based Compensation - Valu

Stock-Based Compensation - Valuation Assumptions on PSU Grants (Details) - Performance Share Units	12 Months Ended
	Dec. 31, 2016Rate	Dec. 31, 2015Rate	Dec. 31, 2014Rate
Share-based Compensation Arrangement by Share-based Payment Award
Expected Volatility Rate	22.00%	22.00%	31.00%
Expected Life	3 years	3 years	3 years
Risk Free Interest Rate	0.88%	0.91%	0.65%

Stock-Based Compensation - Nonv

Stock-Based Compensation - Nonvested Stock Awards Classified in Equity (Details) - Restricted Stock Units (RSUs) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Weighted Average Grant Date Fair Value at Beginning of Period	$ 32.40
Weighted Average Grant Date Fair Value of Shares Granted	28.80	$ 34.08	$ 33.77
Weighted Average Grant Date Fair Value of Shares Vested	31.22
Weighted Average Grant Date Fair Value of Shares Forfeited	30.64
Weighted Average Grant Date Fair Value at End of Period	$ 30.66	$ 32.40
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares
Shares Outstanding Beginning Balance	866
Shares Granted	632
Shares Vested	(587)
Shares Forfeited	(33)
Shares Outstanding Ending Balance	878	866

Fair Value of Cash Settled Awar

Fair Value of Cash Settled Awards (Details) - Cash Settled Awards - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Weighted Average Grant Date Fair Value of Shares Granted	$ 0	$ 33.92	$ 33.85
Fair Value of Awards Vested During the Period	$ 0	$ 4.9	$ 2.1
Fair Value of Share-based Liabilities Paid	$ 2.4	$ 2.5	$ 2.9

Stock option activity (Details)

Stock option activity (Details) - Stock Options $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award
Weighted Average Exercise Price of Shares Outstanding at Beginning of Period | $ / shares	$ 23.02
Weighted Average Exercise Price of Shares Exercised | $ / shares	21.01
Weighted Average Exercise Price of Shares Outstanding at End of Period | $ / shares	23.97
Weighted Average Exercise Price of Exercisable Shares | $ / shares	$ 23.97
Weighted Average Remaining Contractual Term of Outstanding Options	2 years 8 months 12 days
Weighted Average Remaining Contractual Term of Exercisable Option	2 years 8 months 12 days
Options Outstanding, Intrinsic Value | $	$ 10.3
Options, Exercisable, Intrinsic Value | $	$ 10.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding
Shares Outstanding at Beginning of Period | shares	759
Shares Exercised | shares	(242)
Shares Outstanding at End of Period | shares	517
Shares Exercisable | shares	517

Intrinsic Value of Options Exer

Intrinsic Value of Options Exercised and Fair Value of Options Vested (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Intrinsic Value of Options Exercised	$ 3.4	$ 5.6	$ 4
Fair Value of Options Vested	$ 0.1	$ 1.1	$ 2.4

Stock-Based Compensation Expens

Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	$ 21.9	$ 23.8	$ 22.6
Allocated Share-based Compensation Expense, Net of Tax	14.4	15.7	14.9
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	6.6	4.5	2.5
Restricted Stock Units and Cash-Settled Awards
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	14.9	18.6	19
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	0	0.2	0.6
Other Awards
Share-based Compensation Arrangement by Share-based Payment Award
Allocated Share-based Compensation Expense, Before Tax	$ 0.4	$ 0.5	$ 0.5

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award
Cash Received Under Share-based Payment Arrangements	$ 8,500,000	$ 6,400,000	$ 12,300,000
Stock Incentive Plan 2012
Share-based Compensation Arrangement by Share-based Payment Award
Number of Shares Authorized	20,000,000
Number of Shares for Each Full Value Award	1.76
Total Duration of the Stock Incentive Plan	8 years
Award Vesting Period	3 years
Number of Shares Available for Grant	14,200,000
Stock Incentive Plan 2007
Share-based Compensation Arrangement by Share-based Payment Award
Number of Shares Authorized	35,000,000
Number of Shares for Each Full Value Award	2.7
Total Duration of the Stock Incentive Plan	8 years
Award Vesting Period	3 years
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award
Award Vesting Period	3 years
Weighted Average Grant Date Fair Value of Shares Granted	$ 28.41	$ 35.13	$ 34.72
Compensation Cost Not yet Recognized	$ 7,400,000
Period for Recognition of Compensation Cost Not Yet Recognized	1 year 6 months 12 days
Shares Outstanding Ending Balance	429,000	383,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Weighted Average Grant Date Fair Value of Shares Granted	$ 28.80	$ 34.08	$ 33.77
Compensation Cost Not yet Recognized	$ 13,000,000
Period for Recognition of Compensation Cost Not Yet Recognized	10 months 24 days
Fair Value of Awards Vested During the Period	$ 18,300,000	$ 21,400,000	$ 19,800,000
Shares Outstanding Ending Balance	878,000	866,000
Cash Settled Awards
Share-based Compensation Arrangement by Share-based Payment Award
Weighted Average Grant Date Fair Value of Shares Granted	$ 0	$ 33.92	$ 33.85
Fair Value of Awards Vested During the Period	$ 0	$ 4,900,000	$ 2,100,000
Shares Outstanding Ending Balance	0	0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Stock Option Compensation Not yet Recognized	$ 0
Options Granted	0	0	0
Minimum | Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of Stock-based Awards Possible to be Earned	40.00%
Minimum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Award Vesting Period	1 year
Minimum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Award Vesting Period	1 year
Maximum | Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of Stock-based Awards Possible to be Earned	180.00%
Maximum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Award Vesting Period	3 years
Maximum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award
Award Vesting Period	3 years

Reinsurance - Premium Income Da

Reinsurance - Premium Income Data (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Disclosures [Abstract]
Direct Premium Income									$ 8,385	$ 8,151.9	$ 7,899.3
Reinsurance Assumed									236.3	202.8	189.8
Reinsurance Ceded									(263.6)	(272.3)	(291.9)
Premium Income	$ 2,099.2	$ 2,089.4	$ 2,081.6	$ 2,087.5	$ 2,037.8	$ 2,020.8	$ 2,017.5	$ 2,006.3	8,357.7	8,082.4	7,797.2
Ceded Benefits and Change in Reserves for Future Benefits									$ 648.3	$ 662.7	$ 662.7

Reinsurance - Additional Inform

Reinsurance - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016
Number of companies that make up majority of reinsurance recoverable	13
AM Best A Rating or Better | Reinsurer Concentration Risk | Reinsurance Recoverable | Top 13 Reinsurers
Percentage of Concentration Risk	91.00%
AM Best, A- Rating | Reinsurer Concentration Risk | Reinsurance Recoverable | Other Reinsurers
Percentage of Concentration Risk	8.00%
AM Best, Below A- or Not Rated | Reinsurer Concentration Risk | Reinsurance Recoverable | Other Reinsurers
Percentage of Concentration Risk	1.00%
Individual Disability | Unum US
Reinsurance Retention Policy, Reinsured Risk, Percentage	30.00%

Premium Income by Major Line of

Premium Income by Major Line of Business within Each Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information
Premium Income	$ 2,099.2	$ 2,089.4	$ 2,081.6	$ 2,087.5	$ 2,037.8	$ 2,020.8	$ 2,017.5	$ 2,006.3	$ 8,357.7	$ 8,082.4	$ 7,797.2
Accident, Sickness, and Disability
Segment Reporting Information
Premium Income									6,296.7	6,099.2	5,926
Life Insurance
Segment Reporting Information
Premium Income									2,061	1,983.2	1,871.2
Operating Segments
Segment Reporting Information
Premium Income									8,357.7	8,082.4	7,797.2
Operating Segments | Unum US
Segment Reporting Information
Premium Income									5,240.9	4,960	4,659.7
Operating Segments | Unum US | Group Long-term Disability
Segment Reporting Information
Premium Income									1,726.6	1,644.7	1,553.5
Operating Segments | Unum US | Group Short-term Disability
Segment Reporting Information
Premium Income									626.1	607.4	558.1
Operating Segments | Unum US | Group Life
Segment Reporting Information
Premium Income									1,410	1,347.4	1,262.3
Operating Segments | Unum US | Accidental Death & Dismemberment
Segment Reporting Information
Premium Income									140.3	131.7	125.9
Operating Segments | Unum US | Individual Disability
Segment Reporting Information
Premium Income									480.3	478.9	466.1
Operating Segments | Unum US | Voluntary Benefits
Segment Reporting Information
Premium Income									796.5	749.9	693.8
Operating Segments | Unum US | Dental and Vision
Segment Reporting Information
Premium Income									61.1	0	0
Operating Segments | Unum UK
Segment Reporting Information
Premium Income									529.3	576.2	607.2
Operating Segments | Unum UK | Group Long-term Disability
Segment Reporting Information
Premium Income									355.2	397.4	418.9
Operating Segments | Unum UK | Group Life
Segment Reporting Information
Premium Income									105.7	121.5	133.2
Operating Segments | Unum UK | Supplemental
Segment Reporting Information
Premium Income									68.4	57.3	55.1
Operating Segments | Colonial Life
Segment Reporting Information
Premium Income									1,417.1	1,338.6	1,273.7
Operating Segments | Colonial Life | Accident, Sickness, and Disability
Segment Reporting Information
Premium Income									830	789	759.8
Operating Segments | Colonial Life | Life Insurance
Segment Reporting Information
Premium Income									273.8	252.4	231.8
Operating Segments | Colonial Life | Cancer and Critical Illness Colonial
Segment Reporting Information
Premium Income									313.3	297.2	282.1
Operating Segments | Closed Block
Segment Reporting Information
Premium Income									1,170.4	1,207.6	1,256.6
Operating Segments | Closed Block | Individual Disability
Segment Reporting Information
Premium Income									521.9	572.4	624.8
Operating Segments | Closed Block | Long-term Care
Segment Reporting Information
Premium Income									643.9	633.5	630.9
Operating Segments | Closed Block | Other Insurance Product Line
Segment Reporting Information
Premium Income									$ 4.6	$ 1.7	$ 0.9

Selected Operating Statement Da

Selected Operating Statement Data by Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information
Premium Income	$ 2,099.2	$ 2,089.4	$ 2,081.6	$ 2,087.5	$ 2,037.8	$ 2,020.8	$ 2,017.5	$ 2,006.3	$ 8,357.7	$ 8,082.4	$ 7,797.2
Net Investment Income	$ 617.9	$ 611.4	$ 623.3	$ 606.4	$ 636.4	$ 612.1	$ 630.7	$ 602	2,459	2,481.2	2,492.2
Other Income									205.6	211.5	219
Interest and Debt Expense									166	152.8	167.5
Operating Segments
Segment Reporting Information
Premium Income									8,357.7	8,082.4	7,797.2
Net Investment Income									2,459	2,481.2	2,492.2
Other Income									205.6	211.5	219
Operating Revenue									11,022.3	10,775.1	10,508.4
Operating Income (Loss)									1,339.8	1,294	1,307.3
Interest and Debt Expense									166	152.8	154.3
Depreciation and Amortization									600.2	587.1	534.4
Operating Segments | Unum US
Segment Reporting Information
Premium Income									5,240.9	4,960	4,659.7
Net Investment Income									828.7	865.3	878.9
Other Income									113.3	119.2	122.1
Operating Revenue									6,182.9	5,944.5	5,660.7
Operating Income (Loss)									914.2	850	844.9
Interest and Debt Expense									0	0	0
Depreciation and Amortization									353	347	314.2
Operating Segments | Unum UK
Segment Reporting Information
Premium Income									529.3	576.2	607.2
Net Investment Income									118.1	124.9	151
Other Income									0.2	0	0
Operating Revenue									647.6	701.1	758.2
Operating Income (Loss)									128.6	140.6	147.8
Interest and Debt Expense									0	0	0
Depreciation and Amortization									16.4	18	19.2
Operating Segments | Colonial Life
Segment Reporting Information
Premium Income									1,417.1	1,338.6	1,273.7
Net Investment Income									141.5	145.4	145.5
Other Income									1.2	0.1	0.1
Operating Revenue									1,559.8	1,484.1	1,419.3
Operating Income (Loss)									314.2	309.1	299
Interest and Debt Expense									0	0	0
Depreciation and Amortization									222.9	214.6	194.1
Operating Segments | Closed Block
Segment Reporting Information
Premium Income									1,170.4	1,207.6	1,256.6
Net Investment Income									1,352.2	1,320	1,281.5
Other Income									86	89.3	91.8
Operating Revenue									2,608.6	2,616.9	2,629.9
Operating Income (Loss)									129.5	119.1	120
Interest and Debt Expense									6.9	6.6	7.3
Depreciation and Amortization									6.9	6.6	5.9
Operating Segments | Corporate and Other Segment
Segment Reporting Information
Premium Income									0	0	0
Net Investment Income									18.5	25.6	35.3
Other Income									4.9	2.9	5
Operating Revenue									23.4	28.5	40.3
Operating Income (Loss)									(146.7)	(124.8)	(104.4)
Interest and Debt Expense									159.1	146.2	147
Depreciation and Amortization									$ 1	$ 0.9	$ 1

Segment Information Deferred Ac

Segment Information Deferred Acquisition Costs by Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	$ 2,008.5
Deferred Policy Acquisition Cost, Amortization Expense	(493)	$ (482.3)	$ (440.8)
Deferred Acquisition Costs at End of Year	2,094.2	2,008.5
Operating Segments
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	2,008.5	1,901.3	1,829.2
Deferral of Acquisition Costs	592.4	569.7	524
Deferred Policy Acquisition Cost, Amortization Expense	(493)	(482.3)	(440.8)
Adjustment Related to Unrealized Investment Gains and Losses	(9.5)	21.4	(9.2)
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	(4.2)	(1.6)	(1.9)
Deferred Acquisition Costs at End of Year	2,094.2	2,008.5	1,901.3
Operating Segments | Unum US
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	1,136.4	1,096.5	1,051.5
Deferral of Acquisition Costs	314.1	307.3	292.7
Deferred Policy Acquisition Cost, Amortization Expense	(275.2)	(272.3)	(248.1)
Adjustment Related to Unrealized Investment Gains and Losses	1.2	4.9	0.4
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	0	0	0
Deferred Acquisition Costs at End of Year	1,176.5	1,136.4	1,096.5
Operating Segments | Unum UK
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	27.1	30.4	34.3
Deferral of Acquisition Costs	8.2	9.6	10.5
Deferred Policy Acquisition Cost, Amortization Expense	(9.7)	(11.3)	(12.5)
Adjustment Related to Unrealized Investment Gains and Losses	0	0	0
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	(4.2)	(1.6)	(1.9)
Deferred Acquisition Costs at End of Year	21.4	27.1	30.4
Operating Segments | Colonial Life
Movement Analysis of Deferred Policy Acquisition Costs
Deferred Acquisition Costs at Beginning of Year	845	774.4	743.4
Deferral of Acquisition Costs	270.1	252.8	220.8
Deferred Policy Acquisition Cost, Amortization Expense	(208.1)	(198.7)	(180.2)
Adjustment Related to Unrealized Investment Gains and Losses	(10.7)	16.5	(9.6)
Deferred Policy Acquisition Costs Foreign Currency Translation Adjustment And Other	0	0	0
Deferred Acquisition Costs at End of Year	$ 896.3	$ 845	$ 774.4

Assets by Segment (Detail)

Assets by Segment (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information
Total Assets	$ 61,941.5	$ 60,563.6
Operating Segments
Segment Reporting Information
Total Assets	61,941.5	60,563.6
Operating Segments | Unum US
Segment Reporting Information
Total Assets	18,036.6	18,242.4
Operating Segments | Unum UK
Segment Reporting Information
Total Assets	3,101.4	3,432.4
Operating Segments | Colonial Life
Segment Reporting Information
Total Assets	3,923.2	3,776.8
Operating Segments | Closed Block
Segment Reporting Information
Total Assets	33,734.3	33,000.9
Operating Segments | Corporate and Other Segment
Segment Reporting Information
Total Assets	$ 3,146	$ 2,111.1

Reconciliation of Total Revenue

Reconciliation of Total Revenue and Income Before Income Tax to Operating Revenue and Operating Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Revenue Reconciling Item
Total Revenue	$ 2,796.5	$ 2,763.3	$ 2,761.3	$ 2,725.4	$ 2,722.4	$ 2,657.8	$ 2,703.7	$ 2,647.4	$ 11,046.5	$ 10,731.3	$ 10,524.5
Net Realized Investment Gain (Loss)	28.4	11	5.3	(20.5)	(2.7)	(26.6)	0.8	(15.3)	24.2	(43.8)	16.1
Income Before Income Tax	371.2	332.1	340.2	304.2	316.6	298.9	319.8	303	1,347.7	1,238.3	542
Net Realized Investment Gain (Loss)	$ 28.4	$ 11	$ 5.3	$ (20.5)	$ (2.7)	$ (26.6)	$ 0.8	$ (15.3)	24.2	(43.8)	16.1
Operating Segments
Segment Reporting, Revenue Reconciling Item
Total Revenue									11,046.5	10,731.3	10,524.5
Net Realized Investment Gain (Loss)									24.2	(43.8)	16.1
Operating Revenue									11,022.3	10,775.1	10,508.4
Income Before Income Tax									1,347.7	1,238.3	542
Net Realized Investment Gain (Loss)									24.2	(43.8)	16.1
Non-operating Retirement-related Loss									(16.3)	(11.9)	(70)
Make-whole Premium on Early Repayment of Debt									0	0	(13.2)
Reserve Increase for Long-term Care, Before Tax									0	0	(698.2)
Operating Income									$ 1,339.8	$ 1,294	$ 1,307.3

Segment Information Segments -

Segment Information Segments - Additional Information (Detail) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)IntegerRate	Dec. 31, 2015USD ($)Rate	Dec. 31, 2015GBP (£)	Dec. 31, 2014USD ($)	Dec. 31, 2014GBP (£)	Dec. 31, 2015GBP (£)Rate
Supplementary Insurance Information, by Segment
Percentage Ownership of Acquired Business | Rate	100.00%	100.00%				100.00%
Name of Acquired Businesses	H&J Capital, L.L.C., parent of Starmount Life Insurance Company and AlwaysCare Benefits (Starmount)	National Dental Plan Limited and associated companies (National Dental)	National Dental Plan Limited and associated companies (National Dental)
Total Cash Purchase Price to Acquire Business	$ 140.3	$ 54.3	£ 35.9
Business Combination, Contingent Consideration, Liability, Noncurrent	10
Total Revenues of Acquired Business		129.9		$ 24.2	£ 14.7
Assets of Acquiree at Acquisition Date	93.1	28.1				£ 18.6
Liabilities of Acquiree at Acquisition Date	55.7	7.5				5
Goodwill	$ 335.1	230.9
Number of Operating Segments | Integer	3
Payable due 18 Months After Acquisition
Supplementary Insurance Information, by Segment
Business Combination, Contingent Consideration, Liability, Noncurrent	$ 5
Payable due 24 Months After Acquisition
Supplementary Insurance Information, by Segment
Business Combination, Contingent Consideration, Liability, Noncurrent	5
Unum US and Colonial
Supplementary Insurance Information, by Segment
Goodwill	$ 111.2
Unum US
Supplementary Insurance Information, by Segment
Percent of Goodwill Allocated to a Business Segment | Rate	75.00%
Goodwill	$ 271.1	187.6
Colonial Life
Supplementary Insurance Information, by Segment
Percent of Goodwill Allocated to a Business Segment | Rate	25.00%
Goodwill	$ 27.7
Unum UK
Supplementary Insurance Information, by Segment
Goodwill at Acquisition Date		33.7				£ 22.3
Goodwill	$ 36.3	$ 43.3

Commitments and Contingent L118

Commitments and Contingent Liabilities - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Lease Payments Due	$ 189.6
Future Minimum Lease Payments Due Within Twelve Months	50.8
Future Minimum Lease Payments Due Within Two Years	25.8
Future Minimum Lease Payments Due Within Three Years	22.5
Future Minimum Lease Payments Due Within Four Years	18
Future Minimum Lease Payments Due Within Five Years	13.9
Future Minimum Lease Payments Due Thereafter	58.6
Rental Expense	51.4	$ 42.5	$ 44.2
Total Unfunded Commitments	314
Pending Litigation | Unfavorable Regulatory Action | Minimum
Loss Contingencies
Loss Contingency, Estimate of Possible Loss	12
Pending Litigation | Unfavorable Regulatory Action | Maximum
Loss Contingencies
Loss Contingency, Estimate of Possible Loss	$ 15

Statutory Financial Informat119

Statutory Financial Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Traditional U.S. Life Insurance Subsidiaries
Statutory Accounting Practices
Statutory Net Income	$ 855.1	$ 653.7	$ 628.9
Statutory Combined Net Gain (Loss) from Operations	884.6	689.2	623.9
Statutory Combined Capital and Surplus	3,626.9	3,470.3
Captive Reinsurers
Statutory Accounting Practices
Statutory Net Income	48.4	(56.3)	(129.3)
Statutory Combined Net Gain (Loss) from Operations	50.6	(54.3)	$ (130.2)
Statutory Combined Capital and Surplus	$ 1,726.7	$ 1,672.3

Statutory Financial Informat120

Statutory Financial Information - Additional Details (Detail) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2015GBP (£)	Dec. 31, 2014USD ($)	Dec. 31, 2016GBP (£)	Dec. 31, 2015GBP (£)
Fairwind Insurance Company
Statutory Accounting Practices
Statutory Accounting Practices, Permitted Practice, Amount	$ 213	$ 208
Unum Limited
Statutory Accounting Practices
Statutory Net Income | £			£ 60.6
Statutory Combined Capital and Surplus | £						£ 441.5
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments | £					£ 271
Traditional U.S. Life Insurance Subsidiaries
Statutory Accounting Practices
Statutory Net Income	855.1	653.7		$ 628.9
Statutory Combined Capital and Surplus	3,626.9	3,470.3
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments	859.3
Cash and Securities Segregated under Federal and Other Regulations	$ 194.9	$ 284.1

Schedule of Unaudited Quarterly

Schedule of Unaudited Quarterly Results (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Selected Quarterly Financial Information [Abstract]
Premium Income	$ 2,099.2	$ 2,089.4	$ 2,081.6	$ 2,087.5	$ 2,037.8	$ 2,020.8	$ 2,017.5	$ 2,006.3	$ 8,357.7	$ 8,082.4	$ 7,797.2
Net Investment Income	617.9	611.4	623.3	606.4	636.4	612.1	630.7	602	2,459	2,481.2	2,492.2
Net Realized Investment Gain (Loss)	28.4	11	5.3	(20.5)	(2.7)	(26.6)	0.8	(15.3)	24.2	(43.8)	16.1
Total Revenue	2,796.5	2,763.3	2,761.3	2,725.4	2,722.4	2,657.8	2,703.7	2,647.4	11,046.5	10,731.3	10,524.5
Income Before Income Tax	371.2	332.1	340.2	304.2	316.6	298.9	319.8	303	1,347.7	1,238.3	542
Net Income	$ 248	$ 236	$ 236.8	$ 210.6	$ 226.1	$ 203.8	$ 224.3	$ 212.9	$ 931.4	$ 867.1	$ 402.1
Basic Earnings Per Share	$ 1.07	$ 1.01	$ 1	$ 0.88	$ 0.93	$ 0.83	$ 0.90	$ 0.85	$ 3.96	$ 3.51	$ 1.57
Diluted Earnings Per Share	$ 1.07	$ 1.01	$ 1	$ 0.88	$ 0.93	$ 0.83	$ 0.90	$ 0.84	$ 3.95	$ 3.50	$ 1.57

Schedule I - Summary of Inve122

Schedule I - Summary of Investments, Other Than Investments in Related Parties Schedule I - Summary of Investments, Other Than Investments in Related Parties (Details) $ in Millions	Dec. 31, 2016USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	$ 46,425.2	[1]
Amount Shown on the Balance Sheet	51,130.9
United States Government and Government Agencies and Authorities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	1,202.8	[1]
Fair Value of Investments	1,382.4
Amount Shown on the Balance Sheet	1,382.4
States, Municipalities, and Political Subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	1,868	[1]
Fair Value of Investments	2,158
Amount Shown on the Balance Sheet	2,158
Foreign Governments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	714.8	[1]
Fair Value of Investments	914.7
Amount Shown on the Balance Sheet	914.7
Public Utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	6,916.1	[1]
Fair Value of Investments	8,022.7
Amount Shown on the Balance Sheet	8,022.7
Mortgage/Asset-backed Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	2,104.9	[1]
Fair Value of Investments	2,230.4
Amount Shown on the Balance Sheet	2,230.4
All Other Corporate Bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	26,707.1	[1]
Fair Value of Investments	29,467.2
Amount Shown on the Balance Sheet	29,467.2
Redeemable Preferred Stock
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	39	[1]
Fair Value of Investments	41.9
Amount Shown on the Balance Sheet	41.9
Fixed Maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	39,552.7	[1]
Fair Value of Investments	44,217.3
Amount Shown on the Balance Sheet	44,217.3
Mortgages
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	2,038.9	[1]
Amount Shown on the Balance Sheet	2,038.9
Policy Loans
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	3,463.2	[1]
Amount Shown on the Balance Sheet	3,463.2
Derivatives
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	0	[1]
Amount Shown on the Balance Sheet	32.7	[2]
Equity Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	1.1	[1]
Amount Shown on the Balance Sheet	1.2
Miscellaneous Long-term Investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	589.3	[1]
Amount Shown on the Balance Sheet	597.6	[3]
Short-term Investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost of Investments	780	[1]
Amount Shown on the Balance Sheet	$ 780
[1]	The amortized cost for fixed maturity securities and mortgage loans represents original cost reduced by repayments, write-downs from other-than-temporary declines in fair value, amortization of premiums, and/or accretion of discounts.
[2]	Derivatives are carried at fair value.
[3]	The difference between amortized cost and carrying value primarily results from changes in the partnership owner's equity since acquisition.

Parent Company Balance Sheet (D

Parent Company Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Fixed Maturity Securities - at fair value (amortized cost: $215.1; $273.7)	$ 44,217.3	$ 43,354.4
Other Long-term Investments	631.5	583
Short-term Investments	780	807.3
Other Assets	617.3	637.4
Total Assets	61,941.5	60,563.6
Liabilities
Short-term Debt	0	352
Long-term Debt	2,999.4	2,449.4
Other Liabilities	1,675.9	1,501.1
Total Liabilities	52,973.5	51,899.7
Stockholders' Equity
Common Stock	30.4	30.3
Additional Paid-in Capital	2,272.8	2,247.2
Accumulated Other Comprehensive Income (Loss)	(51)	16.1
Retained Earnings	8,744	7,995.2
Treasury Stock	(2,028.2)	(1,624.9)
Total Stockholders' Equity	8,968	8,663.9	$ 8,521.9
Total Liabilities and Stockholders' Equity	61,941.5	60,563.6
Parent Company
Assets
Fixed Maturity Securities - at fair value (amortized cost: $215.1; $273.7)	214.2	273.4
Other Long-term Investments	49	22.7
Short-term Investments	377.9	288.1
Investments in Subsidiaries	11,340.7	10,689.1
Deferred Income Tax	210.7	160.1
Other Assets	473.9	546.4
Total Assets	12,666.4	11,979.8
Liabilities
Short-term Debt	0	352
Long-term Debt	2,735.9	2,125.4
Pension and Postretirement Benefits	638.3	554.1
Other Liabilities	324.2	284.4
Total Liabilities	3,698.4	3,315.9
Stockholders' Equity
Common Stock	30.4	30.3
Additional Paid-in Capital	2,272.8	2,247.2
Accumulated Other Comprehensive Income (Loss)	(51)	16.1
Retained Earnings	8,744	7,995.2
Treasury Stock	(2,028.2)	(1,624.9)
Total Stockholders' Equity	8,968	8,663.9
Total Liabilities and Stockholders' Equity	$ 12,666.4	$ 11,979.8

Parent Company Balance Sheet (P

Parent Company Balance Sheet (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Amortized Cost of Fixed Maturity Securities	$ 39,552.7	$ 39,658.7
Parent Company
Amortized Cost of Fixed Maturity Securities	$ 215.1	$ 273.7

Parent Company Statement of Inc

Parent Company Statement of Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions
Other Income									$ 205.6	$ 211.5	$ 219
Total Revenue	$ 2,796.5	$ 2,763.3	$ 2,761.3	$ 2,725.4	$ 2,722.4	$ 2,657.8	$ 2,703.7	$ 2,647.4	11,046.5	10,731.3	10,524.5
Income Before Income Tax	371.2	332.1	340.2	304.2	316.6	298.9	319.8	303	1,347.7	1,238.3	542
Income Tax Expense (Benefit)									416.3	371.2	139.9
Net Income	$ 248	$ 236	$ 236.8	$ 210.6	$ 226.1	$ 203.8	$ 224.3	$ 212.9	931.4	867.1	402.1
Net Other Comprehensive Income (Loss)									(67.1)	(150.3)	(88.6)
Comprehensive Income									864.3	716.8	313.5
Parent Company
Condensed Financial Statements, Captions
Cash Dividends from Subsidiaries									676.5	671.8	645.2
Other Income									58.4	52.8	116.3
Total Revenue									734.9	724.6	761.5
Interest and Debt Expense									160.1	137.5	132.4
Other Expenses									32.3	16.7	66
Total Expenses									192.4	154.2	198.4
Income Before Income Tax									542.5	570.4	563.1
Income Tax Expense (Benefit)									(20.2)	(16.2)	(24.5)
Income of Parent Company									562.7	586.6	587.6
Equity in Undistibuted Earnings (Loss) of Subsidiaries									368.7	280.5	(185.5)
Net Income									931.4	867.1	402.1
Net Other Comprehensive Income (Loss)									(67.1)	(150.3)	(88.6)
Comprehensive Income									$ 864.3	$ 716.8	$ 313.5

Parent Company Cash Flow Statem

Parent Company Cash Flow Statement (Detail) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2015GBP (£)	Dec. 31, 2014USD ($)
Condensed Financial Statements, Captions
Cash Provided by Operating Activities	$ 1,116.1	$ 1,292.1		$ 1,223.6
Cash Flows from Investing Activities
Proceeds from Sales of Fixed Maturity Securities	911.5	880.1		450.1
Proceeds from Maturities of Fixed Maturity Securities	2,197.8	2,417		1,819.4
Proceeds from Sales and Maturities of Other Investments	336.8	347		235
Purchase of Fixed Maturity Securities	(3,362.8)	(4,305.3)		(2,918.4)
Purchase of Other Investments	(576)	(409.5)		(285.2)
Net Sales (Purchases) of Short-term Investments	6.3	170.6		(69.3)
Net Purchases of Property and Equipment	(85)	(100.2)		(114.5)
Acquisition of Business	(140.3)	(54.3)	£ (35.9)
Other, Net	0	0		0.1
Net Cash Used by Investing Activities	(710)	(713)		(886.6)
Cash Flows from Financing Activities
Issuance of Long-term Debt	609.1	271.4		347.2
Long-term Debt Repayment	(414)	(226.3)		(186.6)
Issuance of Common Stock	8.5	6.4		12.3
Repurchase of Common Stock	(405.2)	(417.9)		(306)
Dividends Paid to Stockholders	(182.6)	(174.2)		(159.4)
Other, Net	(34.4)	(28.1)		(22.9)
Net Cash Used by Financing Activities	(418.6)	(568.7)		(328.6)
Net Increase (Decrease) in Cash and Bank Deposits	(12.5)	10.4		8.4
Parent Company
Condensed Financial Statements, Captions
Cash Provided by Operating Activities	685.4	672.2		683
Cash Flows from Investing Activities
Proceeds from Sales of Fixed Maturity Securities	2.6	7.8		25
Proceeds from Maturities of Fixed Maturity Securities	111.2	112.2		76.1
Proceeds from Sales and Maturities of Other Investments	0.4	26.4		31.9
Purchase of Fixed Maturity Securities	(56.5)	(233.7)		(118.9)
Purchase of Other Investments	(23.3)	0		(19)
Net Sales (Purchases) of Short-term Investments	(89.8)	38.1		(162.1)
Cash Distributions to Subsidiaries	(143.6)	(231)		(316.1)
Net Purchases of Property and Equipment	(55.5)	(78.9)		(102.5)
Acquisition of Business	(140.3)	0		0
Other, Net	0.2	0.1		(0.2)
Net Cash Used by Investing Activities	(394.6)	(359)		(585.8)
Cash Flows from Financing Activities
Issuance of Long-term Debt	609.1	271.4		347.2
Long-term Debt Repayment	(350)	0		0
Issuance of Common Stock	8.5	6.4		12.3
Repurchase of Common Stock	(405.2)	(417.9)		(306)
Dividends Paid to Stockholders	(182.6)	(174.2)		(159.4)
Other, Net	(1)	2.9		1.9
Net Cash Used by Financing Activities	(321.2)	(311.4)		(104)
Net Increase (Decrease) in Cash and Bank Deposits	$ (30.4)	$ 1.8		$ (6.8)

Parent Company Debt Schedule (D

Parent Company Debt Schedule (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument
Long-term Debt, Excluding Current Maturities		$ 2,999.4		$ 2,449.4
Debt Instrument, Unamortized Premium (Discount), Net		9.8		(3.8)
Debt Issuance Costs, Noncurrent, Net		(28.4)		(25.7)
Current Maturities of Long-term Debt		0		352
Debt Issuance Costs, Current, Net		0		(0.4)
Long-term Debt		2,999.4		2,801.4
Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Long-term Debt, Excluding Current Maturities		(3.1)		(2.7)
Current Maturities of Long-term Debt		0		2.4
Parent Company
Debt Instrument
Long-term Debt, Excluding Current Maturities		2,735.9		2,125.4
Debt Instrument, Unamortized Premium (Discount), Net		9.8		(3.8)
Debt Issuance Costs, Noncurrent, Net		(28.4)		(25.7)
Current Maturities of Long-term Debt		0		352
Debt Issuance Costs, Current, Net		0		(0.4)
Long-term Debt		2,735.9		2,477.4
Parent Company | Fair Value Hedge Adjustment, LT Debt
Debt Instrument
Long-term Debt, Excluding Current Maturities		(3.1)		(2.7)
Current Maturities of Long-term Debt		0		2.4
Notes Issued in 1998 with 2018 Maturity Date | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.00%
Year of Maturity	Dec. 31, 2018
Long-term Debt, Excluding Current Maturities		200		200
Notes Issued in 1998 with 2018 Maturity Date | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.00%
Year of Maturity	Dec. 31, 2018
Long-term Debt, Excluding Current Maturities		200		200
Notes Issued in 1998 with 2028 Maturity Date | Senior Notes
Debt Instrument
Year of Maturity	Dec. 31, 2028
Long-term Debt, Excluding Current Maturities		365.8		365.8
Notes Issued in 1998 with 2028 Maturity Date | Parent Company | Senior Notes
Debt Instrument
Year of Maturity	Dec. 31, 2028
Long-term Debt, Excluding Current Maturities		365.8		365.8
Notes Issued in 1998 with 2028 Maturity Date | Minimum | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			6.75%
Notes Issued in 1998 with 2028 Maturity Date | Minimum | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			6.75%
Notes Issued in 1998 with 2028 Maturity Date | Maximum | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.25%
Notes Issued in 1998 with 2028 Maturity Date | Maximum | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.25%
Notes Issued in 2002 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.375%
Year of Maturity	Dec. 31, 2032
Long-term Debt, Excluding Current Maturities		39.5		39.5
Notes Issued in 2002 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			7.375%
Year of Maturity	Dec. 31, 2032
Long-term Debt, Excluding Current Maturities		39.5		39.5
Notes Issued in 2009
Debt Instrument
Stated Interest Rate of Debt			7.125%
Year of Maturity	Sep. 30, 2016
Current Maturities of Long-term Debt		0		350
Notes Issued in 2009 | Parent Company
Debt Instrument
Stated Interest Rate of Debt			7.125%
Year of Maturity	Dec. 31, 2016
Current Maturities of Long-term Debt		0		350
Notes Issued in 2010 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.625%
Year of Maturity	Dec. 31, 2020
Long-term Debt, Excluding Current Maturities		400		400
Notes Issued in 2010 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.625%
Year of Maturity	Dec. 31, 2020
Long-term Debt, Excluding Current Maturities		400		400
Notes Issued in 2012 and 2016 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			5.75%
Year of Maturity	Dec. 31, 2042
Long-term Debt, Excluding Current Maturities		500		250
Notes Issued in 2012
Debt Instrument
Stated Interest Rate of Debt			5.75%
Long-term Debt, Excluding Current Maturities		250
Notes Issued in 2014 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			4.00%
Year of Maturity	Dec. 31, 2024
Long-term Debt, Excluding Current Maturities		350		350
Notes Issued in 2014 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			4.00%
Year of Maturity	Dec. 31, 2024
Long-term Debt, Excluding Current Maturities		350		350
Notes Issued in 2015 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			3.875%
Year of Maturity	Dec. 31, 2025
Long-term Debt, Excluding Current Maturities		275		275
Notes Issued in 2015 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			3.875%
Year of Maturity	Dec. 31, 2025
Long-term Debt, Excluding Current Maturities		275		275
Notes Issued in 2016 | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			3.00%
Year of Maturity	May 15, 2021
Long-term Debt, Excluding Current Maturities		350		0
Notes Issued in 2016 | Parent Company | Senior Notes
Debt Instrument
Stated Interest Rate of Debt			3.00%
Year of Maturity	Dec. 31, 2021
Long-term Debt, Excluding Current Maturities		350		0
Notes Issued 1990 to 1996 | Medium-term Notes
Debt Instrument
Debt Instrument, Maturity Date Range, Start	Dec. 31, 2023
Debt Instrument, Maturity Date Range, End	Dec. 31, 2028
Long-term Debt, Excluding Current Maturities		50.8		50.8
Notes Issued 1990 to 1996 | Parent Company | Medium-term Notes
Debt Instrument
Debt Instrument, Maturity Date Range, Start	Dec. 31, 2023
Debt Instrument, Maturity Date Range, End	Dec. 31, 2028
Long-term Debt, Excluding Current Maturities		50.8		50.8
Notes Issued 1990 to 1996 | Minimum | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.00%
Notes Issued 1990 to 1996 | Minimum | Parent Company | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.00%
Notes Issued 1990 to 1996 | Maximum | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.19%
Notes Issued 1990 to 1996 | Maximum | Parent Company | Medium-term Notes
Debt Instrument
Stated Interest Rate of Debt			7.19%
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt
Debt Instrument
Stated Interest Rate of Debt	7.405%		7.405%
Year of Maturity	Dec. 31, 2038
Long-term Debt, Excluding Current Maturities		226.5		226.5
Notes Issued in 1998 with 2038 Maturity Date | Parent Company | Junior Subordinated Debt
Debt Instrument
Stated Interest Rate of Debt	7.405%		7.405%
Year of Maturity	Dec. 31, 2038
Long-term Debt, Excluding Current Maturities		$ 226.5		$ 226.5

Parent Company Notes - Addition

Parent Company Notes - Additional Details (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 1998	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2013
Repayments of Principal in 2018						$ 200
Repayments of Principal in 2020						400
Repayments of Principal in 2021						350
Repayments of Principal Thereafter						2,071.1
Notional Amount of Derivatives		$ 1,470.3	$ 1,687.4			1,052		$ 1,477.4
Interest Paid	$ 153.6	146.9	145.9
Line of Credit Facility, Maximum Borrowing Capacity						400
Line Of Credit Facility Maximum Borrowing Capacity If Requested						600
Letters of Credit Outstanding		2.1				2.1
Amount Outstanding on Line of Credit		0				0
Parent Company
Repayments of Principal in 2018						200
Repayments of Principal in 2020						400
Repayments of Principal in 2021						350
Repayments of Principal Thereafter						1,807.6
Interest Paid	147.8	130.9	$ 123.6
Line of Credit Facility, Maximum Borrowing Capacity						400
Line Of Credit Facility Maximum Borrowing Capacity If Requested						600
Letters of Credit Outstanding		2.1				2.1
Amount Outstanding on Line of Credit		0				0
Subsidiaries
Stated Interest Rate of Debt							6.85%
Guarantor Obligations, Liquidation Proceeds, Monetary Amount	$ 400
Receive Fixed/Pay Variable
Notional Amount of Derivatives		600				250
Receive Fixed/Pay Variable | Parent Company
Notional Amount of Derivatives		$ 600				$ 250
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt
Proceeds from Issuance of Senior Long-term Debt				$ 300
Stated Interest Rate of Debt	7.405%						7.405%
Liquidation value per capital security					$ 1,000
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt | Parent Company
Proceeds from Issuance of Senior Long-term Debt				$ 300
Stated Interest Rate of Debt	7.405%						7.405%
Liquidation value per capital security					$ 1,000

Schedule III Supplementary I129

Schedule III Supplementary Insurance Information (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs		$ 2,094.2	$ 2,008.5
Reserves for Future Policy Contract Benefits		44,245.9	43,540.6
Unearned Premiums		363.7	384.2
Policy and Contract Benefits		1,507.9	1,484.6
Premium Income		8,357.7	8,082.4	$ 7,797.2
Net Investment Income	[1]	2,459	2,481.2	2,492.2
Benefits and Change in Reserves for Future Benefits	[2]	6,941.8	6,782.8	7,310.8
Amortization of Deferred Acquisition Costs		493	482.3	440.8
All Other Expenses	[3]	2,264	2,227.9	2,230.9
Unum US
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs		1,176.5	1,136.4
Reserves for Future Policy Contract Benefits		11,312.6	11,273.5
Unearned Premiums		46.9	45.5
Policy and Contract Benefits		977.2	940.8
Premium Income		5,240.9	4,960	4,659.7
Net Investment Income	[1]	828.7	865.3	878.9
Benefits and Change in Reserves for Future Benefits	[2]	3,624.3	3,476.7	3,288.1
Amortization of Deferred Acquisition Costs		275.2	272.3	248.1
All Other Expenses	[3]	1,369.2	1,345.5	1,279.6
Premiums Written	[4]	3,564.4	3,353.8	3,144.1
Unum UK
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs		21.4	27.1
Reserves for Future Policy Contract Benefits		2,127.9	2,377.5
Unearned Premiums		110.3	128.2
Policy and Contract Benefits		102.4	114.3
Premium Income		529.3	576.2	607.2
Net Investment Income	[1]	118.1	124.9	151
Benefits and Change in Reserves for Future Benefits	[2]	367.4	394.8	431
Amortization of Deferred Acquisition Costs		9.7	11.3	12.5
All Other Expenses	[3]	141.9	154.4	166.9
Premiums Written	[4]	435.4	453	479.9
Colonial Life
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs		896.3	845
Reserves for Future Policy Contract Benefits		2,103.5	1,989.8
Unearned Premiums		33.5	32
Policy and Contract Benefits		195.8	191.2
Premium Income		1,417.1	1,338.6	1,273.7
Net Investment Income	[1]	141.5	145.4	145.5
Benefits and Change in Reserves for Future Benefits	[2]	726.4	683	660.6
Amortization of Deferred Acquisition Costs		208.1	198.7	180.2
All Other Expenses	[3]	311.1	293.3	279.5
Premiums Written	[4]	1,145	1,088.3	1,042.7
Closed Block
Supplementary Insurance Information, by Segment
Deferred Acquisition Costs		0	0
Reserves for Future Policy Contract Benefits		28,701.9	27,899.8
Unearned Premiums		173	178.5
Policy and Contract Benefits		232.5	238.3
Premium Income		1,170.4	1,207.6	1,256.6
Net Investment Income	[1]	1,352.2	1,320	1,281.5
Benefits and Change in Reserves for Future Benefits	[2]	2,223.7	2,228.3	2,931.1
Amortization of Deferred Acquisition Costs		0	0	0
All Other Expenses	[3]	255.4	269.5	277
Premiums Written	[4]	1,161.8	1,198.5	1,248.6
Closed Block | Long-term Care
Supplementary Insurance Information, by Segment
Reserve Increase for Long-term Care, Before Tax			698.2
Corporate and Other Segment
Supplementary Insurance Information, by Segment
Premium Income		0	0	0
Net Investment Income	[1]	18.5	25.6	35.3
Benefits and Change in Reserves for Future Benefits	[2]	0	0	0
Amortization of Deferred Acquisition Costs		0	0	0
All Other Expenses	[3]	186.4	165.2	227.9
Premiums Written	[4]	$ 0	0	$ 0
Non-operating retirement related loss due to settlement			$ 64.4
[1]	Net investment income is allocated based upon segmentation. Each segment has its own specifically identified assets and receives the investment income generated by those assets.
[2]	Included in 2014 is a reserve charge of $698.2 million in the Closed Block segment related to our long-term care business.
[3]	Includes commissions; interest and debt expense; deferral of acquisition costs; compensation expense; non-operating retirement related loss, which in 2014 included a settlement loss of $64.4 million in the Corporate segment related to a pension plan amendment; and other expenses. Where not directly attributable to a segment, expenses are generally allocated based on activity levels, time information, and usage statistics.
[4]	Excludes life insurance.

Schedule IV Reinsurance (Detail

Schedule IV Reinsurance (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment
Direct Premiums, Life Insurance in Force	$ 854,783.9				$ 827,515.2				$ 854,783.9	$ 827,515.2	$ 790,952.1
Ceded Premiums, Life Insurance in Force	31,882.5				24,062.6				31,882.5	24,062.6	24,416.7
Assumed Premiums, Life Insurance in Force	1,004.7				993.5				1,004.7	993.5	999.7
Premiums, Net, Life Insurance in Force	$ 823,906.1				$ 804,446.1				$ 823,906.1	$ 804,446.1	$ 767,535.1
Life Insurance in Force Premiums, Percentage Assumed to Net	0.10%				0.10%				0.10%	0.10%	0.10%
Gross Amount									$ 8,385	$ 8,151.9	$ 7,899.3
Reinsurance Ceded									263.6	272.3	291.9
Assumed Premiums Earned									236.3	202.8	189.8
Net Amount	$ 2,099.2	$ 2,089.4	$ 2,081.6	$ 2,087.5	$ 2,037.8	$ 2,020.8	$ 2,017.5	$ 2,006.3	$ 8,357.7	$ 8,082.4	$ 7,797.2
Percentage of Amount Assumed to Net									2.80%	2.50%	2.40%
Life Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount									$ 2,202.6	$ 2,150.1	$ 2,056.4
Reinsurance Ceded									151.3	176.3	194.8
Assumed Premiums Earned									9.7	9.4	9.6
Net Amount									$ 2,061	$ 1,983.2	$ 1,871.2
Percentage of Amount Assumed to Net									0.50%	0.50%	0.50%
Accident, Health, and Other Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment
Gross Amount									$ 6,182.4	$ 6,001.8	$ 5,842.9
Reinsurance Ceded									112.3	96	97.1
Assumed Premiums Earned									226.6	193.4	180.2
Net Amount									$ 6,296.7	$ 6,099.2	$ 5,926
Percentage of Amount Assumed to Net									3.60%	3.20%	3.00%

Schedule V Valuation and Qua131

Schedule V Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate reserve (deducted from other long-term investments)
Valuation and Qualifying Accounts Disclosure
Balance at Beginning of Period		$ 1.2	$ 0.3	$ 1.8
Additions Charged to Costs and Expenses		3	1.2	0.4
Additions Charged to Other Accounts	[1]	0	0	0
Deductions	[2]	0	0.3	1.9
Balance at End of Period		4.2	1.2	0.3
Allowance for doubtful accounts (deducted from accounts and premiums receivable)
Valuation and Qualifying Accounts Disclosure
Balance at Beginning of Period		6.2	6.4	5.6
Additions Charged to Costs and Expenses		3.1	1.7	1.4
Additions Charged to Other Accounts	[1]	0	0	0.3
Deductions	[2]	3.1	1.9	0.9
Balance at End of Period		$ 6.2	$ 6.2	$ 6.4
[1]	Additions charged to other accounts are comprised of amounts related to fluctuations in the foreign currency exchange rate.
[2]	Deductions include amounts deemed to reduce exposure of probable losses, amounts deemed uncollectible, and amounts related to fluctuations in the foreign currency exchange rate.