Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

New Accounting Pronouncements and Changes in Accounting Principles

Accounting Updates Adopted in 2020:

Accounting Standards Codification (ASC)	Description	Date of Adoption	Effect on Financial Statements
ASC 350 "Intangibles - Goodwill and Other"	This update eliminated 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. This guidance was applied in the period of adoption.	January 1, 2020	The adoption of this update did not have an effect on our financial position or results of operations.
ASC 820 "Fair Value Measurement"	This update amended the fair value measurement guidance by removing or clarifying certain existing disclosure requirements, while also adding new disclosure requirements. Specifically, this update removed certain disclosures related to Level 1 and Level 2 transfers and removed the discussion regarding valuation processes of Level 3 fair value measurements. The update modified guidance related to investments in certain entities that calculate net asset value to explicitly require disclosure regarding timing of liquidation of the investee's assets and timing of redemption restrictions. The update added disclosures around the changes in unrealized gains and losses in other comprehensive income for recurring Level 3 investments held at the end of the reporting period and adds disclosures regarding certain unobservable inputs on Level 3 fair value measurements. The guidance was applied both retrospectively and prospectively, depending on the specific requirement of the update.	December 31, 2018 for the removal and modification of certain disclosures and January 1, 2020 for the addition of certain disclosures.	The adoption of this update modified our disclosures but did not have an impact on our financial position or results of operations.
ASC 715 "Compensation - Retirement Benefits"	This update amends the defined benefit pension and other postretirement benefit guidance by removing or clarifying certain existing disclosure requirements, while also adding new disclosure requirements. Specifically, this update removes the requirement to disclose the effects of a one-percentage point change in the assumed healthcare cost trend and the requirement to disclose amounts in accumulated other comprehensive income expected to be recognized as part of net periodic benefit cost of the next year. This update adds a requirement to describe the reasons for significant gains and losses related to changes in the benefit obligation for the period. The update also clarifies that the projected benefit obligation (PBO) and accumulated benefit obligation (ABO) and fair value of plan assets are to be disclosed for plans with PBOs or ABOs in excess of plan assets. The guidance is to be applied retrospectively and early adoption is permitted.	December 31, 2020	The adoption of this update modified our disclosures but did not have an impact on our financial position or results of operations.

Accounting Standards Codification (ASC)	Description	Date of Adoption	Effect on Financial Statements
ASC 326 "Financial Instruments - Credit Losses"	This update amended the guidance on the impairment of financial instruments. The update added 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 modified 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 are also required, including information used to develop the allowance for losses. The guidance was applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. For available-for-sale fixed maturity securities, the update was applied prospectively. Other-than-temporary impairment losses recognized on available-for-sale fixed maturity securities prior to adoption of the update cannot be reversed. This guidance was applied in the period of adoption.	January 1, 2020	See the summary table below for the financial statement impacts of this adoption on our financial statement line items at January 1, 2020. In addition, see Note 3 of the "Notes to Consolidated Financial Statements" contained herein in this Item 1 for the additional disclosures required by the update.

Summary of Financial Statement Impacts of Accounting Updates Adopted in 2020:

	Balance at December 31, 2019		Balance at January 1, 2020		Effect of Change
	(in millions of dollars)
Adjustments due to ASC 326
Consolidated Balance Sheets
Assets
Mortgage Loans	$	2,397.0	$	2,388.7	$	(8.3)
Reinsurance Recoverable	4,780.7		4,778.9		(1.8)
Accounts and Premiums Receivable	1,602.9		1,589.4		(13.5)
Liabilities
Deferred Income Tax	95.4		90.4		(5.0)
Other Liabilities	1,856.5		1,856.8		0.3
Stockholders' Equity
Retained Earnings	10,728.7		10,709.8		(18.9)

Accounting Updates Adopted in 2019:

Accounting Standards Codification (ASC)	Description	Date of Adoption	Effect on Financial Statements
ASC 220 "Income Statement - Reporting Comprehensive Income"	This update allowed entities to make an accounting policy election to reclassify the disproportionate tax effects arising as a result of the recognition of the enactment of the tax bill, H.R.1, An Act to Provide Reconciliation Pursuant to Titles II and V of the Concurrent Resolution on the Budget for Fiscal Year 2018, more commonly known as TCJA, from accumulated other comprehensive income to retained earnings. Tax effects that are disproportionate in accumulated other comprehensive income for reasons other than the TCJA may not be reclassified. This update required additional disclosures on whether an entity elects to reclassify the disproportionate tax effects and its policy for releasing tax effects from accumulated other comprehensive income.	January 1, 2019	The adoption of this update expanded certain of our disclosures but had no impact on our financial position or results of operations because we did not make the optional accounting policy election to reclassify the disproportionate tax effects resulting from the TCJA from accumulated other comprehensive income to retained earnings.
ASC 310 "Receivables - Nonrefundable Fees and Other Costs"	This update shortened the amortization period to the earliest call date for certain callable debt securities held at a premium. This update did not impact securities held at a discount.	January 1, 2019	The adoption of this update did not have a material impact on our financial position or results of operations.
ASC 718 "Compensation - Stock Compensation"	This update generally aligned the accounting guidance for share-based payments issued to non-employees with guidance for share-based payments issued to employees. Specifically, the update required non-employee share-based payments to be measured using the grant date fair value of the equity instruments that an entity is obligated to issue when the good has been delivered or the service has been rendered rather than being remeasured through the performance completion date. Additionally, for non-employee share-based payments that contain performance conditions, the update changed the criteria regarding the recognition of compensation cost to when achievement of a performance condition is probable rather than upon actual achievement of the performance condition.	January 1, 2019	The adoption of this update did not have an impact on our financial position or results of operations.
ASC 842 "Leases"	This update changed 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 remained similar to previous accounting requirements for capital and operating leases. For lessors, the guidance modified the classification criteria and the accounting for sales-type and direct financing leases. The guidance was applied using a modified retrospective approach through a cumulative-effect adjustment to retained earnings at the beginning of the period of adoption. In addition, the package of practical expedients available to leases that commenced prior to the date of adoption was applied.	January 1, 2019	The adoption of this update resulted in the recognition of a lease liability of $122.0 million, with a corresponding right-of-use asset of $117.7 million, less an immaterial cumulative-effect decrease to retained earnings of $3.4 million related to our operating leases. There were also immaterial impacts to deferred income tax and income tax payable. This update did not have an impact on our results of operations, but it expanded our disclosures.

Accounting Updates Adopted in 2018:

ASC	Description	Date of Adoption	Effect on Financial Statements
ASC 230 "Statement of Cash Flows"	This update provided 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 addressed eight specific cash flow issues that relate to various types of transactions. The guidance was applied retrospectively.	January 1, 2018	The adoption of this update resulted in the reclassification of certain cash inflows between investing activities and operating activities within our consolidated statements of cash flows. The reclassification primarily related to cash distributions from equity method investees and the bifurcation of those distributions as either returns on investment or returns of investment which resulted in a reclassification of cash inflows from investing activities to operating activities. The remaining portion of the reclassification related to the receipt of proceeds from corporate-owned life insurance benefits which resulted in a reclassification of cash inflows from operating activities to investing activities. The adoption of this update had no effect on our financial position or results of operations.
ASC 606 "Revenue from Contracts with Customers"	These updates superseded virtually all existing guidance regarding the recognition of revenue from customers. Specifically excluded from the scope of these updates are insurance contracts, although our fee-based service products are included within the scope. Our fee-based service products, which are primarily sold in our Unum US segment, are reported in other income within our consolidated statements of income and represent less than one percent of our total revenue. 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. Accordingly, we continue to recognize revenue for these fee-based service products as services are rendered.	January 1, 2018	The adoption of these updates did not have an impact on our financial position or results of operations and did not result in expanded disclosures due to the immaterial nature of our fee-based service products relative to our overall business.

ASC	Description	Date of Adoption	Effect on Financial Statements
ASC 715 "Compensation - Retirement Benefits"	This update required the service cost component of net periodic pension and postretirement benefit costs to be included as a component of compensation costs in an entity's statement of income. Other components of net periodic pension and postretirement benefit costs are required to be presented separately from the service cost along with a disclosure identifying the line items in which these costs are presented in the statement of income. The amendments in this update were applied retrospectively or prospectively depending on the specific requirement of the update.	January 1, 2018	The adoption of this update resulted in the reclassification of service cost from the other expenses line item to the compensation expense line item on our consolidated statements of income but had no effect on our financial position or results of operations. We elected to use the practical expedient for the retrospective application of this update.
ASC 740 "Income Taxes"	This update eliminated the exception that required the tax effect of 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 required 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.	January 1, 2018	The adoption of this update did not have an impact on our financial position or results of operations.
ASC 815 "Derivatives and Hedge Accounting"	This update provided targeted improvements to accounting for hedging activities for both nonfinancial and financial risk components, aligns the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements, eases certain documentation and effectiveness assessment requirements, and enhances transparency through expanded disclosures. The amended presentation and disclosure guidance was adopted prospectively. Early adoption was permitted.	January 1, 2018	We elected to early adopt this update. The adoption of this update did not have an impact on our financial position or results of operations; however, it expanded our disclosures. This update also simplified hedge documentation requirements and expanded available hedging strategies.
ASC 825 "Financial Instruments - Overall"	This update changed 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 clarified 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 included 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 was applied using a modified retrospective approach through a cumulative-effect adjustment to accumulated other comprehensive income with a corresponding adjustment to retained earnings as of the beginning of the fiscal year of adoption.	January 1, 2018	The adoption of this update resulted in a cumulative-effect reduction to accumulated other comprehensive income of $17.5 million with a corresponding increase to retained earnings of $14.5 million, a decrease to other long-term investments of $3.8 million, and a decrease to deferred income tax liability of $0.8 million.