We sponsor several defined benefit pension and other postretirement benefit (OPEB) plans for our employees, including non-qualified pension plans. The U.S. defined benefit pension plans comprise the majority of our total benefit obligation and pension expense. Our U.K. operation maintains a separate defined benefit plan for eligible employees. The U.S. defined benefit pension plans were closed to new entrants on December 31, 2013, and the U.K. defined benefit pension plan was closed to new entrants on December 31, 2002. In 2013, we adopted plan amendments which freeze participation and benefit accruals in our U.S. qualified and non-qualified defined benefit pension plans, effective December 31, 2013. Also in 2013, we adopted amendments to our U.K. pension plan which freeze participation in the plan effective June 30, 2014 and which reduce the maximum rate of inflation indexation from 5.0 percent to 2.5 percent for pension benefits which were earned prior to April 1997 effective at the date of adoption.
The discount rate we used to determine our net periodic benefit costs for our U.S. pension plans for 2014 was 5.30 percent and for 2013 was 4.50 percent for the period January 1, 2013 through the date of remeasurement and 5.00 percent for the period from the date of remeasurement through December 31, 2013. The discount rate used for the net periodic benefit costs for our U.K. pension plan for 2014 was 4.40 percent and for 2013 was 4.50 percent for the period January 1, 2013 through the date of remeasurement and 4.60 percent from the date of remeasurement through December 31, 2013. The discount rate used in the net periodic benefit cost for our OPEB plan for 2014 and 2013 was 5.00 percent and 4.20 percent, respectively.
The long-term rate of return on asset assumption used in the net periodic pension costs for our U.S. qualified defined benefit pension plan for 2014 and 2013 was 7.50 percent for both years. The long-term rate of return on asset assumption used for our U.K. pension plan for 2014 was 6.10 percent and for 2013 was 6.20 percent for the period from January 1, 2013 to the date of remeasurement and 6.35 percent from the date of remeasurement through December 31, 2013. The long-term rate of return on asset assumption used for our OPEB plan was 5.75 percent for both years. The actual rate of return on plan assets is determined based on the fair value of the plan assets at the beginning and the end of the period, adjusted for contributions and benefit payments.
In July 2013, the Financial Accounting Standards Board (FASB) issued a proposed Accounting Standards Update (ASU) on insurance contracts that is intended to bring greater consistency to the accounting for contracts that transfer significant risk between parties and would require a current measure of insurance contracts, including the use of updated assumptions and discounting. The proposed ASU, which would supersede existing guidance on accounting for insurance contracts, calls for retrospective application and would prohibit early adoption. The proposal did not specify an effective date, but instead requested feedback on the appropriate timing.
For additional information on new accounting standards and the impact, if any, on our financial position or results of operations, see Note 1 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.
Other expenses, including compensation expense, were in aggregate lower in 2013 and 2012 relative to the prior year periods due in part to our continued focus on operating effectiveness and expense management. Also contributing to the decline in 2013 relative to 2012 was a reduction in the amortization of our net actuarial loss due to pension plan amendments adopted in 2013 as well as expense reductions associated with reinsurance agreements entered into during 2013. Partially offsetting the lower expenses resulting from active expense management were increased costs for our pension and other postretirement benefit plans in 2012 as compared to 2011. For further discussion of the 2013 pension plan amendments, see Note 9 in the "Notes to Consolidated Financial Statements" contained herein in Item 8.
Risk results for the individual disability - recently issued product line were favorable during 2013 compared to 2012 due to higher claim recoveries and the impact of a release of active life reserves related to the termination of a large inforce policy in 2013. Risk results for voluntary benefits were unfavorable compared to 2012 as a result of the previously discussed reserve increase for unclaimed death benefits. Excluding this reserve increase, risk results for voluntary benefits were slightly favorable in 2013 compared to the prior year due to favorable experience in the life and critical illness product lines.
Certain risks and uncertainties are inherent in the disability insurance business. Components of claims experience, such as incidence and recovery rates, may be worse than we expect. Disability claim incidence and claim recovery rates may be influenced by, among other factors, the rate of unemployment and consumer confidence. Within the group disability market, pricing and renewal actions can be taken to react to higher claim rates or lower discount rates, but these actions take time to implement, and there is a risk that the market will not sustain increased prices. In addition, changes in economic and external conditions may not manifest themselves in claims experience for an extended period of time. The current economic conditions may lead to a higher rate of claim incidence, lower levels of claim recoveries, or lower claim discount rates. We have previously taken steps to improve our risk profile, including reducing our exposure to volatile business segments through diversification by market size, product segment, and industry segment. Claim incidence levels may fluctuate due to the normal volatility that occurs in group disability business or may be related to economic conditions. We continuously monitor key indicators to assess our risks and attempt to adjust our business plans accordingly.
Operating revenue and income for this segment will continue to decline over time as these closed blocks of business wind down, although we do expect additional premium income associated with long-term care rate increases. We also expect a small amount of group long-term care certificates to continue to be issued where we are required to do so under the terms of existing group policies. We expect that this segment may experience volatility in net investment income due to the volatility of bond call premiums relative to historical levels. During 2014, we intend to continue our focus on operational effectiveness, rate increases, and capital management. We continuously monitor key indicators to assess our risks and attempt to adjust our business plans accordingly.
We review these investment policies and guidelines annually, or more frequently if deemed necessary, and recommend adjustments, as appropriate. Any revisions or exceptions are reviewed by the finance committee of Unum Group's board of directors and must be approved by the boards of directors of our insurance subsidiaries.
Reserves for Policy and Contract Benefits: Policy reserves represent future policy and contract benefits for claims not yet incurred. Policy reserves for traditional 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. Interest rate assumptions are based on actual and expected net investment returns. Persistency assumptions are based on our actual historical experience adjusted for future expectations. Morbidity and mortality assumptions 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.
Premium Tax Expense: Premium tax expense is included in other expenses in the consolidated statements of income. For the years ended December 31, 2013, 2012, and 2011, premium tax expense was $137.0 million, $136.0 million, and $134.9 million, respectively.
In October 2010, the FASB issued an update to address the diversity in practice regarding the interpretation of which costs relating to the acquisition of new or renewal insurance contracts qualify as deferred acquisition costs. The amendments in the update require that only incremental direct costs associated with the successful acquisition of a new or renewal insurance contract can be capitalized. All other costs are to be expensed as incurred. We adopted this update effective January 1, 2012 and applied the amendments retrospectively, adjusting all prior periods in our consolidated financial statements and accompanying notes.
As of December 31, 2013 and 2012, we had $630.4 million and $508.8 million, respectively, notional amount of receive fixed, pay fixed, open current and forward foreign currency swaps to hedge fixed income foreign currency-denominated securities and long-term debt. During 2013, we entered into $150.0 million notional amount of receive fixed, pay fixed foreign currency swaps to hedge the currency risk on a portion of the U.S. dollar-denominated debt issued by one of our U.K. subsidiaries. As of December 31, 2012, we had $150.0 million notional amount of receive fixed, pay variable forward starting interest rate swaps to hedge the anticipated purchase of fixed maturity securities. These interest rate swaps were terminated as scheduled in 2013.