As noted in the Consolidated Operations discussion, the Company unlocked the DPAC balance for this segment during 2016 for favorable mortality and for future profit projections related to universal life insurance riders which had not been previously included in DPAC actuarial software models. The latter unlocking increased DPAC balances $0.8 million (decreasing amortization expense) and was recorded in the fourth quarter. The true-up adjustments recorded in each year increased the DPAC balance which conversely reduced amortization expense by a like amount for each year. These true-up adjustments reflect favorable outcomes compared to anticipated experience.
Consistent with the domestic and international life segments, the Company records true-up adjustments to DPAC balances each period to reflect current policy lapse or termination rates, expense levels and credited rates on policies as compared to anticipated experience as well as unlocking adjustments as necessary. The following table identifies the effects of unlocking and true-up adjustments on annuity DPAC balances recorded through amortization expense for 2016, 2015 and 2014.
The fluctuation in reported contract interest amounts for fixed-index annuities is driven by sales levels, the level of the business in force and the effect of positive or negative market returns of option values on projected interest credits. As noted above in the net investment income discussion, the amounts shown for contract interest for fixed-index annuities generally align with the derivative gains/(losses) included in net investment income as the impact of the market value change of index options on asset values aligns closely with the movement of the embedded derivative liability held for these products. However, during periods of equity market movements (gains or losses), in tandem with Company changes in asset management fees assessed on these products (increases or decreases), deviations can occur between index option asset values and the embedded derivative liability. During the years ended December 31, 2016, 2015, and 2014, contract interest was increased/(decreased) by ($15.9 million), $2.0 million, and ($6.5 million), respectively, for this occurrence.
The Company's primary business encompasses its domestic and international life insurance operations and its annuity operations. However, the Company also has small real estate, nursing home, and other investment operations through its wholly-owned subsidiaries. Nursing home operations generated $0.3 million, $1.3 million and $1.6 million of pre-tax earnings in 2016, 2015, and 2014, respectively. The remaining pre-tax earnings in Other Operations of $23.0 million, $29.8 million, and $21.0 million for the years ended December 31, 2016, 2015, 2014, respectively, represent investment income from real estate, municipal bonds, and common and preferred equities held in subsidiary company portfolios principally for tax-advantage purposes. Included in these amounts are semi-annual distributions from a life interest in the Libby Shearn Moody Trust which is an asset held in NWLSM, Inc. Pretax distributions from this trust were $6.0 million, $7.0 million, and $6.0 million in 2016, 2015, and 2014, respectively. In addition to pretax distributions, the 2015 amount also includes additional revenue recorded associated with revaluing the actuarial life interest in the Libbie Shearn Moody Trust.
The Company's overall conservative investment philosophy is reflected in the allocation of its investments, which is detailed below as of December 31, 2016 and 2015. The Company emphasizes investment grade debt securities.
The Company maintains a diversified portfolio which consists mostly of corporate, mortgage-backed, and public utility fixed income securities. Investments in mortgage-backed securities primarily include U.S. government agency pass-through securities and collateralized mortgage obligations ("CMO"). The Company's investment guidelines prescribe limitations by type of security as a percent of the total investment portfolio and all holdings were within these threshold limits. As of December 31, the Company's debt securities portfolio consisted of the following for 2016 and 2015:
The Company requires a minimum specified yield on mortgage loan investments determined by reference to currently available debt security instrument yields, plus a desired amount of incremental basis points. During the past several years, the low interest rate environment has resulted in fewer loan opportunities being available that meet the Company's required rate of return. However, the Company made a concerted effort to grow this part of its investment portfolio during 2016. Mortgage loans originated by the Company totaled $84.6 million and $38.5 million for the years 2016 and 2015, respectively.
The contractual maturities of mortgage loan principal balances at December 31, 2016 and 2015 were as follows:
The Company's market risk liabilities, which include policy liabilities for annuity and supplemental contracts, are managed for interest rate risk through cash flow testing as previously described. As part of this cash flow testing, the Company has analyzed the potential impact on net earnings of a 100 basis point decrease and increases in increments of 100 basis points in the U.S. Treasury yield curve as of December 31, 2016. The potential impact on net earnings from these interest rate changes are summarized below.