Dividends in 2016, 2015 and 2013 include a special $2.00 per share cash dividend to Class A and B common shareholders.
Amortization of deferred acquisition costs and the value of insurance in force changed in 2016 and 2015, compared to prior periods, due to changes in actual and expected profits on the underlying business. Amortization, as well as reserves held on certain interest sensitive products, also changed due to the impact of unlocking. Unlocking generally reflects changes in our projected earned spreads, policy lapses and mortality assumptions. During 2016 and 2014, we also unlocked our assumptions as a result of our analysis of the impact of the low interest rate environment on projected investment and spread income. The impact of unlocking on pre-tax operating income was as follows:
Pre-tax operating income for the Corporate and Other segment increased in 2016, compared to 2015, primarily due to decreases in pre-tax equity loss and amortization of deferred acquisition costs from the impact of unlocking and market performance on our variable business, partially offset by increases in death benefits. Pre-tax operating income decreased in 2015, compared to 2014, primarily due to increases in pre-tax equity loss and in the amortization of deferred acquisition costs from the impact of unlocking and market performance on our variable business.
interest rate environment on projected investment and spread income. The impact of unlocking on pre-tax operating income for the three years was as follows:
Equity loss, before tax, includes our proportionate share of gains and losses attributable to our ownership interest in partnerships, joint ventures and certain companies where we exhibit some control but have a minority ownership interest. Given the timing of availability of financial information from our equity investees, we consistently use information that is as much as three months in arrears for certain of these entities. Several of these entities are investment companies whose operating results are derived primarily from unrealized and realized gains and losses generated by their investment portfolios. As is normal with these types of entities, the level of these gains and losses is subject to fluctuation from period to period depending on the prevailing economic environment, changes in prices of bond and equity securities held by the investment partnerships, timing and success of initial public offerings or exit strategies, and the timing of the sale of investments held by the partnerships and joint ventures. Our low income housing tax credit investments generate pre-tax losses but after-tax gains as the related tax credits are realized. The timing of the realization of tax credits is subject to fluctuation from period to period due to the timing of housing project completions and the approval of tax credits. Equity income, net of related income taxes, was as follows:
Our investment portfolio increased 5.9% to $8,174.7 million at December 31, 2016, compared to $7,722.8 million at December 31, 2015. The portfolio increased due to positive cash flows from operating and financing activities as well as an increase of $89.2 million of net unrealized appreciation of fixed maturities during 2016. Additional details regarding securities in an unrealized gain or loss position at December 31, 2016 are included in the discussion that follows and in Note 2 to our consolidated financial statements included in Item 8. Details regarding investment impairments are discussed above in the "Realized Gains (Losses) on Investments" section under "Results of Operations."
In March 2016, the FASB issued guidance that will impact the accounting for share-based compensation. The guidance will impact several areas including the accounting for excess tax benefits and deficiencies, classification of excess tax benefits within the consolidated statement of cash flows and the accounting for forfeitures. The guidance becomes effective for fiscal years beginning after December 15, 2016. Certain requirements must be adopted prospectively, while others are required to be adopted on a modified prospective basis, or retroactively. We expect the impact of this new guidance on our consolidated financial statements to be immaterial given our limited use of share-based compensation impacted by the new guidance.
In February 2016, the FASB issued a new lease accounting standard, which, for most lessees, will result in a gross-up of the balance sheet. Under the new standard, lessees will recognize the leased assets on the balance sheet and will recognize a corresponding liability for the present value of lease payments over the lease term. The new standard requires the application of judgment and estimates. Also, there are accounting policy elections that may be taken both at transition and for the accounting post-transition, including whether to adopt a short-term lease recognition exemption. The guidance becomes effective for fiscal years beginning after December 15, 2018, with early adoption permitted. The new standard will be applied as of the beginning of the earliest comparative period presented in the financial statements (date of initial application). We are currently evaluating the impact of this guidance on our consolidated financial statements.
Prior year values have been updated for comparability with the amounts as presented under the new accounting guidance discussed in Note 1.
and other instruments that are not widely traded. For those securities for which an externally provided fair value is not available we use cash flow modeling techniques to estimate fair value.
Certain annuity contracts include embedded derivatives that are measured at fair value on a recurring basis. These embedded derivatives are a Level 3 measurement. The fair value of the embedded derivatives is based on the discounted excess of projected account values (including a risk margin) over projected guaranteed account values. The key unobservable inputs required in the projection of future values that require management judgment include the risk margin as well as the credit risk of our company. Should the risk margin increase or the credit risk decrease the discounted cash flows and the estimated fair value of the obligation will increase.
We invest in LIHTC, which generate pre-tax losses but after-tax gains as the related tax credits are realized. The timing of the realization of tax credits is subject to fluctuation from period to period due to the timing of housing project completions and the approval of tax credits. These tax credits, which are reported in equity income, totaled $14.1 million in 2016, $13.5 million in 2015 and $12.2 million in 2014.
We issue new shares to satisfy stock option exercises. Cash received from stock options exercised totaled $2.5 million for 2016, $3.7 million for 2015 and $10.5 million for 2014. The actual tax benefit realized from stock options exercised totaled $1.0 million for 2016, $1.4 million for 2015 and $2.2 million for 2014.