If we are unable to price a fixed maturity security using prices from third party pricing vendors or other sources specific to the asset class, we may obtain a broker quote or utilize an internal pricing model specific to the asset utilizing relevant market information, to the extent available and where at least one significant unobservable input is utilized. These are reflected in Level 3 in the fair value hierarchy and can include fixed maturities across all asset classes. As of December 31, 2017, less than 1% of our total fixed maturities were Level 3 securities valued using internal pricing models. See Item 8. "Financial Statements and Supplementary Data, Notes to Consolidated Financial Statements, Note 14, Fair Value Measurements" for further discussion.
We use certain over-the-counter ("OTC") interest rate contracts that are subject to derivative clearing agreements. These agreements require the daily cash settlement of variation margin based on changes in the fair value of the derivative instrument. Prior to 2017, variation margin for all such interest rate contracts was treated as collateral, which was accounted for separately as an interest-bearing asset or liability. For reporting purposes, we did not offset fair value amounts recognized for the right to reclaim variation margin collateral or the obligation to return variation margin collateral against fair value amounts recognized for derivative instruments executed with the same counterparties under master netting agreements.
We have defined claim frequency as follows for each short-duration product:
The amortization expense for intangible assets with finite useful lives was $45.4 million, $44.5 million and $42.5 million for 2017, 2016 and 2015, respectively. As of December 31, 2017, the estimated amortization expense for the next five years is as follows (in millions):
For those securities that had been in a continuous unrealized loss position greater than or equal to twelve months, Principal Life's consolidated portfolio held 453 securities with a carrying value of $2,369.5 million and unrealized losses of $230.5 million. The average credit rating of this portfolio was A- with an average price of 91 as of December 31, 2016. Of the $230.5 million in unrealized losses, the corporate sector accounts for $141.9 million in unrealized losses with an average price of 89 and an average credit rating of BBB-. The remaining unrealized losses consist primarily of $46.9 million within the commercial mortgage-backed securities sector with an average price of 93 and an average credit rating of AA-. The unrealized losses on these securities can primarily be attributed to changes in market interest rates and changes in credit spreads since the securities were acquired.
Our residential mortgage loan portfolio is composed of home equity mortgages with an amortized cost of $23.0 million and $165.6 million and first lien mortgages with an amortized cost of $1,262.9 million and $1,054.3 million as of December 31, 2017 and December 31, 2016, respectively. Our home equity mortgages decreased due to sales during the fourth quarter of 2017. Our residential home equity mortgages are concentrated in the United States and are generally second lien mortgages comprised of closed-end loans and lines of credit. Our first lien loans are concentrated in Chile and the United States.
ownership rights on these instruments, they are reported as fixed maturities, available-for-sale and mortgage loans, respectively, on our consolidated statements of financial position. Of the securities posted as collateral, as of December 31, 2017 and 2016, $173.3 million and $272.8 million, respectively, could be sold or repledged by the secured party.
These credit derivative transactions are subject to events of default defined within the terms of the contract, which normally consist of bankruptcy, failure to pay, or modified restructuring of the reference entity and/or issue. If a default event occurs for a reference name or security, we are obligated to pay the counterparty an amount equal to the notional amount of the credit derivative transaction. As a result, our maximum future payment is equal to the notional amount of the credit derivative. In certain cases, we also have purchased credit protection with identical underlyings to certain of our sold protection transactions. As of December 31, 2017 and December 31, 2016, we did not purchase credit protection relating to our sold protection transactions. In certain circumstances, our potential loss could also be reduced by any amount recovered in the default proceedings of the underlying credit name.
The maximum length of time we are hedging our exposure to the variability in future cash flows for forecasted transactions, excluding those related to the payments of variable interest on existing financial assets and liabilities, is 2.5 years. As of December 31, 2017, we had $0.0 million of net gains reported in AOCI on the consolidated statements of financial position related to active hedges of forecasted transactions. If a hedged forecasted transaction is no longer probable of occurring, cash flow hedge accounting is discontinued. If it is probable that the hedged forecasted transaction will not occur, the deferred gain or loss is immediately reclassified from AOCI into net income. During 2017 and 2016, we did not have any reclassifications from AOCI into net realized capital gains (losses) as a result of the determination that hedged cash flows were probable of not occurring.
A policyholder dividend obligation ("PDO") is required to be established for earnings in the Closed Block that are not available to stockholders. A model of the Closed Block was established to produce the pattern of expected earnings, assets and liabilities in the Closed Block, adjusted to eliminate the impact of related amounts in AOCI. These projections are utilized to determine ratios that will allow us to compare actual cumulative earnings to expected cumulative earnings.
certain jurisdictions. As of December 31, 2017 and 2016, valuation allowances of $5.2 million and $7.3 million, respectively, had been recorded against the income tax benefits associated primarily with foreign net operating loss carryforwards. Adjustments to the valuation allowance will be made if there is a change in management's assessment of the amount of the deferred income tax assets that are more likely than not to be realized. Provisions of the U.S. tax reform did not affect the valuation allowance assessment.
(2)The portfolios invest primarily in publicly traded equity securities of large U.S. companies.
(5)Certain investments are measured at fair value using the NAV per share (or its equivalent) practical expedient and have not been classified in the fair value hierarchy. Other investments using the NAV practical expedient consist of certain fund interests that are restricted until maturity with unfunded commitments totaling $46.1 million and $57.6 million as of December 31, 2017 and December 31, 2016, respectively. Separate account assets using the NAV practical expedient consist of hedge funds with varying investment strategies that also have a variety of redemption terms and conditions. We do not have unfunded commitments associated with these hedge funds.
As of December 31, 2017, a total of 2.9 million of new shares were available to be made issuable by us for this plan.