Investments | 5 . Investments Fixed Maturity Securities AFS Fixed Maturity Securities AFS by Sector The following table presents the fixed maturity securities AFS by sector. Redeemable preferred stock is reported within U.S. corporate and foreign corporate fixed maturity securities AFS. Included within fixed maturity securities AFS are structured securities including residential mortgage-backed securities (“RMBS”), asset-backed securities (“ABS”) and commercial mortgage-backed securities (“CMBS”) (collectively, “Structured Securities”). September 30, 2018 December 31, 2017 Amortized Gross Unrealized Estimated Amortized Gross Unrealized Estimated Temporary OTTI Temporary OTTI (In millions) Fixed maturity securities AFS: U.S. corporate $ 56,474 $ 2,803 $ 1,022 $ — $ 58,255 $ 53,291 $ 5,037 $ 238 $ — $ 58,090 U.S. government and agency 33,094 2,217 604 — 34,707 35,021 3,755 231 — 38,545 Foreign corporate 25,021 756 913 — 24,864 24,367 1,655 426 — 25,596 RMBS 22,023 826 521 (35 ) 22,363 21,735 1,039 181 (41 ) 22,634 ABS 8,795 44 24 — 8,815 7,808 73 15 — 7,866 State and political subdivision 6,172 852 42 — 6,982 6,310 1,245 3 1 7,551 CMBS 5,529 26 97 — 5,458 5,390 124 26 — 5,488 Foreign government 4,060 433 90 — 4,403 3,887 641 26 — 4,502 Total fixed maturity securities AFS $ 161,168 $ 7,957 $ 3,313 $ (35 ) $ 165,847 $ 157,809 $ 13,569 $ 1,146 $ (40 ) $ 170,272 __________________ (1) Noncredit OTTI losses included in AOCI in an unrealized gain position are due to increases in estimated fair value subsequent to initial recognition of noncredit losses on such securities. See also “— Net Unrealized Investment Gains (Losses).” The Company held non-income producing fixed maturity securities AFS with an estimated fair value of $23 million and $4 million , and unrealized gains (losses) of $0 and ($3) million at September 30, 2018 and December 31, 2017 , respectively. Maturities of Fixed Maturity Securities AFS The amortized cost and estimated fair value of fixed maturity securities AFS, by contractual maturity date, were as follows at September 30, 2018 : Due in One Year or Less Due After One Year Through Five Years Due After Five Years Through Ten Years Due After Ten Years Structured Securities Total Fixed Maturity Securities AFS (In millions) Amortized cost $ 9,061 $ 30,339 $ 29,664 $ 55,757 $ 36,347 $ 161,168 Estimated fair value $ 9,022 $ 30,528 $ 30,003 $ 59,658 $ 36,636 $ 165,847 Actual maturities may differ from contractual maturities due to the exercise of call or prepayment options. Fixed maturity securities AFS not due at a single maturity date have been presented in the year of final contractual maturity. Structured Securities are shown separately, as they are not due at a single maturity. Continuous Gross Unrealized Losses for Fixed Maturity Securities AFS by Sector The following table presents the estimated fair value and gross unrealized losses of fixed maturity securities AFS in an unrealized loss position, aggregated by sector and by length of time that the securities have been in a continuous unrealized loss position at: September 30, 2018 December 31, 2017 Less than 12 Months Equal to or Greater Less than 12 Months Equal to or Greater Estimated Gross Estimated Gross Estimated Gross Estimated Gross (Dollars in millions) Fixed maturity securities AFS: U.S. corporate $ 19,006 $ 695 $ 2,913 $ 327 $ 3,727 $ 57 $ 2,523 $ 181 U.S. government and agency 13,510 171 5,332 433 13,905 76 3,018 155 Foreign corporate 9,817 564 2,036 349 1,677 43 3,912 383 RMBS 9,615 276 3,267 210 3,673 30 3,332 110 ABS 4,321 17 177 7 732 3 358 12 State and political subdivision 935 32 111 10 106 1 120 3 CMBS 3,245 63 357 34 844 6 193 20 Foreign government 1,110 64 156 26 247 6 265 20 Total fixed maturity securities AFS $ 61,559 $ 1,882 $ 14,349 $ 1,396 $ 24,911 $ 222 $ 13,721 $ 884 Total number of securities in an unrealized loss position 4,912 1,116 1,295 1,103 Evaluation of AFS Securities for OTTI and Evaluating Temporarily Impaired AFS Securities As described more fully in Notes 1 and 8 of the Notes to the Consolidated Financial Statements included in the 2017 Annual Report, the Company performs a regular evaluation of all investment classes for impairment, including fixed maturity securities AFS and perpetual hybrid securities, in accordance with its impairment policy, in order to evaluate whether such investments are other-than-temporarily impaired. Current Period Evaluation Based on the Company’s current evaluation of its AFS securities in an unrealized loss position in accordance with its impairment policy, and the Company’s current intentions and assessments (as applicable to the type of security) about holding, selling and any requirements to sell these securities, the Company concluded that these securities were not other-than-temporarily impaired at September 30, 2018 . Future OTTI will depend primarily on economic fundamentals, issuer performance (including changes in the present value of future cash flows expected to be collected), changes in credit ratings, collateral valuation, interest rates and credit spreads. If economic fundamentals deteriorate or if there are adverse changes in the above factors, OTTI may be incurred in upcoming periods. Gross unrealized losses on fixed maturity securities AFS increased $2.2 billion during the nine months ended September 30, 2018 to $3.3 billion . The increase in gross unrealized losses for the nine months ended September 30, 2018 was primarily attributable to increases in interest rates, widening credit spreads and to a lesser extent, the impact of weakening foreign currencies on non-functional currency denominated fixed maturity securities AFS. At September 30, 2018 , $65 million of the total $3.3 billion of gross unrealized losses were from 18 fixed maturity securities AFS with an unrealized loss position of 20% or more of amortized cost for six months or greater. Investment Grade Fixed Maturity Securities AFS Of the $65 million of gross unrealized losses on fixed maturity securities AFS with an unrealized loss of 20% or more of amortized cost for six months or greater, $10 million , or 15% , were related to gross unrealized losses on three investment grade fixed maturity securities AFS. Unrealized losses on investment grade fixed maturity securities AFS are principally related to widening credit spreads since purchase and, with respect to fixed-rate fixed maturity securities AFS, rising interest rates since purchase. Below Investment Grade Fixed Maturity Securities AFS Of the $65 million of gross unrealized losses on fixed maturity securities AFS with an unrealized loss of 20% or more of amortized cost for six months or greater, $55 million , or 85% , were related to gross unrealized losses on 15 below investment grade fixed maturity securities AFS. Unrealized losses on below investment grade fixed maturity securities AFS are principally related to U.S. and foreign corporate securities (primarily industrial and utility securities) and CMBS and are the result of significantly wider credit spreads resulting from higher risk premiums since purchase, largely due to economic and market uncertainty. Management evaluates U.S. and foreign corporate securities based on factors such as expected cash flows and the financial condition and near-term and long-term prospects of the issuers and evaluates CMBS based on actual and projected cash flows after considering the quality of underlying collateral, expected prepayment speeds, current and forecasted loss severity, the payment terms of the underlying assets backing a particular security and the payment priority within the tranche structure of the security. Equity Securities Equity securities are summarized as follows at: September 30, 2018 December 31, 2017 Estimated Fair Value % of Total Estimated Fair Value % of Total (Dollars in millions) Equity securities: Common stock $ 487 57.9 % $ 1,251 75.5 % Non-redeemable preferred stock 354 42.1 407 24.5 Total equity securities $ 841 100.0 % $ 1,658 100.0 % In connection with the adoption of new guidance related to the recognition and measurement of financial instruments (see Note 1 ), effective January 1, 2018, the Company has reclassified its investment in common stock in regional banks of the Federal Home Loan Bank (“FHLB”) system from equity securities to other invested assets. These investments are carried at redemption value and are considered restricted investments until redeemed by the respective FHLB regional banks. The carrying value of these investments at December 31, 2017 was $733 million . Mortgage Loans Mortgage Loans by Portfolio Segment Mortgage loans are summarized as follows at: September 30, 2018 December 31, 2017 Carrying Value % of Total Carrying Value % of Total (Dollars in millions) Mortgage loans: Commercial $ 37,639 61.6 % $ 35,440 60.6 % Agricultural 13,190 21.6 12,712 21.8 Residential 10,271 16.8 10,058 17.2 Subtotal (1) 61,100 100.0 58,210 99.6 Valuation allowances (287 ) (0.5 ) (271 ) (0.5 ) Subtotal mortgage loans, net 60,813 99.5 57,939 99.1 Residential — FVO 323 0.5 520 0.9 Total mortgage loans, net $ 61,136 100.0 % $ 58,459 100.0 % __________________ (1) Purchases of mortgage loans, primarily residential mortgage loans, were $724 million and $1.7 billion for the three months and nine months ended September 30, 2018 , respectively, and $409 million and $1.9 billion for the three months and nine months ended September 30, 2017 , respectively. Information on commercial, agricultural and residential mortgage loans is presented in the tables below. Information on residential mortgage loans — FVO is presented in Note 7. The Company elects the FVO for certain residential mortgage loans that are managed on a total return basis. The carrying value of foreclosed mortgage loans included in real estate and real estate joint ventures was $42 million and $44 million at September 30, 2018 and December 31, 2017, respectively. Mortgage Loans, Valuation Allowance and Impaired Loans by Portfolio Segment Mortgage loans by portfolio segment, by method of evaluation of credit loss, impaired mortgage loans including those modified in a troubled debt restructuring, and the related valuation allowances, were as follows at: Evaluated Individually for Credit Losses Evaluated Collectively for Credit Losses Impaired Loans Impaired Loans with a Valuation Allowance Impaired Loans without a Valuation Allowance Unpaid Principal Balance Recorded Investment Valuation Unpaid Principal Balance Recorded Recorded Valuation Carrying (In millions) September 30, 2018 Commercial $ — $ — $ — $ — $ — $ 37,639 $ 186 $ — Agricultural 13 13 2 111 110 13,067 39 121 Residential — — — 420 377 9,894 60 377 Total $ 13 $ 13 $ 2 $ 531 $ 487 $ 60,600 $ 285 $ 498 December 31, 2017 Commercial $ — $ — $ — $ — $ — $ 35,440 $ 173 $ — Agricultural 22 21 2 27 27 12,664 38 46 Residential — — — 358 324 9,734 58 324 Total $ 22 $ 21 $ 2 $ 385 $ 351 $ 57,838 $ 269 $ 370 The average recorded investment for impaired commercial, agricultural and residential mortgage loans was $0 , $124 million and $369 million , respectively, for the three months ended September 30, 2018 ; and $0 , $104 million and $350 million , respectively, for the nine months ended September 30, 2018 . The average recorded investment for impaired commercial, agricultural and residential mortgage loans was $0 , $31 million and $297 million , respectively, for the three months ended September 30, 2017 ; and $6 million , $28 million and $275 million , respectively, for the nine months ended September 30, 2017 . Valuation Allowance Rollforward by Portfolio Segment The changes in the valuation allowance, by portfolio segment, were as follows: Nine Months 2018 2017 Commercial Agricultural Residential Total Commercial Agricultural Residential Total (In millions) Balance, beginning of period $ 173 $ 40 $ 58 $ 271 $ 167 $ 38 $ 62 $ 267 Provision (release) 13 1 8 22 4 4 10 18 Charge-offs, net of recoveries — — (6 ) (6 ) — (2 ) (11 ) (13 ) Balance, end of period $ 186 $ 41 $ 60 $ 287 $ 171 $ 40 $ 61 $ 272 Credit Quality of Commercial Mortgage Loans The credit quality of commercial mortgage loans was as follows at: Recorded Investment Estimated % of Debt Service Coverage Ratios % of > 1.20x 1.00x - 1.20x < 1.00x Total (Dollars in millions) September 30, 2018 Loan-to-value ratios: Less than 65% $ 31,661 $ 724 $ 12 $ 32,397 86.1 % $ 32,455 86.3 % 65% to 75% 3,648 367 55 4,070 10.8 4,053 10.8 76% to 80% 260 210 56 526 1.4 504 1.3 Greater than 80% 479 167 — 646 1.7 611 1.6 Total $ 36,048 $ 1,468 $ 123 $ 37,639 100.0 % $ 37,623 100.0 % December 31, 2017 Loan-to-value ratios: Less than 65% $ 29,346 $ 1,359 $ 198 $ 30,903 87.2 % $ 31,563 87.5 % 65% to 75% 3,245 95 114 3,454 9.7 3,465 9.6 76% to 80% 149 171 57 377 1.1 363 1.0 Greater than 80% 400 159 147 706 2.0 665 1.9 Total $ 33,140 $ 1,784 $ 516 $ 35,440 100.0 % $ 36,056 100.0 % Credit Quality of Agricultural Mortgage Loans The credit quality of agricultural mortgage loans was as follows at: September 30, 2018 December 31, 2017 Recorded Investment % of Total Recorded Investment % of Total (Dollars in millions) Loan-to-value ratios: Less than 65% $ 12,402 94.0 % $ 12,082 95.0 % 65% to 75% 751 5.7 581 4.6 76% to 80% 32 0.2 40 0.3 Greater than 80% 5 0.1 9 0.1 Total $ 13,190 100.0 % $ 12,712 100.0 % The estimated fair value of agricultural mortgage loans was $13.0 billion and $12.8 billion at September 30, 2018 and December 31, 2017 , respectively. Credit Quality of Residential Mortgage Loans The credit quality of residential mortgage loans was as follows at: September 30, 2018 December 31, 2017 Recorded Investment % of Total Recorded Investment % of Total (Dollars in millions) Performance indicators: Performing $ 9,881 96.2 % $ 9,614 95.6 % Nonperforming 390 3.8 444 4.4 Total $ 10,271 100.0 % $ 10,058 100.0 % The estimated fair value of residential mortgage loans was $10.7 billion and $10.6 billion at September 30, 2018 and December 31, 2017 , respectively. Past Due and Nonaccrual Mortgage Loans The Company has a high quality, well performing mortgage loan portfolio, with 99% of all mortgage loans classified as performing at both September 30, 2018 and December 31, 2017 . The Company defines delinquency consistent with industry practice, when mortgage loans are past due as follows: commercial and residential mortgage loans — 60 days and agricultural mortgage loans — 90 days. The past due and nonaccrual mortgage loans at recorded investment, prior to valuation allowances, by portfolio segment, were as follows at: Past Due Greater than 90 Days Past Due and Still Accruing Interest Nonaccrual September 30, 2018 December 31, 2017 September 30, 2018 December 31, 2017 September 30, 2018 December 31, 2017 (In millions) Commercial $ — $ — $ — $ — $ 167 $ — Agricultural 200 134 105 125 106 36 Residential 390 444 — — 390 444 Total $ 590 $ 578 $ 105 $ 125 $ 663 $ 480 Cash Equivalents The carrying value of cash equivalents, which includes securities and other investments with an original or remaining maturity of three months or less at the time of purchase, was $3.9 billion and $3.1 billion at September 30, 2018 and December 31, 2017 , respectively. Net Unrealized Investment Gains (Losses) Unrealized investment gains (losses) on fixed maturity securities AFS and equity securities and the effect on DAC, VOBA, deferred sales inducements (“DSI”), future policy benefits and the policyholder dividend obligation, that would result from the realization of the unrealized gains (losses), are included in net unrealized investment gains (losses) in AOCI. The components of net unrealized investment gains (losses), included in AOCI, were as follows: September 30, 2018 December 31, 2017 (In millions) Fixed maturity securities AFS $ 4,572 $ 12,349 Fixed maturity securities AFS with noncredit OTTI losses included in AOCI 35 40 Total fixed maturity securities AFS 4,607 12,389 Equity securities — 119 Derivatives 1,096 1,396 Other 66 1 Subtotal 5,769 13,905 Amounts allocated from: Future policy benefits (3 ) (19 ) DAC and VOBA related to noncredit OTTI losses recognized in AOCI (1 ) — DAC, VOBA and DSI (523 ) (790 ) Policyholder dividend obligation (456 ) (2,121 ) Subtotal (983 ) (2,930 ) Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI (7 ) (14 ) Deferred income tax benefit (expense) (992 ) (3,704 ) Net unrealized investment gains (losses) $ 3,787 $ 7,257 The changes in net unrealized investment gains (losses) were as follows: Nine Months (In millions) Balance, beginning of period $ 7,257 Cumulative effects of changes in accounting principles, net of income tax (Note 1) 1,310 Fixed maturity securities AFS on which noncredit OTTI losses have been recognized (5 ) Unrealized investment gains (losses) during the period (8,012 ) Unrealized investment gains (losses) relating to: Future policy benefits 16 DAC and VOBA related to noncredit OTTI losses recognized in AOCI (1 ) DAC, VOBA and DSI 267 Policyholder dividend obligation 1,665 Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI 7 Deferred income tax benefit (expense) 1,283 Balance, end of period $ 3,787 Change in net unrealized investment gains (losses) $ (3,470 ) Concentrations of Credit Risk There were no investments in any counterparty that were greater than 10% of the Company’s equity, other than the U.S. government and its agencies, at both September 30, 2018 and December 31, 2017 . Securities Lending Elements of the Company’s securities lending program are presented below at: September 30, 2018 December 31, 2017 (In millions) Securities on loan: (1) Amortized cost $ 14,069 $ 13,887 Estimated fair value $ 14,435 $ 14,852 Cash collateral received from counterparties (2) $ 14,786 $ 15,170 Security collateral received from counterparties (3) $ — $ 11 Reinvestment portfolio — estimated fair value $ 14,808 $ 15,188 __________________ (1) Included within fixed maturity securities AFS and short-term investments. (2) Included within payables for collateral under securities loaned and other transactions. (3) Security collateral received from counterparties may not be sold or re-pledged, unless the counterparty is in default, and is not reflected on the interim condensed consolidated financial statements. The cash collateral liability by loaned security type and remaining tenor of the agreements was as follows at: September 30, 2018 December 31, 2017 Remaining Tenor of Securities Lending Agreements Remaining Tenor of Securities Lending Agreements Open (1) 1 Month or Less Over 1 to 6 Months Total Open (1) 1 Month or Less Over 1 to 6 Months Total (In millions) Cash collateral liability by loaned security type: U.S. government and agency $ 2,309 $ 6,007 $ 6,470 $ 14,786 $ 2,927 $ 5,279 $ 6,964 $ 15,170 __________________ (1) The related loaned security could be returned to the Company on the next business day which would require the Company to immediately return the cash collateral. If the Company is required to return significant amounts of cash collateral on short notice and is forced to sell securities to meet the return obligation, it may have difficulty selling such collateral that is invested in securities in a timely manner, be forced to sell securities in a volatile or illiquid market for less than what otherwise would have been realized under normal market conditions, or both. The estimated fair value of the securities on loan related to the cash collateral on open at September 30, 2018 was $2.3 billion , 99% of which were U.S. government and agency securities which, if put back to the Company, could be immediately sold to satisfy the cash requirement. The reinvestment portfolio acquired with the cash collateral consisted principally of fixed maturity securities AFS (including U.S. government and agency securities, agency RMBS and ABS), short-term investments and cash equivalents with 67% invested in U.S. government and agency securities, agency RMBS, short-term investments, cash equivalents or held in cash. If the securities on loan or the reinvestment portfolio become less liquid, the Company has the liquidity resources of most of its general account available to meet any potential cash demands when securities on loan are put back to the Company. Repurchase Agreements Elements of the Company’s short-term repurchase agreements are presented below at: September 30, 2018 December 31, 2017 (In millions) Securities on loan: (1) Amortized cost $ 2,468 $ 900 Estimated fair value $ 2,508 $ 1,031 Cash collateral received from counterparties (2) $ 2,460 $ 1,000 Security collateral received from counterparties (3) $ 8 $ — Reinvestment portfolio — estimated fair value $ 2,462 $ 1,000 __________________ (1) Included within fixed maturity securities AFS, short-term investments and cash equivalents. (2) Included within payables for collateral under securities loaned and other transactions. (3) Security collateral received from counterparties may not be sold or re-pledged, unless the counterparty is in default, and is not reflected on the interim condensed consolidated financial statements. The cash collateral liability by loaned security type and remaining tenor of the agreements was as follows at: September 30, 2018 December 31, 2017 Remaining Tenor of Repurchase Agreements Remaining Tenor of Repurchase Agreements 1 Month or Less Total 1 Month or Less Total (In millions) Cash collateral liability by loaned security type: U.S. government and agency $ 2,460 $ 2,460 $ 1,000 $ 1,000 The reinvestment portfolio acquired with the cash collateral consisted principally of fixed maturity securities AFS (including U.S. government and agency securities, agency RMBS and ABS), short-term investments and cash equivalents with 68% invested in U.S. government and agency securities, agency RMBS, short-term investments, cash equivalents or held in cash. If the securities on loan or the reinvestment portfolio become less liquid, the Company has the liquidity resources of most of its general account available to meet any potential cash demands when securities on loan are put back to the Company. Invested Assets on Deposit and Pledged as Collateral Invested assets on deposit and pledged as collateral are presented below at estimated fair value for all asset classes, except mortgage loans, which are presented at carrying value at: September 30, 2018 December 31, 2017 (In millions) Invested assets on deposit (regulatory deposits) $ 47 $ 49 Invested assets pledged as collateral 20,753 20,775 Total invested assets on deposit and pledged as collateral $ 20,800 $ 20,824 The Company has pledged invested assets in connection with various agreements and transactions, including funding agreements (see Note 4 of the Notes to the Consolidated Financial Statements included in the 2017 Annual Report) and derivative transactions (see Note 6 ). Amounts in the table above include invested assets and cash and cash equivalents. See “— Securities Lending” and “— Repurchase Agreements” for information regarding securities on loan, Note 4 for information regarding investments designated to the closed block and “— Equity Securities” for information on common stock holdings in regional banks of the FHLB system, which are considered restricted investments. Variable Interest Entities The Company has invested in legal entities that are VIEs. In certain instances, the Company holds both the power to direct the most significant activities of the entity, as well as an economic interest in the entity and, as such, is deemed to be the primary beneficiary or consolidator of the entity. The determination of the VIE’s primary beneficiary requires an evaluation of the contractual and implied rights and obligations associated with each party’s relationship with or involvement in the entity, an estimate of the entity’s expected losses and expected residual returns and the allocation of such estimates to each party involved in the entity. Consolidated VIEs Creditors or beneficial interest holders of VIEs where the Company is the primary beneficiary have no recourse to the general credit of the Company, as the Company’s obligation to the VIEs is limited to the amount of its committed investment. The following table presents the total assets and total liabilities relating to investment-related VIEs for which the Company has concluded that it is the primary beneficiary and which are consolidated at: September 30, 2018 December 31, 2017 Total Assets Total Liabilities Total Assets Total Liabilities (In millions) Real estate joint ventures (1) $ 1,194 $ — $ 1,077 $ — Renewable energy partnership (2) 107 — 116 3 Investment fund (primarily mortgage loans) (3) 215 — — — Other investments 31 5 32 6 Total $ 1,547 $ 5 $ 1,225 $ 9 __________________ (1) The Company’s investment in these affiliated real estate joint ventures was $1.1 billion and $1.0 billion at September 30, 2018 and December 31, 2017 , respectively. Other affiliates’ investments in these affiliated real estate joint ventures was $113 million and $85 million at September 30, 2018 and December 31, 2017 , respectively. (2) Assets of the renewable energy partnership primarily consisted of other invested assets. (3) The Company’s investment in this affiliated investment fund was $175 million at September 30, 2018 . Other affiliates’ investments in this affiliated investment fund was $40 million at September 30, 2018 . Unconsolidated VIEs The carrying amount and maximum exposure to loss relating to VIEs in which the Company holds a significant variable interest but is not the primary beneficiary and which have not been consolidated were as follows at: September 30, 2018 December 31, 2017 Carrying Amount Maximum Exposure to Loss (1) Carrying Amount Maximum Exposure to Loss (1) (In millions) Fixed maturity securities AFS: Structured Securities (2) $ 34,663 $ 34,663 $ 34,284 $ 34,284 U.S. and foreign corporate 915 915 1,166 1,166 Other limited partnership interests 3,778 6,149 3,561 5,765 Other invested assets 1,755 1,934 2,172 2,506 Real estate joint ventures 36 40 38 43 Total $ 41,147 $ 43,701 $ 41,221 $ 43,764 __________________ (1) The maximum exposure to loss relating to fixed maturity securities AFS is equal to their carrying amounts or the carrying amounts of retained interests. The maximum exposure to loss relating to other limited partnership interests and real estate joint ventures is equal to the carrying amounts plus any unfunded commitments. For certain of its investments in other invested assets, the Company’s return is in the form of income tax credits which are guaranteed by creditworthy third parties. For such investments, the maximum exposure to loss is equal to the carrying amounts plus any unfunded commitments, reduced by income tax credits guaranteed by third parties of $100 million and $117 million at September 30, 2018 and December 31, 2017 , respectively. Such a maximum loss would be expected to occur only upon bankruptcy of the issuer or investee. (2) For these variable interests, the Company’s involvement is limited to that of a passive investor in mortgage-backed or asset-backed securities issued by trusts that do not have substantial equity. As described in Note 12 , the Company makes commitments to fund partnership investments in the normal course of business. Excluding these commitments, the Company did not provide financial or other support to investees designated as VIEs during both the nine months ended September 30, 2018 and 2017 . During the three months ended September 30, 2018, the Company securitized certain residential mortgage loans and acquired an interest in the related RMBS issued. While the Company has a variable interest in the issuer of the securities, it is not the primary beneficiary of the issuer of the securities since it does not have any rights to remove the servicer or veto rights over the servicer’s actions. During the three months ended September 30, 2018, the carrying value and the estimated fair value of the mortgage loans sold were $451 million and $478 million , respectively, resulting in a gain of $27 million , which was included within net investment gains (losses). The estimated fair value of the RMBS acquired in connection with the securitization was $102 million , which was included in the carrying amount and maximum exposure to loss for Structured Securities presented above. See Note 7 for information on how the estimated fair value of mortgage loans and RMBS is determined, the valuation approaches and key inputs, their placement in the fair value hierarchy, and for certain RMBS, quantitative information about the significant unobservable inputs and the sensitivity of their estimated fair value to changes in those inputs. Net Investment Income The components of net investment income were as follows: Three Months Nine Months 2018 2017 2018 2017 (In millions) Investment income: Fixed maturity securities AFS $ 1,849 $ 1,764 $ 5,450 $ 5,274 Equity securities 8 20 29 68 Mortgage loans 728 697 2,087 1,989 Policy loans 79 77 224 230 Real estate and real estate joint ventures 118 104 371 327 Other limited partnership interests 153 163 388 506 Cash, cash equivalents and short-term investments 38 20 87 54 Operating joint venture 2 6 23 12 Other 63 49 206 154 Subtotal 3,038 2,900 8,865 8,614 Less: Investment expenses 252 240 694 659 Net investment income $ 2,786 $ 2,660 $ 8,171 $ 7,955 See “— Related Party Investment Transactions” for discussion of affiliated net investment income and investment expenses. The Company invests in real estate joint ventures, other limited partnership interests and tax credit and renewable energy partnerships, and also does business through an operating joint venture, t he majority of which is accounted for under the equity method. Net investment income from other limited partnership interests and operating joint venture, accounted for under the equity method; and real estate joint ventures and tax credit and renewable energy partnerships, primarily accounted for under the equity method, totaled $98 million and $288 million for the three months and nine months ended September 30, 2018 , respectively, and $106 million and $293 million for the three months and nine months ended September 30, 2017 , re spectively. Net Investment Gains (Losses) Components of Net Investment Gains (Losses) The components of net investment gains (losses) were as follows: Three Months Nine Months 2018 2017 2018 2017 (In millions) Total gains (losses) on fixed maturity securities AFS: Total OTTI losses recognized — by sector and industry: U.S. and foreign corporate securities — by industry: Consumer $ — $ (5 ) $ — $ (5 ) Total U.S. and foreign corporate securities — (5 ) — (5 ) State and political subdivision — — — (1 ) OTTI losses on fixed maturity securities AFS recognized in earnings — (5 ) — (6 ) Fixed maturity securities AFS — net gains (losses) on sales and disposals 137 1 28 41 Total gains (losses) on fixed maturity securities AFS 137 (4 ) 28 35 Total gains (losses) on equity securities: OTTI losses recognized — by security type: Common stock — (4 ) — (16 ) Non-redeemable preferred stock — — — (1 ) Total OTTI losses on equity securities recognized in earnings — (4 ) — (17 ) Equity securities — net gains (losses) on sales and disposals 8 — 16 1 Change in estimated fair value of equity securities (1) 1 — (38 ) — Total gains (losses) on equity securities 9 (4 ) (22 ) (16 ) Mortgage loans 8 (16 ) (25 ) (44 ) Real estate and real estate joint ventures 39 169 139 436 Other limited partnership interests — (30 ) 8 (44 ) Other (2) 8 21 (171 ) (90 ) Subtotal 201 136 (43 ) 277 Change in estimated fair value of other limited partnership interests and real estate joint ventures 12 — 5 — Non-investment portfolio gains (losses) (8 ) (40 ) 17 (93 ) Subtotal 4 (40 ) 22 (93 ) Total net investment gains (losses) $ 205 $ 96 $ (21 ) $ 184 __________________ (1) C hanges in estimated fair value subsequent to purchase for equity securities still held as of the end of the period included in net investment gains (losses) were $5 million and ($22) million for the three months and nine months ended September 30, 2018 , respectively. See Note 1 . (2) Other gains (losses) included a renewable energy partnership realized loss of $0 and $83 million for the three months and nine months ended September 30, 2018 , respectively, and a leveraged lease impairment of $0 and $105 million for the three months and nine months ended September 30, 2018 , respectively. See “— Related Party Investment Transactions” for discussion of affiliated net investment gains (losses) related to transfers of invested assets to affiliates. Gains (losses) from foreign currency transacti |