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Investments (Tables) | 12 Months Ended
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Dec. 31, 2017
Investments [Abstract] |
Net investment income | The significant components of Net investment income are presented in the following table.
Years ended December 31 |  |  |  |  |
(In millions) | 2017 |  | 2016 |  | 2015
Fixed maturity securities | $ | 1,812 |  |  | $ | 1,819 |  |  | $ | 1,751 |
Equity securities | 12 |  |  | 10 |  |  | 12 |
Limited partnership investments | 207 |  |  | 155 |  |  | 92 |
Mortgage loans | 34 |  |  | 41 |  |  | 33 |
Short term investments | 15 |  |  | 8 |  |  | 6 |
Trading portfolio | 12 |  |  | 10 |  |  | 8 |
Other | 1 |  |  | 4 |  |  | 1 |
Gross investment income | 2,093 |  |  | 2,047 |  |  | 1,903 |
Investment expense | (59 | ) |  | (59 | ) |  | (63 | )
Net investment income | $ | 2,034 |  |  | $ | 1,988 |  |  | $ | 1,840 |
Net realized investment gains (losses) | Net realized investment gains (losses) are presented in the following table.
Years ended December 31 |  |  |  |  |
(In millions) | 2017 |  | 2016 |  | 2015
Net realized investment gains (losses): |  |  |  |  |
Fixed maturity securities: |  |  |  |  |
Gross realized gains | $ | 186 |  |  | $ | 204 |  |  | $ | 131 |
Gross realized losses | (64 | ) |  | (138 | ) |  | (197 | )
Net realized investment gains (losses) on fixed maturity securities | 122 |  |  | 66 |  |  | (66 | )
Equity securities: |  |  |  |  |  |  |
Gross realized gains | 1 |  |  | 5 |  |  | 2 |
Gross realized losses | (1 | ) |  | (10 | ) |  | (25 | )
Net realized investment gains (losses) on equity securities | — |  |  | (5 | ) |  | (23 | )
Derivatives | (4 | ) |  | (2 | ) |  | 10 |
Short term investments and other | (25 | ) |  | (9 | ) |  | 12 |
Net realized investment gains (losses) | $ | 93 |  |  | $ | 50 |  |  | $ | (67 | )
Net change in unrealized gains (losses) on investments | Net change in unrealized gains on investments is presented in the following table.
Years ended December 31 |  |  |  |  |
(In millions) | 2017 |  | 2016 |  | 2015
Net change in unrealized gains on investments: |  |  |  |  |
Fixed maturity securities | $ | 728 |  |  | $ | 225 |  |  | $ | (1,114 | )
Equity securities | 32 |  |  | (2 | ) |  | (6 | )
Other | (2 | ) |  | 1 |  |  | 1 |
Total net change in unrealized gains on investments | $ | 758 |  |  | $ | 224 |  |  | $ | (1,119 | )
Components of net other than temporary impairment losses recognized in earnings by asset type | The components of OTTI losses recognized in earnings by asset type are presented in the following table.
Years ended December 31 |  |  |  |  |
(In millions) | 2017 |  | 2016 |  | 2015
Fixed maturity securities available-for-sale: |  |  |  |  |
Corporate and other bonds | $ | 12 |  |  | $ | 59 |  |  | $ | 104 |
States, municipalities and political subdivisions | — |  |  | — |  |  | 18 |
Asset-backed: |  |  |  |  |  |  |
Residential mortgage-backed | 1 |  |  | 10 |  |  | 8 |
Other asset-backed | — |  |  | 3 |  |  | 1 |
Total asset-backed | 1 |  |  | 13 |  |  | 9 |
Total fixed maturity securities available-for-sale | 13 |  |  | 72 |  |  | 131 |
Equity securities available-for-sale | 1 |  |  | 9 |  |  | 25 |
OTTI losses recognized in earnings | $ | 14 |  |  | $ | 81 |  |  | $ | 156 |
Summary of fixed maturity and equity securities | The following tables present a summary of fixed maturity and equity securities.
December 31, 2017 | Cost or Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Unrealized OTTI Losses (Gains)
(In millions) |  |  |  |
Fixed maturity securities available-for-sale: |  |  |  |  |  |  |  |  |
Corporate and other bonds | $ | 17,210 |  |  | $ | 1,625 |  |  | $ | 28 |  |  | $ | 18,807 |  |  | $ | — |
States, municipalities and political subdivisions | 12,478 |  |  | 1,551 |  |  | 2 |  |  | 14,027 |  |  | (11 | )
Asset-backed: |  |  |  |  |  |  |  |  |
Residential mortgage-backed | 5,043 |  |  | 109 |  |  | 32 |  |  | 5,120 |  |  | (27 | )
Commercial mortgage-backed | 1,840 |  |  | 46 |  |  | 14 |  |  | 1,872 |  |  | — |
Other asset-backed | 1,083 |  |  | 16 |  |  | 5 |  |  | 1,094 |  |  | — |
Total asset-backed | 7,966 |  |  | 171 |  |  | 51 |  |  | 8,086 |  |  | (27 | )
U.S. Treasury and obligations of government-sponsored enterprises | 111 |  |  | 2 |  |  | 4 |  |  | 109 |  |  | — |
Foreign government | 437 |  |  | 9 |  |  | 2 |  |  | 444 |  |  | — |
Redeemable preferred stock | 10 |  |  | 1 |  |  | — |  |  | 11 |  |  | — |
Total fixed maturity securities available-for-sale | 38,212 |  |  | 3,359 |  |  | 87 |  |  | 41,484 |  |  | $ | (38 | )
Total fixed maturity securities trading | 3 |  |  |  |  |  |  |  |  | 3 |  |  |
Equity securities available-for-sale: |  |  |  |  |  |  |  |  |
Common stock | 21 |  |  | 7 |  |  | 1 |  |  | 27 |  |  |
Preferred stock | 638 |  |  | 31 |  |  | 1 |  |  | 668 |  |  |
Total equity securities available-for-sale | 659 |  |  | 38 |  |  | 2 |  |  | 695 |  |  |
Total | $ | 38,874 |  |  | $ | 3,397 |  |  | $ | 89 |  |  | $ | 42,182 |  |  |
December 31, 2016 | Cost or Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Unrealized OTTI Losses (Gains)
(In millions) |  |  |  |
Fixed maturity securities available-for-sale: |  |  |  |  |  |  |  |  |
Corporate and other bonds | $ | 17,711 |  |  | $ | 1,323 |  |  | $ | 76 |  |  | $ | 18,958 |  |  | $ | (1 | )
States, municipalities and political subdivisions | 12,060 |  |  | 1,213 |  |  | 33 |  |  | 13,240 |  |  | (16 | )
Asset-backed: |  |  |  |  |  |  |  |  |
Residential mortgage-backed | 5,004 |  |  | 120 |  |  | 51 |  |  | 5,073 |  |  | (28 | )
Commercial mortgage-backed | 2,016 |  |  | 48 |  |  | 24 |  |  | 2,040 |  |  | — |
Other asset-backed | 1,022 |  |  | 8 |  |  | 5 |  |  | 1,025 |  |  | — |
Total asset-backed | 8,042 |  |  | 176 |  |  | 80 |  |  | 8,138 |  |  | (28 | )
U.S. Treasury and obligations of government-sponsored enterprises | 83 |  |  | 10 |  |  | — |  |  | 93 |  |  | — |
Foreign government | 435 |  |  | 13 |  |  | 3 |  |  | 445 |  |  | — |
Redeemable preferred stock | 18 |  |  | 1 |  |  | — |  |  | 19 |  |  | — |
Total fixed maturity securities available-for-sale | 38,349 |  |  | 2,736 |  |  | 192 |  |  | 40,893 |  |  | $ | (45 | )
Total fixed maturity securities trading | 12 |  |  |  |  |  |  | 12 |  |  |
Equity securities available-for-sale: |  |  |  |  |  |  |  |  |
Common stock | 13 |  |  | 6 |  |  | — |  |  | 19 |  |  |
Preferred stock | 93 |  |  | 2 |  |  | 4 |  |  | 91 |  |  |
Total equity securities available-for-sale | 106 |  |  | 8 |  |  | 4 |  |  | 110 |  |  |
Total | $ | 38,467 |  |  | $ | 2,744 |  |  | $ | 196 |  |  | $ | 41,015 |  |  |
Securities in a gross unrealized loss position | The following tables present the estimated fair value and gross unrealized losses of fixed maturity and equity securities in a gross unrealized loss position by the length of time in which the securities have continuously been in that position.
| Less than 12 Months |  | 12 Months or Longer |  | Total
December 31, 2017 | Estimated Fair Value |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Gross Unrealized Losses
(In millions) |  |  |  |  |
Fixed maturity securities available-for-sale: |  |  |  |  |  |  |  |  |  |  |
Corporate and other bonds | $ | 1,354 |  |  | $ | 21 |  |  | $ | 168 |  |  | $ | 7 |  |  | $ | 1,522 |  |  | $ | 28 |
States, municipalities and political subdivisions | 72 |  |  | 1 |  |  | 85 |  |  | 1 |  |  | 157 |  |  | 2 |
Asset-backed: |  |  |  |  |  |  |  |  |  |  |
Residential mortgage-backed | 1,228 |  |  | 5 |  |  | 947 |  |  | 27 |  |  | 2,175 |  |  | 32 |
Commercial mortgage-backed | 403 |  |  | 4 |  |  | 212 |  |  | 10 |  |  | 615 |  |  | 14 |
Other asset-backed | 248 |  |  | 3 |  |  | 18 |  |  | 2 |  |  | 266 |  |  | 5 |
Total asset-backed | 1,879 |  |  | 12 |  |  | 1,177 |  |  | 39 |  |  | 3,056 |  |  | 51 |
U.S. Treasury and obligations of government-sponsored enterprises | 49 |  |  | 2 |  |  | 21 |  |  | 2 |  |  | 70 |  |  | 4 |
Foreign government | 166 |  |  | 2 |  |  | 4 |  |  | — |  |  | 170 |  |  | 2 |
Total fixed maturity securities available-for-sale | 3,520 |  |  | 38 |  |  | 1,455 |  |  | 49 |  |  | 4,975 |  |  | 87 |
Equity securities available-for-sale: |  |  |  |  |  |  |  |  |  |  |
Common stock | 7 |  |  | 1 |  |  | — |  |  | — |  |  | 7 |  |  | 1 |
Preferred stock | 93 |  |  | 1 |  |  | — |  |  | — |  |  | 93 |  |  | 1 |
Total equity securities available-for-sale | 100 |  |  | 2 |  |  | — |  |  | — |  |  | 100 |  |  | 2 |
Total | $ | 3,620 |  |  | $ | 40 |  |  | $ | 1,455 |  |  | $ | 49 |  |  | $ | 5,075 |  |  | $ | 89 |
| Less than 12 Months |  | 12 Months or Longer |  | Total
December 31, 2016 | Estimated Fair Value |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Gross Unrealized Losses |  | Estimated Fair Value |  | Gross Unrealized Losses
(In millions) |  |  |  |  |
Fixed maturity securities available-for-sale: |  |  |  |  |  |  |  |  |  |  |
Corporate and other bonds | $ | 2,615 |  |  | $ | 61 |  |  | $ | 254 |  |  | $ | 15 |  |  | $ | 2,869 |  |  | $ | 76 |
States, municipalities and political subdivisions | 959 |  |  | 32 |  |  | 23 |  |  | 1 |  |  | 982 |  |  | 33 |
Asset-backed: |  |  |  |  |  |  |  |  |  |  |
Residential mortgage-backed | 2,136 |  |  | 44 |  |  | 201 |  |  | 7 |  |  | 2,337 |  |  | 51 |
Commercial mortgage-backed | 756 |  |  | 22 |  |  | 69 |  |  | 2 |  |  | 825 |  |  | 24 |
Other asset-backed | 398 |  |  | 5 |  |  | 24 |  |  | — |  |  | 422 |  |  | 5 |
Total asset-backed | 3,290 |  |  | 71 |  |  | 294 |  |  | 9 |  |  | 3,584 |  |  | 80 |
U.S. Treasury and obligations of government-sponsored enterprises | 5 |  |  | — |  |  | — |  |  | — |  |  | 5 |  |  | — |
Foreign government | 108 |  |  | 3 |  |  | — |  |  | — |  |  | 108 |  |  | 3 |
Total fixed maturity securities available-for-sale | 6,977 |  |  | 167 |  |  | 571 |  |  | 25 |  |  | 7,548 |  |  | 192 |
Equity securities available-for-sale -- Preferred stock | 12 |  |  | — |  |  | 13 |  |  | 4 |  |  | 25 |  |  | 4 |
Total | $ | 6,989 |  |  | $ | 167 |  |  | $ | 584 |  |  | $ | 29 |  |  | $ | 7,573 |  |  | $ | 196 |
Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI | The following table presents the activity related to the pretax credit loss component reflected in Retained earnings on fixed maturity securities still held as of December 31, 2017, 2016 and 2015 for which a portion of an OTTI loss was recognized in Other comprehensive income (loss).
Years ended December 31 |  |  |  |  |
(In millions) | 2017 |  | 2016 |  | 2015
Beginning balance of credit losses on fixed maturity securities | $ | 36 |  |  | $ | 53 |  |  | $ | 62 |
Reductions for securities sold during the period | (9 | ) |  | (16 | ) |  | (9 | )
Reductions for securities the Company intends to sell or more likely than not will be required to sell | — |  |  | (1 | ) |  | — |
Ending balance of credit losses on fixed maturity securities | $ | 27 |  |  | $ | 36 |  |  | $ | 53 |
Contractual maturity | The following table presents available-for-sale fixed maturity securities by contractual maturity.
December 31 | 2017 |  | 2016
(In millions) | Cost or Amortized Cost |  | Estimated Fair Value |  | Cost or Amortized Cost |  | Estimated Fair Value
Due in one year or less | $ | 1,135 |  |  | $ | 1,157 |  |  | $ | 1,779 |  |  | $ | 1,828 |
Due after one year through five years | 8,165 |  |  | 8,501 |  |  | 7,566 |  |  | 7,955 |
Due after five years through ten years | 16,060 |  |  | 16,718 |  |  | 15,892 |  |  | 16,332 |
Due after ten years | 12,852 |  |  | 15,108 |  |  | 13,112 |  |  | 14,778 |
Total | $ | 38,212 |  |  | $ | 41,484 |  |  | $ | 38,349 |  |  | $ | 40,893 |

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