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Investments - Net Investment Income and Investment Gains (Losses) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015
Net Investment Income [Line Items] |  |  |  |
Total investment income | $ 575 | $ 338 | $ 1,613 | $ 1,465
Investment expenses | (14) | (17) | (43) | (46)
Investment gains (losses) | 45 | (50) | 18 | (42)
Net investment income | 561 | 321 | 1,570 | 1,419
Fixed Maturity Securities [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Total investment income | 457 | 449 | 1,352 | 1,344
Investment gains (losses) | 47 | (29) | 34 | (29)
Equity Securities [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Total investment income | 1 | 3 | 8 | 9
Investment gains (losses) | (3) | (18) | (5) | (19)
Derivative Instruments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Investment gains (losses) | 1 | (1) | (12) | 9
Short Term Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Total investment income | 3 | 4 | 8 | 7
Investment gains (losses) |  | (2) | 1 | (3)
Limited Partnership Investments [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Total investment income | 91 | (122) | 98 | 88
Income (Loss) from Trading Portfolio [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Total investment income | 11 | (5) | 113 | (9)
Other [Member] |  |  |  |
Net Investment Income [Line Items] |  |  |  |
Total investment income | $ 12 | $ 9 | $ 34 | $ 26

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- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 + Details
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