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Investments - Net Investment Income and Investment Gains (Losses) (Detail) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Net Investment Income [Line Items] |  |
Total investment income | $ 676 | $ 521
Investment expenses | (19) | (15)
Investment gains (losses) | 31 | 9
Net investment income | 657 | 506
Fixed Maturity Securities [Member] |  |
Net Investment Income [Line Items] |  |
Total investment income | 455 | 446
Investment gains (losses) | (6) | 18
Equity Securities [Member] |  |
Net Investment Income [Line Items] |  |
Total investment income | 30 | 10
Investment gains (losses) | 42 | (15)
Derivative Instruments [Member] |  |
Net Investment Income [Line Items] |  |
Investment gains (losses) | (5) | 5
Short Term and Other [Member] |  |
Net Investment Income [Line Items] |  |
Total investment income | 15 | 9
Investment gains (losses) |  | 1
Income (Loss) from Trading Portfolio [Member] |  |
Net Investment Income [Line Items] |  |
Total investment income | 81 |
Total investment income |  | (3)
Limited Partnership Investments [Member] |  |
Net Investment Income [Line Items] |  |
Total investment income | 81 | 48
Other [Member] |  |
Net Investment Income [Line Items] |  |
Total investment income | $ 14 | $ 11

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- Definition Amount of realized and unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c),9(a)) -URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227 Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585 + Details
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- Definition Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 + Details
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- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 + Details
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