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Commitments, contingencies, and guarantees (Net Realized Gains (Losses) Of Derivative Instrument Activity In Consolidated Statement Of Operations) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | $ 87 | $ (126) | $ (193)
Foreign currency forward contracts [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | 9 | (31) | 31
All Other Futures Contracts And Options [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | (21) | (10) | 9
Convertible Securities [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | [1] | 1 | 8 | (8)
Investment And Embedded Derivative Instruments [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | (11) | (33) | 32
GLB |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | [2] | 364 | 53 | (203)
Single-Stock Future [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | [3] | (261) | (136) | (8)
Other Derivatives |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | (5) | (10) | (14)
Guaranteed Living Benefit And Other Derivative Instruments [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | $ 98 | $ (93) | $ (225)
[1] | 1) Includes embedded derivatives.
[2] | (2) Excludes foreign exchange gains (losses) related to GLB.
[3] | (3) Related to GMDB and GLB blocks of business.

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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