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Commitments, contingencies, and guarantees (Balance Sheet Locations, Fair Values In Asset Or (Liability) Position, And Notional Values/Payment Provisions Of Derivative Instruments) (Detail) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision |  | $ 3,122 | $ 4,666
Convertible Securities [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision | [1] | 6 | 7
Foreign currency forward contracts [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision |  | 2,064 | 2,220
Cross Currency Swap [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision |  | 45 | 95
Futures contracts on notes and bonds [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision |  | 1,007 | 2,344
Futures contracts on equities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision | [2] | 1,553 | 1,316
Other |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision |  | 75 | 214
Other Derivative Instruments [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision |  | 1,628 | 1,530
Guaranteed Minimum Income Benefit |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Notional Value/Payment Provision | [3] | 1,083 | 1,264
Accounts Payable and Accrued Liabilities [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability |  | (30) | (54)
Accounts Payable and Accrued Liabilities [Member] | Convertible Securities [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability | [1] | 0 | 0
Accounts Payable and Accrued Liabilities [Member] | Foreign currency forward contracts [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability |  | (27) | (50)
Accounts Payable and Accrued Liabilities [Member] | Cross Currency Swap [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability |  | 0 | 0
Accounts Payable and Accrued Liabilities [Member] | Futures contracts on notes and bonds [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability |  | (3) | (4)
Accounts Payable and Accrued Liabilities [Member] | Futures contracts on equities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability | [2] | (21) | 0
Accounts Payable and Accrued Liabilities [Member] | Other |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability |  | (2) | (13)
Accounts Payable and Accrued Liabilities [Member] | Other Derivative Instruments [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability |  | (23) | (13)
Other Assets [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset |  | 23 | 33
Other Assets [Member] | Foreign currency forward contracts [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset |  | 14 | 25
Other Assets [Member] | Cross Currency Swap [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset |  | 0 | 0
Other Assets [Member] | Futures contracts on notes and bonds [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset |  | 4 | 6
Other Assets [Member] | Futures contracts on equities |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset | [2] | 0 | 1
Other Assets [Member] | Other |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset |  | 1 | 2
Other Assets [Member] | Other Derivative Instruments [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset |  | 1 | 3
Other Assets [Member] | Guaranteed Minimum Income Benefit |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset | [3] | 0 | 0
Accounts Payable Future Policy Benefits [Member] | Guaranteed Minimum Income Benefit |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Liability | [3] | (550) | (853)
Available-for-sale Securities [Member] | Convertible Securities [Member] |  |  |
Derivatives, Fair Value [Line Items] |  |  |
Derivative Asset | [1] | $ 5 | $ 2
[1] | (1)Includes fair value of embedded derivatives.
[2] | (2) Related to GMDB and GLB blocks of business.
[3] | (3) Includes both future policy benefits reserves and fair value derivative adjustment. Refer to Note 5 c) for additional information. Note that the payment provision related to GLB is the net amount at risk. The concept of a notional value does not apply to the GLB reinsurance contracts.

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