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.