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, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		$ 8,543	$ 3,122
Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		2,185	2,064
Cross Currency Swap [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		45	45
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		5,250	0
Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		1,046	1,007
Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision	[1]	11	6
To be announced [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		6	0
Futures contracts on equities
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision	[2]	507	1,553
Other
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		74	75
Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision		581	1,628
Guaranteed Minimum Income Benefit
Derivatives, Fair Value [Line Items]
Notional Value/Payment Provision	[3]	1,750	1,083
Accounts Payable and Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(153)	(30)
Accounts Payable and Accrued Liabilities [Member] | Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(19)	(27)
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] | Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(115)	0
Accounts Payable and Accrued Liabilities [Member] | Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(19)	(3)
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] | Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative Liability	[2]	0	(21)
Accounts Payable and Accrued Liabilities [Member] | Other
Derivatives, Fair Value [Line Items]
Derivative Liability		0	(2)
Accounts Payable and Accrued Liabilities [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		0	(23)
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		43	23
Other Assets [Member] | Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		15	14
Other Assets [Member] | Cross Currency Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		0	0
Other Assets [Member] | Interest Rate 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		13	4
Other Assets [Member] | Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative Asset	[2]	23	0
Other Assets [Member] | Other
Derivatives, Fair Value [Line Items]
Derivative Asset		2	1
Other Assets [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		25	1
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]	(861)	(550)
Available-for-sale Securities [Member] | Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[1]	9	5
Available-for-sale Securities [Member] | To be announced [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		6	0
Derivative Liability		$ 0	$ 0

[1] Includes fair value of embedded derivatives.

[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 4 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.