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, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Future policy benefits		$ 5,713	$ 5,373
Derivative, Notional Amount		4,567	4,199
Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		2,807	2,579
Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		1,749	1,615
Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		11	5
Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		709	613
Other
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		16	63
Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		725	676
Guaranteed Minimum Income Benefit
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		1,658	1,510
Accounts Payable and Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(52)	(93)
Accounts Payable and Accrued Liabilities [Member] | Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(49)	(78)
Accounts Payable and Accrued Liabilities [Member] | Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(3)	(15)
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]	(17)	(13)
Accounts Payable and Accrued Liabilities [Member] | Other
Derivatives, Fair Value [Line Items]
Derivative Liability		0	0
Accounts Payable and Accrued Liabilities [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability		(17)	(13)
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		44	28
Other Assets [Member] | Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		22	11
Other Assets [Member] | Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		13	13
Other Assets [Member] | Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative Asset	[2]	0	0
Other Assets [Member] | Other
Derivatives, Fair Value [Line Items]
Derivative Asset		0	2
Other Assets [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset		0	2
Other Assets [Member] | Guaranteed Minimum Income Benefit
Derivatives, Fair Value [Line Items]
Derivative Asset		0	0
Accounts Payable Future Policy Benefits [Member] | Guaranteed Minimum Income Benefit
Derivatives, Fair Value [Line Items]
Derivative Liability		(1,089)	(897)
Available-for-sale Securities [Member] | Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	[1]	9	4
Guaranteed Minimum Income Benefit | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross		$ 1,089	$ 897

[1] Includes fair value of embedded derivatives.

[2] Related to GMDB and GLB book of business.(3)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.