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, 2024	Dec. 31, 2023
Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		$ 3,959	$ 3,662
Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		449	2,062
Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	[1]	12	64
Investment And Embedded Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		53	110
Derivative Liability, Subject to Master Netting Arrangement, before Offset		303	136
Derivative, Notional Amount		4,420	5,788
Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount	[2]	1,047	1,157
Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		211	217
Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		1,258	1,374
Fair Value Hedging
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		1,579	1,631
Net Investment Hedging
Derivatives, Fair Value [Line Items]
Derivative, Notional Amount		2,896	1,619
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		146	136
Derivative Liability, Subject to Master Netting Arrangement, before Offset		116	(128)
Derivative, Notional Amount		4,475	3,250
Accounts Payable and Accrued Liabilities [Member] | Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset		295	94
Accounts Payable and Accrued Liabilities [Member] | Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset		8	42
Accounts Payable and Accrued Liabilities [Member] | Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset	[2]	0	37
Accounts Payable and Accrued Liabilities [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset		2	5
Accounts Payable and Accrued Liabilities [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset		2	42
Accounts Payable and Accrued Liabilities [Member] | Fair Value Hedging
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset		0	0
Accounts Payable and Accrued Liabilities [Member] | Net Investment Hedging
Derivatives, Fair Value [Line Items]
Derivative Liability, Subject to Master Netting Arrangement, before Offset		116	128
Other Assets [Member] | Foreign currency forward contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		41	27
Other Assets [Member] | Futures contracts on notes and bonds [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		0	27
Other Assets [Member] | Futures contracts on equities
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset	[2]	35	0
Other Assets [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		0	0
Other Assets [Member] | Other Derivative Instruments [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		35	0
Other Assets [Member] | Fair Value Hedging
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		103	126
Other Assets [Member] | Net Investment Hedging
Derivatives, Fair Value [Line Items]
Derivative Asset, Subject to Master Netting Arrangement, before Offset		43	10
Fixed Maturities [Member] | Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Not Subject to Master Netting Arrangement	[1]	12	56
Equity Securities [Member] | Convertible Securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Not Subject to Master Netting Arrangement	[1]	$ 0	$ 0

[1] Includes fair value of embedded derivatives.

[2] Related to MRB book of business.