Commitments, Contingencies, And Guarantees (Net Realized Gains (Losses) Of Derivative Instrument Activity In Consolidated Statement Of Operations) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2026	Mar. 31, 2025
Other derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		$ (9)	$ (3)
Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		(79)	28
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		(108)	(14)
Not Designated as Hedging Instrument [Member] | Options/Futures/Forward contracts on notes and bonds
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		(7)	(9)
Not Designated as Hedging Instrument [Member] | Investment And Embedded Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		(115)	(23)
Not Designated as Hedging Instrument [Member] | Futures contracts on equities
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative	[1]	45	54
Not Designated as Hedging Instrument [Member] | Other derivative instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		(9)	(3)
Not Designated as Hedging Instrument [Member] | Other Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) on Derivative		$ 36	$ 51

[1] Related to MRB book of business.