Commitments, contingencies, and guarantees (Net Realized Gains (Losses) Of Derivative Instrument Activity In Consolidated Statement Of Operations) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		$ (228)	$ (585)	$ (330)
Foreign currency forward contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		65	(79)	3
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		0	(270)	(115)
All Other Futures Contracts And Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		16	(88)	39
Convertible Securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[1]	0	2	(2)
Investment And Embedded Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		81	(435)	(75)
GLB
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		(202)	(4)	(248)
Futures contracts on equities
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net	[2]	(108)	(138)	(4)
Other Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		1	(8)	(3)
Guaranteed Living Benefit And Other Derivative Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Gain (Loss) on Derivative, Net		$ (309)	$ (150)	$ (255)

[1] Includes embedded derivatives.

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