Accumulated other comprehensive income (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 473,424		$ 473,424
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2018-12 [Member]	Accounting Standards Update 2018-12 [Member]	Accounting Standards Update 2018-12 [Member]	Accounting Standards Update 2018-12 [Member]
Ending Balance			$ 525,330
Unrealized gains (losses) on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (187)	$ 369	(187)	$ 369
Other comprehensive income, net			178	(767)
Ending Balance			(9)	(398)
Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(6,142)	(4,092)	(6,142)	(4,092)
Other comprehensive income, net			(187)	(3,674)
Ending Balance			(6,329)	(7,766)
Long duration insurance contracts [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,541	(4,096)	1,541	(4,096)
Other comprehensive income, net			786	5,968
Ending Balance			2,327	1,872
Defined benefit pension plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(552)	(347)	(552)	(347)
Other comprehensive income, net			51	47
Ending Balance			(501)	(300)
Other AOCI transactions [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	288	43	288	43
Other comprehensive income, net			(48)	189
Ending Balance			240	232
Accumulated other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,052)	(8,123)	(5,052)	(8,123)
Other comprehensive income, net			780	1,763
Ending Balance			(4,272)	(6,360)
Previously Reported [Member] | Unrealized gains (losses) on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(187)	369	(187)	369
Previously Reported [Member] | Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(6,140)	(4,092)	(6,140)	(4,092)
Previously Reported [Member] | Defined benefit pension plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(552)	(347)	(552)	(347)
Previously Reported [Member] | Other AOCI transactions [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	288	43	288	43
Previously Reported [Member] | Accumulated other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(6,591)	(4,027)	(6,591)	(4,027)
Effect of adoption of ASU 2018-12 [Member] | Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(2)		(2)
Effect of adoption of ASU 2018-12 [Member] | Long duration insurance contracts [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,541	(4,096)	1,541	(4,096)
Effect of adoption of ASU 2018-12 [Member] | Accumulated other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 1,539	$ (4,096)	$ 1,539	$ (4,096)