Accumulated other comprehensive income (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 424,791
Other comprehensive income, net	(724)	$ 337
Ending Balance	393,495
Unrealized appreciation of investments, net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	481	370
Other comprehensive income, net	14	166
Ending Balance	495	536
Foreign currency translation [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,346)	(4,603)
Other comprehensive income, net	(794)	145
Ending Balance	(5,140)	(4,458)
Defined benefit pension plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(1,369)	(816)
Other comprehensive income, net	83	67
Ending Balance	(1,286)	(749)
Other AOCI transactions [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(9)	34
Other comprehensive income, net	(27)	(41)
Ending Balance	(36)	(7)
Accumulated other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,243)	(5,015)
Ending Balance	$ (5,967)	$ (4,678)