Other assets impairments, restructuring and other items - Summary of Restructuring Accruals (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Restructuring Cost and Reserve [Line Items]
Beginning balance		$ (122)	$ (215)
Provision		(81)	(39)
Utilization and other	[1]	35	75
Ending balance		(168)	(179)
Employee termination costs [Member]
Restructuring Cost and Reserve [Line Items]
Beginning balance		(115)	(208)
Provision		(79)	(33)
Utilization and other	[1]	33	69
Ending balance		(161)	(172)
Other [Member]
Restructuring Cost and Reserve [Line Items]
Beginning balance		(7)	(7)
Provision		(2)	(6)
Utilization and other	[1]	2	6
Ending balance		$ (7)	$ (7)

[1] Includes adjustments for foreign currency translation.