Pension plans - Net periodic pension expense (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Components of net periodic pension expense
Service cost	$ 111	$ 181	$ 257
Interest cost	640	482	410
Expected return on plan assets	(785)	(975)	(1,008)
Other	2	156	203
Net periodic pension expense	$ (32)	$ (156)	$ (138)