Pension plans - Net periodic pension expense (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Components of net periodic pension expense
Service cost	$ 107	$ 111	$ 181
Interest cost	617	640	482
Expected return on plan assets	(818)	(785)	(975)
Other	41	2	156
Net periodic pension expense	$ (53)	$ (32)	$ (156)