Pension plans - Net periodic pension expense (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Components of net periodic pension expense
Service cost	$ 257	$ 235	$ 224
Interest cost	410	510	618
Expected return on plan assets	(1,008)	(955)	(936)
Amortization of actuarial losses and other	203	171	26
Net periodic pension expense	$ (138)	$ (39)	$ (68)