Pension plans - Defined benefit pension plans - Narrative (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 12,767	$ 12,738	$ 18,792
Amounts recognized in the Consolidated Balance Sheets:
Funded status reflected in assets	1,823	1,510
Funded status reflected in liabilities	1,211	1,656
ABO	12,300	12,200
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2024	895
2025	886
2026	885
2027	896
2028	885
2029 - 2033	4,434
Expected contribution to pension plans during the next year	118
Unfunded Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 1,000	$ 1,100