Pension plans - Projected benefit obligation, plan assets and net funded status (Detail) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Plan assets
Balance at the beginning of the year	$ 13,379	$ 12,592
Employer contributions	111	145
Benefits paid	(810)	(852)
Settlements paid	(354)	(448)
Actual return on plan assets	1,909	1,783
Other	(55)	159
Balance at the end of the year	14,180	13,379	$ 12,592
Benefit obligations
Balance at the beginning of the year	12,767	12,738
Service cost	107	111	181
Interest cost	$ 617	$ 640	482
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Interest Expense, Operating and Nonoperating	Interest Expense, Operating and Nonoperating
Benefits paid	$ (810)	$ (852)
Settlements paid	(354)	(448)
Actuarial (gains) losses and other	(607)	578
Balance at the end of the year	11,720	12,767	$ 12,738
Net funded status - asset (liability)	2,460	612
Balances included in other assets	3,490	1,823
Balances included in accounts payable and other liabilities	$ 1,030	$ 1,211