Employee Benefits - Components of Net Periodic Benefit Cost and Other Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Pension Plans [Member]
Components Of Net Periodic Benefit Cost
Service cost	$ 68	$ 66	$ 137	$ 132
Interest cost	62	55	123	110
Expected return on plan assets	(120)	(113)	(239)	(225)
Prior service cost (credit) amortization		(1)	(1)	(1)
Actuarial loss (gain) amortization	35	43	70	85
Net periodic benefit cost	45	50	90	101
Postretirement Welfare Plan [Member]
Components Of Net Periodic Benefit Cost
Prior service cost (credit) amortization	(2)	(1)	(2)	(2)
Actuarial loss (gain) amortization	(1)	(1)	(3)	(3)
Net periodic benefit cost	$ (3)	$ (2)	$ (5)	$ (5)