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
	Mar. 31, 2022	Mar. 31, 2021
Pension Plans [Member]
Components Of Net Periodic Benefit Cost
Service cost	$ 69	$ 66
Interest cost	61	55
Expected return on plan assets	(119)	(112)
Prior service cost (credit) and transition obligation (asset) amortization	(1)
Actuarial loss (gain) amortization	35	42
Net periodic benefit cost	45	51
Postretirement Welfare Plan [Member]
Components Of Net Periodic Benefit Cost
Prior service cost (credit) and transition obligation (asset) amortization		(1)
Actuarial loss (gain) amortization	(2)	(2)
Net periodic benefit cost	$ (2)	$ (3)