Postretirement Benefit Plans - Amounts Recognized in Other Comprehensive Income (Loss) Related to Postretirement Benefit Plans, Net of Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	$ (684)	$ 2,022	$ 3,405
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(5)	(149)	(1)
Incurred but Not Yet Recognized in FAS Expense	(689)	1,873	3,404
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	(116)	(1,493)	(2,043)
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	265	268	256
Recognition of Previously Deferred Amounts	149	(1,225)	(1,787)
Qualified defined benefit pension plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(698)	1,952	2,987
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(5)	(146)	(1)
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	(133)	(1,490)	(2,019)
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	274	283	274
Retiree medical and life insurance plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	47	(95)	342
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(1)	(1)	0
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	25	36	0
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	(8)	(22)	(29)
Other plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(33)	165	76
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	1	(2)	0
Actuarial gains and (losses) - Recognition of Previously Deferred Amounts	(8)	(39)	(24)
Net prior service credit and (cost) - Recognition of Previously Deferred Amounts	$ (1)	$ 7	$ 11