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, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and losses - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	$ 3,405	$ (1,066)	$ (2,178)
Net prior service credit and cost - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(1)	(1)	(4)
Incurred but Not Yet Recognized in FAS Expense	3,404	(1,067)	(2,182)
Actuarial gains and losses - Recognition of Previously Deferred Amounts	2,043	689	1,148
Net prior service credit and cost - Recognition of Previously Deferred Amounts	(256)	(249)	(240)
Recognition of Previously Deferred Amounts	1,787	440	908
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	2,987	(1,005)	(2,283)
Net prior service credit and cost - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(1)	(7)	(8)
Actuarial gains and losses - Recognition of Previously Deferred Amounts	2,019	668	1,104
Net prior service credit and cost - Recognition of Previously Deferred Amounts	(274)	(269)	(263)
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	342	43	238
Net prior service credit and cost - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	0	6	4
Actuarial gains and losses - Recognition of Previously Deferred Amounts	0	(3)	2
Net prior service credit and cost - Recognition of Previously Deferred Amounts	29	30	33
Other plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and losses - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	76	(104)	(133)
Net prior service credit and cost - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	0	0	0
Actuarial gains and losses - Recognition of Previously Deferred Amounts	24	24	42
Net prior service credit and cost - Recognition of Previously Deferred Amounts	$ (11)	$ (10)	$ (10)