Amounts Recognized in Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Loss Related to Postretirement Benefit Plans and Expected Costs to be Recognized in Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	$ (224)	$ (5,910)	$ 2,937
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(127)	3,040	(69)
Total Incurred but Not Recognized	(351)	(2,870)	2,868
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	1,109	806	973
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	(259)	(100)	42
Total Reclassification Adjustment for Prior Period Amounts Recognized	850	706	1,015
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	(291)	(5,505)	2,751
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(18)	2,959	(69)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	1,034	758	911
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	(251)	(98)	53
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	46	(160)	140
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(102)	(3)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	28	15	28
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	2	3	(11)
Other Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	21	(245)	46
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(7)	84
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	47	33	$ 34
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	$ (10)	$ (5)