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, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	$ (1,161)	$ (1,204)	$ (224)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	1,030	938	1,109
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(219)	(28)	(127)
Total Incurred but Not Recognized	(1,380)	(1,232)	(351)
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	(228)	(230)	(243)
Total Reclassification Adjustment for Prior Period Amounts Recognized	802	708	866
Reclassifications from divestiture of IS&GS business	0	(134)	0
Discontinued Operations | Information Systems & Global Solutions
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts		(9)	(16)
Reclassifications from divestiture of IS&GS business		134
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	(1,172)	(1,236)	(291)
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	974	879	1,034
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(219)	(54)	(18)
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	(229)	(235)	(235)
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	77	94	46
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	12	22	28
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	0	27	(102)
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	10	14	2
Other plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Actuarial gains and (losses) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	(66)	(62)	21
Actuarial (gains) and losses - Recognition of Previously Deferred Amounts	44	37	47
Net prior service credit and (cost) - Incurred but Not Yet Recognized in Net Periodic Benefit Cost	0	(1)	(7)
Net prior service (credit) and cost - Recognition of Previously Deferred Amounts	$ (9)	$ (9)	$ (10)