Stockholders' Equity - Changes in Balance of Accumulated Other Comprehensive Loss, Net of Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	$ (776)	$ 1,477	$ 3,097
Other comprehensive (loss) income before reclassifications	(606)	(1,260)	(1,232)
Amounts reclassified from AOCL
Amounts reclassified from AOCL	1,232	823	574
Other comprehensive income (loss), net of tax	626	(437)	(658)
Reclassification of income tax effects from tax reform	2,400
Ending Balance	1,449	(776)	1,477
Postretirement Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(12,559)	(11,981)	(11,314)
Other comprehensive (loss) income before reclassifications	(501)	(1,380)	(1,232)
Amounts reclassified from AOCL
Amounts reclassified from AOCL	1,202	802	565
Other comprehensive income (loss), net of tax	701	(578)	(667)
Reclassification of income tax effects from tax reform	(2,396)
Ending Balance	(14,254)	(12,559)	(11,981)
AOCI related to postretirement benefit plans, tax benefit	3,900	6,500	6,500
Other, net
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	20	(121)	(130)
Other comprehensive (loss) income before reclassifications	(105)	120	0
Amounts reclassified from AOCL
Amounts reclassified from AOCL	30	21	9
Other comprehensive income (loss), net of tax	(75)	141	9
Reclassification of income tax effects from tax reform	(12)
Ending Balance	(67)	20	(121)
AOCL
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning Balance	(12,539)	(12,102)	(11,444)
Amounts reclassified from AOCL
Other comprehensive income (loss), net of tax	626	(437)	(658)
Reclassification of income tax effects from tax reform	(2,408)
Ending Balance	(14,321)	(12,539)	(12,102)
Recognition of net actuarial losses
Amounts reclassified from AOCL
Amounts reclassified from AOCL	1,455	1,030	938
Amortization of net prior service credits
Amounts reclassified from AOCL
Amounts reclassified from AOCL	(253)	(228)	(239)
Recognition of net prior service credits from divestiture of IS&GS segment
Amounts reclassified from AOCL
Amounts reclassified from AOCL			(134)
Other
Amounts reclassified from AOCL
Amounts reclassified from AOCL	$ 30	$ 21	$ 9

Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings, Tax Effect

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