Income Taxes - Components of Federal and Foreign Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets related to:
Accrued compensation and benefits	$ 595	$ 1,012
Pensions	2,495	5,197
Other postretirement benefit obligations	153	302
Contract accounting methods	487	878
Foreign company operating losses and credits	27	30
Other	154	327
Valuation allowance	(20)	(15)
Deferred tax assets, net	3,891	7,731
Deferred tax liabilities related to:
Goodwill and purchased intangibles	266	378
Property, plant and equipment	239	346
Exchanged debt securities and other	303	418
Deferred tax liabilities	808	1,142
Net deferred tax assets	$ 3,083	$ 6,589