Income Taxes (Details 4) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets (Table Amounts)
Retiree benefits	$ 1,477	$ 2,814
Accrued employee compensation	263	349
Provisions for accrued liabilities	193	295
Inventory	191	287
Stock-based compensation	46	72
Other	39	72
Gross deferred tax assets	2,209	3,889
Less valuation allowance	(26)	(31)
Net deferred tax assets	2,183	3,858
Deferred Tax Liabilities (Table Amounts)
Goodwill	511	798
Property, plant and equipment, net	256	321
Contract accounting differences	898	1,200
Other	43	77
Gross deferred tax liabilities	1,708	2,396
Total net deferred tax assets	$ 475	$ 1,462