Income Taxes Deferred Income Taxes (Details 4) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets (Table Amounts)
Retiree benefits	$ 1,738	$ 1,827
Accrued employee compensation	360	336
Provisions for accrued liabilities	232	166
Inventory	849	684
Stock-based compensation	40	38
Operating lease liabilities	435	411
Tax credits	343	166
Other	112	73
Gross deferred tax assets	4,109	3,701
Less: valuation allowance	(307)	(160)
Net deferred tax assets	3,802	3,541
Deferred Tax Liabilities (Table Amounts)
Goodwill	533	515
Purchased intangibles	201	262
Property, plant and equipment, net	737	584
Operating lease right-of-use assets	423	404
Contract accounting differences	1,513	1,225
Other	84	43
Deferred tax liabilities	3,491	3,033
Total net deferred tax assets	$ 311	$ 508