Income Taxes - Components of Federal and Foreign Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets related to:
Accrued compensation and benefits	$ 926	$ 659
Pensions	2,994	3,057
Contract accounting methods	392	349
Foreign company operating losses and credits	51	49
Other	509	416
Valuation allowance	(13)	(28)
Deferred tax assets, net	4,859	4,502
Deferred tax liabilities related to:
Goodwill and purchased intangibles	363	330
Property, plant and equipment	481	340
Exchanged debt securities and other	547	525
Deferred tax liabilities	1,391	1,195
Net deferred tax assets	$ 3,468	$ 3,307