Income Taxes (Tax Effects Of Temporary Differences Between Reported Earnings And Taxable Earnings) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Retirement benefits	$ 1,042	$ 990
Lease liabilities	373	418
Tax loss and credit carryforwards	311	323
Salaries and wages	259	167
Workers' compensation	167	148
Other	373	367
Deferred assets	2,525	2,413
Valuation allowance	(273)	(291)
Net deferred assets	2,252	2,122
Intangible assets	(1,067)	(1,070)
Lease right-of-use assets	(379)	(418)
Contract accounting methods	(311)	(375)
Property, plant and equipment	(270)	(291)
Capital Construction Fund qualified ships	(59)	(164)
Other	(590)	(359)
Deferred liabilities	(2,676)	(2,677)
Net deferred tax liability	$ (424)	$ (555)

Deferred Tax Assets, Deferred Tax Expense, Right-of-Use Asset

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