Income Taxes (Net Deferred Income Tax Assets and Liabilities) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Examination [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	$ 167	$ 158
Employee benefits	439	382
Contingent and accrued liabilities	118	148
Operating loss and other carry-forwards	293	225
Inventories	1	4
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other	209	194
Other	196	85
Deferred Tax Assets, Valuation Allowance	167	158
Deferred Tax Assets, Net of Valuation Allowance	1,089	880
Property	240	277
Intangibles	663	594
Employee benefits	37	65
Operating lease right-of-use assets	206	192
Other	16	2
Deferred Tax Liabilities, Gross	1,162	1,130
Deferred Tax Liabilities, Net	73	250
Income Tax, Potential U.S. Tax Cost for Repatriation of Foreign Earnings	40	32
Deferred income tax assets related to
Employee benefits	439	382
Contingent and accrued liabilities	118	148
Operating loss and other carry-forwards	293	225
Inventories	1	4
Other	196	85
Valuation allowance	(167)	(158)
Total	1,089	880
Deferred income tax liabilities related to
Property	240	277
Intangibles	663	594
Employee benefits	37	65
Other	16	2
Total	1,162	1,130
Deferred income tax liabilities – net	(73)	(250)
Operating lease right-of-use assets	206	192
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Other	$ 209	$ 194
Minimum
Income Tax Examination [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2021
Tax Credit Carryforward, Expiration Date	Dec. 31, 2021
Maximum
Income Tax Examination [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2040
Tax Credit Carryforward, Expiration Date	Dec. 31, 2040