Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	$ 9,260	$ 7,943	$ 7,584
Deferred tax asset on foreign currency translation adjustments	11	14
Deferred tax asset on net charges related to pension/post-retirement plans	1,805	1,635
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	(5,110)	(5,055)	(4,647)	$ (4,043)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	(984)	(1,543)	(1,694)
Pension and Post-Retirement Plans Losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	$ (4,126)	$ (3,512)	$ (2,953)