Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	$ 7,943	$ 7,584	$ 7,442
Deferred tax asset on foreign currency translation adjustments	14	15
Deferred tax asset on net charges related to pension/post-retirement plans	1,635	1,493
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	(1,543)	(1,694)	(1,165)
Pension/Post-Retirement Plans Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	(3,512)	(2,953)	(2,892)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Components of AOCI	$ (5,055)	$ (4,647)	$ (4,043)	$ (5,093)