Post-Employment Benefits - Pretax Gains and Losses Included in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined benefit plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarial loss	$ 1,231	$ 209	$ 412
Amortization of actuarial loss and prior service credit	(109)	(140)	(107)
Foreign exchange loss (gain) and other	(6)	(13)	46
Total loss (gain)	1,116	56	351
Other post-employment plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actuarial loss	451	(287)	149
Amortization of actuarial loss and prior service credit	(1)	(1)
Total loss (gain)	$ 450	$ (288)	$ 149