Post-Employment Benefits - Net Periodic Benefit Cost (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]
Service cost	$ 269	$ 285	$ 236
Interest cost	259	227	204
Expected return on plan assets	(474)	(439)	(382)
Amortization of actuarial loss and prior service credit	109	140	107
Net periodic benefit cost	163	213	165
Other post-employment plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	25	26	26
Interest cost	29	25	24
Amortization of actuarial loss and prior service credit	1	1	0
Net periodic benefit cost	$ 55	$ 52	$ 50