Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 15	$ 36	$ 43
Interest cost	17	17	52	52
Expected return on plan assets	(18)	(21)	(54)	(63)
Amortization of unrecognized prior service credit	(20)	(21)	(59)	(63)
Net loss amortization	(3)	0	(7)	1
Termination benefits	1	0	1	2
Curtailments	(3)	(1)	(4)	(7)
Net periodic benefit cost	(14)	(11)	(35)	(35)
U.S. | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	76	77	221	245
Interest cost	115	109	343	324
Expected return on plan assets	(202)	(209)	(613)	(634)
Amortization of unrecognized prior service credit	(12)	(12)	(37)	(37)
Net loss amortization	43	63	113	174
Termination benefits	3	1	7	18
Curtailments	5	3	6	7
Settlements	0	0	0	1
Net periodic benefit cost	28	32	40	98
International | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	58	56	178	181
Interest cost	44	43	133	134
Expected return on plan assets	(106)	(106)	(320)	(326)
Amortization of unrecognized prior service credit	(3)	(3)	(9)	(10)
Net loss amortization	16	21	47	64
Termination benefits	0	0	1	0
Curtailments	0	0	0	(1)
Settlements	0	0	0	3
Net periodic benefit cost	$ 9	$ 11	$ 30	$ 45