Pension, Other Postretirement Benefits and Savings Plans - Changes in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Curtailments/settlements/termination benefits	$ 18	$ 6	$ 22
United States
Change in plan assets:
Beginning balance	4,780
Ending balance	4,970	4,780
Non-U.S.
Change in plan assets:
Beginning balance	370
Ending balance	185	370
Pension Plan | United States
Change in benefit obligation:
Beginning balance	(5,009)	(4,734)
Service cost — benefits earned	(4)	(3)	(4)
Interest cost	(126)	(173)	(157)
Actuarial loss	(520)	(477)
Curtailments/settlements/termination benefits	51	12
Benefit payments	373	366
Ending balance	(5,235)	(5,009)	(4,734)
Change in plan assets:
Beginning balance	4,780	4,445
Actual return on plan assets	605	696
Cash funding of direct participant payments	14	20
Settlements	(56)	(15)
Benefit payments	(373)	(366)
Ending balance	4,970	4,780	4,445
Funded status at end of year	(265)	(229)
Pension Plan | Non-U.S.
Change in benefit obligation:
Beginning balance	(3,195)	(2,774)
Newly adopted plans		(19)
Service cost — benefits earned	(30)	(26)	(28)
Interest cost	(56)	(69)	(69)
Plan amendments	(3)	2
Actuarial loss	(123)	(381)
Participant contributions	(3)	(2)
Curtailments/settlements/termination benefits	21	5
Foreign currency translation	(133)	(62)
Benefit payments	140	131
Ending balance	(3,382)	(3,195)	(2,774)
Change in plan assets:
Beginning balance	2,740	2,464
Newly adopted plans		19
Actual return on plan assets	305	252
Company contributions to plan assets	20	39
Cash funding of direct participant payments	22	20
Participant contributions	3	2
Settlements	(8)	(5)
Foreign currency translation	99	80
Benefit payments	(140)	(131)
Ending balance	3,041	2,740	2,464
Funded status at end of year	(341)	(455)
Other Postretirement Benefits
Change in benefit obligation:
Beginning balance	(241)	(234)
Service cost — benefits earned	(2)	(2)	(3)
Interest cost	(8)	(11)	(12)
Actuarial loss	(4)	(6)
Participant contributions	(8)	(12)
Curtailments/settlements/termination benefits		(2)
Foreign currency translation	4	(5)
Benefit payments	23	31
Ending balance	(236)	(241)	(234)
Change in plan assets:
Beginning balance		3
Cash funding of direct participant payments	15	16
Participant contributions	8	12
Benefit payments	(23)	(31)
Ending balance			$ 3
Funded status at end of year	(236)	(241)
Other Postretirement Benefits | United States
Change in plan assets:
Funded status at end of year	(106)	(106)
Other Postretirement Benefits | Non-U.S.
Change in plan assets:
Funded status at end of year	$ (130)	$ (135)