Postretirement Benefit Plans - Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in plan assets
Funded status at end of year	$ 104	$ 104
U.S. | Defined benefit plan
Change in plan benefit obligation
Benefit obligation at beginning of year	960	874
Service cost	18	18	$ 19
Interest cost	31	38	35
Participant contributions	0	0
Benefits paid	(12)	(11)
Settlements	(94)	(66)
Curtailments	0	0
Actuarial loss (gain)	194	107
Plan amendments	0	0
Effects of exchange rate changes	0	0
Benefit obligation at end of year	1,097	960	874
Change in plan assets
Fair value of plan assets at beginning of year	987	869
Actual return on plan assets	164	185
Employer contributions (qualified plans)	0	0
Employer contributions (non-qualified plans)	16	10
Participant contributions	0	0
Benefits paid	(12)	(11)
Settlements	(94)	(66)
Effects of exchange rate changes	0	0
Fair value of plan assets at end of year	1,061	987	869
Funded status at end of year	(36)	27
U.S. | Retiree health care plan
Change in plan benefit obligation
Benefit obligation at beginning of year	359	361
Service cost	3	3	5
Interest cost	13	14	15
Participant contributions	13	13
Benefits paid	(39)	(41)
Settlements	0	0
Curtailments	0	0
Actuarial loss (gain)	40	9
Plan amendments	0	0
Effects of exchange rate changes	0	0
Benefit obligation at end of year	389	359	361
Change in plan assets
Fair value of plan assets at beginning of year	356	330
Actual return on plan assets	58	53
Employer contributions (qualified plans)	1	1
Employer contributions (non-qualified plans)	0	0
Participant contributions	13	13
Benefits paid	(39)	(41)
Settlements	0	0
Effects of exchange rate changes	0	0
Fair value of plan assets at end of year	389	356	330
Funded status at end of year	0	(3)
Non-U.S. | Defined benefit plan
Change in plan benefit obligation
Benefit obligation at beginning of year	2,581	2,411
Service cost	34	31	36
Interest cost	38	43	45
Participant contributions	7	7
Benefits paid	(95)	(103)
Settlements	(8)	(12)
Curtailments	0	(1)
Actuarial loss (gain)	143	193
Plan amendments	1	0
Effects of exchange rate changes	167	12
Benefit obligation at end of year	2,868	2,581	2,411
Change in plan assets
Fair value of plan assets at beginning of year	2,661	2,410
Actual return on plan assets	260	337
Employer contributions (qualified plans)	11	9
Employer contributions (non-qualified plans)	0	0
Participant contributions	7	7
Benefits paid	(95)	(103)
Settlements	(8)	(12)
Effects of exchange rate changes	172	13
Fair value of plan assets at end of year	3,008	2,661	$ 2,410
Funded status at end of year	$ 140	$ 80