Postretirement Benefit Plans - Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Funded status at end of year	$ (37)	$ 101
United States | Defined benefit plan
Change in plan benefit obligation
Benefit obligation at beginning of year:	998	1,030
Service cost	19	22	$ 22
Interest cost	35	42	42
Participant contributions	0	0
Benefits paid	(10)	(9)
Settlements	(100)	(196)
Actuarial loss (gain)	(68)	109
Plan amendments	0	0
Effects of exchange rate changes	0	0
Benefit obligation at end of year	874	998	1,030
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year:	995	1,034
Actual return on plan assets	(56)	123
Employer contributions (qualified plans)	20	25
Employer contributions (non-qualified plans)	20	18
Participant contributions	0	0
Benefits paid	(10)	(9)
Settlements	(100)	(196)
Effects of exchange rate changes	0	0
Other	0	0
Fair value of plan assets at end of year	869	995	1,034
Funded status at end of year	(5)	(3)
United States | Retiree health care plan
Change in plan benefit obligation
Benefit obligation at beginning of year:	414	434
Service cost	5	5
Interest cost	15	17
Participant contributions	11	9
Benefits paid	(41)	(39)
Settlements	0	0
Actuarial loss (gain)	(43)	(15)
Plan amendments	0	3
Effects of exchange rate changes	0	0
Benefit obligation at end of year	361	414	434
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year:	394	434
Actual return on plan assets	(12)	44
Employer contributions (qualified plans)	1	1
Employer contributions (non-qualified plans)	0	0
Participant contributions	11	9
Benefits paid	(41)	(39)
Settlements	0	0
Effects of exchange rate changes	0	0
Other	(23)	(55)
Fair value of plan assets at end of year	330	394	434
Funded status at end of year	(31)	(20)
Non-U.S. | Defined benefit plan
Change in plan benefit obligation
Benefit obligation at beginning of year:	2,469	2,361
Service cost	36	37	34
Interest cost	45	44	52
Participant contributions	7	6
Benefits paid	(87)	(90)
Settlements	(16)	(13)
Actuarial loss (gain)	6	(52)
Plan amendments	7	0
Effects of exchange rate changes	(56)	176
Benefit obligation at end of year	2,411	2,469	2,361
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year:	2,593	2,309
Actual return on plan assets	(52)	148
Employer contributions (qualified plans)	19	56
Employer contributions (non-qualified plans)	0	0
Participant contributions	7	6
Benefits paid	(87)	(90)
Settlements	(16)	(13)
Effects of exchange rate changes	(54)	177
Other	0	0
Fair value of plan assets at end of year	2,410	2,593	$ 2,309
Funded status at end of year	$ (1)	$ 124