Postretirement Benefit Plans - Benefit Obligations and Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Funded status (FVPA – BO) at end of year	$ 101	$ (48)
U.S. | Defined benefit plan
Change in plan benefit obligation
Benefit obligation at beginning of year:	1,030	1,033
Service cost	22	22	$ 22
Interest cost	42	42	43
Participant contributions	0	0
Benefits paid	(9)	(9)
Medicare subsidy	0	0
Actuarial loss (gain)	109	27
Settlements	(196)	(85)
Plan amendments	0	0
Effects of exchange rate changes	0	0
Benefit obligation at end of year (BO)	998	1,030	1,033
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year:	1,034	1,019
Actual return on plan assets	123	79
Employer contributions (qualified plans)	25	15
Employer contributions (non-qualified plans)	18	15
Participant contributions	0	0
Benefits paid	(9)	(9)
Settlements	(196)	(85)
Effects of exchange rate changes	0	0
Other	0	0
Fair value of plan assets at end of year (FVPA)	995	1,034	1,019
Funded status (FVPA – BO) at end of year	(3)	4
U.S. | Retiree health care plan
Change in plan benefit obligation
Benefit obligation at beginning of year:	434	463	434
Service cost	5	5	5
Interest cost	17	20	20
Participant contributions	9	10
Benefits paid	(39)	(38)
Medicare subsidy	0	1
Actuarial loss (gain)	(15)	(27)
Settlements	0	0
Plan amendments	3	0
Effects of exchange rate changes	0	0
Benefit obligation at end of year (BO)	414	434	463
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year:	434	441	434
Actual return on plan assets	44	20
Employer contributions (qualified plans)	1	1
Employer contributions (non-qualified plans)	0	0
Participant contributions	9	10
Benefits paid	(39)	(38)
Settlements	0	0
Effects of exchange rate changes	0	0
Other	(55)	0
Fair value of plan assets at end of year (FVPA)	394	434	441
Funded status (FVPA – BO) at end of year	(20)	0
Non-U.S. | Defined benefit plan
Change in plan benefit obligation
Benefit obligation at beginning of year:	2,361	2,231	2,361
Service cost	37	34	35
Interest cost	44	52	53
Participant contributions	6	6
Benefits paid	(90)	(77)
Medicare subsidy	0	0
Actuarial loss (gain)	(52)	259
Settlements	(13)	(8)
Plan amendments	0	0
Effects of exchange rate changes	176	(136)
Benefit obligation at end of year (BO)	2,469	2,361	2,231
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year:	2,309	2,134	2,309
Actual return on plan assets	148	227
Employer contributions (qualified plans)	56	160
Employer contributions (non-qualified plans)	0	0
Participant contributions	6	6
Benefits paid	(90)	(77)
Settlements	(13)	(8)
Effects of exchange rate changes	177	(133)
Other	0	0
Fair value of plan assets at end of year (FVPA)	2,593	2,309	$ 2,134
Funded status (FVPA – BO) at end of year	$ 124	$ (52)