Postretirement Benefit Plans - Plan Assets by Level Three Hierarchy (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 995	$ 1,034	$ 1,019
U.S. | Defined benefit plan | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	995	1,034
U.S. | Defined benefit plan | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		654	685
U.S. | Defined benefit plan | Fixed income securities and cash equivalents | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	654	685
U.S. | Defined benefit plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		341	349
U.S. | Defined benefit plan | Equity securities | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	341	349
U.S. | Defined benefit plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 1 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 2 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 3 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Defined benefit plan | Level 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		394	434	441	$ 434
U.S. | Retiree health care plan | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	260	251
U.S. | Retiree health care plan | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		245	227
U.S. | Retiree health care plan | Fixed income securities and cash equivalents | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	111	44
U.S. | Retiree health care plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		149	207
U.S. | Retiree health care plan | Equity securities | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	149	207
U.S. | Retiree health care plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		132	180
U.S. | Retiree health care plan | Level 1 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		132	180
U.S. | Retiree health care plan | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Retiree health care plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2	3
U.S. | Retiree health care plan | Level 2 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2	3
U.S. | Retiree health care plan | Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Retiree health care plan | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Retiree health care plan | Level 3 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
U.S. | Retiree health care plan | Level 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,593	2,309	$ 2,134	$ 2,309
Non-U.S. | Defined benefit plan | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	2,363	2,137
Non-U.S. | Defined benefit plan | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,845	1,654
Non-U.S. | Defined benefit plan | Fixed income securities and cash equivalents | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	1,646	1,508
Non-U.S. | Defined benefit plan | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		747	652
Non-U.S. | Defined benefit plan | Equity securities | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	717	629
Non-U.S. | Defined benefit plan | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1	3
Non-U.S. | Defined benefit plan | Other | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	0	0
Non-U.S. | Defined benefit plan | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		23	24
Non-U.S. | Defined benefit plan | Level 1 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		16	19
Non-U.S. | Defined benefit plan | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		7	5
Non-U.S. | Defined benefit plan | Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Non-U.S. | Defined benefit plan | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		206	145
Non-U.S. | Defined benefit plan | Level 2 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		183	127
Non-U.S. | Defined benefit plan | Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		23	18
Non-U.S. | Defined benefit plan | Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Non-U.S. | Defined benefit plan | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1	3
Non-U.S. | Defined benefit plan | Level 3 | Fixed income securities and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Non-U.S. | Defined benefit plan | Level 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Non-U.S. | Defined benefit plan | Level 3 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 1	$ 3

[1] Consists of bond index and equity index funds, measured at net asset value per share.