Employee Benefit Plans - Contributions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Post Retirement Benefit Plan, Future Employer Contribution in Next Fixcal Year		$ 63
2017		1,062
2018		443
2019		445
2020		453
2021		533
Years 2022-2026		2,714
Post employment benefit plan contributions by employer		61	$ 66	$ 71
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit pension plan contributions by employer		178
Defined Benefit Plans, Future Employer Contributions in Next Fiscal Year		350
United States Pension Plan of US Entity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit pension plan contributions by employer		24
Defined Benefit Plans, Future Employer Contributions in Next Fiscal Year		169
2017		852
2018		227
2019		223
2020		225
2021		296
Years 2022-2026		$ 1,433
Discount rate assumptions used to determine benefit obligations		4.00%	4.30%	3.90%
Rate of compensation increase assumptions used to determine benefit obligation		0.20%	0.20%	0.20%
Discount rate assumptions used to determine net periodic benefit costs		4.30%	3.90%	4.80%
Expected return on plan assets assumptions used to determine net periodic benefit cost		7.50%	7.50%	7.80%
Rate of compensation increase assumptions used to determine net periodic benefit cost		0.20%	0.20%	0.20%
Foreign Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit pension plan contributions by employer		$ 154
Defined Benefit Plans, Future Employer Contributions in Next Fiscal Year		181
2017		210
2018		216
2019		222
2020		228
2021		237
Years 2022-2026		$ 1,281
Discount rate assumptions used to determine benefit obligations		2.50%	3.30%	3.10%
Rate of compensation increase assumptions used to determine benefit obligation		2.60%	2.70%	2.60%
Discount rate assumptions used to determine net periodic benefit costs		3.30%	3.10%	4.20%
Expected return on plan assets assumptions used to determine net periodic benefit cost		4.80%	5.20%	6.10%
Rate of compensation increase assumptions used to determine net periodic benefit cost		2.70%	2.60%	2.60%
Postretirement Health Coverage [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2017		$ 63
2018		64
2019		62
2020		61
2021		59
Years 2022-2026		$ 261
Discount rate assumptions used to determine benefit obligations		3.90%	4.10%	3.80%
Discount rate assumptions used to determine net periodic benefit costs		4.10%	3.80%	4.50%
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit pension plan contributions by employer		$ 61
Health care cost trend rate assumed for next year		7.20%	7.50%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)		4.80%	4.90%
Year that the rate reaches the ultimate trend rate		2026	2026
Effect on total service and interest cost components - 1% increase		$ 2
Effect on total service and interest cost components - 1% decrease		(2)
Effect on post-retirement benefit obligation - 1% increase		53
Effect on post-retirement benefit obligation - 1% decrease		(46)
Domestic, tax-qualified, defined benefit plan [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plans, Future Employer Contributions in Next Fiscal Year		145
Scenario, Forecast [Member] | United States Pension Plan of US Entity [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate assumptions used to determine net periodic benefit costs	4.00%
Expected return on plan assets assumptions used to determine net periodic benefit cost	7.00%
Rate of compensation increase assumptions used to determine net periodic benefit cost	0.20%
Scenario, Forecast [Member] | Foreign Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate assumptions used to determine net periodic benefit costs	2.50%
Expected return on plan assets assumptions used to determine net periodic benefit cost	4.10%
Rate of compensation increase assumptions used to determine net periodic benefit cost	2.60%
Scenario, Forecast [Member] | Postretirement Health Coverage [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate assumptions used to determine net periodic benefit costs	3.90%
Minimum [Member] | Domestic, tax-qualified, defined benefit plan [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plans, Future Employer Contributions in Next Fiscal Year		15
Voluntary contribution [Domain] | Domestic, tax-qualified, defined benefit plan [Domain]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plans, Future Employer Contributions in Next Fiscal Year		$ 130