Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 133	$ 128	$ 400	$ 383
Interest cost	382	381	1,144	1,143
Expected return on assets	(683)	(673)	(2,050)	(2,020)
Amortization of prior service costs/(credits)	36	43	107	128
Net remeasurement (gain)/loss	0	0	0	0
Separation programs/other	58	6	70	9
Net periodic benefit cost/(income)	(74)	(115)	(329)	(357)
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	154	116	413	358
Interest cost	155	190	487	587
Expected return on assets	(347)	(329)	(1,012)	(1,018)
Amortization of prior service costs/(credits)	9	9	27	28
Net remeasurement (gain)/loss	0	0	0	11
Separation programs/other	5	16	24	88
Net periodic benefit cost/(income)	(24)	2	(61)	54
Worldwide OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost	13	13	37	37
Interest cost	50	49	148	146
Expected return on assets	0	0	0	0
Amortization of prior service costs/(credits)	(30)	(35)	(89)	(106)
Net remeasurement (gain)/loss	0	0	0	0
Separation programs/other	0	(1)	0	(1)
Net periodic benefit cost/(income)	33	$ 26	96	$ 76
Defined Benefit Plan, Estimated Future Employer Contributions To Funded Plans in Current Fiscal Year	1,500		1,500
Pension And Other Postretirement Expected Benefit Contributions Unfunded Plans	300		300
Pension and Other Postretirement Benefit Contributions and Expected Future Employer Contributions To Funded and Unfunded Plans	1,800		1,800
Defined Benefit Plan, Previous Guidance Estimated Future Employer Contributions To Be Funded Plans in Current Fiscal Year	1,000		1,000
Defined Benefit Plan, Estimated Pull Ahead of Employer Contributions To Funded Plans in Current Fiscal Year	$ 500		500
Pension and Other Postretirement Benefit Contributions			700
Pension and Other Postretirement Benefit Contributions Unfunded Plans			$ 200