Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan Contributions
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description	$ 1,000		$ 1,000
Unfunded Plan
Pension Plan Contributions
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description	350		350
Worldwide OPEB
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	11	$ 13	22	$ 27
Interest cost	52	49	105	98
Expected return on assets	0	0	0	0
Amortization of prior service costs/(credits)	(17)	(28)	(35)	(55)
Net remeasurement (gain)/loss	0	0	0	0
Separation programs/other	0	1	0	1
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	0	0	0
Net periodic benefit cost/(income)	46	35	92	71
Curtailments and Settlements
Net remeasurement (gain)/loss	0	0	0	0
Pension Plan | Funded Plan
Pension Plan Contributions
Payment for Pension and Other Postretirement Benefits			400
Pension Plan | Unfunded Plan
Pension Plan Contributions
Payment for Pension and Other Postretirement Benefits			150
UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	114	136	228	272
Interest cost	409	366	818	733
Expected return on assets	(649)	(722)	(1,298)	(1,444)
Amortization of prior service costs/(credits)	21	35	43	71
Net remeasurement (gain)/loss	(10)	0	(10)	(26)
Separation programs/other	0	3	1	14
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	(50)	0	(50)	(15)
Net periodic benefit cost/(income)	(165)	(182)	(268)	(395)
Curtailments and Settlements
Net remeasurement (gain)/loss	(10)	0	(10)	(26)
UNITED STATES | Pension Plan | Funded Plan
Pension Plan Contributions
Payment for Pension and Other Postretirement Benefits			140
Foreign Plan | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	127	151	256	303
Interest cost	173	173	349	349
Expected return on assets	(281)	(329)	(567)	(663)
Amortization of prior service costs/(credits)	9	7	17	13
Net remeasurement (gain)/loss	0	0	0	0
Separation programs/other	232	16	244	18
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	0	0	0	0
Net periodic benefit cost/(income)	260	18	299	20
Curtailments and Settlements
Net remeasurement (gain)/loss	0	$ 0	0	$ 0
Defined Benefit Plan, Cash and Cash Equivalents | Pension Plan | Funded Plan
Pension Plan Contributions
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year, Description	650		650
Global Redesign | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	(232)		$ (245)
Global Redesign | UNITED STATES | Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Net remeasurement (gain)/loss	(10)
Curtailments and Settlements
Settlements and curtailments	50
Net remeasurement (gain)/loss	$ (10)