Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlements and curtailments	$ 2,200	$ 306	$ 877
Worldwide OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost				$ 43	$ 54	$ 49
Interest cost				211	195	197
Expected return on assets				0	0	0
Amortization of prior service costs/(credits)				(70)	(109)	(120)
Net remeasurement (gain)/loss				551	(366)	293
Defined Benefit Plan Separation Programs and Other				0	1	2
Settlements and curtailments				0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)				735	(225)	421
U.S. Plans | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost				474	544	534
Interest cost				1,570	1,466	1,525
Expected return on assets				(2,657)	(2,887)	(2,734)
Amortization of prior service costs/(credits)				87	143	143
Net remeasurement (gain)/loss				(135)	1,294	(538)
Defined Benefit Plan Separation Programs and Other				22	53	74
Settlements and curtailments				(67)	(15)	(354)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)				(706)	598	(1,350)
NETHERLANDS | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlements and curtailments				(12)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement				(57)
Non-U.S. Plans | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost				506	588	566
Interest cost				691	684	671
Expected return on assets				(1,124)	(1,295)	(1,375)
Amortization of prior service costs/(credits)				33	25	37
Net remeasurement (gain)/loss				2,084	(76)	407
Defined Benefit Plan Separation Programs and Other				398	103	18
Settlements and curtailments				8	(2)	(3)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)				2,596	$ 27	$ 321
Global Redesign | U.S. Plans | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Settlements and curtailments				104
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)				$ 415