Retirement Benefits - Expense (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Effect of Change in Interest Method on Service and Interest Cost Components			$ (580)
Net remeasurement (gain)/loss	$ 3,000	$ 698
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost			510	$ 586	$ 507
Interest cost			1,524	1,817	1,992
Expected return on assets			(2,693)	(2,928)	(2,735)
Amortization of prior service costs/(credits)			170	155	155
Net remeasurement (gain)/loss			900	1,964	641
Defined Benefit Plan Separation Programs and Other			12	17	19
Settlements and curtailments			0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost			423	1,611	579
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost			483	532	468
Interest cost			782	936	1,189
Expected return on assets			(1,339)	(1,480)	(1,534)
Amortization of prior service costs/(credits)			38	47	55
Net remeasurement (gain)/loss			1,876	(974)	2,801
Defined Benefit Plan Separation Programs and Other			81	39	83
Settlements and curtailments			2	0	13
Defined Benefit Plan, Net Periodic Benefit Cost			1,923	(900)	3,075
Worldwide OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			49	60	54
Interest cost			194	236	269
Expected return on assets			0	0	0
Amortization of prior service costs/(credits)			(142)	(204)	(229)
Net remeasurement (gain)/loss			220	(292)	681
Defined Benefit Plan Separation Programs and Other			0	1	0
Settlements and curtailments			0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost			$ 321	$ (199)	$ 775