Retirement Benefits (Components of the Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 178	$ 196	$ 213
Interest cost		537	587	641
Expected return on plan assets		(940)	(977)	(990)
Amortization of prior service (credit) cost		(1)	(1)	(16)
Recognized actuarial loss (gain)		168	271	243
Net periodic benefit (credit) cost		(58)	76	91
Curtailment (gain) loss		(4)	5	(65)
Plan termination		0	0	0
Settlement loss		0	1	0
Total (credit) cost		(62)	82	26
U.S. Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		106	114	91
Interest cost		264	254	253
Expected return on plan assets		(379)	(373)	(346)
Amortization of prior service (credit) cost		0	0	(7)
Recognized actuarial loss (gain)		74	146	112
Net periodic benefit (credit) cost		65	141	103
Plan termination		0	0	0
Total (credit) cost		65	141	103
Non-U.S. Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		72	82	122
Interest cost		273	333	388
Expected return on plan assets		(561)	(604)	(644)
Amortization of prior service (credit) cost		(1)	(1)	(9)
Recognized actuarial loss (gain)		94	125	131
Net periodic benefit (credit) cost		(123)	(65)	(12)
Curtailment (gain) loss	$ (65)	(4)	5	(65)
Settlement loss		0	1	0
Total (credit) cost		(127)	(59)	(77)
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		2	3	4
Interest cost		5	5	11
Expected return on plan assets		0	0	0
Amortization of prior service (credit) cost		4	3	0
Recognized actuarial loss (gain)		(2)	(1)	(1)
Net periodic benefit (credit) cost		9	10	14
Curtailment (gain) loss		0	0	0
Plan termination		0	(128)	0
Settlement loss		0	0	0
Total (credit) cost	$ (125)	9	(118)	14
U.S. Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	1	2
Interest cost		2	2	7
Expected return on plan assets		0	0	0
Amortization of prior service (credit) cost		4	3	0
Recognized actuarial loss (gain)		(2)	(2)	(2)
Net periodic benefit (credit) cost		4	4	7
Plan termination		0	(128)	0
Total (credit) cost		4	(124)	7
Non-U.S. Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost		2	2	2
Interest cost		3	3	4
Expected return on plan assets		0	0	0
Amortization of prior service (credit) cost		0	0	0
Recognized actuarial loss (gain)		0	1	1
Net periodic benefit (credit) cost		5	6	7
Curtailment (gain) loss		0	0	0
Settlement loss		0	0	0
Total (credit) cost		$ 5	$ 6	$ 7