Retirement Benefits Plans - Change in Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
United States pension liabilities [Member]
Change in benefit obligations
Balance at January 1	$ 3,829	$ 4,047
Service cost	111	123	$ 117
Interest cost	125	156	162
Actuarial (gain) loss	52	(179)
Gross benefits paid	(346)	(318)
Currency translation	0	0
Plan amendments	0	0
Other	0	0
Balance at December 31	3,771	3,829	4,047
Accumulated benefit obligation	3,620	3,672
Non-United States pension liabilities [Member]
Change in benefit obligations
Balance at January 1	2,175	2,337
Service cost	63	71	66
Interest cost	62	72	85
Actuarial (gain) loss	355	(23)
Gross benefits paid	(94)	(100)
Currency translation	(245)	(182)
Plan amendments	2	0
Other	(4)	0
Balance at December 31	2,314	2,175	2,337
Accumulated benefit obligation	2,189	2,049
Other postretirement liabilities [Member]
Change in benefit obligations
Balance at January 1	575	676
Service cost	4	6	13
Interest cost	17	24	32
Actuarial (gain) loss	(72)	(66)
Gross benefits paid	(79)	(86)
Currency translation	1	(8)
Plan amendments	0	(1)
Other	27	30
Balance at December 31	$ 473	$ 575	$ 676