Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (68)	$ (73)	$ (128)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	43	52	52
Interest cost	82	79	80
Expected return on plan assets	(81)	(84)	(86)
Amortization of prior service benefit	(33)	(40)	(53)
Amortization of net actuarial loss	34	61	56
Settlements, curtailments, special terminations and other	5		(4)
Total non-operating expense (benefit)	7	16	(7)
Net periodic benefit cost (benefit)	50	68	45
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss
Prior service cost (benefit)	(171)		(1)
Amortization of prior service benefit	33	40	53
Net actuarial (gain) loss	119	(127)	69
Amortization of net actuarial loss	(34)	(61)	(56)
Foreign currency	(1)	(2)
Settlements, curtailments, special termination benefits and other	(5)
Total recognized in other comprehensive income (loss)	(59)	(150)	65
Total recognized in net periodic benefit cost (benefit) and other comprehensive (income) loss	(9)	(82)	110
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	251	288	268
Interest cost	620	563	565
Expected return on plan assets	(1,040)	(1,087)	(1,035)
Amortization of prior service benefit	(24)	(23)	(23)
Amortization of net actuarial loss	366	503	388
Settlements, curtailments, special terminations and other	70		2
Total non-operating expense (benefit)	(8)	(44)	(103)
Net periodic benefit cost (benefit)	243	244	165
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss
Amortization of prior service benefit	24	23	23
Net actuarial (gain) loss	926	(44)	607
Amortization of net actuarial loss	(366)	(503)	(388)
Settlements, curtailments, special termination benefits and other	(35)		(2)
Total recognized in other comprehensive income (loss)	549	(524)	240
Total recognized in net periodic benefit cost (benefit) and other comprehensive (income) loss	792	(280)	405
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	131	143	142
Interest cost	156	157	157
Expected return on plan assets	(299)	(307)	(292)
Amortization of prior service benefit	(12)	(13)	(13)
Amortization of net actuarial loss	78	114	126
Settlements, curtailments, special terminations and other	10	4	4
Total non-operating expense (benefit)	(67)	(45)	(18)
Net periodic benefit cost (benefit)	64	98	124
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss
Prior service cost (benefit)	3	7	6
Amortization of prior service benefit	12	13	13
Net actuarial (gain) loss	344	194	(244)
Amortization of net actuarial loss	(78)	(114)	(126)
Foreign currency	7	(83)	167
Settlements, curtailments, special termination benefits and other	(8)	(4)	(4)
Total recognized in other comprehensive income (loss)	280	13	(188)
Total recognized in net periodic benefit cost (benefit) and other comprehensive (income) loss	$ 344	$ 111	$ (64)