Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (38)	$ (19)	$ (73)	$ (59)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	10	13	32	39
Interest cost	20	20	62	60
Expected return on plan assets	(20)	(21)	(61)	(63)
Amortization of prior service benefit	(9)	(10)	(23)	(30)
Amortization of net actuarial loss	8	15	25	45
Total non-operating expense (benefit)	(1)	4	3	12
Net periodic benefit cost (benefit)	9	17	35	51
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	63	72	188	216
Interest cost	155	141	466	423
Expected return on plan assets	(260)	(272)	(780)	(816)
Amortization of prior service benefit	(6)	(6)	(18)	(18)
Amortization of net actuarial loss	91	126	274	378
Settlements, curtailments, special terminations and other			35
Total non-operating expense (benefit)	(20)	(11)	(23)	(33)
Net periodic benefit cost (benefit)	43	61	165	183
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	32	37	98	110
Interest cost	40	40	118	120
Expected return on plan assets	(75)	(78)	(225)	(235)
Amortization of prior service benefit	(3)	(4)	(9)	(10)
Amortization of net actuarial loss	20	29	59	87
Settlements, curtailments, special terminations and other			1
Total non-operating expense (benefit)	(18)	(13)	(56)	(38)
Net periodic benefit cost (benefit)	$ 14	$ 24	$ 42	$ 72