Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (36)	$ (19)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	11	13
Interest cost	21	20
Expected return on plan assets	(20)	(21)
Amortization of prior service benefit	(7)	(10)
Amortization of net actuarial loss	9	15
Total non-operating expense (benefit)	3	4
Net periodic benefit cost (benefit)	14	17
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	62	72
Interest cost	155	141
Expected return on plan assets	(260)	(272)
Amortization of prior service benefit	(6)	(6)
Amortization of net actuarial loss	91	126
Total non-operating expense (benefit)	(20)	(11)
Net periodic benefit cost (benefit)	42	61
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	33	36
Interest cost	39	40
Expected return on plan assets	(75)	(78)
Amortization of prior service benefit	(3)	(3)
Amortization of net actuarial loss	20	29
Total non-operating expense (benefit)	(19)	(12)
Net periodic benefit cost (benefit)	$ 14	$ 24