Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ (19)	$ (32)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	13	13
Interest cost	20	19
Expected return on plan assets	(21)	(21)
Amortization of prior service benefit	(10)	(13)
Amortization of net actuarial loss	15	14
Total non-operating expense (benefit)	4	(1)
Net periodic benefit cost (benefit)	17	12
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	72	67
Interest cost	141	142
Expected return on plan assets	(272)	(259)
Amortization of prior service benefit	(6)	(6)
Amortization of net actuarial loss	126	97
Total non-operating expense (benefit)	(11)	(26)
Net periodic benefit cost (benefit)	61	41
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	36	33
Interest cost	40	37
Expected return on plan assets	(78)	(69)
Amortization of prior service benefit	(3)	(3)
Amortization of net actuarial loss	29	30
Total non-operating expense (benefit)	(12)	(5)
Net periodic benefit cost (benefit)	$ 24	$ 28