Pension and Postretirement Benefit Plans - Components of net periodic benefit cost and other information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net periodic benefit cost (benefit)
Net periodic benefit cost (benefit)	$ 1	$ (21)	$ (35)	$ (40)
Funded | Postretirement Benefits
Net periodic benefit cost (benefit)
Service cost	11	13	22	26
Interest cost	21	20	42	40
Expected return on plan assets	(21)	(21)	(41)	(42)
Amortization of prior service benefit	(7)	(10)	(14)	(20)
Amortization of net actuarial loss	8	15	17	30
Total non-operating expense (benefit)	1	4	4	8
Net periodic benefit cost (benefit)	12	17	26	34
Funded | United States | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	63	72	125	144
Interest cost	156	141	311	282
Expected return on plan assets	(260)	(272)	(520)	(544)
Amortization of prior service benefit	(6)	(6)	(12)	(12)
Amortization of net actuarial loss	92	126	183	252
Settlements, curtailments, special terminations and other	35		35
Total non-operating expense (benefit)	17	(11)	(3)	(22)
Net periodic benefit cost (benefit)	80	61	122	122
Funded | International | Qualified and Non-qualified Pension Benefits
Net periodic benefit cost (benefit)
Service cost	33	37	66	73
Interest cost	39	40	78	80
Expected return on plan assets	(75)	(79)	(150)	(157)
Amortization of prior service benefit	(3)	(3)	(6)	(6)
Amortization of net actuarial loss	19	29	39	58
Settlements, curtailments, special terminations and other	1		1
Total non-operating expense (benefit)	(19)	(13)	(38)	(25)
Net periodic benefit cost (benefit)	$ 14	$ 24	$ 28	$ 48